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20-12
ATM Switch Router Software Configuration Guide
OL-7396-01
Chapter20 Configuring Frame Relay to ATM Interworking Port Adapter Interfaces
Configuring Frame Relay Frame Size for Frame Relay to ATM Interworking
Note Usually the Frame Relay CTTR with the lowest frame size has the highest SCR for a given CIR. This is
because of the overhead introduced by ATM [5 bytes/Cell + 8 Bytes for the AAL5 trailer + AAL5
Padding].
There are exceptional cases when the padding is greater. For example, in the case of 85 byte and 87 byte
frame-sizes, the convention of lower size does not hold true because of the additional padding added to
an AAL5 in case of 87 byte to 85 byte frame-sizes. In this case, the 87 byte frame-size should be used
because it has the higher SCR.
The easiest way to choose which frame-size to configure is to use the one with highest SCR for the
corresponding CIR. For example, if you have frames sizes 64, 90, 250, 512 1500, and 4000, the best SCR
for the frames is the size 90 for a given CIR. If frame-size 50 is added to the previous list of frame sizes
then CTTR with 50 will have the highest SCR and that should be used.
Configuring and Using Frame Relay Frame Size
To use the Frame Relay frame size feature, requires the following:
• Create a Traffic table row (CTTR) using frame size
• Use that CTTR row while creating a VC (PVC or Soft PVC)
To configure the Frame Relay frame size, perform the following steps, beginning in global configuration
mode:
Use the following steps to configure Frame Relay frame size of an interworking soft PVC.
Step 1 Configure the Frame Relay frame size as part of the CTT row configuration.
Switch(config)# frame-relay connection-traffic-table-row 102 16000 32768 6400 vbr-nrt
frame-size 64
Command Purpose
Step 1
Switch(config)# frame-relay connection-traffic table-row
[index row-index] cirval bcval pirval [beval] {abr | vbr-nrt
| ubr} [frame-size bytes] [atm-row-index]
Configures the frame size used to convert Frame
Relay traffic parameters to their equivalent ATM
traffic parameters.
Step 2
Switch(config)# interface serial card/subcard/port:cgn Select the interface to configure.
Step 3
Switch(config-if)# frame-relay soft-vc dlci_source
dest-address address dlci_destinataion
rx-cttr index tx-cttr index gat
Configure the Frame Relay Soft VC and enable GAT
solution on the VC.
Step 4
Switch(config-if)# end
Switch#
Exits serial interface configuration mode.
Step 5
Switch# show frame-relay connection-traffic table row Confirm the Frame Relay CTT has the frame size
value configured.
Step 6
Switch# show vc interface serial card/subcard/port:cgn dlci Confirm the configured frame size is used in the
serial interface VC.
Step 7
Switch# show running-config interface serial
card/subcard/port:cgn
Confirm GAT is enabled in the serial interface VC.