Data Backup and Bandwidth on Demand

Zhone Technologies, Inc.	IMACS Product Book, Version 4

Figure 26—IMACS Using SINA for ISDN and Leased Line Traffic

The IMACS with a PRI server is used to back up data networks in the event of a circuit outage. In the example shown in Figure 27, an IMACS is used to connect a router to a leased line circuit. The PBX is using the IMACS 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 IMACS. 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 IMACS to accept dial commands using the V.25bis, or to dial a pre-determined number when the IMACS senses DTR. When the router senses that a failure has occurred, it will request bandwidth from the IMACS. If the PRI does not have enough bandwidth to satisfy the router’s request, the IMACS 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.