Chapter 1: Understanding ISDN and the Express XL/XLT
Bridging
In Bridge Mode, the Express XL/XLT can communicate with two remote net- works at a time. The destination is dialed by setting up a Connection List pro- file and choosing Dial on the Dial menu. See Configuration/Connection List on page 63 for instructions on setting up a Connection List profile.
During a two B-channel PPP Multilink call, the Express XLT automatically drops one B-channel and provides it to the POTS port when a telephone call is placed or answered. When a POTS telephone call terminates, the Express XL redials the second B-channel and supplies the bandwidth back to the LAN connection. Since other bandwidth management features are disabled in the factory default configuration, the dialed links remain active until the Hang-upcommand is entered from the Dial menu, terminating the session with the se- lected remote network.
The Connection List described in the next section may be used to automate di- aling and to store additional information specific to the remote site being di- aled (phone numbers, number of B-channels to dial, authentication information, Caller ID, etc.). In addition, Demand Dialing may be enabled to allow idle links to disconnect when not being used to reduce line charges.
Simple Demand Bridging may be configured by enabling the Idle Time-Out parameter under the Configuration/ Connection List [1]/Bandwidth/On De- mand option on the Connection List. Setting this parameter to a non-zero val- ue allows a bridge connection to disconnect after the specified number of seconds with no traffic crossing the ISDN link. Bandwidth can be controlled using the Express XL/XLT’s advanced filtering capability. When new traffic needs to be transmitted, the Express XL/XLT will run each packet through its Demand filters defined for each Connection List profile. If a packet can pass through the filter, then the numbers for that profile are dialed. In addition, when both B-channels are selected for use, the link may be configured to add/ remove the second B-channel based on the amount of traffic crossing the link. The bridged connection is terminated when the Hang-upoption is selected from the Dial menu, but will redial if the demand filter condition is met.
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