call routing.doc

chapter 7
call routing
this section covers call routing in an H.323 video network using the cisco
gatekeeper and IP/VC equipment. calls are router to and from, many different
devices in a number of different ways. this section cobers the different type
of calls routed and methods used.
this chapter contains the following sesions:
• call routing scenarios.
• incoming PSTN to H.323 call routing
• inbound PSTN call routing in a single zone
• inbound PSTN call routing in multi zone environment
• enter zone call routing using hopoff statements
• enter zone call routing using directory gatekeeper
Call routing scenarios:
there are four types of calls that win be routed in an H.323 network(1)H.323
endpoint to H.323 endpoint using E.164 address, (2)H.323 endpoint to
H.323v endpoint using H323-ID, (3)H.323 endpoint to an H.323 service
(gateway or MCU),(4) incoming PSTN to H.323 endpoint or service. each of
the four routing scenarios is discussed below.
• routing calls between H.323 endpoint is the simplest type of call
routing in an H.323 network. Dialing in a single zone require the
endpoint initiating the call to enter the E.164 address of the endpoint
being called (with in most cases will be a 10 –digit fully qualified
E.164 address, including the zone prefix and 7-digit number of the
endpoint ). if the call is an inter zone call thoinitiator must enter the
zone prefix (if the dial plan is using 10 digit E.164 addresses the zone
prefix is part of the E.164 address) and the E.164 address or the
endpoint being called. using this dial string is similar to dialing outside
ones’ area code in the telephony world (in multi zone networks service
prefixes for MCUs and E.164 addresses should contian the zone
prefix).

• routing calls between H.323 endpoints using H.323-ID requires that
the calling station dial the H.323-id of the video terminal being called.
H323-IDs are only supported for alls from video terminel to video
terminal, or video terminal to video terminal adapter(VTA). when
using a VTA care must be take in addressing as some H.320 units
cannot send alphanumeric strings. in these cases, E.164 address are the
only route table mecchanism. between zones, DNS (domain name
service) may be used to reach the H.323 –ID of an endpoint
registered to a remote gatekeeper. this is done by dialing “H323-
ID@domain” this allows the gatekeepers to resolve the remote zone
destination via DNS.
• routing calls from an H.323 endpoint to a service is also fairly simple.
in a single zone an H.323 endpoint will dial the service prefix,
followed by either the conference ID(for an MCU call), or ISDN
telephone number of the H.320 endpoint. routing inter zone calls to
service is also done using the service prefix, but the service prefix will
now contain the zone prefix for MCUs, and use hopoffs for gateways.
• routing calls from the PSTN to H.323 endpoints or services can use of
four methods: MSN/DID, IVR, TCS4 or by using a default extension.
below each of the four PSTN to H.323 routing methods will be
defined, and then applied to a single zone and multi zone enviroment.
figure 7-1 illustrates a multi zone network with video terminals and services
in each zone. table 7-1 shows the dial strings for the four intra and inter zone
call typer. Below dial strings for the scenarios in figure 7-1 are listed.
1. H.323 endpoint to H.323 endpoint :
intra zone call tsmith to jbank: tsmith dials 4085248071
inter zone call tsmith to jcox: tsmith dials 7207125543
2. H.323 endpoint to H.323 endpoint using H.323-ID:
intra zone call tsmith to jbank: tsmith dials
inter zone call tsmith to jcox: tsmith dials

3. H.323 endpoint to service:
intra zone call tsmith to H.320 system: tsmith dials 91212555212