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The Session Initiation Protocol: Internet-Centric Signaling

The Session Initiation Protocol: Internet-Centric Signaling. 네트워크 연구실 류 준 우. Introduction (1). Initiates, modifies, and terminates network sessions Focus on interactive multimedia sessions (Internet phone calls or multimedia conferences)

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The Session Initiation Protocol: Internet-Centric Signaling

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  1. The Session Initiation Protocol:Internet-Centric Signaling 네트워크 연구실 류 준 우

  2. Introduction (1) • Initiates, modifies, and terminates network sessions • Focus on interactive multimedia sessions (Internet phone calls or multimedia conferences) • Used for instant messaging, event notification or managing other session type (ex. Distributed games)

  3. Introduction (2) • Peer-to-Peer signaling Protocol • SIP URL : e-mail 과 비슷한 형태의 identifier를 이용하여 사용자를 식별 • Personal mobility같은 id로 다른 위치나 다른 단말에서 사용이 가능

  4. Components(1) • UAC (User Agent Client)- 요청 Msg로 SIP transaction을 함- 요청 Msg의 존속 기간동안 UAC로 동작 • UAS (User Agent Server)- SIP 요청 Msg에 응답- 요청 메시지의 수용, 거절, 리다이렉트를 처리함

  5. Components (2) • Registrars- domain내의 user 정보를 주고 받는다. - Register 요청 메시지를 수용하는 서버 • Proxy Server- application-layer에서 SIP request, response 를 forwarding 함 • Redirect Server- request를 받아서 다른 주소나 서버로 넘겨준다. • Registrars, Proxy Server, Redirect Server는 같은 Program에서 구현 가능하다.

  6. Protocol architecture H.323 SIP RTSP RSVP RTCP RTP TCP UDP IPv4, IPv6 PPP AAL3/4 AAL5 PPP SONET ATM Ethernet V.34

  7. Signaling • SPI request URI 는 email 주소와 비슷하게 생겼다.user name + host name + parameters • Signaling Msg는 다른 미디어 전송과 전혀 다른 path로 전송된다. • SIP Msg는 transfer protocol에 independent 하게 동작한다.

  8. Describing & Changing Session • SIP use SDP to describe multimedia sessions. • SDP expressed in a simple textual format

  9. SIP Message Format • SIP의 Msg format 은 HTTP처럼 plain text로 되어 있다. • Request Msg. 와 Response Msg로 볼 수 있다. • Request Msg. UAC -> UAS • Response Msg. UAC <- UAS

  10. SIP Messages

  11. Request Messages

  12. Response Messages

  13. Forking • SIP differs from other signaling protocols in that it allows a call request to fork • Automatic call distribution (ACD)ex) same number can ring at home and at work.

  14. Reliability • SIP Msg can be transmitted over unreliable transport protocols • SIP has to take care of reliability on its own. • INVITE Msg응답이 올 때까지 Client는 재전송하고 ACK때 까지 서버는 Responses 재전송 • Response 가 올때까지 Request 재전송

  15. Locating Users • Location User는 User Registration 을 통해서 location mapping 을 만드는 것이다. • User agents 주기적으로 SIP REGISTER request을 사용해 Local registrar server에 등록 한다.

  16. Session Characteristics • Overall session caller’s name, address, organizationcallee’s name, addresssession’s urgency and subject • Media sessionacceptable media format

  17. Security • Need to be secured against eavesdropping and alteration. • SIP inherits the basic and digest authentication mechanisms from HTTP. • Currently, public key cryptography using the PGP format has been defined

  18. Security • Confidentiality- End-to-end encryption Shared secret 또는 Public key- Hop-by-hop encryption기존의 security mechanism (TLS/IPSec) • Authentication- HTTP authentication mechanism 사용 (RFC2617)- TLS/IPSec 인증 기능 사용

  19. Integration with Other Internet Services • SIP addresses are regular URLs and can be embedded in Web pages, e-mail, and any other context where URLs are allowed. • The message body of requests and responses uses the MIME mechanism familiar from e-mail. • SIP messages can thus carry any binary or text object, with servers treating the message body as opaque data.

  20. Telephony Service • 많은 부가 기능을 가질 수 있는 서비스가 전통적인 Telephony Service의 기준이상으로 SIP에서 제공할 수 있다. • 특정 서비스 제공을 위한 요소를 첨가하기 보단 새로 만들어질 많은 서비스를 제공할 수 있는 기본적인 요소를 제공하는 방향을 제시

  21. Multiparty Sessions • Full meshsends an individual copy of the media stream to the others. • Mixerseveral media streams and replicates them to all participants. • Network-layer multicastmost efficiently supported by network-layer multicast

  22. Expression Caller Preference • many of their communications tools and location under a single public identifier.

  23. Quality of Service • SIP messages and data streams are likely to traverse very different parts of the network • SIP를 set-up resource reservations 에 사용하는건 부적합하다. • Can used to negotiate the use of QoS mechanisms

  24. Mobility • One of the central tasks • SIP is to locate one or more IP addresses where a user can receive media streams, given only a generic, locationindependent address identifying a domain. • makes it easy to offer precall terminal mobility

  25. SIP and MGCP/Megaco • MGCP는 Media Gateway와 이를 제어하기 위한 Media Gateway Controller 간에 사용하는 프로토콜입니다

  26. Programming SIP Services • telephony services have been either hard-coded into switches • SIP-based telephony there are at least four choices to create SIP-based services.(language-based APIs, create dedicated languages, SIP servlet is a pice of JAVA code , includesjava applets)

  27. The Applicability of SIP • There are many functions SIP explicitly does not provide • not a session management or conference control protocol. • as media transport, voting and polling, virtual microphone passing, chair election, floor control, and feedback on session

  28. Related work • Telephony signaling protocolschannel-associated signaling -> out-of-band signaling. • ISUP to set up connections between IP endpoints • SIP is related to messaging mechanisms such as Internet e-mail. • The ICEBERG project also considers setup of large-scale sessions using multicast, while Elliott discusses session membership propagation.

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