1. Data communications are the transfer of data from one device to another via some form of transmission medium.
2. simplex mode, only one of the two devices on a link can transmit; the other can only receive
3. half-duplex mode, each station can both transmit and receive, but not at the same time
4. full-duplex mode, both stations can transmit and receive simultaneously 5. A network is a set of devices (often referred to as nodes) connected by
communication links.
6. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network.
7. A link is a communications pathway that transfers data from one device to another 8. Point-to-Point : two and only two devices are connected by a dedicated link.
9. Multipoint : three or more devices share a link.
10. Protocol is a set of rules that govern data communication; the key elements of a protocol are syntax, semantics, and timing.
Standards are necessary to ensure that products from different manufacturers can work together as expected.
11. Local area network: is usually privately owned and links the devices in a single office, building, or campus
12. Metropolitan area network: A network with a size between a LAN and a WAN. It normally covers the area inside a town or a city
13. Wide area network: Spans a large geographic area, e.g., a country or a continent 14. Network device is an eequipment that connects directly to a network segment.
15. A repeater is a network device used to regenerate a signal. Repeaters regenerate analoge or digital signals distorted by transmission loss due to attenuation.
16. Hubs concentrate connections. they take a group of hosts and allow the network to see them as a single unit.
17. Bridges convert network transmission data formats as well as perform basic data transmission management.
18. Workgroup switches add more intelligence to data transfer management.
19. Routers can regenerate signals, concentrate multiple connections, convert data transmission formats, and manage data transfers.
20. Physical topology the actual layout of the wire or media.
21. Logical topology defines how the media is accessed by the hosts for sending data.
22. Bus topology uses a single backbone cable that is terminated at both ends.
23. Ring topology Each node connected to two other nodes
24. A star topology connects all cables to a central point of concentration.
25. An extended star topology links individual stars together by connecting the hubs and/or switches.
26. Mesh topology Every node connected to every other node.
27. Tree Network Topology combination of bus and star topology.
28. Hybrid topology Combine two or more of the other topologies.
29. Broadcast topology simply means that each host sends its data to all other hosts on the network medium.
30. Token passing controls network access by passing an electronic token sequentially to each host.
31. Token Ring A set of rules for constructing message in a local network which only one node “talks” at a time
32. OSI model A set of seven layers that define the different stages that data must go through to travel from one device to another over a network.
33. Application layer Provides network services to application processes such as electronic mail.
34. Error control: Makes sure that the data arrives without errors, in the proper sequence and in a reliable condition.
35. flow control: to make sure that information is sent at the proper speed for the receiving device to be able to handle it.
36. Framing: Divides the stream of bits received from the network layer into data units.
37. Protocols are rules for communication.
38. A connectionless protocol treats each packet independently, the packets may or may not travel to the same destination.
39. A connection-oriented protocol the source first makes a connection with the destination before sending packets, when the connection is established, a sequence of packets can be sent .
40. TCP is a connection-oriented transport protocol that sends data as an unstructured stream of bytes.
41. UDP Provides fast delivery of data but does not guarantee data reliability . 42. Internet Protocol (IP) Responsible for addressing the data to be transmitted and
getting it to its destination.
43. Address Resolution Protocol ( ARP) Responsible for identifying the media access control address (MAC) of the next hop .
44. Internet Control Message Protocol (ICMP) Responsible for providing diagnostic functions and reporting errors due to unsuccessful delivery of data.
45. Internet Group Management Protocol (IGMP) Responsible for the management of multicasting with TCP/IP
46. Network Interface protocol Responsible for placing data on the network medium and receiving data off the network medium.
47. IPv4 Addresses: An IP address is a 32-bit sequence of 1s and 0s 48. Ttransmission is the process of sending and propagating
an analogue or digital information signal over a physical transmission medium 49. amplitude is the instantaneous value of the signal at any time.
50. frequency is the number of repetitions of the period per second; f=1/T Hz.
51. Phase is a measure of the relative position in time within a single period of a signal.
52. wavelength of a signal is the distance occupied by a single cycle.
53. spectrum of a signal is the range of frequencies that it contains.
54. The absolute bandwidth of a signal is the width of the spectrum.
55. The effective bandwidth (or just bandwidth) of a signal is the width of the spectrum that contains a large percentage of all the energy of the signal 56. Baseband : The total capacity of the media is used for one channel 57. Broadband : Divides the total bandwidth into many channels
58. Data--entities that convey meaning; signals are electric or electromagnetic encoding of data.
59. Signaling--the physical propagation of the signal along a suitable medium.
60. Transmission--the communication of data by the propagation and processing of signals.
61. Continuous signal: A signal is continuous (in time) if its limit exists for all time.
62. Discrete signal: A signal is discrete if it takes on only finite number of values.
63. Analog data--continuous values on some interval.
64. Digital data--discrete values.
65. Analog signal--a continuously varying electromagnetic wave that may be propagated over a variety of media, depending on bandwidth.
66. Digital signal--a sequence of voltage pulses that may be transmitted over a wire medium.
67. Analog transmission--transmission of analog signals without regard to content.
68. Digital transmission-- transmission of digital data (using either analog or digital signals).
69. Attenuation a decrease in magnitude of current, voltage, or power of a signal in transmission between points.
70. Thermal noise caused by thermal agitation of electrons in a conductor (No = k Temp is the noise power density--the amount of noise in 1 Hz).
71. Intermodulation noise due to the nonlinear combination of signals of different frequencies.
72. Crosstalk phenomenon in which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel.
73. Delay Distortion occurring when the propagation delay for the transmission medium is not constant over the frequency range of the signal.
List questions:
The five components that make up a data communications system are o Message
o Sender o Receiver o Medium o protocol.
Network classified by distance o Local Area Network (LAN)
o Metropolitan Area Network (MAN) o Wide Area Network (WAN)
End-user devices include o Computers
o Printers o scanners
Physical Topology:
o Bus topology o Ring topology
o A star topology
o An extended star topology o hierarchical topology o Mesh topology o Tree Network o Hybrid topology
network devices:
o repeater o bridge o switch o router o hub
Network operating system o Novell NetWare
o Microsoft Windows Server 2003
Telecommunications Services
o Value Added Networks (VANs) o Virtual Private Networks (VPNs) o Leased lines
Benefits of the OSI Model:
o Reduces complexity o Standardizes interfaces
o Facilitates modular engineering o Ensures interoperable technology o Accelerates evolution
o Simplifies teaching and learning
Tasks of protocols:
o Define how to interpret signals o Identify individual computers
o Initiate and end networked communication
o Manage information exchange across network medium o Determine the type of error checking to be use
Types of protocols:
o A connectionless protocol o A connection-oriented protocol
Application protocols:
o Telnet
o FTP : (File Transfer Protocol)-an internet file transfer protocol.
o TFTP
o SMTP : (Simple Mail Transfer Protocol )-an internet protocol for transferring e-mail.
o LPD o NFS
o SNMP: (Simple Network Management Protocol)-an internet protocol for monitoring networks and its components
o X WINDOWS
Transport Protocols o TCP
o UDP o DNS
Internet Protocols (network layer ) o Internet Protocol (IP)
o Address Resolution Protocol ( ARP)
o Internet Control Message Protocol (ICMP) o Internet Group Management Protocol (IGMP)
Every IP address has two parts o The network portion o The host portion
Benefits of Digital Transmission o Reliability
o Error detection and correction o Encryption
o Compression
Transmission Impairments o Attenuation
o Delay Distortion- o Noise
The OSI model layers:
o Application o Presentation o Session o Transport o Network o Data link
o physical
Advantages and disadvantages
1- Peer to peer network:
Advantages:
Limited cost
No software needed
No powerful computers needed
Easy to install and setup
Disadvantages:
Not suitable for large network 2- Server based network:
Advantages:
Data is safe
Thousands of users
Any type of computers can be connected.
Easy to access and manage data.
Security (to have an administrator)
Toking passing advantages:
o More fault tolerant than Ethernet o No collisions
Toking passing disadvantages:
o Complex o Expensive
Broadcast advantages:
o Simple o Inexpensive o Flexible
Broadcast disadvantages:
o Collisions
