[问题]什么时候用1号信令什么时候用7号信令呢?(页 1) - 核心网 - 通信人家园 论坛|中国第一通信社区 - Powered by Discuz! Archiver: "通信人家园论坛C114中国通信网
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sandy_gz 2006-7-5 10:07
[问题]什么时候用1号信令什么时候用7号信令呢?
是可选的吗?如何依据情况选择?
查看完整版本: [问题]什么时候用1号信令什么时候用7号信令呢?
刚果金 2006-7-5 12:17
７号需要交换机的链路板支持，１号需要ＭＦＣ支持，首先看资源，然后有个不太恰当的比喻：１和７相当于ＧＳＭ和３Ｇ的差别．
switcher 2006-7-5 17:47
可用7号就用7号，没办法才用1号。
woolau 2006-7-5 21:53
顶一个
雪落有声 2006-7-8 23:54
我的理解是，
一号信令：30个话路15出15入，就是说15个出的话路和15个入的话路不能互用
七号信令：30个话路可自由调配出入，每个话路都可能做出或入。
具体用那种信令与组网时的设置有关，需要双方交换机采用同样的信令
不对的地方，请各位批评指正
刚果金 2006-7-9 17:35
[quote][b]以下是引用[i]雪落有声在2006-7-8 23:54:00[/i]的发言：[/b]
我的理解是，
一号信令：30个话路15出15入，就是说15个出的话路和15个入的话路不能互用
七号信令：30个话路可自由调配出入，每个话路都可能做出或入。
具体用那种信令与组网时的设置有关，需要双方交换机采用同样的信令
不对的地方，请各位批评指正
[/quote]关于１号的说法是错误的，没有规定必须１５出１５入，任意调配，甚至可以是双向的（但是有碰头的弊病）．
１和７的主要区别是信令通道的区别，前者是随路信令，后者是共路信令，因此后者有很多优势，学过信令的应该很清楚．
mcg 2006-7-10 17:03
不懂
mlc1072ttd 2006-7-12 15:46
6楼的解释我比较赞同。
calljiji 2006-7-13 15:40
是不是用户线用1号呢,pcm30/32的ts16,而局间就是7号,就不是32字节咯
myswitch 2006-7-14 10:32
什么时候用1号信令什么时候用7号信令呢?是可选的吗?如何依据情况选择?
对于设备来说,什么信令都支持,只要具备相应的软硬件,是可选的.但是具体使用什么信令,需要依据所对接的设备来确定,假如你所对接的设备很老,无法进行改造,它只支持模拟信令,则你也只有使用1号信令或其他模拟信令;反之则无所谓.关键是双方协定.
woolau 2006-7-15 21:17
支持6楼解释
sandy_gz 2006-7-17 16:42
谢谢各位.
ybmgsm 2006-7-29 11:14
现在一号信令主要用于电信，移动一般都用七号信令
sunl71 2006-7-31 15:41
楼上的，谁告诉你电信用一号？电信买那么多STP是用来摆设的啊？
海朗朗 2006-8-2 12:14
13楼明显是移动的卡，带有种族歧视成分！
目前的运营商交换机都支持大部分的信令与协议，并且在自己本网内都采用七号信令，采用MFC方式大部分在市话端局或是极个别的国际局。例如：市话端局与某些小交换机用户之间就采用MFC或PRI方式。至于时隙的使用更是根据具体情况而定，并非一定要前15路出，后15路入。
sxsxxgcsjybc 2006-8-10 15:17
同意15楼
R2信令就是1号信令吧？
myswitch 2006-8-10 16:42
R2信令是1号信令的“父亲”。
mscbschlr 2006-9-24 11:37
6楼好强
peter1028 2006-9-24 21:38
又学到东西了
qiaozhi 2006-9-25 23:14
1，1号是随路信令，7号是共路信令；
2，1号：一个PCM线路对应30个话路，16时隙中的线路信令与话路是相对应的；用户号码
是带内传送的，由记发器进行收发；
7号系统的信令链路与话路逻辑上是分离的，不管是线路信令还是号码信息都通过消息
传送；
3，1号能传送信令内容较少，
7号信令内容丰富；系统较大，分层，分模块很清楚；
[并非原创，只是学习交流]
gyp0196 2006-10-12 11:34
谢谢大家讨论！
tomliang3 2006-11-17 11:07
20 楼的转贴不错
君莫笑 2006-11-17 12:48
呵呵，小弟又学到东西啦
hotplate 2007-1-9 17:52
如果大家需要不同信令之间的匹配，请联系我，我们提供专业设备。
hotplate 2007-1-9 17:53
如果大家需要不同信令之间的匹配，请联系我，我们提供专业设备。
anzi250 2007-1-11 00:54
两个差别很大的,比如说接续速度,对新业务的支持等,现在地方上基本都是7号了.
两者都是局间信令.
不是单方面确定需要使用什么信令的,需要和对端局配合
等待--- 2007-1-12 15:50
学习拉
coffee-5566 2007-2-9 13:59
<p>又学到了。。。</p><p>20楼挺强的哦。。。。。</p><p>支持转贴！！</p>
icerain2005 2007-2-14 15:58
6楼和20楼说的很清楚...不会的话建议先去看看书先
xiong19811209 2007-2-23 10:36
在做一号中继群的时候，在群向的选择中，好象只有入中继和出中继这两个选择，因此一般３０个时隙中１５个做入中继，１５个做出继。而在做７号的时候，就注意主控和非主控
╃→叼嗻煙ヤ 2007-3-26 10:54
阅
haolong153 2007-12-19 10:40
6楼正解
opqning 2008-1-23 21:55
<p>学习学习，又学一点点</p>
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ISDN拨号（一号信令）(2)_IT认证_思科认证_GZU521.COM学习网
ISDN拨号（一号信令）(2)_IT认证_思科认证_GZU521.COM学习网: "您的位置： 学习网(Gzu521.com) -> 考试资料 -> IT认证 -> 思科认证 -> 资料正文
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ISDN拨号（一号信令）(2)
思科认证 点击：39次 发布时间：2006-8-9 【字体：大 中 小】 来源：Gzu521.com
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ppp authentication chap pap
group-range 161 190
!
interface group-async1
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encapsulation ppp
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peer default ip address pool setup_pool
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ISDN拨号（一号信令）(1) Gzu521.com我的学习网
ISDN拨号（一号信令）(1) Gzu521.com我的学习网: "CISCO 36和朗讯程控交换机连接：
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framing no-crc4
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peer default ip address pool setup_pool"
!
version 12.1
no service single-slot-reload-enable
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname router
!
logging rate-limit console 10 except errors
enable password *********
!
username test password 0 test
ip subnet-zero
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no ip finger
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controller e1 3/0
framing no-crc4
ds0-group 1 timeslots 1-15,17-31 type r2-digital r2-compelled
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framing no-crc4
ds0-group 1 timeslots 1-15,17-31 type r2-digital r2-compelled
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unused-abcd 0 1 1 1
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framing no-crc4
ds0-group 1 timeslots 1-15,17-31 type r2-digital r2-compelled
cas-custom 1
unused-abcd 0 1 1 1
country china use-defaults
answer-signal group-b 1
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framing no-crc4
ds0-group 1 timeslots 1-15,17-31 type r2-digital r2-compelled
cas-custom 1
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answer-signal group-b 1
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Understanding Basic VoIP with PBX Trunking
emUnderstanding Basic VoIP with PBX Trunking: "The voice network module on the Cisco 3600 series supports up to two voice interface cards (VICs). These VICs come in three types, each having two ports. Each type provides a slightly different interface for connecting to different types of equipment. The basic types of voice interfaces are: foreign exchange service (FXS), foreign exchange office (FXO), and E&M.
*
The FXO interface is an RJ-11 connector that connects local calls to a public switched telephone network (PSTN) central office (CO), or to a PBX that does not support E&M signaling. This is the interface a standard telephone provides. This is the only voice interface card approved to connect to off-premise lines, and this is its primary use. This interface may be used to provide backup over the PSTN or for Centrex-type operations. The FXO ports on the Cisco 3600 series router can support both loop-start and ground-start modes. (In certain situations, a hardware jumper must be used to make an FXO port operate in ground-start mode.) The ground-start signaling method is used primarily on trunk lines or tie lines between private branch exchanges (PBXs).
*
The FXS interface is also an RJ-11 connector that connects directly to a standard telephone, fax machine, or similar device. The FXS interface supplies ringing voltage, dial tone, and similar signals to FXO devices. As the exercises in module 1 demonstrated, you would use the FXS interface when connecting a phone directly to a router. Basically, the FXS interface mimics the PSTN. The FXS ports on the Cisco 3600 series router can provide the battery at 24-volt DC. They can also support both loop-start and ground-start modes of operation according to the software configuration of the router. Loop start, however, is the most common, because most residential telephones are analog loop-start devices.
*
E&M, which stands for 'Ear and Mouth' (or 'recEive and transMit,' or sometimes 'Earth and Magnet'), is a signaling technique for two- and four-wire telephone and trunk interfaces that is used mainly between PBXs or other network-to-network telephony switches, such as Lucent 5 Electronic Switching System [5ESS], Nortel DMS-100, and so on. The E&M analog interface is an RJ-48S connector used to connect remote calls from an IP network to a PBX for local distribution and between PBX trunk lines (tie lines) or other network-to-network telephony switches. Unlike loop-start or ground-start modes of operation on the FXS/FXO ports, E&M uses separate wires for signaling and voice. There are five types of E&M signaling, as well as two wiring methods.
Exercise care when designing a voice network...
Exercise care when designing a voice network to ensure supervisory signals (discussed in module 1 of this tutorial) are transmitted when expected to avoid common problems such as spurious disconnects, undisconnected lines, and continuous rings. For example, a typical disconnect supervision problem can occur when a given line can be released only by the party who originated the phone call. This problem can be fixed by implementing either disconnect supervision or ground start.
Click to close sidebar.
In the first module of this tutorial, you learned about the basics of analog voice internetworking, including the history of telephony, telephone networks and technology, and the various types of telephony signaling. You know how to configure and troubleshoot a Cisco 3640 router using loop-start access signaling across the FXS interface. In this module you will learn more about trunks, analog E&M signaling, and VoIP configuration using E&M. The Cisco VoIP implementation supports E&M types I, II, III, and V, using both two- and four-wire implementations.
Click on any highlighted term see its pop-up glossary definition. For additional information and more definitions of terms used throughout this course, see the full Glossary. You can access the Glossary at any time by clicking Help.
A basic understanding of trunks is necessary to understanding the use of E&M signaling. A line is a communications path between a customer's telephone and a telephone switch, such as a CO switch or a PBX, whereas a trunk is an actual telephone circuit or path between two switches, at least one of which is usually a CO or a switching center. This type of trunk, where voice is carried over a telco's network, is a CO trunk. Another example of a trunk is a private leased line that interconnects two PBXs, forming a corporate voice network. This type of connection is referred to as a PBX trunk.
Central-Office Trunks
Two-Wire Central-Office Trunks
A hunt group is...
A hunt group is a feature supported by voice-capable Cisco routers that involves the configuration of a group of dial peers on the same router with the same destination pattern. With a hunt group, if a call attempt is made to a dial peer on a specific time slot and that time slot is busy, the router hunts for another time slot on that channel until an available time slot is found.
The Cisco 3640 hunts for a group based on matching numbers.
It is possible to configure hunt groups by setting up multiple dial peers having the same destination pattern. Hunt groups are not configured in this tutorial, and the feature is not enabled in the simulation exercises in this module.
Click to close sidebar.
The most common two-wire CO trunks used in PBX networks employ ground start. These trunks may be restricted such that operation may be outgoing only, incoming only, or both. In the case of outgoing calls (direct outward dialing, or DOD) operation additionally may be restricted to local calling only, versus direct distance dialing (DDD). Most incoming calls are routed to an attendant or to a messaging or answering system. The ringback tone is generated from the local exchange carrier's (LEC's) switch that connects to the PBX. This type of trunk is common.
Most of these trunks are assigned the same phone number within the PSTN, and operate in a 'hunt group' fashion.
Direct Inward Dialing Central Office Trunks
Direct inward dialing (DID) is used to determine how the called number is treated for incoming calls. Incoming calls to a PBX often first flow through an attendant position. DID trunks allow users to receive calls directly from the outside without intervention from the attendant.
Use of DID offers three main advantages:
* It allows direct access to stations from outside the PBX.
* It allows users to receive calls even when the attendant switchboard is closed.
* It takes a portion of the load off the attendants.
To accomplish DID on a trunk, the switch at the PSTN (either the local exchange carrier [LEC] or the inter-exchange carriers [IXC]) transmits the number of the called party to the PBX for routing. DID trunks often use existing two-wire circuits, and typically use ground-start signaling. Four-wire circuits using E&M signaling or digital access are sometimes used as well. To use DID, a block of PSTN telephone numbers generally must be reserved from the IXC or LEC.
DID trunk circuits usually employ either Wink Start or Delay-Dial signaling schemes, so that the network knows that the PBX is ready to accept the incoming address supervision. Wink Start and Delay Dial are discussed in more detail later in this section.
The next module in this tutorial, 'Basic Analog-to-Digital Voice over IP,' covers the use of DID in a VoIP configuration.
Wide-Area Telephone Service Central-Office Trunks
Wide-Area Telephone Service (WATS—sometimes referred to as OUTWATS) trunks are used for outgoing calls. They take advantage of interconnection to the IXC. These trunks require that the PBX output digits to the PSTN switch for routing. The network usually provides answer and disconnect supervision. WATS trunks can operate using either ground-start or loop-start signaling, in addition to E&M signaling. Ringback and busy signals are generated from the remote switch or PBX.
WATS trunks do not have addressable PSTN telephone numbers; therefore, these trunks are typically implemented in a hunt-group fashion within the PBX.
Central-Office 800-Service Trunks
Trunks that provide 800-service are sometimes referred to as INWATS service trunks. These trunks are used for incoming calls and take advantage of interconnection to the IXC. With an 800-service trunk, the PSTN does not output digits to the PBX; incoming calls on these trunk numbers are routed to specific individuals or groups by the PBX. These trunks may utilize loop reverse battery or E&M signaling.
Ringback and busy tones are usually generated by the PSTN switch that is interconnected to the PBX. Generally, these trunks are implemented in a hunt group fashion.
Long-Distance Trunks
Long-distance trunks interconnect to an IXC to allow both incoming and outgoing long-distance calling. They usually operate on two-wire ground-start circuits, or two- or four-wire E&M circuits. If access to the PSTN switch is digital (DS1), then conventional robbed-bit signaling (RBS) is used. (RBS is explained in greater detail in the next module of the Voice Internetworking CIM tutorial.)
Ringback and busy tones are usually generated by the IXC's PSTN switch that is interconnected to the PBX. Generally, these types of trunks are implemented in a hunt-group fashion, and incoming calls are typically routed to an attendant or messaging system.
PBX Trunks
A PBX is a private digital or analog telephone switchboard used to originate and answer calls to and from the public network (via CO trunks). PBXs can be combined with PBX trunks between them. When a caller picks up a handset and dials from within the corporation, the PBX connects that user to an idle line or to an idle trunk in an appropriate trunk group, then returns the appropriate call status signal, such as a dial tone or a ringback. A busy or fast-busy signal is returned if the line or the trunk group is busy. An attendant may be present to answer incoming calls and for user assistance.
FX Trunks
Foreign exchange (FX) circuits may consist of either stations or trunks. An FX line is a special line that is run from a local telephone to a CO switch or PBX switch. In this case, the local telephone is assigned a number on a remote switch; for all inbound and outbound calls, the telephone behaves as if it were connected to the remote switch. Generally, an FX circuit uses a two-wire circuit with loop start signaling. The ringback and busy signals are provided by the switch connected to the CO.
An FX trunk operates in a similar fashion, except that a local trunk provides interconnectivity to a remote switch. For outbound calls, local PBX users dial an access code such as 9, receive a dial tone from the remote switch, then output digits to the remote switch for routing. Incoming calls are either barred, or are routed to a PBX attendant or message system.
Because a trunk circuit is involved, features such as call transferring and call forwarding can also be deployed. These types of activities requires disconnect supervision to release the PBX trunk. This supervision cannot be provided with loop-start signaling, so ground start signaling must be used.
Tie Trunks and Tie Lines
Tie trunks interconnect PBX switches within a customer's network. Tie trunks typically connect both trunks and station lines through a network connection. These circuits are usually heavily used and normally support both incoming and outgoing calls.
Tie trunks are typically four-wire E&M-type circuits, but may often interconnect through DS1 facilities using RBS. The use of two-wire trunks is also allowable; these would typically use ground-start signaling.
Although tie lines are generally considered the same as tie trunks, and the terms are often used interchangeably, there are some technical differences:
* Tie trunks can interconnect both trunks and lines. In tie-trunk operation, routing of a call is totally automatic. The remote PBX usually supplies another dial tone, at which the user must enter the necessary address for the called party at that PBX.
* Tie lines connect only lines throughout a network connection. Routing of a call over tie lines is under control of the user. A user would need to dial an access code (9, for example) to gain access to the desired remote PBX. Tie lines are actually tie trunks that use tone-start type of start-dial supervision and cut-through operation. (Details about start-dial supervision can be found at the end of this section.)
Although the next module will include use of a PBX in the network topology, a complete discussion of PBXs and PBX configuration is out of the scope of this tutorial. To learn about PBX configuration, you should refer to the manuals for the particular PBX that you are using in your network. For additional PBX information, however, please see the related document The Private Branch Exchange (PBX) .
As discussed in module 1, 'Basic Analog Voice over IP,' the primary purpose of signaling in a voice network is to establish a connection. Signaling can be classified into four basic functions:
* Supervisory signaling — Informs the telephone or switch of the status of the local loop and any connected trunks. Supervisory signaling is used to:
o Initiate a call request on line or trunks (called line signaling on trunks).
o Indicate that the call has been answered or the call has been disconnected (disconnect and answer supervision).
o Initiate or terminate charging for calls.
o Recall an operator on an established connection.
* Address signaling — Contains information indicating the destination of a call, such as the telephone number and an area code, an access code, or a PBX tie trunk access code.
* Call progress indicators — Convey call-progress or call-failure information to subscribers or operators by the use of usually audible tones (such as the busy signals, the reorder tone, and the ringback, all of which were discussed in module 1).
* Network management signaling — Controls the bulk assignment of circuits or modifies the operating characteristics of switching systems in a network in response to overload conditions. (These signaling functions will not be covered in detail in this tutorial, but are mentioned here for completeness.)
For a more detailed discussion of signaling, including descriptions of supervision, address, call-progress, and network management signaling, read Signaling, which is included in this tutorial. Also search Cisco Connection Online (CCO) at http://www.cisco.com for more information on this specific topic as well as more available information on treansmitting voice over a data network.
Just as the local loop requires supervisory signaling, so does a trunk. Although loop-start signaling, which is generally used on everyday residential telephones, can also be used on trunks, its use can result in problems that make it an ineffective signaling method for a trunk. With loop start, only the device originating the call can release the connection. Also, loop start would not prevent a trunk from being seized by both parties to a call, a condition referred to as glare. Glare can be tolerable on a local loop, but its occurrence on a trunk would be unacceptable. Ttwo-way handshaking methods were developed to coordinate the sequence of events that occur during a call: the request by the calling end for access to the trunk, followed by the acknowledgment by the called end, then the subsequent seizure of the trunk by the calling end.
The basic types of supervisory signaling used on trunks are: ground start, E&M, and start-dial supervision.
Ground-Start Signaling
In module 1 of this course, you configured the Cisco 3640 router FXS port to use loop-start signaling, because calls were being made using a directly connected analog telephone. Ground start is the access signaling method used on trunk lines or tie lines between PBXs to indicate on-hook/off-hook status to the CO. Ground-start signaling works by using ground and current detectors. Ground start behaves like a loop start, however, the PBXs on both sides—the telco and the customer's telephone—have to agree on the status of a line before a call can be placed. This scenario allows the network to indicate off-hook or seizure of an incoming call independent of the ringing signal.
E&M Signaling Interface Types
Analog trunk circuits connect between automated systems (a PBX) and the network (a CO). The most common form of analog trunk is the E&M interface.
E&M signaling is typically used for trunk lines. It provides native support for both disconnect and answer supervision, as well as glare avoidance. In E&M signaling, separate paths are used for voice and signaling. E&M is normally the only way that a CO switch can provide two-way dialing with DID.
The history of the semantics of E&M circuits dates back to the days of telegraphy, where the main office end had a 'key' that grounded the E circuit, and the other end had a sounder with an electromagnet attached to a battery. Descriptions such as 'ear' and 'mouth' were created to help provide a reference to field personnel as to the direction of a signal in a wire. Note that these terms correspond to the inbound and outbound circuits, known as the E lead and M lead, respectively.
There are five standard types of E&M interfaces, which correspond to the five signaling types:
* E&M Type I Interface Model
* E&M Type II Interface Model
* E&M Type III Interface Model
* E&M Type IV Interface Model
* E&M Type V Interface Model
With each signaling type, the PBX supplies one signal, known as the M signal (mouth), and accepts one signal, known as the E signal (ear). Conversely, the tie-line equipment accepts the M signal from the PBX and provides the E signal to the PBX. The M signal accepted by the tie-line equipment at one end of a tie circuit becomes the E signal output by the remote tie-line interface.
Remember learning about tip and ring in module 1?
* When a user tries to place a call by grounding the 'ring' lead, the PBX at the telco senses the flow of current and grounds the 'tip' lead to indicate the PBX is ready to serve.
* The user's equipment perceives the flow of current on its 'tip' and knows that the PBX is ready to serve.
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The signaling part of the interface has five distinct physical configurations (Types I – V) and the audio interface has two (two- and four-wire). Note that the terms two-wire and four-wire are used to reference the communication protocol of the audio path. The difference between a two-wire and four-wire circuit is whether the audio path is full duplex on one pair or two pairs of wires.
Two full-duplex wires (called tip and ring) carry the audio on two-wire E&M. Four-wire E&M uses four half-duplex wires for the audio path (Tip, Ring, Tip1, and Ring1). Note that a four-wire E&M circuit may have from six to eight physical wires.
Signaling Types
* E — Ear or earth: Signal wire from the trunking (CO or network) side to signaling (user) side
* M — Mouth or magnet: Signal wire from signaling (user) side to trunking (CO or network) side
* SG — Signal ground: Used only on certain types of E&M; sometimes grounded, sometimes not>
* SB — Signal battery: Used on certain types of E&M; sometimes provides -48V Direct Current, sometimes ground, sometimes is not used at all
* T/R — Tip/ring: Used only on a four-wire circuit; carries audio from the signaling (user) side to the trunking (CO/network) side; not used on a two-wire circuit
* T1/R1 — Tip1/ring1: On four-wire circuits, carries audio from the trunking (CO/network) side to the signaling (user) side; on a two-wire circuit, this pair carries the full-duplex audio path
Types I and II are the most popular E&M signaling types in the Americas. Type V is used in the United States, and is very popular in Europe. (SSDC5 is most often found in the United Kingdom.) Similar to Type V, SSDC5A differs in that on- and off-hook states are backward to allow for fail-safe operation: if the line breaks, the interface defaults to off hook (busy). Of all the types, only Types II and V are symmetrical (can be back to back using a crossover cable).
The Cisco 2600 and 3600 series routers currently support types I, II, III, and V utilizing both two- and four-wire implementations. The E&M interface of the Cisco 3600 series presents the 'channel bank,' 'tie equipment,' or 'CO' side of a trunk interface to a PBX. Each E&M signaling type has a unique circuit model and connection diagram. All Cisco analog voice gateway routers have 24V DC designed on the FXS ports. According to EIA 464 standard, any voltage from DC 24 volts to DC 52 volts is acceptable.
Characteristics of E&M Lead Signaling
Type
M Lead
E Lead
Outbound Direction Inbound Direction
Off Hook
On Hook
Off Hook
On Hook
I
Battery
Ground
Ground
Open
II
Battery
Open
Ground
Open
III
Loop current
Ground
Ground
Open
IV
Ground
Open
Ground
Open
V
Ground
Open
Ground
Open
SSDC5
Earth on
Earth off
Earth on
Earth off
Cisco routers expect to see off-hook conditions on the M lead and signal off hook to the remote device on the E lead.
See the following sections and illustrations for individual descriptions of the different types. Each of the following illustrations shows the E&M interface of the PBX on the left, and the corresponding tie-line equipment interface on the right. The symbol V refers to battery voltage, which can be 25 VDC to 65 VDC, and is usually (nominally) -48 VDC.
E&M Type I
In E&M Type I signaling, the battery PBX provides the battery for both the E and M leads. During an off-hook condition, the PBX generates the E signal by grounding the E lead. The PBX detects the E signal by sensing the increase in current through a resistive load. Similarly, in an on-hook condition, the PBX generates the M signal by sourcing a current to the tie-line equipment, which detects it via a resistive load.
The four-wire Type I interface from the PBX has the following characteristics:
* E (pin 7) detector 'floats' at -48V below ground
* M (pin 2) contact has low ohms to ground on hook, and is -48V below ground when off hook
* Approximately 30-150 ohms between T/R (pins 6/3) sometimes in series with 2.2uf of capacitance
* Approximately 30-150 ohms between T1/R1 (pins 5/4) sometimes in series with 2.2uf of capacitance
E&M Type I
The Type I interface requires that the PBX and tie-line equipment share a common signaling ground reference. This setup can be achieved by connecting signal ground from the PBX to the signal-ground (SG) lead (pin 8) of the RJ-48S connector.
Note that the voltage on the E and M leads may not be the same (the E lead may have lower voltage). This asymmetrical signaling scheme is a potential source of interference, which could cause high return current through the grounding system. If two PBXs were not correctly grounded, current could flow down the M lead, causing the remote PBX to erroneously detect a current on the E lead, thus resulting in false seizure of a trunk. Despite this potential problem, E & M signaling is the most common four-wire trunk interface used in North America.
E&M Type II
The E&M Type II interface provides almost complete isolation of signaling power systems by the addition of two additional signaling leads: signal battery (SB) and signal ground (SG). In Type II, each of the two signals has its own return. For the E signal, the E lead works with the SSG lead to allow current to flow from the PBX while the M lead is strapped to the SB lead. This scenario results in the trunk being grounded at each end, eliminating the potential problem associated with Type I, discussed above.
The four-wire Type II interface from the PBX has the following characteristics:
* E lead (pin 7) detector 'floats' at -48V below ground
* SG lead (pin 8) has a low ohms to ground
* M lead (pin 2) contact between M and SB is open when on-hook, and closed when off hook
* M lead floats
* SB lead (pin 1) floats
* Approximately 30-150 ohms between T/R (pins 6/3) sometimes in series with 2.2uF of capacitance
* Approximately 30-150 ohms between T1/R1 (pins 5/4) sometimes in series with 2.2uF of capacitance
E&M Type II
Type II is seen only occasionally in North America, usually on Centrex trunk circuits or Nortel PBX systems.
E&M Type III
E&M Type III signaling is very similar to Type I, except that the battery and ground source for the M lead is supplied by the transmission equipment. Complete power isolation is provided with the M lead, and the facility can establish and control the amount of E lead current. Type III uses the SG lead to provide common ground. The PBX drops the M signal by grounding it, rather than by opening a current loop.
The four-wire Type III interface from the PBX has the following characteristics:
* E lead (pin 7) detector 'floats' at -48V below ground
* M lead (pin 2) contact between M and SG when on hook, and between M and SB when off hook
* SG lead (pin 8) floats
* M lead (pin 2) floats
* SB lead (pin 1) floats
* Approximately 30-150 ohms between T/R (pins 6/3) sometimes in series with 2.2uF of capacitance
* Approximately 30-150 ohms between T1/R1 (pins 5/4) sometimes in series with 2.2uf of capacitance
E&M Type III
There is no evidence that the unbalanced E lead of Type III has caused any interference problems, but one drawback of this interface is its inability to operate in a 'back-to-back' configuration.
This interface is most often used in older CO equipment such as 1/1AESS, 2/2BESS, and 3ESS switches. It is not often seen now because most of these older switches have been replaced.
E&M Type IV
Type IV is symmetric and requires no common ground. Each side closes a current loop to signal; the flow of current is detected via a resistive load to indicate the presence of the signal. The Type IV interface is similar to Type II, with the difference in the operation of the M lead—in Type II, the M lead states are 'open' and 'battery;' Type IV states are 'ground' and 'open.'
The four-wire Type IV interface from the PBX has the following characteristics:
* E lead (pin 7) detector 'floats' at -48V below ground
* SG lead (pin 8) has low ohms to ground
* M lead (pin 2) contact between M and SB is open when on-hook, and closed when off hook
* M lead (pin 2) floats
* SB lead (pin 1) floats
* Approximately 30-150 ohms between T/R (pins 6/3) sometimes in series with 2.2uF of capacitance
* Approximately 30-150 ohms between T1/R1 (pins 5/4) sometimes in series with 2.2uf of capacitance
E&M Type IV
The advantages of Type IV include:
* Accidental shorting of the SB lead (during cable wiring, for example) will not result in an excessive current flow.
* The interface can interconnect to a Type II device.
* The interface can operate in a 'back-to-back' configuration.
Because it can be difficult for an external monitor to distinguish between 'open' and 'ground' states, it can be difficult to obtain test and supporting equipment for a Type IV interface. Type IV is not currently supported by the Cisco 3600 series routers.
E&M Type V
E&M Type V interface is a simplified version of Type IV. It is also a symmetric interface, using only two wires. In the Type V interface, both the switch and the transmission equipment supply battery. The battery for the M lead is located in the signaling equipment, and the battery for the E lead is located in the PBX. Type V requires a common ground between the PBX and the tie line equipment, which is provided via the SG leads.
The Type V interface from the PBX has the following characteristics:
* E lead (pin 7) detector 'floats' at -48V below ground
* M lead (pin 2) contact ground is open when on-hook, and closed when off hook
* Approximately 30-150 ohms between T/R (pins 6/3) sometimes in series with 2.2uF of capacitance
* Approximately 30-150 ohms between T1/R1 (pins 5/4) sometimes in series with 2.2uf of capacitance
E&M Type V
Although this interface does not provide isolation between power systems, there is minimal (or no) return currents in this symmetrical signaling scheme. Type V is the most popular interface outside North America.
E&M Start-Dial Supervision Signaling Protocol
Start-dial supervision is the line protocol used between equipment that takes place after the initial off-hook condition, up to the passing of dial digits to the connected device.
Three principal protocols are used on E&M circuits:
* E&M Immediate Start Signaling
* E&M Wink-Start Signaling
* E&M Delay-Dial Signaling
Wink start is used to notify the remote side it can send dialed number identification service (DNIS) information. Wink acknowledgment is a second wink that is sent to acknowledge the receipt of the DNIS information. Immediate start does not send any winks at all.
The following sections explain how each protocol works. It is important to understand what the protocol is supposed to do when debugging, because call progress anomalies provide clues to the cause.
Immediate Start
E&M Immediate Start is the simplest of protocols. Here, the originating switch goes off hook, waits for a finite period of time (say, 200 ms) then sends the address digits without regard to the remote. Because there is no acknowledgment, or handshaking, between switches, this type of trunk signaling should be used only when there is a dedicated physical or logical trunk between switches. Cisco routers support the use of the Immediate Start protocol.
Immediate Start
Wink Start
E&M Wink Start is the most common of protocols. Wink start is an in-band technique in which the calling switch waits from 140 to 290 ms for an off-hook wink pulse from the called switch before sending the dialed digits. Wink start was developed to minimize glare, which occurs when both ends attempt to seize the trunk at the same time. If there is no wink pulse, an error condition is caused by both ends attempting to place a call on the same trunk.
* In the original Wink Start protocol, the remote responds to an off hook from the originating device with a short wink (transition from on hook to off hook and back again). This wink tells the originating device that the remote device is ready to receive digits. After receiving the addressing digits, the remote then goes off hook for the duration of the call. The originating device maintains off hook for the duration of the call.
* In Wink Start with Wink Acknowledge protocol (sometimes referred to as double wink), the remote responds to an off hook from the originating device with a short wink (transition from on hook to off hook and back again), just as in the original Wink Start. This wink tells the originating side that the remote is ready to receive digits. After receiving the addressing digits, the remote then provides another wink (called an Acknowledgment Wink) that tells the originating side that the terminating side has received the dialed digits. The remote then goes off hook to indicate connection when the ultimate called endpoint has answered. The originating device maintains off-hook status for the duration of the call.
Wink Start normally is not used on trunks that are controlled with message-oriented signaling schemes such as ISDN or Signaling System 7 (SS7). Cisco routers support both wink-start (fgb) and wink-start with wink-acknowledge or double-wink (fgd).
Wink Start
Delay Dial
In E&M Delay Dial mode, the originating device goes off hook and waits for about 200 ms, then checks to see if the remote end is on hook. If so, it then outputs addressing digits. If the remote is off hook, the calling device waits until the remote goes back on hook before transmitting digits. The delay signal says, in effect 'hold on, I'm not ready to receive digits.' This protocol was invented for use with systems that have fewer digit collectors than trunk interfaces. Delay dial is not currently supported by Cisco 3600 series routers.
Delay
Start Dial Supervision Mismatches
Although both ends of a call do not need Start Dial Supervision, mismatches can be a source of problems. Sometimes a PBX has a different Start Dial Supervision protocol for inbound and outbound calls. This setup can lead to erratic behavior if the remote is not configured to properly handle this condition. The following general rule set applies:
* An Immediate-Start interface can usually originate a call to a Wink-Start interface.
* An Immediate-Start interface can usually place a call to a Delay-Dial interface if the delay pulse is shorter than the immediate-start delay. Otherwise, operation is erratic.
* A Wink-Start interface can usually originate a call into a Delay-Dial interface if there is a delay pulse. Otherwise, the call will hang, with only a 50-percent chance of working.
* A Delay-Dial interface can, for the most part, originate a call into an Immediate-Start or Wink-Start interface.
Go on to Configuration of VoIP with E&M Signaling."
*
The FXO interface is an RJ-11 connector that connects local calls to a public switched telephone network (PSTN) central office (CO), or to a PBX that does not support E&M signaling. This is the interface a standard telephone provides. This is the only voice interface card approved to connect to off-premise lines, and this is its primary use. This interface may be used to provide backup over the PSTN or for Centrex-type operations. The FXO ports on the Cisco 3600 series router can support both loop-start and ground-start modes. (In certain situations, a hardware jumper must be used to make an FXO port operate in ground-start mode.) The ground-start signaling method is used primarily on trunk lines or tie lines between private branch exchanges (PBXs).
*
The FXS interface is also an RJ-11 connector that connects directly to a standard telephone, fax machine, or similar device. The FXS interface supplies ringing voltage, dial tone, and similar signals to FXO devices. As the exercises in module 1 demonstrated, you would use the FXS interface when connecting a phone directly to a router. Basically, the FXS interface mimics the PSTN. The FXS ports on the Cisco 3600 series router can provide the battery at 24-volt DC. They can also support both loop-start and ground-start modes of operation according to the software configuration of the router. Loop start, however, is the most common, because most residential telephones are analog loop-start devices.
*
E&M, which stands for 'Ear and Mouth' (or 'recEive and transMit,' or sometimes 'Earth and Magnet'), is a signaling technique for two- and four-wire telephone and trunk interfaces that is used mainly between PBXs or other network-to-network telephony switches, such as Lucent 5 Electronic Switching System [5ESS], Nortel DMS-100, and so on. The E&M analog interface is an RJ-48S connector used to connect remote calls from an IP network to a PBX for local distribution and between PBX trunk lines (tie lines) or other network-to-network telephony switches. Unlike loop-start or ground-start modes of operation on the FXS/FXO ports, E&M uses separate wires for signaling and voice. There are five types of E&M signaling, as well as two wiring methods.
Exercise care when designing a voice network...
Exercise care when designing a voice network to ensure supervisory signals (discussed in module 1 of this tutorial) are transmitted when expected to avoid common problems such as spurious disconnects, undisconnected lines, and continuous rings. For example, a typical disconnect supervision problem can occur when a given line can be released only by the party who originated the phone call. This problem can be fixed by implementing either disconnect supervision or ground start.
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In the first module of this tutorial, you learned about the basics of analog voice internetworking, including the history of telephony, telephone networks and technology, and the various types of telephony signaling. You know how to configure and troubleshoot a Cisco 3640 router using loop-start access signaling across the FXS interface. In this module you will learn more about trunks, analog E&M signaling, and VoIP configuration using E&M. The Cisco VoIP implementation supports E&M types I, II, III, and V, using both two- and four-wire implementations.
Click on any highlighted term see its pop-up glossary definition. For additional information and more definitions of terms used throughout this course, see the full Glossary. You can access the Glossary at any time by clicking Help.
A basic understanding of trunks is necessary to understanding the use of E&M signaling. A line is a communications path between a customer's telephone and a telephone switch, such as a CO switch or a PBX, whereas a trunk is an actual telephone circuit or path between two switches, at least one of which is usually a CO or a switching center. This type of trunk, where voice is carried over a telco's network, is a CO trunk. Another example of a trunk is a private leased line that interconnects two PBXs, forming a corporate voice network. This type of connection is referred to as a PBX trunk.
Central-Office Trunks
Two-Wire Central-Office Trunks
A hunt group is...
A hunt group is a feature supported by voice-capable Cisco routers that involves the configuration of a group of dial peers on the same router with the same destination pattern. With a hunt group, if a call attempt is made to a dial peer on a specific time slot and that time slot is busy, the router hunts for another time slot on that channel until an available time slot is found.
The Cisco 3640 hunts for a group based on matching numbers.
It is possible to configure hunt groups by setting up multiple dial peers having the same destination pattern. Hunt groups are not configured in this tutorial, and the feature is not enabled in the simulation exercises in this module.
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The most common two-wire CO trunks used in PBX networks employ ground start. These trunks may be restricted such that operation may be outgoing only, incoming only, or both. In the case of outgoing calls (direct outward dialing, or DOD) operation additionally may be restricted to local calling only, versus direct distance dialing (DDD). Most incoming calls are routed to an attendant or to a messaging or answering system. The ringback tone is generated from the local exchange carrier's (LEC's) switch that connects to the PBX. This type of trunk is common.
Most of these trunks are assigned the same phone number within the PSTN, and operate in a 'hunt group' fashion.
Direct Inward Dialing Central Office Trunks
Direct inward dialing (DID) is used to determine how the called number is treated for incoming calls. Incoming calls to a PBX often first flow through an attendant position. DID trunks allow users to receive calls directly from the outside without intervention from the attendant.
Use of DID offers three main advantages:
* It allows direct access to stations from outside the PBX.
* It allows users to receive calls even when the attendant switchboard is closed.
* It takes a portion of the load off the attendants.
To accomplish DID on a trunk, the switch at the PSTN (either the local exchange carrier [LEC] or the inter-exchange carriers [IXC]) transmits the number of the called party to the PBX for routing. DID trunks often use existing two-wire circuits, and typically use ground-start signaling. Four-wire circuits using E&M signaling or digital access are sometimes used as well. To use DID, a block of PSTN telephone numbers generally must be reserved from the IXC or LEC.
DID trunk circuits usually employ either Wink Start or Delay-Dial signaling schemes, so that the network knows that the PBX is ready to accept the incoming address supervision. Wink Start and Delay Dial are discussed in more detail later in this section.
The next module in this tutorial, 'Basic Analog-to-Digital Voice over IP,' covers the use of DID in a VoIP configuration.
Wide-Area Telephone Service Central-Office Trunks
Wide-Area Telephone Service (WATS—sometimes referred to as OUTWATS) trunks are used for outgoing calls. They take advantage of interconnection to the IXC. These trunks require that the PBX output digits to the PSTN switch for routing. The network usually provides answer and disconnect supervision. WATS trunks can operate using either ground-start or loop-start signaling, in addition to E&M signaling. Ringback and busy signals are generated from the remote switch or PBX.
WATS trunks do not have addressable PSTN telephone numbers; therefore, these trunks are typically implemented in a hunt-group fashion within the PBX.
Central-Office 800-Service Trunks
Trunks that provide 800-service are sometimes referred to as INWATS service trunks. These trunks are used for incoming calls and take advantage of interconnection to the IXC. With an 800-service trunk, the PSTN does not output digits to the PBX; incoming calls on these trunk numbers are routed to specific individuals or groups by the PBX. These trunks may utilize loop reverse battery or E&M signaling.
Ringback and busy tones are usually generated by the PSTN switch that is interconnected to the PBX. Generally, these trunks are implemented in a hunt group fashion.
Long-Distance Trunks
Long-distance trunks interconnect to an IXC to allow both incoming and outgoing long-distance calling. They usually operate on two-wire ground-start circuits, or two- or four-wire E&M circuits. If access to the PSTN switch is digital (DS1), then conventional robbed-bit signaling (RBS) is used. (RBS is explained in greater detail in the next module of the Voice Internetworking CIM tutorial.)
Ringback and busy tones are usually generated by the IXC's PSTN switch that is interconnected to the PBX. Generally, these types of trunks are implemented in a hunt-group fashion, and incoming calls are typically routed to an attendant or messaging system.
PBX Trunks
A PBX is a private digital or analog telephone switchboard used to originate and answer calls to and from the public network (via CO trunks). PBXs can be combined with PBX trunks between them. When a caller picks up a handset and dials from within the corporation, the PBX connects that user to an idle line or to an idle trunk in an appropriate trunk group, then returns the appropriate call status signal, such as a dial tone or a ringback. A busy or fast-busy signal is returned if the line or the trunk group is busy. An attendant may be present to answer incoming calls and for user assistance.
FX Trunks
Foreign exchange (FX) circuits may consist of either stations or trunks. An FX line is a special line that is run from a local telephone to a CO switch or PBX switch. In this case, the local telephone is assigned a number on a remote switch; for all inbound and outbound calls, the telephone behaves as if it were connected to the remote switch. Generally, an FX circuit uses a two-wire circuit with loop start signaling. The ringback and busy signals are provided by the switch connected to the CO.
An FX trunk operates in a similar fashion, except that a local trunk provides interconnectivity to a remote switch. For outbound calls, local PBX users dial an access code such as 9, receive a dial tone from the remote switch, then output digits to the remote switch for routing. Incoming calls are either barred, or are routed to a PBX attendant or message system.
Because a trunk circuit is involved, features such as call transferring and call forwarding can also be deployed. These types of activities requires disconnect supervision to release the PBX trunk. This supervision cannot be provided with loop-start signaling, so ground start signaling must be used.
Tie Trunks and Tie Lines
Tie trunks interconnect PBX switches within a customer's network. Tie trunks typically connect both trunks and station lines through a network connection. These circuits are usually heavily used and normally support both incoming and outgoing calls.
Tie trunks are typically four-wire E&M-type circuits, but may often interconnect through DS1 facilities using RBS. The use of two-wire trunks is also allowable; these would typically use ground-start signaling.
Although tie lines are generally considered the same as tie trunks, and the terms are often used interchangeably, there are some technical differences:
* Tie trunks can interconnect both trunks and lines. In tie-trunk operation, routing of a call is totally automatic. The remote PBX usually supplies another dial tone, at which the user must enter the necessary address for the called party at that PBX.
* Tie lines connect only lines throughout a network connection. Routing of a call over tie lines is under control of the user. A user would need to dial an access code (9, for example) to gain access to the desired remote PBX. Tie lines are actually tie trunks that use tone-start type of start-dial supervision and cut-through operation. (Details about start-dial supervision can be found at the end of this section.)
Although the next module will include use of a PBX in the network topology, a complete discussion of PBXs and PBX configuration is out of the scope of this tutorial. To learn about PBX configuration, you should refer to the manuals for the particular PBX that you are using in your network. For additional PBX information, however, please see the related document The Private Branch Exchange (PBX) .
As discussed in module 1, 'Basic Analog Voice over IP,' the primary purpose of signaling in a voice network is to establish a connection. Signaling can be classified into four basic functions:
* Supervisory signaling — Informs the telephone or switch of the status of the local loop and any connected trunks. Supervisory signaling is used to:
o Initiate a call request on line or trunks (called line signaling on trunks).
o Indicate that the call has been answered or the call has been disconnected (disconnect and answer supervision).
o Initiate or terminate charging for calls.
o Recall an operator on an established connection.
* Address signaling — Contains information indicating the destination of a call, such as the telephone number and an area code, an access code, or a PBX tie trunk access code.
* Call progress indicators — Convey call-progress or call-failure information to subscribers or operators by the use of usually audible tones (such as the busy signals, the reorder tone, and the ringback, all of which were discussed in module 1).
* Network management signaling — Controls the bulk assignment of circuits or modifies the operating characteristics of switching systems in a network in response to overload conditions. (These signaling functions will not be covered in detail in this tutorial, but are mentioned here for completeness.)
For a more detailed discussion of signaling, including descriptions of supervision, address, call-progress, and network management signaling, read Signaling, which is included in this tutorial. Also search Cisco Connection Online (CCO) at http://www.cisco.com for more information on this specific topic as well as more available information on treansmitting voice over a data network.
Just as the local loop requires supervisory signaling, so does a trunk. Although loop-start signaling, which is generally used on everyday residential telephones, can also be used on trunks, its use can result in problems that make it an ineffective signaling method for a trunk. With loop start, only the device originating the call can release the connection. Also, loop start would not prevent a trunk from being seized by both parties to a call, a condition referred to as glare. Glare can be tolerable on a local loop, but its occurrence on a trunk would be unacceptable. Ttwo-way handshaking methods were developed to coordinate the sequence of events that occur during a call: the request by the calling end for access to the trunk, followed by the acknowledgment by the called end, then the subsequent seizure of the trunk by the calling end.
The basic types of supervisory signaling used on trunks are: ground start, E&M, and start-dial supervision.
Ground-Start Signaling
In module 1 of this course, you configured the Cisco 3640 router FXS port to use loop-start signaling, because calls were being made using a directly connected analog telephone. Ground start is the access signaling method used on trunk lines or tie lines between PBXs to indicate on-hook/off-hook status to the CO. Ground-start signaling works by using ground and current detectors. Ground start behaves like a loop start, however, the PBXs on both sides—the telco and the customer's telephone—have to agree on the status of a line before a call can be placed. This scenario allows the network to indicate off-hook or seizure of an incoming call independent of the ringing signal.
E&M Signaling Interface Types
Analog trunk circuits connect between automated systems (a PBX) and the network (a CO). The most common form of analog trunk is the E&M interface.
E&M signaling is typically used for trunk lines. It provides native support for both disconnect and answer supervision, as well as glare avoidance. In E&M signaling, separate paths are used for voice and signaling. E&M is normally the only way that a CO switch can provide two-way dialing with DID.
The history of the semantics of E&M circuits dates back to the days of telegraphy, where the main office end had a 'key' that grounded the E circuit, and the other end had a sounder with an electromagnet attached to a battery. Descriptions such as 'ear' and 'mouth' were created to help provide a reference to field personnel as to the direction of a signal in a wire. Note that these terms correspond to the inbound and outbound circuits, known as the E lead and M lead, respectively.
There are five standard types of E&M interfaces, which correspond to the five signaling types:
* E&M Type I Interface Model
* E&M Type II Interface Model
* E&M Type III Interface Model
* E&M Type IV Interface Model
* E&M Type V Interface Model
With each signaling type, the PBX supplies one signal, known as the M signal (mouth), and accepts one signal, known as the E signal (ear). Conversely, the tie-line equipment accepts the M signal from the PBX and provides the E signal to the PBX. The M signal accepted by the tie-line equipment at one end of a tie circuit becomes the E signal output by the remote tie-line interface.
Remember learning about tip and ring in module 1?
* When a user tries to place a call by grounding the 'ring' lead, the PBX at the telco senses the flow of current and grounds the 'tip' lead to indicate the PBX is ready to serve.
* The user's equipment perceives the flow of current on its 'tip' and knows that the PBX is ready to serve.
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The signaling part of the interface has five distinct physical configurations (Types I – V) and the audio interface has two (two- and four-wire). Note that the terms two-wire and four-wire are used to reference the communication protocol of the audio path. The difference between a two-wire and four-wire circuit is whether the audio path is full duplex on one pair or two pairs of wires.
Two full-duplex wires (called tip and ring) carry the audio on two-wire E&M. Four-wire E&M uses four half-duplex wires for the audio path (Tip, Ring, Tip1, and Ring1). Note that a four-wire E&M circuit may have from six to eight physical wires.
Signaling Types
* E — Ear or earth: Signal wire from the trunking (CO or network) side to signaling (user) side
* M — Mouth or magnet: Signal wire from signaling (user) side to trunking (CO or network) side
* SG — Signal ground: Used only on certain types of E&M; sometimes grounded, sometimes not>
* SB — Signal battery: Used on certain types of E&M; sometimes provides -48V Direct Current, sometimes ground, sometimes is not used at all
* T/R — Tip/ring: Used only on a four-wire circuit; carries audio from the signaling (user) side to the trunking (CO/network) side; not used on a two-wire circuit
* T1/R1 — Tip1/ring1: On four-wire circuits, carries audio from the trunking (CO/network) side to the signaling (user) side; on a two-wire circuit, this pair carries the full-duplex audio path
Types I and II are the most popular E&M signaling types in the Americas. Type V is used in the United States, and is very popular in Europe. (SSDC5 is most often found in the United Kingdom.) Similar to Type V, SSDC5A differs in that on- and off-hook states are backward to allow for fail-safe operation: if the line breaks, the interface defaults to off hook (busy). Of all the types, only Types II and V are symmetrical (can be back to back using a crossover cable).
The Cisco 2600 and 3600 series routers currently support types I, II, III, and V utilizing both two- and four-wire implementations. The E&M interface of the Cisco 3600 series presents the 'channel bank,' 'tie equipment,' or 'CO' side of a trunk interface to a PBX. Each E&M signaling type has a unique circuit model and connection diagram. All Cisco analog voice gateway routers have 24V DC designed on the FXS ports. According to EIA 464 standard, any voltage from DC 24 volts to DC 52 volts is acceptable.
Characteristics of E&M Lead Signaling
Type
M Lead
E Lead
Outbound Direction Inbound Direction
Off Hook
On Hook
Off Hook
On Hook
I
Battery
Ground
Ground
Open
II
Battery
Open
Ground
Open
III
Loop current
Ground
Ground
Open
IV
Ground
Open
Ground
Open
V
Ground
Open
Ground
Open
SSDC5
Earth on
Earth off
Earth on
Earth off
Cisco routers expect to see off-hook conditions on the M lead and signal off hook to the remote device on the E lead.
See the following sections and illustrations for individual descriptions of the different types. Each of the following illustrations shows the E&M interface of the PBX on the left, and the corresponding tie-line equipment interface on the right. The symbol V refers to battery voltage, which can be 25 VDC to 65 VDC, and is usually (nominally) -48 VDC.
E&M Type I
In E&M Type I signaling, the battery PBX provides the battery for both the E and M leads. During an off-hook condition, the PBX generates the E signal by grounding the E lead. The PBX detects the E signal by sensing the increase in current through a resistive load. Similarly, in an on-hook condition, the PBX generates the M signal by sourcing a current to the tie-line equipment, which detects it via a resistive load.
The four-wire Type I interface from the PBX has the following characteristics:
* E (pin 7) detector 'floats' at -48V below ground
* M (pin 2) contact has low ohms to ground on hook, and is -48V below ground when off hook
* Approximately 30-150 ohms between T/R (pins 6/3) sometimes in series with 2.2uf of capacitance
* Approximately 30-150 ohms between T1/R1 (pins 5/4) sometimes in series with 2.2uf of capacitance
E&M Type I
The Type I interface requires that the PBX and tie-line equipment share a common signaling ground reference. This setup can be achieved by connecting signal ground from the PBX to the signal-ground (SG) lead (pin 8) of the RJ-48S connector.
Note that the voltage on the E and M leads may not be the same (the E lead may have lower voltage). This asymmetrical signaling scheme is a potential source of interference, which could cause high return current through the grounding system. If two PBXs were not correctly grounded, current could flow down the M lead, causing the remote PBX to erroneously detect a current on the E lead, thus resulting in false seizure of a trunk. Despite this potential problem, E & M signaling is the most common four-wire trunk interface used in North America.
E&M Type II
The E&M Type II interface provides almost complete isolation of signaling power systems by the addition of two additional signaling leads: signal battery (SB) and signal ground (SG). In Type II, each of the two signals has its own return. For the E signal, the E lead works with the SSG lead to allow current to flow from the PBX while the M lead is strapped to the SB lead. This scenario results in the trunk being grounded at each end, eliminating the potential problem associated with Type I, discussed above.
The four-wire Type II interface from the PBX has the following characteristics:
* E lead (pin 7) detector 'floats' at -48V below ground
* SG lead (pin 8) has a low ohms to ground
* M lead (pin 2) contact between M and SB is open when on-hook, and closed when off hook
* M lead floats
* SB lead (pin 1) floats
* Approximately 30-150 ohms between T/R (pins 6/3) sometimes in series with 2.2uF of capacitance
* Approximately 30-150 ohms between T1/R1 (pins 5/4) sometimes in series with 2.2uF of capacitance
E&M Type II
Type II is seen only occasionally in North America, usually on Centrex trunk circuits or Nortel PBX systems.
E&M Type III
E&M Type III signaling is very similar to Type I, except that the battery and ground source for the M lead is supplied by the transmission equipment. Complete power isolation is provided with the M lead, and the facility can establish and control the amount of E lead current. Type III uses the SG lead to provide common ground. The PBX drops the M signal by grounding it, rather than by opening a current loop.
The four-wire Type III interface from the PBX has the following characteristics:
* E lead (pin 7) detector 'floats' at -48V below ground
* M lead (pin 2) contact between M and SG when on hook, and between M and SB when off hook
* SG lead (pin 8) floats
* M lead (pin 2) floats
* SB lead (pin 1) floats
* Approximately 30-150 ohms between T/R (pins 6/3) sometimes in series with 2.2uF of capacitance
* Approximately 30-150 ohms between T1/R1 (pins 5/4) sometimes in series with 2.2uf of capacitance
E&M Type III
There is no evidence that the unbalanced E lead of Type III has caused any interference problems, but one drawback of this interface is its inability to operate in a 'back-to-back' configuration.
This interface is most often used in older CO equipment such as 1/1AESS, 2/2BESS, and 3ESS switches. It is not often seen now because most of these older switches have been replaced.
E&M Type IV
Type IV is symmetric and requires no common ground. Each side closes a current loop to signal; the flow of current is detected via a resistive load to indicate the presence of the signal. The Type IV interface is similar to Type II, with the difference in the operation of the M lead—in Type II, the M lead states are 'open' and 'battery;' Type IV states are 'ground' and 'open.'
The four-wire Type IV interface from the PBX has the following characteristics:
* E lead (pin 7) detector 'floats' at -48V below ground
* SG lead (pin 8) has low ohms to ground
* M lead (pin 2) contact between M and SB is open when on-hook, and closed when off hook
* M lead (pin 2) floats
* SB lead (pin 1) floats
* Approximately 30-150 ohms between T/R (pins 6/3) sometimes in series with 2.2uF of capacitance
* Approximately 30-150 ohms between T1/R1 (pins 5/4) sometimes in series with 2.2uf of capacitance
E&M Type IV
The advantages of Type IV include:
* Accidental shorting of the SB lead (during cable wiring, for example) will not result in an excessive current flow.
* The interface can interconnect to a Type II device.
* The interface can operate in a 'back-to-back' configuration.
Because it can be difficult for an external monitor to distinguish between 'open' and 'ground' states, it can be difficult to obtain test and supporting equipment for a Type IV interface. Type IV is not currently supported by the Cisco 3600 series routers.
E&M Type V
E&M Type V interface is a simplified version of Type IV. It is also a symmetric interface, using only two wires. In the Type V interface, both the switch and the transmission equipment supply battery. The battery for the M lead is located in the signaling equipment, and the battery for the E lead is located in the PBX. Type V requires a common ground between the PBX and the tie line equipment, which is provided via the SG leads.
The Type V interface from the PBX has the following characteristics:
* E lead (pin 7) detector 'floats' at -48V below ground
* M lead (pin 2) contact ground is open when on-hook, and closed when off hook
* Approximately 30-150 ohms between T/R (pins 6/3) sometimes in series with 2.2uF of capacitance
* Approximately 30-150 ohms between T1/R1 (pins 5/4) sometimes in series with 2.2uf of capacitance
E&M Type V
Although this interface does not provide isolation between power systems, there is minimal (or no) return currents in this symmetrical signaling scheme. Type V is the most popular interface outside North America.
E&M Start-Dial Supervision Signaling Protocol
Start-dial supervision is the line protocol used between equipment that takes place after the initial off-hook condition, up to the passing of dial digits to the connected device.
Three principal protocols are used on E&M circuits:
* E&M Immediate Start Signaling
* E&M Wink-Start Signaling
* E&M Delay-Dial Signaling
Wink start is used to notify the remote side it can send dialed number identification service (DNIS) information. Wink acknowledgment is a second wink that is sent to acknowledge the receipt of the DNIS information. Immediate start does not send any winks at all.
The following sections explain how each protocol works. It is important to understand what the protocol is supposed to do when debugging, because call progress anomalies provide clues to the cause.
Immediate Start
E&M Immediate Start is the simplest of protocols. Here, the originating switch goes off hook, waits for a finite period of time (say, 200 ms) then sends the address digits without regard to the remote. Because there is no acknowledgment, or handshaking, between switches, this type of trunk signaling should be used only when there is a dedicated physical or logical trunk between switches. Cisco routers support the use of the Immediate Start protocol.
Immediate Start
Wink Start
E&M Wink Start is the most common of protocols. Wink start is an in-band technique in which the calling switch waits from 140 to 290 ms for an off-hook wink pulse from the called switch before sending the dialed digits. Wink start was developed to minimize glare, which occurs when both ends attempt to seize the trunk at the same time. If there is no wink pulse, an error condition is caused by both ends attempting to place a call on the same trunk.
* In the original Wink Start protocol, the remote responds to an off hook from the originating device with a short wink (transition from on hook to off hook and back again). This wink tells the originating device that the remote device is ready to receive digits. After receiving the addressing digits, the remote then goes off hook for the duration of the call. The originating device maintains off hook for the duration of the call.
* In Wink Start with Wink Acknowledge protocol (sometimes referred to as double wink), the remote responds to an off hook from the originating device with a short wink (transition from on hook to off hook and back again), just as in the original Wink Start. This wink tells the originating side that the remote is ready to receive digits. After receiving the addressing digits, the remote then provides another wink (called an Acknowledgment Wink) that tells the originating side that the terminating side has received the dialed digits. The remote then goes off hook to indicate connection when the ultimate called endpoint has answered. The originating device maintains off-hook status for the duration of the call.
Wink Start normally is not used on trunks that are controlled with message-oriented signaling schemes such as ISDN or Signaling System 7 (SS7). Cisco routers support both wink-start (fgb) and wink-start with wink-acknowledge or double-wink (fgd).
Wink Start
Delay Dial
In E&M Delay Dial mode, the originating device goes off hook and waits for about 200 ms, then checks to see if the remote end is on hook. If so, it then outputs addressing digits. If the remote is off hook, the calling device waits until the remote goes back on hook before transmitting digits. The delay signal says, in effect 'hold on, I'm not ready to receive digits.' This protocol was invented for use with systems that have fewer digit collectors than trunk interfaces. Delay dial is not currently supported by Cisco 3600 series routers.
Delay
Start Dial Supervision Mismatches
Although both ends of a call do not need Start Dial Supervision, mismatches can be a source of problems. Sometimes a PBX has a different Start Dial Supervision protocol for inbound and outbound calls. This setup can lead to erratic behavior if the remote is not configured to properly handle this condition. The following general rule set applies:
* An Immediate-Start interface can usually originate a call to a Wink-Start interface.
* An Immediate-Start interface can usually place a call to a Delay-Dial interface if the delay pulse is shorter than the immediate-start delay. Otherwise, operation is erratic.
* A Wink-Start interface can usually originate a call into a Delay-Dial interface if there is a delay pulse. Otherwise, the call will hang, with only a 50-percent chance of working.
* A Delay-Dial interface can, for the most part, originate a call into an Immediate-Start or Wink-Start interface.
Go on to Configuration of VoIP with E&M Signaling."
Cisco - Signaling
Cisco - Signaling: "Signaling
Signaling is defined by Consultative Committee for International Telegraph and Telephone (CCITT) Recommendation Q.9 as 'the exchange of information (other than speech) specifically concerned with the establishment, release, and control of calls, and network management in automatic telecommunications operations.'
In the broadest sense, there are two signaling realms:
* Subscriber signaling
* Trunk signaling (interswitch and/or interoffice)
Signaling is also traditionally classified into four basic functions:
* Supervision
* Address
* Call progress
* Network management
Supervision signaling is used to:
* Initiate a call request on line or trunks (called line signaling on trunks).
* Hold or release an established connection.
* Initiate or terminate charging.
* Recall an operator on an established connection.
Address signaling conveys such information as the calling or called subscriber's telephone number and an area code, an access code, or a Private Automatic Branch Exchange (PABX) tie trunk access code. An address signal contains information indicating the destination of a call initiated by a customer, network facility, and so forth.
Call progress signals are usually audible tones or recorded announcements that convey call-progress or call-failure information to subscribers or operators. These call-progress signals are fully described below.
Network management signals are used to control the bulk assignment of circuits or to modify the operating characteristics of switching systems in a network in response to overload conditions.
There are about 25 recognized interregister signaling systems worldwide, in addition to some subscriber signaling techniques. CCITT Signaling System Number 7 (SSN7) is fast becoming the international/national standard interregister signaling system.
Most installations will probably involve recEive and transMit (E&M) signaling; however, for reference, single frequency (SF) signaling on Tip and Ring loops, Tip and Ring reverse battery loops, loop start, and ground start are also included.
Types I and II are the most popular E&M signaling in the Americas. Type V is used in the United States, but is very popular in Europe. Similar to type V, SSDC5A differs in that on- and off-hook states are reversed to allow for fail-safe operation: if the line breaks, the interface defaults to off-hook (busy). Of all the types, only II and V are symmetrical (can be back-to-back using a cross-over cable). SSDC5 is most often found in England.
Other signaling techniques often used are delay, immediate, and wink start. Wink start is an in-band technique where the originating device waits for an indication from the called switch before sending the dialed digits. Wink start normally is not used on trunks that are controlled with message-oriented signaling schemes such as Integrated Services Digital Network (ISDN) or Signaling System 7 (SS7).
Summary of Signaling System Applications and Interfaces
Signaling System Application/Interface Characteristics
Station Loop
Loop signaling
Basic Station
DC signaling.
Origination at station.
Ringing from Central Office.
Coin Station
DC signaling.
Loop-start or ground-start origination at station.
Ground and simplex paths may be used in addition to the line for coin collection and return.
Interoffice Trunk
Loop Reverse Battery
One-way call origination.
Directly applicable to metallic facilities.
Both current and polarity are sensed.
Can be used on carrier facilities with appropriate facility signaling system.
E&M Lead
Two way call origination.
Requires facility signaling system for all applications.
Facility Signaling System
Metallic DX
Analog SF
Digital Bits in information
Special Service
Loop Type
Standard station loop and trunk arrangement as above.
Ground-start format similar to coin service for PBX-CO trunks.
E & M Lead
E&M for PBX dial tie trunks. E&M for carrier system channels in special service circuits.
North American Practices
The typical North American touchtone set provides a 12-tone set. Some custom sets provide 16-tone signals of which the extra digits are identified by the A-D pushbuttons.
Dual Tone Multifrequency (DTMF) Frequency Pairs
Low Frequency Group (Hz) High Frequency Group (Hz)
1209 1336 1477 1633
697 1 2 3 A
770 4 5 6 B
852 7 8 9 C
941 * 0 # D
Audible tones commonly used in North America
Tone Frequencies (Hz) Cadence
Dial 350 + 440 Continuous
Busy (station) 480 + 620 0.5 sec on, 0.5 sec off
Busy (network) 480 + 620 0.2 sec on, 0.3 sec off
Ring return 440 + 480 2 sec on, 4 sec off
Off-hook alert Multifreq howl 1 sec on, 1 sec off
Recording warning 1400 0.5 sec on, 15 sec off
Call waiting 440 0.3 sec on, 9.7 sec off
Call Progress Tones Used in North America
Name Frequencies (Hz) Pattern Levels
Low tone 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 Various -24 dBm0
61 to 71 dBmC
61 to 71 dBmC
61 to 71 dBmC
61 to 71 dBmC
High tone 480
400
500 Various -17 dBmC
61 to 71 dBmC
61 to 71 dBmC
Dial tone 350 + 440 Steady -13 dBm0
Audible ring tone 440 + 480
440 + 40
500 + 40 2 sec on, 4 sec off
2 sec on, 4 sec off
2 sec on, 4 sec off -19 dBmC
61 to 71 dBmC
61 to 71 dBmC
Line Busy Tone 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 0.5 sec on, 0.5 sec off
Reorder 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 0.3 sec on, 0.2 sec off
6A alerting tone 440 2 sec on, followed by 0.5 sec on, every 10 sec
Recorder warning tone 1400 0.5 sec burst every 15 sec
Reverting tone 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 0.5 sec on, 0.5 sec off -24 dBmC
Deposit coin tone 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 Steady
Receiver off-hook (analog) 1400 + 2060 + 2450 + 2600 0.1 sec on, 0.1 sec off +5 vu
Receiver off-hook 1400 + 2060 + 2450 + 2600 0.1 sec on, 0.1 sec off +3.9 to -6.0 dBm
Howler 480 Incremented in level
Every 1 sec for 10 sec Up to 40 vu
No such number (crybaby) 200 to 400 Freq. modulated at 1 Hz interrupted every 6 sec for 0.5 sec
Vacant code 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 0.5 sec on, 0.5 sec off, 0.5 sec on, 1.5 sec off?
Busy verification Tone (Centrex) 440 Initial 1.5 sec followed 0.3 sec every 7.5 to 10 sec -13 dBm0
Busy verification Tone (TSPS) 440 Initial 2 sec followed 0.5 sec every 10 sec -13 dBm0
Call waiting tone 440 Two bursts of 300 ms separated by 10 sec -13 dBm0
Confirmation tone 350 + 440 3 bursts of 300 ms separated by 10 sec -13 dBm0
Indication of camp-on 440 1 sec every attendant releases from loop -13 dBm0
Recall dial tone 350 + 440 3 bursts, 0.1 sec on, sec off then steady -13 dBm0
Data set answer back tone 2025 Steady -13 dBm
Calling card prompt tone 941 + 1477 followed by 440 + 350 60ms -10 dBm0
Class of service 480
400
500 0.5 to 1 sec once
Order tones
Single
480
400
500 0.5 sec
Double
480
400
500 2 short bursts
Triple
480
400
500 3 short bursts
Quad
480
400
500 4 short bursts
Number checking tone 135 Steady
Coin denomination
3 5 cents
1050-1100 (bell) One tap
slot 10 cents
1050-1100 (bell) Two taps
stations 25 cents
800 (gong) One tap
Coin collect tone 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 Steady
Coin return tone 480
400
500 0.5 to 1 sec once
Coin return test tone 480
400
500 0.5 to 1 sec once
Group busy tone 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 Steady
Vacant position 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 Steady
Dial off normal 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 Steady
Permanent signal 480
400
500 Steady
Warning tone 480
400
500 Steady
Service observing 135 Steady
Proceed to send Tone (IDDD) 480 Steady -22 dBm0
Centralized intercept 1850 500 ms -17 dBm0
ONI order tone 700 + 1100 95 to 250 ms -25 dBm0
Note: Three dots in the pattern mean that the pattern is repeated indefinitely.
Single Frequency In-Band Signaling
SF in-band signaling is widely used in North America. Its most common application is for supervision, such as idle-busy, also called line signaling. It also can be used for dial pulse signaling on trunks. The dynamics of SF signaling requires an understanding of the signal durations and configurations of the E&M circuits, as well as the lead interface arrangements. The following tables show the characteristics of SF signaling, E&M lead configurations, and interface arrangements.
Typical Single Frequency Signaling Characteristics
General
Signaling frequency (tone)
2600 Hz
Idle state transmission
Cut
Idle/break
Tone
Busy/make
No tone
Receiver
Detector bandwidth
+/- 50 Hz @ -7 dBm for E type
+/- 30 Hz @ -7 dBm
Pulsing rate
7.5 to 122 pps
E/M unit
Minimum time for on-hook
33 ms
Minimum no tone for off-hook
55 ms
Input percent break (tone)
38-85 (10 pps)
E lead - open
Idle
- ground
Busy
Originating (loop reverse battery) unit
Minimum tone for idle
40 ms
Minimum no tone for off-hook
43 ms
Minimum output for on-hook
69 ms
Voltage on R lead (-48 V on ring and ground on tip)
On-hook
Voltage on T lead (-48 V on tip and ground on ring)
Off-hook
Terminating (loop reverse battery) unit
Minimum tone for on-hook
90 ms
Minimum no tone for off-hook
60 ms
Minimum output (tone-on)
56 ms
Loop open
On-hook
Loop closed
Off-hook
Transmitter
Low level tone
-36 dBm
High level tone
-24 dBm
High level tone duration
400 ms
Precut
8 ms
Holdover cut
125 ms
Crosscut
625 ms
On hook cut
625 ms
E/M unit
Voltage on M lead
Off-hook (no tone)
Open/ground on M lead
On-hook (tone)
Minimum ground on M lead
21 ms
Minimum voltage on M lead
21 ms
Minimum output tone
21 ms
Minimum no tone
21 ms
Originating (loop reverse battery) unit
Loop current to no tone
19 ms
No loop current to tone
19 ms
Minimum input for tone out
20 ms
Minimum input for no tone out
14 ms
Minimum tone out
51 ms
Minimum no tone out
26 ms
Loop open
On-hook
Loop closed
Off-hook
Terminating (loop) unit
Reverse battery to no tone
19 ms
Normal battery to tone
19 ms
Minimum battery for tone out
25 ms
Minimum reverse battery for no tone
14 ms
Minimum tone out
51 ms
Minimum no tone out
26 ms
Battery on R lead (-48 v)
On-hook
Battery on TY lead (-48 on tip)
Off-hook
Single Frequency Signals Used in E&M Lead Signaling
Calling End Called End
Signal M-Lead E-Lead 2600 Hz 2600 Hz E-Lead M-Lead Signal
Idle Ground Open On On Open Ground Idle
Connect Battery Open Off On Ground Ground Connect
Stop dialing Battery Ground Off Off Ground Battery Stop dialing
Start dialing Battery Open Off On Ground Ground Start dialing
Dial pulsing Ground Open On On Open Ground Dial pulsing
Battery
Off
Ground
Off -hook Battery Ground Off Off Ground Battery Off-hook (answer)
Ring forward Ground Ground On Off Open Battery Ring forward
Battery
Off
Ground
Ringback Battery Open Off On Ground Ground Ringback
Ground
Off
Battery
Flashing Battery Open Off On Ground Ground Flashing
Ground
Off
Battery
On-hook Battery Open Off On Ground Ground On-hook
Disconnect Ground Open On On Open Ground Disconnect
Single Frequency Signals Used in Reverse Battery Tip and Ring Loop Signaling
Calling End Called End
Signal T/R - SF SF - T/R 2600 Hz 2600 Hz T/R - SF SF - T/R Signal
Idle Open Batt-gnd On On Open Batt-gnd Idle
Connect Closure Batt-gnd Off On Closure Batt-gnd Connect
Stop dialing Closure Rev batt-gnd Off Off Closure Rev batt-gnd Stop dialing
Start dialing Closure Batt-gnd Off On Closure Batt-gnd Start dialing
Dial pulsing Open Batt-gnd On On Open Batt-gnd Dial pulsing
Closure
Off
Closure
Off -hook Closure Rev batt-gnd Off Off Closure Rev batt-gnd Off-hook (answer)
Ring forward Open Rev batt-gnd On Off Open Rev batt-gnd Ring forward
Closure
Off
Closure
Ringback Closure Batt-gnd Off On Closure Batt-gnd Ringback
Rev batt-gnd
Off
Rev batt-gnd
Flashing Closure Batt-gnd Off On Closure Batt-gnd Flashing
Rev batt-gnd
Off
Rev batt-gnd
On-hook Closure Batt-gnd Off On Closure Batt-gnd On-hook
Disconnect Open Batt-gnd On On Open Batt-gnd Disconnect
Single Frequency Signals Used for Ringing and Loop-Start Signaling Using Tip and Ring Leads
Call Originating at Central Office End
Signal T/R - SF SF - T/R 2600 Hz 2600 Hz T/R - SF SF - T/R Signal
Idle Gnd-batt Open Off On Gnd-batt Open Idle
Seizure Gnd-batt Open Off On Gnd-batt Open Idle
Ringing Gnd-batt and 20 Hz Open On-off On Gnd-batt and 20 Hz Open Ringing
Off-hook (ring-trip and talk) Gnd-batt Closure Off Off Gnd-batt Closure Off-hook (ring-trip and answer)
On-hook Gnd-batt Closure Off Off Gnd-batt Closure Off-hook
On-hook (hang-up) Gnd-batt Open Off On Gnd-batt Open On-hook (hang-up)
Note: 20 Hz ringing (2 sec on, 4 sec off)
Call Originating at Station End
Signal T/R - SF SF - T/R 2600 Hz 2600 Hz T/R - SF SF - T/R Signal
Idle Open Gnd-batt On Off Open Gnd-batt Idle
Off-hook (seizure) Closure Gnd-batt Off Off Closure Gnd-batt Idle
Start dial Closure Dial tone and gnd-batt Off Off Closure Dial tone and gnd-batt Start dial
Dial pulsing Open-closure Gnd-batt On-off Off Open-closure Gnd-batt Dial pulsing
Waiting answer Closure Audible ring and gnd-batt Off Off Closure Audible ring and gnd-batt Waiting answer
On-hook (talk) Closure Gnd-batt Off Off Closure Gnd-batt Off-hook (answered)
On-hook (hang-up) Open Gnd-batt
Closure On Off Open Gnd-batt On-hook (disconnected)
Off-hook
Single Frequency Signals Used for Ringing and Ground-Start Signaling Using Tip and Ring Leads
Call Originating at Central Office End
Signal T/R - SF SF - T/R 2600 Hz 2600 Hz T/R - SF SF - T/R Signal
Idle Open-batt Batt-batt On On Open-batt
Idle
Seizure Gnd-batt Open On On Gnd-batt
Make-busy
Ringing Gnd-batt and 20 Hz Open On and 20 Hz On Gnd-batt and 20 Hz Open Ringing
Off-hook (ring-trip and talk) Gnd-batt Closure Off Off Gnd-batt Closure Off-hook (ring-trip and answer)
On-hook Gnd-batt Closure On Off Open-batt Closure On-hook
On-hook (hang-up) Gnd-batt Open Off On Gnd-batt Open On-hook (hang-up)
Note: 20 Hz ringing (2 sec on, 4 sec off)
Call Originating at Station End
Signal T/R - SF SF - T/R 2600 Hz 2600 Hz T/R - SF SF - T/R Signal
Idle
Open-batt On On Batt-batt Open-batt Idle
Off-hook (seizure) Ground Open-batt Off On Batt-gnd Open-batt Seizure
Start dial Closure Dial tone and gnd-batt Off Off Closure Dial tone and gnd-batt Start dial
Dial pulsing Open-closure Gnd-batt On-off Off Open-closure Gnd-batt Dial pulsing
Waiting answer Closure Audible ring and gnd-batt Off Off Closure Audible ring and gnd-batt Waiting answer
Off-hook (talk) Closure Gnd-batt Off Off Closure Gnd-batt Off-hook (answered)
On-hook Closure Open-batt On On Batt-batt Open-batt On-hook (disconnected)
On-hook (disconnected)
Closure On Off Open-batt Open-batt On-hook"
Signaling is defined by Consultative Committee for International Telegraph and Telephone (CCITT) Recommendation Q.9 as 'the exchange of information (other than speech) specifically concerned with the establishment, release, and control of calls, and network management in automatic telecommunications operations.'
In the broadest sense, there are two signaling realms:
* Subscriber signaling
* Trunk signaling (interswitch and/or interoffice)
Signaling is also traditionally classified into four basic functions:
* Supervision
* Address
* Call progress
* Network management
Supervision signaling is used to:
* Initiate a call request on line or trunks (called line signaling on trunks).
* Hold or release an established connection.
* Initiate or terminate charging.
* Recall an operator on an established connection.
Address signaling conveys such information as the calling or called subscriber's telephone number and an area code, an access code, or a Private Automatic Branch Exchange (PABX) tie trunk access code. An address signal contains information indicating the destination of a call initiated by a customer, network facility, and so forth.
Call progress signals are usually audible tones or recorded announcements that convey call-progress or call-failure information to subscribers or operators. These call-progress signals are fully described below.
Network management signals are used to control the bulk assignment of circuits or to modify the operating characteristics of switching systems in a network in response to overload conditions.
There are about 25 recognized interregister signaling systems worldwide, in addition to some subscriber signaling techniques. CCITT Signaling System Number 7 (SSN7) is fast becoming the international/national standard interregister signaling system.
Most installations will probably involve recEive and transMit (E&M) signaling; however, for reference, single frequency (SF) signaling on Tip and Ring loops, Tip and Ring reverse battery loops, loop start, and ground start are also included.
Types I and II are the most popular E&M signaling in the Americas. Type V is used in the United States, but is very popular in Europe. Similar to type V, SSDC5A differs in that on- and off-hook states are reversed to allow for fail-safe operation: if the line breaks, the interface defaults to off-hook (busy). Of all the types, only II and V are symmetrical (can be back-to-back using a cross-over cable). SSDC5 is most often found in England.
Other signaling techniques often used are delay, immediate, and wink start. Wink start is an in-band technique where the originating device waits for an indication from the called switch before sending the dialed digits. Wink start normally is not used on trunks that are controlled with message-oriented signaling schemes such as Integrated Services Digital Network (ISDN) or Signaling System 7 (SS7).
Summary of Signaling System Applications and Interfaces
Signaling System Application/Interface Characteristics
Station Loop
Loop signaling
Basic Station
DC signaling.
Origination at station.
Ringing from Central Office.
Coin Station
DC signaling.
Loop-start or ground-start origination at station.
Ground and simplex paths may be used in addition to the line for coin collection and return.
Interoffice Trunk
Loop Reverse Battery
One-way call origination.
Directly applicable to metallic facilities.
Both current and polarity are sensed.
Can be used on carrier facilities with appropriate facility signaling system.
E&M Lead
Two way call origination.
Requires facility signaling system for all applications.
Facility Signaling System
Metallic DX
Analog SF
Digital Bits in information
Special Service
Loop Type
Standard station loop and trunk arrangement as above.
Ground-start format similar to coin service for PBX-CO trunks.
E & M Lead
E&M for PBX dial tie trunks. E&M for carrier system channels in special service circuits.
North American Practices
The typical North American touchtone set provides a 12-tone set. Some custom sets provide 16-tone signals of which the extra digits are identified by the A-D pushbuttons.
Dual Tone Multifrequency (DTMF) Frequency Pairs
Low Frequency Group (Hz) High Frequency Group (Hz)
1209 1336 1477 1633
697 1 2 3 A
770 4 5 6 B
852 7 8 9 C
941 * 0 # D
Audible tones commonly used in North America
Tone Frequencies (Hz) Cadence
Dial 350 + 440 Continuous
Busy (station) 480 + 620 0.5 sec on, 0.5 sec off
Busy (network) 480 + 620 0.2 sec on, 0.3 sec off
Ring return 440 + 480 2 sec on, 4 sec off
Off-hook alert Multifreq howl 1 sec on, 1 sec off
Recording warning 1400 0.5 sec on, 15 sec off
Call waiting 440 0.3 sec on, 9.7 sec off
Call Progress Tones Used in North America
Name Frequencies (Hz) Pattern Levels
Low tone 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 Various -24 dBm0
61 to 71 dBmC
61 to 71 dBmC
61 to 71 dBmC
61 to 71 dBmC
High tone 480
400
500 Various -17 dBmC
61 to 71 dBmC
61 to 71 dBmC
Dial tone 350 + 440 Steady -13 dBm0
Audible ring tone 440 + 480
440 + 40
500 + 40 2 sec on, 4 sec off
2 sec on, 4 sec off
2 sec on, 4 sec off -19 dBmC
61 to 71 dBmC
61 to 71 dBmC
Line Busy Tone 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 0.5 sec on, 0.5 sec off
Reorder 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 0.3 sec on, 0.2 sec off
6A alerting tone 440 2 sec on, followed by 0.5 sec on, every 10 sec
Recorder warning tone 1400 0.5 sec burst every 15 sec
Reverting tone 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 0.5 sec on, 0.5 sec off -24 dBmC
Deposit coin tone 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 Steady
Receiver off-hook (analog) 1400 + 2060 + 2450 + 2600 0.1 sec on, 0.1 sec off +5 vu
Receiver off-hook 1400 + 2060 + 2450 + 2600 0.1 sec on, 0.1 sec off +3.9 to -6.0 dBm
Howler 480 Incremented in level
Every 1 sec for 10 sec Up to 40 vu
No such number (crybaby) 200 to 400 Freq. modulated at 1 Hz interrupted every 6 sec for 0.5 sec
Vacant code 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 0.5 sec on, 0.5 sec off, 0.5 sec on, 1.5 sec off?
Busy verification Tone (Centrex) 440 Initial 1.5 sec followed 0.3 sec every 7.5 to 10 sec -13 dBm0
Busy verification Tone (TSPS) 440 Initial 2 sec followed 0.5 sec every 10 sec -13 dBm0
Call waiting tone 440 Two bursts of 300 ms separated by 10 sec -13 dBm0
Confirmation tone 350 + 440 3 bursts of 300 ms separated by 10 sec -13 dBm0
Indication of camp-on 440 1 sec every attendant releases from loop -13 dBm0
Recall dial tone 350 + 440 3 bursts, 0.1 sec on, sec off then steady -13 dBm0
Data set answer back tone 2025 Steady -13 dBm
Calling card prompt tone 941 + 1477 followed by 440 + 350 60ms -10 dBm0
Class of service 480
400
500 0.5 to 1 sec once
Order tones
Single
480
400
500 0.5 sec
Double
480
400
500 2 short bursts
Triple
480
400
500 3 short bursts
Quad
480
400
500 4 short bursts
Number checking tone 135 Steady
Coin denomination
3 5 cents
1050-1100 (bell) One tap
slot 10 cents
1050-1100 (bell) Two taps
stations 25 cents
800 (gong) One tap
Coin collect tone 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 Steady
Coin return tone 480
400
500 0.5 to 1 sec once
Coin return test tone 480
400
500 0.5 to 1 sec once
Group busy tone 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 Steady
Vacant position 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 Steady
Dial off normal 480 + 620
600 x 120
600 x 133
600 x 140
600 x 160 Steady
Permanent signal 480
400
500 Steady
Warning tone 480
400
500 Steady
Service observing 135 Steady
Proceed to send Tone (IDDD) 480 Steady -22 dBm0
Centralized intercept 1850 500 ms -17 dBm0
ONI order tone 700 + 1100 95 to 250 ms -25 dBm0
Note: Three dots in the pattern mean that the pattern is repeated indefinitely.
Single Frequency In-Band Signaling
SF in-band signaling is widely used in North America. Its most common application is for supervision, such as idle-busy, also called line signaling. It also can be used for dial pulse signaling on trunks. The dynamics of SF signaling requires an understanding of the signal durations and configurations of the E&M circuits, as well as the lead interface arrangements. The following tables show the characteristics of SF signaling, E&M lead configurations, and interface arrangements.
Typical Single Frequency Signaling Characteristics
General
Signaling frequency (tone)
2600 Hz
Idle state transmission
Cut
Idle/break
Tone
Busy/make
No tone
Receiver
Detector bandwidth
+/- 50 Hz @ -7 dBm for E type
+/- 30 Hz @ -7 dBm
Pulsing rate
7.5 to 122 pps
E/M unit
Minimum time for on-hook
33 ms
Minimum no tone for off-hook
55 ms
Input percent break (tone)
38-85 (10 pps)
E lead - open
Idle
- ground
Busy
Originating (loop reverse battery) unit
Minimum tone for idle
40 ms
Minimum no tone for off-hook
43 ms
Minimum output for on-hook
69 ms
Voltage on R lead (-48 V on ring and ground on tip)
On-hook
Voltage on T lead (-48 V on tip and ground on ring)
Off-hook
Terminating (loop reverse battery) unit
Minimum tone for on-hook
90 ms
Minimum no tone for off-hook
60 ms
Minimum output (tone-on)
56 ms
Loop open
On-hook
Loop closed
Off-hook
Transmitter
Low level tone
-36 dBm
High level tone
-24 dBm
High level tone duration
400 ms
Precut
8 ms
Holdover cut
125 ms
Crosscut
625 ms
On hook cut
625 ms
E/M unit
Voltage on M lead
Off-hook (no tone)
Open/ground on M lead
On-hook (tone)
Minimum ground on M lead
21 ms
Minimum voltage on M lead
21 ms
Minimum output tone
21 ms
Minimum no tone
21 ms
Originating (loop reverse battery) unit
Loop current to no tone
19 ms
No loop current to tone
19 ms
Minimum input for tone out
20 ms
Minimum input for no tone out
14 ms
Minimum tone out
51 ms
Minimum no tone out
26 ms
Loop open
On-hook
Loop closed
Off-hook
Terminating (loop) unit
Reverse battery to no tone
19 ms
Normal battery to tone
19 ms
Minimum battery for tone out
25 ms
Minimum reverse battery for no tone
14 ms
Minimum tone out
51 ms
Minimum no tone out
26 ms
Battery on R lead (-48 v)
On-hook
Battery on TY lead (-48 on tip)
Off-hook
Single Frequency Signals Used in E&M Lead Signaling
Calling End Called End
Signal M-Lead E-Lead 2600 Hz 2600 Hz E-Lead M-Lead Signal
Idle Ground Open On On Open Ground Idle
Connect Battery Open Off On Ground Ground Connect
Stop dialing Battery Ground Off Off Ground Battery Stop dialing
Start dialing Battery Open Off On Ground Ground Start dialing
Dial pulsing Ground Open On On Open Ground Dial pulsing
Battery
Off
Ground
Off -hook Battery Ground Off Off Ground Battery Off-hook (answer)
Ring forward Ground Ground On Off Open Battery Ring forward
Battery
Off
Ground
Ringback Battery Open Off On Ground Ground Ringback
Ground
Off
Battery
Flashing Battery Open Off On Ground Ground Flashing
Ground
Off
Battery
On-hook Battery Open Off On Ground Ground On-hook
Disconnect Ground Open On On Open Ground Disconnect
Single Frequency Signals Used in Reverse Battery Tip and Ring Loop Signaling
Calling End Called End
Signal T/R - SF SF - T/R 2600 Hz 2600 Hz T/R - SF SF - T/R Signal
Idle Open Batt-gnd On On Open Batt-gnd Idle
Connect Closure Batt-gnd Off On Closure Batt-gnd Connect
Stop dialing Closure Rev batt-gnd Off Off Closure Rev batt-gnd Stop dialing
Start dialing Closure Batt-gnd Off On Closure Batt-gnd Start dialing
Dial pulsing Open Batt-gnd On On Open Batt-gnd Dial pulsing
Closure
Off
Closure
Off -hook Closure Rev batt-gnd Off Off Closure Rev batt-gnd Off-hook (answer)
Ring forward Open Rev batt-gnd On Off Open Rev batt-gnd Ring forward
Closure
Off
Closure
Ringback Closure Batt-gnd Off On Closure Batt-gnd Ringback
Rev batt-gnd
Off
Rev batt-gnd
Flashing Closure Batt-gnd Off On Closure Batt-gnd Flashing
Rev batt-gnd
Off
Rev batt-gnd
On-hook Closure Batt-gnd Off On Closure Batt-gnd On-hook
Disconnect Open Batt-gnd On On Open Batt-gnd Disconnect
Single Frequency Signals Used for Ringing and Loop-Start Signaling Using Tip and Ring Leads
Call Originating at Central Office End
Signal T/R - SF SF - T/R 2600 Hz 2600 Hz T/R - SF SF - T/R Signal
Idle Gnd-batt Open Off On Gnd-batt Open Idle
Seizure Gnd-batt Open Off On Gnd-batt Open Idle
Ringing Gnd-batt and 20 Hz Open On-off On Gnd-batt and 20 Hz Open Ringing
Off-hook (ring-trip and talk) Gnd-batt Closure Off Off Gnd-batt Closure Off-hook (ring-trip and answer)
On-hook Gnd-batt Closure Off Off Gnd-batt Closure Off-hook
On-hook (hang-up) Gnd-batt Open Off On Gnd-batt Open On-hook (hang-up)
Note: 20 Hz ringing (2 sec on, 4 sec off)
Call Originating at Station End
Signal T/R - SF SF - T/R 2600 Hz 2600 Hz T/R - SF SF - T/R Signal
Idle Open Gnd-batt On Off Open Gnd-batt Idle
Off-hook (seizure) Closure Gnd-batt Off Off Closure Gnd-batt Idle
Start dial Closure Dial tone and gnd-batt Off Off Closure Dial tone and gnd-batt Start dial
Dial pulsing Open-closure Gnd-batt On-off Off Open-closure Gnd-batt Dial pulsing
Waiting answer Closure Audible ring and gnd-batt Off Off Closure Audible ring and gnd-batt Waiting answer
On-hook (talk) Closure Gnd-batt Off Off Closure Gnd-batt Off-hook (answered)
On-hook (hang-up) Open Gnd-batt
Closure On Off Open Gnd-batt On-hook (disconnected)
Off-hook
Single Frequency Signals Used for Ringing and Ground-Start Signaling Using Tip and Ring Leads
Call Originating at Central Office End
Signal T/R - SF SF - T/R 2600 Hz 2600 Hz T/R - SF SF - T/R Signal
Idle Open-batt Batt-batt On On Open-batt
Idle
Seizure Gnd-batt Open On On Gnd-batt
Make-busy
Ringing Gnd-batt and 20 Hz Open On and 20 Hz On Gnd-batt and 20 Hz Open Ringing
Off-hook (ring-trip and talk) Gnd-batt Closure Off Off Gnd-batt Closure Off-hook (ring-trip and answer)
On-hook Gnd-batt Closure On Off Open-batt Closure On-hook
On-hook (hang-up) Gnd-batt Open Off On Gnd-batt Open On-hook (hang-up)
Note: 20 Hz ringing (2 sec on, 4 sec off)
Call Originating at Station End
Signal T/R - SF SF - T/R 2600 Hz 2600 Hz T/R - SF SF - T/R Signal
Idle
Open-batt On On Batt-batt Open-batt Idle
Off-hook (seizure) Ground Open-batt Off On Batt-gnd Open-batt Seizure
Start dial Closure Dial tone and gnd-batt Off Off Closure Dial tone and gnd-batt Start dial
Dial pulsing Open-closure Gnd-batt On-off Off Open-closure Gnd-batt Dial pulsing
Waiting answer Closure Audible ring and gnd-batt Off Off Closure Audible ring and gnd-batt Waiting answer
Off-hook (talk) Closure Gnd-batt Off Off Closure Gnd-batt Off-hook (answered)
On-hook Closure Open-batt On On Batt-batt Open-batt On-hook (disconnected)
On-hook (disconnected)
Closure On Off Open-batt Open-batt On-hook"
CTI论坛: 破解传统语音网
CTI论坛: 破解传统语音网: "局间信令
局间传输通常在数字中继链路上进行，有时也把局间信令称数字中继信令。目前最通用的信令为R2和SS7；国内通常称为１号信令和７号信令。
R2信令
R2信令为一种随路信令（CAS: Channel Associated Signaling）。R2信令是一种基于E1数字网络的国际标准信令，Timeslot 16被预留用来传递其话音通道的信令。但是R2信令并不统一，ITU-T的标准Q.400-Q.490定义了R2信令标准，但不同的国家和地区都有自己的实现方式。
SS7信令
SS7信令为一种共路信令（CCS: Common Channel Signaling）。SS7信令是将呼叫控制信息和其他业务信息通过一张独立的信令网络传输。它比R2信令更高效，更可靠。SS7信令的标准化程度要比R2信令好，但依然存在标准兼容问题。如国内的SS7 称为中国7号信令。
用户端信令
电话用户通常采用两芯双绞线连接到用户交换机。所以用户端信令为面向用户的模拟接口信令，通常也称为模拟接口信令。电话机不同于计算系统，它几乎没有什么智能，只能通过简单的模拟信号来沟通。下面介绍模拟话音的信令。
模拟话音的信令有三种，FXS、FXO和E&M。
FXS（Foreign Exchange Station）
可以理解为计算机通信中的DCE（数据通信设备）接口。通常为电话交换机的用户端口，用来连接具有FXO端口的端设备，如电话机或集团电话。
FXO（Foreign Exchange Office）
可以理解为计算机通信中的DTE（数据终端设备）接口。通常为端设备，连接具有FXS端口的电话交换机设备，如PBX或市话局。
FXS和FXO通过两芯电缆构成环路的断开和闭合与电流信号来完成电话的呼叫控制。
E&M（RecEive and TransMit）
E&M是一种模拟中继信令，主要用于PBX到PBX和PBX到市话局的互连。与FXS/FXO不同，E&M端口之间直接互连，将两台PBX连在一起，通常我们也称为捆绑中继接口（Tie Trunk）。
E&M信令采用４对电缆（８芯）通信。E&M信令有５种类型：TYPE1、TYPE2、 TYPE3、TYPE4和TYPE5，每一种类型有自己的通信方式。
当了解现有的电话网络的连接信令后，企业可以自主的采用多种技术组建自己的电话网，只需要在与市话提供商互连时准备相应的接口。"
局间传输通常在数字中继链路上进行，有时也把局间信令称数字中继信令。目前最通用的信令为R2和SS7；国内通常称为１号信令和７号信令。
R2信令
R2信令为一种随路信令（CAS: Channel Associated Signaling）。R2信令是一种基于E1数字网络的国际标准信令，Timeslot 16被预留用来传递其话音通道的信令。但是R2信令并不统一，ITU-T的标准Q.400-Q.490定义了R2信令标准，但不同的国家和地区都有自己的实现方式。
SS7信令
SS7信令为一种共路信令（CCS: Common Channel Signaling）。SS7信令是将呼叫控制信息和其他业务信息通过一张独立的信令网络传输。它比R2信令更高效，更可靠。SS7信令的标准化程度要比R2信令好，但依然存在标准兼容问题。如国内的SS7 称为中国7号信令。
用户端信令
电话用户通常采用两芯双绞线连接到用户交换机。所以用户端信令为面向用户的模拟接口信令，通常也称为模拟接口信令。电话机不同于计算系统，它几乎没有什么智能，只能通过简单的模拟信号来沟通。下面介绍模拟话音的信令。
模拟话音的信令有三种，FXS、FXO和E&M。
FXS（Foreign Exchange Station）
可以理解为计算机通信中的DCE（数据通信设备）接口。通常为电话交换机的用户端口，用来连接具有FXO端口的端设备，如电话机或集团电话。
FXO（Foreign Exchange Office）
可以理解为计算机通信中的DTE（数据终端设备）接口。通常为端设备，连接具有FXS端口的电话交换机设备，如PBX或市话局。
FXS和FXO通过两芯电缆构成环路的断开和闭合与电流信号来完成电话的呼叫控制。
E&M（RecEive and TransMit）
E&M是一种模拟中继信令，主要用于PBX到PBX和PBX到市话局的互连。与FXS/FXO不同，E&M端口之间直接互连，将两台PBX连在一起，通常我们也称为捆绑中继接口（Tie Trunk）。
E&M信令采用４对电缆（８芯）通信。E&M信令有５种类型：TYPE1、TYPE2、 TYPE3、TYPE4和TYPE5，每一种类型有自己的通信方式。
当了解现有的电话网络的连接信令后，企业可以自主的采用多种技术组建自己的电话网，只需要在与市话提供商互连时准备相应的接口。"
出售 供应信令网关 信令转换器 | [网络设备信息安全-转换器] 中国金融机具网——努力为您带来订单!国内最大的金融设备及安防产品网上市场！
出售 供应信令网关 信令转换器 | [网络设备信息安全-转换器] 中国金融机具网——努力为您带来订单!国内最大的金融设备及安防产品网上市场！: "由于很多厂家的用户交换机不提供七号信令接口，只提供ISDN PRI或中国一号信令接口，因此与局方进行七号信令对接时，便会存在信令接口的问题。FL-300D支持七号信令（SS7）、数字一号信令（DSS1）ISDN PRI、QSIG、中国一号信令（SS1）和V5.2以及环路信令之间的自由互转，从而使得普通的PRI、中国一号信令接口设备能够实现与局方的七号信令（TUP/ISUP）实现对接。
它采用模块化结构，实时嵌入式操作系统，无阻塞交换，最大可处理8路E1。硬件采用进口通信专用器件,功耗低，可靠性高，结构配置灵活, 扩充方便，安装维护简单，是低成本高效率信令转换的最佳方案。
信令网关设备FL-300D已经成功与华为HuaWei、贝尔BELL、阿尔卡特Alcatel、北电Nortel、西门子Siemens、朗讯Lucent、Avaya、中兴ZTE、爱立信Ericsson、奥迪坚Altigen、思科Cisco 等公司的设备实现对接，与国外同类产品相比，有很高的性价比。目前，我公司信令网关设备拥有大量的成功应用案例，已广泛应用于电信、移动、联通等主要通信网络中。
设备特点
提供8个E1接口，可同时4进4出
支持七号信令（ITU-T SS7），完全按照《CCITT七号信令技术规范》和GF001-9001《中国国内电话网No.7信号方式技术规范》。
提供七号信令的第一、第二、第三级MTP及第四级TUP、SCCP、ISUP功能
支持数字一号信令（DSS1），符合ITU-TQ.920-Q.921,Q.930-Q.940
支持中国一号信令（SS1），符合国际GF002-9002的DL信令和MFC信令标准（也可支持不含MFC的中国一号信令，即E&M信令）
支持V5.2信令
全数字时分交换方式，提供512 x 512无阻塞交换
分组、分群交换管理
E1接口支持不定长接续
可任意处理主被叫号码
每个E1接口均可同时拨入和拨出
支持输出原始计费话单功能"
它采用模块化结构，实时嵌入式操作系统，无阻塞交换，最大可处理8路E1。硬件采用进口通信专用器件,功耗低，可靠性高，结构配置灵活, 扩充方便，安装维护简单，是低成本高效率信令转换的最佳方案。
信令网关设备FL-300D已经成功与华为HuaWei、贝尔BELL、阿尔卡特Alcatel、北电Nortel、西门子Siemens、朗讯Lucent、Avaya、中兴ZTE、爱立信Ericsson、奥迪坚Altigen、思科Cisco 等公司的设备实现对接，与国外同类产品相比，有很高的性价比。目前，我公司信令网关设备拥有大量的成功应用案例，已广泛应用于电信、移动、联通等主要通信网络中。
设备特点
提供8个E1接口，可同时4进4出
支持七号信令（ITU-T SS7），完全按照《CCITT七号信令技术规范》和GF001-9001《中国国内电话网No.7信号方式技术规范》。
提供七号信令的第一、第二、第三级MTP及第四级TUP、SCCP、ISUP功能
支持数字一号信令（DSS1），符合ITU-TQ.920-Q.921,Q.930-Q.940
支持中国一号信令（SS1），符合国际GF002-9002的DL信令和MFC信令标准（也可支持不含MFC的中国一号信令，即E&M信令）
支持V5.2信令
全数字时分交换方式，提供512 x 512无阻塞交换
分组、分群交换管理
E1接口支持不定长接续
可任意处理主被叫号码
每个E1接口均可同时拨入和拨出
支持输出原始计费话单功能"
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