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Many new DCE devices such as routers, T3 Multiplexers and
T1 Demultiplexers have started to use the HSSI interface.
HSSI has several advantages over competing serial interfaces
such as V.35 and EIA-530(EIA-422). It can operate at higher
data rates, has superior flow control, amd additional loopback
capability.
EIA-530 is limited in maximum bit rate to about 10 Mbps over
short distances, while V.35 may even be somewhat lower. The
HSSI interface can operate up to 52 Mbits/sec. Using emitter
coupled logic (ECL), current mode drivers limit voltage swings
and lowers the affect of cable capacitance. Differential voltage
swings are typically 0.85V, with a mazimum rise time of 2.3
ns. Differential current mode devices also eliminate the high
peak switching currents which can cause grounding problems
in other logic families.
Gapped timing is not available to EIA-530 or V.35 interfaces
and it is a feature which may be used as an advantage, by
new software and hardware designs. Gapped timing allows the
DCE device to control the flow of data coming from the DTE
by stopping the clock. Most frequently this is used to stop
data flow until buffer space is available. This approach is
an effective solution to RTS/CTS latency problems which can
appear at higher speeds in other interfaces.
Loopback control support for LA, LB and LC is provided in
the IM-HSSI-DTE board. LA and LB are asserted by the DTE (IM-HSSI-DTE),
while LC is asserted by the DCE.
The
IM-HSSI-DTE uses the same form factor as other IM modules
and can be used with either the T1-Master or WAN Master communications
cards. This module is a high speed serial interface adaptor
which follows the HSSI Design Specification Rev. 3.0. It provides
a physical interface between the T1-Master or WAN master cards
and high speed routers, satellite modems, T3 Multiplexers,
T1 Demultiplexers and other devices.
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