network access methods

Network Access Methods

Introduction• BTAM - Basic telecommunications access

method• QTAM - Queued teleprocessing access method• TCAM - Telecommunications access method• VTAM - Virtual telecommunications access

method

Basic telecommunications access method

• A low-level programming interface specified by IBM for use on the IBM System/360

• For start-stop and binary synchronous telecommunications terminals.


• BTAM requires the application program or transaction processing system to handle almost every detail of the protocol.

• Transaction processing is a style of computing that divides work into individual, indivisible operations, called transactions


• This is harder than using a higher-layer protocol, but it permits interfacing to non-standard devices in non-standard ways


• BTAM was an access method for interactively communicating with remote terminals

• BTAM dynamically built CCW's for reading, writing and "polling" terminals

• Dealt with specific responses from those terminals, according to the success or failure of the communication channel.


• A channel command word (CCW) is an instruction to a specialized I/O channel processor which is, in fact, a finite state machine

• Polling refers to actively sampling the status of an external device by a client program as a synchronous activity


• It was not unusual for BTAM and later developed access methods (such as VTAM) to co-exist, supporting different devices simultaneously under the same transaction processing system.


• BM finally withdrew support for BTAM in 2000.

Queued Telecommunications Access Method


• Queued Telecommunications Access Method (QTAM) is an IBM System/360 communications access method incorporating built-in queuing.


• Queuing is referring to message queues• These are software-

engineering components used for interprocess communication (a set of methods for the exchange of data among multiple threads)


• Threads being the smallest sequence of programmed instructions that can be managed independently


• QTAM consisted of a Message Control Program (MCP) and zero or more Message Processing Programs (MPP)

• The MCP handled communications with the terminals, identified input messages and started MPPs to process them as required


• The MCP was assembled by the user installation from a set of macros supplied by IBM.


• These macros defined:• The lines and terminals comprising the

system, • The datasets required, • And the procedures used to process received

and transmitted messages.


• The MPPs, incorporating logic to process the various messages, were supplied by the installation, and used standard OS/360 data management macros.

Telecommunications Access Method


• Telecommunications Access Method (TCAM) is an access method that provides access to terminals units within a teleprocessing network.


• Teleprocessing is a term coined by IBM and is used to describe a computer with the capability of connecting to another computer or network device.


• Though TCAM provided similar functionality to QTAM, which it replaced, It had its advantages over QTAM


• It was said to have:– Improved buffering, with more buffering options.– Improved organization of message queuing on disk

including multiple volume support.– Back-up copies of messages maintained on disk.


• It was said to have:– Improved testing and debugging (including off-line

testing, improved debugging, online terminal testing, and logging.)

– Improved line handling for inquiry applications.


• It was said to have:– "Significantly increases speed and efficiency over

QTAM."– Improved operator monitoring and control.– Binary Synchronous Support.– Checkpointing.


• Binary Synchronous Communication, aka BSC or Bisync,

• Is an IBM character-oriented, half-duplex link protocol, announced in 1967


• Checkpointing is a technique for inserting fault tolerance into computing systems.

• It basically consists of storing a snapshot of the current application state

• It may use it later on for restarting the execution in case of failure.

Virtual TelecommunicationsAccess Method

Virtual Telecommunications Access Method

• VTAM provides an application programming interface (API) for communication applications,

• IT controls communication equipment such as adapters and controllers.


• In modern terminology, VTAM provides a communication stack and device drivers.


• After a series of delay, VTAM was introduced in 1974 as a major component of SNA (Systems Network Architecture)


• VTAM is an access method software that allows application programs to read and write data to and from external devices.

• It is called 'virtual' because it was introduced at the time when IBM was introducing virtual storage


• Some Features Of VTAM Is That:• Supports several network protocol• Supports 'cross-domain' services

QUESITONS

network access methods

Technology

network access methods

remote terminals btam

polling terminals

improved testing

communication channel

terminals units

improved debugging

improved buffering