Verilink 9000 Series (34-00271) Product Manual - Manual (Page 246)

224 C HAPTER 13: X.25
When purchasing X.25 service from a communications provider, learn certain
information needed to configure the MultiPro platform for use on that network.
Some of the more critical parameters are packet size, number of LCNs (logical
channel numbers), and local address.
Packet
Size
This represents the maximum number of bytes of user information that may be
carried in any one data packet. If a message is larger than 256 bytes, the X.25
protocol segments it into as many packets as necessary and reassembles it at the
receiving end.
Number
of LCNs
The number of LCNs (logical channel numbers) assigned to a link determines how
many devices may use the link at any given time. Each device that needs a
connection to a remote destination uses one LCN. There must be enough LCNs to
service the number of devices at a site.
Local
Address
Each access of an X.25 network is assigned a numerical address. This can be
considered as a general address for the location. Each device at a site is assigned a
subaddress which, when combined with the local address, creates one unique
address for that device. Any device in the network can then establish a connection
with that device by specifying its full address.
An X.25 network is usually depicted as a cloud. This cloud is actually made up of
many connected X.25 switches that constantly talk to each other to determine
which pathways might be up or down and what the least congested pathway is.
Their interoperation is completely transparent to the user and therefore represented
simplisticly on a network diagram. Figure 13-2 shows an X.25 cloud with MultiPro
units connected to it. In this case the MultiPro unit is referred to as a PAD (packet
assembler /disassembler). There are also indications as to what the local addresses
are as well as screens from the NMCS showing how the X.25 ports are configured.
LCN Calling Addr. Length Called Addr. Length Called Address Calling Address Facility Field User Data
1 Octet 1 Octet 1-8 Octets 1-8 Octets Variable Variable
Figure 13-1 X.25 Packet
DOWNLOAD CONFIG
MODE BACKUP NET ALARM POWER
PRISM 9111 T R A N S P O R T
®
DOWNLOAD CONFIG MODE BACKUP NET ALARM POWER
PRISM 9111 T R A N S P O R T
®
Unit 001
Unit 002
Local Address:
3138381764
Local Address:
4119670097
HOSTA
X.25
Processor
Figure 13-2 Typical Application using Local Addresses