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20.0 Traffic Shaping:
Given below are the normal sequence of steps and relevant commands
that are required in enabling Frame Relay traffic shaping:
1. Specify the map class name - Use the command
R(config)#
map-class frame-relay <map-class-name>, where <map-class-name>
is the name of map class.
2. Define map class - Typical configuration
steps here may include:
A) Enabling rate enforcement by defining
average and peak rates of traffic.
B) Specifying a custom queue
list for the map class
C) Specifying a priority queue list for
the map class.
D) Enabling BECN feedback to throttle the output
rate on any SVC for the map class.
All the above (A through
D) are optional configuration commands.
3. Enable Frame Relay
on an interface by issuing interface configuration command:
R(config-if)#encapsulation
frame-relay
Note that the default encapsulation type is cisco.
4. Next, enable frame relay traffic shaping on an interface
by issuing the command:
R(config-if)# frame-relay traffic-shaping
5. Specify a Traffic Shaping Map Class for the Interface by
issuing the following command:
R(config-if)# frame-relay class <map-class-name>,
where <map-class-name> is the map class name.
Specifying a
Frame Relay map class for a main interface, results in all the VCs
on its sub interfaces inherit all the traffic shaping parameters
defined for the class.
Traffic shaping is recommended under the following circumstances:
1. If a FR network consists of high speed connections at the
central site and low speed connections (less than 64 Kbps) at branch
offices, bottlenecks may occur at slow links. Traffic shaping is
useful to address this problem.
2. If the FR network occasionally
get congested, traffic can be throttled using BECN, so that the
congestion is overcome. Note that the traffic shaping may not be
useful when a FR network consistently encounters congestion due
to insufficient bandwidth.
3. Also, if the FR network has
to carry different types of protocols, such as IP, SNA it is recommended
to enable traffic shaping. This would allow the prioritization of
time sensitive traffic.
Frame Relay traffic shaping can be achieved through the following
means:
1. By using rate enforcement - Here the average and
peak data rates are defined by using the command:
R(config-map-class)#
frame-relay traffic-rate <average> [peak],
where <average>
is the average rate in bps, which is equivalent to the CIR.
Peak
is optional command - specifies the peak rate in bps.
2.
Adaptive shaping through the use of BECN by using the following
command:
R(config-map-class)# frame-relay adaptive-shaping becn
The above command enables the router to dynamically adjust the rate
at which it sends packets, depending on the BECNs received.
3. Traffic shaping through use of custom queuing:
Custom
queuing is recommended when a particular protocol or service needs
to be given guaranteed transmission rate. The command that enables
custom queuing is:
R(config-map-class)# frame-relay custom-queue-list <list-number>
4. Traffic shaping through use of priority queuing:
Priority
queuing allows absolute priority to be assigned to a protocol or
service. The command that enables priority queue list is:
R(config-map-class)#
frame-relay priority-group <list-number>
Both custom-queue-list
and priority-queue-list commands require that you have previously
defined a custom queue or priority queue respectively.
Only one
form of queuing may be associated with a given map class.
21.0 Back-up Interface configuration:
The backup interface configuration involves the following steps:
1. Configure the primary interface as needed.
2. Configure
the backup (secondary) interface using the command:
R(config-if)#
backup interface <interface-type number>, where <interface-type-number>
is the interface port or slot/port number.
An example, for
assigning BRI0 as the backup, use the command:
R(config-if)#
backup interface bri0
3. Specify the time to wait before
enabling the backup link after the primary link goes down with the
command:
R(config-if)# backup delay {enable-delay} | never} {disable-delay
| never}
where,
enable-delay - is the number of seconds that
elapse after the primary link goes down and before the secondary
(backup) link is activated.
Disable-delay - is the number of
seconds that elapse after the primary line comes up, and before
the secondary (backup) link is deactivated.
Never - prevents
the secondary line from being activated or deactivated.
The following statements are true with respect to backup lines:
1. The command 'backup interface' is used for configuring an
interface for backup operation.
2. A backup line can be configured
to be activated based on the traffic load on the primary line, such
that the backup is activated if the load on primary exceeds certain
percentage of available bandwidth.
3. When an interface is
configured as backup interface to a primary line, the backup route
does not appear in the routing table. However, if the primary line
fails, and the backup is activated, then the backup route shows
up in the route table.
4. If a BRI is used for dial backup,
none of the two B channels are available while the interface is
in standby mode. This can be overcome by using dialer profiles.
Two dialer profiles can be defined, one for the backup line and
the other for regular dial up. Physical BRI interface can be made
member of both the dialer pools. Under these conditions, both B
channels can be used, one for the backup line and the other for
regular dial up.
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