User Manual

System Architecture and Protocol Guide – 9-05 13 © 2005 SkyPilot Networks, Inc.
The operator can use a range of classifiers to control prioritize packets. For instance, an operator may assign a high priority to
packets matching a range of IP addresses and having a defined ToS field setting. Any packets not matching this classification will
be assigned a low priority. The resulting classification is tagged (in the SkyPilot protocol header) so that any intermediary
SkyExtenders can maintain the prioritization.
Upon receiving an Ethernet packet, the SkyGateway first performs the traffic classification. Having designated a packet as having a
high or low priority, the subscriber’s token bucket is checked to see if it has enough tokens for packet transmission. If there are no
tokens in the bucket, tokens may be borrowed. For low priority packets, tokens can be borrowed up to double the configured
downstream rate. For high priority packets, tokens can be borrowed up to three times the configured downstream rate. If a token is
available, the packet is queued to the downstream link—high priority packets to the high priority queue and low priority packets for
the low priority queue. If there are no tokens available, then the packet will be dropped.
The figure below illustrates the SkyGateway QoS mechanisms:
Note that broadcast and multicast packets are also rate-controlled. The default configured downstream rate is 128 kbps.
Upstream QoS
In the upstream direction, the SkyConnector or SkyExtender limits and shapes the user data received over the local 10/100Base-T
Ethernet interfaces. The SkyConnector and SkyExtenders perform the same packet classification and token bucket shaping as the
SkyGateway.