Installation Guide

Table Of Contents
Task 11: Configuring quality of service
Active CIR configuration can be verified via the AP’s Home => Session Status tab.
Bandwidth from the SM Perspective
In the SM, normal web browsing, e-mail, small file transfers and short streaming
video are rarely rate limited with practical bandwidth management (QoS) settings.
When the SM processes large downloads such as software upgrades and long
streaming video or a series of medium-size downloads, the bucket rapidly drains,
the burst limit is reached, and some packets are delayed. The subscriber experience
is more affected in cases where the traffic is more latency sensitive.
Interaction of Burst Allocation and Sustained Data Rate
Settings
If the Burst Allocation is set to 1200 kb and the Sustained Data Rate is set to 128
kbps, a data burst of 1000 kb is transmitted at full speed because the Burst
Allocation is set high enough. After the burst, the bucket experiences a significant
refill at the Sustained Data Rate. This configuration uses the advantage of the
settable Burst Allocation.
If both the Burst Allocation and the Sustained Data Rate are set to 128 kb, a burst is
limited to the Burst Allocation value. This configuration does not take advantage of
the settable Burst Allocation.
If the Burst Allocation is set to 128 kb and the Sustained Data Rate is set to 256
kbps, the actual rate is the burst allocation (but in kbps). As above, this
configuration does not take advantage of the settable Burst Allocation.
High-priority Bandwidth
To support low-latency traffic such as VoIP (Voice over IP) or video, the system
implements a high-priority channel. This channel does not affect the inherent
latencies in the system but allows high-priority traffic to be immediately served. The
high-priority pipe separates low-latency traffic from traffic that is latency tolerant,
such as standard web traffic and file downloads.
The number of channels available on the AP is reduced by the number of SMs
configured for the high-priority channel (each SM operating with high-priority
enabled uses two channels (virtual circuits) instead of one).
A module prioritizes traffic by
reading the Low Latency bit (Bit 3) in the IPv4 Type of Service (ToS) byte in a received
packet. Bit 3 is set by a device outside the system.
reading the 802.1p field of the 802.1Q header in a received packet, where VLAN is
enabled on the module.
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pmp-0957 (April 2015)