Ims Architecture - Cisco ASR 5000 series Product Overview

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Session Control Manager Overview

IMS Architecture

IP Multimedia Subsystem (IMS) specifies a standard architecture for providing combined IP services (voice, data,

multimedia) over the existing public switched domain. IMS is an integral part of the 3GPP, 3GPP2, ETSI, and TISPAN

network model standards that define circuit switched, packet switched, and IP multimedia domain environments. IMS

also supports multiple access methods such as GSM, WCDMA, CDMA2000, WLAN, and wireless broadband access.

The call signaling protocol used in IMS is the Session Initiation Protocol (SIP). The primary component in the network

for resolving and forwarding SIP messages is the Call/Session Control Function (CSCF). The CSCF provides the

control and routing function for all IP sessions accessing the network. CSCFs are located in the control plane or layer of

the Service Delivery Network as shown in the figure below.

When the SCM acts as an Access Border Gateway (A-BG), it uses the RFC3261/P-CSCF to provide a SIP/IMS control

plane access border, as well as a bearer access border control function. Therefore, the A-BG provides all session border

control functions for all SIP UEs attempting to access the mobile network from a network outside of the operator's

control and operations.

Figure 143. IMS Service Delivery Networks Components

Collectively, CSCFs are responsible for managing an IMS session, including generating Call Detail Records (CDRs).

Four functional behaviors are defined for the CSCF:

Interrogating

The following figure shows the general interaction between the CSCF components and the supporting servers.

Application Plane

Multimedia, gaming, and

interactive content

Control Plane

Authorization, call control,

and sesssion management

Bearer Plane

Gateway of network traffic

to control plane

Access/Transport

Network access and

transport of network traffic

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