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Session Control Manager Overview
Product Description ▀
Cisco ASR 5000 Series Session Control Manager Administration Guide ▄
OL-22952-01
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.
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.
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.
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 1.
IMS Service Delivery Networks Components
A p p lic a tio n
S e rv e r
S D P
B illin g /O S S
S y s te m
H S S
C S C F
H o m e
G a te w a y
V o IP
W iF i
IP L A N
P B X
P L M N
M S C
P S T N
V o ic e
A p p lic a tio n P la n e
M u ltim e d ia , g a m in g , a n d
in te ra c tiv e c o n te n t
C o n tro l P la n e
A u th o riz a tio n , c a ll c o n tro l,
a n d s e s s s io n m a n a g e m e n t
B e a re r P la n e
G a te w a y o f n e tw o rk tra ffic
to c o n tro l p la n e
A c c e s s /T ra n s p o rt
N e tw o rk a c c e s s a n d
tra n s p o rt o f n e tw o rk tra ffic
M e d ia
G a te w a y
A c c e s s
G a te w a y
S e rv ic e
D e liv e ry
N e tw o rk
A -B G
Collectively, CSCFs are responsible for managing an IMS session, including generating Call Detail Records (CDRs).
Four functional behaviors are defined for the CSCF:
Four functional behaviors are defined for the CSCF:
Proxy
Interrogating
Serving
Emergency
The following figure shows the general interaction between the CSCF components and the supporting servers.