ICP DAS USA MSM-6226 user manual QoSQuality of Service Configuration

3-22. QoS(Quality of Service Configuration)

The switch supports 5 kinds of QoS, are as follows, MAC Priority, 802.1p Priority, IP TOS Priority, and DiffServ DSCP Priority. Port Based Priority has a special name called VIP Port in the switch. Any packets enter VIP Port will have highest transmitting priority. MAC Priority act on the destination address of MAC in packets. VLAN tagged Priority field is effected by 802.1p Priority setting. IP TOS Priority affects TOS fields of IP header, and you can find it has 8-bit SERVICE TYPE field that specifies how the datagram should be handled. The field could be divided into six subfields as follows, PRECEDENCE (3 bits), D-Type (Delay Priority, 1 bit ), T-Type (Throughput Priority, 1bit), R-Type (Reliability Priority, 1bit ), M-Type (Monetary Cost Priority, 1bit ), and UNUSED (1bit ).

User can randomly control these fields to achieve some special QoS goals. When bits D, T, R, or M set, the D bit requests low delay, the T bit requests high throughput, the R bit requests high reliability, and the M bit requests low cost.

DiffServ DSCP Priority act on DSCP field of IP Header. In the late 1990s, the IETF redefined the meaning of the 8-bit SERVICE TYPE field to accommodate a set of differentiated services (DS). Under the differentiated services interpretation, the first six bits comprise a codepoint, which is sometimes abbreviated DSCP, and the last two bits are left unused.

High Priority Packet streams will experience less delay into the switch. For handing different priority packets, each egress port has designed up to 4 queues. Each QoS is influenced by two scheduling, WRR (Weighted Round Robin) and Strict Priority as well. When you finish to set the priority mapping to the queue, WRR scheduling will distribute the bandwidth according to the weight you set for 4 queues (queue 0 to queue 3). Another scheduling is Strict Priority dedicated for the function named VIP Port of QoS. While we select some ports as the VIP Port, these ports will own the highest transmitting priority in egress queue of the switch.

The QoS functions as we mentioned above are able to enabled at the same time. But, the following precedence will decide whether these functions work or not.

1.Enable both VIP and TOS. Choose priorities of VIP and TOS.

2.Enable both VIP and DSCP. Choose priorities of VIP and DSCP.

3.Enable both TOS and DSCP. Choose "DSCP".

4.Enable both VIP and DSCP. Choose priorities of VIP and DSCP.

5.Enable both 802.1p and TOS. Choose "TOS".

6.Enable both 802.1p and DSCP. Choose "DSCP".

7.Enable both 802.1p and DSCP and TOS. Choose "DSCP".

8.Enable both 802.1p and DSCP and TOS and VIP. Choose priorities of VIP

147	Publication date: Sep, 2009
	Revision A8