- What is an autonomous system?
- What is the difference between an interior routing protocol and an exterior routing protocol?
- Compare the three main approaches to routing. Name a protocol used in each approach.
- List and briefly explain the main functions of the Border Gateway Protocol (BGP).
- BGP’s AS_PATH attribute identifies the autonomous systems through which routing information has passed. How can the AS_PATH attribute be used to detect routing loops?
- BGP provides a list of autonomous systems on the path to the destination. However, this information cannot be considered a distance metric. Why?
- List and briefly describe 3 metrics that can be used for routing.
- Which routing approach is more preferable, distance vector routing or link state routing? Explain.
- Given the following directed graph of an autonomous system (Figure 19.8), provide the routing table maintained by node R10.
- Why can’t distance vector or link state routing be used for exterior routing?
- Describe briefly the 4 types of messages used in BGP.
- Given the following diagram illustrating 3 autonomous systems, provide the routing table maintained by the gateway router R6 as computed by BGP.
IEEE 802.3 CSMA/CD
- Explain the 3 persistent protocols that can be used with CSMA.
- Describe the CSMA/CD algorithm (using a flow diagram).
- Which persistent algorithm works best for IEEE 802.3 CSMA/CD? Explain.
- Explain binary exponential backoff.
- Describe the binary exponential backoff algorithm used in IEEE 802.3 CSMA/CD.
- What is the major negative effect of binary exponential backoff? Explain using an example.
- How are collisions detected?
Signal Propagation Basics
- Define the 3 transmission ranges.
- Define the following signal propagation effects with diagrams:
- shadowing (blocking)
- Prove that the maximum distance d (km) between an antenna with height h (m) and a receiver at the sea level is given by d = 3.57 h, assuming an optical line of sight. Hint: Use the Pythagorean theorem.
- Prove that the maximum distance d (km) between two antennas with height h1 and h2 (m) is given by d = 3.57 (h1 + (h2), assuming an optical line of sight.
- Convert the following free space path loss ratio to decibel. Show calculations.
- What signal propagation effects may cause multipath propagation?
- How does multipath propagation affect the quality of the received signal?
- What is the difference between short-term and long-term fading?
IEEE 802.11 Medium Access Control
- What is a basic service set (BSS)? What is an extended service set (ESS)?
- Draw the diagram of a super-frame in IEEE 802.11 and briefly describe each component of the super-frame.
- Why can’t collisions of frames be detected in a wireless medium?
- Describe the CSMA/CA algorithm (using a flow diagram).
- What is the purpose of different inter-frame space (IFS) values?
- Use the given information to draw a table containing the following information:
Standard / Slot time ST (s) / SIFS (s) / DIFS (s) / PIFS (s)
IEEE 802.11n (5 GHz) / 20
IEEE 802.11n (2.4 GHz)
Note: DIFS = SIFS + 2 x ST
PIFS = SIFS + ST
- Describe the binary exponential backoff algorithm used in CSMA/CA.
- What is the hidden terminal problem?
- What is the exposed terminal problem?
- Consider the following ad hoc network and the following assumptions:
- the distance between any 2 neighbour nodes is d;
- the transmission range is 1.2d and the sensing (detection) range is 1.5d;
- the medium is busy at time (slot) t due a long transmission between C and D;
- node A wants to send a data frame to node B and node X wants to send to node Y at time (slot) t but both detect a busy channel;
- the channel becomes free at time (slot) t+5;
- node A draws random number 9, and node X draws random number 6.
Draw a diagram (similar to the one on slide 36 of the lecture notes) that shows
- the sequence of control and data frames exchanged between A and B, and between X and Y
- the time gaps (e.g., IFS) between frames or between events
- the network allocation vectors (NAV) of the stations hearing the control and data frames.
11. What is co-channel interference?
12. What is adjacent-channel interference?
13. Describe briefly how the PCF works.
14. Consider the sequence of actions within a BSS depicted in the following diagram. Draw a timeline, beginning with a period during which the medium is busy and ending with a period in which the CF-End is broadcast from the AP. Show the transmission periods and the time gaps (IFS).