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Signalling and Control In IP Networks - H.248, H.323 and SIP

Signalling and Control In IP Networks - H.248, H.323 and SIP. Signaling Standards. Media Gateway Control Signalling H.248/Megaco Call Signalling SIP and SIP-T H.323. PSTN. PSTN. Network View. SIP-T. SG. MGC. SG. MGC. SIP. SIP User Agent. H.323 call signalling. H.248 Megaco.

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Signalling and Control In IP Networks - H.248, H.323 and SIP

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  1. Signalling and Control In IP Networks- H.248, H.323 and SIP

  2. Signaling Standards • Media Gateway Control Signalling • H.248/Megaco • Call Signalling • SIP and SIP-T • H.323

  3. PSTN PSTN Network View SIP-T SG MGC SG MGC SIP SIP User Agent H.323 call signalling H.248 Megaco H.248 Megaco H.323 Endpoint MG MG Call signalling Media gateway control signalling Media flows

  4. H.248/MEGACO Overview • MEdia GAteway Control Protocol [RFC3015] • H.248 is ITU-T reference for the same protocol • Protocol for controlling telephony gateway and terminals (IP Phones) • Basis for Vendor Independent Network deployment

  5. H.248/Megaco evolution MGCP proposal by merging IPDC and SGCP (Telcordia & Level 3) IPDC MGCP released as Informational RFC (Oct 99) MGCP I-RFC 2705 SGCP Lucent submits MDCP to ITU-T SG16 (Nov 1999) MDCP (proposal) Consensus between IETF and ITU on Megaco Protocol (March 99) IETF RFC 3015 Megaco/H.248

  6. MG Cn O2=I1+I3 Tb I1 I2 Ta O3=I1+I2 Tc I3 Td Megaco connection model • Based on 3 concepts: • Termination • Identifies an end point for media flows • Implements Signals, and generates Events • Can appear in at most one context. • Permanent (provisioned) terminations can exist outside a context • Context • Defines communication between Terminations, acts as a mixing bridge • Contains 1 or more Terminations • Supports multiple streams • Stream • A context can have multiple streams, each typically for a medium, e.g. audio, video, etc • The MGC specifies which streams a given termination supports O1=I2+I3 Simple, powerful connection/resource model

  7. Megaco/H.248: Commands • Provides control for manipulating terminations and contexts. • Current Command Set:

  8. Packages and profiles • Packages: • Extension mechanism to define new termination and MG behavior • Adds detailed application semantics to the protocol, e.g. a package can define the events for DTMF signaling • Profiles: • Define particular applications of Megaco/H.248 • Created by industry organizations, e.g. TIA • Specifies which packages are to be supported and other protocol options

  9. Megaco/H.248 Standards Status • Standardization of Base Protocol — DONE • Decided as ITU-T Recommendation H.248 in June 2000 • Published as IETF Megaco RFC 3015, in Nov 2000 • Continued work on bug fixes for the base protocol • First issue of H.248 Implementor’s Guide approved, Nov 2000 • Package definition — Rapid Progression • “Starter Kit” (Annex E) defined in base protocol • Additional packages defined as Annexes F, G, J and K to H.248 in Nov 2000 • More ongoing in both IETF and ITU • Megaco/H.248 Interoperability — Second Event Just Completed! • First multi-vendor interoperability event was great success (Aug 2000) • 18 participants including MGCs, MGs, and Test equipment • Ad-hoc group formed to test Megaco/H.248 implementations and collect feedback on specification issues • Line to Line and Line to Trunk calls with and without digit collection completed with bearer path • Second event just occurred last week (Feb 2001)

  10. SIP overview • SIP (Session Initiation Protocol – IETF RFC 2543) • Application-layer signaling protocol for creating, modifying and terminating sessions with one or more participants

  11. SIP overview • Light-weight generic signaling protocol • Used to initiate sessions and invite members to a session • Text-based protocol (good for prototyping) • Syntax is textual and based on HTTP • There have been several bake-offs with different vendors demonstrating interoperability of basic calls

  12. Private IP Network Public IP Network SIP Architectural Model Proxy Server Registrar SIP Agent UAC Redirect Server SIP Agent UAS Location Server UAC UAS

  13. SIP messages • Message consists of initial line, headers and body • There are two types of SIP message • Request • Response • Requests are always initiated by a UAC function • First line containsthe method being invoked, e.g. INVITE • RFC 2543 methods include INVITE, ACK, BYE, REGISTER, CANCEL, OPTIONS • Responses are generated by servers • First linecontains the response code • Headers provide information needed to process or route the message • Body contains Session Description Protocol (SDP) describing media flows or other materials such as encapsulated ISUP messages. • New methods and header types can be added at any time without changing the protocol

  14. SIP status • Base protocol is RFC2543 • — Presently being revised – RFC2543bis is under discussion • Standardized in the IETF as RFC 2543 in March 99 (now being further refined in the SIP working group). • RFC 2543 just covers basic functionality. There are several related internet drafts covering services. • Has rapidly growing industry momentum • Intense efforts underway to develop service-specific extensions

  15. SIP-T • SIP-T = Session Initiation Protocol – Telephony • previously referred to as SIP+ or SIP BCP-T • a collection of internet drafts that extend SIP to support inter-Media Gateway Controller (MGC) communications. • SIP-T is an interface agreement on a collection of standards as opposed to a separate protocol • SIP-T describes how to interwork SIP and ISUP • SIP-T directly negotiates a media connection between gateways. Endpoint information is carried in SDP (Session Description Protocol) which can describe both IP and ATM endpoints.

  16. Proxy SIP enablednetwork MGC 1 MGC 2 IPnetwork SS7 network SS7 network SS7 network Proxy SIP-T purpose PSTN bridging (PSTN - IP - PSTN) PSTN Signaling is carried transparently over the IP network Proxy SIP enablednetwork PSTN to IP interworking SIPagent MGC IPnetwork Proxy

  17. SIP-T Technical Approaches • SIP-T uses two approaches: • Map ISUP message contents to fields in the SIP header for interworking with pure SIP agents • Encapsulate ISUP message within SIP message body for “PSTN bridging”

  18. SIP-T Implementation • Three major extensions required: • INFO method extension to the base protocol in addition to others • Session initiation and teardown is not enough • Mid-Call events • More complex services enabled • MIME Type addition • Standard method of encapsulating legacy signaling • Simplifies Inter-working: • Local variant • Interconnect variant (LCD) • ISUP to SIP Mapping

  19. SIP–T status • Work on SIP-T was initiated by the International SoftSwitch Consortium (ISC) in early 1999. • SIP-T is still a work in progress. The ISC is continuing to develop profiles for SIP and telephony interworking.

  20. H.323Overview • Packet-based multi-media communications system • It includes several protocols • H.225.0 RAS (registration, admission, status …) • H.225.0 Call Signalling • H.245 Logical channel signalling and media control • RFC 1889 RTP/RTCP for media transport • H.450.x Supplementary services • H.225.0 Annex G Inter-domain registration and billing information exchange • The original VoIP protocol suite • Whole System Architecture • Provides Interoperability • Transport independence • Platform and application independence • Multipoint support • Primarily used in corporate networks

  21. H.323 overview continued • Comprised of several protocols: Audio Video Data System Control User Interface G.711 G.722 G.723 G.728 G.729 H.261 H.263 T.120 H.225 H.245 Control Call Control RAS RTP/RTCP AAL5 UDP UDP or TCP ATM IP Lower Layers Vary

  22. H.323 elements and entities Gatekeeper MCU Gateway • Terminals • PCs, IP phones, set-top boxes • Audio • Video (optional) • Data (optional) • Gatekeeper • address translation (IP, telephone) • admission control • cannot generate or terminate calls • Endpoints • can make or receive calls • Realized by terminals and logically present in Gateways • Gateway • Interworking with • other multimedia terminals • GSTN • Multipoint Control Unit (MCU) • Support for multipoint conferences • Always contains a MC • Optionally contains an MP

  23. H.323 current status • H.323 version 4 • Includes many major changes • A significant number of contributions from Nortel Networks • Approved in November 2000 • H.245 and H.225.0 also updated • Currently working on version 5. No release date specified.

  24. H.323/SIP comparison summary SIP is anticipated long-term winner, but H.323 networks will remain for some time, and are a source of revenue in the international market

  25. IETF: IETF home page http://www.ietf.org/ Internet-draft search engine http://search.ietf.org/search/brokers/internet-drafts/query.html RFC search engine http://www.rfc-editor.org/rfcsearch.html Megaco WG charter http://ietf.org/html.charters/megaco-charter.html Megaco documents repository ftp://standards.nortelnetworks.com/megaco/ ftp://standards.nortelnetworks.com/megaco/docs/latest/ ITU: ITU home page http://www.itu.int/ITU-T/index.html SG-16 document repository (H.323, H.248) ftp://standard.pictel.com/avc-site Most Megaco/H.248 related documents should also be available through Megaco WG, above For More Information

  26. Thank You!

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