Hayes Microcomputer Products PC Card - Manual (Page 7)

DIVA T/A PC Card Reference Guide 7
D-Channel
The primary function of the D-channel is to carry common-channel
signaling information to manage and control circuit-switched calls on
B-channels.
The D-channel can also be used for packet-switching or low-speed
telemetry when it is not involved in control signaling. Message
signaling takes priority over data packet-switching.
The D-channel functions at 16 Kbps for Basic Rate Interface or 64
Kbps for Primary Rate Interface. The speed is dependent on the end-
user’s interface.
H-Channel
The H-channel is used for high-speed user data traffic at bit rates
higher than 64Kbps. Examples of services which require these higher
rates are: fast facsimile, teleconferencing, and video. An H-channel
user can subdivide the channel using TDM to meet specific
requirements.
Connecting to ISDN - BRI and PRI
There are two types of access interfaces to the ISDN: Basic Rate
Access (also referred to as Basic Rate Interface (BRI)) and Primary
Rate Access (also referred to as Primary Rate Interface (PRI)).
Basic Rate Access
Basic Rate Interface or Access consists of two B-channels operating
at 64 Kbps and one D-channel operating at 16 Kbps. It is also
commonly referred to as 2B+D.
Primary Rate Access
The primary rate interface is designed for users with large capacity
requirements.
There is no single transmission rate defined for primary rate access. In
North America and Japan, for example, primary rate interface is based
upon the T1 rate (defined in detail shortly) of 1.544 Mbps. In Europe,
by comparison, the rate is 2.048 Mbps.