ELSA LANCOM Business LC-4X00, Manual

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Operating modes and functions
ELSA LANCOM Business
61
Once the IPX router is fully configured and is ready for operation, it proceeds to establish
connections to all remote stations which can be reached via the routing tables and then
exchanges SAP and RIP information with these networks. The router saves this data to
its internal SAP and RIP tables.
RIP and SAP tables
RIP and SAP information is sorted alphabetically in the relevant tables. RIPs are thus only
ordered by network and SAPs by service type first, then by server name.
The RIP and SAP tables are updated with each new RIP or SAP packet. The router only
incorporates in its table SAP information for which it also has a corresponding RIP entry
to ensure that only those services are offered (SAP) which can also be reached (RIP). The
entries on the tables indicate, in addition to the information on reachable routes and
services, how many routers the path to the destination (hops) passes through or how
much time a data packet needs in the destination network (tics = approx. 1/18 of a
second), for instance. The router selects the path with the fewest tics and the lowest
hop count from the tables and stores only this route if the RIP information offers several
different routes to a destination network, for instance.
RIP tables can hold 64 entries and SAP tables 128. If each new packet updates the
tables, it stands to reason that the old entries must also disappear at some stage. Entries
are artificially aged to do this. The age of all entries on RIP/SAP tables derived from local
data transfers is incremented by 1 point every 60 seconds. A new RIP or SAP packet for
an entry resets the age to zero. The route or service can be designated unreachable
(down) once a selectable age of between 1 and 60 is reached. The entry is deleted when
this elapsed time doubles. Additionally, any RIP and SAP information related to this
remote station is deleted from the tables and replaced with new information when a
connection is established.
So many routers around here...
If the establishment of simultaneous network connections to a greater number of remote
stations is required than the number of B channels available, then it's time for a second
(third...) router. The same entries are made in the routing tables for all routers to ensure
that the brothers function in perfect harmony with each other and that the network really
can always find a contact. The same routing information is then sent in the RIP packets
to each router, albeit with a higher tic and hop count (
Setup/IPX-module/LAN-
config/RIP-SAP-scal.
activate). This marks these routes as a sort of stand-by
in the event that all channels are busy on the device addressed.