TCP and UDP Transport Level Protocols

Comprehensive vocabulary flashcards covering the UDP and TCP protocols, including header structures, flags, connection states, and reliability mechanisms based on the lecture notes.

UDP (User Datagram Protocol)

A transport layer protocol specified in RFC $768$ that is datagram-oriented and simple; it does not guarantee delivery or perform flow control, congestion control, or retransmission.

UDP Header Length

A fixed size of $8$ bytes that identifies sending and receiving processes, length, and checksum.

UDP Checksum

An error-checking value calculated on the UDP header and data; though previously optional, it is now mandatory by default according to RFC $1122$.

TCP (Transmission Control Protocol)

A connection-oriented, reliable, and full-duplex transport service specified in RFCs such as $793$, $1122$, and $1323$.

TCP Segment

The formal name for the packets exchanged at the TCP layer.

Sequence number

A $32$-bit field in the TCP header identifying the byte number of the first byte of data in the segment; it wraps to $0$ after reaching $2^{32} - 1$.

ACK number (acknowledgment)

Indicates the next sequence number expected by the sender, equivalent to the sequence number of the last successfully received byte $+ 1$.

Header length (TCP)

A $4$-bit field specifying the number of $32$-bit words in the header, with a maximum value of $60$ bytes ($15 \times 4$).

CWR (Congestion Window Reduced)

A TCP flag used by the transmitter to signal that it has reduced its transmission speed.

ECE (ECN Echo)

A TCP flag used by the sender to confirm receipt of a packet with the Explicit Congestion Notification (ECN) flag enabled in the IP header.

RST (Reset)

A TCP flag used to reset a connection when an incoming packet appears unrelated to the current connection.

SYN (Synchronize)

A TCP flag used to synchronize sequence numbers during the initiation of a connection.

END (FIN)

A TCP flag indicating that the sender has finished its data transmission.

Window size

A TCP header field used for flow control indicating the number of bytes the receiver can accept, with a maximum value of $65,535$ bytes.

MSS (Maximum Segment Size)

The maximum number of data bytes a TCP end should receive to avoid IP fragmentation, calculated as $\text{MTU} - 20 - 20$.

Three-Way Handshake

The protocol used to establish a TCP connection involving a client SYN, a server SYN/ACK, and a final client ACK.

ISN (Initial Sequence Number)

A (pseudo)randomly selected starting sequence number used to prevent 'reincarnation' where old segments are confused with current ones.

TIME_WAIT status

A TCP state where the system waits for $2 \times \text{MSL}$ (Maximum Segment Lifetime) to ensure the final ACK was received and to discard delayed segments.

FIN_WAIT_2 State

A TCP state where one end waits for the final connection closure (END/FIN) from the other end, which remains in the CLOSE_WAIT state.

Urgent pointer

A field valid when the URG flag is set to $1$, indicating an offset to the sequence number used for transmitting priority data.

Window Scale Factor

An option specified in RFC $1323$ that allows the TCP buffer size to be increased to nearly $1$ GB.