Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-12-29
2003-11-04
Kizou, Hassan (Department: 2662)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C709S223000
Reexamination Certificate
active
06643289
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to data communication systems and more particularly, to a method of improving notification and handling of device status changes in MPOA enabled ATM based networks.
BACKGROUND OF THE INVENTION
Multi-Protocol Over ATM (MPOA)
The majority of networks, e.g., IP networks, are constructed from a plurality of nodes grouped together to form one or more subnets. Subnets are often built using various LAN technologies, with Ethernet and Token Ring being the most popular. Nodes in different subnets cannot normally communicate with each other. A router permits a node in one subnet to communicate with a node on a different subnet. Most internetwork layer protocols utilize routers to permit communications across subnet boundaries.
LAN Emulation (LE), as defined by the ATM Forum, provides Emulated LANs (ELANs) which emulate the services of Ethernet and Token Ring LANs across an ATM network. LE allows a subnet to be bridged across an ATM/LAN boundary. LE permits a single ATM network to support multiple ELANs. Utilizing ELANs, internetwork layer protocols can operate over an ATM network in essentially the same way they operate over Ethernet or Token Ring LANs. Although LE provides an effective means for bridging intra-subnet data across an ATM network, inter-network traffic still must be forwarded through routers.
The Next Hop Resolution Protocol (NHRP) and Multicast Address Resolution Server (MARS) protocols defined by the Internetworking Over NBMA (ION) Working Group, also permit internetwork layer protocols to operate over an ATM network. These protocols permit the ATM network to be divided into multiple ION subnets, also known as Logical IP Subnets (LISs) or Local Access Groups (LAGs). Routers are required, however, to interconnect these subnets. NHRP, however, allows intermediate routers to be bypassed on the data path. NHRP provides an extended address resolution protocol that permits Next Hop Clients (NHCs) to send queries between different subnets. Queries are propagated by Next Hop Servers (NHSs) along the routed path as determined by standard routing protocols. This enables the establishment of ATM VCCs across subnet boundaries, permitting inter-subnet communication without requiring routers in the data path.
Notwithstanding the availability of LANE and NHRP, a common situation exists wherein communicating LAN devices are behind LANE edge devices. The use of Multi-Protocol Over ATM (MPOA) permits these edge devices to perform internetwork layer forwarding and establish direct communications without requiring that the LANE edge devices comprise full function routers.
MPOA functions to provide an efficient transfer of inter-subnet unicast data in a LE environment. MPOA integrates LE and NHRP so as to preserve the benefits of LE, while allowing inter-subnet, internetwork layer protocol communication over ATM VCCs without requiring routers in the data path. MPOA provides a framework for effectively synthesizing bridging and routing with ATM in an environment of diverse protocols and network technologies. This framework provides a unified paradigm for overlaying internetwork layer protocols on ATM. MPOA is capable of using both routing and bridging information to select a shortcut through the ATM cloud to the egress MPC.
MPOA permits the physical separation of internetwork layer route calculation and forwarding, a technique known as virtual routing. This separation has the advantages of: (1) allowing efficient inter-subnet communications; (2) increasing manageability by decreasing the number of devices that must be configured to perform internetwork layer route calculation; (3) increases scalability by reducing the number of devices participating in internetwork layer route calculation; and (4) reduces the complexity of edge devices by eliminating the need to perform internetwork layer route calculation.
MPOA provides MPOA Clients (MPCs) and MPOA Servers (MPSs) and defines the protocols that are required for MPCs and MPSs to communicate. MPCs function to issue queries for shortcut ATM addresses and to receive replies from the MPS using these protocols. MPOA also functions to ensure interoperability with the existing infrastructure of routers. MPOA Servers utilize routers that run standard internetwork layer routing protocols, e.g., Open Shortest Path First (OSPF), providing a smooth integration with existing networks.
The primary function of the MPC is to source and sink internetwork shortcuts. The MPC performs internetwork layer forwarding but does not run internetwork layer routing protocols. The MPC detects ingress flows of packets that are forwarded over an ELAN to a router that comprises an MPS. When it recognizes a flow that could benefit from a shortcut that bypasses the routed path, it uses an NHRP based query/response protocol to request the information required to establish a shortcut to the destination. If a shortcut is available, the MPC caches the information in its ingress cache, sets up a shortcut VCC and forwards frames for the destination over the shortcut.
The MPC receives egress internetwork data frames from other MPCs to be forwarded to its local interface and/or users. For frames received over a shortcut, the MPC adds the appropriate encapsulation/header and forwards them to the higher layers. The encapsulation is provided to the MPC by the egress MPS and stored in the egress cache in the MPC. Note that an MPC is able to service multiple LECs and communicates with multiple MPSs. In addition, there may be multiple MPCs in an edge device. A given LEC, however, may be associated with only a single MPC.
An MPS is the logical component of a router that provides internetwork layer forwarding information to the MPCs. It comprises a full NHRP implementation with extensions as defined in the ATM Forum Multi-Protocol Over ATM Specification Version 1.0, AF-MPOA-0087.000, July 1997, incorporated herein in its entirety by reference. The MPS interacts with its local NHS and routing functions to reply to MPOA queries from ingress MPCs and provides encapsulation information to egress MPCs. Note that an MPS converts between MPOA requests and replies and NHRP requests and replies on behalf of MPCs. In addition, there may be multiple MPSs in a router. A given LEC, however, may be associated with only a single MPS.
An MPOA solution generally comprises a plurality of MPOA control flows and MPOA data flows. All control and data flows are carried over ATM VCCs. Control flows use MPOA control VCCs. Note that these VCCs can be used for other protocols (e.g., LE, etc.) as well in a multiplexed mode. Data flows, on the other hand, are carried over either LE VCCs (i.e., the default path) or over shortcut VCCs established via MPOA.
MPOA performs the following operations: configuration, discovery, target resolution, connection management and data transfer. Configuration includes obtaining the appropriate configuration information in both MPC and MPS. Normally, MPOA components receive configuration information from the LECS. Discovery involves MPCs and MPSs learning of each other's existence. MPOA components automatically discover each other using extensions to the LE LE ARP protocol that carry the MPOA device type (i.e., MPS, MPC) and ATM address. This information may change and must be periodically verified and updated if necessary. An MPOA device type TLV can be included in the following LE messages: LE_REGISTER request and response, LE ARP request and response and targetless LE_ARP request.
Target resolution denotes the determining of the mapping of a target to an egrss ATM address, an optional tag and a set of parameters used to setup a shortcut to forward packets across subnet boundaries.
Connection management entails creating, maintaining and terminating VCCs for the purpose of transferring control information and data. MPOA components establish VCCs between each other as necessary to transfer control and data messages over the ATM network. The goal of MPOA is the efficient transfer of unicast data within the ATM cloud. Uni
Aizicovich Ronit
Gershon Benny
Katzri Lior
Natanson Sarit Shani
3Com Corporation
Kizou Hassan
Levitan Dmitry
Zaretsky Howard
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