Evan Roggenkamp VoIP/IP Telephony

 Designed for ISDN networks originally  Tuned to work over TCP/IP  Protocol Suite Built With: (some of them)  H. 225 – Handles call setup/teardown and Q. 931 Operations  H. 225 RAS (registration & admission status) – Handles gatekeeper signaling  H. 245 – Feature Negotiation  H. 261/H. 263 – Video Conferencing  H. 450 – Supplementary services (Hold, transfer)  T. 120 – Data Transfer, Application Sharing

 Reasons to use H.323  Widely supported – interoperable (Cisco Default)  Many call routing and manipulation options  Supports, voice, video, data conferencing  Supports fractional PRI support  Supports Caller-ID support on FXO or T1 Cards  PRI Call Preservations  Non-facility associated signaling support (allows you to pull one signaling channel for multiple channels of data)  H. 323 Gatekeeper

 Call Flow Process:  Call comes in from the PSTN. Enters the H. 323 Gateway. Send it to call manager.  CCM & H. 323 Gateway exchange H. 225 setup messages  CCM & H. 323 Gateway exchange H. 245 feature negotiation  Once the call has been set up and the features negotiated, the Call Manager rings the phone using SCCP.  RTP Streams sent between the PSTN, H. 323, & to the phone. It does not go through the call manager anymore.  When the line hangs up a SCCP message is sent from the phone to CCM, and a H. 225 teardown is sent from there to the H.323 Gateway effectively ending the process.  See VISIO  *Fast start combines H. 225 and H. 245 in one process. This is the default on cisco routers.

 VOIP  G. 729 Codec (6729R8)  VAD Enabled (bandwidth preservation) – generally disabled: hardware intensive)  DTMF Relay Disabled  Preference 0 (Failover, duplicate dial- peers pointing to same destination)  Audio = DSCP EF Signaling/DSCP AF31 (QoS)  Huntstop Disabled (keeps hunting)  RSVP = Best Effort  Fax Relay Disabled  Playout Delay = 40ms (de-jitter buffer)  POTS  DID is disabled (external internal)  Preference 0  Digit strip enabled (strips explicitly defined numbers i.e. outside line)  Register w/gatekeeper  Huntstop Disabled

 H. 323 Components  H. 323 Terminal – must run a full version of the H. 323 protocol suite  Cisco IP Phone is not a true H. 323 Terminal “H. 323 compliant”  H. 323 Gateway – transition and communicate from to a H. 323 network to a non H. 323 network or a different H. 323 network.  Gatekeeper has multiple functions  Are not required for smaller establishments (2 – 3 sites)  Bandwidth control  PSTN re-direction (failover/quality of service)  Management of your entire network  Address translation  Multipoint Control Unit  Device that handles primarily conference calls.  Mixes multiple signals and send them out a single stream

 Without a Gatekeeper, a call is made and H. 225 negotiates the setup process over the WAN or the PSTN. Once the call is negotiated, H. 245 negotiates the call features. Once successful, RTP becomes active and voice travels between the phones.  Gatekeeper can be a Cisco router, a Microsoft IIS Server, a free open-source PBX application, or many other devices.  Before any calls are made, the Gateway is preconfigured to register with the Gatekeeper: Registration Request (RRQ) The gatekeeper will reply with Registration Confirmed (RCF) Errors will produce a RRJ.  A call goes into the Gateway from extension 4401 and the Dial Peer in the gateway says to consult the Gatekeeper. This is an Admission Request message (ARQ). If the Gatekeeper ok’s the Request, it sends a Admission Confirm message (ACF) back to the Gateway. All of these things (RRQ/RCF; ARQ/ACF) is sent using H RAS. (This is what is used to communicate with a Gatekeeper) The gateway will then send the Gateway the IP address of the router it needs to set up the requested call.  Now that the Gateway of the originating call knows the IP address of the remote Router it needs to query to set up a call to extension 4402, H. 225 comes into play again and asks the remote Gateway permission to set up a call. The Gateway does not know, so it asks the Gatekeeper (ARQ) if it is okay to set up the call. If it does (ACF) the remote Gateway accepts the request for connect. The call is considered set up and H. 245 comes into play between the two Gateways to negotiate features. The Gatekeeper keeps track of the bandwidth that this call has consumed in the WAN cloud.  Once the call has ended the Gateways send a Disconnect Request (DRQ) to the Gatekeeper, who will then reply with a Disconnect Confirmed (DCF). The call is disconnected and the Gatekeeper recalculates available WAN link bandwidth.

 users/h323forum/papers/h.323_ white_paper.pdf users/h323forum/papers/h.323_ white_paper.pdf  users/packetizer/papers/h323/h3 23_protocol_overview.pdf users/packetizer/papers/h323/h3 23_protocol_overview.pdf  ip/tutorials/h323.pdf ip/tutorials/h323.pdf  training-videos training-videos