H.323 Cheatsheet

These notes taken from the Nortel VoIP Technologies and CVoice 6.0 class book

Well known ports

TCP/UDP 1718 - Gatekeeper discovery
TCP/UDP 1719 - Reg w/ gatekeeper
TCP/UDP 1720 - H.225 destination (h.323 host call)

H.323 suite

ITU-T approved 1996
P2P prpto where end devices initiate sessions
Widely used with GWs gatekeepers, 3rd party H323 client
IP address is NEEDED to make CM aware
H323 never registered with CUCM onoy IP addr avail to confirm comm is possible

H.245 control signaling
H.225 call signaling
H.225 RAS Control (registration administration services)

Video

H261/H263 Codecs

Components

media gateway - translates media to different types of networks - converts one (signalling) media stream to another
H.323 gw - translates media between different VoIP networks. transforms audio (media) recieved into a format that the data net can use. CODECs. Adjusts timing and protocols. Maps dest tel# to dest gw ip addr(?).
Call Servers - Handles H.323 call control
gatekeeper - call control, media access, bw mgmt between endpoints, address translation, admissions control, zone control, coordinates access to other servers, manages call routing, maps dest tel nums to their end point IP addrs.
MCUs (Multipoint Control Units) - conf call units. for centralized conf - receives and regenerates audio streams. For decentralized conf - coordinates conf, but audio stream goes direct from one phone to others.
IP terminals and clients - endpoints.
IP backbone network

Cisco capable devices

VG224
2600XM, 2800
3700, 3800

Protocols

H.225 - Call Signaling. Terminal to GW signaling (Registration, Administration, and Status (RAS))
H.235 - authentication, privacy, and integrity
H.245 - Control Signaling. negotiates CODECS, capabilities, opening /closing logical channels for media streams. flow contorl, general indications.

Basic Conversation

Term endpt A	GK	Term endpt B
---ARQ-->
<--ACF---
--Setup->		--Setup-->
<-Call Proceeding--		<-Call Proceeding--
		<--ARQ---
		--ACF/ARJ->
<-Alerting--		<-Alerting--
<-Connect--		<-Connect--

<-H.245 Capabil Exch->		<-H.245 Capabil Exch->
--H.245 Open Log Chan->		--H.245 Open Log Chan->
--H.245 Open Log Chan Ack->		--H.245 Open Log Chan Ack->

<------RTP/RTCP------>

H.225 Setup
H.225 POTS/PSTN Call Setup
H.245 Cap Exchange
H.245 Open Logical chna
H.245 Open Log Chan Ack

Fast Connect Call Setup
H.225/H.245 Setup (combine Q.931/H.225 call signaling and H.245 cap/log channel exchange)
H.225/H.245 Connect

Design Considerations

Consider using H.323 enabled firewalls with proxy servers due to dynamic media sockets.
Be conscious of NAT and VPNs.
Make sure H323 version is the same. Backward compatability not always clean. Can mess up gatekeepers. Also transport proto tcp (v1) and udp (v2).
RTP, RTCP, H.225 all have encoding and interop problems with diff versions and diff vendors.

Gatekeeper zones

Only one gatekeeper per zone. Only run on primary sig svr
Gatekeeper in diff zones use IP Multicast Proto to exchange peer routing info and to set up IP virt trunk calls between phones in diff zones
IGMP (IDs members of multicast groups per subnet and provides mechanisms tby which queriers and hosts can join and leave multicast groups) needs to be configured on l2/l3 devices in net
IP multicast need to be routed/switched correctly. Something like DVMRP and/or PIM need to be configured also.

Cisco Notes

H.323 Gateway can register by H.323 Gatekeeper.

Advantages of H.323 gateways

dial plans can be (must be) configured on gateway
translations can be defined per gateway
regional conditions can be met within multisite deployments
call routing config can be more specific than on CM
no need for extra SRST call routing config
no dependncy on CM version
more voice interface types supported
ISDN NFAS is supported
Fax support is advanced
call preservation was enhanced for PRI call since IOS 12.4(9)T. (e.g. better than MGCP
Call Admission Control

H.323 Network COmponents

Cisco Unified Border Element (Session Border Controller)
Gatekeeper
Gateways
MCU (Multiple Control Unit) - included in MeetingPlace
H.323 Terminal
H.324 Terminal (POTS)
H.320 Terminal (ISDN)

MCUs

3 types of conferences

centralized - Multipoint processor (MP) mixes and switches audio, video and data, and talks directly to endpoints
distributed - endponts multicast their audio, video and data to all participants in conference. mixing happens at endpoints

hybrid (centralized and distributed) - can occur where streams (control channel) managed by MC, but one stream relies on multicast for transmission

ad-hoc - 2 endpoints convert their relationship to point-to-point conference. other endpoints become part of conference by accepting invitation from current participant, or endpoint can request to join conference directly

Distributed Deployment Model - Gatekeeper should be used...

Relationships

GW to GW

GW to Gatekeeper

Gatekeeper to gatekeeper