Postech DP&NM Lab Session Initiation Protocol (SIP) Date: Seongcheol Hong DP&NM Lab., Dept. of CSE, POSTECH Date: Seongcheol Hong DP&NM Lab., Dept. of CSE, POSTECH

(2/21) Postech DP&NM Lab Contents Introduction -History SIP -Functions -Components and Architecture -Messages and Syntax Overview of SIP Operation -Proxy Mode -Redirect Mode Other Issues -SDP, Security and Services

(3/21) Postech DP&NM Lab Introduction SIP – Session Initiation Protocol -A signaling protocol, widely used for setting up and tearing down multimedia communication sessions such as voice and video calls over the Internet -Other feasible application Video conferencing and streaming multimedia distribution Instant messaging and online games -SIP was accepted as a 3GPP signaling protocol and permanent element of the IMS architecture for IP based streaming multimedia services in cellular systems SIP is -Situated at the session layer in the OSI model -Designed to be independent of the underlying transport layer SIP can run on TCP, UDP or SCTP -Text-based, allowing for humans to read and analyze SIP messages

(4/21) Postech DP&NM Lab History Mark Hadley’s SIP (Session Invitation Protocol) -Henning Schulzrinne’s SCIP (Simple Conference Control Protocol) RFC 2543 by IETF MMUSIC (Multiparty Multimedia Session Control) WG IETF SIP WG RFC 3261 (the latest version of the specification)

(5/21) Postech DP&NM Lab SIP Functions IETF-standardized peer-to-peer signaling protocol User location -Locate user given -style address -Personal mobility Different terminal, Same identifier, Any location User capabilities -(re)-negotiate session parameters User availability -Determination of willingness of the called party to engage in communications Session setup Session management -Manual and automatic forwarding (name/number mapping) -Terminate and transfer calls

(6/21) Postech DP&NM Lab Multimedia Protocol Stack

(7/21) Postech DP&NM Lab SIP Components UAC (User-Agent Client) -Caller application, call initiation UAS (User-Agent Server) -Caller application, accept, redirect, refuse call User Agent = UAC + UAS -IP phone, PC, conference bridge Redirect Server -Returns new location for requests Proxy Server -Routes call requests Registrar -Maintains mappings from names to addresses

(8/21) Postech DP&NM Lab SIP Architecture

(9/21) Postech DP&NM Lab SIP Addressing SIP uses -style addresses to identify users -Typically, same as user’s address: -Written as URL, e.g., Can add parameters, such as type (user=“phone”) or transport protocol tel URLs (RFC 2806) -can use tel URLs for telephone numbers, e.g., tel: or fax:

(10/21) Postech DP&NM Lab SIP Messages Text, not binary, format Look very similar to HTTP/1.1 Requests and responses are similar except for first line Requests and responses can contain message bodies: -Typically session descriptions, but also ASCII or HTML

(11/21) Postech DP&NM Lab SIP syntax Field names and some tokens (e.g. media type) are case-insensitive Everything else is case-sensitive White-space doesn’t matter except in first line Multi-valued header fields can be combined as a comma-list

(12/21) Postech DP&NM Lab SIP Methods

(13/21) Postech DP&NM Lab SIP responses

(14/21) Postech DP&NM Lab Overview of Operation

(15/21) Postech DP&NM Lab SIP Operation in Proxy Mode

(16/21) Postech DP&NM Lab SIP Operation in Redirect Mode

(17/21) Postech DP&NM Lab SDP (RFC 2327) SDP (Session Description Protocol) -To convey information about media streams in multimedia sessions -To allow the recipients of a session description to participate in the session -In multicast based sessions on the Internet A mean to communicate the existence of a session A mean to convey sufficient information to enable joining and participating in the session Multimedia session -A set of multimedia senders and receivers and the data streams flowing from senders and receivers -A session can comprise one or more RTP sessions

(18/21) Postech DP&NM Lab Security & Privacy SIP signaling can be encrypted -S/MIME SIP can be transported over -IPSec -TLS SIP can carry encryption key for media in SDP “Anonymizer” service can be used to conceal identity

(19/21) Postech DP&NM Lab SIP Services SIP service creation Gateway service to the PSTN User preferences Presence Instant communications Universal messaging – voice mail SIP-PSTN-mobile phone interworking Mobility and user location ENUM: Telephone number based directory Third party call control: PC – phone Voice portal

(20/21) Postech DP&NM Lab References RFC3261, Session Initiation Protocol, Henning Schulzrinne, “The Session Initiation Protocol (SIP),” SIP tutorial, 2001 SIP Forum,

(21/21) Postech DP&NM Lab Questions