Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1999-05-20
2003-03-11
Olms, Douglas (Department: 2732)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S466000, C370S467000, C370S465000, C709S200000, C709S222000, C709S223000, C709S226000, C709S230000, C709S239000
Reexamination Certificate
active
06532241
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to computer networks and, more particularly, to management of entities in a multi-protocol computer network.
BACKGROUND OF THE INVENTION
Data communications in a computer network involves the exchange of data between two or more entities interconnected by communication links and subnetworks. These networks are typically software programs executing on hardware computer platforms which, depending on their roles within a network, may serve as host stations, end stations or intermediate stations. Examples of intermediate stations include routers, bridges and switches that interconnect communication links in subnetworks; an end station may be a computer located on one of the subnetworks. More generally, an end station connotes a source of or target for data that typically does not provide routing or other services to other computers on the network. A local area network (LAN) is an example of a subnetwork that provides relatively short-distance communication among the inter-connected stations; in contrast, a wide area network (WAN) facilitates long-distance communication over links provided by public or private telecommunications facilities.
End stations typically communicate by exchanging discrete packets or frames of data according to predefined protocols. In this context, a protocol represents a set of rules defining how the stations interact with each other to transfer data. Such interaction is simple within a LAN, since these are typically “multicast” networks: when a source station transmits a frame over the LAN, it reaches all stations on that LAN. If the intended recipient of the frame is connected to another LAN, the frame is passed over a routing device to that other LAN. Collectively, these hardware and software components comprise a communications network and their interconnections are defined by an underlying architecture.
Most computer network architectures are organized as a series of hardware and software levels or “layers” within each station. These layers interact to format data for transfer between, e.g., a source station and a destination station communicating over the network. Specifically, predetermined services are performed on that data as it passed through each layer, and the layers communicate with each other by means of the pre-defined protocols. This design permits each layer to offer selected services to other layers using a standardized interface that shields the other layers from details of actual implementation of the services. The lower layers of these architectures are generally standardized and implemented in hardware and firmware, whereas the higher layers are usually implemented in the form of software. Examples of such communications architectures include the System Network Architecture (SNA) developed by International Business Machines (IBM) Corporation and the Internet Communications Architecture.
The Internet architecture is represented by four layers termed, in ascending interfacing order, the network interface, internetwork, transport and application layers. The primary internetwork layer protocol of the Internet architecture is the Internet Protocol (IP). IP is primarily a connectionless protocol that provides for internetworking routing, fragmentation and reassembly of exchanged packets—generally referred to as “datagrams” in an Internet environment—and which relies on transport protocols for end-to-end reliability. An example of such a transport protocol is the Transmission Control Protocol (TCP), which is implemented by the transport layer and provides connection-oriented services to the upper layer protocols of the Internet architecture. The term TCP/IP is commonly used to denote this architecture; the TCP/IP architecture is discussed in
Computer Networks,
3
rd edition
, by Andrew S. Tanenbaum, published by Prentice-Hall, PTR in 1996, all disclosures of which are incorporated herein by reference, particularly at pages 28-54.
SNA is a communications framework widely used to define network functions and establish standards for enabling different models of IBM computers to exchange and process data. SNA is essentially a design philosophy that separates network communications into several layers termed, in ascending order, the physical control, the data link control, the path control, the transmission control, the data flow control, the presentation services and the transaction services layers. Each of these layers represents a graduated level of function moving upward from physical connections to application software.
In the SNA architecture, the data link control layer is responsible for transmission of data from one end station to another. Bridges or devices in the data link control layer that are used to connect two or more LANs so that end stations on either LAN are allowed to access resources on the LANs. Connection-oriented services at the data link layer generally involve three distinct phases: connection establishment, data transfer and connection termination. During connection establishment, a single path or connection, e.g., an IEEE 802.2 logical link control type 2 (LLC2) or “data link control” connection, is established between the source and destination stations. Once the connection has been established, data is transferred sequentially over the path and, when the LLC2 connection is no longer needed, the path is terminated. Reliable communication of the LLC2 (DLC) is well known and described by Andrew Tanenbaum in his book
Computer Networks, Second Edition
, published in 1988, all disclosures of which are incorporated herein by reference, especially at pages 253-257.
FIG. 1
is a schematic block diagram of a conventional computer network
100
having a host computer coupled to a Token Ring (TR) network TR
1
and an end station coupled to TR
2
. The TR networks are of the type that support Source/Route Bridging (SRB) operations with respect to the contents of a routing information field (RIF) of a frame. The host computer is preferably a SNA host entity comprising a host mainframe computer
110
coupled to a channel-attached router or a front end processor (FEP), such as an IBM 3745 network control processor, hereinafter referred to as the “host network connection”
112
. In addition, the end station is an SNA entity
114
comprising a “physical unit” (PU) and a “logical unit” (LU) which consists of logical services by which a user may access the SNA network. A control unit
106
(such as IBM 3174) interconnects TR
1
and TR
2
such that the SRB network
100
effectively functions as a LAN. SNA protocols, such as a hierarchical sub-area SNA protocol that defines a connection path between the PU and host, are used throughout the network.
In an alternate embodiment of network
100
, Remote Source Route Bridging (RSRB) routers
1
,
2
operate in conjunction with the host network connection
112
to provide IP connectivity over a TCP/IP cloud
110
with the SNA network
100
. RSRB is a software component in each router that permits transmission of TR frame traffic across an IP network. Specifically, RSRB functions to give the IP network the appearance of a single, virtual token ring (VTR) “hop” in a TR network. The association of the two adjacent RSRB routers is called a “peer” relation and this relation must exist to exchange RSRB traffic across the VTR.
The PU entity communicates with the host by exchanging TR frames over LLC2 connections or sessions through the SRB network. Each TR frame
120
includes a RIF
122
that contains source route information in the form of ring number/bridge number pair “hops” within a path between the stations. An LLC2 session is established between the stations using a special TR frame, called an explorer frame. The explorer frame is used by a source (PU) to “discover” the path to a destination (host); thereafter, a Set Asynchronous Balanced Mode Extended (SABME) frame is sent from the PU to the host to establish a logical connection between the end stations, and the host responds to the SABME frame with an Unnumbered Acknowledgment (UA) fram
Clouston Robert
Ferguson Darin
Cesari and McKenna LLP
Cisco Technology Inc.
Nguyen Van Kim T.
Olms Douglas
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