Data Transmission Networks: Delays, Losses, and Tools
Fiber Types and Distances
Q20. What are the three types of fiber in use? What are the distances they can cover without needing repeaters?
A20.
- Multimode Step-Index Fiber:
- Copper: 2000 meters at 100 Mbps.
- Multimode Graded-Index Fiber: Covers 3000 meters at 100 Mbps.
- Singlemode Fiber: Up to 80km.
Repeaters and Hubs
Q21. What are repeaters and hubs?
A21. Repeaters strengthen the signal by repeating electrical signals, amplifying both the signal and any noise. Hubs distribute the amplified signal across all their ports, also amplifying both signals and noise.
Network Cards
Q22. What are Network Cards? What is their purpose?
A22. Network cards, also known as network interface cards (NICs) or adapters, provide the physical connection between devices.
Residential Access: Modem Redial
Q23. Describe the operation of residential access using modem redial.
A23. Modem redial provides speeds up to 56kbps with direct access to the router. It does not allow simultaneous voice and data signal navigation.
Residential Access: Cable Modem
Q24. Describe the operation of residential access using a cable modem.
A24. Cable modems share TV signals over cable and broadband. A single TV channel can carry several broadband channels, and the cable modem channel is shared among multiple users.
Chapter 11: Data Transmission Events
Data Transmission Events and Packet Loss
Q25. What events in a data transmission network using communication data justify the loss of packets on the network?
A25. Packet loss occurs when the queue buffer is unable to accommodate all packets waiting for transmission, leading to delays in reaching the destination (time-out), or when packets contain corrupted bits.
Causes of Delays and Losses
Q26. Why do delays and losses occur in communication using a data network?
A26. Delays and losses are caused by network congestion (a virtual path with an excess of packets waiting for transmission) or interference causing loss or damage to packets.
Sources of Delay
Q27. What are the four sources of delay in the transmission of packets in a data network switching package? Describe each.
A27.
- Processing Delay: The time it takes for network nodes to process packets.
- Queueing Delay: The time packets spend waiting in the buffer of the transmission device.
- Transmission Delay: The time it takes to transfer the bits of the packet.
- Propagation Delay: The time it takes for the signal to travel through the communication medium.
Calculating Processing Delay
Q28. How can you calculate the processing delay of nodes in the network?
A28. Processing Delay = Packet Size / Processing Speed
Calculating Transmission Delay
Q29. How can you calculate the transmission delay of packets in the communication links?
A29. Transmission Delay = Packet Size (L) / Bandwidth (R)
Calculating Propagation Delay
Q30. How can you calculate the propagation delay of packets in the communication links?
A30. Propagation Delay = Length of Link (d) / Propagation Speed (s, approximately 200,000 km/s)
Calculating Total Delay
Q31. How to calculate the total delay in the communication network using data?
A31. Total Delay = Sum of Processing Delays + Queueing Delays + Transmission Delays + Propagation Delays
Effect of Bandwidth and Packet Queue
Q32. What is the effect of Bandwidth, Full Package, and the average number of packets in the delay queue?
A32.
- If L*a/R is close to 0, the delay is small.
- If L*a/R is less than 1, the delay is larger.
- If L*a/R is greater than or equal to 1, more bits are entering than the link’s transmission capacity, and the average delay increases exponentially.
Where:
L = Packet Size
a = Average packet arrival rate
R= Bandwidth
Network Delay Measurement Tools
Q33. What are the two tools (network commands present in the operating systems of hosts) to measure the delay of packets on the Internet?
A33. Ping and Traceroute.
Functional Difference: Ping vs. Traceroute
Q34. What is the functional difference between PING and traceroute?
A34. Ping determines the access time between the origin and destination hosts. Traceroute checks the status of each router involved in the path from source to destination.
Ping and Traceroute: Interchangeability
Q35. Can we say that ping and traceroute do the same thing? Can one replace the other?
A35. The two have similar functions, but Traceroute is more comprehensive. Ping can replace Traceroute, but this will result in a loss of quality in the response data.