Part 7 Chapters 29-31. Client/Server Networks Local Area Network (LAN) –Made up of servers and...
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Transcript of Part 7 Chapters 29-31. Client/Server Networks Local Area Network (LAN) –Made up of servers and...
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