java:

Build a Defragment class with two public methods: addFrag and toString. The addFrag method will be called each time a new packet fragment arrives. Each fragment will come with four pieces of information:

Packet ID. Each fragment will have a packet ID number. This number will identify the original packet that the fragment came from. You can use the Packet ID to group fragments together as you reassemble them.

Fragment Offset. The Fragment Offset is the number of bytes this fragment is from the beginning of the original packet. A Fragment Offset of zero indicates the first fragment of a packet; a Fragment Offset of 65,535 would indicate a fragment that starts at the very last byte of a packet. On the real Internet, the Fragment Offset must always be a multiple of 8; for this assignment, you should not make that assumption.

Fragment Length. Each fragment will contain a positive number of bytes. On the real Internet, fragments lengths are frequently about 1500 bytes, but the length could be as small as 1 or as large as 65,536.

More Fragments Bit. Each fragment includes a bit (zero or one) indicating whether there are more fragments from the original packet. The very last fragment of a packet will always contain a More Fragments value of zero; all previous fragments will have a one.

Your declaration for the addFrag method will thus be:

public void addFrag(int id, int froff, int length, boolean morefrag);

Your implementation should make use of several instances of the List ADT from the textbook -- a list of fragments for a given packet that is currently being reassembled; you could be reassembling several packets at once, so you will need a list of such lists; and a list of packets that have been completely reassembled. Several of these lists could be sorted and/or indexed; it is up to you whether to use linked- or array-based implementations. Do not rely on the built-in Java collection class libraries, such as ArrayList, Vector, and their friends.

Example Run:

A 2000-byte packet with ID 1234, in three chunks. Input:

ID FrOff Len MF 1234 0 1000 1 1234 1000 500 1 1234 1500 500 0

Output:

Packet 1234, 2000 bytes