SIP | Session Initiation Protocol in Cellular Networks

Explore SIP, the session initiation protocol, and its role in voice over LTE within an IMS network, including signaling through the EPC to registrar server.

SIP benefits explain how the session initiation protocol controls multimedia calls, locates users, stores user presence, and manages setup, modification, and teardown of sessions in IMS networks.

Explore the SIP network elements inside an IMS network, including the user agent, registrar server, proxy server, redirect server, location server, and gateway, all governed by the session control function.

Describe the user agent as the SIP entity that can send requests and respond, distinguishing the user agent client (sends SIP requests) from the user agent server (replies to requests).

Explore how a SIP user agent initiates a call with an invite, gains a 200 response, and forms a dialogue, then handles media setup and tear down with a bye.

Explain the SIP network architecture, including user agents, proxy, registrar, location server, and S-CSCF, with gateways to PSTN, and illustrate SIP URIs identifying users and services.

Explore how a user registers on the ims network using a sip register message, via proxy and registrar, and uses sip uri, contact address, and media address for voice calls.

Describe the basic sip call flow: a user agent sends an invite to a proxy, which uses registrar and location to reach the recipient, with 100, 180, and 200 responses.

Explore how SIP call flow works in cellular networks, detailing invite messages, proxy and registrar roles, and call progress codes from 100 to 200, plus proxy modes.

Describe how the SIP location server stores user agent contacts and enables proxy routing, with registrar updates and DNS name resolution guiding invites for call setup.

Explain how sip messages function as requests and responses, detailing types like invite, acknowledge, cancel, register, options, info, subscribe, notify, update, and how sdp enables media negotiation.

Trace a sip invite message in a wireshark trace, detailing header and sdp body. Highlight the request line, via, udp transport, destination, and headers from, to, call-id, cseq, and contact.

Explore session expiry timers and minimum session expiry in SIP for cellular networks, including proxy negotiation, 100 release handling, and the 183 session progress flow.

Learn how SIP uses SDP in the message body, while the header carries control information, to define media sessions, negotiate codecs, and manage hold via re-invite.

Install and set up Wireshark to monitor SIP signaling flows, including invite and 200 ok, register messages, and analyze VoIP, IMS, and VLT signaling.

Explore the Wireshark graphical interface to install, open trace files, filter sip traffic, and analyze invite, 180 ok, 200 ok, with the flow of messages for volte and sip calls.

Analyze a SIP invite message in Wireshark, including VoLTE and VoIP invites, and detail the request, headers, body, and SDP media and codecs.

Analyze a SIP register request in Wireshark, tracing registration flows from initial 401 unauthorized to a successful 200 OK, highlighting nonce, authorization digest, and sequence handling.