Apart from the data transfer rate in transmission direction, the same consideration applies also to the receiving direction. Due to its 10 or 100 Mbps Ethernet interface, the LANCOM’s WAN interface is fed by clearly fewer data from the broadband modem than would actually be receivable. All data packets received on the WAN interface are transferred to the LAN with equal rights.
In order to be able to prioritize incoming data as well, thus an artificial “brake” must be added also in this direction. Like already incorporated for the upstream direction, the data transfer rate of the interface is therefore adapted to the provider’s offer in the downstream direction. For a standard DSL connection thus e.g. a downstream rate of 768 kbps applies. Again, the gross data rate can be entered here, if known.
Reducing the receiving bandwidth makes possible to treat received data packets suitably. Preferred data packets will be directly passed on to the LAN up to the guaranteed minimum bandwidth, all remaining data packets are running into congestion. This congestion produces generally a delayed confirmation of the packets. For a TCP connection, the sending server will react to this delay by reducing its sending frequency and adapting itself to the available bandwidth.
The following queues operate on the receiving side:
- Deferred Acknowledge Queue Each WAN interface contains additionally a QoS reception queue, which takes up those packets that should be „slowed down“. The storage period of each individual packet depends on its length and on the actual permitted reception bandwidth on the receiving side. Packets with a minimum reception bandwidth assigned by a QoS rule are passing through without any further delay, as long as the minimum bandwidth is not exceeded.
- Standard reception queue All packets that do not need special treatment because of an active QoS rule on the receiving side end up here. Packets of this queue are directly passed on resp. confirmed without consideration of maximum bandwidths.