Post on 17-Dec-2015
transcript
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RR
RR
S
SS
s
s s
s
ss
s
ss
s
R
s
R
Backbone
To internet or wide area network
Organization Servers
Gateway
Departmental Server
Campus Network
3
Interdomain level
Intradomain level
LAN level
Autonomous systemor domain
Border routers
Border routers
Internet service provider
Intradomain and Interdomain levels
4
RA
RB
RC
Route server
NAP
National service provider A
National service provider B
National service provider C
LAN
NAPNAP
(a)
(b)
5
Control
1
2
3
N
Line Card
Line Card
Line Card
Line CardIn
terc
onne
ctio
nFa
bric
Line Card
Line Card
Line Card
Line Card
1
2
3
N
…… ……
Components of Generic Switch/Router
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Buffering
• Wherever contention is possible– input port (contend for fabric)– internal (contend for output port)– output port (contend for link)
• Head-of-Line Blocking
– input buffering
Switch
2
21
Port 1
Port 2
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Workstation-Based
• Aggregate bandwidth – 1/2 of the I/O bus bandwidth – capacity shared among all hosts connected to switch– example: 800Mbps bus can support 8 T3 ports
CPU
Main memory
I/O bus
Interface 1
Interface 2
Interface 3
• Packets-per-second – must be able to switch
small packets– 100,000 packets-per-
second is achievable– e.g., 64-byte packets
implies 51.2Mbps
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Self-Routing Fabrics
• Banyan Network– constructed from simple 2 x 2 switching elements– self-routing header attached to each packet– elements arranged to route based on this header– no collisions if input packets sorted into ascending order– complexity: n log2 n
001
011
110
111
001
011
110
111
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High-Speed IP Router
• Switch (possibly ATM)
• Line Cards + Forwarding Engines– link interface– router lookup (input)– common IP path (input)– packet queue (output)
• Network Processor
– routing protocol(s)
– exceptional cases
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High-Speed Router
Line card(forwarding buffering)
Line card(forwarding buffering)
Lin
e ca
rd(f
orw
ardi
ng
buff
erin
g)
Lin
e ca
rd(f
orw
ardi
ng
buff
erin
g)
RoutingCPU
Buffermemory
Routing softwarew/ router OS
Routing softwarew/ router OS
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t
t
t
t
31 2
31 2
321
Release
Connect request
CR
CR Connect confirm
CC
CC
Delays in virtual-circuit switching
15
SW 1
SW 2
SW n
Connect request
Connect request
Connect request
Connect confirm
Connect confirm
…
Signaling for virtual-circuit setup
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Identifier Outputport
15 15
58
13
13
7
27
12
Nextidentifier
44
23
16
34
Entry for packetswith identifier 15
Example virtual-circuit routing table
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Packet buffer
Transmission link
Arrivingpackets
Packet discardwhen full
Packet buffer
Transmissionlink
Arrivingpackets
Class 1 discardwhen full
Class 2discardwhen thresholdexceeded
(a)
(b)
FIFO Queuing:
FIFO Queuing with discard priority
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Transmission link
Packet discardwhen full
High-prioritypackets
Low-prioritypackets
Packet discardwhen full
When high-priorityqueue empty
HOL Priority queuing
19
Sorted packet buffer
Transmissionlink
Arrivingpackets
Packet discardwhen full
Taggingunit
Sorting packets according to priority tag
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Transmission link
Packet flow 1
Packet flow 2
Packet flow n
C bits/second
Approximatedbit-levelround robinservice
Fair queuing
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Queue 1@ t=0
Queue 2@ t=0
1
t1 2
Fluid-flow system:both packets served at rate 1/2
Both packetscomplete serviceat t=2
0
1
t1 2
Packet-by-packet system:queue 1 served first at rate 1;then queue 2 served at rate 1.
Packet from queue 2being served
Packet fromqueue 1 beingserved
Packet fromqueue 2 waiting
0
Fluid-flow and packet-by-packet FQ
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Rounds Generalize so R(t) is continuous, not discrete
R(t) grows at rate inverselyproportional to nactive(t)
Computing finishing times
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Queue 1@ t=0
Queue 2@ t=0
2
1
t3
Fluid-flow system:both packets served at rate 1/2
Packet from queues served at rate 1
0
2
1
t1 2
Packet-by-packet fair queueing:queue 2 served at rate 1
Packet fromqueue 1 beingserved at rate 1
Packet fromqueue 2 waiting
0 3
Fluid-flow and packet-by-packet FQ
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Queue 1@ t=0
Queue 2@ t=0
1
t1 2
Fluid-flow system:packet from queue 1served at rate 1/4;
Packet from queue 1 served at rate 1
Packet from queue 2served at rate 3/4 0
1
t1 2
Packet-by-packet weighted fair queueing:queue 2 served first at rate 1;then queue 1 served at rate 1.
Packet from queue 1being servedPacket from
queue 2 beingserved
Packet fromqueue 1 waiting
0
Weighted Fair Queuing