Browse Prior Art Database

Addressing Source Routing in an ATM Emulated LAN

IP.com Disclosure Number: IPCOM000113791D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 6 page(s) / 322K

Publishing Venue

IBM

Related People

Basso, CL: AUTHOR [+10]

Abstract

Disclosed are methods and mechanisms which enable the transport of source routed LAN frames in an ATM Emulated LAN environment. Specifically, this disclosure prescribes frame formats and protocols associated with source routing bridge registration, resolution of bridge physical addresses into ATM addresses, encapsulation and transmission of source routed frames through the emulated LAN, and reception of source routed frames.

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This is the abbreviated version, containing approximately 23% of the total text.

Addressing Source Routing in an ATM Emulated LAN

      Disclosed are methods and mechanisms which enable the transport
of source routed LAN frames in an ATM Emulated LAN environment.
Specifically, this disclosure prescribes frame formats and protocols
associated with source routing bridge registration, resolution of
bridge physical addresses into ATM addresses, encapsulation and
transmission of source routed frames through the emulated LAN, and
reception of source routed frames.

      The LAN Emulation service provides for the transport of LAN
data traffic over an ATM network.  Such a LAN emulation service
allows ATM-attached endstations to communicate using current LAN
applications.  The LE service also allows for communication with
traditional LANs over ATM using existing LAN applications.  ATM-LAN
bridges are necessary to facilitate any communication between an ATM
Emulated LAN environment and a traditional LAN environment.  These

ATM-LAN bridges must operate according to existing bridging methods -
namely, Transparent Bridging and Source Routing.  See [1]  for a
complete description of the differences between these bridging
methods.

      Transparent Bridging (TB) allows for endstations to send and
receive LAN frames transparently across interconnected LANs [2] TB
bridging uses a spanning tree algorithm to build a tree which ensures
that there exists a single path between any two stations in the
bridged LAN.  Transparent bridges then use destination address tables
to forward frames toward their destination along the spanning tree
path.  Source Routing bridging, on the other hand, requires that
endstations determine explicit bridged routes and include this
routing information in each source routed frame.  Source routing
bridges then forward frames toward their destination based upon this
routing information.  The Routing Information Field (RIF) is included
in all source routed frames and has the format pictured in Fig. 1.

      The Routing Control field consists of information used by the
SR bridge to determine whether to forward the frame along a single
route or multiple routes.  The RC field is followed by a list of
Route Descriptors (RDs) which explicitly define a route through the
bridged LAN.  Each RD consists of a network-unique 12-bit segment
identifier plus a 4-bit bridge number that is used to differentiate
between two or more bridges when they connect the same two LANs
(parallel bridges).  An SR bridge will only forward a frame which
contains a RIF that specifies its Bridge configuration - that is, the
segment ID of the receiving LAN (port), the Bridge number of this
bridge (BN), and the segment ID of the forwarding LAN (port).  In the
following sections, we suggest a solution to the problem of bridging
between an ATM emulated LAN and a traditional LAN using Source
Routing (SR) bridging methods.  Specifically, we specify methods
which may be used by the LAN Emulation service to provide direct
co...