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The following table shows you the internal layer-2 and layer-3 QoS mapping on the EMG2881-T20A. On
the EMG2881-T20A, traffic assigned to higher priority queues gets through faster while traffic in lower
index queues is dropped if the network is congested.
Table 39 Internal Layer2 and Layer3 QoS Mapping
LAYER 2
PRIORITY
IEEE 802.1P USER
QUEUE
PRIORITY
(ETHERNET
PRIORITY)
0
1
1
2
2
0
3
3
4
4
5
5
6
6
7
7
Token Bucket
The token bucket algorithm uses tokens in a bucket to control when traffic can be transmitted. The
bucket stores tokens, each of which represents one byte. The algorithm allows bursts of up to b bytes
which is also the bucket size, so the bucket can hold up to b tokens. Tokens are generated and added
into the bucket at a constant rate. The following shows how tokens work with packets:
• A packet can be transmitted if the number of tokens in the bucket is equal to or greater than the size
of the packet (in bytes).
• After a packet is transmitted, a number of tokens corresponding to the packet size is removed from
the bucket.
Chapter 9 Applications
LAYER 3
TOS (IP
PRECEDENCE)
0
0
1
2
3
4
5
6
7
EMG2881-T20A User's Guide
85
IP PACKET LENGTH
DSCP
(BYTE)
000000
000000
>1100
001110
250~1100
001100
001010
001000
010110
010100
010010
010000
011110
<250
011100
011010
011000
100110
100100
100010
100000
101110
101000
110000
111000
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