Why is signaling seven called "seven" signaling?

A. What is the seven signaling system

1. The origin of seven signaling

The transmission of any actual application information between communication devices is always accompanied by the transmission of some control information, which works according to the established

communication protocols and transmits the application information securely, reliably and efficiently to the destination. These information in the computer network

called protocol control information, and in the telecommunications network called signaling (Signal). English data also often use "Signalling" (

signaling process) term, but most of the Chinese technical data only use the word "signaling", that is, "signaling" includes both "Signal" and

"Signalling" two meanings.

Signaling is divided into two categories: user signaling and inter-office signaling. The former is between the user's terminal equipment (e.g., telephone) and

the telephone exchange of the telephone office, and the latter is between two exchanges connected by trunks.

Inter-office signaling with the road signaling (CAS) and **** road signaling (CCS) two categories, the former use of inter-office trunk lines to transmit signaling (

that is, the user's voice and signaling in the same line to pass); the latter use of a separate channel or line to transmit signaling. Signaling System No. 7

Signaling System No. 7 (abbreviated as Signaling System No. 7 or SS7) is a type of inter-office digital **** circuit signaling.

Human beings have used signaling since 1878 when telephone exchanges were first used to provide telephone service to the public. With the development of telephone

Telephone switch from manual switching, electromechanical switching to electronic switching, the signaling used by the development of the first signaling to the current

Today is promoting the seventh signaling. One signaling by artificial telephone exchange operator with ringing to send signaling; two signaling adopted

with dialing pulse, send signaling, but not put into use. No. 3 signaling for single-tone in-band signaling; No. 4 signaling for dual-tone

in-band signaling; No. 5 signaling the use of six voice frequencies in the combination of two frequencies to transmit a variety of signaling, namely, in-band Dual Tone Multi-Frequency signaling

order (DTMF: Dual Tone Multi-Frepuency). In order to apply the development of digital program-controlled switches, the International Telegraph and Telephone Consultative Committee

Inquiry Committee (CCITT) in 1968 put forward the six signaling, six signaling for *** road signaling, message length is fixed, for 28 bits

. Considering the development trend of digital communications to ISDN (Integrated Services Digital Network), CCITT in 1980 proposed a strong generality

Seven signaling system, since then, the seven signaling system after a number of expansion and modification, has formed a complete signaling system. No. 7

Signaling system to the network message mode in the signaling point between the transmission of signaling, it and the International Organization for Standardization ISO's open system interconnection

model (OSI model) has a corresponding relationship.

2. Why the Seven Signaling System

The Seven Signaling System separates signaling and voice paths and adopts high-speed data link to transmit signaling, thus it has the features of fast transmission speed, short call setup time, large signaling capacity, flexibility in changing and expanding the capacity, low investment in signaling equipment, and high utilization rate of the voice path.

The Seven Signaling System is derived from the OSI model. Seven signaling system from the telephone network, but its application is not limited to the voice path switching, it can be said, it is the main

potential applications are non-voice path service, voice path service intelligence and integrated service digital network. In these areas, other signaling

is unable to help.

The seventh signaling system in the telephone network superimposed on a *** road signaling network, telephone network circuit switching, and *** road signaling network

Practice packet switching, the two complement each other, so that the traditional telephone network capacity has been greatly improved. Telephone network inter-office signaling in the *** road

Signaling network transmission in addition to fast speed, high reliability, large capacity, signaling network can also be set up on the database server

server, network management and monitoring centers, with voice recognition function of the intelligent node, so that the advanced intelligent network AIN become a reality.

In addition, the seven signaling system is also a cellular mobile communication network, PCN (Personal Communication Network), ATM

network and other data communication network basis.

Second, seven signaling system structure

1.*** Road signaling network structure

Conceptually, the seven signaling is a kind of independent from the telecommunications network on the signaling, this network is called *** Road signaling

net or called seven signaling network, which consists of a number of signaling points, signaling points are generally by the 64Kbps digital link connection. A typical

signaling network includes SSP, SCP and STP signaling points.

SSP (Service Switching Points) is a type of telephone office that can perform a variety of seven signaling application services (subscriber call handling

, 800 number service, other party pay phones, etc.) of a program-controlled digital switchboard. Among them, telephone offices that provide subscriber call processing using only the No. 7 signaling

are called CCSSOs (Common Channel Signalling Switching Office

s). Generally, CCSSO or SSP functions can be performed by simply upgrading the software and adding some hardware to an existing program-controlled digital switch. However, this software is very expensive, an SSP software price of millions of dollars.

SCP (Service Control Points) is a special signaling point that can provide database services, 800 numbers, letter

Card phones and many other special services must be achieved with the help of the SCP. SCP is usually a large multi-computer system is constructed

into a database server that can handle millions of database query requests per day. millions of database query requests per day.

STP (Signallint Transfer Points) is **** road signaling network equipment, its main function is signaling in

transfer, signaling routing and full address (Globale Title) translation. An STP can support hundreds of links, and to improve the reliability of the signaling network,

STPs are usually configured in pairs.

*** Road signaling network is often a regional network, or national network, or international network, it is a large number of nodes, reliability requirements

high, complex management and maintenance. For this reason, the network must be configured in a number of network operation support system OSS, which is connected to the STP and SCP, to

they implement management control.

*** Road signaling network is generally a hierarchical structure, the following example of the United States to illustrate. From the scope of influence of telecommunications management

, the United States is divided into seven regions (Regions), each region is divided into a number of neighborhoods, each of which belongs to a local telecommunications company

Operation and management of the first region by the Bell operating companies to control their own local telecommunications companies. In contrast, the U.S. **** road signaling

order network is a two-tier structure (Figure 1).

@@12S10300.GIF; Figure 1.*** Road signaling network structure@@

In order to the reliability of the network and load balancing, each region to set up two pairs of RSTP (Regional STP), two SCP.

Each SCP to set up two databases, database CMSDB (Call CMSDB (Call Management Services Data Base) is used for 800 number

services, and LIDB (Line Information Data Base) is used for credit card phone service, collect call service

and third party pay phone service. The two copies of the database are identical on both SCPs, so that in the event of a failure of one SCP, the other SCP can continue to provide the service.

One SCP has a copy of the LIDB (Line Information Data Base), which is used for credit card telephony services, collect calls and third-party payphone services.

RSTPs in one region are directly connected to RSTPs in other regions, or interconnected through other long-distance signaling networks. In each region

Establish a signaling engineering management center SEAC. each cell to set up one or more LSTP (Licak STP), all LSTP and

RSTP connection. Each LSTP is connected to all SSPs and CCSSOs in the cell. Typical practices for telephone offices and signaling network connections are

, convergence office (AT) programmed switches upgraded to AT/SSP, end office (CEO) programmed switches upgraded to EO/CCSSO. not all

end office must have CCSSO functionality, the United States is still nearly 30% of the end office does not have seven signaling capabilities.

2. Protocol structure

Currently, seven signaling according to the function can be divided into six parts (Figure 2): MTP, SCCP, TCAP, OMAP, ISUP and MAP.

With the development of seven signaling applications, TCAP will also add other applications on the part.

@@12S10301.GIF;Figure 2.The protocol structure of No.7 signaling system@@

MTP (Message Transfer Part) is divided into three levels: SDL (Signalling Data Link), SLF (Signali

ng Link Functions) and SNF (Signalling Network Funtions). The functions of the first level of SDL correspond to the physical link layer of the OSI

model. The function of the second level SLF corresponds to the data link layer of the OSI model, and its protocol is similar to HDLC, which

is responsible for the point-to-point communication processing, and the main function of the third level SNF is the identification and distribution of messages, the routing of messages, the

volume management of the signaling network, the routing management, and the link management.

SCCP (Signalling Conection Control Part) is the third level of MTP complement, it and SNF together

responds to the network layer of the OSI model. SCCP protocol function is divided into four levels: Class0, Class1, Class2, Class3. In addition to connection control

SCCP performs translation of fully qualified addresses and end-to-end routing.

TCAP (Transaction Capabilities Application Part) provides the support needed for transaction processing

for signaling seven applications, which corresponds to the application layer of the OSI model, with a protocol similar to OSI's ROS.

OMAP (Operation Maintenance and Administration Part) of the main function of network management and maintenance

protection, it is similar to the OSI CMIP protocol.

ISUP (ISDN User Part) is the most complex part of the seven signaling, its main function is in the two program-controlled exchanges

switch (ISDN switch) between the caller and the called user to establish a voice path (call establishment), the release of the voice path (call

call release), line monitoring, additional business processing. In addition to ISUP, the International Telegraph and Telephone Consultative Committee (CCITT) has defined

TUP (Telephone User Part) and DUP (Data User Part), TUP performs voice path switching signaling and DUP performs

non-voice switching signaling.

The main function of MAP (Mobile Applecation Part) is to support cellular mobile communications, and its protocol is not yet complete.

Different signaling points include different parts of the seven signaling. STP includes only MTP and SCCP; SCP includes MTP, S

CCP, TCAP and database query-based applications (e.g., 800-number service, other party's pay phone service, etc.); CCSSO generally includes only

MTP and ISUP; while SSP includes various parts of signaling number seven.

At present, the United States has two standardization organizations issued by the seven signaling protocols are valued; the first is the CCITT issued by the Q

series of protocols, and the second is the U.S. Bellcore Communications Research Corporation issued by the T series of protocols. They are basically the same, but there are some

important differences. In addition, Bellcorp also issued a large number of TR series technical documents, they are implementation-oriented protocols, detailed

body, is the industry standard for North American signaling network.TR series does not include OMAP, for SCCP only use the connectionless service. In addition, the TR series

defines specifications for toll-free (800 number), credit card, collect, third-party, CLASS, and other

seven signaling applications that are not well defined in CCITT's Q-series, and therefore the North American signaling implementations

refer to the TR series of technical documents.

Three, the application of seven signaling

1. Call signaling

One of the most basic applications of seven signaling is to replace the old one to six signaling, used as a modern digital program-controlled switching bureau

Inter-bureau signaling, control the inter-bureau call connection. Compared with the old inter-office signaling, No. 7 signaling for inter-office signaling has many advantages: (1)

signaling transmission speed is high, call succession time is short; (2) signaling capacity is large, a 64kbps link can theoretically handle tens of thousands of

talking road; (3) flexible, easy to expand; (4) dialog road interference is small, high quality of the talking road; (5) end-to-end signaling or subscriber signaling can be delivered.

CLASS (Customer Local Area Signalling Services) represents a set of special telephony service features, which

includes automatic callback, automatic re-call, subscriber tracking, caller name transfer, call selective acceptance, and so on, and so on, in 13 kinds of functions. These features or

service characteristics cannot be provided by the user's telephone alone.

2. 800 number service

According to statistics, in 1993, the United States handled 80 million to 100 million 800 number calls per day, with an annual turnover of tens of billions of dollars, and an annual growth rate

of 15 to 20%. 800 number service is a huge market, attracting various telecommunication companies, and it is one of the most important revenues for them

. The so-called 800 telephone number is a company to provide customers with a special telephone number, the number of the area code for 800 (virtual

area code), the customer to use this phone and the company to talk to the company's business when the company pays for the cost of calling the customer free of charge. 800

Number telephone number is a virtual logical telephone number, a company may have a lot of actual telephone number, but 800 number telephone number is a virtual logical telephone number, a company may have many actual telephone number, but 800 number telephone number is a virtual logical telephone number. A company may have many actual phone numbers, but the 800 number is only

one, and a customer may dial this number from anywhere to speak with a function of the company, so there is a process of converting the

800 number into an actual phone number. The realization of this process depends on the signaling network of the SCP.

3. Other party pay phone

Other party pay phone (ABS: Alternate Billing Service) there are three forms: the first form is a credit card phone

Talk, which is different from our popular magnetic card phone (in English, magnetic card phone called debet card call), the first form is the credit card phone

This is different from our popular magnetic card phone (in English, magnetic card phone is called debet card call). debet card call); the second form

type is called pay phone (collect billing call or collect call); the third form is a third party pay phone

(third number billing call). Before the establishment of the *** road signaling network, the other party billing calls rely on the telephone exchange operator

to realize, with the *** road signaling network, the other party billing calls are basically automated, convenient and efficient.

4. Advanced Intelligent Network (AIN)

Advanced Intelligent Network (AIN)

Advanced Intelligent Network (AIN)

The *** road signaling network introduced two new nodes: Adjunct and IP. Adjunct's function is similar to

To the SCP, which is directly linked to the program-controlled switches with the SSP function, to provide them with direct and fast database services and call

The platform function of processing. The platform function of call processing. Telephone exchange administrators (and even users) can use the platform features to design telephony

service features for their own exchanges, and, of course, the PBX software must be upgraded to AIN software.

In an AIN switch, a subscriber's call processing is divided into a number of phases, with a trigger checkpoint defined after each phase

, and the AIN switch software detects the events generated by the switch at each checkpoint. The call processing of the phone is done by both the AIN switch and Adj

unct*** (traditional call processing is done exclusively in the switch). the AIN does the general processing, and when an event is detected at the checkpoint, the processing is passed to Adjunct for completion. what Adjunct does can be designed by the administrator using the platform's functionality to get the most out of the call processing, but it's not the only one.

Designed to allow for different telephony service features.

IP (Intelligent Peripherals) is a network intelligence device that connects directly to the AIN switch, and its main

function is voice recognition. If the network administrator defines the "voice recognition" feature at a breakpoint, the user can enter the called phone number in voice

, at which point the AIN switch must send the voice number to the IP to translate it into a numeric number for subsequent

call processing.

5. Cellular mobile communication system

Cellular mobile communication system needs to add at least three kinds of nodes in the **** road signaling network: MSC, HLR and VLR. cellular mobile

Communication system will be a communication area divided into a number of CELL, and each CELL to set up a MSC (Mobile Switching Cent< /p>

er).

er), responsible for the communication of wireless users in the CELL. MSC is a wireless switch using seven signaling, which includes seven signaling

in the MTP, SCCP, TCAP and MAP. in the cellular mobile communication system, each wireless user must be in the database HLR (Home

Location Register) and VLR (VLR). Register) and VLR (Visitor Lolcation Register).

Cellular mobile communication system includes many seven signaling processes, the most important two signaling processes are: Registrati

on and Intersystem Handoff/Intersystem Handback Register is a mobile user automatically registered in the VLR

process. When a mobile subscriber crosses the boundary between two CELLs, the communication processing is delivered from one MSC to another,

this is the Intersystem Handoff signaling process, and vice versa for the Intersystem Handback signaling process.

MAP protocol is still in the process of improvement, most of the vendors currently use the protocol standard is the EIA/TIA transition standard IS-

41-B.

6. Other applications

Seven signaling has a broad application prospects. In addition to the above five applications, it can be used as internal signaling for ATM and B-ISDN

networks. In addition, due to the expansion of the scale of the data communications network, the technical complexity of the enhancement of the network operation and maintenance

, management, testing and troubleshooting of the contradiction is increasingly prominent, the best way to solve this problem is to use the seven signaling OMA

P protocols in the *** road signaling network to establish a network management and maintenance centers. Because the signaling network is a fast, reliable packet

switching network, network management center operators can communicate with the network for remote real-time testing, diagnostics, monitoring, control and

management, and does not interfere with normal data communications.

Four, China's seven signaling network construction problems

In recent years, China's telecommunications industry has developed rapidly, large and medium-sized cities in the telephone network of the digital program-controlled has been close to Europe and the United States and

Japan and other developed countries in the level of communication, some of the inter-bureau signaling has been replaced by DTMF seven signaling system. Seven signaling system for the first time

the use of China is the introduction of S1240 program-controlled digital switch in 1987, since then, with a variety of advanced foreign communications equipment

precision, especially the introduction of program-controlled digital switch, seven signaling system applications in the gradual expansion of the scope of certain major cities are also proposed to be

construction of the seven signaling system of the protocol standards have also done a lot of work, in 1987, the protocol standards of the seven signaling system to be

Constructing a lot of work, in 1987, the inter-bureau signaling has been replaced by the DTMF to the seven signaling system. In 1987, China issued "China's domestic municipal telephone exchange NO.7 signaling method

Technical specifications" (provisional provisions), in August 1990 and reissued the "China's domestic telephone network NO.7 signaling method technical specifications

Fan" (provisional provisions). The Ministry of Posts and Telecommunications (Provisional Provisions) adopted CCITT's Q-series standards, but only included MTP, TUP and the monitoring part of signaling

network.

However, whether in the seven signaling protocols, or in the seven signaling network construction and application, China is still

in a very backward situation, there are many problems to be solved. These issues include:

(1) as one of the most important applications of the seven signaling 800 service and ABS can be promoted in China? Is it in line with China's

national conditions?

(2) The Ministry of Posts and Telecommunications (provisional regulations) does not include the operation specification of the 800 service and ABS of the seven signaling, if China

promotes the 800 service and ABS similar to that of the U.S.A., what standards are adopted?

(3) Is it necessary to establish a nationwide *** road signaling network in China, and if so, what structure is adopted? Is it possible to adopt

American-style secondary structure?

(4)In recent years, China's data communication network has been developing rapidly, but the maintenance and management methods are backward, and the availability of communication facilities is low,

Should we set up an advanced and comprehensive network management and control center on the basis of the **** road signaling network? If so, how should it be implemented?

These issues, to be further studied.

These questions need to be further studied.