3com 8807 User Guide

Conventional packet network treats all packets equally. Each switch/router 
processes all packets in First-in-First-out (FIFO) mode and then transfers them to 
the destination in the best effort, but it provides no commitment and guarantee to 
such transmission performance as delay and jitter.

With fast growth of computer networks, more and more data like voice and video 
that are sensitive to bandwidth, delay and jitter are transmitted over the network. 
This makes growing demands on quality of service (QoS) of networks.

Ethernet technology is a widely-used network technology dominant for 
independent LANs and many LANs based on Ethernet are organic parts of the 
Internet. In addition, Ethernet access is becoming one of the major access modes 
for Internet users. Therefore it is inevitable to consider Ethernet QoS if we want to 
achieve point-to-point global QoS solution. Ethernet switching devices then 
naturally need to provide different QoS guarantee for different types of services, 
especially for those which are sensitive to delay and jitter.

The following terms are involved in QoS.

It refers to all packets passing thought the switch.

Traffic classification is the technology that identifies the packets with a specified 
attribute according to a specific rule. Classification rule refers to a packet filtering 
rule configured by an administrator. A classification rule can be very simple. For 
example, the switch can identify the packets of different priority levels according 
to the ToS (type of service) field in the packet headers. It can also be very complex. 
For example, it may contain information of the link layer (layer 2), network layer 
(layer 3) and transport layer (layer 4) and the switch classifies packets according to 
such information as MAC address, IP protocol, source address, destination address 
and port ID. Classification rule often is limited to the information encapsulated at 
the packet header, rarely using packet contents.

Packet filtering refers to filtering operation applied to traffic flow. For example, the 
deny operation drops the traffic flow which matches the classification rule and 
allows other traffic to pass. Ethernet switches use complex classification rules, so 
that traffic flow can be filtered purposefully to enhance network security.

There are two key steps in packet filtering:

Step 1: Classify the traffic at the port according to a specific rule.