ELEN 602 Lecture 18

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ELEN 602 Lecture 18

• Packet switches
• Traffic Management

2
Gateway
Organization Servers
To internet or wide area network
s
s
Backbone
R
R
R
S
Departmental Server
S
S
R
R
R
s
s
s
s
s
s
s
s
s
Campus Network
3
Intradomain and Interdomain levels
Interdomain level
Border routers
Internet service provider
Autonomous system or domain
Border routers
LAN level
Intradomain level
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National service provider A
(a)
National service provider B
NAP
NAP
National service provider C
(b)
NAP
RA
RB
Route server
LAN
RC
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Components of Generic Switch/Router
Control
1
Line Card
Line Card
1
2
2
Line Card
Line Card
3
Interconnection Fabric
3
Line Card
Line Card




N
N
Line Card
Line Card
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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

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Crossbar Switches
8
Workstation based Router
CPU
I/O
Bus
1
NIC Card
2
NIC Card
NIC Card
3
Main Memory


N
NIC Card
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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

• 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

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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
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Virtual-circuit Packet Switching
Packet
Packet
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Delays in virtual-circuit switching
t
Connect request
1
3
2
CC
t
Release
3
CR
1
2
CC
t
Connect confirm
1
2
CR
3
t
Figure 7.19
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Signaling for virtual-circuit setup
Connect request
Connect request
Connect request
SW 1
SW n
SW 2

Connect confirm
Connect confirm
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Example virtual-circuit routing table
Output port
Next identifier
Identifier
12
44
13
Entry for packets with identifier 15
15
15
23
13
27
16
58
7
34
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FIFO Queuing
(a)
Packet buffer
Arriving packets
Transmission link
Packet discard when full
FIFO Queuing with discard priority
(b)
Packet buffer
Arriving packets
Transmission link
Class 1 discard when full
Class 2 discard when threshold exceeded
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HOL Priority queuing
Packet discard when full
High-priority packets
Transmission link
Low-priority packets
When high-priority queue empty
Packet discard when full
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Sorting packets according to priority tag
Sorted packet buffer
Arriving packets
Tagging unit
Transmission link
Packet discard when full
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Fair queuing
Approximated bit-level round robin service
Packet flow 1
Packet flow 2
C bits/second
Transmission link
Packet flow n
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Fluid-flow and packet-by-packet FQ
Queue 1 _at_ t0
Fluid-flow system both packets served at rate
1/2
1
Queue 2 _at_ t0
Both packets complete service at t2
t
0
2
1
Packet from queue 2 waiting
Packet-by-packet system queue 1 served first at
rate 1 then queue 2 served at rate 1.
1
Packet from queue 2 being served
Packet from queue 1 being served
t
0
2
1
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Computing finishing times
Generalize so R(t) is continuous, not discrete
R(t) grows at rate inversely proportional to
nactive(t)
23
2
Fluid-flow system both packets served at rate
1/2
Queue 1 _at_ t0
1
Queue 2 _at_ t0
Packet from queue s served at rate 1
t
0
2
3
Packet-by-packet fair queueing queue 2 served at
rate 1
Packet from queue 2 waiting
1
Packet from queue 1 being served at rate 1
t
2
1
3
0
Fluid-flow and packet-by-packet FQ
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Queue 1 _at_ t0
Fluid-flow system packet from queue 1 served at
rate 1/4 Packet from queue 1 served at rate 1
Queue 2 _at_ t0
1
Packet from queue 2 served at rate 3/4
t
0
2
1
Packet from queue 1 waiting
Packet-by-packet weighted fair queueing queue 2
served first at rate 1 then queue 1 served at
rate 1.
1
Packet from queue 1 being served
Packet from queue 2 being served
t
0
2
1
Weighted Fair Queuing