Specifications

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from subscribers that were received at rates that exceed an agreed upon
threshold limit and packets that are within the threshold limit. Above-threshold
packets can be dropped more aggressively. A packet is dropped only if both the
queue profile and the port profile indicate to drop the packet. A port profile is
used to ensure that packets are not dropped when other queues are
underutilized.
Each outgoing PIC interface--either logical (I.e. an OC3 channel in an OC12
SONET PIC) or physical--on a DS3 or SONET PIC represents a port. The
decision to drop a packet from an Mxxx CoS queue is determined by a drop
profile. The probability that a packet will be dropped is related to how full the
queue is. This relationship is configurable by the user.
Example: SONET OC12/SDH STM4 QueuingExample: SONET OC12/SDH STM4 Queuing
u All queuing done at out-going FPC (I/O Manager ASIC)
u 4 queues per port (DS3 or SONET)
u Queues serviced via weighted-round-robin mechanism
Out-bound
FPC
(I/O Manger
ASIC)
OC12 PICOC12 PIC
WRRWRR
WRR
WRR
WRRWRR
WRRWRR
OC12 PICOC12 PIC
OC12 PIC
OC12 PIC
OC12 PICOC12 PIC
Having two profiles allows the ISP to drop out of threshold traffic more
aggressively than traffic that was received within a service agreement threshold.
A packet is dropped only if both the queue profile and the port profile say drop.
Checking the port profile ensures that packets in a particular queue are not
dropped if other queues are underutilized. Unused interface bandwidth is shared
between queues.
Packet over Packet over
bandwidth bandwidth
threshold?threshold?
No: PLP No: PLP
not setnot set
Yes: PLP setYes: PLP set
Queue Packet Based Queue Packet Based
on:on:
•• IP Precedence bitsIP Precedence bits
•• Incoming Physical Incoming Physical
InterfaceInterface
•• Incoming Logical Incoming Logical
InterfaceInterface
•• Destination IP Destination IP
addressaddress
•• Application type Application type
(future)(future)
Apply Drop Profiles within Apply Drop Profiles within
each Queueeach Queue
•• Applied to packet at Applied to packet at
head of queuehead of queue
•• 1 of two drop profiles, 1 of two drop profiles,
depending on PLPdepending on PLP
•• Probability of drop Probability of drop
dependent upon queue fill dependent upon queue fill
levellevel
Apply Drop Profiles within Apply Drop Profiles within
each Queueeach Queue
•• Applied to packet at Applied to packet at
head of queuehead of queue
•• 1 of two drop profiles, 1 of two drop profiles,
depending on PLPdepending on PLP
•• Probability of drop Probability of drop
dependent upon queue fill dependent upon queue fill
levellevel
ReRe--write Precedence write Precedence
BitsBits
•• To carry queuing To carry queuing
informationinformation
•• To carry PLP To carry PLP
informationinformation
Transmit Transmit
PacketPacket
Receive Receive
Packet on Packet on
Incoming Incoming
PICPIC
PFE does route lookup, PFE does route lookup,
sends notification for sends notification for
queuing on Outgoing FPCqueuing on Outgoing FPC
Outgoing FPC
Incoming PIC
Weighted
Round Robin
servicing of
queues
The figure above presents a logical overview of the Mxxx COS mechanisms.
Each incoming PIC supports token-bucket policing. Packets that exceed an
agreed-upon service threshold are either dropped or marked by setting the
Packet Loss Priority (PLP) bit.