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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.
Basic telecommunications access method
Basic telecommunications access method
• 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
Basic telecommunications access method
• This is harder than using a higher-layer protocol, but it permits interfacing to non-standard devices in non-standard ways
Basic telecommunications access method
• 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.
Basic telecommunications access method
• 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
Basic telecommunications access method
• 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.
Basic telecommunications access method
• BM finally withdrew support for BTAM in 2000.
Queued Telecommunications Access Method
Queued Telecommunications Access Method
• Queued Telecommunications Access Method (QTAM) is an IBM System/360 communications access method incorporating built-in queuing.
Queued Telecommunications Access Method
• 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)
Queued Telecommunications Access Method
• Threads being the smallest sequence of programmed instructions that can be managed independently
Queued Telecommunications Access Method
• 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
Queued Telecommunications Access Method
• The MCP was assembled by the user installation from a set of macros supplied by IBM.
Queued Telecommunications Access Method
• These macros defined:• The lines and terminals comprising the
system, • The datasets required, • And the procedures used to process received
and transmitted messages.
Queued Telecommunications Access Method
• 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
• Telecommunications Access Method (TCAM) is an access method that provides access to terminals units within a teleprocessing network.
Telecommunications Access Method
• 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.
Telecommunications Access Method
• Though TCAM provided similar functionality to QTAM, which it replaced, It had its advantages over QTAM
Telecommunications Access Method
• 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.
Telecommunications Access Method
• 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.
Telecommunications Access Method
• It was said to have:– "Significantly increases speed and efficiency over
QTAM."– Improved operator monitoring and control.– Binary Synchronous Support.– Checkpointing.
Telecommunications Access Method
• Binary Synchronous Communication, aka BSC or Bisync,
• Is an IBM character-oriented, half-duplex link protocol, announced in 1967
Telecommunications Access Method
• 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.
Virtual Telecommunications Access Method
• In modern terminology, VTAM provides a communication stack and device drivers.
Virtual Telecommunications Access Method
• After a series of delay, VTAM was introduced in 1974 as a major component of SNA (Systems Network Architecture)
Virtual Telecommunications Access Method
• 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
Virtual Telecommunications Access Method
• 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
Virtual Telecommunications Access Method
• Some Features Of VTAM Is That:• Supports several network protocol• Supports 'cross-domain' services
QUESITONS
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