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QoS/DSCP (the DiffServ model)
DSCP-ECN defines QoS at Layer 3 (Network Layer). The Differentiated Services (DiffServ) model
is based on packet marking and router queuing disciplines. The marking is done by adding a field
to the IP header, called the DSCP (Differentiated Services Codepoint). This is a 6-bit field that
provides 64 different class IDs. It gives an indication of how a given packet is to be forwarded,
known as the Per Hop Behavior (PHB). The PHB describes a particular service level in terms of
bandwidth, queueing theory, and dropping (discarding the packet) decisions. Routers at each
network node classify packets according to their DSCP value and give them a particular forwarding
treatment; for example, how much bandwidth to reserve for it.
Below are the setting options of DSCP (DiffServ Codepoint). Specify the DSCP value for each
application (0~63).
Note that different vendors of network devices might have different methodologies and unique
implementations. Shown below is a sample corresponding information from a Cisco switch. You
should enter a DSCP tag value according to the information provided by the network devices.
QoS Baseline/Technical Marketing Classification and Marking Recommendations
Application
IP Routing
Voice
Interactive Video
Streaming-Video
Locally-defined Mission-
Critical Data
Call-signaling
Transactional Data
Network Management
Bulk Data
Layer3 Classification
IPP
PHB
6
CS6
5
EF
4
AF41
4
CS4
3
-
3
AF31/CS3
2
AF21
2
CS2
1
AF11
Layer 2 CoS/MPLS EXP
DSCP
48
6
46
5
34
4
32
4
25
3
26/24
3
18
2
16
2
10
1
VIVOTEK
32
QoS B
User's Manual - 107
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