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, , 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