OSI/TS Configuration and Management Manual

Managing a Transport Connection
OSI/TS Configuration and Management Manual—424831-001
6-2
Protocol Negotiation
Protocol Negotiation
During the connection-establishment phase, correspondent transport peer entities
negotiate the services they will provide on the transport connection. The main issues to
be decided are:
Connection-Initiation Tasks
OSI/TS initiates the connection-establishment procedure upon receiving a T-CONNECT
request service primitive from a local transport user. After the transport connection is
established, OSI/TS completes the request by returning a T-CONNECT confirm service
primitive to the same user.
As the initiator of connection establishment, OSI/TS performs the following tasks
during connection establishment:
1. Requests a subnetwork connection. OSI/TS checks the NSP to see if a subdevice
for an existing transport connection, with the same NSAP, has already been
configured. If not, and if the transport subdevice is not configured for multiplexing,
OSI/TS adds and starts a new X25AM subdevice for WANs, or adds a new
TLAM/PAM port for LANs. For WANs, OSI/TS establishes a network connection,
if one is not already available.
2. Builds a CR-TPDU. OSI/TS builds a CR-TPDU and sends it over the subnetwork
connection to the remote transport entity.
3. Completes the connection if the initiation is successful. On reception of a valid CC-
TPDU from the remote transport entity, OSI/TS makes any necessary adjustments to
accommodate changes to the negotiated parameters.
4. Returns an error if the initiation fails. OSI/TS returns a T-CONNECT confirm
service primitive to the transport user.
5. If OSI/TS does not receive a valid CC-TPDU from the remote peer entity before the
connection timer times out, it informs the transport user by issuing file-system error
140.
The following subsections describe these steps in more detail.
Class The transport protocol class to be used over the life of the
transport connection
TPDU size The size of the protocol data units to be transferred between
transport peer entities
Expedited PDUs Whether transport entities will handle expedited protocol data
units
Checksums Whether transport entities will calculate and validate checksums
in class 4
Extended format Whether extended format will be used