Alteon OS Application Guide

Using DSCP Values to Provide QoS

The six most significant bits in the TOS byte of the IP header are defined as DiffServ Code Points (DSCP). Packets are marked with a certain value depending on the type of treatment the packet must receive in the network device. DSCP is a measure of the Quality of Service (QoS) level of the packet.

Differentiated Services Concepts

To differentiate between traffic flows, packets can be classified by their DSCP value. The Dif- ferentiated Services (DS) field in the IP header is an octet, and the first six bits, called the DS Code Point (DSCP), can provide QoS functions. Each packet carries its own QoS state in the DSCP. There are 64 possible DSCP values (0-63).

Version

ToS

Length

ID Offset TTL Proto FCS SIP

DIP Data

Length

 

 

 

 

Differentiated Services Code Point (DSCP)

unused

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

7

 

6

 

5

 

4

 

3

 

2

 

1

 

0

 

 

 

 

 

 

 

Figure 7-2Layer 3 IPv4 packet

The GbESM can perform the following actions to the DSCP:

„Read the DSCP value of ingress packets

„Re-mark the DSCP value to a new value

„Map the DSCP value to an 802.1p priority

Once the DSCP value is marked, the GbESM can use it to direct traffic prioritization.

Per Hop Behavior

The DSCP value determines the Per Hop Behavior (PHB) of each packet. The PHB is the for- warding treatment given to packets at each hop. QoS policies are built by applying a set of rules to packets, based on the DSCP value, as they hop through the network.

134 „ Chapter 7: Quality of Service

42C4911, January 2007

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Nortel Networks 42C4911 manual Using Dscp Values to Provide QoS, Differentiated Services Concepts, Per Hop Behavior
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42C4911 specifications

Nortel Networks 42C4911 is a key hardware component designed to meet the needs of modern telecommunications infrastructure. As part of Nortel's extensive portfolio, the 42C4911 has made a significant impact on network design and operation, particularly in enterprises requiring reliable and efficient communication solutions.

One of the standout features of the 42C4911 is its modularity. This allows for flexible configurations and upgrades, enabling organizations to adapt to changing technology requirements and business demands. The design philosophy behind the 42C4911 emphasizes scalability, allowing users to start with a basic setup and expand it as their networking needs grow. This feature is particularly appealing to medium and large enterprises that anticipate increased data and communication requirements over time.

In terms of technology, the 42C4911 supports various telecommunications standards, making it versatile for multiple applications. It typically integrates with other Nortel equipment and can work with third-party devices, ensuring seamless interoperability across different platforms. This is critical as organizations look to create unified communications systems that can handle voice, data, and video traffic efficiently.

The 42C4911 is known for its robust performance and reliability. It is designed to operate continuously under demanding conditions, which is essential for organizations that rely on constant connectivity for their operations. Its built-in redundancy features help safeguard against potential failures, thus enhancing the overall stability of the network. This reliability is further complemented by Nortel's commitment to high-quality manufacturing standards, ensuring that users receive a durable and efficient product.

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Overall, the Nortel Networks 42C4911 stands out as a versatile and powerful component in the telecommunications landscape. Its modular design, compatibility with diverse technologies, reliability, and emphasis on security make it an appealing choice for organizations looking to enhance their networks. As companies continue to navigate the complexities of communication, devices like the 42C4911 play a crucial role in ensuring that they remain connected and efficient.
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