HP 200 Series Services And Applications page 261

Using Synchronous Pass-Through to Consolidate Synchronous Traffic
Special Considerations
Figure 7. Pin-Outs for Null-Moden Cable for V.35 Connection
Special Considerations
Sync pass-through may be used only to provide communication between
devices attached to synchronous ports on the router. Sync pass-through
cannot be used to connect a synchronous device to a LAN-attached device.
In his June 21, 1991, Data Communications article "Router Backbones
Unite Terminals and LANs", Anura Gurugé describes a potential perform-
ance problem using sync pass-through. Extended LAN traffic is charac-
teristically bursty. Bursts of LAN-to-LAN traffic can cause variable
response-time delays on interactive terminals. According to Gurugé, variable
response-time delays are one of the most annoying problems for interactive
terminal users. To compensate for this delay, he recommends increasing
backbone capacity by up to four times the sync pass-through line rate. Thus,
up to 38.4 Kbit/s of additional capacity may needed on the backbone
network for the addition of one 9.6 Kbit/s sync pass-through circuit.
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