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43 Cards in this Set
- Front
- Back
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Network Benefits |
Used to share software, hardware and data Resource sharing Communication |
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Network classification |
PAN-personal area network 1m LAN-local area network :room building campus MAN- metropolitan area network :city WAN-wide area network : country planet |
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Network Architecture: layering |
Layers to reduce design complexity. Series of layers called design architecture |
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OSI Model |
Open System Interconnection International standard, 7 layer model Application, Presentation, session, transcript, network, data link, physical |
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TCP/IP Model |
4 layer model. Omits some OSI layers and uses the IP as the network layer. Connection oriented Application, transcript, internet, link |
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IP Protocol |
Connectionless Packets are independently routed Packets can be delivered out of sequence Best effect service |
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Physical Layer |
Sends bits as signals |
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Data Link Layer |
Send frames of info |
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Network Layer |
Sends packets over multiple links |
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Transport |
Provides end to end delivery |
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Protocol |
Rules of communication between peers |
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UTP(Unshielded Twisted Pair) |
Consists of 2 insulated copper wires twisted together to reduce electrical interference Used in phone lines and LANs Ethernet: Cat5, Cat5e, Cat6, Cat6a, Cat7 |
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Coax Cable |
Better shielding and more bandwidth for longer distance than twisted pair Copper core surrounded by insulated material, encased in braided conductor covered in plastic Baseband and broadband |
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Baseband |
For LANs; use digital transmission; 1-2Gbps for 1km |
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Broadband |
For cable tvs. Uses analog transmission. 500 Mbps for up to 100km |
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Fiber Cables |
3 components: Transmission medium — ultra thin fiber of glass Light source — LED or laser diode Photodetector — generates electrical pulse when light falls on it |
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Fiber Advantages |
Fast, long distances with few repeaters, resistant to interference, secure, lightweight, unaffected by power line surges and electromagnetic interference(EMI) |
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Single Mode Fiber |
Small core so that light can’t bounce around and can travel in a straight line Typically used with lasers |
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Multimode Fiber |
Step index and graded index Lowest quality, medium quality |
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Satellite Transmission |
Listen to incoming signal then rebroadcasts it on a different frequency to avoid interference with incoming signal Support data rate 5-10 Mbps Involves propagation delay due to elevation of satellites. More suited for long distance transmissions |
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Connection v Connectionless |
Connection must establish connection before sending data. Connectionless is the opposite |
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Multiplexing |
Combine multiple input sources into one channel |
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FDM |
Analog Frequency division multiplexing: divide entire bandwidth by frequency |
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TDM |
Time division multiplexing Digital divide bandwidth into time slots and use round robin Example: T1(digital) |
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Circuit Switching |
Connection oriented: phone |
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WDM |
Wavelength Division Multiplexing 4 beams combined into shared fiber and split at the end |
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Packet Switching |
Connectionless Greater line utilization greater since packets can share links Calls are never blocked and can prioritize packets |
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Virtual Circuits |
Call request packet Call accept packet Packets follow same route Connection oriented Still shared |
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Datagram |
Packets routed independently Packets can get out of sequence Connectionless Can handle failures better Routing decisions at each node |
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Framing |
Start and end flags with bit stuffing. Allows frames to contain an arbitrary number of bits. |
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Error Control |
Deals with determining that an error has occurred and correcting errors Requires errors to be detected at the receiver Typical retransmit the unacknowledged frames after timer expires on sending side Timer protects against lost acknowledgments |
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Parity Bits |
Appended to the end of each word in the frame. The value of this bit is selected so that the word has an even number of 1s (even parity) or and number of 1s (odd parity) Only 50% success rate |
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Ethernet |
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CSMA/CD |
Carrier sense multiple access with collision detection Mac protocol for bus LANs such as Ethernet Carrier sense: listens to determine if transmission is in progress If line is busy, station waits. Else, transmits Two or more stations may attempt to transmit at the same time— collision If collision, waits random amount of time then attempts to retransmit |
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Ethernet Cabling |
10base5: LAN operates at 10Mbps uses baseband signaling and can support up to 500meters 10base2 10base-T: twisted pair. Central hub. Most popular |
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Ethernet frame Structure |
7 byte preamble Start of frame byte Addresses: MAC addresses and 6bytes each Length: how many bytes are present in data field Data : 0-1500 bytes Pad: used to bad out frame in case less than 46bytes since frame must be at least 64 bytes long |
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Ethernet Performance |
Efficiency decreases as the number of stations trying transmit increases due to the increased probability of collisions 30% line utilization considered heavy load Larger the frame size, higher the efficiency or utilization |
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Round Robin MAC protocol (Token ring) |
Token Bit circulates around the ring Each station forwards the token if it doesn’t have a frame to transmit Station with data to send seizes the token and begins sending its frame for length of time (THT) Each station forward frame Destination notices address and saves a copy as it forwards When frame returns to sender, it drains it firm the ring and reinserts a tokentike
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Token Ring Monitor Station |
Indentured and addresses situations dealing with a lost token and an orphan frame |
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Lost token |
Monitor station knows number of frames on the ring and calcs the max THT. Keeps a timer of time since last token passed. If time is more than max it inserts a new token |
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Orphan frame |
Frame can get orphaned if the sending station goes down before it can drain its frame. As frame passes by monitor it sets the monitor bit in the header. If it sees a frame with its bit already set it knows it is an orphan frame. Monitor then drains the ring and inserts a new token |
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Token Ring Performance |
Under light load where few stations have to send data, performance is fair but is overhead of passing the token Under heavy load where most stations have data to send, performance is excellent and utilization approaches 100%. |
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Stop and Wait |
1. Sender sends a frame 2. Receiver indicates willingness to accept another frame by sending an ack 3. Sender must wait until receive ack before sending next frame 4. Receiver can stop flow by withholding ack Works fine when sent in large frames but inefficient otherwise |
