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computer over an asynchronous RS232 link and use the AT command set for setup
and control, much like conventional analog modems. Each brand has its own AT
command extension for setting up parameters that are unique to ISDN. In the past,
there were many interoperability problems between different brands of ISDN
terminal adapters. These problems were due mostly to the variety of rate adaptation
protocols that were available in V.110 and V.120 as well as bonding schemes for
the two B channels. The industry has now converged to synchronous PPP protocol
with PPP multilink for linking two B channels.
Some terminal adapter manufactures integrate V.34 (analog modem) capability into
their terminal adapters. This enables customers with a single ISDN line to handle
either ISDN or conventional analog calls by taking advantage of the simultaneous
voice/data capabilities of ISDN services. New technology also enables a terminal
adapter to operate as the digital server side for 56K(X2/56Flex) clients.
Typically, you would like to connect to an ISDN terminal adapter over an RS232
serial interface using asynchronous protocol at rates up to 230.4Kbps. However, the
maximum AS/400 baud rate for asynchronous over RS232 is 115.2Kbps.
Unfortunately, this restricts the maximum byte transfer rate to 11.5k bytes/sec, while
the terminal adapter with multi-linking is capable of 14/16k bytes uncompressed.
Some terminal adapters support synchronous over RS232 at 128Kbps, but AS/400
maximum baud rate for synchronous over RS232 is 64Kbps. The AS/400 is capable
of running asynchronous over V.35 at rates up to 230.4Kbps, but terminal adapter
manufacturers generally do not offer such a configuration. Interface converters that
convert RS232 to V.35 interface could be a reasonable solution for the problem, but
this approach has not evaluated for AS/400. Another possibility is to use terminal
adapters with V.35 interface synchronous protocol at rate of 128Kbps. Although this
class of terminal adapters exists, it does not appear that many offer synchronous
Multilink PPP.
T1/E1
A T1 connection bundles together twenty-four 64Kbps (DS0) time division
multiplexed (TDM) channels over 4-wire copper circuit. This creates a total
bandwidth of 1.544Mbps. An E1 circuit in Europe and other parts of the world
bundles together thirty-two 64Kbps channels for a total of 2.048Mbps.
TDM allows multiple users to share a digital transmission medium by using
pre-allocated time slots. Many digital PBXs take advantage of T1 service to import
multiple call circuits over one T1 line instead of having 24 wire pairs routed between
the PBX and telephone company.
It is important to note that T1 can be shared between voice and data. A company’s
telephone service may come over a subset of a T1 link’s 24 channels, for instance,
leaving remaining channels available for internet connectivity.
A T1 multiplexer device is needed to manage the 24 DS0 channels when a T1 trunk
is shared between multiple services. For a single data-only connection, the circuit
can be run unchannelized (no TDM is performed on the signal). Consequently, a
simpler CSU/DSU device can be used.
Typically, you can connect to a T1/E1 CSU/DSU or multiplexer over V.35 or RS 449
serial interface with synchronous protocol at rates at a multiple of 64Kbps to
1.544Mbps or 2.048Mbps. The CSU/DSU or multiplexer provides the clocking in the
network.
114 OS/400 TCP/IP Configuration and Reference V4R4