Chabot College
ELEC 99.08
Wide Area Network Introduction
CISCO NETWORKING ACADEMY
WANs
CISCO NETWORKING ACADEMY
WAN Technologies
Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
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WAN technologies
Physical and Data Link
Layer 2
Layer 1
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WAN: Layer 1
WAN physical layer protocols describe
how to provide connections.
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The WAN interface
Your Ethernet LAN connects to your
router. But what does you router
connect to?
? WAN
802.3 LAN
Cat5 UTP
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Regional Bells Provide Media
SF
PACBELL
NY
Regional Bells usually provide the media for WideArea Network connectivity.
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WAN Pipes
More….
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The WAN interface
How do routers connect to the phone
companies lines?
to phone company
CISCO NETWORKING ACADEMY
Data Terminal Equipment
Routers are usually considered DTEs.
DTEs are devices at the end of a user’s
network that serve as a data source,
destination, or both.
The router is a DTE, or
Data Terminal Equipment
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Data Terminal Equipment
Your home computer can also be a DTE.
How do you connect to the phone
company’s network at home?
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DTEs and DCEs
At home, you connect to the phone
company’s network using a modem.
modem
to phone company
CISCO NETWORKING ACADEMY
Data Circuit Equipment
A modem is a type of DCE, or Data
Circuit-Termination Equipment. It’s the
device at the end of the service
provider’s network (phone company).
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Data Circuit Equipment
• Another type of DCE is a CSU/DSU
– Channel Service Unit
– Data Service Unit
• CSU/DSU is located at the end of the
service provider’s network (phone
company).
• connects to router Serial port.
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DTEs and DCEs
A DTE interfaces with a DCE to gain
access to the phone company’s network.
Customer’s
Network
DTE
PC
Router
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DCE
Modem
CSU/DSU
Phone
Company’s
Network
DTEs and DCEs
• Router to CSU/DSU connection:
– Serial port on router
– V.35 port on CSU/DSU
– V.35 Cable between
CSU/DSU
DTE
CISCO NETWORKING ACADEMY
DCE
DTEs and DCEs
Typical WAN configuration:
Oakland
Hayward
CSU/DSU
CSU/DSU
phone
company
digital line
DTE
DCE
CISCO NETWORKING ACADEMY
DCE
DTE
DTEs and DCEs
Our Lab’s unusual configuration:
No digital phone lines, no CSU/DSUs.
The WAN is simulated in our lab.
Therefore, one router must play the DCE role - very unusual.
Oakland
Hayward
Serial interface
DTE
CISCO NETWORKING ACADEMY
Serial interface
V.35 Cables
Back-to-Back
DCE
WAN: Layer 2
WAN data-link protocols describe how
frames are carried between systems on
a single data path.
– point-to-point
– multipoint
– multiaccess (Frame Relay)
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WAN at Layer 2
dedicated
switched
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Data Link Layer: WAN Protocols
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HDLC
High-level Data Link Control
– usually used when connecting one router directly
to another (point-to-point)
– also is capable of supporting multipoint
connections (multiple point-to-point)
(test question)
– requires dedicated private digital lines
– HDLC implementations are proprietary
– Cisco serial interfaces default to HDLC
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PPP
Point-to-Point Protocol
– used in point-to-point dedicated connections
– used by
• routers over dedicated digital lines
• POTS users over dial-up (circuit switched) lines
(Windows & Mac dial-up networking)
– descendant of SLIP
– open standard (RFC 1661)
– allows authentication (PAP, CHAP)
– allows multiple layer 3 protocols
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Frame Relay
Frame Relay
– packet switched
– private dedicated digital lines not required
– one physical link can handle multiple logical links (multiaccess)
– descendant of X.25
– simplified frame (no error correction) relies on today’s
superior data links
– very fast
– cheap: pay for what you use
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ISDN
Integrated Services Digital Network
– circuit switched - (over digital voice/data line)
– designed to transmit voice, data, video over
existing phone lines
– used primarily for remote access via modems
– not very fast (especially BRI - 128 Kbps)
– may disappear with the emergence of cable
modems and DSL
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WAN Technology Options
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