Browse Prior Art Database

Bridge for Interconnecting Local Area Networks Having Different Architectures

IP.com Disclosure Number: IPCOM000102575D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 6 page(s) / 220K

Publishing Venue

IBM

Related People

Dixon, RC: AUTHOR [+4]

Abstract

A method for bridging token-ring (IEEE 802.5) and carrier-sense multiple-access with collision detection (CSMA/CD) type LANs (e.g., IEEE 802.3) at the media access control (MAC) layer is described.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 27% of the total text.

Bridge for Interconnecting Local Area Networks Having Different Architectures

       A method for bridging token-ring (IEEE 802.5) and
carrier-sense multiple-access with collision detection (CSMA/CD) type
LANs (e.g., IEEE 802.3) at the media access control (MAC) layer is
described.

      The invention is described in the following sections as
follows:
-  A description of the data bases that the bridge maintains, and
-  Decision trees that describe how the bridge makes forwarding
decisions.

      The bridge maintains two data bases.   One contains the source
addresses detected on the CSMA/CD port; the other contains the source
addresses and routing information for stations on the token-ring
network.

      The CSMA/CD data base supports two types of entries: static and
dynamic.  Static entries are configurable entries received from LAN
management and are saved in nonvolatile RAM.  Dynamic entries are
created as part of the bridge's learning process.

      After power-on initialization, the CSMA/CD data base is
initialized with static entries.  The bridge enters the learning
state in which it listens to all frames on the CSMA/CD port and saves
each unique source address in its data base.  While in this state,
the bridge does not forward any frames.  The bridge leaves the
learning state after a configurable amount of time and begins normal
operations. During normal operations, the bridge updates the data
base whenever a new source address is detected on an CSMA/CD frame.

      The token-ring data base is initialized with no entries.  The
bridge does not learn any addresses until it begins normal
operations.  The bridge adds entries in this data base only for those
stations whose frames have been forwarded on the CSMA/CD port.

      The CSMA/CD data base represents known stations on the CSMA/CD
LAN whereas the token-ring data base represents only those token-ring
stations for which the bridge has forwarded a frame.  Associated
source routing information is also retained for each token-ring
source address.

      Dynamic entries have an Aging Time attribute, which determines
how long an inactive entry stays in the data base.  This permits the
bridge to dynamically adapt to changes in the network configuration.

      The aging time of the entries in the CSMA/CD data base is
updated whenever messages from the CSMA/CD stations are received.
The aging time of the entries in the token-ring data base is updated
whenever messages, received from the CSMA/CD port, are forwarded to
the token- ring stations.

      The bridge supports up to a combined total of 2048 entries in
the CSMA/CD and token-ring address data bases. The maximum number of
entries in the token-ring data base is limited to 1024.

      After the address data base is full, the bridge does not
forward traffic from any new stations.  The bridge again accepts
traffic from new stations after dynamic entries are aged and removed
...