Ieee 802.1P Prioritizing; Figure 1-43. Prioritizing Packets - Nortel BayStack 450-24T Using Manual

Using the BayStack 450 10/100/1000 Series Switch

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).
Before
CRC
PVID = 2
Priority = 6
Data
SA
DA
802.1Q Switch
Untagged member
of VLAN 2
Outgoing
untagged packet
(unchanged)
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.
1-74
Port configuration
parameters
Port 1 Port 2 Port 3
Port 5
transmit
queue
Port 6 Port 7 Port 8
CRC
Data
SA
DA
Tagged member
of VLAN 2 (Port 5)
High
CRC* Data
Low
(*Recalculated)
8100
16 bits
Key
Priority
CFI
VID
Tag SA DA
Priority = 6 CFI VID = 2
3 bits 1 bit 12 bits
After
- User_priority
- Canonical format indicator
- VLAN identifier
BS45024A
309978-D Rev 01