In Windows NT 4.0, RAS supports basic multilink capabilities--the combination of multiple physical links into one logical link. Typically, two or more Integrated Services Digital Network (ISDN) lines or
modem links are bundled together for greater bandwidth.
In Windows 2000, BAP and Bandwidth Allocation Control Protocol (BACP) enhance multilink capabilities by dynamically adding or dropping links on demand. BAP is especially valuable to operations that have
carrier charges based on bandwidth utilization.
The PPP Multilink protocol combines the bandwidth of two or more communication lines to create a single virtual connection, providing dynamically available bandwidth based on need. Routing and Remote Access can use PPP Multilink over multiple modems, ISDN, or X.25 connections. Both the client and the remote access server must have the PPP Multilink protocol enabled. Note: As you have
learned in your Windows NT 4.0 studies, in order for callback security to function properly on a multilink connection, both lines must use a single phone number. This is because the Properties dialog box
for callback allows you to enter only a single phone number. It is consider best practice to disable PPP Multilink on servers that have callback security enabled. This issue is most commonly encountered
with BRI ISDN interfaces. BRI ISDN uses two phone links, each with a different phone number, to provide a multilinked 128K connection when joined.
BAP or BACP?
The terms BAP and BACP are sometimes used interchangeably to refer to bandwidth-on-demand functionality. Both protocols are PPP control protocols and work together to provide bandwidth on demand. BAP provides a very efficient mechanism for controlling connection costs while dynamically providing optimum bandwidth. You can enable PPP Multilink and BAP protocols on a server-wide basis on the PPP tab in the Properties dialog box for each remote access server.
You configure BAP settings through remote access policies. Using these policies, you can specify that an extra line will be dropped if link utilization drops below 75 percent for one group and below 25 percent for another group. You will learn more about remote access policies later in this course.
Note: BAP is a PPP control protocol that is used to dynamically add or remove additional links to an MPconnection. BACP is a PPP NCP (Network Control Protocol) that elects a favored peer in case both PPP peers request to add or remove a connection at the same time. For more information about the multilink protocol, go to the Resources page to view RFC 1990. For more information
about BAP/BACP, go to the Resources page to view RFC 2125. The next lesson wraps up this module.