Transcript Wide Area Networks

Chapter 10
Wide Area Networks
Contents
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The need for Wide area networks (WANs)
Point-to-point approaches
Statistical multiplexing, TDM, FDM approaches
Dial-up, T/ DS links
X.25, Frame relay, ATM
SONET
DWDM
WANs and TCP/ IP stack
2
Need
Point - X.25/FR/
SONET
point
ATM
DWDM
Definition
• WANs are physical or logical networks that
provide data communications to a large
number of independent users. These users are
usually spread over a larger geographic area
than a LAN
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WANs and
TCP/ IP
Need
Point - X.25/FR/
SONET
point
ATM
DWDM
The need for WANs
• LANs are very effective at connecting computers
within offices
• Links are short, so dedicated link to each PC is not
too expensive
• But many organizations have offices in many
states and countries
• Web pages, email servers are located world-wide
• As users spread over large distances, link costs
become very high
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WANs and
TCP/ IP
Need
Point - X.25/FR/
SONET
point
ATM
DWDM
The need for WANs (contd.)
• Broadcast lowers costs of LAN equipment
• But as number of users increases, CSMA slows
down the network significantly
• As number of network users increases, need
mechanisms to merge traffic from multiple
users
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WANs and
TCP/ IP
Need
Point - X.25/FR/
SONET
point
ATM
DWDM
Roads and computer networks
• There are many similarities between the
challenges and design solutions used in road
networks and computer networks
• Neighborhood networks are like LANs
• Interstate networks are like WANs
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WANs and
TCP/ IP
Need
Point - X.25/FR/
SONET
point
ATM
DWDM
Local intersection as LAN node
Stop sign promotes carrier sensing
White car will wait till black car passes
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WANs and
TCP/ IP
Need
Point - X.25/FR/
SONET
point
ATM
DWDM
Interstate exit as WAN node
Existing traffic does not
stop for merging traffic
Shared lanes
Merging lane: Exit
ramp for local traffic
Merging lane: Entry
ramp for local traffic
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WANs and
TCP/ IP
Need
Point - X.25/FR/
SONET
point
ATM
DWDM
Categories of WANs
• Point-to-point
– Dial-up
– T/ DS
• Statistical multiplexing
– X.25, Frame relay, ATM
• TDM
– SONET
• FDM/ WDM
– Fiber optics
• MPLS
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WANs and
TCP/ IP
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SONET
point
ATM
DWDM
Point-to-point WANs
Internet in 1969
• Earliest WANs used
dial-up networking
940
– Use phone line to
connect to a remote
computer
#2
SRI
#4
Utah
PDP 10
– Leverage existing
communication
network
– End stations perform
routing
360
#3
UCSB
#1
UCLA
Sigma 7
Phone lines
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WANs and
TCP/ IP
Need
Point - X.25/FR/
SONET
point
ATM
DWDM
T/ DS carriers
• Phone companies realized business
opportunity in providing data services
• Combined (multiplexed) data carrying capacity
of multiple phone lines to provide high speeds
• Offered as T/ DS carriers
–T=
– DS =
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WANs and
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Need
WAN built using T-carriers
T1
T1
Branch
T1
Branch
T1
HQ
Branch
Branch
Point - X.25/FR/
SONET
point
ATM
DWDM
WANs and
TCP/ IP
Need
Point - X.25/FR/
SONET
point
ATM
DWDM
T/ DS carriers
• Formally, t-carriers are the physical line, DS is
the signal carried by the line
– Both terms used interchangeably in the industry
• Offer point-to-point connection like dial-up
No. of phone lines aggregated
T-carrier name
1
DS name
Data rate
DS-0
64 kbps
24
T-1
DS-1
1.544 mbps
96
T-2
DS-2
6.312 mbps
672
T-3
DS-3
44.736 mbps
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WANs and
TCP/ IP
Need
Point - X.25/FR/
SONET
point
ATM
DWDM
Statistically multiplexed WANs
• Point-to-point is very
inefficient when network
grows
T1
A
A
T1
B
B
A
T1 B2
B1
– No switching within network
– Inefficient use of bandwidth
– Reduces “burstiness”
T1
X.25/ FR/ ATM
A
T1
T1
A
T1
T1
• Statistical multiplexing
allows WANs to aggregate
traffic
Carrier
B access
point
B
A
B2
Carrier
access B1
point
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WANs and
TCP/ IP
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Point - X.25/FR/
SONET
point
ATM
DWDM
Reducing “burstiness”
100
90
80
Percentage link utilization
70
60
A
50
B
40
A+B
30
20
10
0
8:00
9:00
10:00
11:00
12:00
13:00
14:00
15:00
16:00
17:00
Time of day
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Need
Point - X.25/FR/
SONET
point
ATM
DWDM
Virtual circuits
A-A
VC = 2
VC = 1
A
VC = 3
B2
B-B2
X.25/ FR/ ATM
A
B
Carrier
access
point
Carrier
access
point
B1
B-B1
Connection
A-A
B-B1
B-B2
Virtual-circuit ID
1
2
3
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Need
Point - X.25/FR/
SONET
point
ATM
DWDM
X.25/ Frame relay/ ATM
• Shared network services offered by telcos
– Multiple end users can share the same
infrastructure
– Aggregation similar to interstate system
• End users connect to shared network using
point-to-point links such as T1/ T3
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WANs and
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Point - X.25/FR/
SONET
point
ATM
DWDM
X.25/ Frame relay/ ATM
• When data packets enter shared network, carrier
assigns label based upon destination
• Shared network uses labels to direct packets to
correct destinations
• Each label is called a virtual channel
– Data link layer technologies
– Many virtual channels can be carried over a single
physical link, limited only by link capacity
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WANs and
TCP/ IP
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Point - X.25/FR/
SONET
point
ATM
DWDM
X.25/ Frame relay/ ATM
• X.25
– Standardized by CCITT in 1976
– Data rates: 56 kbps – 2 mbps
• Frame relay
– Specified/ standardized in 1990 (Cisco)/ 1992 (CCITT)
– Data rates: 56 kbps – 45 mbps
• ATM
– Standardized: 1992 by CCITT
– Data rates: 1.544 mbps – 622.080 mbps
– Pricing: ~ $400/ mbps/port (domestic) – upto $4,000/
mbps/port (internationally)
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WANs and
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Point - X.25/FR/
SONET
point
ATM
DWDM
TDM WANs
• Available line data rate divided into time slots
– Physical layer technology
• Each virtual channel given one or more slots
• Commercially available as SONET services
– Synchronous Optical NETwork
– Synchronous Digital Hierarchy (SDH) in Europe
– Offered as optical carrier (OC) services
• Pricing generally dependent on distance: ~ $15/
mbps/ mile
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WANs and
TCP/ IP
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Point - X.25/FR/
SONET
point
ATM
DWDM
TDM WANs
• X.25/ Frame relay/ ATM often transported
over SONET links
• SONET data rates first standardized in 1988 by
CCITT
SONET service names
Data rate
Data + overhead
OC-1
50.112 mbps
51.84 mbps
OC-3
150.336 mbps
155.52 mbps
OC-12
601.344 mbps
622.08 mbps
OC-48
2.405,376 gbps
2.488,320 gbps
OC-192
9.621,504 gbps
9.953,280 gbps
OC-768
38.486,016 gbps
39.813,120 gbps
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WANs and
TCP/ IP
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Point - X.25/FR/
SONET
point
ATM
DWDM
FDM WANs
• Optical fiber has very high bandwidth
– Capable of supporting extremely large data rates
– No single user needs such high bandwidths
• Available line bandwidth split into multiple
lower bandwidth channels
– Like lanes on interstate highways
– Vehicles are not wide enough to use entire road
width
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WANs and
TCP/ IP
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Point - X.25/FR/
SONET
point
ATM
DWDM
FDM WANs
• DWDM channel frequencies standardized by ITUT as ITU grid in 2001
– 3 bands: L band, C band, S band
– 50 channels/ band = 150 channels total
– Data rates up to 10 gbps possible per DWDM channel
• DWDM commonly used in network core
– Considered below physical layer
• Each FDM channel on a DWDM link may
transport a SONET signal, which in turn may
transport multiple ATM channels
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WANs and
TCP/ IP
Need
Point - X.25/FR/
SONET
point
ATM
DWDM
WANs and TCP/ IP stack
• Where are WAN technologies positioned on
the TCP/ IP stack?
• Typically, multiple WANs traversed by packet
from source to destination
• Routers interface between WANs
– Hence WANs typically considered a data link layer
technology
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WANs and
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Point - X.25/FR/
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point
ATM
DWDM
WANs and TCP/ IP stack
• Traceroute to Google
Network layer
Destination IP address passed
to network layer to determine
next WAN
Data routed to correct WAN for
onward transmission
WAN 1 technology confirms
router is WAN destination
WAN 2 technology frames
data for transmission
Incoming frame from WAN 1
Router
Outgoing frame to WAN 2
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WANs and
TCP/ IP
Summary
• WANs are long distance links that aggregate
traffic from multiple networks
• WANs generally have very high data rates
• WAN types include point-to-point, statistically
multiplexed, TDM and FDM
• Carriers define virtual circuits for each sourcedestination pair of nodes
• WANs operate at the data link layer
Case study – UAVs
• Remote wars were fought with soldiers
• Now, increasingly de[end upon satellite based
WAN networks
• UAVs
Hands-on exercise
• OPNET
– Download academic version of software
• Approx. 50 MB
– Run scenario
– Collect statistics
Network design exercise
• Choosing appropriate WAN technologies
• Adding routers to the network