Browse Prior Art Database

Hybrid Network Bridge

IP.com Disclosure Number: IPCOM000108713D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 6 page(s) / 203K

Publishing Venue

IBM

Related People

Griefer, AD: AUTHOR [+2]

Abstract

Modern interactive computing requires more transmission capacity for remote terminals than is possible using the existing public switched telephone network. In particular, graphical user interfaces such as the Xwindow System demand more transmission capacity than even the expected Integrated Services Digital Network Basic Rate Interface will deliver, especially when bit-mapped graphics are to be displayed. The described design for a network bridging system addresses this problem by exploiting the unbalanced, bursty nature of interactive traffic and using a dual-medium design, resulting in high performance at low cost. It is well suited to remote display terminals (called X-Terminals) designed for use with the Xwindow system. HYBRID BRIDGE CONCEPT

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Hybrid Network Bridge

       Modern interactive computing requires more transmission
capacity for remote terminals than is possible using the existing
public switched telephone network.  In particular, graphical user
interfaces such as the Xwindow System demand more transmission
capacity than even the expected Integrated Services Digital Network
Basic Rate Interface will deliver, especially when bit-mapped
graphics are to be displayed.  The described design for a network
bridging system addresses this problem by exploiting the unbalanced,
bursty nature of interactive traffic and using a dual-medium design,
resulting in high performance at low cost.  It is well suited to
remote display terminals (called X-Terminals) designed for use with
the Xwindow system.
HYBRID BRIDGE CONCEPT

      The essence of this invention is the separation of transmission
paths for in- and outbound interactive traffic, using media well
suited to the data rates required.  In particular, a shared high
speed broadcast channel 3 is used in the host network-to-terminal
direction and (slower) conventional switched facilities 4 are used in
the reverse direction, as shown in Fig. 1.

      The utility of this design is based on the low per-user cost of
high speed broadcast media such as TV cable systems, coupled with the
fact that the vast majority of bits transmitted for an interactive
graphics terminal session are from the host to the display.  In the
opposite direction, keystrokes and cursor positioning information
require much less capacity, an amount consistent with conventional
transmission using the public switched telephone network (PSTN) and
analog modems.

      The environment for which this design is planned is
packet-switched transmission between local area networks (LANs).
Users at graphics terminals 6 are remote from a LAN 8 on which
services are desired.  LAN data packets intended for remote terminals
are received by a host network bridge (HNB) 2 and forwarded on the
shared broadcast path 3 to all remote network bridges (RNBs) 5, which
ignore all broadcast traffic except that addressed to the associated
terminal(s) 6.  A terminal's RNB 5 forwards packets intended for the
host network on a point-to-point path (for example, a dial-up modem
link), as shown in Fig. 1.
HOST -> TERMINAL PATH IMPLEMENTATION

      The HNB 2 behaves as a conventional remote  LAN  bridge for
traffic intended for remote destinations: it examines all packets
transmitted on the host site LAN, discarding all but those addressed
to a remote destination. For security reasons, a manually prepared
list of authorized remote addresses may be preferred; however,
acquisition of remote addresses may be automatic, based on addresses
found in packets received over the reverse path.

      Packets chosen for forwarding are stored in a queue for
transmission of the broadcast link 3, which is envisioned to be at T1
transmission rate (1.544 Mbits/second) or faster. The...