What is the size of the TCP sequence number field?

What is the size of the TCP sequence number field?

• A. 32 bits
• B. 16 bits
• C. 64 bits
• D. 128 bits

Answer: (A)

TCP uses a 32-bit sequence number field to label the position of each byte in the data stream. That means the sequence space runs from 0 up to 2^32 minus 1, allowing roughly 4 billion bytes per connection before the numbers wrap around. When the maximum is reached, the numbers wrap to zero and TCP comparisons are done using modular arithmetic to keep the ordering correct. This size strikes a practical balance: it provides a large enough range for typical connections while keeping the header compact. A 16-bit field would cap at about 64 KB, which would severely limit long-lived connections, while 64- or 128-bit fields would be unnecessarily large and waste header space.

TCP uses a 32-bit sequence number field to label the position of each byte in the data stream. That means the sequence space runs from 0 up to 2^32 minus 1, allowing roughly 4 billion bytes per connection before the numbers wrap around. When the maximum is reached, the numbers wrap to zero and TCP comparisons are done using modular arithmetic to keep the ordering correct. This size strikes a practical balance: it provides a large enough range for typical connections while keeping the header compact. A 16-bit field would cap at about 64 KB, which would severely limit long-lived connections, while 64- or 128-bit fields would be unnecessarily large and waste header space.