LZW case:-

A special circumstance arises in the LZW procedure when the dictionary item sent is the last one entered into the dictionary; this item is not yet fully formed by the receiver. Consider the message ababababab. The initial dictionary consists of 1:a, 2:b. The message will be sent as 1, 2, 3, 5, ... , and the dictionary will be 1:a, 2:b, 3:ab, 4:ba, 5:aba....

However, when 5 is sent, the receiver will not yet have completed the construction of that dictionary entry. After receiving 3, the receiver will know that item 5 is abX, where X is unknown. So when the next transmission is 5, the receiver can translate it as abX and realize that the X in the dictionary item must be a because it is the first symbol of the transmission after receiving 3. This special case is part of the LZW method. Suppose the initial alphabet is 1:a, 2:d, 3:-. Translate the sequence 2 1 2 3 1 3 4 10 9 5 4.