This section focuses on SRX and J-series specific CoS capabilities that are designed to work with Frame Relay. The virtual channel and adaptive shaping features help to optimize Frame Relay–based transport. Note that currently you cannot combine the functionality of an adaptive shaper with that of a virtual channel.
Porter are connected via a 0 CIR Frame Relay service terminating in a
500 Kbps port. With the newly added DiffServ-based CoS infrastructure
now in place, the idea of a 0 CIR service has been revisited. The result
is a decision to pay extra for a guaranteed CIR of 256 Kbps, with the
ability to burst to port speed via an EIR of 244 Kbps (CIR + EIR = port
Simply configuring a scheduler or shaper that allows the router to send at maximum speed, all the time, is problematic because during network congestion only the CIR traffic is guaranteed for delivery. Ideally, you want to send at the EIR rate only when the network is not congested, and then fall back to the CIR when congestion is detected, in an effort to ensure that congestion-induced discards do not negate your CoS SLAs. This capability is exactly what adaptive shaping provides.
The configurations at
Porter are updated to support
adaptive shaping. The modified configuration at
Bock is shown:
[edit class-of-service] lab@Bock#
trigger becn shaping-rate 256k;
}[edit class-of-service] lab@Bock# ...