Combined application of Ethernet minimum frame length and TCP/IP

Combined application of Ethernet minimum frame length and TCP/IP

@ (computer network)

Running the TCP/IP protocol on a fast Ethernet with an average round trip delay of RTT = 20ms, assuming TCP has a maximum window size of 64KB, ask at this time the maximum data transfer rate that the TCP protocol can support is approximately (C)
A. 3.2mbit/s
B. 12.8 Mbit/s
C. 25.6mbit/s
D. 51.2mbit/s

Analysis: The problem of the shortest frame length is discussed in detail at the data link layer. Do not see how TCP joins after thinking.

In fact, the nature of the problem is still the same, the transmission of data itself from the high to the low, low-level is pragmatic, responsible for the actual work. In other words, when we discuss the minimum frame length problem of the data link layer, the transmission delay is greater than the RTT to detect the conflict. In the TCP layer to think about the problem, although the level is different, but the same way of thinking, that is, send delay is greater than RTT.

At the data link layer, the contention period is RTT because of the conflicting issues that are detected by the CSMA/CD protocol. The data sent is a data frame. The data sent by TCP requires IP encapsulation and the overhead of framing, but these headers and control overhead are negligible compared to 64KB. Therefore, the direct set maximum transfer rate is v.

64kb÷v≥rtt→v≤64kb20ms=25.6mbit/s 64KB \div v \geq rtt\rightarrow v \leq \frac{64kb}{20ms} = 25.6mbit/s

Therefore, the maximum transfer rate is 25.6mbit/s.