Review Questions

1.        Describe the medium access algorithm used in Token Ring.

2.        Which functions are carried out by the active monitor?

3.        Why are Token Ring networks able to retain connectivity if one of the computers forming the ring is powered down?

Due to a bypass capability of Token Ring network adapter.  

4.        Specify the maximum allowed data field sizes for:

·                Ethernet

·                Token Ring

·                FDDI

·                Bluetooth

5.        On what basis is the maximum token turnaround time chosen for the Token Ring network?

To ensure that a media access time for a network station doesn’t exceed a certain limit.  

6.        Which element of the Token Ring network restores synchronization of the bit flow?

A repeater of an active monitor.

7.        What are advantages of the early token-release mechanism?

Shared media is used more effective.

8.        What features do FDDI and Token Ring have in common, and how do they differ?

9.        Which elements of FDDI networks ensure fault tolerance?


10.     FDDI is fault tolerant. Does this mean that under conditions of any single cable breakdown the network can continue normal operation?


11.     What are the consequences of duplicated cable breakdown in FDDI rings?

A ring will be divided onto two separate rings.

12.     What will happen if a single attachment station (SAS) cable is damaged in an FDDI network?

The station will be disconnected from a ring.

13.     Which methods of signal encoding are used in IEEE 802.11 networks?


14.     What type of medium does the DS use for transmitting data among BSSs?

Wired and wireless

15.     What is the influence of the hidden terminal effect?

Collisions take place more often

16.     How does the MAC layer in 802.11 networks detect collisions?

There is no an acknowledgement of a frame which caused a collision.  

17.     Is it possible for a station belonging to an 802.11 network to transmit a frame to another station belonging to the same BSS using AP?


18.     What is the purpose of dividing the time period allowed for frame transmission into slots in DCF? What needs to be taken into account when choosing slot duration?

Dividing a transmission period onto slots reduces a probability of a collision. Slot size is chosen in such a way that its value is greater than a signal propagation time between any two stations of a network plus a period which a station needs to recognise that a medium is busy.   If such a condition is met, a station can correctly recognise an event when some other station starts to transmit a frame by listening to slots that precede a slot which was chosen by a station for its own transmission,

19.     Why does PCF always have priority over DCF?

PCF mode has a lesser interpacket gap than DCF mode

20.     How are Bluetooth piconets joined into a scatternet?

A node called a bridge is a member of several piconets; such a node transfer data between piconets which it is belong to.  

21.     Why are not all 625 bits of a Bluetooth time slot used for frame transmission?

Because some slots are used to synchronise a receiver and a transmitter.

22.     In which cases can a single Bluetooth frame carry data of one, two, or three SCO channels?

When FEC is not used then a frame carries data of three SCO channels; when 2/3 FEC is used then a frame carries data of two SCO channels; when 1/3 FEC is used then a frame carries no data of SCO channels.  

 23.     What switching methods are used in Bluetooth?

Circuit switching for voice and packet switching for data.

24.     Why was master–slave architecture chosen for Bluetooth?

Because the technology is designed to accommodate very simple devices (along with sophisticated ones) for which a slave mode is more appropriate.

25.     How do network adapter and concentrator port performance influence network performance?

26.     How do concentrators support back-up links?

By means of blocking ports that support back-up links.

27.     According to their main function — repeating a signal — concentrators are classified as devices operating at the physical layer of the OSI model. Provide examples of auxiliary concentrator functions for which the concentrator needs information from higher-layer protocols.

Blocking of unauthorised access.

28.     What are the differences between modular and stack concentrators?

29.     Why are special ports used for interconnecting concentrators?


P1. Evaluate the maximum time of waiting for access to the medium in a Token Ring network with 160 stations and operating at 16 Mbps.

By default the token holding time is 10 ms, so that if each station of the ring has data to send then the maximum waiting time will be 159 * 10 = 1.59 s.

P2. A Token Ring network includes 100 stations. The total length of the ring is 2,000 m. The transmission rate is 16 Mbps. The token-holding time is chosen to be 10 msec. Each station transmits frames of a fixed size of 4,000 bytes (with the header) and fully uses the token-holding time for transmitting all of its frames. Calculate the gain produced by using the early token-release mechanism in this network.


P3. IEEE 802.11 and Bluetooth networks operate within the same territory. The 802.11 network uses the FHSS physical-layer specification for data transmission at 1 Mbps. The Bluetooth network operates with a standard chipping rate of 1,600 Hz, and the 802.11 network supports a chipping rate of 50 Hz. Both networks use 79 channels in the
2.4 GHz range.

Determine the proportion of frames in each network that are corrupted because of the use of the same frequency channel by both networks. For precision, consider that all data in the Bluetooth network are transmitted in one-slot frames, and the 802.11 network uses frames of the maximum length.