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Development of SIP-H.323 Gateway Project

Explore the development of a SIP-H.323 Gateway Project, addressing protocol conversion, product comparisons, H.323 and SIP insights, and protocol flows. Learn about the motivation, large deployment base of H.323 terminals, and the future of SIP and H.323.

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Development of SIP-H.323 Gateway Project

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  1. Development of SIP-H.323 Gateway Project Ruston Hutchens 20th APAN Meeting, Taipei, Taiwan Tuesday 23rd August 2005 v2

  2. SIP-H.323 Gateway project • Motivation • Large deployment base of H.323 terminals (over 2.9 million calls placed over the AARNet H.323 VoIP network in 2004) • Will SIP replace H.323? Will H.323 die instantly? Will these protocols run in parallel? • As a pre-requisite to using SIP, we need either an endpoint that has a SIP protocol stack, or • a means to translate the SIP messages to the protocol that is natively supported

  3. SIP and H.323 comparisons Taken from www.sipcenter.com

  4. SIP and H.323 comparisons Taken from www.sipcenter.com

  5. SIP and H.323 comparisons Taken from www.sipcenter.com

  6. Ways to achieve protocol conversion We have used three products to convert SIP to H.323 and vice-versa Asterisk – Open source PBX (http://www.asterisk.org/) Cisco Multiservice IP-to-IP Gateway (http://www.cisco.com) “Back to Back” gateway (AS5300 with 2xE1) REMEMBER: We’re only converting the call signalling, RTP is the same. (media transcoding is not required) *Other products becoming available eg: Yate http://yate.null.ro/pmwiki/ - Yet another Telephony engine

  7. H.323 protocol stack – see, it’s confusing Source: www.protocols.com

  8. H.323 protocol flow – with gatekeeper Source: www.protocols.com

  9. H.225 Protocol • H.225.0 is a standard which covers narrow-band visual telephone services defined in H.200/AV.120-Series Recommendations. It specifically deals with those situations where the transmission path includes one or more packet based networks. • H.225.0 describes how audio, video, data and control information on a packet based network can be managed to provide conversational services in H.323 equipment. • H.225 messages include • ALERTINGCALL PROCEEDINGCONNECTCONNECT KNOWLEDGEPROGRESSSETUPSETUP ACKNOWLEDGE Source: www.protocols.com

  10. H.245 Protocol • H.245 is line transmission of non-telephone signals. It includes receiving and transmitting capabilities as well as mode preference from the receiving end, logical channel signalling, and Control and Indication. Acknowledged signalling procedures are specified to ensure reliable audiovisual and data communication. • H.245 messages are in ASN.1 syntax. They consist of an exchange of messages. MultimediaSystemControlMessage message types can be defined as request, response, command and indication messages. The following lists SOME of the additional message sets are available: • Master Slave Determination messages • Terminal capability messages • Logical channel signalling messages • Round Trip Delay messages • Communication Mode Messages • TerminalID • Commands and Indications Source: www.protocols.com

  11. RAS Protocol • The Registration, Admission and Status (RAS) channel is used to carry messages used in the gatekeeper discovery and endpoint registration processes which associate an endpoint's alias address with its call signalling channel transport address. The RAS channel is an unreliable channel. Since the RAS messages are transmitted on an unreliable channel, H.225.0 recommends time-outs and retry counts for various messages. An endpoint or gatekeeper which cannot respond to a request within the specified timeout may use the Request in Progress (RIP) message to indicate that it is still processing the request. An endpoint or gatekeeper receiving the RIP resets its timeout timer and retry counter. • Source: www.protocols.com

  12. SIP UA INVITE (with SDP) ACK INVITE With auth ACK 200 OK 100 Trying 100 Trying 180 Ringing 407 Auth Req 200 OK (with SDP) BYE RTP SIP Protocol Flow

  13. SIP UA IP-IP Gateway H.323 ACK INVITE (with sdp) ACK Open logical channel inc TCS 100 Trying Call Proceeding 200 OK (with SDP) 180 Ringing Open logical channel BYE Close logical channel Alerting Connecting Close logical channel ACK RTP SIP to H.323 Protocol Flow

  14. H.323 Endpoint IP-IP Gateway SIP UA Setup INVITE (no sdp) ACK with SDP 100 Trying 180 Ringing BYE Call Proceeding Close logical channel Alerting Connecting 200 OK (with SDP) Term capability set Master/slave det. Open logical channel ACK Terminal Cap Set + ACK, MS ACK Close logical channel ACK Term capability ACK Master/slave ACK Open logical channel RTP H.323 to SIP Protocol Flow – note delayed SDP

  15. Cisco • SIP-H.323 and H.323-SIP support was introduced in IOS release 12.3(11)T • Supports Voice calls. Video is supported for some calls • Not a big performance impact, as no media transcoding is involved. At worst case, just copy the media stream from input buffer to output buffer • Costs money (2 cisco routers, 1or 2 ‘expensive’ software license)

  16. Back to back gateway • Achieved through the use of two E1 ports on a gateway • ISDN cross-over cable is connected between the two • Requires 2x media encode-decode • Increases latency • Relatively easy to setup

  17. Asterisk • Asterisk “likes” media to flow-through, rather than flow-around. • Supports Voice and Video • Asterisk must know about the RTP protocol before it will allow calls to be setup • H.323 is not a supported channel type “out of the box”. You need to compile a separate channel driver – version-ing IS a problem • Free

  18. SIP-H.323 Gateway Network Architecture (Cisco IP-IP Gateway)

  19. SIP-H.323 Gateway Network Architecture (Asterisk Server)

  20. Codec Negotiation • Currently both IP-IP gateway and Asterisk products have issues selecting the correct codec • Back to back gateway does not have this issue, as it converts to ISDN first • IP-IP Gateway only “supports” H.323 fast-start

  21. Dial plan issues • Desire for “A” party not required to be aware of “B” party’s technology • Other option to have an “access code” – this requires either the user to know the B party’s technology type, or the SIP proxy or gatekeeper to insert a routing prefix

  22. Product comparisons • Asterisk: Was never designed to do what we are asking of it. It was designed as a soft-PABX, with small-medium number of telephones attached, and small numbers of trunk connections • H.323 support is an “add on”, and is not supported all that well. • Back-to-back is not elegant, with some latency introduced, and possible voice quality degradation

  23. Product Comparisons • Cisco IP-IP Gateway/Gatekeeper • Was originally designed as a H.323 – H.323 product. • Has very good H.323 support • Was not designed as a softswitch, so does not support large “routing tables”. Routing is achieved by adding dial-peers. Each dial peer requires approximately 6kb of memory. • While this allows 5000 theoretical dial peers on an “average” router, this becomes unmanageable

  24. SIP and H.323 Feature compatibility • Obviously, some features exist only in one protocol, but not in the other. Regardless of how good the protocol converter is, if features don’t exist in the protocol standard, they can’t be supported) • Examples include: • Security • Presence • Support for different types of sessions (IM)

  25. Support • Back to back gateway can use almost any device that has 2 or more E1/T1 ports, and supports sip calls and H.323 calls. In our case, we used a Cisco AS5300, which is supported by Cisco • Cisco IP-IP Gateway is supported by Cisco • Asterisk support can be purchased from the creator, Digium Inc, as well as other 3rd parties.

  26. Acknowledgements • We wish to acknowledge the assistance of Cisco Systems with assistance configuring and fault-finding the IP-IP gateway/gatekeeper • We wish to acknowledge the assistance of Broadreach Services +61 2 8270 1000 for some assistance configuring the Asterisk product

  27. Ethereal: Voip call analysis

  28. Opportunities for use within the APAN community • This could be used to peer different country’s dissimilar Voice (and Video) over IP networks. Some results for Research Networks, and their members could be: • Cheaper telephone calls • Easier video conferencing for users • Better collaboration • If you’re interested, please contact the author, or attend the APAN SIP-H.323 working group meeting On Friday, at 14:00 in room H

  29. www.aarnet.edu.au

  30. IP to IP Gateway/Gatekeeper – Other uses • What are the uses? • Peering two H.323 networks • Network demarcation (hide internals of network) • Dial plan translation • CDR billing record collection point

  31. IP to IP Gateway/Gatekeeper – other uses • What are the uses? (cont) • Gateway to Internet for IP Phones • Can act as a “firewall” for IP phones Eg. All calls to Internet destinations are made through the IP-IP gateway, so the phone does not need to be visible from the Internet • Present a single IP address to the outside world • Demarcation point for collecting CDRs from phones

  32. IP-IP International Gateway/Gatekeeper GDS peering configuration

  33. www.aarnet.edu.au

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