Problem description:
Why is signaling No.7 called "signaling No.7"? Is there a "two" or "three" signal?
Analysis:
some
I. What is Signaling System No.7
The origin of 1 .7 signaling
The transmission of any practical application information between communication devices is always accompanied by the transmission of some control information, which is in accordance with the established
Application information is transmitted to the destination safely, reliably and effectively. This information is in the computer network
It is called protocol control information, but it is called signal in telecommunication network. English materials often use "signaling" (
Signaling process), but most Chinese technical materials only use the word "signaling", that is, "signaling" includes both "signal" and "signal".
"Signaling" has two meanings.
Signaling is divided into user signaling and inter-office signaling according to use. The former acts on user terminal equipment (such as telephone) and
Between the exchanges in the telephone office, the latter works between two exchanges connected by trunk lines.
Inter-office signaling can be divided into two categories: associated signaling (CAS) and * * signaling (CCS). The former uses inter-office trunk lines to transmit signaling (
That is, user voice and signaling are transmitted on the same line); The latter uses a separate channel or line to transmit signaling. No.7 signaling
Signaling System No.7 (SS7 for short) is a kind of inter-office digital signaling.
Since 1878 first used telephone exchange to provide telephone service to the public, human beings have used signaling. consume electricity
Telephone exchange has developed from manual exchange and electromechanical exchange to electronic exchange, and the signaling used has also developed from 1 to when.
It marks that No.7 was promoted today. 1 signaling is sent by the operator of the manual telephone exchange through ringing; No.2 signaling
Dial pulses are used to send signaling, but they are not put into use. Signaling No.3 is single-tone in-band signaling; Signaling number four is dual tone.
In-band signaling; Signaling No.5 uses two combinations of six tones to transmit various signaling, that is, in-band dual-tone multi-frequency signals.
Dual tone multi-frequency In order to adapt to the development of digital program-controlled switches, international telegraph and telephone consultation
CCITT proposed signaling No.6 in 1968. No.6 signaling is * * * signaling, and the message length is fixed at 28 bits.
. Considering the development trend of digital communication to ISDN (Integrated Services Digital Network), CCITT proposed in 1980 that it is very universal.
Since then, the No.7 signaling system has been expanded and modified many times, and has formed a complete signaling system. No. seven
The signaling system transmits signaling between signaling points in the form of network messages and is interconnected with the open system of ISO.
The model (OSI model) has a corresponding relationship.
2. Why adopt No.7 signaling system?
Signaling system No.7 separates signaling from voice path, and uses high-speed data link to transmit signaling, so it has transmission speed.
Fast, short call setup time, large signal capacity, flexible change and expansion, low signaling equipment investment and high telephone channel utilization.
Features. Although the No.7 signaling system originated from the telephone network, its application is not limited to the exchange of voice channels, which can be said to be the most important.
Its potential applications are non-voice service, voice service intelligence and integrated service digital network. In these areas, other signals
Is powerless.
No.7 signaling system has a * * signaling network superimposed on the telephone network, which is circuit-switched, while the * * signaling network.
The realization of packet switching complements each other and greatly improves the capacity of traditional telephone networks. Inter-office signaling of telephone network is on * * * road.
In addition to the characteristics of high speed, high reliability and large capacity, the signaling network can also be equipped with database services.
Server, network management and monitoring center, intelligent node with voice recognition function, etc. And make the advanced intelligent network become a reality.
In addition, the No.7 signaling system is also a cellular mobile communication network, PCN (Personal Communication Neork) and ATM.
Network and other data communication networks.
Second, the structure of No.7 signaling system
1.*** signaling network structure
Conceptually, No.7 signaling is a kind of signaling that runs on a network independent of the telecommunication network, and this network is called * * * signaling.
Network, or No.7 signaling network, is composed of multiple signaling points, which are generally connected by 64Kbps digital links. typical
Signaling network includes SSP, SCP and STP.
SSP (service switching point) is a kind of service switching point that can execute various No.7 signaling applications (user call processing
, 800 service, collect call, etc. ) in the private branch exchange. Among them, only letter No.7 is provided.
The telephone office that handles user calls is called CCSSO (Common Channel Signaling Exchange).
S). Generally speaking, CCSS can be realized by upgrading the existing program-controlled switch software and adding some hardware.
Function of o or SSP. However, this kind of software is very expensive, and the price of a SSP software is millions of dollars.
SCP (service control point) is a special signaling point, which can provide database services. Telephone number 800 and letters
Many special business functions, such as card phone, must be realized by SCP. SCP usually consists of a large multi-machine system.
A successful database server can handle millions of database query requests every day.
STP(Signallint Transfer Points) is a special equipment for * * * signaling network, and its main function is signaling.
Transmission, signaling routing and translation of global headlines. In order to improve communication, a STP can support hundreds of links.
For the reliability of the network, STP is usually always configured in pairs.
* * * Signaling network is often a regional network, or a national network, or an international network, which has many nodes and requires reliability.
High and complicated management and maintenance. Therefore, the network must be equipped with multiple network operation support systems OSS, which are connected with STP and SCP.
They exercise management control.
* * * Signaling networks are generally hierarchical. Take the United States as an example. From the perspective of the influence scope of telecom management
The United States is divided into seven regions, and each region is divided into several communities, and each community belongs to a local telecommunications company.
Operation and management, the first area is controlled by the local telecom company Bell Operation Company. Accordingly, the United States * * * road letter.
Wang Ling has a two-level structure (Figure 1).
@@ 12S 10300。 GIF map 1. * * * Signaling network structure
For network reliability and load balance, two pairs of RSTP (regional STP) and two SCPs are set in each area.
Each SCP is equipped with two databases, and the database cmsdb (Call Management Service Database) is used for No.800..
Service, LIDB database (line information database) is used for credit card telephone service and collect telephone service.
And third-party pay phone service. The two database copies on the two SCPs are identical. When one SCP fails, the other scp
Another SCP can continue to provide services.
RSTP in one area is directly connected with RSTP in other areas, or interconnected by other long-distance signaling networks. Within each area
Establish SEAC signal engineering management center. Each cell is provided with one or more LSTP(Licak STP), all LSTP and LSTP.
RSTP connection. Each LSTP is connected with all SSPs and CCSSO in the cell. The typical way to connect the telephone office and the signaling network is
, the program-controlled switch of tandem office (AT) is upgraded to AT/SSP, and the program-controlled switch of end office (CEO) is upgraded to EO/CCSSO. Not all of them
All end offices must have CCSSO function, and nearly 30% of end offices in the United States still do not have signaling function No.7.
2. Protocol structure
At present, signaling No.7 can be divided into six parts by function (Figure 2):MTP, SCCP, TCAP, OMAP, ISUP and map. follow
With the development of No.7 signaling application, TCAP will add other application parts.
@@ 12S 1030 1。 GIF figure 2. Protocol Structure of Signaling System No.7
MTP (message passing part) is divided into three levels: SDL (signaling data link) and SLF (signaling I).
Ng link function) and SNF (signaling link function). The function of the first-level SDL corresponds to OSI.
Physical link layer of the model. The function of the second layer SLF corresponds to the data link layer of the OSI model, and its protocol is similar to HDLC.
Responsible for point-to-point communication processing. The main functions of the third layer SNF are message identification and distribution, message routing and signaling network.
Traffic management, route management and link management.
SCCP (signaling connection control part) is a supplement to the third layer of MTP, and it is combined with SNF.
It should be in the network layer of OSI model. The protocol functions of SCCP are divided into four categories: 0, 0, 2 and 3. chlorine
Ass0 and Class 1 have no connection to perform network services, while Class2 and Class3 have connections to perform network services. Split connection control
In addition, SCCP also performs the translation of full name address and end-to-end routing.
Tcap (transaction capabilities application part) provides transaction processing for the application of No.7 signaling.
The required support corresponds to the application layer of OSI model, and its protocol is similar to ROS of OSI.
The main function of OMAP is network management and maintenance.
Protection, which is similar to the CMIP protocol of OSI.
ISUP(ISDN user part) is the most complicated part of No.7 signaling, and its main function is to exchange between two program-controlled switches.
The machine (ISDN switch) establishes a voice path (call establishment) between the calling and called users, and the voice path is released (call
Call release), line monitoring, supplementary service processing, etc. In addition to ISUP, CCITT, the International Telegraph and Telephone Advisory Committee, also decided.
It means TUP (telephone user part) and DUP (data user part). TUP performs session exchange signaling and DUP performs it.
Non-voice exchange signaling.
The main function of Map is to support cellular mobile communication, and its protocol is not perfect.
Different signaling points include different parts of No.7 signaling. STP only includes MTP and SCCP；; SCP includes MTP
CCP, TCAP and applications based on database query (such as 800 service, collecting telephone service from others, etc. ); CCSSO usually only includes
MTP and ISUP；; And SSP includes all parts of No.7 signaling.
At present, the signaling protocol No.7 promulgated by two American standardization organizations has attracted people's attention. The first is Q released by CCITT.
Series protocol, and the other is the T series protocol issued by Bellcore Communication Research Company of the United States. Basically the same, but there are some.
Important difference. In addition, Bellcorp has published a large number of TR series technical documents, which are implementation-oriented protocols with detailed specifications.
Body is the industrial standard of North American signaling network. TR series does not contain OMAP, and only connectionless services are used for SCCP. In addition, the TR system
The column defines toll-free phone (No.800), credit card phone, collect phone, third-party collect phone, category and so on.
The operating specification of No.7 signaling application is not perfect in CCITT Q series. Therefore, the implementation of North American signaling
Refer to TR series technical documents.
Application of No.3 and No.7 Signaling
1. session signaling
One of the most basic applications of No.7 signaling is to replace the old No.1 to No.6 signaling as the office of modern digital program-controlled exchange.
Inter-office signaling controls the connection of inter-office calls. Compared with the old inter-office signaling, No.7 signaling has many advantages as inter-office signaling: (1)
The signaling transmission speed is fast and the call connection time is short; (2) The signal capacity is large, and a 64kbps link can theoretically handle tens of thousands.
Speech path; (3) flexible and easy to expand; (4) the interference of the dialogue path is small, and the quality of the dialogue path is high; (5) Deliverable end-to-end signaling or user letters.
Order; (6) It can make the voice service intelligent, even though the traditional telephone service has class characteristics.
Class (Customer Local Signaling Service) stands for a special set of telephone service functions. This package
It includes 13 functions such as automatic callback, automatic recall, user tracking, caller name transmission, and incoming call selection acceptance. These functions or
Service features are not provided by the user's phone alone.
2.800 service
According to statistics, in 1993, the United States handled 80 million to/kloc-0,000,800 telephones every day, with an annual turnover of tens of billions of dollars and an annual growth rate.
Yes 15 ~ 20%. No.800 service is a huge market, which attracts various telecom companies and is one of their most important incomes.
. The so-called 800 telephone number is a special telephone number provided by the company to customers. The area code of this number is 800 (virtual
Area code), when customers use this phone to talk to the company, the cost is paid by the company, and the calling customer is free. Eight hundred
The telephone number 1 is a virtual logical telephone number. A company may have many actual phone numbers, but only 800 phone numbers.
First, customers can call this number anywhere and ask to speak to the functional department of the company, so there is a problem.
The process of converting 800 telephone numbers into actual telephone numbers. The realization of this process depends on the SCP of the signaling network.
3. collect call
There are three forms of alternative billing service (ABS): the first form is credit card.
In other words, it is different from the popular magnetic card phone in China (in English, the magnetic card phone is called debet card call); The second form
The called type is collect call or collect call; The third form is a third-party pay phone.
Before the establishment of the * * signaling network, the other party's pay phone relied on the telephone operator.
Only in this way can it be realized. With the * * signaling network, the other party's pay phone is basically automated, convenient and efficient.
4. Advanced Intelligent Network (AIN)
Advanced intelligent network introduces two new nodes in * * * signaling network: attachment node and IP node. Appendices have a similar function.
In SCP, it is directly connected with the SPC exchange with SSP function, providing them with direct and fast database services and calls.
Platform function of processing. Administrators (even users) of the telephone office can use the platform function to design telephones for their own exchanges.
Service function, of course, the program-controlled switch software must also be upgraded to AIN software.
In AIN switch, the user's telephone processing process is divided into many stages, and a trigger checkpoint is defined after each stage.
AIN switch software detects switch-generated events at each checkpoint. The call processing of telephone consists of AIN switch and adj.
Unct*** is completed at the same time (traditional call processing is completely completed in the switch). AIN is usually processed and tested at the checkpoint.
When the event occurs, the processing will be submitted to attendant for completion. The work completed by the attachment can be completed by the administrator using the platform function.
Design to obtain different telephone service characteristics.
IP (Intelligent Peripheral) is a kind of network intelligent equipment, which is directly connected with AIN switch and mainly
The function is speech recognition. If the network administrator defines the "speech recognition" function at the breakpoint, the user can use this phrase.
Enter the called phone number by voice. At this point, the AIN switch must send the voice number to IP and convert it into a digital number before continuing.
Telephone processing.
5. Cellular mobile communication system
Cellular mobile communication system needs to add at least three kinds of nodes in * * * signaling network: MSC, HLR and VLR. Cell movement
The communication system divides a communication area into many cells, and an MSC (Mobile Switching Center) is set in each cell.
Er), responsible for the communication of wireless users in the cell. MSC is a wireless switch using No.7 signaling, including No.7 signaling.
In the cellular mobile communication system of MTP, SCCP, TCAP and MAP in, every wireless user must register in the database HLR(Home
Location register) and VLR (visitor location register).
Cellular mobile communication system includes many No.7 signaling processes, among which the two most important signaling processes are: registration.
Mobile users automatically register On and intersystem handover/intersystem handover registers in VLR.
Process. When a mobile user crosses the boundary between two cells, communication processing is switched from one MSC to another.
This is a signaling process of inter-system handover, and vice versa.
MAP protocol is still in the process of improvement. At present, the protocol standard adopted by most manufacturers is the transitional standard formulated by EIA/TIA.
4 1-B .
6. Other applications
No.7 signaling has a broad application prospect. In addition to the above five applications, it can also be used as ATM network and B-ISDN.
Internal signaling of the network. In addition, due to the expansion of data communication network scale, the enhancement of technical complexity and the operation and maintenance of the network.
The contradiction between management, testing and fault diagnosis is increasingly prominent. The best way to solve this problem is to use OMA of No.7 signaling.
P protocol establishes network management and maintenance center in * * * signaling network. Because the signaling network is a fast and reliable data packet.
In the switching network, the operator of the network management center can carry out remote real-time testing, diagnosis, monitoring, control and
Management, and does not interfere with the normal data communication.
Fourth, build China No.7 signaling network.
In recent years, China's telecommunications industry has developed rapidly, and the digital program control of telephone networks in large and medium-sized cities has approached Europe and the United States.
At the level of developed countries such as Japan, some inter-office signaling has been replaced by DTMF for the No.7 signaling system. Signaling system title No.7
The second application in China was when S 1987 was introduced into private branch exchange, and since then, it has cooperated with various advanced foreign communication equipment.
With the introduction of equipment, especially program-controlled PBX, the application scope of No.7 signaling system is gradually expanding, and some big cities are planning.
In order to establish the protocol standard of seven-order system, a lot of work has also been done. 1987, releasing "Signaling Party No.7 of China Domestic Telephone Office".
Type-I technical specification (interim provisions),1In August, 990, the Technical Specification for Signaling Mode No.7 of China Domestic Telephone Network was re-promulgated.
Fan (Interim Provisions). The Ministry of Posts and Telecommunications adopts CCITT's Q series standards, but only includes MTP, TUP and signaling.
Monitoring part of the network.
However, whether in the formulation of No.7 signaling protocol or in the construction and application of No.7 signaling network, China still lags behind.
There are many problems to be solved in the very backward situation. Such issues included questions on the following:
(1) As one of the most important applications of No.7 signaling, can No.800 service and ABS be popularized in China? Is it in line with China?
National conditions?
(2) The (Interim Provisions) formulated by the Ministry of Posts and Telecommunications do not include the No.7 Signaling No.800 service and the operating specifications of ABS. If China.
What standards are used to promote service 800 and ABS similar to those in the United States?
(3) Will China establish a national signaling network with * * * channels, and if so, what structure will it adopt? Can it be adopted?
American secondary structure?
(4) In recent years, China's data communication network has developed rapidly, but the maintenance and management methods are backward, and the availability of communication facilities is low.
Should an advanced integrated network management control center be established on the basis of * * * signaling network? If so, how to achieve it?
These problems need further study.