Module 1
WANs and Routers
Overview
Students completing this module should be able to:
• Identify organizations responsible for WAN standards
• Explain the difference between a WAN and LAN and the type of
addresses each uses
• Describe the role of a router in a WAN
• Identify internal components of the router and describe their functions
• Describe the physical characteristics of the router
• Identify common ports on a router
• Properly connect Ethernet, serial WAN, and console ports
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Introduction to WANs
These are the major characteristics of WANs:
• They connect devices that are separated by wide geographical areas.
• They use the services of carriers such as the Regional Bell Operating
Companies (RBOCs), Sprint, MCI, VPM Internet Services, Inc., and
Altantes.net.
• They use serial connections of various types to access bandwidth over
large geographic areas.
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Introduction to WANs
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Routers offer many services, including internetworking and WAN interface
ports.
Switches in the WAN provide connectivity for voice, data, and video
communication.
Modems include interface voice-grade services, channel service units/digital
service units (CSU/DSUs) that interface T1/E1 services, and Terminal
Adapters/Network Termination 1 (TA/NT1s) that interface with Integrated
Services Digital Network (ISDN) services.
Communication servers concentrate dial-in and dial-out user communication.
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Introduction to WANs
There are different
layer 2 encapsulation
types – Cisco’s serial
interfaces default to
Cisco HDLC
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Physical Layer Standards
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Data Link Layer
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CSU/DSU and Digital Local Loops
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The communications link needs signals in an appropriate
format.
The Channel Service Unit (CSU) receives and transmits
signals from and to the WAN line and provides a barrier for
electrical interference from either side of the unit. The CSU
can also echo loopback signals from the phone company
for testing purposes.
The Data Service Unit (DSU) manages line control, and
converts input and output between RS-232C, RS-449, or
V.xx frames from the LAN and the time-division multiplexed
(TDM) DSX frames on the T-1 line. The DSU manages
timing errors and signal regeneration. The DSU provides a
modem-like interface between the computer as Data
Terminal Equipment (DTE) and the CSU.
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The CSU/DSU may also be built into the
interface card of the router.
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Introduction to Routers in a WAN
Routers connect and allow communication
between two networks and determine the best
path for data to travel through the connected
networks.
RAM
• Stores routing tables
• Holds ARP cache
• Holds fast-switching cache
• Performs packet buffering (shared RAM)
• Maintains packet-hold queues
• Provides temporary memory for the configuration file
of the router while the router is powered on
• Loses content when router is powered down or
restarted
NVRAM
• Provides storage for the startup configuration file
• Retains content when router is powered down or
restarted
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Introduction to Routers in a WAN
Flash memory
• Holds the operating system image (IOS)
• Allows software to be updated without removing
and replacing chips on the processor
• Retains content when router is powered down or
restarted
• Can store multiple versions of IOS software
• Is a type of electronically erasable,
programmable ROM (EEPROM)
Read-only memory (ROM) has the following
characteristics and functions:
• Maintains instructions for power-on self test
(POST) diagnostics
• Stores bootstrap program and basic operating
system software
• Requires replacing pluggable chips on the
motherboard for software upgrades
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Interfaces
• Connect router to network for
frame entry and exit
• Can be on the motherboard
or on a separate module
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Router LANs and WANs
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Smaller broadcast domains
Connecting Layer 3 networks
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Router LANs and WANs
• Routers are the backbone devices of large intranets and of the Internet.
• They operate at Layer 3 of the OSI model, making decisions based on
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network addresses.
The two main functions of a router are the selection of best path for
and the switching of frames to the proper interface.
Routers accomplish this by building routing tables and exchanging
network information with other routers.
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Router Role in a WAN
• The WAN physical layer describes the interface between the data
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terminal equipment (DTE) and the data circuit-terminating equipment
(DCE).
Generally, the DCE is the service provider and the DTE is the attached
device. In this model, the services offered to the DTE are made
available through a modem or a CSU/DSU.
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Router Role in a WAN
• The primary WAN role of a router is therefore not routing, but providing
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connections to and between the various WAN physical and data-link
standards.
For example, a router may have an ISDN interface using PPP
encapsulation and a serial interface terminating a T1 line using Frame
Relay encapsulation.
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Academy Approach to Hands-on Labs
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In the academy lab, devices that make up the WAN cloud
are simulated by the connection between the back-to-back
DTE-DCE cables.
One of the routers will provide the clock rate (later).
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Router Internal Components
• CPU
• RAM
• Flash
• NVRAM
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• Buses
• ROM
• Interfaces
• Power Supply
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Router Physical Characteristics
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Router External Connections
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Management Port Connections
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Management Port Connections
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Connecting Console Interfaces
When connected using the console interface, the computer is acting
as a “dumb terminal”.
The PC can at the same
time be connected to the
router via its NIC – then it
is part of the network
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<Router Output>
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Connecting Console Interfaces
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Connecting Console Interfaces
<Router Output>
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Connecting LAN Interfaces
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Connecting WAN Interfaces
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Connecting WAN Interfaces
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Connecting WAN interfaces
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Summary
An understanding of the following key points should have
been achieved:
• WAN and LAN concepts
• Role of a router in WANs and LANs
• WAN protocols
• Encapsulation Types
• The identification and description of the internal
components of a router
• The physical characteristics of a router
• The common ports on a router
• How to connect router console, LAN, and WAN ports
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