This set of Data communication and Networking Multiple Choice Questions and Answers (MCQs) focuses on “Metropolitan Area Networks MAN – IEEE 802.6 – DQDB (Distributed Queues, Dual Bus) ”.
PRACTICE IT NOW TO SHARPEN YOUR CONCEPT AND KNOWLEDGE
1. Each device in a DQDB system is connected _______.
- to just one bus
- to two buses
- in a single ring structure
- none of the above
B. to two buses
2. A DQDB device accesses a bus link through _______.
- contention
- token passing
- distributed queues
- CSMA/CD
C. distributed queues
3. A DQDB device accesses a bus link through _______.
- contention
- token passing
- distributed queues
- CSMA/CD
C. distributed queues
4. Each DQDB bus is _______.
- unidirectional
- bi-directional
- connected to just the end stations
- none of the above
A. unidirectional
5. Traffic on a DQDB bus _______.
- moves in both directions
- alternates between buses
- moves in one direction
- none of the above
C. moves in one direction
6. If DQDB slots are generated on device X, then _______.
- device X has no upstream stations
- device X has no downstream stations
- device X has no queues
- device X can never transmit data
A. device X has no upstream stations
7. If device Y is the end of a DQDB bus, then _______.
- device Y has no upstream stations
- device Y has no downstream stations
- device Y has no queues
- device Y can never transmit data
B. device Y has no downstream stations
8. If device X is neither the beginning nor the end of a DQDB bus, then _______.
- device Z has no upstream stations
- device Z has no downstream stations
- device Z has no queues
- none of the above
D. none of the above
9. In a DQDB with _______ devices, no queues are needed.
- 2
- 3
- 4
- any of the above
A. 2
10. If device X has 10 downstream stations and 3 upstream stations, how many stations are on the DQDB bus?
- 10
- 13
- 14
- 28
C. 14
11. To send data, a DQDB station needs to _______.
- insert data into any empty slot
- capture a token
- make a reservation on the bus traveling in the upstream direction
- make a reservation on the bus traveling in the downstream direction
C. make a reservation on the bus traveling in the upstream direction
12. The DQDB _______ store requests for slots.
- queues
- switches
- packets
- reservations
A. queues
13. In a DQDB queue, slot requests are ordered according to _______.
- station size
- proximity to the slot-generating station
- packet size
- the time they were received
D. the time they were received
14. When DQDB is implemented as a ring, _______ the slots.
- one station generates
- two stations generate
- all stations generate
- none of the above
A. one station generates
15. When DQDB is implemented as a ring and then a link or a station fails, _______ the slots
- one station generates
- two stations generate
- all stations generate
- none of the above
B. two stations generate
16. The _______ layer in the DQDB protocol splits the data stream coming from the upper layer into 48-byte segments.
- physical
- data link
- MAC
- LLC
C. MAC
17. Data from the LLC or upper layers are divided into _______-byte segments by the DQDB MAC layer.
- 5
- 48
- 53
- 64
B. 48
18. The DQDB MAC layer adds a _______ -byte header to each 48-byte segment
- 5
- 43
- 58
- 64
A. 5
19. The polynomial used for the DQDB CRC is x8 + x2 + x + 1. The divisor is therefore _______ bits
- 7
- 8
- 9
- 10
C. 9
20. The polynomial used for the DQDB CRC is x8 + x2 + x + 1. What is the divisor?
- 100001011
- 100000111
- 101000101
- 111000111
B. 100000111
21. The polynomial used for the DQDB CRC is x8 + x2 + x + 1. This means the CRC remainder is _______ bits in length.
- 7
- 8
- 9
- 10
B. 8
22. The DQDB header consists of _______ field(s).
- one
- two
- four
- five
D. five
23. The _______ field controls access to the DQDB bus.
- access
- address
- type
- priority
A. access
24. The DQDB _______ field holds a 20-bit VCI used in MAN and WAN transmissions
- access
- address
- type
- priority
B. address
25. How many types of DQDB payloads are possible?
- 1
- 2
- 3
- 4
D. 4
26. How many DQDB priority types are possible?
- 1
- 2
- 3
- 4
D. 4
27. The DQDB _______ subfield indicates the occupancy status of the slot
- busy (B)
- slot type (ST)
- reserved (R)
- previous slot read (PSR)
A. busy (B)
28. The DQDB _______ subfield defines the type of transmission (packet or isochronous).
- busy (B)
- slot type (ST)
- reserved (R)
- previous slot read (PSR)
B. slot type (ST)
29. When the destination DQDB station has read the slot contents, it sets the _______ subfield to 0
- busy (B)
- slot type (ST)
- reserved (R)
- previous slot read (PSR)
D. previous slot read (PSR)
30. Which subfield in the access field is not currently in use by DQDB?
- busy (B)
- slot type (ST)
- reserved (R)
- previous slot read (PSR)
C. reserved (R)
31. A DQDB slot is the same size as a cell in _______.
- B-ISDN
- PPP
- ISDN
- ATM
D. ATM
32. Which bit is set by a station to reserve a slot?
- ST
- PSR
- RQ
- B
C. RQ
33. When a _______ uses DQDB, the address field is all 1s.
- LAN
- MAN
- WAN
- b and c
A. LAN
