comm + networks

• What is baud rate?

  The number of signal changes in the medium per second
• What is Bit rate?


  The number of bits that are transmitted over a medium per second
• What is latency?

  the difference in time between an action being initiated and its effect being noticed
• What is serial data transmission?


  • Data is sent one bit at a time over a wire
  • Used for medium to long distances - like mice and keyboards
• What is parallel data transmission?


  • Uses multiple parallel wires in order to send multiple bits between components in a computer simultaneously
• Advantages of serial transmission (over parallel transmission)?

  • cheaper as only uses one wire
  • doesn’t suffer from skew
  • thus making it more reliable over long distances
• What is synchronous transmission?

  • a clock signal is shared between the sender and the receiver
  • used to time when signals are sent
• What is asynchronous transmission?

  • start and stop bits are used to indicate where the transmission starts and stops
  • sender and reciever must have the same Baud rate
• Describe a physical star network topology?


  Each client has its own direct connection to a central hub
• Describe a physical bus network topology?


  Uses a backbone cable and a terminator
• Advantages of a physical bus topology?

  • no central hub, reducing chances of network failure and decreasing cost of installation
  • inexpensive to install, as small amounts of cable are required
• Disadvanatages of a physical star topology?


  • if central hub fails, all communication is stopped
  • expensive to isntall due to amount of cable required
• Disadvantages of a physical bus toplogy?


  • multiple clients using the same backbone = risk of collisions
  • if backbone fials, the entire network fails
  • shared backbone, reduces privacy as every client can see packets, not intended for them
• Advantages of a physical star toplogy?


  • easy to add and remove clients from a network
  • failure of one cable has no effect on the rest of the network
  • pakctes are sent directly to the recipient, preserivg privacy
  • eliminates collsions,, as one cable per device
• Describe peer-to-peer networking?:

  • no shared server
  • every client has equal status
  • all clients which provide services
  • more cost effective, as no need for a powerful server
• Name the four layers of the TCP/IP stack?

  • application
  • transport
  • network
  • link
• What is the purpose of FTP?


  h
• What is a thick client network?


  • strong, powerful clients, more expensive to set up
  • independence eliminates the requirements for a server
  • harder to maintain as no facility to issue updates and manage security
  • less betwork traffic - quieter communication channels reducing the likelihood of data collisions
• Name fields typically included in a packet?

  • port number
  • packet number
  • Source address
  • data
  • checksum
  • destination address
• What is a checksum used for?

  To check if the contents of the packet have been corrupted or changed during transmission
• How is a checksums value determined?

  Calculated from the contents of the packet
• Describe the role of a router in packet switching.

  • connects two networks together
  • uses the most efficient path to destination
  • updates routes to reflect network congestion etc
  • Router determines which router to send packet to next
• State a weakness of ceasar ciphers?

  • Each letter is always encrypted to the same letter
  • Thus letters in ciphertext will have the same frequcny of letters in the plain text
• State two conditions that must be met for the vernam cipher to offer complete security?

  1. key must be truly random. 2. key must be at least as long as the plaintext
• Describe what Uniform Resource Locators (URLs) are used for in a RESTful application?


  • Each resource is represented by a URL
  • Entering a URL causes the server to (use CRUD to) retrieve (the relevant) data;
• how REST enables CRUD to be mapped to database functions using SQL?


  GET ->SELECT, POST -> INSERT, DELETE -> DELETE, PUT -> UPDATE
• State two reasons why JSON might have been chosen to encode the data instead of XML?

  • easier for humans to read
  • more compact - uses less memory
• Functions of the network layer of the TCP/IP stack?

  adds the correct IP address for each packet's source and destination
• Function of the link layer of the TCP/IP stack?

  controls physical connections between pieces of hardware in a network

  adds MAC addresses to packets
• What are MAC addresses?

  Media Access control-
• What do MAC addresses do?

  identify the hardware to which a packet should be sent
• What is the function of the transport layer?

  establishes a virtual end to end, virtual path

  between the sender and reciever

  thelayer then splits the transmission into pakcets
• Features of a packet?

  sequence number

  port number
• SSH port?

  22
• FTP ports?

  20 and 21
• HTTP port?

  80
• HTTPS port?

  443
• POP3 ports?

  110 and 995
• SMTP ports?

  25, 587, 465
• client connecting to database steps?

  • client server request
  • web browser
  • sends http