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Suppose that \(N\) Ethernet stations, all trying to send at the same time, require \(N / 2\) slot times to sort out who transmits next. Assuming the average packet size is 5 slot times, express the available bandwidth as a function of \(N\).

Short Answer

Expert verified
\(\frac{5}{\frac{N}{2} + 5}\)

Step by step solution

01

Understanding the problem

Determine the time required for sorting out which station transmits next and the time taken for the average packet transmission.
02

Calculate sorting time

Given that it takes \(N/2\) slot times to sort out who transmits next.
03

Determine packet transmission time

Given that the average packet size equates to 5 slot times.
04

Compute total time per transmission

The total time for one complete cycle (sorting + transmission) is \(\frac{N}{2} + 5\) slot times.
05

Express the available bandwidth

The available bandwidth in terms of the number of stations \(N\) and the number of successful transmissions per slot time is given by \(\frac{5}{\frac{N}{2} + 5}\). This represents the fraction of time utilized for transmitting useful data.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

network stations
Network stations are the computers or devices connected to a network. In an Ethernet network, these stations communicate with each other by transmitting data packets. Each station must wait for its turn to send data to avoid collisions, which can happen if two stations try to send data at the same time. The number of network stations, represented as \(N\), impacts the overall network performance and bandwidth.
slot time
Slot time is a critical concept in Ethernet networks. It represents the time window during which the network is checked for collisions. The length of a slot time is determined by the maximum network propagation delay. In this problem, sorting out which station will transmit next takes \( \frac{N}{2} \) slot times, where \(N\) is the number of stations.
packet transmission
Packet transmission refers to the sending of data packets from one network station to another. Each packet has a size, and in this problem, the average packet size is given as 5 slot times. This means it takes 5 slot times to send one packet completely without any interruptions.
available bandwidth
Available bandwidth is the measure of the network's ability to transmit data. It's affected by the time spent sorting out which station will send next and the actual transmission time of packets. It's expressed as the fraction of time used effectively for transmission. For \(N\) stations, the available bandwidth is represented as \( \frac{5}{\frac{N}{2} + 5} \). This formula shows that as the number of stations \(N\) increases, the time needed to sort out transmissions also increases, reducing the available bandwidth.
network efficiency
Network efficiency is about how well a network uses its available resources. In the context of Ethernet, it's about maximizing the amount of data successfully transmitted versus the time spent on managing transmissions and collisions. The available bandwidth formula \( \frac{5}{\frac{N}{2} + 5} \) indicates network efficiency. With fewer stations, sorting time is less, and efficiency is higher. As the number of network stations increases, more time is spent deciding who transmits next, lowering efficiency.

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Most popular questions from this chapter

Suppose that we attempt to run the sliding window algorithm with SWS = RWS = 3 and with MaxSeqNum \(=5 .\) The Nth packet DATA[ \(N]\) thus actually contains \(N\) mod 5 in its sequence number field. Give an example in which the algorithm becomes confused; that is, a scenario in which the receiver expects DATA[5] and accepts DATA[0]-which has the same transmitted sequence number-in its stead. No packets may arrive out of order. Note this implies MaxSeqNum \(\geq 6\) is necessary as well as sufficient.

Suppose \(A, B\), and \(C\) all make their first carrier sense, as part of an attempt to transmit, while a fourth station D is transmitting. Draw a timeline showing one possible sequence of transmissions, attempts, collisions, and exponential backoff choices. Your timeline should also meet the following criteria: (i) initial transmission attempts should be in the order \(A, B, C\), but successful transmissions should be in the order \(\mathrm{C}, \mathrm{B}, \mathrm{A}\), and (ii) there should be at least four collisions.

Suppose you are designing a sliding window protocol for a 1-Mbps point-to- point link to a stationary satellite revolving around the earth at \(3 \times 10^{4} \mathrm{~km}\) altitude. Assuming that each frame carries \(1 \mathrm{~KB}\) of data, what is the minimum number of bits you need for the sequence number in the following cases? Assume the speed of light is \(3 \times 10^{8} \mathrm{~m} / \mathrm{s}\). (a) \(\mathrm{RWS}=1\) (b) RWS = SWS

Consider an ARQ protocol that uses only negative acknowledgments (NAKs), but no positive acknowledgments (ACKs). Describe what timeouts would need to be scheduled. Explain why an ACK-based protocol is usually preferred to a NAK- based protocol.

The text suggests that the sliding window protocol can be used to implement flow control. We can imagine doing this by having the receiver delay ACKs, that is, not send the ACK until there is free buffer space to hold the next frame. In doing so, each ACK would simultaneously acknowledge the receipt of the last frame and tell the source that there is now free buffer space available to hold the next frame. Explain why implementing flow control in this way is not a good idea.

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