QoS Traffic Requirements Data

Different applications have different traffic characteristics.

Different versions of the same application can have different traffic characteristics.

Classify data into relative-priority model with no more than four to five classes:

Mission-Critical Apps: Locally defined critical applications

Transactional: Interactive traffic, preferred data service

Best-Effort: Internet, e-mail, unspecified traffic

Less-Than-Best-Effort (Scavenger): Napster, Kazaa, peer-to-peer applications

Different applications have different traffic characteristics.

Different versions of the same application can have different traffic characteristics.

Classify data into relative-priority model with no more than four to five classes:

Mission-Critical Apps: Locally defined critical applications

Transactional: Interactive traffic, preferred data service

Less-Than-Best-Effort (Scavenger): Napster, Kazaa, peer-to-peer applications

The QoS requirements for data traffic vary greatly. Different applications may make very different demands on the network (for example, a human resources application versus an automated teller machine application). Even different versions of the same application may have varying network traffic characteristics.

While data traffic can demonstrate either smooth or bursty characteristics depending upon the application, data traffic differs from voice and video in terms of delay and drop sensitivity. Almost all data applications can tolerate some delay and generally can tolerate high drop rates.

Because data traffic can tolerate drops, the retransmit capabilities of TCP become important and, as a result, many data applications use TCP.

In enterprise networks, important (business-critical) applications are usually easy to identify. Most applications can be identified based on TCP or UDP port numbers. Some applications use dynamic port numbers that, to some extent, make classifications more difficult. Cisco IOS software supports network-based application recognition (NBAR), which you can use to recognize dynamic port applications.

It is recommended that data traffic be classified into no more than four to five classes as described in the graphic. There will still remain additional classes for voice and video.

QoS Traffic Classes

This topic describes how to divide traffic into traffic classes.

Step 2:

Divide Traffic into Classes

After the majority of network traffic has been identified and measured, use the business requirements to define traffic classes.

Because of its stringent QoS requirements, voice traffic will almost always exist in a class by itself. Cisco has developed specific QoS mechanisms such as low-latency queuing (LLQ) that ensure that voice always receives priority treatment over all other traffic.

After you have defined the applications with the most critical requirements, you define the remaining traffic classes using the business requirements.

Example: Traffic Classification

A typical enterprise might define five traffic classes as follows:

■ Voice: Absolute priority for Voice over IP (VoIP) traffic

■ Mission-critical: Small set of locally defined critical business applications

■ Transactional: Database access, transaction services, interactive traffic, preferred data services

■ Scavenger (less-than-best-effort): Napster, Kazaa, and other point-to-point applications

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