Technical data

BLADE OS 5.1 Application Guide
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 Chapter 7: Quality of Service BMD00136, November 2009
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
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 14 Layer 3 IPv4 Packet
The G8000 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 G8000 can use it to direct traffic prioritization.
7 6 5 4 3 2 1 0
Differentiated Services Code Point (DSCP)
unused
Version
Length
To S
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ID
Offset TTL
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FCS
DIP
SIP
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