3Com Router User Manual

							Configure Frame Relay257
Perform the following configurations in interface view.
Ta b l e 296   Configure Frame Relay Compression on multipoint interface
By default, Frame Relay payload compression is disable.
On the 3Com Router, both the Frame Relay main interfaces and sub-interfaces can 
be multipoint interfaces.
Enable/Disable TCP/IP 
Header Compression on 
InterfacesFrame Relay supports TCP/IP header compression. Only when the packet format of 
Frame Relay interface is nonstandard, can TCP/IP header compression be 
executed. TCP/IP header compression can be designated both on the interface and 
on configuring static address mapping.
Perform the following task in synchronous interface view.
Ta b l e 297   Enable/Disable TCP/IP Header Compression on Interfaces
By default, interfaces use initiative compression.
Configure Frame Relay 
Fragment (FRF.12)
1Configure Frame Relay Fragment Attributes
When voice and data are transmitted concurrently, transmission of a large data 
packet will occupy the bandwidth for a relatively long time. This will cause delay 
and even drop of voice packets behind it, and hence degrade the voice quality. The 
purpose of configuring Frame Relay fragmentation is to shorten voice delay and 
ensure real-time voice transmission. After configuring fragmentation, large 
packets will be fragmented into small data fragments. These smaller and less 
delay-causing data fragments and the voice packets are interspersed for 
transmission to ensure an even flow of voice packets into the networks. 
Ta b l e 298   Configure Frame Relay Fragment
OperationCommand
Create a Frame Relay map, and enable Frame Relay 
compression on the DLCIfr map { ip | ipx } 
protocol-address dlci dlci 
compression frf9
Delete the Frame Relay map, and disable Frame 
Relay compressionundo fr map { ip | ipx } 
protocol-address dlci dlci
OperationCommand
Enable TCP/IP Header Compression on Interfacesfr compression vj [ passive ]
Disable TCP/IP Header Compression on Interfacesundo fr compression vj
OperationCommand
Create a Frame Relay classfr class class-name
Delete a Frame Relay classundo fr class class-name
Configure the Frame Relay fragment sizefragment fragment-size { 
data-level | voice-level }
Disable Frame Relay fragmentationundo fragment [ fragment-size { 
data-level | voice-level } ]
Associate a Frame Relay class with a Frame 
Relay interface or PVCfr-class class-name 
						

							258CHAPTER 17: CONFIGURING FRAME RELAY
Configure Frame Relay 
QoSQuality of Service (QoS) is a set of technologies adopted to meet the users 
requirements in throughput, delay jitter, delay and packet loss ratio. Briefly 
speaking, QoS technologies provides network services of different qualities for 
different requirements.
On a Frame Relay interface, the user can use the general QoS to provide the 
services, such as traffic policing, traffic shaping, congestion management, and 
congestion avoidance. For details, please refer to the relative description in the 
part of  
QoS.
Furthermore, a Frame Relay network has its own QoS mechanisms, including 
Frame Relay traffic shaping, Frame Relay traffic policing, Frame Relay congestion 
management, Frame Relay discard eligibility (DE) rule list and Frame Relay 
queueing management. According to different requirements, the network service 
provider can provide various services, such as bandwidth restriction and 
bandwidth reservation.
Compared with the general QoS, Frame Relay QoS can provide the service of QoS 
for each PVC on an interface. However, the general QoS can only provide the 
service of QoS on the whole interface. Therefore, the Frame Relay QoS can provide 
more flexible quality services for users.
Figure 81   Frame Relay QoS application
Frame Relay Traffic Shaping
The Frame Relay traffic shaping can control the normal traffic size and the burst 
traffic size transmitted from a PVC and enable the Frame Relay PVC to transmit 
these packets at a relatively average rate.
In a Frame Relay network, the bottleneck will often occur at the boundary of 
segments if the bandwidths of different segments do not match. As shown in 
Figure 82, Router B transmits packets to Router A at the rate of 128 kbps whereas 
the maximum interface rate of Router A is only 64 kbps. In this case, the 
bottleneck will occur at the place where Router A is connected to the Frame Relay 
network, and thereby resulting in the congestion that prevents the data from 
normal transmitting.
Remove the association between a Frame Relay 
class
 and a Frame Relay interface or PVC
undo fr-class class-name
Enable the Frame Relay traffic shapingfr traffic-shaping
Disable the Frame Relay traffic shapingundo fr traffic-shaping
Frame Relay
Network
Traffic Shaping  Traffic Policing
Router B Router  A
DTE
NNI
DCE
Congestion
 Management DE Rule
Data flow direction 
						

							Configure Frame Relay QoS259
Figure 82   Frame Relay traffic shaping
If the Frame Relay traffic shaping is applied on the outgoing interface Serial 0 on 
Router B, the interface will be able to transmit packets at 64 kbps, a relatively 
average rate, so as to avoid the network congestion. Even if the congestion occurs 
to the network, Router B can still transmit packets at 32 kbps.
Frame Relay traffic shaping is applied on the outgoing interface on a router. It can 
provide for the users the parameters like Committed Information Rate Allowed 
(CIR ALLOW), Committed Information Rate (CIR), Committed Burst Size (CBS) and 
Excess Burst Size (EBS).
When the network is in normal, the Frame Relay PVCs can transmit packets at the 
rate of CIR ALLOW. In this case, the packet traffic transmitted at an interval of Tc is 
CBS. Furthermore, the Frame Relay traffic shaping allows the PVCs to transmit 
packets at a rate exceeding CIR ALLOW in case of the burst, and the traffic 
exceeding the CBS can be EBS at maximum.
When the network congestion occurs, if the Frame Relay switch device has been 
configured with the function of congestion management, it will notify the router 
of network congestion. Upon receiving the notification, the router will eventually 
slow down the transmit rate to the CIR, so as to ease the congestion, then users 
can transmit data at the rate of CIR. After this, if no notifications of network 
congestion are received within a certain period of time, the router will eventually 
raise the transmit rate from the CIR back to the CIR ALLOW.
Figure 83   Fundamentals of Frame Relay traffic shaping
As shown in Figure 83, the parameters of Frame Relay traffic shaping are 
respectively set to be: CIR ALLOW= 64 kbps, CIR = 32 kbps, CBS = 64000 bit, EBS 
= 64000 bit, and interval Tc = CBS / CIR ALLOW = 1s. Within the first interval Tc, 
the PVC-transmitting burst traffic size equals to CBS+EBS. Beginning from the 
second Tc, the transmitted traffic size within each interval Tc becomes CBS. At the 
3s, the router receives the Frame Relay packet whose backward explicit congestion 
Data flow direction
   Frame-relay network
Router A Router B128 kbps
64 kbps
DTE DTES0 S0
CIR ALLOW = 64kbps
CIR = 32kbps
CI R£º 32 k bps   CIR ALLOW£
º 64 k bps
0s 1s 4s3s 2s 6s5s
RAT E
TI ME CI R A L L OW+EI R£º 128 Kbps 
						

							260CHAPTER 17: CONFIGURING FRAME RELAY
notification (BECN) flag bit is 1, indicating that the congestion has occurred to the 
network, and the transmit rate of the PVC will be lowered to CIR.
Frame Relay Queueing Management
To ensure that the packets on the PVCs can be transmitted at an average rate in 
the process of Frame Relay traffic shaping, a queueing mechanism should be 
adopted to manage the packets. Generally, except that the Frame Relay interface 
owns one interface queue, the Frame Relay PVC does not have its own transmit 
queue. However, after the Frame Relay traffic shaping is enabled on the Frame 
Relay interface, all the PVCs belonging to this interface will own their independent 
queues, and all the packets t transmitted from the PVCs will enter the Frame Relay 
PVC queues first.
Besides the Frame Relay PVC queues, the Frame Relay interface also owns an 
interface queue. In the case that the Frame Relay traffic shaping is not enabled, 
there will only be the Frame Relay interface queue. After it is enabled, both Frame 
Relay PVC queues and the Frame Relay interface queue will exist. Their relations 
are illustrated in 
Frame Relay queueing.
Figure 84   Frame Relay queueing
The Frame Relay PVC queueing types include FIFO (First-In First-Out Queueing), PQ 
(Priority Queueing), CQ (Custom Queueing), and WFQ (Weighted Fair Queueing).
The FIFO, PQ, CQ, WFQ, and PIPQ (PVC Interface Priority Queueing) queues can be 
used on a Frame Relay interface. Among them, FIFO, PQ, CQ, and WFQ queues 
are general queues. For the detailed introduction, refer to the part of 
 QoS. PIPQ 
can only be applied on the Frame Relay interface. It is similar to PQ, but aiming at 
the PVCs on an interface. When the Frame Relay traffic shaping is enabled on an 
interface, the queueing type on the interface can only be either FIFO or PIPQ.
PIPQ is applied on a Frame Relay interface. There are four types of PIPQ: top, 
middle, normal and bottom. Their queueing priorities are listed in descending 
order. The packets on the same PVC can only enter one type of PIPQ queue, and 
the packets on different PVCs enter different PIPQ queues on the interface, 
depending on the priorities of the PVCs. The PIPQ transmitting policy is as follows: 
Based on the queueing priority, transmit the packets in the queue with low priority 
after those in the queue with high priority are transmitted.
Frame Relay Traffic Policing
Frame Relay policing monitors the traffic that flows into the network from each 
PVC, and restricts it in a certain range. If the traffic size on a PVC exceeds the 
range set by the user, the router will adopt the measures like discarding the 
packets, so as to protect the network resources and the profit of the operator.
PVC Queue
Interface queue 
						

							Configure Frame Relay QoS261
Figure 85   Frame Relay traffic policing
As shown in the above figure, Router A at the user side transmits packets at 192 
kbps to Router B at the switching side. However, Router B only wants to provide 
the 64 kbps bandwidth for Router A. In this case, you need to configure the Frame 
Relay traffic policing at the DCE side of Router B.
Frame Relay traffic policing can only be applied on the DCE interface on a router. It 
can monitor the traffic transmitted from the DTE side. When the traffic size is 
smaller than 
CBS, the packets can be normally transmitted, and the router will not 
process the packets. When the traffic size is larger than CBS and smaller than EBS 
+ CBS, the packets can be normally transmitted. In this case, however, as for those 
packets in the traffic exceeding CBS, the router will mark the flag bit of DE in the 
Frame Relay packet headers to 1. When the traffic size is larger than CBS + EBS, 
the router will transmit the traffic within CBS + EBS, and discard the traffic 
exceeding CBS + EBS. As for the traffic of EBS which is the size exceeding CBS, the 
router will mark the flag bit of DE in the Frame Relay packet headers to 1.
Figure 86   Fundamentals of Frame Relay traffic policing
As shown in the above figure, the parameters of Frame Relay traffic policing are 
respectively set to be: CIR ALLOW = 64 kbps, CBS = 64000 bit, EBS = 64000 bit, 
and interval Tc = CBS / CIR ALLOW = 1s.
 When the interval is in the range of 0 to 
2s, DTE will transmit packets to DCE at 64 kbps and DCE will normally forward 
these packets at 64 kbps. When the interval is in the range of 2 to 4ms, DTE will 
transmit packets at 100 kbps, and DCE will forward them at 100 kbps. In this case, 
however, the flag bit of DE in the headers of packets exceeding 
CBS will be set to 
1. After 4 seconds, DTE will transmit the packets to DCE at 150 kbps, and DCE will 
forward them at 128 kbps. As for the packets exceeding 
CBS but within CBS + 
EBS
, the flag bit of DE in their headers will be set to 1, and the packets exceeding 
CBS + EBS will be discarded directly.
   Frame-relay
network
Router
ARouter
B
192 kbps 64 kbpsDTE DCE
CIR ALLOW = 64 kbps
CBS = 8000 bit
EBS = 8000 bit S0 S0NNI
  CI R A L L OW£
º 64 Kbps
0ms 125ms 500ms 375ms 250ms750ms 625ms
RAT E
TI ME CI R A L L OW+EI R£º 128 Kbps
       100 Kbps        150 Kbps
DE Discarded
Transmit 
						

							262CHAPTER 17: CONFIGURING FRAME RELAY
Frame Relay Congestion Management
Frame Relay congestion management can process the Frame Relay packets 
whenever there is network congestion. It will discard the packets that are marked 
with the DE flag bit. At the same time, it will notify other devices on the network 
about the congestion. 
Frame Relay congestion management is applied at the output interface on a Frame 
Relay switched device. If there is no congestion, the router will normally forward 
the Frame Relay packets without doing any special processing on them. Once 
there is congestion, the packets that are marked with the DE flag bit will be 
discarded. As for the forward packets to be forwarded, the router will set the 
FECN flag bit in the Frame Relay packet headers to 1. As for the backward packets 
on the same PVC, the router will set the BECN flag bit in the Frame Relay packet 
headers to 1. If there is no backward packets to be forwarded after a certain 
period, the router will automatically transmit the Q922A Test Reponse packets 
with the BECN flag bit 1 to the calling DTE.
Figure 87   Frame Relay congestion management
Frame Relay DE rule list
In a Frame Relay network, the packets that are marked with DE flag bit will be first 
discarded once there is congestion. The DE rule lists are applied on the Frame 
Relay PVCs on a router, and each of them contains multiple DE rules. If a packet 
transmitted on a PVC complies with the rules in the DE rule list, its DE flag bit will 
be set to 1, and the packets like it will be discarded first if the congestion occurs 
on the network.
Configure Frame Relay 
classThe 3Com Router system integrates the QoS on Frame Relay PVCs into Frame 
Relay class. Thereby, it provides a flexible overall solution to Frame Relay traffic 
control and quality service. Before configuring the QoS such as Frame Relay traffic 
shaping, you need to create a Frame Relay class, and configure various QoS 
parameters on it. Such a Frame Relay class equals to a set of QoS network service 
solution.
 Then, the user can associate it with a Frame Relay PVC. It is equivalent to 
applying a set of QoS scheme to the Frame Relay PVC. Different PVCs can use 
different 
Frame Relay classes as well as a single Frame Relay class.
Frame Relay class configuration includes:
■Create a Frame Relay class
■Associate the Frame Relay class with the Frame Relay interface or a PVC
■Configure the Frame Relay class parameters
1Create a Frame Relay class
Perform the following configurations in system view.
Frame-relay network
Router B Router ADTENNI DCE
BECN
FECN
Data flow direction 
						

							Configure Frame Relay QoS263
Ta b l e 299   Create/Delete a Frame Relay class
By default, no Frame Relay class is created.
After creating the Frame Relay class using this command, the user will enter the 
frame relay class view under which you can configure the parameters like CIR.
2Associate the Frame Relay class with the Frame Relay interface or a PVC
Please configure the association between a Frame Relay class and an interface in 
interface view, and configure the association between a 
Frame Relay class and a 
PVC in DLCI view.
Ta b l e 300   Associate the Frame Relay class with the Frame Relay interface or a PVC
By default, no Frame Relay class is associated with the Frame Relay interface or the 
Frame Relay PVC.
When using the command fr-class, if the specified Frame Relay class does not 
exist, this command will first create a 
Frame Relay class (but not enter the frame 
relay class view) and then associate it with the current interface or PVCs.
The command undo fr-class will remove the association between the specified 
Frame Relay class and the interface/PVCs without deleting the actual Frame Relay 
class
. In this case, if using the display current-configuration command to 
view the configurations of the router, you can still see the configuration of the 
Frame Relay class. To delete the Frame Relay class, use the undo fr class 
command.
When a Frame Relay PVC implements QoS, it will search for the corresponding 
Frame Relay class in the following sequence: 
■If there is a Frame Relay class associated with the PVC, use the QoS parameters 
configured to the 
Frame Relay class.
■If there is no Frame Relay class associated with the PVC but a Frame Relay class 
associated with the interface to which the PVC belongs, use the QoS 
parameters configured to this 
Frame Relay class.
3 Configure the Frame Relay class parameters
In frame relay class view, the user can configure the parameters for the QoS, such 
as Frame Relay traffic shaping, Frame Relay traffic policing, Frame Relay 
congestion management, and Frame Relay queueing management. The following 
sections will cover the parameter settings in detail.
Configure Frame Relay 
Traffic ShapingFrame Relay traffic shaping configuration includes:
■Enable the Frame Relay traffic shaping
■Create a Frame Relay class
■Associate the Frame Relay class with the Frame Relay interface or a PVC
OperationCommand
Create a Frame Relay classfr class class-name
Delete a Frame Relay classundo fr class class-name
OperationCommand
Associate a Frame Relay class with a Frame 
Relay interface or PVCfr-class class-name
Remove the association between a Frame Relay 
class
 and a Frame Relay interface or PVC
undo fr-class class-name 
						

							264CHAPTER 17: CONFIGURING FRAME RELAY
■Configure the parameters of Frame Relay class
1Enable the Frame Relay traffic shaping
Perform the following configurations in synchronous serial interface view.
Ta b l e 301   Enable/Disable the Frame Relay traffic shaping
By default, the Frame Relay traffic shaping is not enabled on the interface.
The function of Frame Relay traffic shaping is applied on the outgoing interfaces 
on a router. Usually it is applied at the DTE end on a Frame Relay network.
2Create a Frame Relay class
Refer to the previous section “Configure Frame Relay class” for the configuration 
procedure in detail.
3Associate the Frame Relay class with the Frame Relay interface or a PVC
Refer to the previous section “Configure Frame Relay class” for the configuration 
procedure in detail.
4Configure the Frame Relay class parameters for Frame Relay traffic shaping 
Perform the following configurations in frame relay class view.
Ta b l e 302   Configure the parameters of Frame Relay class
The commands cbs, ebs, and cir allow can be used to set the inbound and 
outbound parameters. However, only the outbound parameters are effective for 
the Frame Relay traffic shaping.
OperationCommand
Enable the Frame Relay traffic shapingfr traffic-shaping
Disable the Frame Relay traffic shapingundo fr traffic-shaping
OperationCommand
Set the CBS of a Frame Relay PVCcbs [ outbound ] burst-size
Restore the CBS of a Frame Relay PVC to the 
default valueundo cbs [ outbound ]
Set the EBS of a Frame Relay PVCebs [ outbound ] 
excess-burst-size
Restore the EBS of a Frame Relay PVC to the 
default valueundo ebs [ outbound ]
Set the CIR ALLOW of a Frame Relay PVCcir allow [ outbound ] 
rate-limit
Restore the CIR ALLOW of a Frame Relay PVC to 
the default valueundo cir allow [ outbound ]
Set the CIR of a Frame Relay PVCcir rate-limit
Restore the CIR of a Frame Relay PVC to the 
default valueundo cir
Enable the adaptive adjustment function of 
traffic shapingtraffic-shaping adaptation becn 
[ percentage ]
Disable the adaptive adjustment function of 
traffic shapingundo traffic-shaping adaptation 
becn
Set the reserved band width of Frame Relay PVCreserved-bandwidth 
bandwidth-percentage
Restore the reserved band width of a Frame 
Relay PVC to the default valueundo reserved-bandwidth 
						

							Configure Frame Relay QoS265
Numerically, the value of CBS should not be less than CIR ALLOW, otherwise, the 
large packets may not be sent.
Configure Frame Relay 
Traffic PolicingFrame Relay traffic policing configuration includes:
■Enable the Frame Relay traffic policing
■Create a Frame Relay class
■Associate the Frame Relay class with the Frame Relay interface or a PVC
Configure the parameters of Frame Relay class for Frame Relay traffic policing
1Enable the Frame Relay Traffic Policing
Perform the following configurations in synchronous serial interface view.
Ta b l e 303   Enable/Disable the Frame Relay traffic policing
By default, the Frame Relay traffic policing is not enabled on the interface.
The function of Frame Relay traffic policing is applied on the interface receiving 
the Frame Relay packets on a router. It can only be applied at the DCE side on a 
Frame Relay network.
2Create a Frame Relay class
Please refer to the above section “Configure Frame Relay class” for the 
configuration procedure in detail.
3Associate the Frame Relay class with the Frame Relay interface or a PVC
Please refer to the above section “Configure Frame Relay class” for the 
configuration procedure in detail.
4Configure the parameters of Frame Relay class for Frame Relay traffic policing
Perform the following configurations in frame relay class view.
Ta b l e 304   Configure the parameters of Frame Relay class
The commands cbs, ebs, and cir allow can be used to set the inbound and 
outbound parameters on a PVC. However, only the inbound parameters are 
effective for the Frame Relay traffic policing.
OperationCommand
Enable the Frame Relay traffic policingfr traffic-policing
Disable the Frame Relay traffic policingundo fr traffic-policing
OperationCommand
Set the CBS of a Frame Relay PVCcbs [ inbound ] burst-size
Restore the CBS of a Frame Relay PVC to the default 
valueundo cbs [ inbound ]
Set the EBS of a Frame Relay PVCebs [ inbound ] 
excess-burst-size
Restore the EBS of a Frame Relay PVC to the default 
valueundo ebs [ inbound ]
Set the CIR ALLOW of a Frame Relay PVCcir allow [ inbound ] 
rate-limit
Restore the CIR ALLOW of a Frame Relay PVC to the 
default valueundo cir allow [ inbound ] 
						

							266CHAPTER 17: CONFIGURING FRAME RELAY
Configure Frame Relay 
Congestion 
ManagementThere are two ways to set the congestion threshold. One is to configure the 
congestion threshold for a PVC in a specified 
Frame Relay class, another is to 
configure the congestion threshold for the overall interface in interface view. The 
router determines whether there is congestion on the interface according to the 
ratio that the current queue length on the Frame Relay interface or PVC occupies 
the total queue length on the interface. If the ratio is greater than the threshold 
set by the user, the router will assume that there is congestion, and will process 
the packets with the corresponding methods, such as discarding.
Frame Relay congestion management include the congestion management on the 
Frame Relay interface and the congestion management on the Frame Relay PVC.
1Configure the congestion management policy on a Frame Relay interface
Perform the following configurations in synchronous serial interface view.
Ta b l e 305   Configure the congestion management policy on a Frame Relay interface
By default, the congestion management is not enabled on a Frame Relay interface.
When the congestion management is enabled on a Frame Relay interface, the 
queueing type on the interface can only be either FIFO or PIPQ.
2Configure the congestion management policy on Frame Relay PVC
Perform the following configurations in frame relay class view.
Ta b l e 306   Configure the congestion management policy on a Frame Relay PVC
By default, the congestion management is not enabled on Frame Relay PVCs.
When the congestion management is enabled on a Frame Relay PVC, the 
queueing type on the PVC can only be FIFO.
Only when the Frame Relay traffic shaping is enabled on the interface where a 
PVC is located, can the congestion management take effect on the PVC.
OperationCommand
Enable a Frame Relay interface to discard the 
packets that are marked with DE flag bit in the 
case of congestionfr congestion-threshold de 
queue-percentage
Disable the Frame Relay interface to discard the 
packets that are marked with DE flag bit in the 
case of congestionundo fr congestion-threshold 
de
Enable a Frame Relay interface to process the 
BECN and FECN flag bits in the case of congestionfr congestion-threshold ecn 
queue-percentage
Disable the Frame Relay interface to process the 
BECN and FECN flag bits in the case of congestionundo fr congestion-threshold 
ecn
OperationCommand
Enable a Frame Relay PVC to discard the packets 
that are marked with DE flag bit in the case of 
congestioncongestion-threshold 
dequeue-percentage
Disable the Frame Relay PVC to discard the packets 
that are marked with DE flag bit in the case of 
congestionundo congestion-threshold de
Enable the Frame Relay PVC to process the BECN 
and FECN bits in the case of congestioncongestion-threshold ecn 
queue-percentage
Disable the Frame Relay PVC to process the BECN 
and FECN bits in the case of congestionundo congestion-threshold ecn