Signaling Basic Concepts of CCS 7 Training Center

Signaling Basic Concepts of CCS 7 Training Center Zhongxing Telecom Pakistan (Pvt. ) Ltd

Overview n n n The relationship between signaling network and telecom network The development of No. 7 signaling system The development goal of No. 7 signaling system

The Development Goal 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 (Forming or characterized by a sequence)and highly reliable transmission with no loss and no repetition.

Signaling----Definition It is the dialog language for the communication between various parts of the telecom network.

Signaling----Classification Subscriber signaling: Between sub. & switch Working area inter-office: Control the setup and release of call Monitoring signals: Monitor the changes of call states or conditions in the lines Signaling function Selection signals： Routing information Operation signals: Management and maintenance of telecom networks

Channel Associated Signaling： Transmitting path Common Channel Signaling

Common Channel Signaling (CCS) In telephony, Common Channel Signaling (CCS), in the US also Common Channel Interoffice Signaling (CCIS), is the transmission of signaling information (control information) on a separate channel from the data, and, more specifically, where that signaling channel controls multiple data channels……. Channel Associated Signaling (CAS), also known as per-trunk signaling (PTS), is a form of digital communication signaling. As with most telecommunication signaling methods, it uses routing information to direct the payload of voice or data to its destination. With CAS signaling, this routing information is encoded and transmitted in the same channel as the payload itself.

Common Channel Signaling System v ISDN line terminal s v v S Signaling terminal R e gi s t e r Signaling terminal Exchange B v+s Exchange A Line terminal v+s v s Line terminal ISDN line terminal

Channel Associated Signaling Register v+s Line terminal Register v+s Exchange B Exchange A Line terminal v+s v+s

Advantages of CCS Compared with Channel Associated Signaling, Common Channel Signaling has many important advantages n n Information can be switched between processors much faster than in channelassociated signaling. With a huge signal capacity, it can hold dozens or even hundreds of different kinds of signals, thus providing more new services.

n n 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. Since line signaling is no longer needed, trunk devices can be used both in calls from A to B, and in calls from B to A. In such bi-directional working modes, even less circuits are required than when trunk circuits are respectively used in single call directions.

n n n When a call is being set up, signals related to this call can be sent. In this way, the subscriber can change the already setup connections. For example, the subscriber can transfer one call to another place, or request a third party to join the present connections. Signals can be switched between processors so as to be used for maintenance or network management. The No. 7 line signaling can provide powerful support for ISDN, IN, TMN (telecommunication management Network)and cellular mobile communication systems, as this signaling is their basis.

Disadvantages of CCS n n 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 (A Sudden Disorder). The SS 7 systems that every transnational corporation produces are having some problems in compatibleness.

SS 7 Protocol System Structure User Part ISUP DUP TUP MTP 3（NETWORK SCCP LAYER） MTP 2（DATA Link LAYER） MTP 1（PHYSICAL LAYER） Message Transfer Part

ISUP (ISDN User Part): ISUP supports basic telephone call connect/disconnect between end offices. ISUP was derived from TUP, but supports ISDN and intelligent networking functions. DUP (Data User part): DUP defines the necessary call control, and facility registration and cancellation related elements for international common channel signalling by use of SS 7 for circuit-switched data transmission services. TUP (Telephone User Part): TUP is an analog protocol that performs basic telephone call connect and disconnect.

L 4 L 3 User part Logical path Signal network function L 2 Signaling link Logical path function L 1 Signaling data Physical path link function User part Signal network function Signaling link function Signaling data link function

Example The President of a Chinese company is communicating with the President of a Pakistani Company , however neither speaks the other’s language. Each employs an English translator and the translated messages are sent by the Fax operator over physical communication channel. Thus, the two presidents are communicating with each other through five layers below them

Company A (China) Chinese President Effective Communication Company B (Pakistan) Pakistani President Write to paper Translator Print to paper Fax Operator Telegraph Fax Operator physical communication channel

Common Channel Signaling Network n The CCS 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 source points n OPC (Originating Point Code) The SP that generate signaling messages n DPC (Destination Point Code) The SP that receives signaling point code.

Signaling 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. That is, they are the middle node points during signaling transfer. OPC or DPC is 14 -bit address (24 -bit for China

n n OPC or DPC is not absolute. OPC and DPC are relative, the OPC of certain Office, for other Offices, is DPC. For example, the SP of switch A is 2_2_2, and SP of switch B is 3_3_3. If you work in switch A then 2_2_2 is OPC for A, and 3_3_3 is DPC for A. Voice channels B A 2_2_2 Signaling link C 3_3_3

SIGNALING LINK It refers to the signaling message channel that connects an SP and another SP( or STP). SIGNALING LINK SET A bunch of signaling links directly connecting two SP (including STP) form one signaling link set. ROUTE One such set usually includes all parallel signaling links. ROUTE SET It is also possible to set several routes between two SP

ROUTE SET ROUTE 3 Link Set 2 ROUTE 1 Link Set 1 ROUTE 2 Link

The Associated Mode In this mode, Messages related to the voice channel connecting two switches are sent on the signaling link that directly connects two switches. Voice channels A B Signaling link

The Quasi- Associated mode This can be called a special case of the nonassociated 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. Voice Channels A B Signaling link C

Functions of Signaling Data Link Level The 1 st level defines the physical, electrical, and functional features of the signaling data link, and is thus 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 64 kbit/s.

Functions of the Signaling Link 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.

n Error check n n Error Correction n n FSN, BSN, FIB, Basic Error Correction and Preventive Cyclic Retransmission (PCR) Error Monitoring of Signaling Link n n 16 bit Check Code Prevents the retransmission when error occurs Flow Control n Prevent the link congestion if the load on the link is too heavy

The Signaling Network 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 originating node (OPC) and the destination point code or( DPC).

n Message Routing n n Message Distribution n n Selecting the signaling link that is used by each signaling message to be transmitted Send the message to a user part or level 3 functions after receiving the message Message Authentication n To determine whether a signaling point is the destination point of a message after the signaling point receives the message.

The User Part n n 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) and the signaling connection control part (SCCP)

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