Seamless communication service with intelligent edge devices

Details Seamless communication service with intelligent edge devices Seamless communication service with intelligent edge devices

2000-08-15

2002-01-08

Vincent, David R. (Department: 2661)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S437000

Reexamination Certificate

active

06337863

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to computer networking. More particularly, the present invention relates to devices and methods for seamlessly interconnecting stations over an asynchronous transfer mode (ATM) network.
BACKGROUND OF THE INVENTION
A local area network (LAN) segment is a computer sub-network which includes multiple stations in the same physical area communicating by forwarding messages on a shared LAN media Stations on different LAN segments in the same physical area often communicate through a shared LAN switching fabric, which selectively forwards messages received over the fabric to the destination LAN segment. Stations on different LAN segments in different physical areas, in contrast, often communicate over an ATM network which interconnects multiple LAN switches or bridges on the edge of the network. In such an arrangement, each LAN switch or bridge selectively forwards messages received over the ATM network to the destination LAN segment.
An ATM network may be a “backbone” network in a campus environment or a wide area network (WAN). Importantly, an ATM network may not only support multiple LAN segments in different physical areas; it may also support multiple virtual LANs (VLANs). A VLAN is an aggregate of LAN segments which are part of the same logical group, but not necessarily the same physical group. By limiting the flow of messages across VLAN boundaries, an ATM network can conserve network bandwidth and enhance network security.
Communication over ATM networks differs from communication on LAN segments, and from communication between LAN segments over LAN switches and bridges, in terms of the way messages are delivered. A station desiring to communicate with another station on the same LAN segment does not need to know where the destination station is located within the segment. Instead, the source station relies on the broadcast capability of the LAN media to propagate all messages to all stations on the segment An interface on the intended destination station captures the message. Other interfaces on the segment ignore the message. Similarly, if a message propagated on a LAN segment is destined for a station on a different LAN segment associated with the same LAN switch or bridge, the LAN switch or bridge interconnecting the two segments will typically capture and propagate the message on a switching fabric connecting the two segments. In turn, an interface on the LAN switch or bridge associated with the intended destination LAN segment captures and propagates the message on the segment. Other interfaces on the LAN switch/bridge ignore the message. Again, there is no requirement that the source station know where the intended destination station resides within the network for successful communication. Rather, communication between the stations on different LAN segments over the LAN switch/bridge is “seamless” because the stations can communicate as if they are on the same LAN segment.
In contrast, ATM networks are not broadcast-oriented. Communicating over an ATM network, whether implemented as a backbone or WAN, requires that point-to-point connections be established across the ATM network. This requires that the location of the intended destination station be known prior to message forwarding over the network. Thus, a desire has arisen for services which extend LAN-type “plug-and-play” to ATM networks by meeting ATM's requirement of point-to-point connections without having to configure on every source station a point-to-point mapping over the ATM network to every possible destination station.
One way to provide such seamless communication is to have devices on the edge of the ATM network (e.g., LAN switches or bridges) learn the locations Q all stations connected to the network and provide the necessary connections over the network. A widely-used technique for creating such an environment is the ATM Forum's LAN Emulation (LANE) protocol. This technique emulates a LAN environment using LANE services (including a configuration server, a control server, a broadcast and unknown server) which assists multiple LANE “clients” in communicating over the ATM network. The clients are the devices on the edge of the ATM network, typically LAN switches or bridges. Where the client is a LAN switch or bridge, the client is assigned an ATM address. Behind the client are multiple stations with distinct media access control (MAC) addresses. When a message is presented for forwarding over the ATM network, the client typically resolves the destination MAC address encoded in the message, which is a unique address of a station behind another client, to the ATM address of the other client provided by the control server. By doing so, the LANE protocol allows clients to set-up connections across the ATM network dynamically on an “as needed” basis. This allows seamless communication between stations behind one client and stations behind another client.
The ATM Forum's LANE protocol, however, has certain limitations. First, the LANE protocol concentrates control functions for the entire “emulated LAN” in centralized servers. Such concentration of resources means that failure of a single server can bring down the entire service. Second, LANE protocol requires that each participating client follow detailed configuration, join, registration, learning and connection set-up procedures. Third, LANE protocol requires that messages be formatted for the particular LAN media which the ATM network is “emulating” (e.g., Token Ring) before forwarding the messages over the ATM network. This often necessitates media translations before message forwarding can proceed. Such requirements have hindered the robustness of seamless communication over ATM networks.
Accordingly, there is a need for a simple and less cumbersome service for providing seamless communication over an ATM network.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a service for seamless communication over an ATM network which will not be brought down in the event of a single point failure.
It is another object of the present invention to provide a service for seamless communication over an ATM network with efficient message forwarding over optimized, permanently configured connections.
It is another object of the present invention to provide a service for seamless communication over an ATM network which is self-configuring.
It is another object of the present invention to provide a service for seamless communication over an ATM network which can support multiple LAN media types.
It is another object of the present invention to provide a service for seamless communication over an ATM network which can support multiple VLANs.
It is another object of the present invention to provide a service for seamless communication over an ATM network which can operate in multiple instances on a single interface (or multiple interfaces) of a single edge device.
These and other objects of the present invention are achieved using a plurality of intelligent devices at the edge of an ATM network which serve as peer members of one or more instances of a seamless communication service.
In one aspect of the invention, configured on each member of a service instance are a “broadcast out” table which associates other members with a single, point-to-multipoint “broadcast out” virtual circuit and a member table which associates each other member with a point-to-point “direct” virtual circuit and a point-to-point “broadcast in” virtual circuit.
In another aspect of the invention, the service instance is self-configuring. A single edge device is selected as a “master” member for purposes of service configuration. Other edge devices seeking to join the service are supplied with the ATM address of the master member and use the address to advertise their respective ATM addresses to the master member. The master-member, in turn, advertises the addresses to all joining members so that joining members can configure member and “broadcast out” tables associating other members with virtual cir

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