In the 4B/5B encoding (Table 2.2), only two of the 5-bit codes used end in two 0s. How many possible 5-bit sequences are there (used by the existing code or not) that meet the stronger restriction of having at most one leading and at most one trailing 0? Could all 4-bit sequences be mapped to such 5-bit sequences?

Table 2.2

Table 2.2 4B/5B 4-bit data symbol 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 encoding. 5-bit code 11110 01001 10100 10101 01010 01011 01110 01111 10010 10011 10110 10111 11010 11011 11100 11101