Which element stores per-connection state, sequence numbers, and timers within the TCP stack?

• A. Transport Control Block
• B. TLS session
• C. DNS cache
• D. AR Receiver Table

Answer: (A)

In TCP, the per-connection state, including sequence numbers and timers, is stored in the Transmission Control Block, often called the Transport Control Block. This data structure holds all the essential details for a single TCP connection: the send and receive sequence numbers, the acknowledgment numbers, window sizes, and the various timers (such as retransmission and persistence timers). It also tracks the current connection state (like SYN_SENT or ESTABLISHED) and is created when a connection starts and torn down when it ends. This organization keeps each TCP connection’s information isolated and actively managed.

TLS sessions are about encryption and security state for a connection, not the core TCP connection management. DNS cache stores hostname-to-IP mappings for lookups, not per-connection sequencing or timers. AR Receiver Table isn’t a standard TCP concept either. So the Transmission Control Block best fits the role described.