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LANCOM Reference Manual LCOS 3.50 ̈ Chapter 9: Quality of Service
174
Quality of Service
data packets it is still able to receive, and thus brakes the data stream already
within the router. As a result, the queues will automatically fill up.
Different is the case, if an Ethernet interface represents the connection to the
WAN. From the LANCOM’s point of view, the connection to the Internet via
an external broadband modem looks like an Ethernet segment. On the dis-
tance from the LANCOM to the DSL modem, data will be transferred with full
LAN speed of 10 or 100 Mbps. Because of an equal input and output speed,
no natural congestion will be produced then. Furthermore, the Ethernet
between the LANCOM and the broadband modem does not report anything
about the capacity of the connection. The consequence: a congestion will only
be happen within the broadband modem. But because no queues are
deployed therein, surplus data will be lost. Thus a prioritisation of “preferred”
data is not possible!
To solve this problem, the transfer rate of the LANCOM’s WAN interface will
be reduced artificially. This interface will thereby be adjusted to the transfer
rate that is available for the actual data transport towards the WAN. For a
Queues
100 MBps
54 MBps
64 KBit/s
n x 64 kBps
128 KBps
Internet
100 MBps
54 MBps
100 MBps
128 KBps
dropped data
n x 64 kBps
Internet