Session Initiation ProtocolSession Initiation Protocol

Presenter: Kideok Cho (kdcho@mmlab.snu.ac.kr)

2005. 10. 19

ContentsContents

Session Initiation Protocol– SIP Entities– SIP Messages– Message Flow in SIP

Extending SIPCurrent Status of SIPConclusion

Session Initiation ProtocolSession Initiation Protocol

Main goal– Originally designed to invite users to existing multi

media conference– Today, used to create, modify, and terminate multi

media sessions– To deliver a “session description” to a user at their

current location

RFC3261 and some related RFCs– About 70 related-RFCs

Session DescriptionSession Description

Contains– Information for the remote user to join the session– Such as, IP address, Port #, codecs

Most common format– Session Description Protocol (SDP), RFC 2327

v=0o=Alice 26764646 46734 IN IP4 192.0.01s=Let’s talk about swimming techniquesc=IN IP4 192.0.0.1t=0 0m=audio 20000 RTP/AVP 0a=sendrecvm=video 20002 RTP/AVP 31a=sendrecv

SIP Uniform Resource Identifier SIP Uniform Resource Identifier (URI)(URI)

SIP URI: e-mail-like address– Consists of user name and domain– sip:kdcho@mmlab.snu.ac.kr

To provide personal mobility– Public URI vs. Current URI

• sip:kdcho@yonsei.ac.kr– Need to map public URI to current URI

• Registrar

SIP Entities (1/2)SIP Entities (1/2)

User Agent– SIP endpoint: usually handled by users– User Agent Client (UAC)– User Agent Server (UAS)

Registrar– Maintains public URI to current URI

mappings– Accepts REGISTER requests– Update a location database with the contact

information

SIP Entities (2/2)SIP Entities (2/2)

Proxy Server– SIP Router– Receives SIP messages from a user agent or anoth

er proxy server– Routes it towards its destination

Redirect Server– Maps the SIP address of the called party into new

address(es) and returns them– Unlike Proxy server, Redirect server don’t pass the

request on to other servers

SIP messagesSIP messages

Request Methods– INVITE, REGISTER, ACK, BYE, CANCEL, etc

Response type– Provisional: 1xx class

• Provisional, searching, ringing, queuing etc.

– Final: 2xx, 3xx, 4xx, 5xx, 6xx class• Success• Redirection, forwarding• Request failure, server failure, global failure

Message FormatMessage Format

SIP is a textual request-response protocolStart lineA number of header fieldsEmpty lineOptional message body

INVITE sip:laptop1@factoryA.com SIP/2.0Via: SIP/2.0/UDP pc33.company.com; branch=33Max-Forwards: 70To: sip:latptop1@factoryA.comFrom: sip:TN@company.comCall-id: 1234@pc33.company.comCseq: 1 INVITEContact: sip:TN@pc33.company.com

v=0o=Alice 26764646 46734 IN IP4 192.0.01s=Let’s talk about swimming techniquesc=IN IP4 192.0.0.1t=0 0m=audio 20000 RTP/AVP 0a=sendrecv

SIP/2.0 200 OKVia: SIP/2.0/UDP pc33.company.com; branch=33Max-Forwards: 70To: sip:latptop1@factoryA.comFrom: sip:TN@company.comCall-id: 1234@pc33.company.comCseq: 1 200 OKContact: sip:TN@pc33.company.com

v=0o=Alice 26764646 46734 IN IP4 192.0.01s=Let’s talk about swimming techniquesc=IN IP4 192.0.0.1t=0 0m=audio 30000 RTP/AVP 0a=sendrecv

SIP Call RedirectionSIP Call Redirection

3. LocationRequest

4. LocationReply

Alice

Bob

SIPproxy

RedirectServer

LocationServer

SIPproxy

1. INVITE

10. 200 OK

2. INVITE

5. 302 Moved Temporarily

6. INVITE

8. 200 OK

7. INVITE

9. 200 OK

11. ACKMedia Session

Extending SIP (1/2)Extending SIP (1/2)

Event Notification (RFC 3265)– To obtain the status of a given resource– To track changes in that status– E.g. online, offline

Alice Alice’s VoicemailSUBSCRIBEEvent: message-summary

200 OK

NOTIFYMessage-Waiting: yesMessage-Account: sip:alice@vmail.example.comVoice-Message: 2/8 (0/2)

200 OK

Extending SIP (2/2)Extending SIP (2/2)

User Agent Capability (RFC 3840)– SIP methods it supports– Video, audio, text communication– Business or personal communication, etc

Signaling Compression (RFC 3320)– Textual encoding makes SIP messages grow

dramatically as soon as several extensions are used at the same time

2005.10.5.

2005.10.18.

IP Multimedia Subsystem (IMS)IP Multimedia Subsystem (IMS)

To offer Internet services everywhere and at any time using cellular technologies

Session Control Protocol– SIP(RFC 3261) was chosen among the three

candidates (BICC, H.323, SIP)

tElephone NUmber Mapping (ENUM)tElephone NUmber Mapping (ENUM)

Protocol to identify ordinary phones, fax machines, pagers, email clients, etc, by one E.164 number

INTERNET

TelephoneNetwork

ENUM DNS

ENUM No.

Email / SIP / URL

Telephone No.

Mobile No.

Fax No.

From Jaeyoung Choi’s presentation

ConclusionConclusion

Session Initiation Protocol is new standard

Many advantages– Text-based encoding– Application layer protocol

Many extensions– Makes SIP more useful– VoIP, IMS, ENUM, etc

Any Question?Any Question?