SS7 Protocol Suite There are two essential components to all telephone calls. The first, and most obvious, is the actual content—our voices, faxes, modem data, etc. Telephony signaling is concerned with the creation of standards for the latter to achieve the former. These standards are known as protocols.
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SS7 Protocol Suite There are two essential components to all telephone calls. The first, and most obvious, is the actual content—our voices, faxes, modem data, etc.
Telephony signaling is concerned with the creation of standards for the latter to achieve the former. These standards are known as protocols. SS7 or Signaling System Number 7 is simply another set of protocols that describe a means of communication between telephone switches in public telephone networks. They have been created and controlled by various bodies around the world, which leads to some specific local variations, but the principal organization with responsibility for their administration is the International Telecommunications Union or ITU-T.
Signalling System Number 7 SS 7 or C7 is the protocol used by the telephone companies for interoffice signalling. In the past, in-band signalling techniques were used on interoffice trunks.
This method of signalling used the same physical path for both the call-control signalling and the actual connected call. This method of signalling is inefficient and is rapidly being replaced by out-of-band or common-channel signalling techniques.
SS7 Protocol layers: The SS7 network is an interconnected set of network elements that is used to exchange messages in support of telecommunications functions. The SS7 protocol is designed to both facilitate these functions and to maintain the network over which they are provided.
Like most modern protocols, the SS7 protocol is layered. Signaling links utilize DS—0 channels and carry raw signaling data at a rate of 56 kbps or 64 kbps 56 kbps is the more common implementation. It ensures that the two end points of a signaling link can reliably exchange signaling messages. It incorporates such capabilities as error checking, flow control, and sequence checking.
It ensures that messages can be delivered between signaling points across the SS7 network regardless of whether they are directly connected. It includes such capabilities as node addressing, routing, alternate routing, and congestion control. The first of these is the capability to address applications within a signaling point. The MTP can only receive and deliver messages from a node as a whole; it does not deal with software applications within a node. While MTP network-management messages and basic call-setup messages are addressed to a node as a whole, other messages are used by separate applications referred to as subsystems within a node.
Examples of subsystems are call processing, calling-card processing, advanced intelligent network AIN , and custom local-area signaling services CLASS services e. The SCCP allows these subsystems to be addressed explicitly. It is used for database services such as calling card, , and AIN as well as switch-to-switch services including repeat dialing and call return. To date, the most fully developed and deployed of these capabilities are procedures for validating network routing tables and for diagnosing link troubles.
IP Multimedia Subsystem (IMS) Call Flows
The preconditions for this call flow are: The calling IMS subscriber is currently roaming outside the home network. The called user is registered in the home network. The caller and the called user require resource reservation before the call can be setup. Resource allocation via PDP context activation. Originating and terminating end initiated call releases are also covered. SDP signaling involved in exchanging quality of service information. One such service is network wide publication and subscription of presence information.
VoLTE Call Flow and Procedures