Using a systems network architecture logical unit activation...

Details Using a systems network architecture logical unit activation... Using a systems network architecture logical unit activation...

2000-09-28

2002-05-14

Burgess, Glenton B. (Department: 2153)

Electrical computers and digital processing systems: multicomput

Network computer configuring

C709S221000

Reexamination Certificate

active

06389465

ABSTRACT:

TECHNICAL FIELD
The present invention relates to computer programming and, in particular, to a method and system for dynamically indicating the active logical units (LUs) of a Systems Network Architecture (SNA) communications network in a Gateway between the SNA network and another computing network.
BACKGROUND OF THE INVENTION
The Systems Network Architecture (SNA) is a widely used and highly successful communications framework developed by IBM that defines network functions and establishes standards for enabling computers to exchange and process data. SNA provides a coherent structure that enables users to establish and manage their networks and to change or expand them in response to new requirements and technologies. SNA includes products, combinations of hardware and programs designed in accordance with SNA specifications. In addition to a large number of computer terminals for both specific industries and general applications, IBM's SNA product line includes host processors, communication controllers, adapters, modems, and data encryption units. The SNA product line also includes a variety of programs and programming subsystems, such as telecommunications access methods, network management programs, distributed application programs and network control programs (NCPs).
SNA describes rules that enable users to transmit and receive information through their computer networks. As shown in
FIG. 1
, SNA utilizes a tree-structured architecture with a mainframe host computer
101
acting as the network control center. The architecture with a mainframe host computer
101
acting as the network control center. The network also includes terminals
102
, front-end processors
103
, workstations
104
, and cluster controllers
105
. The boundaries described by the mainframe host computer
101
, front-end processors
103
, cluster controllers
105
, workstations
104
and terminals
102
are referred to as the network's domain
108
. SNA network nodes include the various equipment attached to the network, such as the front-end processors
103
and the terminals
102
. Unlike a switched telephone network that establishes physical paths between terminals for the duration of a session, SNA establishes a logical path between network nodes, such as the terminals
102
, and routes each message with addressing information contained in the SNA protocol.
FIG. 2
displays the SNA communication protocol stack. SNA utilizes a communications stack for transferring data between computers, such as between the mainframe host computer
101
and the workstation
104
shown in
FIG. 1
SNA utilizes five layers for communication within a domain: a function management layer
201
, a data flow control layer
202
, a transmission control layer
203
, a path control layer
204
, and a data-link control layer
205
. The layers form a sequence from a lowest layer (the data-link control layer
205
) to the highest layer (the function management layer
201
). The layers divide the processing necessary for communicating between computers into discrete units. The data-link control layer
205
in the communications stack typically interacts with the physical medium used for transferring the data, such as coaxial cables. The function management layer
201
, as the top layer of the communications stack, provides services to application programs, and the middle layers of the communications stack typically are responsible for routing and maintaining a connection.
A local computer transfers data to a remote computer when an application program first passes the data to the function management layer
201
of the communications stack of the local computer. The function management layer
201
then processes the data and sends the data to the next lowest layer in the communications stack, the data flow control layer
202
. Thereafter, each layer in turn processes the data until the data reaches the bottom layer, the data-link control layer
205
, where the data is sent to the remote computer over the transfer medium. The data-link control layer
205
, as the bottom layer of the communications stack, may also receive data from the transfer medium and pass the data up the communications stack. Each layer performs its specific processing on the data until the data reaches the function management layer
201
. The function management layer
201
processes the data and sends the data to an application program.
SNA utilizes various protocols including the Synchronous Data Link Control (SDLC), Data Link Control (DLC 802.2), and Data Link Control over Channel or Fiber Optics (DLC Channel/ESCON) protocols. SDLC is a bit-oriented synchronous communications protocol developed by IBM. SDLC provides high speed data transfer between SNA devices, such as the mainframe host computer
101
and the workstation
104
shown in FIG.
1
. SDLC forms data into packets, known as frames, with as many as
128
frames transmitted sequentially in a given data transfer. As shown in
FIG. 3
, each frame
300
comprises a header
301
, text
302
, and a trailer
303
. The header
301
consists of framing bits
301
a
indicating the beginning of the frame, address information
301
b
and various control data
301
c.
The text
302
, or data payload, consists of as many as seven blocks of data, each having as many as 512 characters. A Request Unit (RU) is a basic unit of data in SNA. The trailer
303
comprises a frame check sequence (FCS)
303
a
for error detection and correction. A set of framing bits
303
b
mark the end of the frame
300
. SDLC supports device communications generally conducted over high speed, dedicated private line, digital circuits. SDLC can operate in either point-to-point or multipoint network configurations. DLC over Local Area Network (LAN) specification 802.2 Ethernet or Token Ring, Bus and Tag Channel, and Enterprise System Connection (ESCON) may all be utilized as low-level protocols to accomplish SNA traffic exchange with. a mainframe computer.
A logical unit (LU) is an SNA access port for network nodes such as the workstation
104
shown in FIG.
1
. Each LU denotes the beginning or end of a communications system. In a bisynchronous network, an LU is a port through which a user accesses network services. An LU may support sessions with a system services control point (SSCP) on the mainframe host computer and with other LUs. LU 6.2, also known as advanced program-to-program communication (APPC), is a version of the LU that allows for peer-to-peer or program-to-program communications. The LU 6.2 protocol standard frees application programs from network-specific details. For example, on an IBM PC, an LU 6.2-equipped program accepts commands and passes them on to an SDLC card that communicates directly with the mainframe host computer or a token ring handler. LU 6.2 also creates a transparent environment for application-to-application communications, regardless of the types of systems used or their relative locations. For example, LU 6.2 enables users to develop application programs for peer-to-peer communications between PCs and IBM host computers. LU 6.2 also increases the processing power of the PC without the constraints of mainframe-based slave devices, such as the IBM 3274/3276 controllers.
Other LU types include LU 0 through LU 4, LU 6.1, and LU 7. LU 0 is non-architected so that transmitted data can be interpreted based upon user-defined rules. LU 0 is a peer-to-peer (program-to-program) type of data communication. The application program interface is more flexible but has fewer built-in capabilities than LU 6.2. LU 0 is mainly used for applications, such as file transfers, in which the protocols used are defined by the file transfer programs running at each end of the communication system.
LU 1 serves in sending SNA Character String (SCS) data streams from hostbased applications to remote terminals, such as 3270 printers or 3770 RJE type computer terminals. LU 2 is suited for communications to 3270-type computer terminals. Communications sessions with 3270-type printers use LU 3. LU 4 is a peer-to-peer commu

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