Specifications

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After the route lookup, packet notifications are sent to the outgoing FPC for
transmission. The I/O manager on the outgoing FPC houses the COS queues for
all of the interfaces on the FPC. The packet notifications are queued based on IP
Precedence Bit information, incoming physical or logical port, destination IP
address, or application type (e.g. VoIP, telnet, http). The classification based on
application type will be available in a future release of JUNOS.
One of the two, drop profiles is applied to each queue, depending on the value of
the PLP bit. If the packet is not dropped, then it is serviced according the
weighted round robin algorithm running between the four classes of queues.
Finally, before transmission, there is a configurable option to rewrite the three-bit
precedence field within the IP header of the packet. The field can be rewritten to
carry the class information and the PLP status for the packet.
2.7.2 Application of Class Of Service
Subscriber
M20
Provider 1
M40
Provider 2
M20
M40
Access router receiving traffic bound for
subscriber:
•
• Queue packets based on destination
address and CoS agreement with
subscriber
Access router receiving traffic from
subscriber:
• Set PLP bit if above threshold
• Queue packets based on incoming port
and CoS agreement with subscriber
• Re-write precedence bits to carry PLP
and queuing information
Core router:
•• Queue packets based on information in
precedence field
• Apply drop profiles based on PLP
information carried in precedence field
If the M20 router is deployed as an access router, facing subscribers at the edge
of the ISP’s network, then the M20 router can be used to police a service level
agreement, using the PLP bit. If incoming data rates exceed agreed-upon limits
then the PLP bits within the offending packets can be set, marking the packets as
out of profile. The M20 router can then be more aggressive about dropping out-
of-profile traffic. In addition, as an access router, the M20 router can classify
packets based on incoming port (ie by subscriber) enabling the ISP to offer
premium service to customers who desire it. Finally, the M20 router can rewrite
the bits in the precedence field to carry the PLP and CoS information with the
packet as it travels through the network.
As a core router, the M40 (or M160) can queue packets based on the information
carried in the precedence field of the incoming packets (ie. Based on CoS
information gathered at the edge of the network.) The M40 core router can also
apply drop profiles to packets based on the PLP information carried within those
packets.
As an edge router facing another provider, the M20 router can rewrite the
precedence field within a packet to hide proprietary CoS classification from other
providers. In addition, the M20 router can queue packets (based on destination
address) bound for subscribers according to agreements made with those
subscribers.
2.7.3 Traffic Policing
Internet Processor II's policing counters give Junos the ability to classify packets
and assign different packet flows to different policing thresholds. The ability to
configure a filter against a logical interface, in either the incoming or outgoing
direction, where at least one of the actions is to assign a packet to a policer. The
policers are configurable to either drop out-of-profile packets or set the PLP bit on
those packets.
Examples of ways to use this feature:
§ Policing on a logical interface basis (e.g., have a single bandwidth
threshold for a VLAN, Frame Relay VC or ATM VC)