OSI/TS Configuration and Management Manual

OSI Transport Services
OSI/TS Configuration and Management Manual—424831-001
5-4
Class 1: Error Recovery
Class 0 is best suited for nonmultiplexed applications for which the rate of errors
generated by the subnetwork is acceptable. It provides the highest performance for
applications that can tolerate the absence of error handling.
Class 1: Error Recovery
Protocol class 1 provides the services of class 0, plus error recovery. It provides
mechanisms for recovering from subnetwork reset or disconnect indications. Under this
protocol, OSI/TS retains transport protocol data units (TPDUs) until they are
acknowledged by the corresponding peer entity. If the subnetwork issues a disconnect
indication during a transport connection, OSI/TS attempts to establish a new connection
through the subnetwork.
Class 1 provides no mechanisms for detecting errors not reported by the subnetwork.
Transport connections established using this protocol cannot be multiplexed onto the
same subnetwork connection.
Class 1 is best suited for nonmultiplexed applications for which the rate of subnetwork
disconnects and resets is not acceptable.
Class 2: Multiplexing
Protocol class 2 provides the services of class 0, plus multiplexing. It provides transport
connections that can be multiplexed onto the same subnetwork connection. This
protocol does not provide mechanisms for error recovery or error detection.
Class 2 is best suited for multiplexed applications for which the rate of errors generated
by the communication subnetwork is acceptable. OSI/TS supports explicit flow control
for class 2.
Class 3: Multiplexing and Error Recovery
Protocol class 3 combines the services of classes 1 and 2. It provides transport
connections that can recover from signaled subnetwork resets and disconnects, and that
can also be multiplexed onto the same subnetwork connection. This protocol, however,
cannot detect unsignaled subnetwork errors.
Class 3 is best suited for multiplexed applications for which the rate of subnetwork
disconnects and resets is unacceptable.
Class 4: Multiplexing and Error Detection
Protocol class 4 provides transport connections with the capabilities of class 3, plus the
ability to detect and recover from unsignaled subnetwork failures.
Error Detection and Recovery
OSI/TS provides a number of error detection and recovery mechanisms. The services
vary according to the transport protocol class. Table 5-3 shows the services that OSI/TS
provides in each class of transport connection.