Data Communication Flashcards
1
Q
What is serial and parrallel data transfer?
A
- Serial - One bit at a time along a single wire
- Parallel- Simultaneous transmission of multiple bits along multiple wires
2
Q
Parallel vs Serial?
A
Parallel can become out of sync, and cross talk can happen between the wires, is faster, skew can appen, used for short distances. (used in internal busses)
Serial needs less wires, and is easier to amplify the signal due to this, used for long distance
3
Q
What is baud rate?
A
The rate(frequency) at which signals on a wire may change
4
Q
what is bit rate?
A
the number of bits transmitted per second.
(usually baud rate unless more then 2 voltages are used in order to send more bits per signal change)
5
Q
What is bandwidth?
A
the range of frequencies that it may transmit.
6
Q
what is latency?
A
the time delay that can occur between the moment somthing is initiated and the moment its effect begins.
(cased by distance and processing delay)
7
Q
Relaionship between bandwidth and bit rate?
A
Direct
W bps can be acived with 2W Hz
8
Q
What is asyncronus serial data transmission?
A
The arival of the data cannot be predicted by the recivior. A start and stop bit are used to syncronise the transmitter and recivor tempororily.
(the two clocks arent in sync)
9
Q
disadvantages of asyncronus?
A
Extra bits are needed (called overhead)
becomes very out of sync at high speeds.
10
Q
What are the start and stop bits?
A
- Used in asyncronus serial transmission
- They are of different states (eg 0 and 1)
- Start bit cause the recivors clock to start (so its in time with baud rate)
- Stop bit allows recivor to process the recieved bits
- They indicate when data is being transmitted
11
Q
where does the parity bit go in asyncronus packets?
A
before the stop bit
12
Q
What is handshaking?
A
The process of agreeing via an exchange of signals which protocol will be used between the sender and the recivor. Eg speed, parity, startnstop bits.
- Checks that both are ready to recieve
- Tells its sending
- Tells its recieved
- Tells its ready to recive more data
13
Q
What are flow control signals?
A
Happen on alternate wires (or in the main wire) they are signals that happen during transmission. Eg request to send, clear to send.
14
Q
advantages of asyncronus coms
A
- No sync needed meakes it simple
- cheaper - less hardware
- Faster setup - Good for irregular messages eg keyboard
15
Q
sYCRONOUS COMS ADVANTAGE
A
- less overhead
- used more in real time coms
- easier error recovery
16
Q
asyncronus coms disadvantage
A
- large overhead
- complex error handling
17
Q
syncronous disadvantages
A
- hardware is more expensive
- more complex
- servers must be running
18
Q
what does a modem do?
A
Changes the digital signal to an analogue frequency and sends it across analogue link (or the other way around)
19
Q
What kind of signal is used on LAN and WAN
A
Baseband -LAN = lower cost,good at shgort distances
Broadband-WAN, long distance - would be expensive if one one chanell could be used at once
20
Q
what is broadband?
A
Use modulated signals with a carrier wave, many signals can be trasmitted at once on different channels with a different frequency of carrier wave.
21
Q
what is baseband?
A
the signal occupies the entire bandwidth so only 1 signal can happen at once
22
Q
wHAT IS MODULATION
A
Chaninging a carrier signal
23
Q
types of modulation
A
- Amplitude modulation - Ampuitude changes
- Frequency Modulation - Freequency changes
- Phase modulation
24
Q
Why do networking?
A
- Sharing of hardware
- Sharing of software
- Sharing of information
- communication between users
- Easier to instal n update aplication programs by distributing throughout the network
- enables centralised support and maintenance eg backup n virus protection
- enables access control and monitoring
25
Downsides of networking?
* Hardware and software costs
* Slower access to network resourses
* One component failing may affect many users
* people become dependant on the network
26
What is a LAN
a collection of connected computers confined to one site.
27
What is a WAN
a collection of connecdted computers spread across a wide geographical area, and could be used by large organisations with unique coms system.
28
what is internetworking?
connecting networks together
29
what is a stand alone computer?
A NON NETWORKED COMPUTER, NEEDS ITS OWN PERIPHERALS AND SOFTWARE.
30
circuit switching and packet switching?
Circuit- a route throught network mustr be found before coms
Packet- a path isnt needed first
31
What is a bus network?
Single shared bi-deirectinal communication channel, can connect severeal.
32
pros n cons to bus network?
1. Cheaper to cable- less wire
2. easier to constuct and add stations to
1. The backbone breaking will stop coms to many users
2. Sharing of cable can lead to xzturation which degrades proformance
33
What is a star network
Has a central computer (hub), EACH COMPUTER HAS ITS OWN CONNECTION TO THE HUB
(signal gets sent to all lines from the hub)
34
pros to star networking
1. Proforms well under load
2. Cable failure obnly effects on station
3. fits well into office layout
4. easy to add new cables
5. can have different speeds for each station
35
cons to star netwqorking
1. expensive to cable
2. hubfailure leads ro total failure
3. hub is expensive
36
How are networks eg etehernet normally made (topology)
A mix between star and bus. Each connection from a star is a bus network
37
HArdware needed for networking
* Some kind of cables
* NEtwork adapter (connects a computer to a network)
38
What is a network adapter
Connects a comnputer to a network.
Has a buffer for data being passed through it from the parellel to serial.
Adds address information, which is unique to the hardware. This contructs a frame to be transmitten on the network.
39
What is ethernet using
syncoronous transmittion
baseband
bus
40
ethernet frame
* Preamble
* Destination adress
* Source address
* type
* Data
* error checking
41
what is the hardware address
a 48 bit address written in hex.
00-0d-d4-56-3f-40
where the first 3 pairs identify the manufacturere and the last are unique to the device
42
How does ethernet sending work to avoid collisions? (CSMA/CD protocol)
* Listen
* When quiet send frame of data
* Liten to check for collision
* If there was one, back off for a random time then try again.
43
problems with a ethernet bus?
Shared cable limits amaount of data that can be sent at once.
44
How to solve ethernet bus porblems?
Divide the network up into segments (network segments), usuing bridges or multiple network cards
each segment is a seperate collision domain
only cross to another segment if they are addressed to there.
45
What is switched ethernet
* Similar to a hub but more intelligent
* IT inspects the destination address and opens the required port by using a table of addresses.
* Wired in star topology
* Uses Unshilded twisted pair wires.
46
What is a switch
A multi port bridge working at the data link layer (similar to a rounter on the network layer)
47
What is wifi
wireless network uses IEEE 802.11 tech
slower, more vunrable then wired
encrypted using WPA2
48
What is a thin client network?
* A network where all processing takes place in a central server; the clients are terminals with little processing power, storage space, or installed programs.
* Means less money needs to be spent on individual stations
* Software can easily be maintained
* Data and software is accessable by all
* Needs a fast central server and good contection to the server.
49
What is peer to peer networking?
* A network has no dedicated servers, all computers are equal and are called peers.
* No centralised security
* Each user is admin to its own device and is responsible for what that device shares.
* No centralised login
50
When might you use a peer to peer lan?
* Fewer then 10 users
* USers in same area, and computers at users decks.
* Security isnt an issue
* Organisation/network will have limited growth in the future.
51
What is a peer t peer aplication?
all computers act as sevrers for the application eg skype.
52
How can large files be sent using p2p wans and protocols?
useing bittorrent protocal.
Large file is split into smaller parts and send to users requasting it, each user gets a different part and will recive the others from the other users,
This reduces the bandwidth needed from the source.
53
What is a server based network?
* The role of the client and server is seperate
* Server provides the services
* Client requests services from the server
* The server provides centralised security, access control, resourses, admin.
54
What is a dedicated server?
One that isnt used as a workstation and is purly functioning as a server providing functions to the clients.
55
What is web 2.0?
* Software is a service that is accesed over the internet.
* Web based applications
* Constant updates ythat dont require porting for platforms.
* Eg google search, windows live.
56
What is the internet?
a collection of LANs and computers that are interconnected by a WAN
57
What is the world wide web?
a system of interlinked hypertext documents accessed via the internet.Part of the application layer, and uses HTTP/HTTPS as the application layer protocol
58
Benifits/cons of Software as a service?
* No need to install and run application
* No need to update each users software
* user doesnt need to provide the required hardware#
* Ongoing revenue for company
* LEss pirating.
* If payed it could be a recuring fee
* Less control over software version
59
What is Ajax?
Web technology that allows for only the part of the page being used to load.
LEads to less bynes needed to be sent for dynamic data, and a smoother display on the browser.
60
What is web services architechture?
where all components of a system are services, this allows for dynamic changes to happen more easily.
61
Wha is bluetooth?
a wireless protocol for exchanging data over a short distance.
62
What is a wireless network?
Any type of lan where the nodes are connected by radio waves not wires.
63
What is a router?
a device that recieves packets from one host/router and uses the destination ip address the packets conatain to pass them to another host/router
64
how are ip adresses asigned?
By the ISP, The ISP obtain allocations of ip adresses from a local/national internet registry
65
what are non-routable ip addresses?
used for home, office etc networks.
They are set aside when it isnt nessasary to have a public ip address
66
what ip adresses are non routable?
10. 0.0.0 to 10.255.255.255
172. 16.0.0 to 172.31.255.255
192. 168.0.0 to 192.168.255.255
67
what is a gateway?
A device used to connect networks using different protocols so that info can be passed bwteen them.
(a router is a gateway)
68
What is a subnet mask?
Used to allow more ip addresses.
tells you what part of the ip is the host, and which is the network.
69
What doe sa gateway do?
Translates protocols between lans and wans.
The gateway is the destination of a packet, which will, then pass rth edata onto the next host/network.
70
What is a dns server?
domain name system, they keep track of the association between domain name and ip address.
71
WHat is the default gateway?
the address of the pc on the netwrodk, used after the network has been found using the ipaddress and subnetmask.
72
Threats that networking allowes?
* Viruses
* Worms
* SPam
* Trojans
* Phishing
* Pharming
* Survelance
* KEyloggers
* DDOS
* Data Access
* Processing power stealing
* Remote login
73
What is a virus?
A small program attached to another program or data file. It replicates itself by attaching to other programs. Usually attacks computer.
74
what is spam?
Eg many many emails being sent
75
WHat is a worm?
a small program that exploits a network security weakness, to replicate itself throughout computer networks. Attacks computers.
76
What is a trojan?
a program that hides itself as desirable software such as a game but it attacks the computer it infects.
77
What is phishing?
when someone tries to get you to give them your persaonal information.
Can be used to commit identity theft or fraud.
78
WHat is pharming?
when a phisher changes dns server information to direct customers to their site.
79
How can a user proctet itself from internet threats?
* Firewall
* Encryption
* packet filtering
* Spam filters
* proxy servers
* Anti virus software
80
What is firewall?
a hardware device or program that controls traffic between the internet and network
81
what can a firewall do?
* Prevent unautorised access to your network
* hide ytour network formt he internet
* control output access
* log access
* Blocks certain ips, mac addresses, port numbers, domains
82
What is packet filtering?
The firewall analyses the packets that are sent against some firewall rules. It will either allow it or block it.
83
How does a proxy server provide sercurity?
the host computer doesnt have to come into contact with the web server. Host ip isnt given out.
84
What are the two forms of firewall?
* Software for a specific pc
* Sophisticated software ad hardware built into the router.
85
WHy use encryption?
* Store info securly eg passwqords and p-ersonal info
* transmit messages so that only the sneder and recivor can see the plaintext.
86
what is encryption?
using an algothrithm and a kety to convert a messages data into a form that is not understandable without the key to decrypt it.
87
WHat s symetric encryption?
encryption that can be decrypted if the encryption algothrithm is known.
88
What is the one time pad method of encryption?
* A conpletly random key is generated each time a message is encoded.
Problems
* Must be random key
* How do you get the key to the user
89
WHat is asymetric encryption(public key encryption)?
The method that is used (in hybrid)
* There is one key to encrypt and one ket to decrypt.
* The encryption key is public and is distributed.
* The decryption key is private to the owner.
90
How is asymetric encryptiona ctually used and why?
As the encrytion/decryption is slow as it involves very large primes a hybrid system is used.
A proctocol Secure sockets layer, geenrates a session key which is used to symetrically encrypt the message.
The session key is then encrypted using the public key of the reciver.
91
What is a digital signature and why is it used?
ITs used to authenticate the sender is the correct person, and that the message is genuine and untampered.
92
How does a dignital signature work?
* Hash (digest) is created of the message.
* The hash is encrypted using the private key of the sender. (the signature)
* The signature is attached to message and encrypted using the public key of the reciver.
* Message sent to a certificatuion autority who check Sender is correct person, by attaching their correct public key then using their encryption.
* Reciver decryps CA's message to get message and public key of sender.
* Reciver gets the messge and decrypts it with their private key
* They decrypt the signature with the senders public key
* Hash the encrypted message and check it matcheds the decrypted digest.
93
4 steps of sending encrypted data?
1. Server sends public key to client via trusted thrid party who digitally sign it
2. Client confirms - Server will then use its private key to digitally sign some data to the client, who uses public key to ckeck its them.
3. Client generates a one time symettric session key, and encrypts it with public key. Server decrypts with its private.
4. The session key can now be used for transmission.
94
Three types of conputer securty protocols
* Authentication - Checking sender is the correct sender
* Authorisation - Check that users have the correct permissions
* Acounting - to track down any security breach via logs.
