For example, the IuCS interface provides
connectivity from the Radio Network Control (RNC) to the circuit-switched network
(through the MSC). The IuPS, on the other hand, provides an interface to the packetswitched
network.
Therefore, voice traffic is routed from the UMTS network via the IuCS interface
while data is routed through the IuPS interface (through the SGSN). The Iub interfaces
to the radio nodes, while the Iur interfaces to other RNCs in the network.
Figure 1.10 Wireless reference points GSM to IMS
IMS
VoIP
UMTS
GPRS
PSTN
Other
PLMN
Other
pocket
network
Other
IMS
network
Circuit
switched
network
GMSC
MSC
BSC
BTS BTS
GSM
VLR
HLR
SMS
GMSC
GGSN
SGSN
P-CSCF I-CSCF S-CSCF MRFC
MRFP
MGCF
SGW
IM-MGW
BGCF
SGSN
RNC RNC
Node B Node A
AS HSS SLF
E D
A
H
Gs
Gb
Gs
Gn
Gn Gm Cx
Mg
Mw
Mi
Mn
Mn
Mw Cx
ISC
Gi
Gp
Gc
Mw
Sh
Mj
Mb
SS7
Mr
Mk
Mp
Gr
Gd
A-bis A-bis IuCS IuPS
Iur
Iub
Iub
Dx
Dh
Architecture of the IMS 25
So far I have just described 3G wireless. The IMS is the next phase of wireless, depicted
to the right of Figure 1.10. Notice that the figure also includes Media Gateway
Control Functions (MGCFs) representing VoIP connections, even though we are talking
about wireless evolution. These would interface to any ISUP (or BICC) trunking supported
in the network. The IMS interfaces are prefixed by M followed by a lowercase
letter.
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