formulas and applications Flashcards
Familiarise variables, formulas and their applications
What is the formula for total transmission time for a frame of size L bits over a link of rate R and distance d?
Time= L/R + d/v
Where:
L: Frame length (bits)
R: Transmission rate (bps)
d: Distance between nodes
v: Propagation speed in medium
What does the variable L/R represent in a transmission delay formula?
Transmission delay — time to push all bits into the link
What does d/v represent in a transmission delay formula?
Propagation delay — time for a bit to travel from sender to receiver
Formula for channel efficiency in Stop-and-Wait ARQ?
η= L/L+2TpR
Where:
L: Frame size (bits)
Tp: Propagation time
R: Transmission rate
What is the efficiency of a Go-Back-N ARQ protocol?
𝜂=𝑊/1+2𝑎
Where:
W: Window size
𝑎=𝑇𝑝/𝑇𝑓 : Normalized propagation time
𝑇𝑓: Frame transmission time
In PPP, what are the byte stuffing escape sequences for 0x7E and 0x7D?
0x7E becomes 0x7D 0x5E
0x7D becomes 0x7D 0x5D
Formula to calculate link utilization?
𝑈=UsefulDataRate/ TotalTransmissionRate
What formula determines the number of crosspoints in a crossbar switch?
Ncrosspoints = 𝑛×𝑛,
where 𝑛 is number of inputs/outputs
What is the bit rate for a TDM system with
𝑁 channels each transmitting at 𝑅 bps?
Total rate = 𝑁×𝑅
What is the bandwidth requirement for a signal sampled at 𝑓𝑠 Hz with 𝑏 bits/sample?
Bitrate = 𝑓𝑠 × 𝑏
Q: What is the formula for transmission delay?
A: Transmission Delay = Packet Length (L) / Transmission Rate (R)
Q: What is the formula for propagation delay?
A: Propagation Delay = Distance (d) / Propagation Speed (s)
Q: What is the total nodal delay?
A: Total Delay = Processing + Queuing + Transmission + Propagation
Q: What is the formula for throughput?
A: Throughput = Total Data Sent / Total Time
Q: What is the formula for link utilization?
A: Utilization = Useful Time / Total Time
Q: How do you calculate round-trip time (RTT)?
A: RTT = 2 × Propagation Delay
Q: Formula for utilization in Stop-and-Wait ARQ?
A: Utilization = L / (L + 2RTT × R)
Q: How do you calculate Bit Error Rate (BER)?
A: BER = Number of Errors / Total Bits Sent
Q: What does the Shannon Capacity formula calculate?
A: C = B × log₂(1 + S/N), where B = bandwidth, S/N = signal-to-noise ratio
Q: How do you calculate the efficiency of Slotted ALOHA?
A: Efficiency = G × e^(-G), where G = average number of frames per slot
Q: How is window size related to bandwidth-delay product in sliding window protocols?
A: Window Size = Bandwidth × RTT
Q: What is the Go-Back-N ARQ retransmission condition?
A: Retransmit all frames starting from the one with error
Q: In Selective Repeat ARQ, what happens on error?
A: Only the erroneous frame is retransmitted
Q: What is the maximum utilization of Pure ALOHA?
A: Maximum Efficiency = 1 / (2e) ≈ 18.4%
Q: What is the maximum utilization of Slotted ALOHA?
A: Maximum Efficiency = 1 / e ≈ 36.8%
Bits in Transit (Bandwidth-Delay Product)
BitsinTransit=DataRate(bps)×PropagationDelay(s)
Can a connection-oriented, reliable message transfer service be provided across a connectionless packet network?
Yes, by adding reliability features at higher layers (e.g., the transport layer). Protocols like TCP provide reliability by using sequence numbers, acknowledgments, retransmissions, flow control, error control and congestion control to ensure correct delivery over an unreliable network like IP
Can a connectionless datagram transfer service be provided across a connection-oriented network?
Yes. A connectionless service can be built on top of a connection-oriented network by sending independent messages without using the connection features. The higher layer can treat the underlying connection as a transparent channel, providing no reliability or ordering by design.
