Traditional SS7 Protocol

1. Message transfer part 2 (MTP2)

MTP2 corresponds to OSI Layer 3 (the data link layer) and such is the lowest protocol in the stack.Sitting on the phisical layer, its provide a realiable means of transfer for siganling information between two direcly connected singaling point (SPs),ensuring that the signaling information is delivered in the sequence and error free

MTP2 performs the following functions:

1.Delimination of signal units
2.Alignment of signal units
3.Siganling link error detection
4.Siganling link error correction by retransmission
5.Signaling link initial alignment
6.Error monitoring and reporting
7.Link flow control

Message transfer part 3 (MTP3)

The primary purpose of this protocol is to route message between SS7 network node in the reliable manner.This responsibility is devided into two categories:

1.Signaling message handling (SMH)

2.Siganling network management (SNM)

SMH is concerned with the routing message to the appropriate network destination.Each node analyzes the incoming message based on its destination point code (DPC) to detemine whether the message is destined for that node.If the receiveing node is the destination, the incoming message is delivered to the appropriate MTP3 user.If the receiving node is not the destination and the message has routing capability, i.e, is an STP, an attempt us made to route the message
SNM is set of message and procedures whose purporse is to handle network failure in a manner that allows message continue to reach their destiantion whenever possible.These procedures work together to coordinates SS7 resource that are becoming available or unavaiable with the demand of user traffic

ISDN user part (ISUP)

ISUP is responsible for setting up and releasing trunk used for inter exchange calls.As its name implies, ISUP was created to provide core network signaling that is compatible with ISDN access siganling.The combination of ISDN access signaling and ISUP network signaling provides end to end transport mechanism for signaling data between subscribers.ISUP provides siganling for both non ISDN and ISDN traffic, in fact the majority of ISUP signaled traffic currently originates from analog acccess signaling like that used by telephone service phone

The primay benefits of ISUP are its speed,increased signaling badwidth and standardization of message exchange.Providing faster call setup times than Channel Associated Signaling (CAS), it ultimately uses trunk resource more effectively.The difference in post dial delay for calls using ISUP trunk is quite noticeable to the subscriber who make a call that traverses several switches
ISUP consists of call processing, suplementary service and maintenance functions.

Signaling Connection Control Part (SCCP)

SCCP sits on top of MTP3 in the SS7 protocol stack.The SCCP provides additional network layer function to provide trandfer of noncircuit-related (NCR) signaling information,appliation management and alternative and more flexible methods of routing
SCCP was developed after the MTP and together with the MTP3 it provides the capabilities corresponding to layer 3 of the OSI references model

SCCP provides the folowing additional capabilities over the MTP:

1.Enhance MTP to meet OSI layer 3

2.Powerfull and flexible routing mechanism

3.Enhance transfer capability, including segmentation/reassembly when message is too large to fit into one Message Signal Unit (MSU

4.Connectionless and connection-oriented data transfer services

5.Management adn addressing of subsystem (primarly database-driven applicaiton)

Transction capabilities applicaiton (TCAP)

TCAP allows service at network to communicate with each other using an agrees upon of data elements.Prior to SS7, one of the problem with implementing swtiching service beyond the boundary of the lcoal switch was the propreitary nature of the switches.TCAP provides a generic interface between service that is based on the concept of componnents.Componnects comprise the instructure that service applications exchange at different nodes