
Configuring Dial Services
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117353-B Rev. 00
Selective PRI Service
Your ISDN service provider may offer a service option with only a fixed number
of B channels out of the full complement of B channels for PRI. This subset of
channels is offered at an economical rate.
The ISDN service provider limits the number of channels by keeping the
unavailable channels busy. Consequently, the router can use only what is
available.
If you select this option, you must select only those channels available for
communication. For example, if the provider offers channels B1 through B6, you
configure only channels 1 through 6. You should not select all the B channels;
your configuration should match your service.
PRI Multirate
PRI multirate enables you to group B channels in multiples of 64 Kb/s to
dynamically allocate bandwidth on a call-by-call basis. Depending on how many
B channels you combine, the bandwidth can range from 128 Kb/s to 1472 Kb/s.
This allows you to choose the most suitable bandwidth for an application.
Applications such as dial backup and video conferences benefit from the
flexibility of multirate service. These applications require more than one
B channel but not the full complement of B channels for PRI. Also, ISDN service
providers offer multirate service at lower tariffs than other ISDN services.
Multirate is especially useful when frame relay is used across an ISDN line. You
can group multirate dial lines to provide backup connections if the primary
connection fails.
Multirate service is available for all three dial services on the ASN, using only the
Dual MCT1 Net Module, and on the BLN and BCN, using only the Dual or Single
Port MCT1 and QMCT1 Link Modules. The following switches for North
America and Canada support multirate service:
• AT&T 5ESS
• AT&T 4ESS
•DMS-100
For these switches, you can group from 2 to 23 B channels, supplying bandwidth
from 128 Kb/s to 1472 Kb/s.
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