SIP (Session Initiation Protocol) is a signaling protocol used to create, manage and terminate sessions in an IP based network. This course is for beginners and aims to give a brief introduction to SIP before one ventures into the long RFC documents.

1. Take a sip of SIP
Paul Sarstiuc, Romeo Vidrascu, Marius Trestioreanu
Bucharest
18 April 2016

2. 2
SIP – Session Initiation Protocol
 Content
– VoIP
– SIP History
– SIP Architecture
– Addressing SIP
– SIP Messages
– SIP Flow
– WireShark and SIP Filters
– SIP Flow – WireShark
– Supplementary Services
– SDP - WireShark

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VoIP stereotypes
 VoIP means free calls
 SIP is a collection of protocols
 SIP is better than H323
 SIP is a voice signaling protocol

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VoIP
 VoIP
– VoIP: Voice over Internet Protocol
 IP Telephony
 Internet Telephony
 Voice over Broadband (VoBB)
 Broadband Telephony
 Broadband Phone
– Alternative to PSTN
– Single infrastructure for Data, Voice and Video
– More demand for video conferences is easily satisfied with VoIP
– Cost savings on long distance calls
– Easier connectivity: customers are to be reached at multiple points
under the same “telephone number”
– Communication Services
 Voice/Video
 Fax
 Voice/Messaging Application

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VoIP
 VoIP Protocols
– SIP – Session Initiation Protocol
– H.323
– IMS – IP Multimedia Subsystem
– MGCP – Media Gateway Control Protocol
– RTP – Real-time Transport Protocol
– RTCP – Real-time Transport Control Protocol
– SDP – Session Description Protocol
– Skype Protocol (proprietary)
– TCP – Transmission Control Protocol
– UDP – User Datagram Protocol
– TLS – Transport Layer Security

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SIP OSI
 SIP vs. OSI

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History
 SIP History
– Feb. 22, 1996 draft-ietf-mmusic-scip-00; IDMS paper
– Feb. 22, 1996 draft-ietf-mmusic-sip-00
– Dec. 2, 1996 draft-ietf-mmusic-sip-01
– March 27, 1997 draft-ietf-mmusic-sip-02
– July 31, 1997 draft-ietf-mmusic-sip-03
– November 11, 1997 draft-ietf-mmusic-sip-04
– May 14, 1998 draft-ietf-mmusic-sip-05
– June 17, 1998 draft-ietf-mmusic-sip-06
– July 16, 1998 draft-ietf-mmusic-sip-07
– August 7, 1998 draft-ietf-mmusic-sip-08
– September 18, 1998 draft-ietf-mmusic-sip-09
– September 28, 1998 Last call
– November 12, 1998 draft-ietf-mmusic-sip-10
– December 15, 1998 draft-ietf-mmusic-sip-11
– January 15, 1999 draft-ietf-mmusic-sip-12
– February 2, 1999 Approved
– March 17, 1999 RFC 2543
– July 3, 2002 RFC 3261 (SIP: Session Initiation Protocol), RFC 3262 (Reliability of Provisional Responses
in Session Initiation Protocol (SIP)), RFC 3263 (Session Initiation Protocol (SIP): Locating SIP Servers), RFC
3264 (An Offer/Answer Model with Session Description Protocol (SDP)), RFC 3265 (Session Initiation Protocol
(SIP)-Specific Event Notification), RFC 3266 (Support for IPv6 in Session Description Protocol (SDP))
published

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SIP Architecture
 Network Elements:
– UA – User Agent
 UAC – User Agent Client [request]
 UAS – User Agent Server [response]
– Server Elements [RFC 3261]
 Proxy Server [phone – proxy – proxy – phone]
 Registrar [REGISTER]
 Redirect Server [3XX]
– Other Network Elements
 SBC – Session Border Controller
 Gateway

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SIP Architecture
 Network Elements

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SIP addressing
 URI – Uniform Resource Identifier
 sip:username:password@host:port
 E.g.: sip:John@sipgatedomain.org
 Secure transmission
– sips:… instead of sip:…
– TLS – Transport Layer Security

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SIP Messages
 SIP Requests:
– REGISTER
– INVITE
– ACK
– CANCEL
– BYE
– OPTIONS
– SUBSCRIBE
– REFER
– NOTIFY
 SIP Responses:
– Provisional (1xx)
– Success (2xx)
– Redirection (3xx)
– Client Error (4xx)
– Server Error (5xx)
– Global Failure (6xx)

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SIP Messages - REGISTER

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SIP Messages - INVITE

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SIP Messages - ACK

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SIP Messages - CANCEL

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SIP Messages - BYE

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SIP Messages - OPTIONS

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SIP Messages – 100 Trying

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SIP Messages – 200 Ok

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SIP Messages – 401 Unauthorized

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SIP Flow
 Direct SIP Call Between 2 UAs

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SIP Flow
 Call via Proxy

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SIP Flow
 Call via Proxy with No Answer

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SIP Flow
 Registration

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WireShark and SIP Filters
 Wireshark
– Free, open-source packet analyzer
– Network Troubleshooting and Analysis
– Software and communications protocol development
– Education.
 Popular Filters:
– sip
– sdp
– udp
– tcp
– rtp
– sip.To
– sip.to.addr

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SIP Flow - WireShark
 WireShark Capture

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SIP Flow - WireShark
 WireShark: Telephony – VoIP Calls – Flow

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Supplementary Services
– Call Hold
– Call Transfer
– Call Conference
– Call Forwarding
 on busy
 no answer
 unconditional

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Supplementary Services
 HOLD

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Supplementary Services
 HOLD

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Supplementary Services
 Transfer

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SDP - WireShark

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SDP - WireShark
 Session Description Protocol Version - 0
 Owner / Creator of the session or Owner / Creator. Identification is made by:
– Owner username. User.
– Session ID. ID of the session. Random number as a unique identifier of the session.
– Session Version. Version.
– Network Type. Tipe network. Always IN.
– Address Type. It can be IP4 (IPv4) or IP 6 (IPv6).
– Address (IP). IP Address. (200.57.7.197)
– Session Name. Name of the session.
 Connection Information:
– C = Connection Type Network (IN)
– Connection Address Type: (IP4 or IPv6)
– Connection Address: (200.57.7.197)
 Time Description, active time. (t): 0 0, start stop time = 0. [unrestricted and permanent session].
 Media Description, name and address (m): audio 40376 RTP / AVP 4 0 8 18. Type of data being transported (audio or telephone session in this
case), UDP port used (40 376), protocol used (Real Time Transport Protocol RTP / AVP Audio Video Profiles). Codecs formats:
– 8 G.711 PCMA
– 18 G.729
– 4 G.723
– 0 G.711 PCMU
 Media Attribute (a). This is a list of format codes outlined above with data from Sample rate or sampling frequency, fieldname, etc.
 Media Attribute (a). SendRecv. So send / receive.

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Q & A
Thank You !