Next hop resolution protocol cut-through to LANs

Details Next hop resolution protocol cut-through to LANs Next hop resolution protocol cut-through to LANs

1997-11-12

2001-02-13

Rinehart, Mark (Department: 2756)

Electrical computers and digital processing systems: multicomput

Computer-to-computer data routing

C709S237000, C709S244000

Reexamination Certificate

active

06189041

ABSTRACT:

TECHNICAL FIELD
The present invention relates in general to data processing networks, and in particular, to Asynchronous Transfer Mode networks.
BACKGROUND INFORMATION
Asynchronous Transfer Mode (ATM) is an emerging network technology that is designed to transport information between communicating stations in a point-to-point fashion. The interest in ATM is its promise of high bandwidths and quality of service. ATM is a connection oriented architecture, in contrast to network architectures that are structured to broadcast data from the source to the destination. In ATM, the source negotiates a connected path to the destination before it proceeds to transmit its information to the recipient. ATM protocols (or “rules,” usually implemented in software) define the communications necessary to establish the connection. An ATM attached device has an ATM address in addition to any other network addresses it might have, depending on the particular ATM configuration within which it is incorporated. Some possible configurations will be described subsequently. Once a connection is established, the source station transmits its data only to the destination (a “unicast”).
In contrast to connection oriented architectures are broadcast networks. In these, data is sent from a source station to a destination station by broadcasting it to all addresses where the recipient plucks it off the network while the other stations on the network ignore traffic not bound for them. Broadcast architectures provide one motivation for structuring a “network” as a set of interconnected subnetworks or “subnets.”
In a large network, the proliferation of broadcast packets would overwhelm the network. Another simply reflects the nature of the pattern of growth of network communication generally. Although a particular network may start out as a freestanding Local Area Network (LAN), eventually end-station users will probably want to avail themselves of the services available on other networks, and look to connect “their network” with other “networks.” When this occurs, it is intuitive, as well as more precise, to view the resulting network structure as a set of subnets within a larger network, for example, an “internetwork.” However, a station on one internetworking subnet that wishes to communicate with a destination on another subnet can only do so if there is connectivity between the subnet in which the source resides and the subnet in which the destination resides.
Communications methodologies between subnets are usually termed to as “layer-3” protocols. This refers to the layered architecture networking model of the International Standards Organization (ISO). This model is illustrated in FIG.
1
. Layer-3 may sometimes be referred to as the “network” layer, and is equivalent to the “internetworking” layer in the TCP/IP model.
Connectivity between layer-3 subnets is provided by a device termed a “router.” When a source station on one layer-3 subnet wishes to communicate with a destination station on another layer-3 subnet, it broadcasts the data in the usual way. However, now it is the router that plucks the data packets off the first subnet and forwards it to the destination station via the destination station's layer-3 subnet to which the router is also attached.
Numerous types of networks coexist in the data communications industry. In addition to ATM, there may be LANs, Wide Area Networks (WANs), and others. There is a need in the industry for interconnection between different network architectures and, in particular, users of preexisting LANs have a need to connect to emerging high speed network technologies, such as ATM. The need for incorporating or interfacing preexisting networks (more precisely subnetworks) into an ATM environment has led to the specification of several methodologies to support preexisting network architectures within ATM.
One such methodology is the Logical IP Subnetwork (LIS). In LIS, the ATM serves as the direct replacement for the “wires” and LAN segments connecting traditional “layer-3 ” protocol source and destination stations (collectively, end-stations) and routers. In the traditional internetworking architecture, one or more LANs may be grouped into internetworking, or layer-3 , subnetworks, hereafter referred to as “subnets.” Within a layer-3 subnetwork, end-stations communicate with each other by broadcasting traffic as described previously.
A LIS is simply a layer-3 subnet within an ATM network. When a station on one LIS wishes to communicate with another station in the same LIS it does so by using ATM protocols. In order to do this, it must learn the ATM address of the destination. It does this through the medium of an ATM Address Resolution Protocol Server which resolves the layer-3 address of the destination into its ATM address. The source station sends a request, an ATM Address Resolution Protocol request (ATMARP_Request), to a server in the LIS that provides the ATM address of the destination based on its layer-3 address. The layer-3 address is the address by which the destination is identified with respect to its internetworking subnet. By contrast, communication between a source on one LIS and a destination on a second LIS proceeds just as if the communicating devices were traditional LANs residing on different internetwork subnets. The traffic is sent to a router based on the layer-3 address of the destination. The router then forwards the data through the appropriate destination LIS, or to a second router if the router on the source LIS is not a member of the destination LIS.
Another methodology is the emulated LAN (ELAN) which simulates classical LAN protocols in an ATM environment. (Classical LAN protocols, for example Ethernet and Token Rings, are referred to as legacy LANs.) The protocols that provide the specification for ELANs are called LAN emulation (LANE). Layer-3 protocols run on top of ELANs just as they do in legacy LANs. Hosts attached to the ELAN include emulation software that allows them to simulate legacy LAN end stations. Such hosts are called LAN Emulation Clients (LEC). The LEC software hides the ATM from the LAN protocols within the LEC device, and a LEC can utilize those protocols as if it were a legacy LAN. A LEC can also provide a standard LAN service interface to a layer-3 entity in the same layer-3 subnet. Such a LEC is a LAN Switch that is usable to interface a legacy LAN with an ELAN.
Communication between LECs on an ELAN can be effected over the ATM. Each LEC has a physical, or Media Access Control (MAC) address associated with it, as well as an ATM address. For one LEC on a ELAN to communicate with another, it must obtain the ATM address of the destination LEC, given the destination MAC address. This address resolution is mediated through a LAN Emulation Server (LES). The source LEC issues a LANE Address Resolution Protocol Request (LE_ARP_Request) to the LES. Provided the destination station has previously registered its MAC address, ATM address pair with the LES serving the ELAN, the LES returns the ATM address of the destination to the requesting LEC in an ELAN Address Resolution Protocol Reply (LE_ARP_Reply). The source LEC can then use the ATM address to establish a connection to unicast data to the destination, a so-called data-direct Virtual Channel Connection (VCC), and transmit its data to the destination thereon.
Should the destination not have registered with the LES, the source communicates with the destination using conventional LAN methodology. This is mediated through a Broadcast and Unknown Server (BUS). The LEC sends its data to the BUS which then broadcasts it. Just as in a legacy LAN, the broadcast data is plucked from the network by the destination station, and is ignored by the other devices on the network. Exactly the same process is used if the destination is on a subnetwork, either a legacy LAN or an ELAN, in a different layer-3 subnet. In that case, the broadcast data is gathered by a router connected to the ELAN and forwarded via layer-3 protocols to the destination, as described hereinabove, just as if

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