Database Reference
In-Depth Information
P-CSCF handles User-to-Network Interface (UNI) interactions and is the
first point of contact within the IMS network for the User Equipment (UE). The
P-CSCF address is discovered by the UE using a P-CSCF discovery mechanism.
The P-CSCF forwards the SIP messages received from the UE to an I-CSCF or
S-CSCF (and vice versa). P-CSCF keeps track of UE registration information
(like UE contact information and S-CSCF address) and active call sessions. The
Session Boarder Gateway in the P-CSCF role performs correlation and tunneling
of signaling and media sessions across the interface between the IMS core network
and the access network towards SIP clients.
The Home Subscriber Server (HSS), is a master user database that supports
the IMS network entities that actually handle calls. It contains the subscription-
related information (subscriber profiles), performs authentication and authoriza-
tion of the user, and can provide information about the subscriber's location and
IP information.
Application Server (AS) is a Session Initiation Protocol (SIP) application
server that provides real time peer-to-peer communication services. IMS enables
M2M servers to be realized as specific ASs and M2M devices, which host an IMS
client, that can be controlled by and participate in IMS dialogs.
4
Interworking Between M2M and IMS
IMS system and M2M system can co-exist without any direct connection, or they
can interwork on different levels when they can benefit one from another with
reusing functionalities (e.g. M2M authentication, authorization uses mechanisms
in IMS) that enhance a service or help achieve a complex service (IMS service
uses data from M2M devices). One example is when the IMS service uses data
from an M2M system in order to provide better service, e.g. getting the context
from M2M [ 14 ] and from that context service adapt its' behaviour. Another
example, that is given in this paper, is when M2M application triggers IMS
service and uses IMS as mobility layer for M2M device. The two ways of IMS
and M2M system interworking are shown as in Figs. 3 and 4 .
As already described in Sect. 2 , M2M device connects directly or via M2M
gateway to an M2M network. Both figures show that M2M application is a part
of an M2M network (NA). SIP application is integrated in NA, and in that way
IMS and M2M are interworking in the network layer. In the IMS system, in order
to access to IP Multimedia services, the IMS user agent (IMS UA) must first
register in IMS. After the IMS UA registers and authenticates in IMS network,
multimedia sessions can be routed to some other IMS UA. Interworking between
IMS and M2M in the M2M area network can be achieved by collocating M2M
application and IMS user agent while connecting both to M2M network and IMS
core network.
In Fig. 3 , the device application (DA) in the device contains the IMS UA and
the device is a part of IMS and M2M system. However, in Fig. 4 M2M gateway
contains the gateway application (GA) that contains IMS UA, and in this case
M2M gateway is a part of IMS and M2M. M2M device capabilities determine
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