Limitations That Are Common For Cos On Ppp And Mlppp Interfaces - Juniper ACX1000 Configuration Manual

ACX Series Universal Access Router Configuration Guide

Limitations That are Common for CoS on PPP and MLPPP Interfaces

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The following restrictions apply for configuring CoS on PPP and MLPPP interfaces on
ACX Series routers:
For interfaces with PPP encapsulation, you can configure interfaces to support the
IPv4, Internet Protocol Control Protocol (IPCP), PPP Challenge Handshake
Authentication Protocol (CHAP), and Password Authentication Protocol (PAP)
applications.
Drop timeout, which defines a recovery method for any packets dropped by the member
links in a link services or multilink bundle, is not applicable for ACX routers.
Loss of traffic occurs during a change of CoS configuration; you cannot modify
scheduling attributes instantaneously. The link moves to the down state for PPP, and
the protocol is denoted as down for MLPPP interfaces.
Scheduling and shaping capabilities are based on the CIR-EIR model and are not in
accordance with the weighed fair queuing mode. The minimum transmit speed is 32
Kbps, and the minimum difference that can be supported between the transmit rate
and shaping rate is also 32 Kbps.
Buffer size is calculated in terms of packets using 256 bytes as the average packet
size. For example, if you configure a 10 percent buffer size for TI interfaces, the buffer
allocated as 1.536 Mbps * (10/100) * (0.1 sec) = 15360 bits. The following formula
computes the configured queue length:
Queue length configured = Buffer/average packet size = (15360/256)/8 = 7.5 = 8
packets.
Because there are no shared buffers, the usage of "buffer-size" and "buffer-size exact"
attributes result in the same behavior.
Only two loss priority levels, namely low and high, are supported. Traffic that arrives
from the Packet Forwarding Engine with a medium-high priority is treated as high
priority traffic. Although you can configure the medium-high loss priority type when
you configure the action for a firewall term, it is considered by the system as high priority
traffic.
A fixed, in-built mapping between forwarding class and queue number as follows is
performed: Best-effort is queue 0, expedited-forwarding is queue 1, assured-forwarding
is queue 2, and network-control is queue 3
For WRED configurations, the difference between maximum fill-level and minimum-fill
level is a number raised to the power of 2 in terms of number of packets (x^2).
Otherwise, the lower fill-level is tuned to turn the difference into a value raised to the
power of 2. For example, queues contain a size of 64 packets. If the following
configuration is performed:
fill-level 50 drop-probability 0;
fill-level 100 drop-probability 100;
For the lower fill level, the minimum number of packets is 32. However, if you specify
the fill-level to be 45 instead of 50, the lower fill level is 28. Because 64 - 28, which
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