Using Bandwidth Limits in Your Network
As discussed earlier, one of the most useful features of a gatekeeper is bandwidth
control—being able to efficiently utilize your WAN bandwidth while leaving
www.syngress.com
While the latter format may seem appealing, since each of your
users will have a unique e-mail address, in practice it is rarely used.
Commonly E.164 addressing is used in H.323 networks. One reason is
people are used to dialing E.164 numbers for voice and video calls, not
e-mail addresses. Another reason is E.164 addressing typically leads to a
more organized, hierarchical addressing system. Most companies
already have a telephone addressing system in place. You can configure
your H.323 similarly to your existing dialing plan. For example if your
company uses four-digit telephone extensions, your existing and H.323
dialing plan might look like that shown in Table 5.2.
Table 5.2 Sample H.323 Dialing Plan
H.323 Configured Meaning of How the Call
Dial Pattern Dial Pattern Is Routed
9* Dial 9 and any The call is directed to the
number of digits PSTN (outside call).
5…. Dial 5 and any The five-digit number is
four digits routed to the Chicago office.
4…. Dial 4 and any The five-digit number is
four digits routed to the Dallas office.
3…. Dial 3 and any The five-digit number is
four digits routed to the Atlanta office.
8* Dial 8 and any The call is a video confernumber
of digits ence call and routed to
a video gateway.
Using this plan, you would probably install gateways that use T1
lines to access the PSTN via a local carrier. Calls beginning with “9”
would get routed to these gateways. You might use gateways that
create Voice over IP (VoIP) sessions for calls to the Chicago, Dallas, or
Atlanta offices (using the internal data network). Calls beginning with
“3, 4, or 5” would get routed to these gateways. You might install videoconferencing
gateways that could complete videoconferencing calls.
Calls beginning with “8” would get routed to these gateways.
Voice and Video Gatekeeper Design • Chapter 5 143
sufficient bandwidth for other applications. Since the gatekeeper can act as a
“bandwidth policeman,” it can save money by allowing calls to use internal WAN
circuits rather than the traditional PSTN.Yet it is also intelligent enough to limit
the number of calls based on the bandwidth limits you configure.
There are several ways to limit bandwidth utilization in your network. For
example, the gatekeeper can limit the bandwidth used by any given session (voice
or video call). If you are not yet prepared to support video (or any other highbandwidth)
calls in your network, you could limit the bandwidth of a session to
the bandwidth used by a voice call.Thus, if you use g.711 CODECs in your network,
calls use approximately 80 Kbps (64 Kbps of data plus some IP overhead).
You could configure the following command to limit the bandwidth used by any
call to 80 Kbps:
bandwidth session default 80
To limit the total amount of H.323 traffic—both within a zone and to and
from that zone from other zones—use the total keyword.This command limits
the total H.323 traffic for all zones to 1 Mbps:
bandwidth total default 1000
To limit the bandwidth to and from a particular zone, use the interzone
keyword. Meanwhile, to limit bandwidth into and out of the sales zone to
512 Kbps, use:
bandwidth interzone zone sales 512