21-08-2012, 05:06 PM
Signaling System for GSM Networks
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Introduction to Signaling Systems
Signaling : Signaling is defined as a mechanism by virtue of which network entities exchange information amongst themselves , which are required to set up a communication path.
Signaling System : Signaling system is defined as a set of methods or rules followed by network entities to exchange information required for communication set up.
Examples of Signaling Systems :
SS#7 or CCS#7 (Common Channel Signaling #7)
CAS (Channel associated Signaling)
DTMF (Dual Tone – Multi frequency)
Channel Associated Signaling (CAS)
In CAS each and every speech channel is associated with a signaling channel. This means for each speech channel a separate signaling channel is required.
Advantages of CCS
Higher signaling capacity.
More number of speech/data channels as there is only one signaling channel.
Central offices can exchange information , not related to speech/data between themselves e.g. subscriber data.
Various high end features like roaming are possible by using CCS7.
CCS7 Network Components
The CCS7 Network consists of the following Components :
SP -Signaling Point : The SP is the source or originating entity of the signaling message.
STP-Signaling Transit Point : These entities transfer the signaling message to another SP or STP without processing the signaling message.
SRP – Signaling Relay Point : These are STPs with ability tp process the signaling message.
SEP – Signaling End Point : The SEP is defined to be the terminating point of the signaling message
CCS7 Terminologies
SPC : SPC is defined as signaling point code which uniquely identifies each element within the SS7 network.
Signaling Links : The signaling links transmit signaling messages between the communicating entities.
Signaling Link Set : A signaling link set is a collection of signaling links between two signaling entities.
Signaling Route : A signaling route is defined to be the path through which signaling messages are exchanged between two entities. There can be multiple signaling routes between two SPCs, wherein there will be one primary route and several alternate routes.
SS7 Routing Modes
Associated Mode :
In the associated mode, the signaling link is routed together with the circuit group belonging to the link. In other words, the signaling link is directly connected to signaling points which are also the terminal points of the circuit group. This mode of signaling is recommended when the capacity of the traffic relation between the signaling points A and B is heavily utilized.
Quasi associated mode :
In the quasi-associated mode of signaling, the signaling link and the circuit group run along different routes, the circuit group connecting the signaling point. A is directly connected with the signaling point B. For this mode the signaling, the circuit group is carried out via one or more defined signaling transfer points. This signaling mode is favorable for traffic relations with low capacity utilization, as the various signaling links can be used for several destinations.