5.6 Optional Configurations
5.6.1 B-channel aggregation

It is possible to fine-tune configuration of a router to provide for more flexible and efficient connectivity. As shown in the Figure, B-channel aggregation is a mechanism for combining two or more B channels into a single ISDN pipe for the equivalent of 128 Kbps or greater bandwidth. You must use Multilink PPP (MLP) to get the full bandwidth-otherwise, you have two separate 64-Kbps channels. MLP lets you load balance across the two B channels.

Bandwidth on demand (BOD) provides a dynamic method of enabling you to use only the amount of bandwidth that is required to do the job. BOD permits the decision to obtain more bandwidth to be deferred until it's really needed.

Cisco IOS software offers two methods of combining the B channels to obtain BOD:

  • Use a generic BOD, a Cisco proprietary implementation of BOD, which is based on a proprietary algorithm available in all systems that are running Cisco IOS Release 10.0 and later.

  • Use MLP to allocate additional bandwidth when needed.

Lab Activity 
  Given a Central site Cisco-IOS router with ISDN PRI capability and branch office site Cisco-IOS routers with ISDN BRI capability, configure all routers so that you can place an ISDN call between your three company sites.