Chapter 9: Data Transmission

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Madeline Copeland
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1 Chapter 9: Data Transmission MULTIPLE CHOICE 1. In practical terms, parallel data transmission is sent: a. over short distances only c. over any distance b. usually over long distances d. usually over a coaxial cable A 2. The five-level teletype code was invented by: a. the Morkum Company c. Western Union b. the Teletype Company d. Emile Baudot 3. Data codes are also called: a. character codes c. they do not have any other name b. character sets d. both a and b C 4. Digital data that is not being used to carry characters is called: a. FIGS data c. numerical data b. binary data d. all of the above 5. Character codes include: a. alphanumeric characters c. graphic control characters b. data link control characters d. all of the above 6. ASCII stands for: a. American Standard Character-set 2 b. American Standard Code for Information Interchange c. American Standard Code 2 d. Alphanumeric Standard Code for Information Interchange 7. BS, FF, and CR are examples of: a. nonstandard character codes c. control characters b. escape characters d. none of the above C 8. LF stands for: a. Line Feed c. Line Forward

2 b. Link Feed d. Link Forward A 9. UART stands for: a. Universal Asynchronous Receiver-Transmitter b. Unidirectional Asynchronous Receiver-Transmitter c. Unaltered Received Text d. Universal Automatic Receiver for Text A 10. In asynchronous transmission, the transmitter and receiver are: a. frame-by-frame synchronized using the data bits b. frame-by-frame synchronized using a common clock c. frame-by-frame synchronized using the start and stop bits d. not synchronized at all, hence the name "asynchronous" C 11. In asynchronous transmission, the time between consecutive frames is: a. equal to zero c. equal to the start and stop bit-times b. equal to one bit-time d. not a set length 12. In synchronous transmission, the frames are: a. about the same length as ten asynchronous frames b. much longer than asynchronous frames c. 128 bytes long d bytes long 13. Synchronous transmission is used because: a. no start and stop bits means higher efficiency b. it is cheaper than asynchronous since no UARTS are required c. it is easier to implement than asynchronous d. all of the above A 14. In synchronous transmission, the receiver "syncs-up" with the transmitter by using: a. the clock bits c. the CRC bits b. the data bits d. a separate clock line 15. To maintain synchronization in synchronous transmission: a. long strings of 1s and 0s must not be allowed b. transmission must stop periodically for resynchronization c. the clock circuits must be precisely adjusted d. the channel must be noise-free

3 A 16. BISYNC: a. is an IBM product c. requires the use of DLE b. is a character-oriented protocol d. all of the above 17. HDLC: a. is an IBM product c. is identical to SDLC b. is a bit-oriented protocol d. all of the above 18. The use of flags in SDLC requires: a. "bit-stuffing" c. FEC b. different flags at either end of a frame d. ARQ A 19. The initials ARQ are used to designate: a. automatic request for resynchronization c. automatic receiver queue b. automatic request for retransmission d. automatic request for queue 20. ARQ is used to: a. correct bit errors c. put data into a temporary buffer b. correct synchronization problems d. none of the above A 21. FEC stands for: a. Fixed Error Control c. Forward Error Correction b. Forward Error Control d. False Error Condition C 22. VRC is another name for: a. FEC c. LRC b. ARQ d. parity 23. CRC stands for: a. Control Receiver Code c. Cyclic Redundancy Check b. Correct Received Character d. Cycle Repeat Character C 24. Huffman codes: a. allow errors to be detected but not corrected b. allow errors to be detected and corrected c. allow alphanumeric data to be corrected

4 d. allow alphanumeric data to be compressed 25. Run-length encoding is used to: a. encrypt data c. correct data b. compress data d. none of the above 26. Public-key encryption: a. allows the use of digital signatures c. avoids the "password problem" b. is used to convey symmetric keys d. all of the above 27. SDLC stands for: a. Synchronous Data Link Control c. Synchronous Data Link Character b. Synchronous Data Line Control d. Synchronous Data Line Character A 28. HDLC is: a. a bit-oriented protocol c. an ISO standard b. based on SDLC d. all of the above COMPLETION 1. Parallel transmission can be used only for distances. short 2. The term "baud" was named after Emil. audot 3. Data codes are also called codes. character 4. The code is a 7-bit code commonly used in communication between personal computers. ASCII 5. The two letters designate the code character used to advance a printer to the next page. FF

5 6. An asynchronous frame begins with the bit. start 7. An asynchronous frame ends with the bit. stop 8. At the end of an asynchronous frame, the line will be at the level. mark binary 1 9. An integrated circuit called a is used in an asynchronous communication system to convert between parallel and serial data. UART 10. When receiving digital data, are used to hold data until they can be read. buffers 11. Synchronous communication is more than asynchronous since there are fewer "overhead" bits. efficient 12. There must be sufficient 1-to-0 to maintain synchronization in synchronous transmission. transitions 13. Clock sync is derived from the stream of bits in synchronous transmission. data 14. In the protocol, each frame begins with at least two SYN characters. ISYNC 15. In HDLC, each frame starts with an 8-bit. flag 16. The first eight bits of an SDLC frame are BCC stands for check character.

6 block 18. DLE stands for data link. escape 19. HDLC uses bit- to prevent accidental flags. stuffing 20. errors cause many consecutive bits to be bad. urst 21. FEC stands for error correction. forward 22. An scheme corrects errors by requiring the retransmission of bad blocks. ARQ 23. Parity fails when an number of bits are in error. even 24. CRC codes are particularly good at detecting errors. burst 25. Huffman coding and run-length encoding are examples of data. compression 26. A is an encoding scheme that is not public in order to protect data. cipher 27. A is often used to generate an encryption key because it is easier to remember. password 28. If the key is enough, private-key encryption can be quite secure. long 29. Messages cannot be using a public key. decrypted 30. Because it is -intensive, public-key encryption can be slow.

7 computation SHORT ANSWER 1. How many different characters could be encoded using a six-bit code? What is the numerical difference between ASCII 'a' and ASCII 'A' if you treat them as hexadecimal (hex) numbers? 20 hex (32 decimal) 3. The ASCII codes for the characters '0' through '9' are what hex numbers? 30H to 39H 4. If an asynchronous frame is used to send ASCII characters in the form of bytes (8 bits), what is the shortest time it could take to send 1000 characters if each bit in a frame is 1 msec long? 10 seconds 5. Suppose an asynchronous frame holds 8 bits of data, a parity bit, and two stop bits (it could happen). Calculate the efficiency of the communication system. 66.7% 6. Suppose a synchronous frame has 16 bits of non-data in the front and a 16-bit BCC at the end. The frame carries 1024 bytes of actual data. Calculate the efficiency of the communication system. 97.0%

Lecture / The Data Link Layer: Framing and Error Detection

Lecture / The Data Link Layer: Framing and Error Detection Lecture 2 6.263/16.37 The Data Link Layer: Framing and Error Detection MIT, LIDS Slide 1 Data Link Layer (DLC) Responsible for reliable transmission of packets over a link Framing: Determine the start