Consider sending a 2100-byte chunk of data using TCP from Host A to Host B. TCP

Question

Consider sending a 2100-byte chunk of data using TCP from Host A to Host B. TCP segments are carried in IP datagrams (with a 20-byte header). IP datagrams are carried in a data link frame (with a 10-byte header). The maximum segment size for TCP is 800 bytes. The physical layer protocol can support a data rate of 1 Mbps. Assume a total round-trip time of 10 ms between the sender and the receiver.

a)How many frames will need to be sent from Host A to Host B? What is the size of each TCP segment? Explain.

b)Suppose the data must be sent over three links (from Host A to the first router, from the first router to the second router, and from the second router to Host B). How long will it take to create a TCP connection, deliver the data from Host A to Host B, and close the connection? Ignore any effects of TCP congestion control or flow control. Assume all links are lightly loaded so there are no queuing delays. Clearly state any assumptions made in determining the result. Include protocol diagram.

Explanation / Answer

Yes, whole packet will be lost if fragment is lost.

Yes and no. TCP can also send segments larger than IP packets. If it does, and if IP packets are fragmented, and if a fragment is lost, the whole IP packet is lost, which will require retransmission of the whole TCP segment. (Normally, TCP sets its MSS to fit within a packet's MTU.)Not unless you define further what you mean. Also TCP or UDP are L4, IP is L3.

Each L3 link/hop should support same MTU. Different L3 links/hops can have different MTUs. If L3 packet is larger than the next L3 link/hop it desires to transit, packet must be fragmented to fit, or it will be dropped.

All L2 link/hops should support same MTU, otherwise too large frames will be dropped. Yes routers normally can, especially if they support different media. For example, most serial WAN media support larger MTUs than does Ethernet. (Token ring also supports larger MTU than Ethernet.)On routers, you're more likely to find MTU can be configured be routed interfaces. Switches, though, often work with just one media, usually Ethernet, so if they support different L2 MTUs (e.g. jumbos), often all the hardware is enabled or not

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