Ieee 802.1P Prioritizing; Figure 38 Prioritizing Packets - Nortel 2000 Using Manual

128 Chapter 2 Network configuration

IEEE 802.1p prioritizing

For more information on prioritizing traffic, refer to Chapter 4, "Policy-enabled
networks."
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). Untagged packets received by the switch on that port are
tagged according to the priority level you assign to the port (see

Figure 38 Prioritizing packets

Before
CRC
PVID = 2
Priority = 6
Data
SA
DA
802.1Q Switch
Untagged member
of VLAN 2
Outgoing
untagged packet
(unchanged)
The newly tagged frame is read within the switch and sent to the port's high or low
transmit queue for disposition.
208700-B
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
Figure
Tag SA DA
Priority = 6 CFI VID = 2
3 bits 1 bit 12 bits
After
- User_priority
- Canonical format indicator
- VLAN identifier
BS45024A
38).