Nortel 450-24t 用户指南
Using the BayStack 450 10/100/1000 Series Switch
1-74
309978-D Rev 01
IEEE 802.1p Prioritizing
You can use the VLAN Configuration screens to prioritize the order in which the
switch forwards packets, on a per-port basis. For example, if messages from a
specific segment are crucial to your operation, you can set the switch port
connected to that segment to a higher priority level (by default, all switch ports are
set to Low priority). When the switch receives untagged packets on that port, the
untagged packets are tagged according to the priority level that you assign to the
port (see Figure 1-43).
switch forwards packets, on a per-port basis. For example, if messages from a
specific segment are crucial to your operation, you can set the switch port
connected to that segment to a higher priority level (by default, all switch ports are
set to Low priority). When the switch receives untagged packets on that port, the
untagged packets are tagged according to the priority level that you assign to the
port (see Figure 1-43).
Figure 1-43.
Prioritizing Packets
The newly tagged frame is read within the switch and sent to the port’s high or low
transmit queue for disposition (see Figure 1-44). The port transmit queue example
shown in Figure 1-44 applies to all ports on the BayStack 450 switch.
transmit queue for disposition (see Figure 1-44). The port transmit queue example
shown in Figure 1-44 applies to all ports on the BayStack 450 switch.
BS45024A
Port 6
Port 7
Port 8
Port 1
PVID = 2
Priority = 6
Po
rt
4
Po
rt
5
Port 2
Port 3
802.1Q Switch
High
Low
Key
Priority
CFI
VID
CFI
VID
- User_priority
- Canonical format indicator
- VLAN identifier
- Canonical format indicator
- VLAN identifier
Tagged member
of VLAN 2 (Port 5)
of VLAN 2 (Port 5)
Port configuration
parameters
parameters
Port 5
transmit
queue
Untagged member
of VLAN 2
After
Before
DA
SA
Data
CRC
(*Recalculated)
Outgoing
untagged packet
(unchanged)
DA
SA
Data
CRC
DA
SA
Data
CRC*
Tag
VID = 2
Priority = 6
16 bits
3 bits
1 bit
12 bits
8100
CFI