OSI/TS Configuration and Management Manual

OSI Transport Services
OSI/TS Configuration and Management Manual—424831-001
5-3
Protocol Classes
Protocol Classes
During connection establishment, the OSI/TS subdevice and the corresponding transport
peer entity negotiate the protocol class they will use to manage the connection.
OSI/TS supports transport protocol classes 0, 1, 2, 3, and 4. All five classes can be used
with connection-mode network service. Only class 4 can be used with connectionless
network service. In general, only classes 0, 1, 2, and 3 are used for communicating over
wide area networks; class 4 is used over local area networks. Although OSI/TS supports
class 4 for wide area networks, use of this protocol class is not recommended since it
reduces system performance.
The protocol classes are described below. Error recovery, error detection, and
multiplexing are described later in this section.
Class 0: Simple Class
Protocol class 0 does not provide error recovery or error detection. Transport
connections established with this protocol cannot be multiplexed onto the same
subnetwork connection.
Responding address
Specifies the address (TSAP) of the responding (remote)
transport user to which transport connection has been
established. It must be the same as the called address in
the connect request and indication service primitives.
Disconnect reason In the disconnect request from the responding (remote)
transport user, specifies the reason for the disconnect.
Transport user data
Passes unchanged in the file-system buffer between the
OSI/TS subsystem and the application. Table 5-2
lists the
maximum size for user data that OSI/TS allows for each
type of service primitive.
Table 5-2. Maximum Length of Transport User Data
Service Primitive Class Maximum Octets of User Data
T-CONNECT 0
1, 2, 3, 4
0
32
T-DATA All Unlimited
T-EXPEDITED DATA 0
1, 2, 3, 4
Not available
16
T-DISCONNECT 0
1, 2, 3, 4
0
64
Called address
Specifies the transport service access point (TSAP) address
of the responding (remote) transport user.