The Passport 4400 supports the ISDN basic rate interface (BRI). There are two types of ISDN interface modules, one supporting an ISDN S/T interface, and the other supporting an ISDN U interface. BRI supports two 64 kb/s bearer (B) channels and one 16 kb/s data (D) channel, referred to as 2B+D.
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Note: The Passport 4400 currently supports only one B-channel on the ISDN WAN interface module. |
The D-channel can be used to carry setup and user packet data across the network. For the Passport 4400, the D-channel will be reserved for ISDN-related call setup messages and other out-of-band signaling only. No user data is transmitted over the D-channel. Once the link to the WAN is established over the D-channel, user data traffic is carried over the B-channel.
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