Installing and Administering OSI Transport Services

38 Chapter 1

HP OTS/9000 Resources

How OTS/9000 Uses the X.25 Network

OTS/9000 supports the Connection-Oriented Network Service (CONS)

and Connectionless Network Service (CLNS) over the X.25 network. The

main objectives of X.25 are:

• forming the control and data packets

• exchanging these packets

• establishing and supervising virtual circuits

OTS/9000 is primarily concerned with the virtual circuit (VC) objective,

leaving the other objectives to the X.25 product.

When a connection is to be established, a virtual circuit is established at

the network layers. “Virtual”' implies that it is not necessary for a

dedicated connection to exist between systems, but that a logical

association be made through a network based on the source and

destination addresses of the two systems. This does not mean that there

cannot be dedicated circuits. X.25 allows both permanent virtual circuits

(PVC) and switched virtual circuits (SVC), with the distinction based on

how long the association is valid. A PVC maintains a permanent

association. An SVC maintains the association only for the current

connection call.

NOTE OTS/9000 supports only SVCs.

System addresses are based on the X.121 standard which uses a

sequence of 15 deecimal digits (0-9) that includes a subaddress of 0 to 5

digits. When conﬁguring local system addresses (in ots_subnets), the

system address is constructed by concatenating the X.121 address from

the X.25 conﬁguration with the subaddress speciﬁed by the

snet_x25_subaddress parameter. The physical address speciﬁed by the

dest_phys_address parameter in X.25 ots_dests entries is a system

address and contains both the X.25 address and the subaddress.

Null subaddresses can be used for both CONS and CLNS X.25

subnetwork switches that do not support subaddressing. Subaddresses

are unique on a particular link and cannot be shared by different X.25

applications. (See the HP OTS Addendum for information on the

snet_x25_subaddress parameter for deﬁning null subaddresses.)