User manual

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Actiontec Broadband Router User Manual
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Appendix A Quality of Service
Ingress Data
The 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
Router cannot queue packets, since in most cases the local network (LAN) is much
faster then the Internet (WAN), and when the 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)
• No borrowing mechanism
• When reserving Rx bandwidth, it is strictly taken from the bandwidth of all
other classes
Furthermore, the 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).
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.
Diffserv defines a field in IP packet headers referred to as the Differentiated Services
Codepoint (DSCP). Hosts or routers passing traffic to a Diffserv-enabled network
will typically mark each transmitted packet with an appropriate DSCP. The DSCP
markings are used by Diffserv network routers to appropriately classify packets and
to apply particular queue handling or scheduling behavior