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WANs
 A wide-area network (WAN) is a data
communications network spanning a large
geographic area
 Major characteristics of WANs:
 Connect devices that are separated by wide
geographical areas.
 Use the services of carriers such as the Regional Bell
Operating Companies (RBOCs), Sprint, MCI, and VPM
Internet Services, Inc. TSTT, Cable and Wireless (Ja)
to establish the link or connection between sites.
 Use serial connections of various types to access
bandwidth over large geographic areas
 Operate at the physical layer and the data link layer of
the OSI reference model

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WANs
 The following devices are used in WANs:
 Routers provide internetworking and WAN
interface ports.
 Switches provide connectivity for voice, data,
and video communication.
 Modems include interface voice-grade
services, channel service units/digital service
units (CSU/DSUs) for T1/E1 services, and
Terminal Adapters/Network Termination 1
(TA/NT1s) for ISDN services.
 Communication servers concentrate dial-in
and dial-out user communication.

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WAN Protocols
 WAN data link protocols describe how
frames are carried between systems on a
single data link
 Protocols are designed to operate
over dedicated point-to-point,
multipoint, and multi-access switched
services such as Frame Relay

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Routers
 Router has the following components:
 CPU
 Memory
 System Bus
 Input/Output Interfaces
 Routers connect and allow communication
between two networks and determine the best
path for data to travel through the connected
networks
 Routers has Internetwork Operating System
software (IOS) to run configuration files
 Configuration files contain the instructions and
parameters that control the flow of traffic in and
out of the routers

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Routers
 The main internal components of the
router are:
 Random access memory (RAM)
 Nonvolatile random-access memory
(NVRAM)
 Flash memory
 Read-only memory (ROM)
 Interfaces

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Routers
 RAM, also called dynamic RAM (DRAM)
 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

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Routers
 NVRAM
 Provides storage for the startup
configuration file
 Retains content when router is powered
down or restarted

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Routers
 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)

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Routers
 Read-only memory (ROM)
 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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Routers
 Interfaces
 Connect router to network for frame
entry and exit
 Can be on the motherboard or on a
separate module
 Connect the router to LANs and WANs

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Routers
 Routers can be used to segment
LANs, but they are mainly used as
WAN devices

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Routers
 Routers have both LAN and WAN
interfaces
 The two main functions of a router
 Selection of best path
 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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Routers
 A correctly configured internetwork
provides the following:
 Consistent end-to-end addressing
 Addresses that represent network
topologies
 Best path selection
 Dynamic or static routing
 Switching

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WANs and the OSI Model
 A WAN operates at the physical layer and at
the data link layer
 The WAN physical layer describes the
interface between the data terminal
equipment (DTE) and the data circuit-
terminating equipment (DCE)
 DCE connects to the service provider (eg. Via
modem)
 DTE (router), the services offered to the DTE
are made available through a modem or a
CSU/DSU

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Routers
 The main function of a router is to transmit
data using Layer 3 addresses
 This process is also called routing. Routing
occurs at the network layer, which is
Layer 3
 If a WAN operates at Layers 1, 2, and 3, is a
router a LAN device or a WAN device?
 The answer is both, as is so often the case in the
field of networking. A router may be exclusively a
LAN device, it may be exclusively a WAN device,
or it may sit at the boundary between a LAN and
a WAN and be a LAN and WAN device at the same
time.

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Routers
 One of the roles of a router in a WAN
is to route packets at Layer 3, but this
is also a role of a router in a LAN
 Therefore routing is not strictly a WAN
role of a router
 When a router uses the physical and data
link layer standards and protocols that
are associated with WANs, it is operating
as a WAN device

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Routers
 Therefore, the main role of a router in a
WAN is not to route, it is to provide
connections between the various WAN
physical and data-link standards
 These standards and protocols that define
and structure a WAN connection operate at
Layers 1 and 2
 The router must be able to move a stream
of bits from one type of service, such as
ISDN, to another, such as a T1, and change
the data link encapsulation from PPP to
Frame Relay

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Routers in WAN
 WAN physical layer standards and protocols:
 EIA/TIA-232
 EIA/TIA-449
 V.24
 V.35
 X.21
 G.703
 EIA-530
 ISDN
 T1, T3, E1, and E3
 xDSL
 SONET (OC-3, OC-12, OC-48, OC-192)

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Routers in WAN
 WAN data link layer standards and protocols:
 High-level data link control (HDLC)
 Frame Relay
 Point-to-Point Protocol (PPP)
 Synchronous Data Link Control (SDLC)
 Serial Line Internet Protocol (SLIP)
 X.25
 ATM
 LAPB
 LAPD
 LAPF

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Labs
 In the lab, all the networks will be connected
with serial or Ethernet cables and the
students can see and physically touch all the
equipment
 In the real world serial cables are not
connected back to back
 In the lab, devices that make up the WAN
cloud are simulated by the connection
between the back-to-back DTE-DCE cables;
the connection from one router interface s0/0
to another router interface s0/1 simulates the
whole circuit cloud

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Router Internal Components
 CPU
 RAM
 Flash
 NVRAM
 Busses
 ROM
 Input/Output Interfaces
 Power Supply

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 CPU
 system initialization
 routing functions
 network interface control
 RAM
 used for routing table information
 fast switching cache
 running configuration
 packet queues
 run time space for executable Cisco IOS
 Upgraded by adding DIMMs

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 Flash
 stores a full Cisco IOS software image
 images can be upgraded by loading a new
image into flash
 adding or replacing the flash Single In-Line
Memory Modules (SIMMs) or PCMCIA cards
can upgrade the amount of flash
 NVRAM
 store the startup configuration
 devices retain contents when power is removed

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 Buses
 System bus is used for communication
between the CPU and the interfaces and/or
expansion slots, transfers the packets to and
from the interfaces
 The CPU bus is used by the CPU for
accessing components from router storage,
transfers instructions and data to or from
specified memory addresses

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 ROM
 Read-only memory (ROM) is used for
permanently storing startup diagnostic code
(ROM Monitor)
 ROM runs hardware diagnostics during router
bootup and loading the Cisco IOS software
from flash to RAM
 They can only be upgraded by replacing the
ROM chips in the sockets

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 Interfaces
 local-area network (LANs) – Ethernet, token
ring
 Wide-area network (WANs) - serial, ISDN,
and integrated Channel Service Unit (CSUs)
 The WAN interfaces may be a fixed
configuration or modular
 Console/AUX - serial ports used primarily for
the initial configuration of the router

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 Power Supply
 The power supply provides the necessary
power to operate the internal components

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Router Physical Characteristics

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Router Physical Characteristics
*

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Router External Connections
 LAN interfaces allow the router to connect to
the Local Area Network media
 Wide Area Network (WAN) connections
provide connections through a service
provider to a distant site or to the Internet
 The management port (Console and Auxiliary)
provides a text-based connection for the
configuration and troubleshooting of the
router
 EIA-232 asynchronous serial ports
 Connected to a communications port on a computer
 Computer must run a terminal emulation program

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Management Ports
 The console port and the auxiliary (AUX)
port are management ports
asynchronous serial ports
non-network connections
console port is recommended for this
initial configuration
 Management ports used for
configuring the router
monitoring the system
troubleshooting problems

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Management Ports
 The router can be configured from a
remote location by dialing to a modem
connected to the console or auxiliary
port on the router
 The console port is preferred for
troubleshooting because
 It does not depend on networks services
 It displays router startup, debugging, and
error messages by default
 The console port can be used for disaster
and password recovery procedure

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Connecting Console Interfaces
 To connect to the console port
 a rollover cable
 RJ-45 to DB-9 adapter
 HyperTerminal

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Connecting Console Interfaces
 Configure terminal emulation software on the
PC for:
 The appropriate com port
 9600 baud
 8 data bits
 No parity
 1 stop bit
 No flow control
 Connect the RJ-45 connector of the rollover
cable to the router console port
 Connect the other end of the rollover cable to
the RJ-45 to DB-9 adapter
 Attach the female DB-9 adapter to a PC

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Hyperterminal
COM Port
9600 Baud
8 Data Bits
No Parity
1 Stop Bit
No flow
control

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Connecting LAN Interfaces
 Router is connected to the LAN using
an Ethernet or Fast Ethernet interface
 The router communicates with the LAN
via a hub or a switch using a Straight-
through cable
 When Ethernet connection of the router
is connected directly to the computer
or to another router a crossover cable
is required

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Connecting WAN Interfaces
 WAN connection types are leased line, circuit-
switched, and packet-switched
 For each type of WAN service, the customer
premises equipment (CPE), often a router,
is the data terminal equipment (DTE)
 Service provider uses a data circuit-
terminating equipment (DCE) device,
commonly a modem or channel service
unit/data service unit (CSU/DSU), which
converts the data from the DTE into a form
acceptable to the WAN service provider

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Connecting WAN Interfaces
 Selecting the proper serial cable:
 What is the type of connection to the Cisco
device?
 Is the network system being connected to
a DTE or DCE device?
 What signaling standard does the device
require?
 What is the gender of the connector
required on the cable? If the connector
has visible projecting pins, it is male. If the
connector has sockets for projecting pins, it
is female

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Router Serial WAN Connectors

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