BayStack 450 10/100/1000 Series Switches
302401-D Rev 00 1-53

IEEE 80 2.1p Prio rit i zi ng

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

connecte d to th at se gment to a hi gher prior ity leve l (b y defaul t, all swi tch port s are

set to Low priority). Untagged packets received by the switch on that port are

tagged accord ing to the pr iority level you assign to the port (see Figure 1-34).

Figure 1-34. Prioritizing Packets

The newly tagged frame i s read within t he switc h and sen t to t he port’s high or lo w

transmit queue for disposition (see Figure 1-35). The port transmit queue example

shown in Figure 1-35 applies to all ports on the BayStack 450 switch.

BS45024A
Port 6 Port 7 Port 8
Port 1
PVID = 2
Priority = 6
Port 4
Port 5
Port 2 Port 3
802.1Q Switch High
Low
Key
Priority
CFI
VID
- User_priority
- Canonical format indicator
- VLAN identifier
Tagged member
of VLAN 2 (Port 5)
Port configuration
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
DASADataCRC* Tag
VID = 2Priority = 6
16 bits 3 bits 1 bit 12 bits
8100 CFI
kombk.book Page 53 Tuesday, June 29, 1999 3:25 PM