Module 1: WANs and Routers

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Module 1: WANs and Routers


Clark College Business & Industry
Winter 2004

Steve Raymond

Module 1 Overview

A WAN is a data network that covers or connects LANs across a large geographic area.

It is important to understand the physical layout of a router, including components and WAN/LAN
ports (interfaces).

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

1.1 WANs

1.1.1 Introduction to WANs

WANs can cover cities, states, countries or the globe. WANs usually run over circuits
supplied by telephone companies or other carriers.

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

They use serial connections of various types to access bandwidth over large
geographic areas.

WANs are different than LANs in that they interconnect LANs in different areas. Usually
routers are the devices that exist on each end of the WAN circuit.

WANs operate at layer 1 (physical) and layer 2 (data link) of the OSI model.

1.1 WANs

1.1.1 Introduction to WANs continued

Routers offer many services, including internetworking and WAN interface ports.

Switches in the WAN provide connectivity for voice, data, and video

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 Integrated Services Digital
Network (ISDN) services.

Communication servers concentrate dial
in and dial
out user communication.

WAN Standards agencies:

International Telecommunication Union
Telecommunication Standardization
Sector (ITU
T), formerly the Consultative Committee for International Telegraph and
Telephone (CCITT).

International Organization for Standardization (ISO).

Internet Engineering Task Force (IETF).

Electronic Industries Association (EIA).

1.1 WANs

1.1.1 Introduction to WANs continued

Review of DTE vs.. DCE equipment:

Rule of thumb: DTE devices are usually male type connectors and point towards the
network “cloud”.

1.1 WANs

1.1.2 Introduction to routers in the WAN

A router is just a special purpose computer. It has a CPU, memory, a backplane bus, and
input/output connections to LANs and WANs called “interfaces”.

Routers have operating systems just like PCs. Cisco routers use “Internetwork Operating
System” or “IOS” for short.

Configuration files are the text
based list of instructions which tell a router how to configure

Cisco routers have the following types of memory: RAM, NVRAM, flash memory, ROM
and each memory bank has its own function:

RAM: stores routing tables, ARP cache, packet buffering, router configuration while
powered on, and is lost when router resets or is powered off.

NVRAM: permanent storage of the startup configuration file. Does not get erased
across reboots or power cycles.

Flash: stores the IOS compressed binary image. Can contain multiple versions of IOS,
and provides an EEPROM function where it can be erased and re

ROM: Similar to PC BIOS, contains the POST function, bootstrap code, and can be
replaced by changing chips on the router’s motherboard.

Router interfaces can be either integrated into the router motherboard (2500
series) or
pluggable interface modules (2600

1.1 WANs

1.1.3 Router LANs and WANs

Remember that one purpose of routers is to create additional broadcast domains to reduce
network contention and increase available bandwidth. While routers can segment
LANs into multiple broadcast domains, they are much more frequently used to connect
LANs to WANs.

Routers operate at layer 3 of the OSI model. Routers find the best path through the network
given multiple possibilities and switch the frames through to the outgoing interface.

Routers also maintain tables of the paths through the network and may exchange these tables
with other routers.

A functioning Internetwork provides the following services:

Consistent end
end addressing

Addresses that represent network topologies

Best path selection

Dynamic or static routing


1.1 WANs

1.1.4 Router role in WAN

As said before a WAN usually operates at layers 1 and 2 of the OSI model. But why do
routers play a large part in WANs if they are layer 3 devices? Don’t forget that
although a router’s main job is layer 3 path selection through a network, it still has
layer 1 interfaces to layer 2 networks and can route layer 3 packets across these

WAN physical layers usually describe the cabling and connector types which interface data
terminal equipment DTE user equipment with data
circuit terminating equipment DCE
from the service provider.

Physical (layer 1) WAN standards:









T1, T3, E1, and E3


3, OC
12, OC
48, OC

1.1 WANs

1.1.4 Router role in WAN continued

Data link (layer 2) WAN standards:

level data link control (HDLC)

Frame Relay

Point Protocol (PPP)

Synchronous Data Link Control (SDLC)

Serial Line Internet Protocol (SLIP)






1.1 WANs

1.1.5 Academy approach to hands
on labs

Note again that in our academic scenario, the lab equipment is connected back
back with
serial (DTE to DCE connectors) or Ethernet connections. The purpose for doing so is
the simulate how the routers function when connected to actual carrier circuits (the
network “cloud).

Just be aware that in a production environment customer networks plug into the telephone
company demarcation point, with the telco providing the DCE interface and customer
providing DTE equipment.

1.2 Routers


Router internal components

1.2 Routers


Router internal components continued


The Central Processing Unit (CPU) executes instructions in the operating system.
Among these functions are system initialization, routing functions, and network
interface control. The CPU is a microprocessor. Large routers may have multiple


access memory (RAM) is used for routing table information, fast switching
cache, running configuration, and packet queues. In most routers the RAM provides
run time space for executable Cisco IOS software and its subsystems. RAM is usually
logically divided into main processor memory and shared input/output (I/O) memory.
Shared I/O memory is shared among interfaces for temporary storage of packets. The
contents of RAM are lost when power is removed. RAM is generally dynamic random
access memory (DRAM) and can be upgraded by adding additional Dual In
Memory Modules (DIMMs).


Flash memory is used for storage of a full Cisco IOS software image. The router
normally acquires the default IOS from flash. These images can be upgraded by
loading a new image into flash. The IOS may be in uncompressed or compressed form.
In most routers an executable copy of the IOS is transferred to RAM during the boot
process. In other routers the IOS may be run directly from flash. Adding or replacing
the flash Single In
Line Memory Modules (SIMMs) or PCMCIA cards can upgrade the
amount of flash.

1.2 Routers


Router internal components continued


Nonvolatile random
access memory (NVRAM) is used to store the startup
configuration. In some devices, NVRAM is implemented using separate electronically
erasable programmable read
only memory (EEPROMs) in some devices. In other
devices it is implemented in the same flash device from which the boot code is loaded.
In either case these devices retain contents when power is removed.


Most routers contain a system bus and a CPU bus. The system bus is used for
communication between the CPU and the interfaces and/or expansion slots. This bus
transfers the packets to and from the interfaces.

The CPU bus is used by the CPU for accessing components from router storage. This bus
transfers instructions and data to or from specified memory addresses.


only memory (ROM) is used for permanently storing startup diagnostic code
(ROM Monitor). The main tasks for ROM are hardware diagnostics during router
bootup and loading the Cisco IOS software from flash to RAM. Some routers also have
a scaled down version of the IOS that can be used as an alternative boot source. ROMs
are not erasable. They can only be upgraded by replacing the ROM chips in the

1.2 Routers


Router internal components continued


The interfaces are the router connections to the outside. The three types of
interfaces are local
area network (LANs), wide
area network (WANs), and
Console/AUX. The LAN interfaces are usually one of several different varieties of
Ethernet or Token Ring. These interfaces have controller chips that provide the logic
for connecting the system to the media. The LAN interfaces may be a fixed
configuration or modular.

The WAN interfaces include serial, ISDN, and integrated Channel Service Unit (CSUs). As
with LAN interfaces, WAN interfaces also have special controller chips for the
interfaces. The WAN interfaces may be a fixed configuration or modular.

The Console/AUX ports are serial ports used primarily for the initial configuration of the
router. These ports are not networking ports. They are used for terminal sessions from
the communication ports on the computer or through a modem.

Power Supply

The power supply provides the necessary power to operate the internal
components. Larger routers may use multiple or modular power supplies. In some of
the smaller routers the power supply may be external to the router.

1.2 Routers

1.2.2 Router physical characteristics

1.2 Routers

1.2.?3 Router external connections

This picture of the external rear of a 2600
series router shows at least some of the physical
interfaces that appear on this model:

1.2 Routers

1.2.?4 Management port connections

The management ports are the serial console and auxiliary ports for initially configuring or
troubleshooting a router out
band. The router console port is connected to the serial
port of of a PC or other terminal for local administration. The auxiliary port is
connected to a modem and phone line which can be dialed into by a remote

1.2 Routers

1.2.5 Connecting console interfaces

To connect a PC to a router console, use a terminal program such as Window’s
hyperterminal and the following settings:


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.

Lab Activity

Lab Exercise: Connecting Console Interfaces

This lab is to connect a PC to a router using a console or rollover cable.

1.2 Routers

1.2.6 Connecting LAN interfaces

LAN connectivity is usually via cat5 Ethernet cabling. Other types may be used but
Ethernet is the most common.

Lab Activity

Lab Exercise: Connecting Router LAN Interfaces

This lab is to identify the Ethernet or Fast Ethernet interfaces on the router, and identify and
locate the proper cables to connect the router and PC to a hub or switch.

1.2 Routers

1.2.7 Connecting WAN Interfaces

WAN interfaces can take more diverse forms than LAN interfaces. WAN links generally fall
into these categories:

Lease lines (full and fractional T1, T3, SONET circuits)

Packet switched (frame relay, ATM)

Circuit switched (ISDN, analog modem lines)

Serial connections are the most common connector type. In our labs, the routers usually
have DB
60 type connectors meant for interfacing with an external CSU/DSU. The
2600 routers have WIC cards that contain an integrated CSU/DSU and therefore have
an RJ48 jack meant to plug into a telco circuit such as T1.

1.2 Routers

1.2.7 Connecting WAN Interfaces continued

Lab Activity

Lab Exercise: Connecting WAN Interfaces

This lab is to identify the serial interfaces on the router and identify and locate the proper
cables to interconnect the routers.