ZyXEL Communications VMG8324-B10A series User Manual page 154

Chapter 9 Quality of Service (QoS)
Table 56 Internal Layer2 and Layer3 QoS Mapping
PRIORITY
QUEUE
4
5
6
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.
• If there are no tokens in the bucket, the Device stops transmitting until enough tokens are
generated.
• If not enough tokens are available, the Device treats the packet in either one of the following
ways:
In traffic shaping:
• Holds it in the queue until enough tokens are available in the bucket.
In traffic policing:
• Drops it.
• Transmits it but adds a DSCP mark. The Device may drop these marked packets if the network
is overloaded.
154
LAYER 2 LAYER 3
IEEE 802.1P USER
PRIORITY TOS (IP
(ETHERNET PRECEDENCE)
PRIORITY)
4 2
5 3
6 4
5
7 6
7
IP PACKET
DSCP
LENGTH (BYTE)
010110
010100
010010
010000
011110 <250
011100
011010
011000
100110
100100
100010
100000
101110
101000
110000
111000
VMG8324-B10A / VMG8324-B30A Series User's Guide