Northern UTA220/UTA220k - Manual (Page 41)

UTA220/UTA220k
4-7
ISDN
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.