WANs and Router Basics

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WANs and Router Basics

Semester 2

Chapter 2: WANs & Routers


Table of Contents


WAN Devices


WAN Standards


WAN Technologies


Router Basics


Router User Interface

WAN Devices


WAN Routers


WAN Switches


WAN Servers


Modems and other connection devices

Table of Contents

WAN Services


WANs provide for the exchange of data
packets/frames between the LANs they support.


A WAN interconnects LANs that are usually
separated by large geographic areas.


WANs often move traffic at lower than LAN
speeds.


WAN devices include …

Routers


Routers maintain their role as “traffic cops”


Routers can operate as...


Internal Routers


Backbone Routers


Area Border Routers


Autonomous System Boundary Routers


WAN Switches


Service provider equipment that connects to
WAN bandwidth for voice, data and video
communications. They function much like a LAN
switch but carrying larger amounts of traffic and
usually a specific WAN technology.

Modems and other connection
devices


Sometimes just special ports on a router, special
configurations on a router, sometime separate
devices like modems.


Interface the existing LAN technology with the
WAN technology they are connected to. These
devices are specific to each technology.


WAN Servers


Concentrates dial
-
in and dial
-
out services.


Equipment is usually at the service provider’s
site.

WAN Standards

Table of Contents

WAN Standards


What layers of the OSI model do WAN standards
describe?


Physical and Data Link Layers

WAN Physical Layer


Protocols that describe how to provide electrical,
mechanical, operational, and functional
connections for WAN services.


These services are most often obtained from
WAN service providers such as telephone
companies, cable companies, and dedicated fiber
sellers.

WAN Physical Layer


Several physical layer standards specifying this
interface between the ISP and your router are...


EIA/TIA
-
232


EIA/TIA
-
449


V.24


V.35


X.21


G.703


EIA
-
530

WAN Data
-
Link Layer


WAN data link protocols describe how frames are
carried between systems on a single data link.


They include protocols designed to operate over
all physical layer standards.



Most common Layer 2 WAN Technologies
include:

WAN Data
-
Link Encapsulations


High
-
Level Data Link Control (HDLC)


Cisco default encapsulation; typically used between
routers running Cisco IOS


Streamlined: not a lot of overhead


Frame Relay


uses high
-
quality digital facilities;


uses simplified framing with no error correction
mechanisms (connectionless!!);


New; Becoming more and more popular


WAN Data
-
Link Encapsulations


PPP (Point
-
to
-
Point Protocol)


A little slower


Can check for link quality and allows password
authentication at Layer 2


Not proprietary so used more often than HDLC for
less expensive WAN connections.

WAN Technologies

The following overview of WAN
categories uses some of the physical and
data link layer standards we talked about.

Table of Contents

WAN Technologies Overview

Dedicated


T1, E1, T3, E3


xDSL


SONET

Analog


Dial
-
up modems


Cable modems


Wireless

Switched

Circuit
Switched



POTS



ISDN

Packet
Switched



X.25



Frame


Relay

Cell
Switched



ATM



SMDS

WAN Technologies Overview

Dedicated


T1, E1, T3, E3


xDSL


SONET

Analog


Dial
-
up modems


Cable modems


Wireless

Switched

Circuit
Switched



POTS



ISDN

Packet
Switched



X.25



Frame


Relay

Cell
Switched



ATM



SMDS

Dedicated Digital Services


T series

in U.S. and
E series

in Europe


Uses time division multiplexing to “slice up” data and
assign time slots for transmissions


T1 = 1.544 Mbps


T3 = 44.736 Mbps


E1 = 2.048 Mbps


E3 = 34.368 Mbps


Uses twisted pair & fiber


Extremely popular


Moderate cost

Dedicated Digital Services provide full
-
time
connectivity through a point
-
to
-
point link

Dedicated Digital Services


Digital Subscriber Lines (xDSL)
;

the x stands
for a family of technologies


New WAN Technology for home use; decreasing
bandwidth with increasing distance from the phone
companies CO.


Data rates as high as 51.84 Mbps but more common
to be in the 100s of Kbps


Varieties include HDSL, SDSL, ADSL, & VDSL


Moderate expense and getting cheaper

Dedicated Digital Services


Synchronous Optical Network

(SONET)


Specialized high bandwidth technology for use at
various Optical Carrier speeds (OC) ranging from
51.84 Mbps (OC
-
1) to 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.

WAN Technologies Overview

Dedicated


T1, E1, T3, E3


xDSL


SONET

Analog


Dial
-
up modems


Cable modems


Wireless

Switched

Circuit
Switched



POTS



ISDN

Packet
Switched



X.25



Frame


Relay

Cell
Switched



ATM



SMDS

Analog Services


Dial
-
up Modems

(switched analog)


Limited to 56 kbps


Works with existing phone network


Low cost and widespread usage

Analog Services


Cable Modems

(Shared Analog)


Puts data signals on the same cable as television
signals


Increasing in popularity


Maximum bandwidth can be 10 Mbps, though this
degrades as more users attach to a given network
segment (behaving like an unswitched LAN)


Cost is relatively low; usage is small but increasing;
the medium is coaxial cable.

Analog Services


Terrestrial


Bandwidths typically in the
11 Mbps range


Cost is relatively low


Line
-
of
-
sight is usually
required


Usage is moderate


Satellite


Can serve mobile users
and remote users


Usage is widespread


Cost is very high

Wireless

WAN Technologies Overview

Dedicated


T1, E1, T3, E3


xDSL


SONET

Analog


Dial
-
up modems


Cable modems


Wireless

Switched

Circuit
Switched



POTS



ISDN

Packet
Switched



X.25



Frame


Relay

Cell
Switched



ATM



SMDS

Circuit Switched Services


Plain Old Telephone System

(POTS)


Not

a computer data service but...


POTS is an important component of our communication
infrastructure and


It is still the standard for designing reliable networks

Circuit Switched Services


Integrated Services Digital Network

(ISDN)


Historically important
--
first dial
-
up digital service


Cost is moderate; max. bandwidth = 128 kbps for BRI
(Basic Rate Interface)


2 B channels @ 64kps and 1 D channel @ 16kps


B channels are voice/data channels; D for signaling

B

B

D

WAN Technologies Overview

Dedicated


T1, E1, T3, E3


xDSL


SONET

Analog


Dial
-
up modems


Cable modems


Wireless

Switched

Circuit
Switched



POTS



ISDN

Packet
Switched



X.25



Frame


Relay

Cell
Switched



ATM



SMDS



Packet Switched Services


X.25

(Connection
-
oriented)


Older WAN technology developed in 1970s


Reliable
--
X.25 has been extensively debugged and
is now very stable
--
literally no errors in modern X.25
networks


Store & Forward
--
Since X.25 stores the whole frame
to error check it before forwarding it on to the
destination, it has an inherent delay (unlike Frame
Relay) and requires large, expensive memory
buffering capabilities.

Packet Switched Services


Frame Relay

(Connectionless)


More efficient and much faster than X.25


Packet switched version of ISDN (which is circuit
switched); data rates up to 44.736Mbps with 56kbps
and 384kbps being the most popular


Used mostly to forward LAN IP and IPX packets but
can be used to forward other types of traffic


Primary competitive advantage is its low cost

WAN Technologies Overview

Dedicated


T1, E1, T3, E3


xDSL


SONET

Analog


Dial
-
up modems


Cable modems


Wireless

Switched

Circuit
Switched



POTS



ISDN

Packet
Switched



X.25



Frame


Relay

Cell
Switched



ATM



SMDS



Cell Switched Services


Asynchronous Transfer Mode

(ATM)


Relatively new WAN Technology related to
broadband ISDN; max. bandwidth = 622 Mbps


Developed in order to provide one technology for
both WANs and LANs to transport data, video, and
voice. (High Cost)


Key Benefits:


One network for all traffic
--
voice, data, video


Compatible with current wiring infrastructure (cable plant)


Very flexible and scalable


Simplifies network management

Cell Switched Services


Switched Multimegabit Data Service

(SMDS)


Closely related to ATM; SMDS is the MAN
(Metropolitan Area Network) implementation of ATM


High Cost with max. bandwidth 44.736 Mbps


Router Basics

Table of Contents

Internal Components

RAM

NVRAM

Flash

ROM

Interfaces

Console

Auxiliary

RAM


Temporary storage for router configuration files


RAM content is lost on power down or restart


Stores...


Routing tables


ARP cache


Fast switching cache


Packet buffering


And Packet hold queues

NVRAM


Non
-
volatile RAM


Stores backup/startup configuration files


Content is
not

lost when router is powered down
or restarted.

Flash


Holds the Cisco IOS (Internet Operating System)


Allows updating of software without replacing the
Flash chip


Multiple versions of IOS can be stored


Retained on power down


ROM


Contains POST (Power On Self Test)


A bootstrap program (loads the Cisco IOS)


And operating system software


Backup, trimmed down version of the IOS


Upgrades require installing new chip set

Interfaces


Network connections through which packets
enter and exit the router


Attached to the motherboard or as separate
modules.

Router User Interface

Table of Contents

User EXEC Modes


User mode


Limited mode used for checking the routers status,
looking at routing tables, etc.


You
cannot

configure the router


Once you’ve typed the password to enter user mode,
you will see the > prompt. The word “Router” will be
the name of the router.


Password:

Router
>

Means you’re in
user mode

Privileged EXEC Modes


Privileged mode


Does everything User mode does


Full power to configure the router


In user mode, you enter the command “enable” and
then the privileged password


Router> enable

Password:

Router
#



Means you’re in
privileged mode

Command Lists


To get a list of commands available in either user
mode or privileged mode, enter a
?

at the prompt.

Router> ?

Router# ?


Since the available commands will be more than
the screen can hold, you will get the
--
More
--

message at the bottom.


Hitting the
space bar

will advance the screen to
show the next page.


ip

flash:

interfaces

ipx

version

parser

Router# show ?

Getting Help on a Command


The ? can be used with a partial command to learn all
the available commands that match what you entered.


To use this help feature, enter the partial command, then
tap the
space bar
, then type
?


For example...

The Router returned all
the available commands
for “show”

Error Indicator


When you’ve entered an error in the command
string, a carat (
^
) symbol will indicate where the
error occurred.


For example...

Router# show runing
-
config


^

% Invalid input detected at the ‘^’ marker

Labs


We are going to do 2 basic router labs so you can
get a feel for their hardware and software
components. If you go on to the Cisco
Networking Academy, you will work with them
extensively.