Installing and Administering OSI Transport Services

Chapter 1 33
HP OTS/9000 Resources
How OTS/9000 Finds a Remote End System
How OTS/9000 Finds a Remote End
System
After a brief review of what an end system and an intermediate system
are, this section describes how routing information is obtained and
provided, and how OTS/9000 uses it.
A system can act as an end system or as an intermediate system. OTS
can function only as an ES.
• An end system (ES) initiates or responds to a communication (it
supports layers 1 through 7).
• An intermediate system (IS) forwards communication traffic across
subnetworks (it supports layers 1 through 3).
• Routing means establishing a path across the subnetwork(s) and
intermediate system(s) so that data is exchanged between end
systems. Normally, an ES communicates directly with another ES.
That is, they are connected to the same subnetwork. If the local ES
cannot directly reach the remote ES, the local ES makes the first
“hop” to an IS. The IS determines the best path to the remote ES.
OTS/9000 can function as:
• An ES connected to a single subnetwork.
• An ES connected to multiple subnetworks. OTS/9000 is capable of
choosing different routes for sending a PDU, but it does not forward
PDUs.
OTS/9000 does not function as an IS.
Routing information can be provided dynamically through the ES-IS
protocol, or it can be provided statically through the osiadmin
configuration screens. Remote LAN systems that support the ES-IS
protocol periodically multicast their NSAP and MAC addresses. By
default, OTS/9000 records these addresses in a routing table. These
dynamic table entries are discarded after a period of time specified by the
remote system. Static table entries, that do not time-out, can be
configured using osiadmin. When the routing table is full, any new
dynamic routing information is ignored.