What is Signaling

In Communication system, the messages that are required to co-ordinate different entities.

Signaling messages are described in interface, protocols & specifications.

INTERFACES :- It refers to the connecting point between 2 adjacent network entities.

PROTOCOLS :- Its a set of rules to be defined for exchanging information between connecting points.

Types of Signaling :-

In telephone network, signaling is divided into 2 parts -
1. Access Signaling - Signaling between subscriber terminal (telephone) & the local exchange

2. Trunk Signaling (Inter-exchange signaling) - It is used for signaling between exchanges. Inter-exchange signaling information is usually transported on one of the time slot in PCM link, either in association with the speech channel or independently.

These are of 2 types :-

1. Channel Associated Signaling (CAS) - In CAS, speech channel (in-band) or a channel closely associated with speech channel (out-band), is used for signaling.

2. Common Channel Signaling (CCS) - In CCS, a dedicated channel completely seperate from speech channel is used for signaling. Due to high capacity, in CCS one signaling channel can serve a large no. of speech channel.

Line Signals :- They are used during the 'duration of a call' to monitor the status of the connection & traffic circuit, e.g. seizure, answers signals, etc.

Register Signals :- They are used during the setup phase of a call to transfer address & category information e.g. dailed B number, etc.

Line signals & register signals are used in CAS system.

In CCS, signaling messages (data packets) are transmitted over time slot in a PCM link reserved for the purpose of signaling. The System is designed to use a common data channel (signaling link) as the carrier of all signals required by a large no. of traffic channels.

Signaling Interfaces :-

These are A, B, C, D, zz, 39/xx, Q, T1, SIGTRAN, ISUP interface, etc.

A,B,C,D are already defined in previous Interfaces post,

ZZ:- Its between MSCe's (Mobile Switching Center Emulation). It compiles with the SIP-T (Session Initiation Protocol for Telephone). It provide the inter-office call control function for narrowband circuit-switched domain services.

39/xx:- Its between MGW (Media Gateway) & MRFP (Media Resource Function Processor). It compiles with Megaco/H.248. Its is used when MSCe controls dynamic & static resources of transmission nodes (IP/TDM) in the MGW during call processing, including terminal attributes, terminal connectivity & mobile streams.

Q:- Its between MSCe & MC (Message Center). It Compiles with MAP (Mobile Application Part) of SS7 (Signaling System 7) to support SMS (Short Message Services).

T1:- Its between MSCe & SCP (Service Control Point). It compiles with WIN of SS7 to support IN (Intelligent Network) services.

SIGTRAN:- Its between MSCe & SG (Signaling Gateway). It is used to transmit circuit switching signaling messages over IP (Internet Protocol) network.

ISUP interfaces :- The gateway office provides the interfaces between PSTN (Public Switch Telephone Network) & other mobile network devices & controls incoming & outgoing calls through ISUP or TUP of SS7.


Signaling Protocols :-
       These are

• SS7 (Including ISUP, MAP & BSAP)
• SIP (Session Initiation Protocol)
• H.248

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