PRESENT SITUATION

1
PRESENT SITUATION
Time-based telephony charges
Concept of local call or long distance call
2
CONTEXTShift of telecommunication traffic from
telecom network to IP networkConsequence
Replacement and not convergence
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VoIP DATA TRANSFER
IP Packet
) ) )
10101010000101001010101010100101010101001010100010
01
10101010000101001010101010100101010101001010100010
01
( ( (
10101010000101001010101010100101010101001010100010
01
IP Packet
10101010000101001010101010100101010101001010100010
01
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What is SIP?

• Signaling protocol for setting up real-time
  communication sessions.
• 2)Provides two functions
• - Discovery
• - Session Management (setup- modification-
  tear-down)
• 3)SIP is used in concert with other protocols
• - Session Description Protocol (SDP)
• - Real-Time Protocol (RTP)
• - Real-Time Control Protocol (RTCP)
• 4)Common applications include voice (telephony),
  video, presence and instant messaging

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Where Does SIP Stand ?
User Interface
RTCP
SIP
SDP
RTP
UDP
TCP
IP
Link Physical Layer
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SIP STACK LAYERS
APPLICATION User Interface
TRANSACTION USER User Agent Client Proxy Core
User Agent Server
TRANSACTION Client Transaction Server
Transaction
PARSER
TRANSPORT
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SIP Messages

• SIP Requests
• INVITE - Establish a session with offer/answer
• ACK - Acknowledge a response to an INVITE
• BYE - Terminate an existing SIP session
• CANCEL - Cancel a pending request
• REGISTER Temporarily bind a device URI to an
  Address-of-Record (AOR)
• OPTIONS Query capabilities of server or UA

• SIP Responses
• 1xx - Informational Messages.
• 2xx - Successful Responses.
• 3xx - Redirection Responses.
• 4xx - Request Failure Responses.
• 5xx - Server Failure Responses.
• 6xx - Global Failures Responses.

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SIP INVITE Request

• INVITE sipbob_at_biloxi.com SIP/2.0
• ViaSIP/2.0/UDP pc33.atlanta.combranchz9hG4bK776
  
• Max-Forwards 70
• To Bob ltsipbob_at_biloxi.comgt
• From Alice ltsipalice_at_atlanta.comgttag1928301774
  
• Call-ID a84b4c76e66710_at_pc33.atlanta.com
• CSeq 314159 INVITE
• Contact ltsipalice_at_pc33.atlanta.comgt
• Content-Type application/sdp
• Content-Length 142

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SIP INVITE Response

• SIP/2.0 200 OK
• Via SIP/2.0/UDP server10.biloxi.com
• branchz9hG4bKnashds8received192.0.2.3
• Via SIP/2.0/UDP pc33.atlanta.com
• branchz9hG4bK776asdhds received192.0.2.1
  
• To Bob ltsipbob_at_biloxi.comgttaga6c85cf
• From Alice ltsipalice_at_atlanta.comgttag1928301774
  
• Call-ID a84b4c76e66710_at_pc33.atlanta.com
• CSeq 314159 INVITE //This number has not changed
• Contact ltsipbob_at_192.0.2.4gt
• Content-Type application/sdp
• Content-Length 131

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SIP Entities
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Mobility Through REGISTER Request
Bob at Work
Registrar Server
Bob moves from office to home and reREGISTERs
Location Service
1 REGISTER
2 Update (non-SIP)
Register Server uploads registration
information to a Location Service.
3 Response (non-SIP)
4 200 OK
Bob at Home
5 REGISTER
Bob optionally clears all registrations.
6 Update (non-SIP)
7 Response (non-SIP)
8 200 OK
Bob reREGISTERs at Home Phone location.
9 REGISTER
10 Update (non-SIP)
11 Response (non-SIP)
12 200 OK
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Session Establishment using INVITE
Alice
Bob
1 INVITE
2 100 Trying
3 180 Ringing
4 200 OK
5 ACK
Media Session
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SIP Signaling in a Forked Call
Bob (Work)
Bob (Home)
Alice
Proxy Server
INVITE
100 Trying
INVITE
INVITE
100 Trying
100 Trying
180 Ringing
180 Ringing
180 Ringing
180 Ringing
200 OK
200 OK
CANCEL
ACK
200 OK
487 Request Cancelled
ACK
Media Session
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Session modification using INVITE
Alice
Bob
1 INVITE sdp1
2 180 Ringing
3 200 OK sdp2
4 ACK
Media Session
The failure of the re-INVITE does not cause the
initial Media Session to Fail
5 INVITE sdp3
6 488 Not Acceptable
7 ACK
8 INVITE sdp3
The success of the second re-INVITE establishes a
New Media Session which replaces the old session.
9 200 OK 5 sdp4
10 ACK
New Media Session
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SIP CALL FLOW
Alice
Proxy 1
Registrar
Proxy 2
Bob
Application Layer
Application Layer
UAC
Proxy Core
UAS
Proxy Core
UAS
CT
ST
CT
ST
ST
CT
ST
CT
Parser
Parser
Parser
Parser
Transport Layer
Transport Layer
Transport Layer
Transport Layer
Transport Layer
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Control Flow on Client Side
User Interface
Transaction User
CT n
CT 1
CT 2
Response queue
Response queue
Response queue
Transport
Parser
Network
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Control Flow on Server Side
User Interface
Transaction User
ST n
ST 1
ST 2
Response queue
Response queue
Response queue
Transport
Parser
Network
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Limitations of SIP

• SIP provides methods to control sessions, but
  does not specify the applications and services
  that will use those sessions
• -Result no guarantee of application
  behavior.
• SIP does not mandate or include specific quality
  of service (QoS) capabilities.