WATERS NETWORK SYSTEMS
™ ProSwitch
®
-
2600M User’s Manual
Page
25
QoS Status
– Use this function to enable or disable QoS. QoS is enabled by default.
DiffServ Expedite Forwarding
– Use this function to enable or disable DiffServ EF. This switch can map
IETF DifferServ classes to its priority classes and transfer DiffServ packets with the following queue
mapping:
Tx Queues
P3
P2
P1
P0
IETF NM+EF
AF0
AF1
BE0
Note
:
DiffServ
is the abbreviation for "
Differentiated Service
". Differentiated Services provides a simple method
of classifying services of various applications.
Expedited Forwarding
(EF) has a single
codepoint
(DiffServ
value). EF minimizes delay and jitter and provides the highest level of aggregate quality of service. Any traffic
that exceeds a set traffic limit may be discarded. The simplicity of DiffServ to prioritize traffic belies its flexibility
and power. When DiffServ uses specific application types to identify and classify constant-bit-rate traffic, it will
be possible to establish well-defined aggregate flows that may be directed to fixed bandwidth pipes. As a result,
you could share resources efficiently and still provide guaranteed service.
DiffServ
is enabled by default.
ToS/VLAN Tag Preference –
Use this function to select the preference priority information in packets,
priority in ToS or priority in VLAN tag. ToS is the abbreviation for
Type of Service
and it is an 8-bit field in
an IP packet. Here is the explanation of the bits:
Bit 0-2 - Precedence. This 3 bits (value 0~7) indicate the priority of the IP
packet.
Bit 3 – Delay. If this bit is set (1), it requires low delay.
Bit 4 - Throughput. If this bit is set (1), it requires high throughput.
Bit 5 - Reliability. If this bit is set (1), it requires high reliability.
Bit 6-7 - Unused.
The content of ToS is set by the application on the network.
ToS for Xmit
- You can select the bit field in ToS for transmit priority mapping. [7:5] is Bit 0-2 (Precedence)
of ToS. [4:2] is Bit 3-5 (Delay/ Throughput/Reliability) of ToS.
ToS for Drop
- You can select the bit field in ToS for drop priority mapping. [7:5] uses Bit 0-2 (Precedence)
of ToS. [4:2] uses Bit 3-5 (Delay / Throughput / Reliability) of ToS.
WRED Drop Priority Setting
- WRED is the abbreviation of "
Weighted Random Early Detection/Discard
".
WRED is a congestion avoidance mechanism. When a packet belonging to a queue for which WRED is
enabled arrives, actions take place. The Average Queue Size (AQS) is calculated. If the AQS is less than
the minimum WRED threshold, the packet is enqueued. (Enqueued means the packet is waiting in the
queue for its turn to be sent.) Otherwise, the packet is dropped or enqueued accordingly to the Drop
Percentage of the packet within a WRED class. The setting of WRED parameters can influence this
behavior. It is possible to set WRED parameters for each aggregate of packets (Class).
You can define two WRED drop rates (
Low Drop Rate
and
High Drop Rate
). There are three levels for
each drop rate setting:
Level 1
defines the drop percentage when the queue is 75% full.
Level 2
defines the drop percentage when the queue is 87.5% full.
Level 3
defines the drop percentage when the queue is 100% full. It is always 100% drop because
the queue is already full.
