ELSA LANCOM Business 6000, Manual

Page: 140 / 174

Technical basics
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ELSA LANCOM Business 6000
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140
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RIP and SAP tables are matched with each new RIP or SAP packet. So that
only such services are provided (SAP) which are also accessible (RIP), the
router includes only this SAP information in its table, for which there is also
a corresponding RIP entry. Besides the information on accessible routes and
services, the entries of the tables also indicate, for example, how many
routers must be crossed before reaching the destination (hops) or how much
time a data packet requires in order to reach the destination network (tics =
ca. 1/18 seconds). If, for example, several routes are offered to a destination
network via the RIP information, the router selects the route with the least
tics and the smallest hopcount according to the tables and stores only this
route.
RIP tables can contain 64 entries, SAP tables can contain 128 entries. When
each new packet updates the tables, the older entries will naturally
disappear after some time. In addition, the entries become artificially aged.
For all entries in the RIP/SAP tables which were acquired via local data
exchange, the age is increased every 60 seconds by one. A new RIP or SAP
packet for an entry sets the age back to zero. After an adjustable age from 1
to 60, the route or service is designated as inaccessible (Down). If double this
amount of time has transpired, the entry is removed. In addition, all RIP and
SAP information concerning this remote station is deleted from the tables
when a connection is established and is replaced with new information.
7.4.6 There are so many routers here...
If connection setup to more remote stations is simultaneously desired in a
network than a router can realize, then it is time for a second (or more...)
router. In order for the interaction of the routers to function smoothly and to
ensure that the network always locates a contact partner, the same entries
are carried out in the routing table in all routers. The same routing informa-
tion is transmitted to each router with higher tic and hopcount via RIP packets
(connect
Setup/IPX module/LAN-config/RIP-SAP-scal.)
.
These routes are thus highlighted as reserves when all channels are occupied
on the device that is addressed.
7.4.7 Redundant routes
If a router receives information with a RIP packet about routes having the
same tic and hopcount as its own routes (redundant routes), these routes
naturally do not have to be disclosed to the sender again. It sends these