Browse Prior Art Database

Protocol for Seamless Mobility Transitions in Transparent Bridging Local Area Networks

IP.com Disclosure Number: IPCOM000116910D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 135K

Publishing Venue

IBM

Related People

Grover, GA: AUTHOR [+3]

Abstract

Disclosed is a scheme to support mobility in transparent bridging Local Area Networks (LANs). To support mobility, a frame is sent from the new location of a mobile unit to its old location bearing the mobile's MAC address in the source address field of the frame after a change of location.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 41% of the total text.

Protocol for Seamless Mobility Transitions in Transparent Bridging
Local Area Networks

      Disclosed is a scheme to support mobility in transparent
bridging Local Area Networks (LANs).  To support mobility, a frame is
sent from the new location of a mobile unit to its old location
bearing the mobile's MAC address in the source address field of the
frame after a change of location.

      When Mobile Units (MUs) communicate via Access Points (AP) to
fixed transparent bridging Local Area Networks (LANs), such as
Ethernet, they may be inaccessible to other units in portions of the
LAN for significant periods of time as a result of moving from one
access point to another.  This can happen in wired or wireless
networks where a mobile user can disconnect its device from one
access point and connect it to another one.  This state of partial
disconnection can be remedied by a simple procedure disclosed in this
report which resets the distributed routing tree of the MU with
respect to the LAN's bridges.  Although the access point can be just
a port on the wired network or it can be a base station through which
a wireless MU can connect to the fixed network, we describe our
scheme for the case that a wireless MU communicates over a wireless
link to a transparent bridging LAN.  However, this scheme can be
easily implemented when MUs are connected to the LAN by wired links.

      For transparent bridging LANs such as Ethernet, transparent
bridging provides a natural relearning mechanism such that a mobile
unit moving about among a set of access points or base stations which
have the appearance of Ethernet bridges will, for the most part, have
the data begin to flow correctly along the new paths without any
special switching operation.  Conceptually, this occurs because of
the following simple properties which transparent bridges such as
Ethernet bridges possess:
  1.  The routing possibilities offered by a set of bridges is
       constrained to a distributively defined spanning tree, so that
       for any one position of the MU relative to the tree there is
one
       and only one path for it's MAC address to any other MAC
address
       on the LAN.
  2.  When a message is received by a bridge, it's source address is
       retained in a bridge cache and associated with the port on
which
       the message entered, so that the direction of the source
address
       relative to this node in the tree has been learned, and is
used
       in the future to correctly forward messages whose destination
is
       that address.
  3.  When a message is received by a bridge, if it's destination
       address is not present in the bridge cache, then the bridge,
       since it has no knowledge of the destination's location
relative
       to itself, broadcasts the packet on all ports except the one
it
       was received on.

The effect of these properties is...