Term
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Definition
Tell Java which names you plan to use and what types of value or object can be associated with each name
1. Instance variable declaration
2. Local variable declarations
3 Formal parameter declarations |
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| Ex of Instance Variable declaration |
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Definition
| private Netconnection toServer; |
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| Ex of Local Variable declaration |
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| Ex of parameter declaration |
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the JButton which in
public void buttonClicked(JButton which) { |
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Tell Java to perfrom a particular action, commands
1. mutator method invocations
2. assignments
3. Compound statements
4. if statements |
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| Ex of mutator method invocations |
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Definition
| contentPane.add(aButton); (change objects states) |
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| toServer = new NetConnection(...); |
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if(condition) {
statement
}else if{
statement |
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Describes variables or objects. They appear on the right hand side of assignments or as actual parameters in invocations and constructions
1. constructions
2. accessor method invocations
3. literals
4. variable names
5. formulas |
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| new JButton("Click Here"); |
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| Ex of accessor method invocations |
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Definition
hostName.getText(); toServer.in.nextLine(); Accessor methods access information about a the state of an object |
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"cortland.cs.williams.edu"
300 |
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"USER" + id.getText()
WINDOW_WIDTH/2 |
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| Having digits, Expressed in digits, using or giving a reading in digits |
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| one unit signal that is not part of message but signals when it begins |
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| Ethernet time variables (R,D,L,T,c,W,Q,M |
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Definition
R = the rate at which bits are transmitted (measured in bits per second. This is what the Ethernet paper calls C)
D = number of data bits in each entry
L = the maximum allowed length of a network (measured in meters)
c = the speed at which signals propagate on network cables (measured in meters/second --- close to the speed of light)
W = the expected number of slots of contention before a successful transmission
Q = the number of active stations attached to the network
M = the minimum allowable packet size (measured in bits) |
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| variable to measure true/false |
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| D/R (amount it takes to get the entire message on the wire) |
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| L/C (amount it takes for a bit of that message to travel down the wire) |
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| Get a substring for tom in addr1 which is tom@cortland.edu |
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| what indexOf will spit out if addr1 which is tom@cortland.edu addr1.indexOf( d, 12); |
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| Common structure of while loops |
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Definition
1. Initialize (buttonDisplayed =1)
2. Condition
3. Does the work of the loop
4. Increment step - makes sure condition becomes false so loop doesn't run forever |
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| Worst Case amount of time you have to wait to detect a collision |
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| any collection is a thing (or empty) that is that thing plus everything else in the collection next to it |
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| number of bits in ASCII code |
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| 16 (65536 = 2^16 possible symbols - used for all the world's alphabet |
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| no codeword used in the scheme appears as a prefix of any other codeword. Guaranteed to produce coded messages that are uniquely decodable |
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Definition
Replace the two least used symbols with a new symbol:
• Represent the new symbol as pair composed of
symbols it replaces
• Assume new symbol occurs as often as the symbols it
replaces
• REPEAT UNTIL THERE IS ONLY ONE SYMBOL LEFT! |
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| Sender and Sendee agree to a certain amount of time that a signal for that amount of time is one bit of information |
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| informs the computer that the text that follows describes a new class (ex:public class TouchyButton extends GUIManager |
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| specifies the actions to be performed when this program is first started ex:public TouchyButton(){ |
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| named sequence of program instruction Ex: public void buttonClicked() { |
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| branching broadcast communication system for carrying digital data among locally distributed computing stations |
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| Time division multiplexing |
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| refers to taking turns when two computers try to use a network at the same time |
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| self-synchronizing transmission system |
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Definition
| based on the contents of the message sender and receiver can figure out the message without precise time measurements |
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| carrier sense multiple access with collision detection (CSMA/CD) |
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Definition
Transmissions initiated by a station defer to any which may already be in progress. Once started, if interference with other packets is detected, a
transmission is aborted and rescheduled by its source station. After a certain period of interference-free transmission,a packet is heard by all stations and will run to completion without interference. Ethernet controllers in colliding stations each generate random retransmission intervals to avoid repeated collisions. The mean of a packet's retransmission intervals is adjusted as a function of collision history to keep Ether utilization near
the optimum with changing network load. |
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Definition
| Each packet has a source and destination, both of which are identified in the packet's header. A packet placed on the Ether eventually propagates to all stations. Any station can copy a packet from the Ether into its local memory, but normally only an active destination station matching its address in the packet's header will do so as the packet passes. |
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| packet with address 0 that will go to everyone |
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A = (1-(l/Q))^(Q-l) where Q is the # of computers with a message to transmit. Comes from the equation N/Q*(1-(1/Q))^(N-1) with assumption N=Q where N = The total number of computers
that are trying to send |
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| w = (1 - A)/A where A is probability exactly one computer attempts a transmission in a given slot |
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| E = (P/C)/((P/C) + (W*T)) where W is the average number of times it takes to succeed in sending and T is the delay that one collision causes |
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| Preamble: 8 bytes Destination address: 6 bytes Source Address: 6 bytes Length 2 bytes Data: Min 46 Checksum: 4bytes |
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| data in transmission is based only on whether a signal is or is not being sent regardless of any underlying signal frequency; ethernet uses this |
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| different frequencies are used to encode different signals |
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| computers do not transmit when the computer is aware of a signal on the cable |
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| while a computer is transmitting it continues to listen to the message. If it changes to sound like a different signal than the one it was supposed to transmit it will detect a collision and stop transmitting |
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| after carrier sense detects there is a something being transmitted it will continue to sense the cable until it detects the entire packet has been sent. Then it begins to send its own packet. |
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| once a computer senses a collusion it sends a jamming signal then stops transmitting until system is idle then it picks a "random" wait time and will repeat if necessary until the messages get through |
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| high delay good line sharing |
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| low delay reserved lines waste capacity |
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| medium delay and line sharing better error check |
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| optimal fiber network that connects computers in a circle which takes turns in order |
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| Computers take IP and puts it in correct protocol which when it arrives gets translated back into IP |
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| takes message from server and then adds it to cache and fetches it recursively |
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| if(the packet is for this comp) {deliver to the correct application} else if(the destination is on one of my networks) { send packet to destination } else { send packet to a good router} |
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| the first three bytes are for network address the next three you make up |
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| computer that is part of two or more distinct networks and is configured to relay messages between networks to which it is connected |
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| Frame format for wireless network |
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Definition
Control/16/Duration/16/DestinationAdd1
/48/SourceAdd1/48/DestinationAdd2/48
/SequenceControl/48/SourceAdd2/48/
Data/2312/Checksum/32/ Wireless frame also has a preamble but it goes in a few different places...longer than ethernet preamble |
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| Control and duration field wireless packets |
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Definition
| help the process wireless networks use to approximate carrier sense |
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| Control field in wireless packets |
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Definition
| used to distinguish special RTS and CTS packets from data packets |
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| Duration field in wireless packet |
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| used to hold transition duration info essential to the process of virtual carrier sense |
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| purpose of Internet Protocl |
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Definition
| serves as an intermediate language used to simplify the construction of software required to translate between other protocols |
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| translation after/for receiving packet |
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| In hardware, there will be wireless and Ethernet transmission/wireless then there will be software that translate both forms to IP and then can untranslate IP into the other format |
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| How IP can simplify the task of constructing client programs |
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Definition
| our program will send and receive all of its messages in IP to the software that translates it into either Ethernet or wireless |
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Definition
| program associated with the top-most window on your screen |
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| How information is displayed on your computer |
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Definition
input comes in from the keyboard or network messages and the operating system decides what application program the information should be sent to
then the application program sends what they what displayed to the operating systems display software which will display it on the screen |
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| Where all incoming messages are translated to IP |
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| operating system before being sent out to application programs |
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| the illusion that all the networks connected by routers form a single network |
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| independent networks that make up the virtual network |
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Goes in data field of Ethernet or wireless packet
IP version/4/Hdr len/4/Service class/8/
Packet Length/16/Packet Number/16/ FragmentNumber/16/TTL/8/Protocol/8/
Error Check/16/From Addr/32/To Addr/32/
DATA (up to 65516 bytes) |
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Definition
| packet # and fragment # are used to enable the receiving comp to identify and reassemble the fragments of a single message |
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| putting one packet inside the data field of another packet of a different format |
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| physical network standards |
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Definition
| 802.3 Ethernaet, 802.11 wireless |
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Definition
| groups of 4 binary digits are replaced by a single hexadecimal equivalent |
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| how 802.xx address are assigned |
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Definition
| first 24 bits of an address notates a manufacturer next 24 bits are chosen so they do not overlap with any other next 24 bits that the manufacturer has made |
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| Ethernet Broadcast address |
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| convert to dotted decimal notation |
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| take an IP address and break the sequence of binary digits that form the address into four 8 bit subsequences then translate them to decimal notation and put periods in between |
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| first 16 bits (6 digits) are associated with a physical network operated by my Internet service provider |
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| How classes open up new IP address |
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| Three classes for size of network...machines on smaller networks will have no network prefix while machines on bigger networks will have network prefix |
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| maintains a database listing the names and IP addresses of many machines and the addresses of servers that can be used to look up other names |
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| collection of saved IP addresses that correspond to domain name servers |
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| Dynamic Host Configuration Protocol. DHCP server must be installed in each physical network. Tells computers their IP address, the IP address of a good router and IP address of at least one DNS |
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Definition
| when machine is first connected to the internet they will send a broadcast packet out to every machine in the network. All the machines will ignore it except for the DHCP server which will send back the information |
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| if it is important to limit access to authorized users than a list of hardware addresses and IP addresses can be set up so that a when the DHCP server recieves a hardware address they just look at the list. If you don't have to limit access the server can just assign any number not in use. To ensure this number is not in use it put it in a list for a time limit called lease. Once the lease is up, the server sends a message to the machine saying that it must renew its IP address. When the machine leaves the network, once the lease is up the number will be usable once again |
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| How to fill out Ethernet source address |
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Definition
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| How to fill out ethernet destination address |
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Definition
| ARP - will place IP address in a broadcast packet...if machine is that IP address than they will send back a packet with their Ethernet address |
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| list of recently used Ethernet address and their corresponding IP addresses |
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| every entry in the table contains network prefix and the address of the best router to use as the first step to get to that network |
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| 1. Mark starting point as KNOWN with length 0 2. Identify eacn neighbor of start as ADJACENT 3. Set first step of each neighbor to itself 4. Set route length of each neighbor to first step distance 5. While you don't know how to reach all the cities {6. Select adj city with shortest route 7. Identify adj city with shortest route as KNOWN 8. Mark neighbors of new KNOWN city that were DISTANT as ADJACENT 9. update path lengths and record first steps to ADJACENT neighbors of new KNOWN city} |
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| periodic messages from every other machine in the network about hwo long it takes for info to travel to all destinations connected to the sender that would provide the necessary complete description of the network |
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| Important Internet routing protocol with the basis of Dijkstra's algorithm |
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| Transport Control Protocol- a general purpose transport protocol |
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| Connection orientation, point to point communication, complete reliability, Full duplex communication, stream interface, reliable connection startup and graceful connection close |
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| protocol that provides a connection from one application on one computer to another application on another computer |
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| Each TCP packet is encapsulated in a IP packet which sends it to another computer and the TCP packet gets delivered to the application |
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| when TCP receives data it sends an acknowledgment back to the sender. Whenever it sends data TCP starts a timer. If the timer expires before an acknowledgment arrives the sender retransmits the data |
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| TCP monitors current delay on each connection and adapts the retransmission timer to accommodates changing transmissions |
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| TCP uses this to control flow of data. When a connection is established each end of the connection allocates a buffer to hold incoming data. acks also send back the remaining buffer size...if buffer size equals 0 than the receiver will receive a zero window and must stop sending data |
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| describes messages in in three way handshake used to create a connection |
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| describes messages in three way handshake used to close a connection |
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| used to establish or end connections where host 1 will send FIN + ACK to host 2 who will send FIN+ACK back to host 1 who will send an ACK to host 2 if creating a connection a random 32 bit sequence is generated |
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| Network Address Translation |
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| a router like a home router takes from IP addresses and replaces them with its own IP address than it puts those values in a chart with inside/outside IP address and Port number |
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| 3d matching problem, partition problem |
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