Specifications

2-28

Reference Guide

Model No.

Running Head

ISDN Primary Rate Interface (PRI) Server Applications

2.6.5 Data Backup and Bandwidth on Demand

This integrated access system with a PRI server is used to back up data networks in the event

of a circuit outage. In the example shown in Figure 2-17, an IAD is used to connect a router

to a leased line circuit. The PBX is using the IAD equipped with a PRI server card to connect

to the PRI circuit. In normal operation, both the voice traffic and the data traffic simply pass

through the IAD. In the event that the leased line circuit is dropped the router will sense the

loss of data and attempt to dial bandwidth via its second line. This second port can be

configured on the IAD to accept dial commands using the V.25bis, or to dial a pre-determined

number when the IAD senses DTR. When the router senses that a failure has occurred, it will

request bandwidth from the IAD. If the PRI does not have enough bandwidth to satisfy the

router’s request, the IAD rejects the call. The router will then request another call with smaller

bandwidth requirements and will monitor the original leased line for presence of data. When

the router detects that the leased line is back in operation, it will switch its transmission path

back to its original state, and drop the ISDN connection.

This configuration is utilized to provide bandwidth-on-demand during peak utilization times

such as nightly backups. With this application, the PBX utilizes the PRI bandwidth on a

call-by-call basis during the day, and the router utilizes the leased line. At a pre-determined

time-of-day, the router would request all or the majority of the PRI bandwidth. The router

utilizes both the leased circuit and the ISDN circuit for a set period of time. For example, the

PRI line would be used during the day to carry the voice calls, at night the PRI line would be

used to increase the bandwidth available for the nightly computer systems backup. The router

routes packets over both the leased line and the PRI line until the backup was complete. At

that time, it would disconnect the PRI call.

Figure 2-17. IAD using a PRI Server Card for Data Backup

T1/E1

Backbone

network

T1/E1

Router

T1/E1

V.25bis/DTR

Dialing

PRI

IAD

PBX

IAD

PBX

ISDN

Network

V.25bis/DTR

Dialing