Functions - D-Link DFL-1600 User Manual

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choke points in large WANs.
23.1.1

Functions

The simplest way to obtain QoS in a network, seen from a security as well
as a functionality perspective, is to have the components in the network,
known as traffic shapers, be responsible for network traffic control in
well-defined choke points. A D-Link firewall has an extensible traffic shaper
integrated inside.
The traffic shaper works by measuring and queuing IP packets, in transit,
with respect to a number of configurable parameters. Differentiated rate
limits and traffic guarantees based on source, destination, and protocol
parameters can be created, much the same way firewall rules are
implemented. The main functions can be summarized as follows:
Applying bandwidth limits by queuing packets that would exceed
configured limits into packet buffers, and sending them later when the
momentary demand for bandwidth is lower.
Dropping packets if the packet buffers are full. The packet to be
dropped should be chosen from those that are responsible for the
congestion.
Prioritizing traffic according to the administrator's choice; if the
traffic in a higher priority increases while a communication line is full,
traffic in lower priorities should be temporarily limited to make room
for the high-priority traffic.
Providing bandwidth guarantees. This is typically accomplished by
treating a certain amount of traffic (the guaranteed amount) as a
higher priority, and traffic exceeding the guarantee as the same
priority as "any other traffic", which then gets to compete with the
rest of the non-prioritized traffic.
Well-built traffic shapers do not normally work by queuing up immense
amounts of data and then sorting out prioritized traffic to send before
sending non-prioritized traffic. Rather, they attempt to measure the
amount of prioritized traffic and then limit the non-prioritized traffic
dynamically, so that it will not interfere with the throughput of prioritized
traffic.
D-Link Firewalls User's Guide
Chapter 23. Traffic Shaping