HP 600 Series, Services And Applications

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Using Synchronous Pass-Through
to Consolidate Synchronous Traffic
Routers and high-speed WAN links have been used to create corporate
internetworks. These internetworks connect LANs and provide communica-
tion among any systems and nodes attached to the LANs. There are many
devices, however, such as SNA 3270 and 3770 terminals in most corporate
networks, that are not connected to the extended LAN internetworks.
Instead, these devices are typically connected to a parallel network. Parallel
networks are expensive both for monthly connection charges and for
network support.
Synchronous pass-through (also called sync pass-through) is a new feature
of HP router software versions 5.70 and later that allows synchronous traffic
(HDLC, SDLC, LAPB) to be consolidated with LAN-to-LAN traffic on
HP-router-based internetworks. This application note describes how sync
pass-through works and examines several sync pass-through applications.
Figure 1 shows an extended LAN internetwork where sync pass-through is
used to connect synchronous interactive and printing terminals. Multiple
IBM 3174 cluster controllers in a multi-drop configuration are connected to
an IBM 3745 at site A over the extended LAN. Similarly, at site B, an HP 3000
running SNA IMF and SNA NRJE is connected to the IBM 3745 at site A
using sync pass-through over the extended LAN. Using sync pass-through, a
point-to-point circuit can be defined to convey synchronous traffic from one
location to another in the extended LAN.
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