User's Manual
Conguring Quality of Service
A.2 Trac Shaping
A
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A.2c Ingress Data
The FiOS Router can control outgoing data fairly easily. It can queue packets,
delay them, give precedence to other packets, or drop them. This helps in
resolving upload (Tx) traffic bottlenecks, and in most cases is sufficient. However,
in the case of download (Rx) traffic bottlenecks, the ability to control the flow is
much more limited. The FiOS Router cannot queue packets, since in most cases
the local network (LAN) is much faster than the Internet (WAN), and when the
FiOS Router receives a packet from the Internet, it passes it immediately to the
local network.
QoS for ingress data has the following limitations, which do not exist for
outgoing data:
QoS can only be applied to TCP streams (UDP streams cannot be delayed);t
no borrowing mechanism;t
and when reserving Rx bandwidth, it is strictly taken from the bandwidth of t
all other classes.
Furthermore, the FiOS Router cannot control the behavior of the ISP, which may
not have proper QoS handling. Unfortunately, this is a common situation. Let’s
look at a scenario of downloading a large file and surfing the Internet at the
same time. Downloading the file is distinguished by small requests, followed
by very large responses. This may result in blocking HTML traffic at the ISP.
A solution for such a situation is limiting the bandwidth of low-priority TCP
connections (such as the file download).
A.2d Differentiated Services Code Point Settings
In order to understand what DSCP is, one must first be familiarized with the
Differentiated Services model.
Differentiated Services (Diffserv) is a Class of Service (CoS) model that
enhances best-effort Internet services by differentiating traffic by users, service
requirements, and other criteria. Packets are specifically marked, allowing
network nodes to provide different levels of service, as appropriate for voice
calls, video playback, or other delay-sensitive applications, via priority queuing or
bandwidth allocation, or by choosing dedicated routes for specific traffic flows.