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Reply To: ss7 in voip


Okay…i chose the wrong term. SIP and h.323 use a distributed model with intelligent endpoints which can make decisions. The common thread for all these “signaling” protocols is that they all help with:
-establishing media connection
-teardown of media connection
-modification of media connection

H.323 came from the ITU.
H.225 for call signaling
RAS to define GK communication
H.245 for media negotiation
GK is an optional component added for additional control as well as scale.

SIP came from the IETF RFC2543. Leverages work done in other drafts and leverages existing Internet protocols. i.e. SMTP headers. Optional components of SIP are: Redirect, Registrar, Proxy, Location servers. SIP does not require a proxy as a proxy is an optional component in RFC2543. This has not changed in any of the bis supplements I have seen thus far.

MGCP/Megaco/H.248/IPDC/SGCP are all control type protocols where the endpoints are dumb and must be told what to do. This requires a call agent or media gateway controller. Whatever you want to call it.

SS7 is based on ITU Q.700-709
Q.710 for MTP
Q721-725 for SCCP
Q730 TUP
Q771-775 ISUP
Q791-795 TCAP
and a few others.
MTP defines the first 3 layers of the OSI model for the signaling links.
ISUP provides the call control function for circuits.
SCCP is kind of like the TCP/UDP for TCAP and higher protocl layers.
TCAP communications to network databases