Session Initialization Protocol (SIP) Presented by: Aishwarya Gurazada CISC856: TCP/IP and upper layer protocols May 5 th 2011 Some slides borrowed from the presentations of Lei Luo Che-Yu Kuo

What is SIP? An IETF defined application-layer control (signaling) protocol for creating, modifying and terminating sessions Sessions are primarily audio and video calls over IP SIP incorporates elements of HTTP request-response model, text-based protocol, URL (SIP uses URI’s) and SMTP for header style such as To, From, and Subject 2

Motivation The telephony applications introduced signaling into IP network SIP was designed to mimic the call setup and signaling characteristics of the traditional telephone network over an IP infrastructure What does SIP do? SIP enables Internet endpoints (called user agents) to discover one another and to agree on a characterization of a session they would like to share As users may move between endpoints, they may be addressable by multiple names, and they may communicate in several different media 3

Facets of Establishing a Call User location: SIP enables the creation of an infrastructure of network hosts (called proxy servers) which could find in locating a user User availability: determination of the willingness of the called party to engage in communications User capabilities: media and media parameters to be used Session management: supports transfer, termination, and modification of sessions 4

SIP Protocol Stack SIP is rather a component that can be used with other IETF protocols to build a complete multimedia architecture. 5 SIP Enabled-IP Network IP Network PSTN Network Request : Invite Response :OK Acknowledgment RTP (real time protocol) defines a standardized packet format for delivering audio and video over IP networks Media Gateway Control Protocol (MEGACO) for controlling gateways SIP/PSTN Gateway SDP( Session Description Protocol) for describing multimedia sessions during signaling

SIP – Transport Layer TCP  TCP provides a reliable transport layer, but at a cost of complexity and transmission delay over the network. UDP  UDP is the simplest way of transmitting chunks of data from one host to another in an IP network. Provided that the amount of data to be sent at once is not too big SCTP  SCTP preserves boundaries  SCTP avoids head of line blocking 6

SIP Client-Server Architecture 7 User Agent – Hard phone Mike Registrar Server Proxy Server Redirect Server Kate Sam SIP Gateway PSTN Network User Agent – Softphone Servers Gateway Register- my IP address INVITE Kate INVITE from mike INVITE kate Location to find kate Kate’s & Sam’s location Jim INVITE jim

SIP Operation SIP addressing Locating the end user SIP messages- methods & responses Sending SIP requests : SIP transactions

SIP Addressing SIP clients are identified by SIP URI (Uniform Resource Indicator) URI’s look like addresses of the form The communication is user-to-user instead of device-to-device The needs to be resolved to by using a SIP Proxy server and DNS lookups at the time of call examples sip:J.T. Kirk 9

Locating the End User When client wants to send a request URI, the client will either send it to  Locally configured Proxy server or  IP address & port corresponding to the request URI xyz.com proxy Server Jim needs to know the CURRENT IP address of Jane to send request Locates Jane Server can locate Jane by looking up its “location service” database provided that Jane is registered Request Location service Request Jim needs to call Jane

SIP Message Format generic-message = Request-Line / Status-Line (Response) message-header (fields) CRLF [ message-body ] 11 INVITE sip: SIP/2.0 Via: SIP/2.0/UDP lab.high- voltage.org:5060;branch=z9hG4bKfw19b Max-Forwards: 70 To: G. Marconi From: Nikola Tesla ;tag=76341 Call-ID: j2qu348ek2328ws CSeq: 1 INVITE Subject: About That Power Outage... Contact: Content-Type: application/sdp Content-Length: 158 Request-Line Header fields v=0 o=Tesla IN IP4 lab.high-voltage.org s=Phone Call c=IN IP t=0 0 m=audio RTP/AVP 0 a=rtpmap:0 PCMU/8000 Message body

Request Line Request-Line = Method SP Request-URI SP SIP-Version CRLF 12 REGISTER registering contact information INVITE, ACK, CANCEL setting up sessions BYE terminating sessions OPTIONS querying servers about their capabilities User to which the request is addressed SIP version INVITE SIP/2.0

Status Line Status-Line = SIP-Version SP Status-Code SP Reason-Phrase CRLF 13 SIP/2.0 1xx: Provisional -- request received, continuing to process the request; 2xx: Success -- the action was successfully received, understood, and accepted; 3xx: Redirection -- further action needs to be taken in order to complete the request; 4xx: Client Error -- the request contains bad syntax or cannot be fulfilled at this server; 5xx: Server Error -- the server failed to fulfill an apparently valid request; 6xx: Global Failure -- the request cannot be fulfilled at any server. The Reason-Phrase is intended to give a short textual description of the Status-Code. SIP/ Ringing

Message Header fields ParameterDescription Call-ID Uniquely identifies a particular session Cseq A monotonically increasing sequence number used to identify the sequence of requests associated with a given Call-ID From A SIP URL that identifies the initiator of the request. May include a “friendly name” (e.g John) To A SIP URL that identifies the recipient of the request. May include a “friendly name” Via Indicates the path taken by the request 14

15 Tesla Marconi INVITE 180 Ringing 200 OK ACK Media Session BYE 200 OK Simple SIP session establishment example Marconi Accepted

16 Alice Proxy Server Bob INVITE 180 Ringing 200 OK ACK Media Session BYE 200 OK INVITE 180 Ringing 200 OK SIP call example with proxy server

17 AliceRegistrar Server REGISTER Contact: 200 OK SIP registration example

18 SUBSCRIBE 200 OK NOTIFY 200 OK … NOTIFY 200 OK MESSAGE 200 OK MESSAGE 200 OK SIP presence and instant message example

SIP Registration Server 19 Alice Registrar Server SIP/ OK Via: SIP/2.0/UDP :5060; branch=z9hG4bKus19 To: Alice From: Alice ;tag=3431 CSeq: 1 REGISTER Contact: ;expires=3600 Content-Length: 0 SIP/2.0 REGISTER sip:registrar.udel.edu Via: SIP/2.0/UDP :5060; branch=z9hG4bKus19 Max-Forwards: 70 To: Alice From: Alice ;tag=3431 Call-ID: CSeq: 1 REGISTER Contact: Content-Length: 0 SIP/2.0 REGISTER sip:registrar.udel.edu Via: SIP/2.0/UDP :5060; branch=z9hG4bKus19 Max-Forwards: 70 To: Alice From: Alice ;tag=3431 Call-ID: CSeq: 1 REGISTER Contact: Content-Length: 0 SIP/ AUTHORIZATION REQUIRED Via: SIP/2.0/UDP :5060; branch=z9hG4bKus19 To: Alice From: Alice ;tag=3431 CSeq: 1500 REGISTER Contact: ; Proxy-Authenticate: Digest realm=“eecis.udel.edu", nonce="4db894763e920f6ec021e68a3e87b098dc4a c8f9" Content-Length: 0 SIP/2.0 REGISTER sip:registrar.udel.edu Via: SIP/2.0/UDP :5060; branch=z9hG4bKus19 To: Alice From: Alice ;tag=3431 CSeq: 1 REGISTER Contact: ;expires=3600 Proxy-Authorization: Digest username=“alice", realm=“eecis.udel.edu, nonce="4db894763e920f6ec021e68a3e87b098dc4ac8 f9”, uri= “response="d e daae084cd5b5”, Content-Length: 0 SIP/2.0 REGISTER sip:registrar.udel.edu Via: SIP/2.0/UDP :5060; branch=z9hG4bKus19 To: Alice From: Alice ;tag=3431 CSeq: 1 REGISTER Contact: ;expires=3600 Proxy-Authorization: Digest username=“alice", realm=“eecis.udel.edu, nonce="4db894763e920f6ec021e68a3e87b098dc4ac8 f9”, uri= “response="d e daae084cd5b5”, Content-Length: 0

Simple Call Establishment 20 INVITE SIP/2.0 Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Call-ID: j2qu348ek2328ws Cseq: 1 IINVITE Contact: Subject: Where are you exactly? INVITE SIP/2.0 Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Call-ID: j2qu348ek2328ws Cseq: 1 IINVITE Contact: Subject: Where are you exactly? SIP/ Ringing Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Call-ID: j2qu348ek2328ws Cseq: 1 INVITE Contact: SIP/ Ringing Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Call-ID: j2qu348ek2328ws Cseq: 1 INVITE Contact: SIP/ OK Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Call-ID: j2qu348ek2328ws Cseq: 1 INVITE Contact: SIP/ OK Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Call-ID: j2qu348ek2328ws Cseq: 1 INVITE Contact: v=0 o=alice IN IP4 alice.udel.edu s=Phone Call c=IN IP t=0 0 m=audio RTP/AVP 0 a=rtpmap:0 PCMU/8000 v=0 o=bob IN IP4 tower.yahoo.com s=Phone Call c=IN IP t=0 0 m=audio RTP/AVP 0 a=rtpmap:0 PCMU/8000 SIP/2.0 ACK Via: SIP/2.0/UDP :5060; branch=z9hG4bK321g To: Bob From: Alice ;tag=42 Call-ID: j2qu348ek2328ws Cseq: 1 ACK SIP/2.0 ACK Via: SIP/2.0/UDP :5060; branch=z9hG4bK321g To: Bob From: Alice ;tag=42 Call-ID: j2qu348ek2328ws Cseq: 1 ACK Inserts a “From” tag and sets the session parameters Inserts a “To” tag and sets the session parameters Call ID, from and to tags identify a dialog AliceBob

SIP Proxy Server 21 Alice Bob Outbound proxy server Inbound proxy server Location server DNS server Media (RTP) INVITE SIP/2.0 Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Subject: Where are you exactly? Contact: INVITE SIP/2.0 Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Subject: Where are you exactly? Contact: INVITE SIP/2.0 Via: SIP/2.0/UDP proxy.yahoo.com:5060; branch=z9hG4bKtiop3 Via: SIP/2.0/UDP proxy.udel.com:5060; branch=z9hG4bK Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Subject: Where are you exactly? Contact: INVITE SIP/2.0 Via: SIP/2.0/UDP proxy.yahoo.com:5060; branch=z9hG4bKtiop3 Via: SIP/2.0/UDP proxy.udel.com:5060; branch=z9hG4bK Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Subject: Where are you exactly? Contact: 100 Trying 180 Ringing 200 OK ACK BYE 200 OK INVITE SIP/2.0 Via: SIP/2.0/UDP proxy.udel.com:5060; branch=z9hG4bK Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Subject: Where are you exactly? Contact: INVITE SIP/2.0 Via: SIP/2.0/UDP proxy.udel.com:5060; branch=z9hG4bK Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Subject: Where are you exactly? Contact: SIP Trapezoid

SIP Proxy Server 22 INVITE Bob Alice Bob’s voic Bob’s Phone INVITE Bob 486 Busy Here INVITE Bob Proxy servers can make flexible “routing decisions” to decide where to send a request. Location Service Proxy Server

SIP Redirect Server 23 INVITE SIP/2.0 Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Subject: Where are you exactly? Contact: INVITE SIP/2.0 Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=42 Subject: Where are you exactly? Contact: Alice Bob Redirect Server SIP/ Moved Permanently Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob ;tag=64 From: Alice ;tag=42 Subject: Where are you exactly? Contact: SIP/ Moved Permanently Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob ;tag=64 From: Alice ;tag=42 Subject: Where are you exactly? Contact: ACK INVITE SIP/2.0 Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=13473 Subject: Where are you exactly? Contact: INVITE SIP/2.0 Via: SIP/2.0/UDP :5060; branch=z9hG4bKmp17a To: Bob From: Alice ;tag=13473 Subject: Where are you exactly? Contact:

Terminal Mobility- Pre-call 24 Home Proxy/registrar Mobile -JIM JANE REGISTER 200 OK INVITE ACK Media Session 200 OK INVITE 200 OK

Terminal Mobility- Mid Call 25 INVITE 200 OK ACK Media Session Home Network Visited Network

Personal Mobility 26 INVITE Bob Alice Bob’s Cell Phone INVITE Bob Bob’s Office Phone INVITE Bob Bob’s Home Phone In parallel search, a proxy issues several requests to possible user locations upon receiving an incoming request. 200 OK CANCEL Location Service Proxy Server

Session Mobility Transfer and Retrieval  Transfer means to move the session on the current device to one or more other devices  Retrieval means to cause a session currently on another device to be transferred to the local device Whole and Split Transfer  The set of session media may either be transferred completely to a single device or split across multiple devices 27

Transfer Modes Mobile Node (MN) Control Mode  Mobile Node (MN) uses a third party call control  It establishes a SIP session with the local device used in the transfer and updates its session with the CN (corresponding node), using the SDP parameters to establish media sessions between the CN and the local device  it requires the MN to remain active to maintain the sessions Session Hands off Mode  MN completely transfers the session signaling and media to another device Addressing of Devices  All devices are assumed to have dedicated SIP URI’s  A device has a unique URI and registers a separate contact URI for itself 28

29 Local Device INVITE 200 OK local Parameters INVITE local Parameters Mobile Node Corresponding Node ACK CN Parameters 200 OK CN parameters Media Session ACK Media Session

30 Local Device Mobile Node Corresponding Node REFER,refer-to Media Session 200 OK ACK NOTIFY 200 OK BYE 200 OK 200 Accepted INVITE, Replaces Media Session

References J. Rosenberg, SIP: Session Initialization Protocol, RFC 3261, 2002 A. Johnston, SIP: Understanding the Session Initialization Protocol, 2nd edition 31

Questions 32