Transcript WAN Technologies

WAN Technologies
Ch 7 Lecture 1
WAN Connectivity
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Provided through:
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Public Networks - PSTN and Internet
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Public Switched Telephone Network (PSTN)
Also known as Plain Old Telephone System
(POTS)
Private Networks
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Leased lines
PSTN
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International phone infrastructure
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Media
Equipment
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Cheap (Economical)
Readily available
Highly accessible
Disadvantages
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Software
Advantages
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Satellites
Antennas
Routers
Other devices
Speed (slow)
Security
Good option for small organizations
Private Networks
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Rent/lease
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Media
Equipment
Considerations
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Layout
Level of complexity
Security level
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Fiber, copper, or wireless
Protocols
Administration
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In-house
Outsourced
WAN Services
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WANs provide for the exchange of data
packets/frames between routers/bridges and
the LANs they support.
A WAN interconnects LANs that are usually
separated by large geographic areas.
WANs connect devices. Such devices include
routers, modems, etc.
Routers
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Routers offer many services including:
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Internetworking
WAN serial interfaces
Routers can operate as...
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Internal Routers
Backbone Routers
Autonomous System Boundary Routers
WAN Standards
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What layers of the OSI model do WAN
standards describe?
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Physical and Data Link Layers
Switching Methods
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Switching – moving data from one
location to another via a communication
path
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Packet-switching **Most popular
Circuit-switching
Message-switching
Packet Switching
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Message is broken into packets
Encapsulated with header
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Uses independent routing
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Source and destination addresses
Router chooses the best path based on routing tables
Packets may get to the destination out of
order/sequence
TCP re-sequences the packets
Two types of Packet Switching
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Virtual Circuit
Datagram
Virtual Circuit
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Logical connection/link between source and
destination is established
The link has an id and the packets also contain that
id.
Remains active for as long as devices are available or
short term (only for length of transmission)
Established path (all packets use the same path)
Used for connection-oriented services such as
streaming video
Datagram Packet Switching
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Sent best effort
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packets may be sent through different
paths
Received in non-sequential order
TCP reconstructs
Circuit-Switching
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Telephone conversation is good analogy
Requires dedicated physical connection
for duration of transmission session
Guaranteed transfer rate
Inefficient - once a session is
established, transmission path is not
available to others.
WAN Technologies Overview
Dedicated
• T1, E1, T3, E3
• xDSL
• SONET
Circuit
Switched
• POTS
• ISDN
Switched
Packet
Switched
• X.25
• Frame
Relay
Analog
• Dial-up modems
• Cable modems
• Wireless
Cell
Switched
• ATM
• SMDS
Dedicated Digital Services
Dedicated Digital Services provide full-time
connectivity through a point-to-point link
 T series in U.S. and E series in Europe
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Uses time division multiplexing to “slice up”
data and assign time slots for
transmissions
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T1 = 1.544 Mbps
T3 = 44.736 Mbps
E1 = 2.048 Mbps
E3 = 34.368 Mbps
•Uses twisted pair & fiber
•Extremely popular
•Moderate cost
Digital Subscriber Lines (DSL)
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WAN technology for home use;
decreasing bandwidth with increasing
distance from the phone companies CO.
Data rates 100Kbps - 51.84 Mbps
Moderate expense and getting cheaper
Dedicated Digital Services
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Synchronous Optical Network
(SONET)
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51.84 Mbps (OC-1) -- 9,952 Mbps (OC-192)
Uses lasers to divide the wavelength of the
light into sections that can carry large
amounts of data (Wave Division
Multiplexing)
Very expensive; used by large ISPs and
other Internet backbone entities.
Circuit Switched Services
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Plain Old Telephone System (POTS)
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Not a computer data service but...
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POTS is an important component of our
communication infrastructure and
It is still the standard for designing reliable
networks
Dial-up Modems
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Limited to 56 kbps
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Works with existing phone network
Low cost and widespread usage
Cable Modems
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Data signals on the same cable as
television signals
Increasing in popularity
Maximum bandwidth 10 Mbps, though
this degrades as more users attach to a
given network segment
Cost is relatively low
Wireless
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Terrestrial
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Bandwidths typically
in the 11 Mbps range
Cost is relatively low
Line-of-sight is
usually required
Usage is moderate
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Satellite
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Can serve mobile
users and remote
users
Usage is widespread
Cost is very high
Circuit Switched Services
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Integrated Services Digital
Network (ISDN)
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Historically important--first dial-up digital service
Cost is moderate
max. bandwidth = 128 kbps for BRI (Basic Rate
Interface)
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2 B channels @ 64kps AND
1 D channel @ 16kps
 B (bearer) channels are voice/data channels;
 D (delta) channel for signaling