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Page 701 / 998 Scroll up to view Page 696 - 700
QoS implementation for DIFFSERV
QOS
7-5
iMG/RG Software Reference Manual (Quality of Service)
classifier profile cp1 set rule rule1 srcaddr 20.20.20.1
255.255.255.255
To configure a rule to assign priority value 1, use the command:
classifier profile cp1 set rule rule1 priority 1
To configure a rule to assign a meter Id to a packet matching the rule use the command:
classifier profile MF set rule Gold meterid 1
Add the profile to an existing transport using the command:
transport set default classifier profile <profile>
Typically, you would use the Classifier with the Meter to provide a full policing QoS implementation.
7.1.3.2.2 Marking packets
The Classifier incorporates the functionality of a DIFFSERV Marker. It can be configured to mark packets with a
specific DSCP. You can set a classifier rule to configure marking using the CLI command
CLASSIFIER PRO-
FILE SET RULE MARK DSCP
This command allows you to set a particular DSCP for a specific rule.
If the rule is matched, the DSCP will be written into the DS (or ToS) field in the header of the IP packet and the
checksum for the IP header will also be updated.
For example, a router at the edge of a network might classify packets according to their source and destination
address and port number, and then mark the packet with a specific DSCP. A router in the core of the network
would only need to examine the DSCP field to determine the traffic class of the packet.
The Classifier is not used to mark packets originated by applications running on the device itself. For locally
originated traffic, local applications such as VoIP allow to set the value of the IP header DS field, instead of using
the default value of 0.
7.1.3.3 Meter
The Meter is used to measure and police the rate of incoming traffic streams. The Meter does not examine out-
going packets and is placed after the Classifier in the receive data path.
The Meter is layered on top of the Classifier. The Classifier classifies (or segregates) incoming traffic stream on
the interface to which it is attached, into multiple traffic streams according to configured rules. Each traffic
stream then gets metered by the Meter device (provided a meter instance has been configured for the stream).
Metering is done against the meter profile configured by the user to measure that stream.
Page 702 / 998
QOS
QoS implementation for DIFFSERV
iMG/RG Software Reference Manual (Quality of Service)
7-6
7.1.3.3.1 How metering works
The Meter device compares temporal properties of the incoming traffic stream against configured parameters.
There are two types of meter:
•
Two-level meter
This meter informs whether a packet is in profile (Green) or out of profile (Red).
•
Three-level meter
This informs whether a packet is completely in profile (Green), partially in profile (Yellow) or out of profile
(Red).
The meter profile consists of a collection of parameters that define how the metering of packets is to be per-
formed. There are three different meter profiles that can be used with the above meter types.
•
Token bucket
meter profile (used with two-level meter).
•
srTCM (single rate three color marker)
meter profile (used with three-level meter).
•
trTCM (two rate three color marker)
meter profile (used with three-level meter).
These meter profiles differ in the algorithms that they use to decide if a packet is in or out of profile. The fol-
lowing sections describe the above profiles.
7.1.3.3.2 Token bucket meter profile
A two-level meter profile called the Token bucket meter profile consists of two parameters:
•
Committed information rate (CIR)
•
Committed burst size (CBS)
If the packet stream's average rate is within CIR and the burst size is within CBS then the packet is marked
Green, otherwise the packet is marked Red.
7.1.3.3.3 srTCM (single rate three color marker) meter profile
A three-level meter profile named as srTCM (single rate three color marker) meter profile consists of three
parameters:
•
Committed information rate (CIR)
•
Committed Burst Size (CBS)
•
Excess Burst Size (EBS)
If the packet stream's average rate is within CIR and the burst size is within CBS then the packet is marked
Green. If the packet stream's average rate is within CIR and the burst size is not within CBS but within
"CBS+EBS" then the packet is marked Yellow. Otherwise, the packet is marked Red.
Page 703 / 998
QoS implementation for DIFFSERV
QOS
7-7
iMG/RG Software Reference Manual (Quality of Service)
7.1.3.3.4 trTCM (two rate three color marker) meter profile
Another three-level meter profile named as trTCM (two rate three color marker) meter profile consists of four
parameters:
•
Committed information rate (CIR)
•
Committed burst size (CBS)
•
Peak Information rate (PIR)
•
Peak burst size (PBS)
If the packet stream's average rate is within CIR and the burst size is within CBS then the packet is marked
Green. If the packet stream's average rate is within PIR and the burst size is within PBS then the packet is
marked Yellow. Otherwise the packet is marked Red.
7.1.3.3.5 Metering packets
The Meter device will take one of the following actions for each packet which has been metered:
•
Drop (default action for Red packets): Drop the packet buffer.
•
Set DSCP value in IP header: Set the DSCP value in the DS field in the header of the IP packet. The Meter
will overwrite the DSCP value the packet had before metering. The checksum for the IP packet is also
updated following an update to the DSCP value.
•
Pass (Default Action for green and yellow packets): Does not set any DSCP value in the IP header. The
packet has the same DSCP value it had before metering.
The above actions can be configured by the user.
For every metering result, the Meter will also set a drop priority value in the buffer.
This drop priority value is used by the Algorithmic dropper (if configured) that is used by the
Scheduler
in order
to select a packet to drop if the system detects congestion in queues.
The following drop priority values can be set in the buffer:
•
If the packet is completely in profile (Green) then a low drop priority value '0' is set in the buffer.
•
If the packet if partially in profile (Yellow) then a medium drop priority value '1' is set in the buffer.
•
If the packet is out of profile (Red) then a high drop priority value '2' is set in the buffer.
The following diagram illustrates the complete metering process:
Page 704 / 998
QOS
QoS implementation for DIFFSERV
iMG/RG Software Reference Manual (Quality of Service)
7-8
FIGURE 7-2
Metering for Traffic Control
Note that the
Meter
uses the TRUE
size of the IP packet for metering. For example, if the Meter receives an
Ethernet packet with the following structure:
•
14 bytes Ethernet header.
•
100 bytes of IP packet (20 bytes IP header + 80 bytes payload).
•
4 bytes of Ethernet padding & FCS.
For these types of packets, the Meter will uses 100 bytes for metering calculations. Therefore, don't be sur-
prised if the Meter is configured at 100kbps and you send an Ethernet packet stream of 118 kbps (Ethernet
packet size 118bytes) which is unaffected by the Meter process.
Incoming Packet
Meter Packet
Check Action
Discard Packet
Set Drop Priority
Set DSCP Value
Action == Drop
Set DSCP?
Page 705 / 998
QoS implementation for DIFFSERV
QOS
7-9
iMG/RG Software Reference Manual (Quality of Service)
7.1.3.3.6 Configuring the meter
To configure the Meter, use the following CLI commands:
1.
Create a profile using one of the commands:
METER ADD PROFILESRTCM
METER ADD PROFILETOKENBUCKET
METER ADD PROFILETRTCM
The metering algorithm type and associated parameters are specified in the command options.
2.
By default, green and yellow packets are passed and red packets are dropped. But, you can override these
default settings and configure the profile to drop, mark or pass packets for a sp
ecific result, using the fol-
lowing commands:
METER SET PROFILE {GREEN | RED | YELLOW} ACTION DROP
METER SET PROFILE {GREEN | RED | YELLOW} ACTION MARK DSCP
METER SET PROFILE {GREEN | RED | YELLOW} ACTION PASS
3.
Add the profile to an existing transport using the command:
TRANSPORTS SET DEFAULT METER INSTANCE PROFILE
Multiple meter instances can be added to the same transport.
Note:
Note that the meter can be assigned only on the ethernet transport named default
7.1.3.4 Scheduler
On the gateways, the Scheduler is used to schedule outgoing packets, belonging to different priority streams, for
transmission on an outgoing interface as per the configured service discipline.
Note:
If the Scheduler is configured on a network interface (actually it’s only supported on ADSL interface), all
packets transmitted through that network interface driver are first processed by the Scheduler Device.
The Scheduler device provides the following functions:
•
Algorithmic dropper
•
Queuing
•
Scheduling
•
Shaping
These components can be configured in the Scheduler to provide all the above functions or a subset of the
above functions, depending on the network requirements. The possible combinations are:
•
Shaping only.

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