Cisco Sg3008 Manual

							Quality of Service
Configuring QoS - General
493 Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version) 
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Configuring QoS - General
The QoS Properties Page contains fields for setting the QoS mode for the system 
(Basic, Advanced, or Disabled, as described in the “QoS Modes” section). In 
addition, the default CoS priority for each interface can be defined.
Setting QoS Properties
To select the QoS mode:
STEP 1Click Quality of Service > General > QoS Properties.
STEP  2Set the QoS mode. The following options are available:
•Disable—QoS is disabled on the device.
•Basic—QoS is enabled on the device in Basic mode. 
•Advanced—QoS is enabled on the device in Advanced mode. 
STEP  3Select Port/LAG and click GO to display/modify all ports/LAGs on the device and 
their CoS information.
The following fields are displayed for all ports/LAGs:
•Interface—Type of interface.
•Default CoS—Default VPT value for incoming packets that do not have a 
VLAN Tag. The default CoS is 0. The default is only relevant for untagged 
frames and only if the system is in Basic mode and Trust CoS is selected in 
the Global Settings page. 
Select Restore Defaults to restore the factory CoS default setting for this 
interface.
STEP  4Click Apply. The Running Configuration file is updated.
To set QoS on an interface, select it, and click Edit.
STEP 1Enter the parameters.
•Interface—Select the port or LAG.
•Default CoS—Select the default CoS (Class-of-Service) value to be 
assigned for incoming packets (that do not have a VLAN tag).  
						

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STEP  2Click Apply. The interface default CoS value is saved to Running Configuration file.
Configuring QoS Queues 
The device supports 4 for each interface. Queue number four is the highest 
priority queue. Queue number one is the lowest priority queue.
There are two ways of determining how traffic in queues is handled, Strict Priority 
and Weighted Round Robin (WRR). 
•Strict Priority—Egress traffic from the highest-priority queue is 
transmitted first. Traffic from the lower queues is processed only after the 
highest queue has been transmitted, thus providing the highest level of 
priority of traffic to the highest numbered queue. 
•Weighted Round Robin (WRR)—In WRR mode the number of packets sent 
from the queue is proportional to the weight of the queue (the higher the 
weight the more frames are sent). For example, if there are a maximum of 
four queues possible and all four queues are WRR and the default weights 
are used, queue 1 receives 1/15 of the bandwidth (assuming all queues are 
saturated and there is congestion), queue 2 receives 2/15, queue 3 receives 
4/15 and queue 4 receives 8 /15 of the bandwidth. The type of WRR 
algorithm used in the device is not the standard Deficit WRR (DWRR), but 
rather Shaped Deficit WRR (SDWRR). 
The queuing modes can be selected in the Queue page. When the queuing mode 
is by strict priority, the priority sets the order in which queues are serviced, 
starting with Queue 4 or Queue 8 (the highest priority queue) and going to the next 
lower queue when each queue is completed. 
When the queuing mode is Weighted Round Robin, queues are serviced until their 
quota has been used up and then another queue is serviced.
It is also pos sible to as sign some of the lower queues to WRR , while keeping some 
of the higher queues in strict priority. In this case traffic for the strict priority 
queues is always sent before traffic from the WRR queues. Only after the strict 
priority queues have been emptied is traffic from the WRR queues forwarded. 
(The relative portion from each WRR queue depends on its weight).
To select the priority method and enter WRR data. 
STEP 1Click Quality of Service > General > Queue.
STEP  2Enter the parameters. 
						

							Quality of Service
Configuring QoS - General
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•Queue—Displays the queue number.
•Scheduling Method: Select one of the following options:
-
Strict Priority—Traffic scheduling for the selected queue and all higher 
queues is based strictly on the queue priority.
-
WRR—Traffic scheduling for the selected queue is based on WRR. The 
period time is divided between the WRR queues that are not empty, 
meaning they have descriptors to egress. This happens only if strict 
priority queues are empty.
-
WRR Weight—If WRR is selected, enter the WRR weight assigned to the 
queue.
-
% of WRR Bandwidth—Displays the amount of bandwidth assigned to 
the queue. These values represent the percent of the WRR weight.
STEP  3Click Apply. The queues are configured, and the Running Configuration file is 
updated.
Mapping CoS/802.1p to a Queue 
The CoS/802.1p to Queue page maps 802.1p priorities to egress queues. The 
CoS/802.1p to Queue Table determines the egress queues of the incoming 
packets based on the 802.1p priority in their VLAN Tags. For incoming untagged 
packets, the 802.1p priority is the default CoS/802.1p priority assigned to the 
ingress ports.
The following table describes the default mapping when there are 4 queues:
802.1p 
Value s
(0-7, 7 being 
the highest)Queue
(4 queues 1-
4, 4 being the 
highest 
priority)Notes
0 1 Background
11 Best Effort
2 2 Excellent Effort
3 3 Critical Application - LVS 
phone SIP 
						

							Quality of Service
Configuring QoS - General
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By changing the CoS/802.1p to Queue mapping (CoS/802.1p to Queue) and the 
Queue schedule method and bandwidth allocation (Queue page), it is possible to 
achieve the desired quality of service in a network.
The CoS/802.1p to Queue mapping is applicable only if one of the following exists:
•The device is in QoS Basic mode and CoS/802.1p trusted mode
•The device is in QoS Advanced mode and the packets belong to flows that 
are CoS/802.1p trusted
Queue 1 has the lowest priority, queue 4 or 8 has the highest priority.
To map CoS values to egress queues:
STEP 1Click Quality of Service > General > CoS/802.1p to Queue.
STEP  2Enter the parameters.
•802.1p—Displays the 802.1p priority tag values to be assigned to an egress 
queue, where 0 is the lowest and 7 is the highest priority.
•Output Queue—Select the egress queue to which the 802.1p priority is 
mapped. Either four or eight egress queues are supported, where Queue 4 
or Queue 8 is the highest priority egress queue and Queue 1 is the lowest 
priority.
STEP  3For each 802.1p priority, select the Output Queue to which it is mapped. 
STEP  4Click Apply. 801.1p priority values to queues are mapped, and the Running 
Configuration file is updated.
43 Video
5 4  Voice - Cisco IP phone 
default
64 Interwork Control - LVS 
phone RTP
74 Network Control 802.1p 
Value s
(0-7, 7 being 
the highest)Queue
(4 queues 1-
4, 4 being the 
highest 
priority)Notes 
						

							Quality of Service
Configuring QoS - General
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Mapping DSCP to Queue
The DSCP (IP Differentiated Services Code Point) to Queue page maps DSCP 
values to egress queues. The DSCP to Queue Table determines the egress 
queues of the incoming IP packets based on their DSCP values. The original VPT 
(VLAN Priority Tag) of the packet is unchanged.
By simply changing the DSCP to Queue mapping and the Queue schedule method 
and bandwidth allocation, it is possible to achieve the desired quality of services 
in a network.
The DSCP to Queue mapping is applicable to IP packets if:
•The device is in QoS Basic mode and DSCP is the trusted mode, or
•The device is in QoS Advanced mode and the packets belongs to flows that 
is DSCP trusted
Non-IP packets are always classified to the best-effort queue.  
						

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The following tables describe the default DSCP to queue mapping for a 4-queue 
system:
To  m a p  D S C P  t o  q u e u e s :
STEP 1Click Quality of Service > General > DSCP to Queue.
The DSCP to Queue page contains Ingress DSCP. It displays the DSCP value in 
the incoming packet and its associated class. 
STEP  2Select the Output Queue (traffic forwarding queue) to which the DSCP value is 
mapped. 
STEP  3Click Apply. The Running Configuration file is updated.
DSCP63 55 47 39 31 23 15 7
Queue 33433211
DSCP62 54 46 38 30 22 14 6
Queue 33433211
DSCP61 53 45 37 29 21 13 5
Queue 33433211
DSCP60 52 44 36 28 20 12 4
Queue 33433211
DSCP59 51 43 35 27 19 11 3
Queue 33433211
DSCP58 50 42 34 26 18 10 2
Queue 33433211
DSCP57 49 41 33 25 17 9 1
Queue 33433211
DSCP56 48 40 32 24 16 8 0
Queue 33433211 
						

							Quality of Service
Configuring QoS - General
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Configuring Bandwidth
The Bandwidth page enables users to define two values, Ingress Rate Limit and 
Egress Shaping Rate, which determine how much traffic the system can receive 
and send. 
The ingress rate limit is the number of bits per second that can be received from 
the ingress interface. Excess bandwidth above this limit is discarded. 
The following values are entered for egress shaping:
•Committed Information Rate (CIR) sets the average maximum amount of 
data allowed to be sent on the egress interface, measured in bits per 
second 
•Committed Burst Size (CBS) is the burst of data that is allowed to be sent, 
even though it is above the CIR. This is defined in number of bytes of data.
To enter bandwidth limitation:
STEP 1Click Quality of Service > General > Bandwidth.
The Bandwidth page displays bandwidth information for each interface. 
The % column is the ingress rate limit for the port divided by the total port 
bandwidth.
STEP  2Select an interface, and click Edit.
STEP  3Select the Port or LAG interface. 
STEP  4Enter the fields for the selected interface:
•Ingress Rate Limit—Select to enable the ingress rate limit, which is defined 
in the field below. 
•Ingress Rate Limit—Enter the maximum amount of bandwidth allowed on 
the interface. 
NOTEThe two Ingress Rate Limit fields do not appear when the interface 
type is LAG.
•Ingress Committed Burst Size (CBS)—Enter the maximum burst size of 
data for the ingress interface in bytes of data. This amount can be sent even 
if it temporarily increases the bandwidth beyond the allowed limit. This field 
is only available if the interface is a port.
•Egress Shaping Rate—Select to enable egress shaping on the interface. 
						

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•Committed Information Rate (CIR)—Enter the maximum bandwidth for the 
egress interface. 
•Egress Committed Burst Size (CBS)—Enter the maximum burst size of data 
for the egress interface in bytes of data. This amount can be sent even if it 
temporarily increases the bandwidth beyond the allowed limit.
STEP  5Click Apply. The bandwidth settings are written to the Running Configuration file.
Configuring Egress Shaping per Queue
In addition to limiting transmission rate per port, which is done in the Bandwidth 
page, the device can limit the transmission rate of selected egressing frames on a 
per-queue per-port basis. Egress rate limiting is performed by shaping the output 
load.
The device limits all frames except for management frames. Any frames that are 
not limited are ignored in the rate calculations, meaning that their size is not 
included in the limit total.
Per-queue Egress rate shaping can be disabled.
To define egress shaping per queue:
STEP 1Click Quality of Service > General > Egress Shaping per Queue.
The Egress Shaping Per Queue page displays the rate limit and burst size for each 
queue.
STEP  2Select an interface type (Port or LAG), and click Go.
STEP  3Select a Port/LAG, and click Edit.
This page enables shaping the egress for up to eight queues on each interface. 
STEP  4Select the Interface.
STEP  5For each queue that is required, enter the following fields:
•Enable Shaping—Select to enable egress shaping on this queue
.
•Committed Information Rate (CIR)—Enter the maximum rate (CIR) in Kbits 
per second (Kbps). CIR is the average maximum amount of data that can be 
sent.  
						

							Quality of Service
Configuring QoS - General
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•Committed Burst Size (CBS)—Enter the maximum burst size (CBS) in bytes. 
CBS is the maximum burst of data allowed to be sent even if a burst exceeds 
CIR.
STEP  6Click Apply. The bandwidth settings are written to the Running Configuration file.
VLAN Ingress Rate Limit 
NOTEThe VLAN Rate Limit feature is not available when the device is in Layer 3 mode.
Rate limiting per VLAN, performed in the VLAN Ingress Rate Limit page,
 enables 
traffic limiting on VLANs. When VLAN ingress rate limiting is configured, it limits 
aggregate traffic from all the ports on the device. 
The following constraints apply to rate limiting per VLAN:
•It has lower precedence than any other traffic policing defined in the 
system. For example, if a packet is subject to QoS rate limits but is also 
subject to VLAN rate limiting, and the rate limits conflict, the QoS rate limits 
take precedence. 
•It is applied at the device level and within the device at the packet 
processor level. If there is more than one packet processor on the device, 
the configured VLAN rate limit value is applied to each of the packet 
processors, independently. Devices with up to 24 ports have a single 
packet processor, while devices of 48 ports or more have two packet 
processors. 
To define the VLAN ingress rate limit:
STEP 1Click Quality of Service > General > VLAN Ingress Rate Limit.
This page displays the VLAN Ingress Rate Limit Table.
STEP  2Click Add.
STEP  3Enter the parameters.
•VLAN ID—Select a VLAN.
•Committed Information Rate (CIR)—Enter the average maximum amount 
of data that can be accepted into the VLAN in Kilobytes per second. 
						

							Quality of Service
QoS Basic Mode
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•Committed Burst Size (CBS)—Enter the maximum burst size of data for the 
egress interface in bytes of data. This amount can be sent even if it 
temporarily increases the bandwidth beyond the allowed limit. Cannot be 
entered for LAGs.
STEP  4Click Apply. The VLAN rate limit is added, and the Running Configuration file is 
updated.
TCP Congestion Avoidance
The TCP Congestion Avoidance page enables activating a TCP congestion 
avoidance algorithm. The algorithm breaks up or avoids TCP global 
synchronization in a congested node, where the congestion is due to various 
sources sending packets with the same byte count.
To configure TCP congestion avoidance:
STEP 1Click Quality of Service > General > TCP Congestion Avoidance.
STEP  2Click Enable to enable TCP congestion avoidance, and click Apply.
QoS Basic Mode
In QoS Basic mode, a specific domain in the network can be defined as trusted. 
Within that domain, packets are marked with 802.1p priority and/or DSCP to signal 
the type of service they require. Nodes within the domain use these fields to 
assign the packet to a specific output queue. The initial packet classification and 
marking of these fields is done in the ingress of the trusted domain.
Workflow to Configure Basic QoS Mode
To configure Basic QoS mode, perform the following:
1. Select Basic mode for the system by using the QoS Properties page. 
2. Select the trust-behavior using the Global Setting page. The device supports 
CoS/802.1p trusted mode and DSCP trusted mode. CoS/802.1p trusted mode 
uses the 802.1p priority in the VLAN tag. DSCP trusted mode use the DSCP 
value in the IP header.