Quality of Service
316
9.3
The queue concept
BAT54-Rail/F..
Release
7.54
06/08
As long as the interval for the minimum bandwidth is not exceeded (i.e.
up to the end of the current second), all packets in this queue are treated
without further special priority. All packets of this queue, of the "secured
queue" and the "standard queue" share now the existing bandwidth. The
packets are taken in order from the queues when sending in exactly the
same sequence, in which they have been placed into these queues. If
the interval runs off, all blocks, which are at this time still in the "Urgent
queue II" up to the exceeding of the in each case assigned minimum
bandwidth, are placed again into the "Urgent queue I". The rest remains
in the "Urgent queue II".
With this procedure it is guaranteed that prioritized connections do not
crush the remaining data traffic.
D Secured queue
This queue does not have a separate priority. However, packets in this
queue are never dropped (transmission guaranteed).
D Packets with ToS “High Reliability“
D Packets with DiffServ “Assured Forwarding“
D Standard queue
The standard queue contains all not classified data traffic. Packets in this
queue are dropped at first when packets cannot be delivered fast
enough.
The queue concept can, however, only work out when a “traffic congestion“
of data packets has been accumulated at the interface from LAN to the WAN.
Such a congestion is created when the interface within the BAT can submit
fewer data to the WAN than data are delivered in peak periods from the LAN.
This is e.g. the case, if the interface to the WAN is an integrated ADSL inter-
face with comparatively low transmission speed (“upstream”). The integrated
ADSL modem automatically reports back to the BAT how many 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.
Queues
100 MBps
54 MBps
64 KBit/s
n x 64 kBps
128 KBps
Internet
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