Signalling and Control  In IP Networks  -  H.248, H.323 and SIP
Signaling Standards <ul><li>Media Gateway Control Signalling </li></ul><ul><ul><li>H.248/Megaco </li></ul></ul><ul><li>Cal...
Network View SG MG MGC SG MG MGC SIP User Agent H.323 Endpoint Call signalling Media gateway control signalling Media flow...
H.248/MEGACO  Overview <ul><li>ME dia  GA teway  Co ntrol Protocol  [RFC3015] </li></ul><ul><li>H.248 is ITU-T reference f...
H.248/Megaco evolution SGCP MGCP Megaco/H.248 I-RFC 2705 MGCP released as Informational RFC (Oct 99) MGCP proposal  by mer...
Megaco architecture <ul><li>Media Gateway Layer (MG) </li></ul><ul><ul><li>Implements connections  </li></ul></ul><ul><ul>...
Megaco connection model <ul><li>Based on 3 concepts: </li></ul><ul><li>Termination </li></ul><ul><ul><li>Identifies an end...
<ul><li>Provides control for manipulating terminations and contexts.  </li></ul><ul><li>Current Command Set: </li></ul>Meg...
Packages and profiles <ul><li>Packages: </li></ul><ul><ul><li>Extension mechanism to define new termination and MG behavio...
Megaco/H.248 Standards Status <ul><li>Standardization of Base Protocol —  DONE </li></ul><ul><ul><li>Decided as ITU-T Reco...
SIP overview <ul><li>SIP ( S ession  I nitiation  P rotocol  – IETF RFC 2543) </li></ul><ul><li>Application-layer signalin...
SIP overview <ul><li>Light-weight generic signaling protocol </li></ul><ul><li>Used to initiate sessions and invite member...
SIP Architectural Model SIP Agent Registrar Proxy Server Redirect Server Location Server SIP Agent UAS UAC UAC UAS Private...
SIP messages <ul><li>Message consists of initial line, headers and body </li></ul><ul><li>There are two types of SIP messa...
SIP status <ul><li>Base protocol is RFC2543 </li></ul><ul><ul><li>—  Presently being revised – RFC2543bis is under discuss...
SIP-T <ul><li>SIP-T = Session Initiation Protocol – Telephony </li></ul><ul><ul><li>previously referred to as SIP+ or SIP ...
SIP-T purpose PSTN bridging (PSTN - IP - PSTN) PSTN Signaling is carried transparently over the IP network PSTN to IP inte...
SIP-T Technical Approaches <ul><li>SIP-T uses two approaches: </li></ul><ul><ul><li>Map ISUP message contents to fields in...
SIP-T Implementation <ul><li>Three major extensions required: </li></ul><ul><ul><li>INFO method extension to the base prot...
SIP–T status <ul><li>Work on SIP-T was initiated by the International SoftSwitch Consortium (ISC) in early 1999. </li></ul...
H.323   Overview <ul><li>Packet-based multi-media communications system </li></ul><ul><li>It includes several protocols  <...
H.323  overview continued  <ul><li>Comprised of several protocols: </li></ul>System Control User Interface Data Video Audi...
H.323 elements and entities <ul><li>Endpoints </li></ul><ul><li>can make or receive calls </li></ul><ul><li>Realized by te...
H.323 current status <ul><li>H.323 version 4 </li></ul><ul><ul><li>Includes many major changes </li></ul></ul><ul><ul><li>...
H.323/SIP comparison summary SIP is anticipated long-term winner, but H.323 networks will remain for some time, and are a ...
For More Information <ul><li>IETF: </li></ul><ul><ul><li>IETF home page   </li></ul></ul><ul><ul><ul><li>http://www. ietf ...
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Signalling and Control In IP Networks: H.248, H.323 and SIP

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  • H.248/MEGACO ( ME dia GA teway Co ntrol Protocol) Overview H.248 designation is ITU-T reference IETF Megaco Protocol spec and ITU H.248 spec are synonymous, IETF RFC number is RFC2885 word-for-word identical in technical content.  can be used as a single international specification supported by both key standards bodies on data (IETF) and telecom (ITU) side of the fence, very broadly accepted across the industry.  Stimulus protocol for controlling simplified access/telephony gateway and terminals (IP Phones) Basis for Vendor Independent Network deployment Unifying protocol for Succession Solutions Gateways
  • The general architecture and requirements for Megaco and the various types of gateways are defined in RFC2085.
  • Packages and profiles Packages: Simple, clean ,flexible, powerful extension mechanism to define new termination behavior Define information content on top of the protocol Termination properties, signals, events, statistics Profiles: Define particular applications of Megaco/H.248 at MG side Structure and package/termination requirements Specific selections on optional elements (for example, transport and encoding) Any other behavior definition required for the application Constitutes an application level agreement between MGC and MG Allows assumption on minimum capabilities, MG organization Very good for interoperability of particular applications!
  • SIP Overview SIP (Session Initiation Protocol) is an application-layer control (signaling) protocol for creating, modifying and terminating sessions with one or more participants. Peer protocol Intelligence in the user terminal has been submitted to the IETF as RFC 2543 on the standards track (now under the SIP working group). Currently RFC2543bis is the updated version undergoing review. RFC 2543 just covers basic functionality. There are several related internet drafts covering services (for example, draft-ietf-mmusic-sip-cc-01). has rapidly growing industry momentum at system and device level.
  • A more practical representation of the architecture shows that the proxy serves as a security point (of sorts) for crossing between the boundaries of different networks.
  • Response codes 1xx interim 200 success 3xx redirect 4xx client error 5xx server error 6xx global failure
  • Bis is german for 2 nd Reference Expiry Draft-ietf-session-timer-02 Sip For Telephones Jan 2001 Draft-ietf-sip-call-flows-01 SIP Telephone Call Flow Examples Sep 2000 draft-mahy-sip-message-waiting-00 draft-thomas-sip-mime-osp-token-00 draft-culpepper-sip-info-event-00 draft-schulzrinne-sip-911-00 draft-moyer-sip-appliances-framework-00 draft-calhoun-sip-aaa-reqs-00 draft-camarillo-3pcc-qos-00 draft-nishigaya-sip-ccpp-00 draft-rosenberg-sip-sctp-00 Continued on next page…
  • Currently IETF SIP working group Mmusic – MM user se
  • SIP-T Provides support for PSTN signaling transparency – PSTN Bridging Allow interoperability between MGCs from different vendors. PSTN origination - PSTN termination (SIP bridging) The ingress MGC performs encapsulation performs translation The egress MGC Interprets message body generates ISUP Provides a bridge between existing PSTN subscribers and new SIP based services – Interworking PSTN origination - IP termination MGC — perform encapsulation — perform translation IP end-point — ignore ISUP IP origination - PSTN termination IP end-point — originate SIP MGC — generate ISUP Support for both VoIP and VoATM based networks
  • Note that in addition to the 3 major extensions listed, there are several other issues that when resolved will undoubtedly add several items to this list.
  • IETF SIP working group Mailing list : http://www.egroups.com/group/sip-t Web Page : http://www.softarmor.com/sipwg/teams/sipt/index.html
  • Two basic types of elements: Gatekeepers Endpoints Gatekeepers provide address translation and call control services to the endpoints. They are also responsible for bandwidth control. A single gatekeeper manages a set of terminals. Terminals are end user devices capable of providing multi-media services with another terminal. You can assume that a terminal always supports voice but video and data are considered optional. Gateways provide the interface between terminals and external networks Multipoint Control Units (MCU) support multi-conferencing between three or more terminals or gateways. The MCU is made up of two components: Multipoint Controller (MC) An optional Multipoint Processor (MP) The MC supports negotiation capabilities between terminals and resource control while the MP performs mixing and switching functions.
  • Nortel supports H323, implemented on enterprise products Favors SIP, future protocol for internet service enable … With SIP-T as transitional solution for legacy telephony BICC is transitional solution for legacy network, but its role is limited.
  • Signalling and Control In IP Networks: H.248, H.323 and SIP

    1. 1. Signalling and Control In IP Networks - H.248, H.323 and SIP
    2. 2. Signaling Standards <ul><li>Media Gateway Control Signalling </li></ul><ul><ul><li>H.248/Megaco </li></ul></ul><ul><li>Call Signalling </li></ul><ul><ul><li>SIP and SIP-T </li></ul></ul><ul><ul><li>H.323 </li></ul></ul>
    3. 3. Network View SG MG MGC SG MG MGC SIP User Agent H.323 Endpoint Call signalling Media gateway control signalling Media flows SIP-T SIP H.323 call signalling H.248 Megaco H.248 Megaco PSTN PSTN
    4. 4. H.248/MEGACO Overview <ul><li>ME dia GA teway Co ntrol Protocol [RFC3015] </li></ul><ul><li>H.248 is ITU-T reference for the same protocol </li></ul><ul><li>Protocol for controlling telephony gateway and terminals (IP Phones) </li></ul><ul><li>Basis for Vendor Independent Network deployment </li></ul>
    5. 5. 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) IPDC
    6. 6. Megaco architecture <ul><li>Media Gateway Layer (MG) </li></ul><ul><ul><li>Implements connections </li></ul></ul><ul><ul><li>Implements or controls end device features (including UI) </li></ul></ul><ul><ul><li>No knowledge of call level features </li></ul></ul><ul><li>Media Gateway Control Protocol </li></ul><ul><ul><li>Master / slave control of MGs by MGCs </li></ul></ul><ul><ul><ul><li>Connection control </li></ul></ul></ul><ul><ul><ul><li>Device control and configuration </li></ul></ul></ul><ul><ul><ul><li>Events and signals </li></ul></ul></ul><ul><ul><li>Orthogonal to call control protocols </li></ul></ul><ul><li>Media Gateway Control Layer (MGC) </li></ul><ul><ul><li>Contains all call control intelligence </li></ul></ul>IP Phone Media Gateway Analog Media Gateway Call control (eg. H.323, SIP…) PSTN, ATM, etc PSTN line Media Gateway lines Call Agent Media Gateway Controller PSTN trunking Media Gateway trunks
    7. 7. Megaco connection model <ul><li>Based on 3 concepts: </li></ul><ul><li>Termination </li></ul><ul><ul><li>Identifies an end point for media flows </li></ul></ul><ul><ul><li>Implements Signals , and generates Events </li></ul></ul><ul><ul><li>Can appear in at most one context. </li></ul></ul><ul><ul><li>Permanent (provisioned) terminations can exist outside a context </li></ul></ul><ul><li>Context </li></ul><ul><ul><li>Defines communication between Terminations, acts as a mixing bridge </li></ul></ul><ul><ul><li>Contains 1 or more Terminations </li></ul></ul><ul><ul><li>Supports multiple streams </li></ul></ul><ul><li>Stream </li></ul><ul><ul><li>A context can have multiple streams, each typically for a medium, e.g. audio, video, etc </li></ul></ul><ul><ul><li>The MGC specifies which streams a given termination supports </li></ul></ul>O1=I2+I3 Simple, powerful connection/resource model MG T a T b C n T c T d I2 O2=I1+I3 I1 I3 O3=I1+I2
    8. 8. <ul><li>Provides control for manipulating terminations and contexts. </li></ul><ul><li>Current Command Set: </li></ul>Megaco/H.248: Commands
    9. 9. Packages and profiles <ul><li>Packages: </li></ul><ul><ul><li>Extension mechanism to define new termination and MG behavior </li></ul></ul><ul><ul><li>Adds detailed application semantics to the protocol, e.g. a package can define the events for DTMF signaling </li></ul></ul><ul><li>Profiles: </li></ul><ul><ul><li>Define particular applications of Megaco/H.248 </li></ul></ul><ul><ul><li>Created by industry organizations, e.g. TIA </li></ul></ul><ul><ul><li>Specifies which packages are to be supported and other protocol options </li></ul></ul>
    10. 10. Megaco/H.248 Standards Status <ul><li>Standardization of Base Protocol — DONE </li></ul><ul><ul><li>Decided as ITU-T Recommendation H.248 in June 2000 </li></ul></ul><ul><ul><li>Published as IETF Megaco RFC 3015, in Nov 2000 </li></ul></ul><ul><ul><li>Continued work on bug fixes for the base protocol </li></ul></ul><ul><ul><li>First issue of H.248 Implementor’s Guide approved, Nov 2000 </li></ul></ul><ul><li>Package definition — Rapid Progression </li></ul><ul><ul><li>“ Starter Kit” (Annex E) defined in base protocol </li></ul></ul><ul><ul><li>Additional packages defined as Annexes F, G, J and K to H.248 in Nov 2000 </li></ul></ul><ul><ul><li>More ongoing in both IETF and ITU </li></ul></ul><ul><li>Megaco/H.248 Interoperability — Second Event Just Completed! </li></ul><ul><ul><li>First multi-vendor interoperability event was great success (Aug 2000) </li></ul></ul><ul><ul><ul><li>18 participants including MGCs, MGs, and Test equipment </li></ul></ul></ul><ul><ul><ul><li>Ad-hoc group formed to test Megaco/H.248 implementations and collect feedback on specification issues </li></ul></ul></ul><ul><ul><ul><li>Line to Line and Line to Trunk calls with and without digit collection completed with bearer path </li></ul></ul></ul><ul><ul><li>Second event just occurred last week (Feb 2001) </li></ul></ul>
    11. 11. SIP overview <ul><li>SIP ( S ession I nitiation P rotocol – IETF RFC 2543) </li></ul><ul><li>Application-layer signaling protocol for creating, modifying and terminating sessions with one or more participants </li></ul>
    12. 12. SIP overview <ul><li>Light-weight generic signaling protocol </li></ul><ul><li>Used to initiate sessions and invite members to a session </li></ul><ul><li>Text-based protocol (good for prototyping) </li></ul><ul><li>Syntax is textual and based on HTTP </li></ul><ul><li>There have been several bake-offs with different vendors demonstrating interoperability of basic calls </li></ul>
    13. 13. SIP Architectural Model SIP Agent Registrar Proxy Server Redirect Server Location Server SIP Agent UAS UAC UAC UAS Private IP Network Public IP Network
    14. 14. SIP messages <ul><li>Message consists of initial line, headers and body </li></ul><ul><li>There are two types of SIP message </li></ul><ul><ul><li>Request </li></ul></ul><ul><ul><li>Response </li></ul></ul><ul><li>Requests are always initiated by a UAC function </li></ul><ul><ul><li>First line contains the method being invoked, e.g. INVITE </li></ul></ul><ul><ul><li>RFC 2543 methods include INVITE, ACK, BYE, REGISTER, CANCEL, OPTIONS </li></ul></ul><ul><li>Responses are generated by servers </li></ul><ul><ul><li>First line contains the response code </li></ul></ul><ul><li>Headers provide information needed to process or route the message </li></ul><ul><li>Body contains Session Description Protocol (SDP) describing media flows or other materials such as encapsulated ISUP messages. </li></ul><ul><li>New methods and header types can be added at any time without changing the protocol </li></ul>
    15. 15. SIP status <ul><li>Base protocol is RFC2543 </li></ul><ul><ul><li>— Presently being revised – RFC2543bis is under discussion </li></ul></ul><ul><li>Standardized in the IETF as RFC 2543 in March 99 (now being further refined in the SIP working group). </li></ul><ul><ul><li>RFC 2543 just covers basic functionality. There are several related internet drafts covering services. </li></ul></ul><ul><li>Has rapidly growing industry momentum </li></ul><ul><ul><li>Intense efforts underway to develop service-specific extensions </li></ul></ul>
    16. 16. SIP-T <ul><li>SIP-T = Session Initiation Protocol – Telephony </li></ul><ul><ul><li>previously referred to as SIP+ or SIP BCP-T </li></ul></ul><ul><ul><li>a collection of internet drafts that extend SIP to support inter-Media Gateway Controller (MGC) communications. </li></ul></ul><ul><ul><li>SIP-T is an interface agreement on a collection of standards as opposed to a separate protocol </li></ul></ul><ul><li>SIP-T describes how to interwork SIP and ISUP </li></ul><ul><li>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. </li></ul>
    17. 17. SIP-T purpose PSTN bridging (PSTN - IP - PSTN) PSTN Signaling is carried transparently over the IP network PSTN to IP interworking MGC Proxy Proxy SIP enabled network IP network SIP agent MGC 1 MGC 2 Proxy Proxy SIP enabled network IP network SS7 network SS7 network SS7 network
    18. 18. SIP-T Technical Approaches <ul><li>SIP-T uses two approaches: </li></ul><ul><ul><li>Map ISUP message contents to fields in the SIP header for interworking with pure SIP agents </li></ul></ul><ul><ul><li>Encapsulate ISUP message within SIP message body for “PSTN bridging” </li></ul></ul>
    19. 19. SIP-T Implementation <ul><li>Three major extensions required: </li></ul><ul><ul><li>INFO method extension to the base protocol in addition to others </li></ul></ul><ul><ul><ul><li>Session initiation and teardown is not enough </li></ul></ul></ul><ul><ul><ul><li>Mid-Call events </li></ul></ul></ul><ul><ul><ul><li>More complex services enabled </li></ul></ul></ul><ul><ul><li>MIME Type addition </li></ul></ul><ul><ul><ul><li>Standard method of encapsulating legacy signaling </li></ul></ul></ul><ul><ul><ul><li>Simplifies Inter-working: </li></ul></ul></ul><ul><ul><ul><ul><li>Local variant </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Interconnect variant (LCD) </li></ul></ul></ul></ul><ul><ul><li>ISUP to SIP Mapping </li></ul></ul>
    20. 20. SIP–T status <ul><li>Work on SIP-T was initiated by the International SoftSwitch Consortium (ISC) in early 1999. </li></ul><ul><li>SIP-T is still a work in progress. The ISC is continuing to develop profiles for SIP and telephony interworking. </li></ul>
    21. 21. H.323 Overview <ul><li>Packet-based multi-media communications system </li></ul><ul><li>It includes several protocols </li></ul><ul><ul><li>H.225.0 RAS (registration, admission, status …) </li></ul></ul><ul><ul><li>H.225.0 Call Signalling </li></ul></ul><ul><ul><li>H.245 Logical channel signalling and media control </li></ul></ul><ul><ul><li>RFC 1889 RTP/RTCP for media transport </li></ul></ul><ul><ul><li>H.450.x Supplementary services </li></ul></ul><ul><ul><li>H.225.0 Annex G Inter-domain registration and billing information exchange </li></ul></ul><ul><li>The original VoIP protocol suite </li></ul><ul><li>Whole System Architecture </li></ul><ul><ul><li>Provides Interoperability </li></ul></ul><ul><ul><li>Transport independence </li></ul></ul><ul><ul><li>Platform and application independence </li></ul></ul><ul><ul><li>Multipoint support </li></ul></ul><ul><li>Primarily used in corporate networks </li></ul>
    22. 22. H.323 overview continued <ul><li>Comprised of several protocols: </li></ul>System Control User Interface Data Video Audio Lower Layers Vary IP UDP or TCP UDP RTP/RTCP Call Control RAS H.245 Control H.225 T.120 H.261 H.263 G.711 G.722 G.723 G.728 G.729 AAL5 ATM
    23. 23. H.323 elements and entities <ul><li>Endpoints </li></ul><ul><li>can make or receive calls </li></ul><ul><li>Realized by terminals and logically present in Gateways </li></ul><ul><li>Gatekeeper </li></ul><ul><li>address translation (IP, telephone) </li></ul><ul><li>admission control </li></ul><ul><li>cannot generate or terminate calls </li></ul><ul><li>Gateway </li></ul><ul><li>Interworking with </li></ul><ul><ul><li>other multimedia terminals </li></ul></ul><ul><ul><li>GSTN </li></ul></ul><ul><li>Multipoint Control Unit (MCU) </li></ul><ul><li>Support for multipoint conferences </li></ul><ul><li>Always contains a MC </li></ul><ul><li>Optionally contains an MP </li></ul><ul><li>Terminals </li></ul><ul><li>PCs, IP phones, set-top boxes </li></ul><ul><ul><li>Audio </li></ul></ul><ul><ul><li>Video (optional) </li></ul></ul><ul><ul><li>Data (optional) </li></ul></ul>Gatekeeper MCU Gateway
    24. 24. H.323 current status <ul><li>H.323 version 4 </li></ul><ul><ul><li>Includes many major changes </li></ul></ul><ul><ul><li>A significant number of contributions from Nortel Networks </li></ul></ul><ul><ul><li>Approved in November 2000 </li></ul></ul><ul><li>H.245 and H.225.0 also updated </li></ul><ul><li>Currently working on version 5. No release date specified. </li></ul>
    25. 25. 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 <ul><li>Rapidly growing industry momentum, at system and device level </li></ul><ul><li>Growing interest in SIP-Phones and soft clients, products appearing </li></ul><ul><li>Established now, primarily system level </li></ul><ul><li>Few if any H.323-base telephones </li></ul><ul><li>End-user primarily driven by Siemens, Microsoft (NetMeeting), Intel </li></ul>Industry acceptance <ul><li>No real end-device features std, yet </li></ul><ul><li>Many options for advanced telephony features (need to make specific choices) </li></ul><ul><li>Astounding progress, velocity </li></ul><ul><li>H.450.x series provides minimal feature set only, pure peer approach </li></ul><ul><li>Adding ( mixed peer/stimulus approach soon poor architecture) </li></ul><ul><li>Slow moving </li></ul>Status w.r.t. end device <ul><li>Modular, simplistic design </li></ul><ul><li>Easily extended & updated </li></ul><ul><li>Based on Web principals (“Internet-friendly”) </li></ul><ul><li>Readily extensible beyond telephony </li></ul><ul><li>Complex, monolithic design </li></ul><ul><li>Difficult to extend & update </li></ul><ul><li>Based on H.320 conferencing and ISDN Q.931 legacy (“Bell headed”) </li></ul><ul><li>Limited potential beyond telephony </li></ul><ul><li>Some QoS built in… CODEC types specified </li></ul><ul><li>Higher degree of interoperability </li></ul>Properties <ul><li>IETF SIP, MMusic, ... </li></ul><ul><li>ITU-T SG-16 </li></ul>Stds Body SIP H.323
    26. 26. For More Information <ul><li>IETF: </li></ul><ul><ul><li>IETF home page </li></ul></ul><ul><ul><ul><li>http://www. ietf .org/ </li></ul></ul></ul><ul><ul><li>Internet-draft search engine </li></ul></ul><ul><ul><ul><li>http://search. ietf .org/search/brokers/internet-drafts/query.html </li></ul></ul></ul><ul><ul><li>RFC search engine </li></ul></ul><ul><ul><ul><li>http://www. rfc -editor.org/ rfcsearch .html </li></ul></ul></ul><ul><ul><li>Megaco WG charter </li></ul></ul><ul><ul><ul><li>http:// ietf .org/html.charters/ megaco -charter.html </li></ul></ul></ul><ul><ul><li>Megaco documents repository </li></ul></ul><ul><ul><ul><li>ftp://standards. nortelnetworks .com/ megaco / </li></ul></ul></ul><ul><ul><ul><li>ftp://standards. nortelnetworks .com/ megaco /docs/latest/ </li></ul></ul></ul><ul><li>ITU: </li></ul><ul><ul><li>ITU home page </li></ul></ul><ul><ul><ul><li>http://www. itu . int /ITU-T/index.html </li></ul></ul></ul><ul><ul><li>SG-16 document repository (H.323, H.248) </li></ul></ul><ul><ul><ul><li>ftp://standard. pictel .com/ avc -site </li></ul></ul></ul><ul><ul><li>Most Megaco/H.248 related documents should also be available through Megaco WG, above </li></ul></ul>
    27. 27. Thank You!

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