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FIGURE 1.

General Panel

TRAFFIC PRIORITY

Traffic Priority allows you to manage and avoid traffic congestion by defining in-

bound and outbound priority rules for each device on your gateway. These rules

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QoS Section

determine the priority that packets, traveling through the device, will receive.

QoS parameters (DSCP marking and packet priority) are set per packet, on an

application basis.

You can set QoS parameters using flexible rules, according to the following pa-

rameters:



Source/destination IP address, MAC address or host name



Device



Source/destination ports



Limit the rule for specific days and hours

The Router supports two priority marking methods for packet prioritization:



DSCP



802.1p Priority

The matching of packets by rules is connection-based, known as Stateful

Packet Inspection (SPI). Once a packet matches a rule, all subsequent packets

with the same attributes receive the same QoS parameters, both inbound and

outbound.

A packet can match more than one rule. Therefore:



The first class rule has precedence over all other class rules (scanning is

stopped once the first rule is reached).



The first traffic-priority (classless) rule has precedence over all other traffic-

priority rules.



There is no prevention of a traffic-priority rule conflicting with a class rule. In

this case, the priority and DSCP setting of the class rule (if given) will take

precedence.

Connection-based QoS also allows inheriting QoS parameters by some of the

applications that open subsequent connections. For instance, you can define

QoS rules on SIP, and the rules will apply to both control and data ports (even if

the data ports are unknown):



SIP



MSN Messenger/Windows Messenger



TFTP



FTP



MGCP



H.323



Port Triggering applications



PPTP



IPSec

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FIGURE 2.

Traffic Priority Panel

To set traffic priority rules:

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1.

Click 'Traffic Priority' under the 'QoS' tab in the 'Services' screen. The 'Traffic

Priority' screen will appear. This screen is divided into two identical sections,

one for 'QoS input rules' and the other for 'QoS output rules', which are for

prioritizing inbound and outbound traffic, respectively. Each section lists all

the gateway devices on which rules can be set. You can set rules on all de-

vices at once, using the 'All devices' entry.

2.

After choosing the traffic direction and the device on which to set the rule,

click the appropriate New Entry link. The 'Add Traffic Priority Rule' screen

will appear.

This screen is divided into two main sections, 'Matching' and 'Operation', which

are for defining the operation to be executed when matching conditions apply.

-

Matching:

Use this section to define the rule's conditions, which are the LAN

computer's parameters to be matched.

-

Operation:

Set rule priority with Quality of Service.

3.

Click 'OK' to save the settings.

TRAFFIC SHAPING

Traffic Shaping is the solution for managing and avoiding congestion where a

high speed LAN meets limited broadband bandwidth. A user may have, for ex-

ample, a 100 Mbps Ethernet LAN with a 100 Mbps WAN interface router. The

router may communicate with the ISP using a modem with a bandwidth of

2Mbps. This typical configuration makes the modem, having no QoS module,

the bottleneck. The router sends traffic as fast as it is received, while its well-

designed QoS algorithms are left unused. Traffic shaping limits the bandwidth of

the router, artificially forcing the router to be the bottleneck.

A traffic shaper is essentially a regulated queue that accepts uneven and/or

bursty flows of packets and transmits them in a steady, predictable stream so

that the network is not overwhelmed with traffic.

While Traffic Priority allows basic prioritization of packets, Traffic Shaping pro-

vides more sophisticated definitions. Such are:



Bandwidth limit for each device



Bandwidth limit for classes of rules



Prioritization policy



TCP serialization on a device

Additionally, you can define QoS traffic shaping rules for a default device.

These rules will be used on a device that has no definitions of its own. This en-

ables the definition of QoS rules on Default WAN, for example, and their main-

tenance even if the PPP or bridge device over the WAN is removed.

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FIGURE 3.

Traffic Shaping Panel

DSCP SETTINGS

In order to understand what is Differentiated Services Code Point (DSCP), one

must first be familiarized with the Differentiated Services model.

Differentiated Services (Diffserv) is a Class of Service (CoS) model that en-

hances best-effort Internet services by differentiating traffic by users, service

requirements and other criteria. Packets are specifically marked, allowing net-

work 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.