Using Dscp Values to Provide QoS

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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
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

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.

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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.

Nortel Networks 42C4911 manual Using Dscp Values to Provide QoS, Differentiated Services Concepts

Models: 42C4911

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