SIP:
An application layer signaling protocol
that defines initiation, modification and
termination of interactive, multimedia
communication sessions between
users.”
Sip is client server protocol.
Works independent of the underlying network
transmission protocol and indifferent to media
i.e: it doesn’t transfere data
It provides mechanisms to:
_ Establish a session
_ Maintain a session
_ Modify and Terminate a session
Mobility
_ Supports user mobility by proxying and redirecting
requests to a user’s current location.
_ The user can be using a PC at work, PC at home,
wireless phone, IP phone, or regular phone.
_ Users must register their current location.
_ Proxy servers will forward calls to the user’s current
location.
_ Example mobility applications include presence and
call forking.
Used Protocols:
RSVP - to reserve network resources.
_ RTP (Real Time Transport Protocol) - to transport real
time data
_ RTSP (Real Time Streaming Protocol) - for controlling
delivery of streaming media.
_ SAP (Session Advertisement Protocol) - for
advertising multimedia session via multicast.
Capabilities:
· Determine location of target points – Support address
resolution, name mapping, call redirection
· _ Determine media capabilities – SIP uses Session
Description Protocol (SDP) for this
· _ Determine availability – returns a message why the
remote party cannot be contacted
· _ Establish a session between end points – also support
mid call changes, changes of media characteristics or
codec
· _ Handles termination of calls – transfer of calls
· Permits interaction between devices via
signalling messages
_ These messages can:
· _ Register a user with a system
· _ Invite a users to join an interactive session
· _ Negotiating the terms and conditions of a session
· _ Establish a media stream between 2 or more end
· points
· _ Terminate a session
SIP Components
SIP User Agents
_ User Agent Clients (UAC)
_ User Agent Servers (UAS)
SIP Servers
_ Proxy server
_ Location server
_ Redirect server
_ Registrar server
Sip components communicate with each other by messages
MESSAGE TYPES
There are two types of SIP messages:
_ Requests—sent from the client to the server.
_ Responses—sent from the server to the client.
MESSAGE PARTS
SIP messages are composed of the following three parts: start line, header, body.
WorkFlow
CALL FLOW
1. The calling User Agent Client sends an INVITE message to
Bob’s SIP address: sip:bob@acme.com. This message also
contains an SDP packet describing the media capabilities of the
calling terminal.
2. The UAS receives the request and immediately responds with a
100-Trying response message.
3. The UAS starts “ringing” to inform Bob of the new call. Simultaneously
a 180 (Ringing) message is sent to the UAC.
4. The UAS sends a 182 (Queued) call status message to report that the
call is behind two other calls in the queue.
5. The UAS sends a 182 (Queued) call status message to report that the
call is behind one other call in the queue.
6. Bob picks up the call and the UAS sends a 200 (OK) message to the
calling UA. This message also contains an SDP packet describing the
media capabilities of Bob’s terminal.
7. The calling UAC sends an ACK request to confirm the 200 (OK)
response was received.
SESSION TERMINATION
The session termination call flow proceeds as follows:
1. The caller decides to end the call and “hangs-up”. This results
in a BYE request being sent to Bob’s UAS at SIP address
sip:bob@lab.acme.com
2. Bob’s UAS responds with 200 (OK) message and notifies Bob that the
conversation has ended.
Summary:
SIP bey2ool le client mo3ayan enta now metwasal bel client el folany basss, enta etkallem ma3ah in ur own way(P2P or Client-Server mesh shoghlet el SIP enno ye7adedo)
THUS
We need another protocol for actual transmission of data (ex:RTP)
SO
We will integrate client class of SIP with that of full duplex peers(FADY) + Server class of SIP = Phase1
