Northern UTA220/UTA220k B-Channel Data Protocols, D-Channel Signaling Protocols, Layer One, Isdn

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B-Channel Data Protocols

To allow greater flexibility for your DTE, there are three rate adaption protocols available for use on the B-channel: TLink, V.120, and Bonding. These protocols allow your DTE to operate both synchronously and asynchronously, and at a different speed than the B-channel.

•TLink is a Northern Telecom proprietary rate adaption protocol. It supports synchronous and asynchronous rate adaption at a variety of speeds.

•V.120 is a CCITT protocol that supports synchronous and asynchronous rate adaption, and also provides link-layer error control. Although errors on a digital network are more rare than on an analog telephone line, they are possible. V.120 provides an end-to-end protocol for detecting and correcting any such errors. V.120 also performs buffering and can thus support flow control to and from the DTE.

•BONDING is a new protocol standard from the Bandwidth ON Demand INteroperability Group. It combines the bandwidth of several 56 kbps or 64 kbps channels, and can bond from 2 to 31 channels at once, if the channels are available. The high speed data, which must be a multiple of 56 kbps or 64 kbps, comes in on the DTE interface and is split to the various channels. On the opposite end the data is recombined into the original data stream and sent to the DTE interface.

To use a rate adaption protocol, the DCEs (e.g., TAs) at both ends of the link must support it and must be configured to use it. In general, since it is more flexible and supports error control, V.120 should be used for most applications, and thus it is the default protocol in the UTA220.

D-Channel Signaling Protocols

The D-channel conveys signaling information and, optionally, packet-switched data, to the network switch. This data is passed in message blocks defined by the ISDN signaling protocols. These protocols vary somewhat depending on the network switch installed at the telephone company's central office. As mentioned earlier, several de-facto protocol standards, are used for the D-channel signaling between the TA and the switch.

The TA signaling protocols function on three protocol layers.

Each of these layers is described below.

Layer One

The physical layer includes components and interfaces needed to provide a physical communications path. All ISDN switches use the same physical layer protocols for the Basic Rate Interface, which are based on CCITT Recommendation I.430.

UTA220/UTA220k 4-7