OutlineOverviewNO.7 signaling protocol system structureThe signaling messages structure of No.7 signalingThe Telephone User Part (TUP)

OverviewNo.7 are common channel signaling systems The No.7 signaling system (abbreviated as SS7) was first stipulated by the CCITT in 1980 (in the orange cover book), and was twice modified and supplemented in 1984 (blue book) and in 1988 (white book). The general goal of the No.7 signaling system is to suggest an internationally standardized common channel signaling system with general applications fields so that the digital communication networks with digital SPC switches can work in the best status. Furthermore, such networks can provide sequential and highly reliable transmission with no loss and no repetition.

OverviewYou will study

Basic conception NO.7 signaling system

Signaling systemDefinitionIt is the dialog language for the communication betweenvarious parts of the telecom network. It ensures thenetwork to operate normally as an integer.

Signaling systemClassificationWorking areaSubscriber signaling:between sub. and switchInter-officecontrol the setup and release of callMonitoring signals: monitor the changes of call states or conditions in the linesSelection signalsin routingOperation signalsmanagement and maintenance of telecom networksSignaling function

Signaling systemClassificationCommon channel signalingChannel associated signalingTransmitting path

Signaling systemChannel Associated Signaling

Exchange A RegisterRegister Exchange B Line terminalLine terminalv+sv+sv+sv+sv+sv+sSubscriber Line Signaling

Signaling systemCommon Channel Signaling System

Signaling systemAdvantages of Common channel signalingCompared with channel associated signaling, common channel signaling has many important advantages:Information can be switched between processors much faster than in channel-associated signaling.With a huge signal capacity, it can hold dozens or even hundreds of different kinds of signals, thus providing more new services. With a great flexibility, it can provide more new services simply by modifying software to increase signals. Line signaling device is not needed any more at any trunk station, which shall greatly reduce investment costs.

Signaling systemDisadvantages of Common channel signaling The error rate of the common channel signaling system must be very low.Its reliability must be much higher than the channel associated signaling system. This is because once the data link fails, all related calls between the two related switches shall be affected.Bi-directional trunk working modes exist conflict of seizure. The SS7 systems that every transnational corporation produces are having some problems in compatibleness.

Signaling systemDefinition Signaling system includes a set of integrated signaling and operation procedure.Signaling system is the collection of software and hardware which generatetransmitreceive and recognize the signaling.

OutlineOverviewNO.7 signaling protocol system structureThe signaling messages structure of No.7 signalingThe Telephone User Part (TUP)

NO.7 signaling protocol system structureOutlineSystem structure and the function of every layerMessage structure

NO.7 signaling protocol system structureThe common-channel signaling network consists of the following parts: Signaling point (SP)It refers to the node in the signaling system that provides common channel signaling. SP can also be divided into OPC (Origination Point Code) and DPC (Destination Point Code). Actually, SP is part of a switching system.

NO.7 signaling protocol system structureSignaling transfer point (STP) It refers to SP that transfer signaling messages from one signaling link to another. They are neither source points, nor destination points. OPC or DPC is 14-bit address for CCITT (24-bit for China)

NO.7 signaling protocol system structure2_2_23_3_38_8_5

NO.7 signaling protocol system structure

NO.7 signaling protocol system structure

NO.7 signaling protocol system structureROUTE 2ROUTE 3ROUTE 1LinkLink Set 2Link Set 1ROUTE SET

NO.7 signaling protocol system structureNon-associated modeThis is as shown in Figure 4.3.2-1 (b). Signaling messages between A and B are transferred by several signaling links according to the current network status, but the voice circuit is the direct route between A and B. In other cases, the common channel signaling messages are transferred on different paths. This mode is normally not used, as it is rather difficult to exactly identify a route at any given time

NO.7 signaling protocol system structureThe quasi-associated mode This can be called a special case of the non-associated mode. In this mode, signaling messages between switches A and B go through the several preset concatenated signaling links, but voice signals go through the direct channels between A and B. Normally, different transmission carriers are used in the common channel signaling systems and their related voice links.

NO.7 signaling protocol system structureThe earliest structure of No.7 signaling protocol systemUser partMessage transfer part

NO.7 signaling protocol system structure

NO.7 signaling protocol system structureMTP: Message Transfer PartSCCP: Signaling Connection Control PartTCAP: Transaction Capabilities Application Part TUP: Telephone User PartISUP: Isdn User PartMAP: Mobile Application PartOMAP: Operations, Maintenance and Administration PartINAP: Intelligent Network Application Part CAP: CAMEL Application PartBSSAP: Base Station Subsystem Application Part

NO.7 signaling protocol system structureFunctions of the physical level (The first level)The 1st level defines the physical, electrical, and functional features of the signaling data link, and is similar to the OSI physical layer. It determines the connection method with the data link, and provides an information carrier for the signaling link. In digital transmission, signaling data links are usually digital channels at 64kbit/s.

NO.7 signaling protocol system structureFunctions of the signaling link level (The second level)The second level defines the signaling message transmission functions and procedure related to its transfer on a signaling data link. The second level and the first signaling data link used as a whole as an information carrier, provide a signaling link between two signaling points for the reliable transfer of messages.

NO.7 signaling protocol system structureFunctions of the signaling link level (The second level) Signal unit demarcation and localizationError check16 bit check codeError correctionFSN;BSN;FIB;BIB; basic error correction and preventive cyclic retransmission(PCR)Initial localizationwhen recovering links after the first starting and the link is failedError monitoring of signaling linkprevent the overmuch retransmission when error occursFlow controlprevent the link congestion if the load on the link is too heavy

NO.7 signaling protocol system structureFunctions of the signaling network function level (The third level) Within a signaling network, each switching node is allocated a signaling point code, which is 14-bit address (24-bit for China). Every CCITT No.7 message then contains the point code of the origination node (OPC) and the destination point code ( DPC).Message routingselecting the signaling link that is used by each signaling message to be transmitted.

NO.7 signaling protocol system structureMessage distributionsend the message to a user part or level-3functions after receiving the messageMessage authenticationto determine whether a signaling point is the destination point of a message after the signaling point receives the message.Signaling service managementcontrol message routing etc.Signaling link managementcontrol the locally connected link groupSignaling route management

NO.7 signaling protocol system structureFunctions of the user part (The fourth level)The user part is the fourth function level of the NO.7 signaling system. Its main function is to control the setup and release of various basic calls. The major user parts include the telephone user part (TUP), the ISDN user part (ISUP)

OutlineOverviewNO.7 signaling protocol system structureThe signaling messages structure of No.7 signalingThe Telephone User Part (TUP)

The Telephone User Part (TUP)The label of phone signaling message Each signaling message is a set of information used separately by the different No.7 signaling user part. To label the original and destination point of each signaling message, in each signaling message unit there is the messages channeling label with a fixed length.The label of telephone signaling messages is as shown in Figure 4.5.1-1. It includes three fields: the destination signaling point code (DPC), the originating signaling point code (OPC), and the circuit identification code (CIC).The first transmitted bit

The circuit identification code CICThe circuit identification code is distributed to each phone circuit, by bilateral agreement or preset principles:The 2048kb/s digital channel For the 2048kb/s digital channel, the 5 lowest bits in the 12-bit CIC is the time slot code of the voice channel.The other 7 bits represent the codes of the PCM systems between DPC and OPC. Primary group (E1) consists of 32 time slots, 25=32so that 5 bits are enough. 27=128 128*32=4096 voice channelsOne 64kb/s No 7 link is able to service for 4096 trunks.

The Telephone User Part (TUP)The 8448Kb/s digital channel For the 8448Kb/s digital channel, the 7 lowest bits in the 12-bit CIC is the time slot code of the voice channel, and the other 5 bits represent the codes of the PCM systems between DPC and OPC. Second order group consists of 4 Primary group 32*4=12827=128 lowest bits for E2 are enough.27=128 and 25=32128*32=4096 voice channelsone 64kb/s No 7 link is able to service for 4096 trunks.

ISDN User Part (ISUP)

Some in common use messages:

ISDN User Part (ISUP)Succeed call flow

ISDN User Part (ISUP)Unsuccessful call flow

ISDN User Part (ISUP)Difference between TUP and ISUP messageFrom the message format ,TUP message is much more suitable for define one by one ,add a new message need define a new message formatISUP message provide a uniform format, convenience for computer process; ISUP message have Compulsory variable part and optional part , messages are more abundance;Add some enhanced functions ,like non-calling service, end to end subscriber signaling supplementary service ,etc;ISUP can accomplish all functions of TUP.

CCITT:OSI 1 2 PPT