User`s guide

Signamax 

 065-7726SPOE / 065-7726SPOE-FP 24-Port 10/100BaseT/TX
PoE Managed Switch User Manual
Publication date: February 2010
Revision A1.0
132
3-17. QoS (Quality of Service) Configuration
The switch supports 5 kinds of QoS, 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 acts on the DSCP field of the 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.