Automatic SDLC role configuration on router interfaces

Details Automatic SDLC role configuration on router interfaces Automatic SDLC role configuration on router interfaces

1999-07-08

2004-01-06

Ton, Dang (Department: 2666)

Multiplex communications

Pathfinding or routing

C370S465000

Reexamination Certificate

active

06674742

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to computer networks and, more particularly, to configuration of devices in a computer network employing the Synchronous Data Link Control (SDLC) protocol.
BACKGROUND OF THE INVENTION
Data communications in a computer network involves the exchange of data between two or more entities interconnected by communication links. These entities are typically software programs executing on hardware computer platforms which, depending on their roles within a network, may serve as end stations or intermediate stations. Examples of intermediate stations may include bridges, switches and routers that interconnect the communication links to enable transmission of data between the end stations, which may comprise a computer. 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.
Communication software executing on the end stations correlate and manage data communication with other end stations. The 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. In addition, network routing software executing on the routers allows expansion of communication to other end stations. 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 predefined 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 Systems 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
, 3rd edition, by Andrew S. Tanenbaurn, published by Prentice-Hall, PTR in 1996, all disclosures of which are incorporated herein by reference, particularly at pages 28-44.
SNA is a communications framework widely used to define network functions and establish standards for enabling different models of 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, data link control, path control, the transmission control, the data flow control, the presentation services and the transaction services layers. These layers are arranged to form a protocol stack in each communicating station of the network.
FIG. 1
is a schematic block diagram of a prior art SNA protocol stack
100
, wherein each layer of the stack represents a graduated level of function moving upward from physical connections (physical layer
102
) to application software (transaction services layer
114
).
In the SNA architecture, the data link control layer
104
is responsible for providing error-free transmission of data over a communication link between stations. An example of a bit-oriented protocol for data link control of a communication channel is the synchronous data link control (SDLC) protocol. Reliable communication in the data link layer (e.g., SDLC) 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.
SDLC identifies two types of stations: primary and secondary. Only one station on a SDLC link is a primary station; all other stations on the link are secondary stations. The role of a primary station is to control the operation of the data link between the primary and secondary stations. For example, the primary station may initiate data transmissions from the secondary stations by polling the secondary stations in a predetermined order. Secondary stations can then transmit if they have outgoing data. The primary station also establishes and “tears down” communication links and channels. Examples of communication channels and link types supported by the SDLC protocol include point-to-point and multipoint links, half-duplex and full-duplex transmission facilities, and circuit-switched and packet-switched networks.
FIG. 2
is a schematic block diagram of a SNA computer network
200
having a hierarchical topology. The network
200
comprises a plurality of stations that are defined by the SNA architecture in terms of physical units (PUs) and that communicate in a master-slave relationship as defined by the SDLC protocol. Specifically, a host mainframe
202
(e.g., a PU of type 5.0) is coupled to a front end processor, FEP
210
(e.g., a PU of type 4.0). The FEP
210
is configured to communicate with external devices, such as cluster controllers (CC)
220
, each of which provides a concentrated data link interface for a number of locally-attached end stations
230
. The cluster controllers
220
and end stations
230
manifest as PU type 2.0 devices.
Applications executing on end stations
230
typically access the network through logical units (LU) of the stations; accordingly, in a typical SNA network, a communication session connects two LUs in a LU—LU session. Activation and deactivation of such a session is addressed by Advanced Peer to Peer Networking (APPN) functions, which include session establishment and session routing within an APPN network. During session establishment, an APPN end node requests an optimum route for a session between two LUs; this route is calculated and conveyed to the end node by an APPN network node. Intermediate session routing occurs when the APPN network node is present in a session between the two end nodes.
An APPN network node is a full-functioning APPN router node having all APPN base service capabilities, including session services functions. An APPN end node, on the other hand, is capable of performing only a subset of the functions provided by an APPN network node. In an APPN network, all nodes are of a PU 2.1 device type. APPN network and end nodes are well-known and are, for example, described in detail in Systems Network Architecture Advanced Peer to Peer Networking Architecture Reference IBM Doc SC30-3422 and APPN Networks by Jesper Nilausen, printed by John Wiley and Sons, 1994, at pgs 11-83.
According to the SDLC protocol, the master-slave relationship exists between each of the stations of the network and manifests as a hand-shaking sequence between the stations. For example,

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