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Example: Configuring Large Delay Buffers for Slower Interfaces

Set large delay buffers on interfaces configured on a Channelized OC12 IQ PIC. The CoS configuration binds a scheduler map to the interface specified in the chassis configuration. For information about the delay-buffer calculations in this example, see Table 32.

chassis {
fpc 0 {
pic 0 {
q-pic-large-buffer; # Enabling large delay buffer
max-queues-per-interface 8; # Enabling eight queues (M320 and T-series)
}
}
}

Configuring the Delay Buffer Value for a Scheduler

You can assign to a physical or logical interface a scheduler map that is composed of different schedulers (or queues). The physical interface’s large delay buffer can be distributed to the different schedulers (or queues) using the transmit-rate and buffer-size statements.

The example shows two schedulers, sched-best and sched-exped, with the delay buffer size configured as a percentage (20 percent) and temporal value (300,000 microseconds), respectively. The sched-best scheduler has a transmit rate of 10 percent. The sched-exped scheduler has a transmit rate of 20 percent.

The sched-best scheduler’s delay buffer is twice that of the specified transmit rate of 10 percent. Assuming that the sched-best scheduler is assigned to a T1 interface, this scheduler receives 20 percent of the total 500,000 microseconds of the T1 interface’s delay buffer. Therefore, the scheduler receives 18,750 bytes of delay buffer:
available interface bandwidth * configured percentage buffer-size * maximum buffer = queue buffer
 
1.5 Mbps * 0.2 * 500,000 microseconds = 150,000 bits = 18,750 bytes

Assuming that the sched-best scheduler is assigned to a T1 interface, this scheduler receives 300,000 microseconds of the T1 interface’s 500,000-microsecond delay buffer with the traffic rate at 20 percent. Therefore, the scheduler receives 11,250 bytes of delay buffer:

available interface bandwidth * configured percentage transmit-rate * configured temporal buffer-size = queue buffer
 
1.5 Mbps * 0.2 * 300,000 microseconds = 90,000 bits = 11,250 bytes
class-of-service {
schedulers {
sched-best {
transmit-rate percent 10;
buffer-size percent 20;
}
sched-exped {
transmit-rate percent 20;
buffer-size temporal 300000;
}
}
}

Configuring the Physical Interface Shaping Rate

In general, the physical interface speed is the basis for calculating the delay buffer size. However, when you include the shaping-rate statement, the shaping rate becomes the basis for calculating the delay buffer size. This example configures the shaping rate on a T1 interface to 200 Kbps, which means that the T1 interface bandwidth is set to 200 Kbps instead of 1.5 Mbps. Because 200 Kbps is less than 4xDS0, this interface receives 4 seconds of delay buffer, or 800 Kbps. For more information, see Table 33.
class-of-service {
interfaces {
t1-0/0/0:1:1 {
shaping-rate 200k;
}
}
}

Complete Configuration

This example shows a Channelized OC12 IQ PIC in FPC slot 0, PIC slot 0 and a channelized T1 interface with Frame Relay encapsulation. It also shows a scheduler map configuration on the physical interface.
chassis {
fpc 0 {
pic 0 {
q-pic-large-buffer;
max-queues-per-interface 8;
}
}
}
interfaces {
coc12-0/0/0 {
partition 1 oc-slice 1 interface-type coc1;
}
coc1-0/0/0:1 {
partition 1 interface-type t1;
}
t1-0/0/0:1:1 {
encapsulation frame-relay;
unit 0 {
family inet {
address 1.1.1.1/24;
}
dlci 100;
}
}
}
class-of-service {
interfaces {
t1-0/0/0:1:1 {
scheduler-map smap-1;
}
}
scheduler-maps {
smap-1 {
forwarding-class best-effort scheduler sched-best;
forwarding-class expedited-forwarding scheduler sched-exped;
forwarding-class assured-forwarding scheduler sched-assure;
forwarding-class network-control scheduler sched-network;
}
}
schedulers {
sched-best {
transmit-rate percent 40;
buffer-size percent 40;
}
sched-exped {
transmit-rate percent 30;
buffer-size percent 30;
}
sched-assure {
transmit-rate percent 20;
buffer-size percent 20;
}
sched-network {
transmit-rate percent 10;
buffer-size percent 10;
}
}
}
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