Installing and Administering OSI Transport Services

32 Chapter 1
HP OTS/9000 Resources
Supported Services and Functionality
Transport Functionality
The Transport layer corresponds to layer 4 of the OSI reference model.
As with the Session layer, the Transport layer provides cooperating
applications with a standard protocol to organize and exchange user
data. Unlike Session, the Transport is implemented with a greater
knowledge of the underlying network configuration. Therefore, its
definition involves details hidden from the Session layer entity.
The level of Transport sophistication and capabilities are divided into
classes of operation, 0 through 4. OTS/9000 implements the following:
• An application using the Connectionless Network Service (CLNS)
must use TP (Transport) class 4.
• An application using the Connection-Oriented Network Service
(CONS) can use TP classes 0, 2, or 4.
• OTS supports Transport (TP) classes 0, 2, and 4 over CONS/X.25 and
TP class 4 over a CLNS IEEE 802.3 or FDDI LAN and CLNS/X.25.
• TP 0 is the only alternate class OTS supports.
When an administrator configures a class parameter for CONS
communications, they can force the use of class 0 only or offer a preferred
multiplexing class (TP 2 or TP 4). On the connect request, the transport
user can select the preferred class, with or without class 0 as an
alternative, or simply select class 0. For example, if an application
requests an alternate class of 0 and multiplexing, OTS/9000 may propose
TP 2 with an alternate of TP 0 and send the connect request. If the
remote does not allow TP 2, TP 0 is used to make the connection.