Using Dscp Values To Provide Qos; Differentiated Services Concepts - Lenovo Flex System Fabric CN4093 Application Manual

Using DSCP Values to Provide QoS

Differentiated Services Concepts

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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.
To differentiate between traffic flows, packets can be classified by their DSCP
value. The Differentiated 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).
Figure 22. Layer 3 IPv4 Packet
Length
ToS
Differentiated Services Code Point (DSCP)
7 6 5
The CN4093 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 CN4093 can use it to direct traffic
prioritization.
ID Offset TTL
Proto
unused
4 3 2 1
FCS SIP DIP
0
Chapter 13: Quality of Service
Data
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