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

For APRICOT, Feb 27, Signaling Standards Media Gateway Control Signalling –H.248/Megaco Call Signalling –SIP and SIP-T –H.323

For APRICOT, Feb 27, Network View SG MG MGC SG MG MGC SIP User Agent H.323 Endpoint PSTN Call signalling Media gateway control signalling Media flows SIP-T SIP H.323 call signalling H.248 Megaco H.248 Megaco

For APRICOT, Feb 27, 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

For APRICOT, Feb 27, H.248/Megaco evolution SGCP MGCP Megaco/H.248 I-RFC 2705 MGCP released as Informational RFC (Oct 99) MGCP proposal by merging IPDC and SGCP (Telcordia & Level 3) Consensus between IETF and ITU on Megaco Protocol (March 99) Lucent submits MDCP to ITU-T SG16 (Nov 1999) IETF RFC 3015 MDCP (proposal) MDCP (proposal) IPDC

For APRICOT, Feb 27, Megaco architecture Media Gateway Layer (MG) Implements connections Implements or controls end device features (including UI) No knowledge of call level features Media Gateway Control Protocol Master / slave control of MGs by MGCs –Connection control –Device control and configuration –Events and signals Orthogonal to call control protocols Media Gateway Control Layer (MGC) Contains all call control intelligence Call control (eg. H.323, SIP…) IP Phone Media Gateway PSTN, ATM, etc Analog Media Gateway PSTN line Media Gateway lines Call Agent Media Gateway Controller PSTN trunking Media Gateway trunks

For APRICOT, Feb 27, 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 MG TaTa TbTb CnCn TcTc TdTd I2 O2=I1+I3 I1 I3 O3=I1+I2 O1=I2+I3 Simple, powerful connection/resource model

For APRICOT, Feb 27, Provides control for manipulating terminations and contexts. Current Command Set: Megaco/H.248: Commands

For APRICOT, Feb 27, 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

For APRICOT, Feb 27, 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)

For APRICOT, Feb 27, SIP overview SIP (Session Initiation Protocol – IETF RFC 2543) Application-layer signaling protocol for creating, modifying and terminating sessions with one or more participants

For APRICOT, Feb 27, 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

For APRICOT, Feb 27, SIP Architectural Model Private IP Network Public IP Network SIP Agent Registrar Proxy Server Redirect Server Location Server SIP Agent UAS UAC UAS

For APRICOT, Feb 27, 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 contains the method being invoked, e.g. INVITE –RFC 2543 methods include INVITE, ACK, BYE, REGISTER, CANCEL, OPTIONS Responses are generated by servers –First line contains 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

For APRICOT, Feb 27, 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

For APRICOT, Feb 27, 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.

For APRICOT, Feb 27, SIP-T purpose PSTN bridging (PSTN - IP - PSTN) PSTN Signaling is carried transparently over the IP network PSTN to IP interworking MGC 1 MGC 2 Proxy SIP enabled network IP network SS7 network MGC Proxy SIP enabled network IP network SS7 network SIP agent

For APRICOT, Feb 27, SIP-T Technical Approaches SIP-T uses two approaches: 1.Map ISUP message contents to fields in the SIP header for interworking with pure SIP agents 2.Encapsulate ISUP message within SIP message body for “PSTN bridging”

For APRICOT, Feb 27, 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

For APRICOT, Feb 27, SIP–T status Work on SIP-T was initiated by the International SoftSwitch Consortium (ISC) in early SIP-T is still a work in progress. The ISC is continuing to develop profiles for SIP and telephony interworking.

For APRICOT, Feb 27, H.323 Overview Packet-based multi-media communications system It includes several protocols –H RAS (registration, admission, status …) –H Call Signalling –H.245 Logical channel signalling and media control –RFC 1889 RTP/RTCP for media transport –H.450.x Supplementary services –H 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

For APRICOT, Feb 27, H.323 overview continued Comprised of several protocols: System Control User InterfaceDataVideoAudio Lower Layers Vary IP UDP or TCP UDP RTP/RTCP Call Control RAS H.245 Control H.225 T.120H.261 H.263 G.711 G.722 G.723 G.728 G.729 AAL5 ATM

For APRICOT, Feb 27, Gatekeeper MCUGateway Endpoints can make or receive calls Realized by terminals and logically present in Gateways Gatekeeper address translation (IP, telephone) admission control cannot generate or terminate calls Gateway Interworking with other multimedia terminals GSTN Multipoint Control Unit (MCU) Support for multipoint conferences Always contains a MC Optionally contains an MP Terminals PCs, IP phones, set- top boxes Audio Video (optional) Data (optional) H.323 elements and entities

For APRICOT, Feb 27, 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 also updated Currently working on version 5. No release date specified.

For APRICOT, Feb 27, H.323/SIP comparison summary H.323SIP Stds Body ITU-T SG-16IETF SIP, MMusic,... Properties Complex, monolithic design Difficult to extend & update Based on H.320 conferencing and ISDN Q.931 legacy (“Bell headed”) Limited potential beyond telephony Some QoS built in… CODEC types specified Higher degree of interoperability Modular, simplistic design Easily extended & updated Based on Web principals (“Internet- friendly”) Readily extensible beyond telephony Status w.r.t. end device H.450.x series provides minimal feature set only, pure peer approach Adding ( mixed peer/stimulus approach soon poor architecture) Slow moving No real end-device features std, yet Many options for advanced telephony features (need to make specific choices) Astounding progress, velocity Industry acceptance Established now, primarily system level Few if any H.323-base telephones End-user primarily driven by Siemens, Microsoft (NetMeeting), Intel Rapidly growing industry momentum, at system and device level Growing interest in SIP-Phones and soft clients, products appearing 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

For APRICOT, Feb 27, For More Information IETF: –IETF home page –Internet-draft search engine –RFC search engine –Megaco WG charter –Megaco documents repository ftp://standards.nortelnetworks.com/megaco/ ftp://standards.nortelnetworks.com/megaco/docs/latest/ ITU: –ITU home page –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 APRICOT, Feb 27, Thank You!