Quality of Service
BAT54-Rail/F..
Release
7.54
06/08
9.3
The queue concept
317
Different is the case, if an Ethernet interface represents the connection to the
WAN. From the BAT’s point of view, the connection to the Internet via an ex-
ternal broadband modem looks like an Ethernet segment. On the distance
from the BAT 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
BAT 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, sur-
plus data will be lost. Thus a prioritization of “preferred” data is not possible!
To solve this problem, the transfer rate of the BAT’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 stan-
dard DSL connection, the DSL interface is thus adjusted in the BAT to the
appropriate upstream rate (e.g. 128 kbps).
9.3.2 Queues for receiving direction
Apart from the data transfer rate in transmission direction, the same consid-
eration applies also to the receiving direction. Due to its 10 or 100 Mbps Eth-
ernet interface, the BAT’s WAN interface is fed by clearly fewer data from the
broadband modem than would actually be receivable. All data packets re-
ceived on the WAN interface are transferred to the LAN with equal rights.
Data rates indicated by providers are mostly likely net rates. The gross
data rate, which is available for the interface is a little bit higher than the net
data rate guaranteed by the provider. If you know the gross data rate of
your provider, you can enter this value for the interface and slightly in-
crease in this way the data throughput. However, with entering the net data
rate you play safe in any case!
100 MBps
54 MBps
100 MBps
128 KBps
dropped data
n x 64 kBps
Internet
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