In this way, P-CSCF does not need to contact I-CSCF for S-CSCF's address.
It calculates sum of Mw commands needed from P-CSCF to I-CSCF and from P-CSCF to S-CSCF.
The proposed FIM scheme is analyzed by developing a testbed using Open IMS core  to set up IMS entities including HSS, P-CSCFs, I-CSCF, and S-CSCF as illustrated in Figure 7.
Testbed setup Parameters Values Network servers P-CSCF, I-CSCF, S-CSCF, hss Servers' physical type Wired physical UEs' physical type Wireless physical Antenna type Omni antenna Parameter variations Delay 0-90 milliseconds Number ofhops 1-5 Number of handovers 1-10 Table 2: Improvement of FIM scheme over other schemes.
Interrogating-CSCF (I-CSCF) is the contact point at operator's network for users from that network or roamed users which are using services and are located within network operator's service area.
2) P-CSCF examines request and sends to appropriate I-CSCF with all needed information.
where [[bar.T].sub.P-CSCF]--mean service time of P-CSCF; [[bar.T].sub.S-CSCF] --mean service time of S-CSCF; [[bar.T].sub.I-CSCF]--mean service time of I-CSCF; [[bar.T].sub.HSS]--mean service time of HSS; [[bar.T].sub.serv] --common mean service time of IMS system node.
Summary of Signaling Protocols in IMS Protocol Reference Point SIP Gm, Mw, ISC, Ma, Mm, Mg, Mi, Mj, Mk, Mr Dismeter Cx, Dx, Sh, Dh, Gx, Rx, Ro, Rf MAP (Mobile Si Application Part) H.248 Mp, Mn HTTP Ut Not specified Ml, Mx, Ix, Iq Protocol Involved entities SIP UE, P-CSCF, I-CSCF
, S-CSCF, AS, IBCF, MGCF, BGCF, MRFC Dismeter I-CSCF
, S-CSCF, HSS, SLF, AS, SIP AS, OSA SCS, OSA SCF, IM-SSF, PCRF, MRCF, OCS, BCF, MGCF, IBCF, CDF MAP (Mobile IM-SSF, HSS Application Part) H.248 MRFC, MGCF, IMS-MGW HTTP UE, AS Not specified E-CSCF, LRF, BGCF, IBCF, TrGW, P-CSCF Table 2.