HP 3000 Manuals HP 3000 Manuals
The Functional Layers of SNA
An SNAnetwork consists of a set of Network Addressable Units
(NAUs)connected by a common path control network. The logical connection
between NAUs is called a session. Each NAU is organized into functional
layers. Each layer serves the next highest layer in its own node and
relates to its peer layer on another node. Direct communication with
another node occurs only at the lowest layer of a network. The
functional layers of SNA
implemented by the SNA IMF and SNA link products, beginning with the
lowest level, are as follows:
* Physical Control, which sends and receives bits between nodes. It
defines the mechanical and electrical interfaces and the bit-level
data flow to the network.
* Data Link Control, which schedules and sends data across a link
(physical connection) between two nodes and monitors errors that
occur on the link.
* Path Control, which provides paths between end users (terminal
operators, programs, or devices) and routes data between these end
users.
* Transmission Control, which synchronizes and paces session-level
data traffic, checks the sequence numbers of requests, and codes
and decodes end user data.
* Data Flow Control, which monitors and controls the flow of data
between two logically connected Network Addressable Units.
* Presentation Services, which formats data to be displayed or
printed.
* Application, which provides services that directly support end
users such as resource sharing, file transfers, remote file
access, and data management on LU-LU sessions.
You can find introductory material about SNA and data communications in
the Communicating With IBM primer and the Getting Started with SNA Node
Management manual.
SNA IMF, along with the SNA link product, implements the seven functional
layers of SNA.