Diagram:

Explanation:

I.NETWORK SERVICE PART (NSP) OF SS7:

• The NSP provides ISDN nodes with a highly reliable and efficient means of exchanging traffic using connectionless services.

MESSAGE TRANSFER PART (MTP) OF SS7:

• The function of MTP is to ensure that signaling traffic can be transferred and delivered reliably between the end-users and the network.

• MTP is provided at three levels.

1. Signaling Data Link Functions (MTP Level 1):

• This level provides an interface to the actual physical channel over which communication takes place.

• Physical channels may include copper wire, twisted pair, fiber, mobile radio or satellite link.

• This level uses 64 kbps transmission.

2. Signaling Link Function (MTP Level 2):

• It provides a reliable link for the transfer of traffic between two directly connected signaling points.

• Variable packet messages, called message signal units (MSUs) are defined in MTP level 2.

• MTP level 2 also provides flow control data between two signaling points as a means of sensing link failure.

3. Signaling Network Function (MTP Level 3):

• It provides procedures that transfer messages between signaling nodes.

• There are two types of MTP Level 3 functions: signaling message handling and signaling network management.

4. Signaling Message Handling:

• This is used to provide routing, distribution and traffic discrimination (discrimination is the process by which a signaling point determines whether or not a packet data message is intended for it‟s user or not).

5. Signaling Network Management:

• This allows the network to reconfigure in case of node failures and has provisions to allocate alternate routing facilities in case of congestion or blockage in parts of the network.

II. SIGNALING CONNECTION CONTROL PART (SCCP):

• The SCCP provides enhancement to the addressing capabilities provided by the MTP.

• SCCP also provides the ability to address global title messages or non-billed numbers.

• Different classes of service provided by SCCP are:

o Class 0: Basic connectionless.

o Class 1: Sequenced connectionless.

o Class 2: Basic connection-oriented.

o Class 3: Flow control connection oriented.

o Class 4: Error recovery and flow control connection oriented.

III. SS7 USER PART:

• SS7 user part provides call control and management functions and call setup capabilities to the network.

The SS7 user part includes the following:

a) Integrated Services Digital Network User Part (ISUP):

• The ISUP provides the signaling functions for carrier and supplementary services for voice, data and video in an ISDN environment.

• ISUP uses the MTP for transfer of messages between different exchanges.

• In addition to the basic bearer services in an ISDN environment, the facilities of user-to-user signaling, closed user group, calling line identification and call forwarding are provided.

b) Transaction Capabilities Application Part (TCAP):

• The TCAP part in SS7 refers to the application layer which invokes the services of the SCCP and the MTP in a hierarchical format.

• One application at a node is thus able to execute an application at another node and use these results.

c) Operation Maintenance and Administration Part (OMAP):

• The OMAP functions include monitoring, coordination and control function to ensure that trouble-free communications are possible.

SS7 Services:

Touch star:

1. This kind of service is also known as CLASS and is a group of switch-controlled services that provide its users with certain call management capabilities.

2. Services such as call return, call forwarding, repeat dialing, call block, call tracing and caller ID are provided.

800 Services:

1. These services were introduced by Bell Systems to provide toll-free access to the calling party and to the services and database which is offered by the private parties.

2. The costs associated with the processing of the calls are paid by the service subscriber.

3. The service is offered in two plans known as the 800-NXX plan and the 800 database plan.

4. In the 800-NXX plan the first six digits of an 800 call are used to select the interexchange carrier (IXC).

5. In the 800 database plan, the call is looked up in a database to determine the appropriate carrier and routing information.

Alternate Billing Service and Line Information Database (ADB/LIDB):

1. These services use the common channel signaling (CCS) network to enable the calling party to bill a call to a personal number (third party number, calling card or collect, etc.) from any number.