The Workings of the Internet

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30 Οκτ 2013 (πριν από 3 χρόνια και 11 μήνες)

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The Workings
of the Internet

CECS 5030

with Cathie Norris,

Jennifer Smolka & Gerald Knezek

Overview


Layered Organization


Topologies


Network Transports


Access Methods


Routing


ISO/OSI Model


Developed by International Organization
for Standardization in 1974


Consists of seven layers


Each with unique function


Each hands off functions to adjacent layer


Modules (layers) may be replaced with
another of equal functionality (Xerox vs.
Novell, for example)

OSI Model Layers

Physical

Data Link

Network

Transport

Session

Presentation

Application

Transmission of binary signal

Transfer of units of information,
framing, and error checking

Delivery of packets of information,
which includes routing

Provision for end
-
to
-
end reliable
and unreliable delivery

Establishment and maintenance
of sessions

Data formatting and encryption

Network applications such as file
transfer and terminal emulation

OSI Layer

Function Provided

Network Topologies


Architectural “drawings” that show the
overall physical configuration for a given
communications system


Determine access methods and rules used
to design and implement a communication
system


Represent the drawing of your network
cable plant


Three main types: star, ring, and bus

Network Topologies


Linear Bus
-

Ethernet/IEEE 802.3
10Base2 and 10Base5


Star Wired Bus
-

Ethernet/IEEE 802.3i
10BaseT


Star Wired Ring
-

Token Ring/IEEE
802.5


Dual Counter Rotating Ring
-

FDDI/ANSI X3T9.5


Wireless
-

Product Specific

Star Topology


First used with the telephone switches


Centralized hub with all stations connected


No single point of failure effects the whole
network, except the hub


Oldest and most popular topology


Better network management

Central Hub

Node

Node

Node

Node

Ring Topology


All stations (repeaters) are enclosed in a
loop


Each receives the signal and repeats it on
the other side to its “downstream” neighbor


Data is transmitted in one direction only


Single point of failure when one station
quits repeating


Management processes invoked that
dynamically remove a station allowing the
ring to return to an operational state

Ring Topology

Node

Node

Node

Node

Data Direction

Receiver

Transmitter

Repeater

Bus Topology


Also known as linear bus


Uses a single length of cable with all
stations attached to it


The network is terminated at its endpoints
(not a closed loop)


A break on the single cable will bring
down all attachments on the network


The bus topology is most commonly used
for Ethernet networks

Bus Topology

Node

Node

Node

Star
-
Wired Bus Topology


Each node is attached to
hub


When one node fails, it
doesn’t affect the other
nodes


The hub is a single point
of failure for all nodes


Hub failure causes all
nodes to lose connectivity

Node

Node

Node

Node

Node

Node

Concentrator
Hub

Physical Media


Physical media provide the connections
between network devices that make
networking possible


There are four main types of physical
media in widespread use today:


Coaxial Cable


Twisted Pair


Fiber Optic Cable


Wireless Media

Thick Coaxial Cable


Used in the first Ethernet networks


Type RG
-
11 / 10Base5


Usually orange/black


Thickness of a small garden hose


Very expensive and heavy cable


Two strands along the axis


Conductor down the center


Insulator surrounds conductor


Shielded mesh serves as outside

Thin Coaxial Cable


Alternative to Thick Ethernet Cable


Type RG
-
58 / 10Base2 / “Cheapnet”


Usually black


Thickness of a pencil


More flexible than thick Ethernet


Reduced the cost of the cabling


Flexible

Twisted Pair Cable


Phone Systems



Twisted Pair Cable consists of two copper
wires, usually twisted around each other
to cancel out any noise in the circuit



Two main type of Twisted Pair Cabling


Shielded Twisted Pair (STP)


Unshielded Twisted Pair (UTP)

Shielded Twisted Pair (STP)


Shielded twisted pair is the original
media used for token ring networks




STP can be used for high
-
speed
networks, such as FDDI or ATM, where
shielding is important

Unshielded Twisted Pair
(UTP)


Most commonly used twisted pair cable


Uses common telephone wire


UTP was standardized by the IEEE 802.3
committee in October of 1990


UTP for LANs is now classified as:


Category 3
-

used for LANs up to 10 Mbps


Category 4
-

used for LANs up to 16 Mbps


Category 5
-

used for LANs up to 100 Mbps


Fiber Optic Cable


Uses light signals transmitted over a
very thin filament, usually made of glass



Advantage over other types of media


security against eavesdropping


immunity to interference


maximum length of a single
segment



Most expensive of all media

Wireless Media


Connect your computer to your cell
phone?



Problems with stability of connection



Have wireless for a long time



Commercial Satellite


Geostationary Orbit


Microwave Wavelength


Expensive

Wireless Media


A number of wireless media are used in
internetworking, e.g.:



Microwave



Commercial Radio wave



Infrared signaling (Palm Synching)


Concentrators/Hubs


Hubs allow multiple users to be connected
to a single network as a shared device



The more users on a hub the slower the
response time


Network Transports


Ethernet / Fast Ethernet / IEEE 802.3



Token Ring / IEEE 802.5



FDDI / FDDI/ANSI X3T9.5



Wireless/IEEE 802.11

Ethernet Cable Names

How Ethernet Works



Sent the message and listens for a
response



An access method based on the Carrier
Sense Multiple Access with Collision
Detection (CSMA/CD) algorithm



Cooperative effort between Digital, Intel,
and Xerox produced Ethernet version 1.0
in 1980

How Ethernet Works



Ethernet was adopted with modifications
by the standards committees IEEE 802.3
and ANSI 8802/3



Most widely used network system today


Normal Ethernet Operation

Data

Address mismatch

packet discarded

Address mismatch

packet discarded

Address match

packet processed

Send data

to node D

Transmitted packet seen

by all stations on the LAN

(broadcast medium)

A

C

B

D

Final Ethernet Issues


Ethernet is an access method that
strictly adheres to the CSMA/CD
algorithm



Ethernet is a multiprotocol solution



Ethernet is usually hardware (firmware),
not software

How Token Ring Works


Token Ring controls which PC can send
messages by passing a token from
station to station around the ring



When a PC wants to transmit it will
replace the token with a “frame”
(message)



The frame is passed from PC to PC until
it reaches its destination

How Token Ring Works


The destination PC makes a copy of the
“frame” (message) and marks the frame
to indicate that it got the message



The frame circulates around the
network until it gets back to the sender



The sender, seeing that the message
has been received, replaces it with a
new token

Wide Area Network (WAN)
Topologies


Dedicated Circuits


56Kb


T
-
1


DS
-
3



Frame
-
Relay


56Kb to T
-
1 speeds



Integrated Services Digital Network (ISDN)

Inter
-
networking


Networks have their restrictions



Thick coaxial cable maximum length is
500 meters



LANs are broadcast
-
oriented



Proper network design is impossible
using repeaters

Inter
-
networking


Properly extending the LAN requires
special devices known as bridges and
routers



A LAN that uses bridges is called an
extended LAN



A LAN that uses routers is called an
internet or inter
-
network



A gateway between dissimilar
networks

Inter
-
networking


Bridges and routers are data
-
forwarding
devices that forward packets to one or
more LANs



They allow for more efficient
networks to be designed

Inter
-
networking Categories

Physical

Data Link

Network

Transport

Session

Presentation

Application

Repeaters

Bridges

Routers

Gateways

Repeaters


Extend the network by interconnecting
multiple segments


Have transformed into wiring
concentrators (hubs)


Low cost


Can be used to interconnect different
wiring types but not different access
methods


e.g. Coax to twisted pair

Bridge Designs


Cascaded


Locates on bridge next to another in a
pillar fashion


Backbone


For networks with many LANs


Backbone cable is run vertically in
building’s riser


LAN “ribs” run on each floor


Star


Used in wide area networks or remote
bridged networks


Cascaded

Cable segment 1

Cable segment 2

Cable segment 3

Terminal Server

Terminal

Workstation

File Server

Host

Backbone


Fiber

backbone

Floor 1

Floor 20

Terminal

Workstation

Host

Workstation

Star

California

Virginia

North Carolina

Texas

Serial line

Serial line

Serial line

Introduction to Routers


Routers are data forwarding devices but operate
differently than a bridge


Routers separate networks into regions.


Each region is assigned a unique network number


These network numbers are unique for each network
they are assigned to


Packet forwarding is based on these network Ids


Routers route packets based on a protocol as well as
a network ID


Most routers today are multiprotocol in that one box
can forward different protocol packets


Routers, like bridges, can be used locally or remotely


Routing


Most network protocols were designed with network
-
layer
routing


Routers base forwarding decisions on an embedded
network number in the network layer header of the packet


Network numbers can be thought of as area codes in the
phone system


Must use the area code to call different areas


Any number of end stations may be assigned to one
network number


Most routers do not keep track of individual end
stations’ addresses


Network numbers group network stations into one or more
network numbers


Taken as a whole, routers combine networks and form
internets

Routers
-

Operation

Network 1

Network 2

B

C

Destination network address is local

transmit packet directly to the end station

Destination

network

number

is different

Find router

and give packet

to the router

Router sends

packet directly

to the end station

MAC address

for the router

Router Z

Node P

Node A

Node D

Routing Diagram

Network 1

Network 2

Network 3

Network 4

A

B

C

D

E

F

G

H

MAC Addresses

Router Z

Router Y

Router X

Multiprotocol Routers


LANs currently operate with many different types of
protocols


Apple Computers can use AppleTalk


UNIX workstations use TCP/IP


Client/Server applications could use Novell
NetWare


To require one router for each protocol on the LAN is
not efficient


Multiprotocol routers were invented to handle this


Arrived around 1986


Routes not only based on the network IDs but are
able to pass the packet to the correct protocol
processor by examining the Type of packet


Gateways


Complex devices that provide for a
protocol translation during data
forwarding


Examples are:


TCP/IP to SNA


asynchronous to synchronous serial
stream


Gateways differ from bridges and routers


Perform protocol translation of the
incoming packet to match the
outgoing stream

References


From Networking 101

Jim Cabral, Puget Technology Group, Inc. &

Tammy Ruth, Children’s Hospital and Medical Center


cabralje@pugettech.com

truth@chmc.org


www.pugettech.com