Dolby Laboratories DP503 - Manual (Page 86)

E-2
Inverse Multiplexing
Inverse Multiplexing is the process of distributing a high bandwidth
bitstream (like the default Dolby Fax format which operates at 256 kbps
using Dolby AC-2) onto multiple ISDN BRI-channels. The default Dolby
Fax format requires the ISDN unit to split up the 256 kbps bitstream into
four separate calls, each at 64 kbps. Another function of inverse
multiplexing is to synchronize the four calls as they travel over the ISDN
network. In some situations, one of the calls may take a longer path,
depending on network traffic, which then becomes delayed in relation to the
other calls; the worst case would be one of the calls being routed via
satellite which could delay the call by up to 500 msec. The ISDN unit also
provides buffering for the incoming bitstream so that it can re-synchronizes
all of the individual calls in order to reconstruct the original 256 kbps
bitstream.
Several different inverse multiplexing methods are available in the DP503,
as shown in the following list, and are discussed individually below.
AIM STATIC 64
AIM STATIC 56
BONDING-1 64
BONDING-1 56
AIM DELTA 56
(1 CHNL 56)
(1 CHNL 64)
AIM STATIC 64
AIM (Ascend Inverse Multiplexing) is Ascend's proprietary inverse
multiplexing method which calculates the inter-channel delay and then
stores that delay value in a buffer. Once the call is connected, the delay
value remains constant, i.e., “static.” The 64 kbps reference refers to
its use on 64 kbps ISDN B-channels.
AIM STATIC 56
This format is identical to AIM STATIC 64 and is used when
connecting to either 56 kbps ISDN or Switched 56 lines.
BONDING-1 64
BONDING refers to Bandwidth On Demand Interoperability Group,
which is an inverse multiplexing standard that manufacturers of ISDN
units have agreed to support to maintain compatibility. This version of
inverse multiplexing is basically identical to AIM STATIC, but is used
with the Dolby Fax system when connecting to locations that use an
ISDN unit that is not manufactured by Ascend. In addition to Ascend,
ADtran, Promptus and Motorola are some of the companies that
support BONDING.
MAIN