Precedence

1
0
1
2
3
4
5
6
7
Service Selector
Precedence
Bits 0 - 2 1 1 1 - Network Control 1 1 0 -
Internetwork Control 1 0 1 - Critical functions 1
0 0 - Flash Override 0 1 1 - Flash 0 1 0 -
Immediate 0 0 1 - Priority 0 0 0 - Routine
Bits 3 - 6 1 0 0 0 minimize delay 0 1 0
0 maximize throughput 0 0 1 0 maximize
reliability 0 0 0 1 minimize monetary cost 0 0 0
0 normal best effort service bit 7 0 reserved
for future use
2
Priority 16 admission filter applied to packets
with community attribute 300
AS 1
AS 3
128.0.0.0/16
128.0.0.0/16 advertised to AS 2 via eBGP
128.0.0.0/16 community 300 advertised to AS 3
BGP community 300 applied to 128.0.0.0/16
eBGP
Priority 16 admission filter applied to
packets from 128.0.0.0.16
iBGP
Priority 16 admission filter applied to packets
with community attribute 300
AS 2
High Priority multi-provider transit path
3
Queuing System
Ingress Requests
Output Requests
High Priority Queue
A
A
A
A
A
B
B
B
B
B
A
A
Default Queue
Classification Function
B
4
Scheduler Input Queues
Forwarding Process
Output Queues
5
Burst sending at double rate
Queuing load within the network to smooth the
send burst
6
4
2
1
2
3
4
5
FIFO Output Queue
1
3
Forwarder
5
Scheduler Input Queues
7
1
2
1
2
3
4
FIFO Output Queue
3
Forwarder
4
Scheduler Input Queues
8
Output Driver selects packet from
highest priority queue
Priority 7 Queue
Scheduler selects queue priority based on
packet classification
Priority 6 Queue
Priority 5 Queue
Priority 4 Queue
Priority 3 Queue
Priority 2 Queue
Priority 1 Queue
Priority 0 Queue
9
Scheduler selects queue priority based on
packet classification
Queued Packets
200 byte selection
High Priority
150 byte selection
Medium Priority
100 byte selection
Low Priority
Class Based Scheduler with Round Robin Servicing
10
Queued Packets
600 byte service window
Average packet size 60 bytes
10 packets 600 bytes
400 byte service window
Average packet size 150 bytes
3 packets 450 bytes
200 byte service window
Average packet size 1500 bytes
1 packet 1500 bytes
Service Rotation Interval 2550 bytes
11
Queued Packets
60000 byte service window
Average packet size 60 bytes
1000 packets 60000 bytes
40000 byte service window
Average packet size 150 bytes
89 packets 40050 bytes
20000 byte service window
Average packet size 1500 bytes
14 packets 21000 bytes
Service Rotation Interval 121050 bytes
12
GPS Scheduling Model
Trailing bit of packet 3
GPS bit-level Scheduler
Trailing bit of packet 1
Packet Reassembler
Trailing bit of packet 2
1
3
2
Receiver Queue
Transmission path
Sender Queues
WFQ Scheduling Model
WFQ Scheduler
Packet Receiver
1
3
2
1
3
2
Transmission path
Receiver Queue
Sender Queues
13
Queued Packets
Flow 1 Queue
Flow 2 Queue
Transmission path
Flow 3 Queue
Weighted Fair Queuing Scheduler
14
Network Access Server
Core Network
LAN Switches
Core Routers
Service Router
Access Servers
Server Platforms
WFQ Enabled
15
Probability function applied to either queue or
discard packet
Incoming Packets
Empty Queue slots
Flow 2
Buffer Queue
Flow 3
Early Drop Packet Discard
Threshold queue size for early random discard to
be applied
16
Incoming Packets
Queue full condition causes the queue scheduler
to activate random drop process
Flow 2
Buffer Queue
Flow 3
Random Drop Packet Discard
Randomly selected packet to be discarded to make
space for the next queued packet
17
Token Stream
T
T
T
Token Bucket
T
T
T
T
T
T
T
Input Packet Queue
Rate Governed Output Packet Stream
Token Regulator
18
Token Stream
T
T
T
Token Bucket
T
T
T
T
Input Packet Queue
Constant rate Output Packet Stream
Token Regulator
19
Token Stream
T
T
T
Rate-enforced Discarded packets
Token Bucket
Maximum available burst rate
T
T
Input traffic burst
T
Input Packets
Rate Governed Output Packet Stream
Token Regulator
Burst Rate limited Output Stream
Burst Capacity
Token Rate
Input traffic rate profile
Output traffic rate profile
20
Token Stream
T
T
T
Token Bucket
Rate-enforced Delayed packets
Input traffic burst
T
Input Packet queue
Rate Governed Output Packet Stream
Token Regulator
Smoothed Rate Output Stream
Token Rate
Input traffic rate profile
Output traffic rate profile
21
Token Stream
T
Token Stream
T
T
T
T
T
T
Token Bucket
T
Token Bucket
T
T
Input traffic burst
T
Input Packets
Burst Rate Governed Output Packet Stream
Burst Rate Smoothed Output Packet Stream
Smoothed Burst Rate limited Output Stream
Burst Rate limited Output Stream
Token Rate2
Token Rate1
Input traffic rate profile
Intermediate traffic rate profile
Output traffic rate profile
22
Token Stream
T
T
T
Out of Profile Marked packets
Token Bucket
T
T
Input traffic burst
T
Input Packets
Rate Governed Output Packet Stream
Token Regulator
Out of Profile Data
Marked Output Stream
Token Rate
In Profile Data
Input traffic rate profile
Output traffic rate profile
23
RED selects packets from randomly selected flows
to discard
End-to-End Traffic flows
x
x
x
Interior congestion point with RED enabled
24
Once the average queue capacity reaches a certain
threshold, RED begins to select flows from which
to discard packets, so that congestion (buffer
exhaustion) can be avoided. The more the queue
fills up, the greater the probability of packet
discard.
1
Probability of Discard
Queue max.
0
Average Queue Depth
25
For lower weighted traffic the RED function is
triggered at lower average queue sizes, while
heavier weighted traffic uses a higher average
queue length to trigger random packet discard.
1
Low weight discard probability
Heavy weight discard probability
Probability of Discard
Queue max.
0
Average Queue Depth
26
Network Congestion Point
Randomly selected TCP Data packets with CE bit
set in the IP header
All outgoing data packets have ECT bit set in IP
header
ECN Sender
ECN Receiver
TCP ACK packets with ECN-ECHO option set
27
Network Path selected from A to B minimizes the
path metric. If the metric is inversely
proportional to the delay bandwidth product then
this path will have minimal delay and maximal
path capacity
25
19
20
19
10
5
B
2
5
25
A
28
Path Bandwidth 256K Path metric 14
C
1024K
B
1024K
256K
Link speed
2
A
D
2
10
Link metric
Bandwidth metric Cost 2048/ bandwidth
1
2048K
E
1
I
2048K
G
3
3
3
768K
F
3
3
J
768K
768K
768K
768K
H
Path Bandwidth 768K Path metric 17
29
Currently selected path will experience
increasing delays as the interior buffers
saturate with traffic, making the alternate path
more attractive in terms of dynamic link metrics.
Routing Oscillation
30
Jitter component
Voice
Voice
With Fragmentation and Interleaving
Voice
Voice
Fragment 4
Fragment 3
Fragment 2
Fragment 1
Jitter component
31
compressed header
RTP header Compressor
Low speed link
RTP header Expander
RTP/UDP/IP header
Shared flow context for header compression