sip overview. sip2 contents what is sip? sip benefits sip message structure sip components sip...
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SIP Overview
SIP 2
Contents What is Sip? SIP Benefits SIP message structure SIP components SIP mobility
SIP 3
What is SIP? Sip is signaling protocol defined by the Internet Engin
eering Task Force (IETF) for initiating, managing and terminating voice and video sessions across packet networks
A textual based client-server protocol Application layer protocol It’s not Transport Protocol It’s not QoS Reservation Protocol
SIP 4
SIP history Work began in 1995 in IETF mmusic WG 03/1999: RFC 2543, 153 pages, 6 methods 11/1999: SIP WG formed 11/2000: draft-ietf-sip-rfc2543bis-02, 171 pages, 6
methods
SIP 5
SIP benefits Integration with existing protocols
Integration well with Web(Http) and e-mail(Smtp) Simplicity Simple protocol vs H.323
Textual based, so parsing generation are simple Extensibility
HTTP and SMTP extensibility Modularity
Initiation,termination,change,user location, basic registration. Separating notion of a session to invite a user
Scalability Off DNS, BGP Server processing.
SIP 6
SIP Messages
SIP Requests: INVITE – Initiates a call by inviting user to
participate in session. ACK - Confirms that the client has received a
final response to an INVITE request. BYE - Indicates termination of the call. CANCEL - Cancels a pending request. REGISTER – bind a permanent address to current
location OPTIONS – Used to query the capabilities of a
server.
SIP 7
SIP Response Codes 1yz Informational
100 Trying 180 Ringing (processed
locally) 181 Call is Being
Forwarded 2yz Success
200 ok 3yz Redirection
300 Multiple Choices 301 Moved Permanently 302 Moved Temporarily
4yz Client error 400 Bad Request 401 Unauthorized 404 Not Found 405 Method not Allowed 407 Proxy Authentication Re
quired 415 Unsupported Media Typ
e 482 Loop Detected 486 Busy Here
5yz Server failure 500 Server Internal Error
6yz Global Failure 600 Busy Everywhere
SIP 8
Invite Message Example
INVITE sip:[email protected] SIP/2.0Via: SIP/2.0/UDP here.com:5060From: BigGuy <sip:[email protected]>To: LittleGuy <sip:[email protected]>Call-ID: [email protected]: 1 INVITESubject: Happy ChristmasContact: BigGuy <sip:[email protected]>Content-Type: application/sdpContent-Length: 147
Response Status SIP/2.0 200 OKVia: SIP/2.0/UDP here.com:5060From: BigGuy <sip:[email protected]>To: LittleGuy <sip:[email protected]>;tag=65a35Call-ID: [email protected]: 1 INVITE Subject: Happy ChristmasContact: LittleGuy <sip:[email protected]>Content-Type: application/sdpContent-Length: 134
Request Method
“receive RTP G.711-encoded audio at 100.101.102.103:49172”
v=0o=UserA 2890844526 2890844526 IN IP4 here.coms=Session SDPc=IN IP4 100.101.102.103t=0 0m=audio 49172 RTP/AVP 0a=rtpmap:0 PCMU/8000
v=0 o=UserB 2890844527 2890844527 IN IP4 there.com s=Session SDP c=IN IP4 110.111.112.113 t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000
Message Header Fields
Payload
SIP 9
Address Header Fields From: message originator To: final recipient Request-URI: current destination; may change along
signaling path Contact: appears in INVITE / OPTIONS / ACK / REGISTER
requests and in responses. It indicates direct response address to which subsequent transactions are sent.
A UA may send subsequent BYE or ACK to Contact: address (unless configured to use an outbound proxy).
It includes redirection address in 3xx and 485 responses. It includes additional error information in 4xx, 5xx, and 6xx
responses. It may include preference weights. It includes current location in REGISTER requests. Multiple Contact: header fields may be included.
SIP 10
Session Description Protocol (SDP)
Convey sufficient information to enable participation in a multimedia session
SDP includes description of: Session name and purpose Times the session is active Media to use Information where to send and
receive media Contact information
SIP 11
Session Description Protocol (SDP)
o=sisalem 28908044538 289080890 IN IP4 193.175.132.118
s=SIP [email protected]=IN IP4 126.16.69.4v=0t=28908044900 28908045000m=audio 49170 RTP/AVP 0 a=rtpmap:0 PCMU/8000
SIP 12
SIP Distributed Architecture
Redirect Server
Location Server
Registrar Server
User Agent
Proxy Server
SIP/PSTN Gateway
PSTN
SIP Components
Proxy Server
H.323
SIP/H.323 Gateway
SIP 13
SIP Components User agent(user application)
UA Client(caller) UA Server(called party)
Proxy Server Redirect Server Register
SIP 14
User Agents An application that initiates,
receives and terminates calls. User Agent Clients (UAC) – An entity
that initiates a call. User Agent Server (UAS) – An entity
that receives a call.
Both UAC and UAS can terminate a call.
Both SW and HW available
SIP 15
Proxy Server An intermediary program that acts as both a server
and a client to make requests on behalf of other clients.
Requests are serviced internally or by passing them on, possibly after translation, to other servers.
Interprets, rewrites or translates a request message before forwarding it.
Stateless proxy server No information about the message is stored
Stateful proxy server Forking reliability
SIP 16
SIP Operation in Proxy Mode
User [email protected] on left-hand side is initiating a call to [email protected] right-hand side; Callee registered with his server previously
[email protected] [email protected]
Location Server
Proxy/Registrar
INVITE sip:[email protected]: sip:[email protected]: sip: [email protected]: [email protected]
#4
INVITE sip:[email protected] From: sip:[email protected] To: sip: [email protected] Call-ID: [email protected]
#1
Callee@
support
#3
Cal
lee
#2
OK 200From: sip:[email protected]: sip: [email protected]: [email protected]
#5OK 200 From: sip:[email protected]: sip: [email protected]: [email protected]
#6
ACK [email protected]#7
Media stream #8
SIP 17
Location Server A location server is used by a SIP
redirect or proxy server to obtain information about a called party’s possible location(s).
Locating service LDAP SQL
SIP 18
Redirect Server
After location service to look up a user, location information is sent back to the caller in a redirection class response, which concludes the transaction.
Unlike a proxy server, the redirect server does not forward SIP request.
Unlike a user agent server, the redirect server does not accept or terminate calls.
SIP 19
SIP Operation in Redirect Mode
Redirect Server/Location Server
Proxy
ACK [email protected]#8
Cal
lee
#2
INVITE [email protected]#1
302 moved temporarilyContact: [email protected]
#4
Callee@
home.com
#3
INVITE [email protected]#6
ACK [email protected]#5
OK 200#7
SIP 20
Registrer Server A server that accepts REGISTER requests. The register server may support authenticat
ion. A registrer server is typically co-located with
a proxy or redirect server and may offer location services.
SIP 21
SIP Registration
SIP 22
Simplified SIP Call Setup and Teardown
302 (Moved Temporarily)
INVITE
200 (OK)200 (OK)
ACK
INVITE302
(Moved Temporarily)ACK
INVITE
180 (Ringing)180 (Ringing)180 (Ringing)
200 (OK)ACKACK ACK
RTP MEDIA PATH
BYEBYE BYE
200 (OK)200 (OK) 200 (OK)Call Teardown
MediaPath
Call Setup
INVITE
Location/Redirect ServerProxy Server Proxy Server User AgentUser AgentINVITE
SIP 23
SIP and Terminal MobilitySIP and Terminal Mobility
Home Network
HP
Visited Network
FPSignalling
Cell 2
Cell 1REGISTER
#1
REGISTER #2
SIP 24
SIP and Terminal MobilitySIP and Terminal Mobility
Home Network
HP
Visited Network
FPSignallingData
Cell 2
Cell 1
INVITE#1
INVITE#2
INVITE#3
#4
SIP 25
SIP and Terminal MobilitySIP and Terminal Mobility
Home Network
HP
Visited Network
FPSignallingData
Cell 2
Cell 1
REGISTER#3
REGISTER
#2
#1
reINVITE #3
#4