Part 7

Chapters 29-31

Client/Server Networks• Local Area Network (LAN)

– Made up of servers and clients• Servers or ‘hosts’ are computers that perform specific

functions– File servers– Electronic mail servers– Web servers

• Network Operating System– Manages the movement of files and data on a

network by maintaining the rules that govern file transfer, communications, and system operation

• Microsoft NT, 2000• Novell• Unix

Types of Clients• Clients

– Personal computers attached to a server via a LAN

• Fat Client– Computers that run most of the their programs from their

own hard drive and use a minimum of network services

• Thin Client– Computers that run all of their programs and services from a

server• Use their own microprocessor• May have no hard drive at all

• Dumb Terminal– No local computer, no CPU– A monitor and a keyboard used as an interface to a

mainframe computer

Peer to Peer Network

• In a peer to peer network, there is no central server

• Computers talk directly to each other and act as clients and servers to every other node

• Able to share services such as printers, internet connections

• Creates a dynamic gaming environment

Wide Area Network(WAN)

• WANs are groups of smaller LANs• Cover a wider geographical area than LANs• Connected via communication links capable

of fast data transfer– Telephone lines– Satellites– Wireless connections

• Also connected via the internet through virtual private networks (VPNs) that encrypt information to keep others from seeing it

How Networks Connect

• Network Interface Card (NIC)– Usually a PCI card that connects the PC to the

network backbone

• Ethernet– The most common protocol or communication

rules used in LANs• Not a single product

• Transmission Speeds– 10BASE-T, speeds up to 10Mbps– 100BASE-T, speeds up to 100Mbps – also called

Fast Ethernet– Gigabit Ethernet, speeds up to 1,000Mbps

Network Connections and Cabling

• NIC Connections– RJ-45

• Most common• Looks like an oversized telephone connection• Uses twisted copper wire as medium, similar to

phone lines

– Coaxial or BNC• Not as common• Looks like cable TV, same cable and connectors

Network Connections and Cabling

• Twisted Pair Cable– Also called CAT 5

• Name short for ‘Category 5’ wiring schema• Name describes cables, connections, and

connectors

– Capable of 10BASE-T, 100BASE-T and 1000Mbps speeds

– Can sustain a break in the cable without disrupting the entire network

Network Connections and Cabling

• Coaxial Cable Networks– Each terminal in a network connects

through a ‘T’ connector– Creates a ‘daisy chain’ from computer

to computer– Last node must have a terminator– Any break in the cable stops network

from functioning

Ethernet Network Operation

• All nodes on the network are ‘branches’ off a common line

• Each node has a unique address• Each NIC sends and receives

information through a ‘transceiver’– The transceiver broadcasts a message to all

other nodes on the network– The message includes the destination and

source, error checking packets, and the data itself

Ethernet Network Operation

• Each node inspects the addressing info of each message to determine if it is destined for it– Nodes ‘ignore’ messages not addressed to

them

• When a node sees a message with its address, it– Checks it for errors– Sends an acknowledgement to the sender

Ethernet Network Operation

• Network Collisions– Happen when two nodes try to send

information simultaneously– Creates a recognizable pattern of

electrical interference on the cable– The first sender to detect a collision

sends a signal to jam the network so no other nodes can transmit data

Ethernet Network Operation

• Jamming node completes transmission while network is blocked

• Each node waits a random amount of time before re-transmitting

• Process continues until nodes transmit data without collisions

Phone and Power Line LANs

• Networks are cable of running over existing electrical or telephone lines in homes– Data is represented by using on/off pulses

or different frequencies• On-Off pulses used on electrical networks• Different frequencies used on telephone networks

• Phone line networks usually out perform electrical networks

Phone and Power Line LANs

• Limitations– Phones not usually located in every room –

therefore network is limited to rooms where phone lines exist

– Power line networks currently much slower and less common than phone line networks

• Advantages– Phone line networks are faster– Power line networks usually connect to every

room in a house• Can connect to appliances that are network

compatible

The 7 Layer OSI Model

• Open Systems Interconnection reference model

• 7 layers – Application– Presentation – Session– Transport – Network– Data link– Physical

The 7 Layer OSI Model

• The OSI Reference Model describes seven layers of related functions that are needed at each end when a message is sent from one party to another party in a network

• Is the basis for all network communications

The 7 Layer OSI Model

• Application Layer (7)– The only part the user sees– Converts a message’s data into bits and

attaches a hearder identifying the sending and receiving computers

• Presentation Layer (6)– Translates message into a form the receiving

computer can understand– Can compress and encrypt data– Adds a header specifying the language,

compression and encryption methods used

The 7 Layer OSI Model

• Session Layer (5)– Manages the setting up and taking down of

the association between two communicating end points that is called a connection

• Transport Layer (4)– Ensures the reliable arrival of messages and

provides error checking mechanisms and data flow controls

The 7 Layer OSI Model

• Network Layer (3)– Network layer knows the address of the

neighboring nodes in the network, packages output with the correct network address information, selects routes

• Data Link Layer (2)– Supervises the transmission, checks the

checksum, addresses and duplicates the packets, keeps a copy until all packets have been received by the next point in the path

The 7 Layer OSI Model

• Physical Layer (1)– Supports the electrical or mechanical

interface to the physical medium. For example, this layer determines how to put a stream of bits from data link layer on to the pins for a parallel printer interface, an optical fiber

The 7 Layer OSI Model• At the receiving node, the layered process is

reversed – Physical layer receives and converts message into

bits– Data link layer recalculates the checksum, confirms

arrival, logs packets – Network layer recounts packets for security– Transport layer reassembles packets – Session Layer holds message until it is complete– Presentation layer decrypts, expands and translates

message– Application layer identifies recipient, directs data to

the correct application

How Data Travels the Internet

• Data leaves your PC and travels via a communication medium to a Router – Routers connect different networks– Determine the best path to your destination

based on the paths it knows

• Data may travel over telephone lines, microwave, or satellite links to another large network that contains your destination

How Data Travels the Internet

• Data may travel to a Network Access Point to be forwarded to a smaller network– Network Access points are large mainframe

computers that pass data among each other to access smaller networks that are contained within them

• Large supercomputers usually located at Universities around the US

• The original infrastructure of the Internet

How Data Travels the Internet

• Repeaters– Amplify or refresh data along the path

• Bridges link LANs together so that data from one type of network protocol can be sent to a different type of network– From a MS network to a UNIX network and

back

• Gateways– Similar to bridges, translate data between

differing types of networks

How Data Travels the Internet

• When data reaches the destination, packets of data are grouped, error checked, and passed to the recipient as a complete message

Digital Subscriber Lines(DSL)

• Different than dial-up Internet access– A dedicated point to point circuit– Requires a NIC and a DSL modem– Uses the same phone line as your

telephone – simultaneously• Uses different frequencies to transmit

data vs. voice

– More than one type of DSL

Digital Subscriber Lines(DSL)

• Asymmetric DSL or ADSL– More bandwidth or carrying capacity

downstream to your PC and upstream from your PC

– Downstream usually contains richer data – graphics, audio, video

– Upstream usually contains much smaller amounts of data – URLs, email, small files

Digital Subscriber Lines(DSL)

• Access and transmission speeds depend on quality of phone lines and distance from the switching office– VDSL – very high speed DSL

• Downstream speeds up to 10-26Mbps, must be within 4,500 feet from a switch

– ADSL• Downstream up to 6-8Mbps, within 18,000 feet from

switch

• Users of DSL should employ their own firewall to prevent hackers from accessing PCs

How Cable Modems Work

• Computer data sent along the same cables that supply cable TV, but at differing frequencies

• Cable modem users receive all data that is sent from all other users of cable modem– All downloads from all other users

• Couplers/Splitters separate signals to PC and TV respectively

How Cable Modems Work

• Each cable modem acts as the screening device to filter data

• Modems only accept packets that are addressed to it

• Modems reassemble packets and pass them to the NIC in the PC

• Users should employ their own firewall to prevent hackers from accessing PCs

Wireless Phones

• Cellular phones work on a system of overlapping ‘cells’

• Cells are made up by transmitters that cover an area with a signal roughly shaped in a circle

• Multiple transmitters form an overlapping pattern of cells that together form a continuous network of coverage able to be accessed by cell phones and other wireless devices