User's Manual

Receiving Data from a Child

If a child node has data queued for transmission upstream and is not in active communication with its parent, it will signal the need

by transmitting a Bandwidth Request message in the next contention slot. The details of the Bandwidth Request, including the

priority of the data queued, is stored by the parent node and accessed by the scheduler.

In the current SkyPilot system, child status is polled by the parent. Having made the decision to poll status from a given child node,

a parent transmits a Poll Request message in the next scheduled mini-slot with that child. Upon being polled, a child node

immediately transmits a packet up to the maximum size specified in the Poll Request message.

The polling of a child continues as long as upstream bandwidth is queued plus an additional integration period of 0.5 seconds after

the queue is emptied. This continued periodic polling allows an active node to make a low-latency upstream transfer by avoiding

the need for the child node to contend. The parent also utilizes any unused bandwidth to poll recently active nodes beyond the 0.5

second integration period.

In addition to the dedicated Poll Request message, a parent node can also include a Poll Request with a data frame transmitted to

a child. A future revision of the SkyPilot protocol may replace the Poll Request messages with upstream bandwidth grants that

directly allocate one or more transmit opportunities to a child node. Both of these mechanisms increase bandwidth efficiency by

removing the Poll Request message overhead and propagation delay.

Quality of Service

The SkyPilot Carrier-Class Broadband Wireless System supports the following Quality of Service (QoS) features:

• Subscriber Rate Control

An operator can define maximum upstream and downstream data rates for a subscriber. This rate control is implemented at

the ingress points; i.e. at the SkyGateway in the downstream direction, and at the SkyConnector/SkyExtender in the upstream

direction.

• Packet Prioritization

An operator may prioritize individual subscriber packets based on a range of parameters. This classification is completed at

the ingress points and the packets marked as having a high or low priority. This prioritization is then maintained by any

intermediary SkyExtenders.

Downstream QoS

The downstream QoS functionality is implemented by the SkyGateway and any intermediary SkyExtenders. The SkyGateway limits

and shapes the user data received over the local 10/100Base-T Ethernet interface using a token bucket-based algorithm. The

SkyGateway maintains a token bucket for every SkyConnector, every SkyExtender DualBand, and every SkyExtender providing

subscriber termination). The depth of each token bucket is defined by the maximum allowable burst size, and is filled with tokens at

a constant rate derived from the configured maximum data rate.

The SkyGateway classifies all Ethernet packets received on the 10/100Base-T Ethernet interface in accordance with the

configuration specified by the operator. For each individual subscriber (SkyConnector or SkyExtender) the operator may designate

packets as having a high priority using one or more of the following means:

• Source/Destination IP Address

A single IP address, a number of IP addresses, an IP address range or a number of IP address ranges. This classifier can be

used to prioritize packets exchanged between a subscriber and a voice gateway.

• IP Type of Service (ToS)

An IP header field that is used by certain protocols/equipment to indicate packet priority and type.

• IP Protocol Type

An IP header field used to indicate the packet protocol type.

• IEEE 802. 1p

A Layer 2 protocol that is used to mark the priority of individual Ethernet packets.