KSZ8893-MQL Micrel Semiconductor, Inc., KSZ8893-MQL Datasheet - Page 41

• Manufacturer Part Number: KSZ8893-MQL
• Description: Integrated 3-Port 10/100 Managed Switch with PHYs
• Manufacturer: Micrel Semiconductor, Inc.

Advanced VLAN features, such as “Ingress VLAN filtering” and “Discard Non PVID packets” are also supported
by the KSZ8893MQL. These features can be set on a per port basis, and are defined in register 18, 34 and 50 for
ports 1, 2 and 3, respectively.
QoS Priority Support
The KSZ8893MQL provides Quality of Service (QoS) for applications such as VoIP and video conferencing.
Offering four priority queues per port, the per-port transmit queue can be split into four priority queues: Queue 3 is
the highest priority queue and Queue 0 is the lowest priority queue. Bit [0] of registers 16, 32 and 48 is used to
enable split transmit queues for ports 1, 2 and 3, respectively. If a port's transmit queue is not split, high priority
and low priority packets have equal priority in the transmit queue.
There is an additional option to either always deliver high priority packets first or use weighted fair queuing for the
four priority queues. This global option is set and explained in bit [3] of register 5.
Port-Based Priority
With port-based priority, each ingress port is individually classified as a high priority receiving port. All packets
received at the high priority receiving port are marked as high priority and are sent to the high-priority transmit
queue if the corresponding transmit queue is split. Bits [4:3] of registers 16, 32 and 48 are used to enable port-
based priority for ports 1, 2 and 3, respectively.
802.1p-Based Priority
For 802.1p-based priority, the KSZ8893MQL examines the ingress (incoming) packets to determine whether they
are tagged. If tagged, the 3-bit priority field in the VLAN tag is retrieved and compared against the “priority
mapping” value, as specified by the registers 12 and 13. The “priority mapping” value is programmable.
The following figure illustrates how the 802.1p priority field is embedded in the 802.1Q VLAN tag.
Micrel
November 2005
FID+SA found in Dynamic
MAC Table?
No
Yes
Bytes
802.1q VLAN Tag
Preamble
8
Bits
DA
6
Action
Learn and add FID+SA to the Dynamic MAC Address Table
Update time stamp
Tagged Packet Type
(8100 for Ethernet)
Table 14. FID+SA Lookup in VLAN Mode
16
Figure 6. 802.1p Priority Field Format
SA
6
VPID
2
802.1p
TCI
2
3
41
1
length
2
VLAN ID
12
LLC
46-1500
Data
KSZ8893MQL/MQLI
M9999-111705
FCS
4