ZyXEL Communications FMG Series, User Manual

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Chapter 5 Advance
FMG Series User’s Guide
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The following table shows you the internal layer-2 and layer-3 QoS mapping on the FMG. On the FMG,
traffic assigned to higher priority queues gets through faster while traffic in lower index queues is
dropped if the network is congested.
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.
• If there are no tokens in the bucket, the FMG stops transmitting until enough tokens are generated.
Table 15 Internal Layer2 and Layer3 QoS Mapping
PRIORITY
QUEUE
LAYER 2 LAYER 3
IEEE 802.1P USER
PRIORITY (ETHERNET
PRIORITY)
TOS (IP
PRECEDENCE)
DSCP
IP PACKET LENGTH
(BYTE)
0 1 0 000000
1 2
2 0 0 000000 >1100
3 3 1 001110
001100
001010
001000
250~1100
4 4 2 010110
010100
010010
010000
5 5 3 011110
011100
011010
011000
<250
6 6 4 100110
100100
100010
100000
5 101110
101000
7 7 6 110000
111000
7