Module 14 – Transport Layer (Cisco ITN v7.0)

Vocabulary flashcards summarizing key transport layer terms, focusing on TCP, UDP, port numbers, reliability, flow control, and related concepts introduced in Cisco ITN Module 14.

Transport Layer

OSI layer responsible for logical, end-to-end communications between applications on different hosts and for segmenting, reassembling, and managing multiple conversations.

Conversation Multiplexing

Technique that allows multiple application conversations to share the same network resources simultaneously by using port numbers.

Segment

A unit of data encapsulated by the transport layer (TCP) for transmission across a network.

Datagram

A unit of data encapsulated by the transport layer (UDP); sent without establishing a connection.

Transmission Control Protocol (TCP)

Connection-oriented transport protocol that provides reliable, ordered delivery, flow control, and congestion avoidance.

User Datagram Protocol (UDP)

Connectionless, best-effort transport protocol offering minimal overhead and no guaranteed delivery or ordering.

Connection-Oriented Protocol

Protocol that establishes, manages, and terminates a session before data transfer begins (e.g., TCP).

Connectionless Protocol

Protocol that sends data without prior session setup or guaranteed delivery (e.g., UDP).

Stateful Protocol

A protocol, like TCP, that keeps track of the state of the communication session.

Stateless Protocol

A protocol, like UDP, that does not retain session information between messages.

Flow Control

TCP mechanism that adjusts the rate of data transmission so the receiver can process data reliably.

Same-Order Delivery

TCP feature ensuring segments are reassembled in the exact order they were sent.

Sequence Number

32-bit TCP header field used to label bytes for ordered delivery and loss detection.

Acknowledgment Number

32-bit TCP field indicating the next byte the receiver expects, confirming receipt of previous data.

Sliding Window

Dynamic TCP flow-control method in which the receiver advertises how many bytes it can accept.

Initial Sequence Number (ISN)

First sequence number chosen during TCP connection establishment to synchronize byte numbering.

Selective Acknowledgment (SACK)

Optional TCP feature allowing a receiver to acknowledge non-contiguous segments it has successfully received.

Maximum Segment Size (MSS)

Largest amount of TCP payload a host can receive in one segment; commonly 1,460 bytes with IPv4.

Maximum Transmission Unit (MTU)

Largest frame size a network medium can carry; Ethernet MTU is typically 1,500 bytes.

Congestion Avoidance

Set of TCP algorithms and timers designed to reduce transmission rate when network congestion is detected.

Port Number

16-bit value in TCP/UDP headers that identifies the sending or receiving application process.

Well-Known Ports

Port numbers 0–1,023 reserved for common server applications (e.g., HTTP 80, HTTPS 443).

Registered Ports

Port numbers 1,024–49,151 assigned by IANA to specific user or vendor applications.

Dynamic / Ephemeral Ports

Port numbers 49,152–65,535 chosen by a client OS at run time for temporary use in a session.

Socket

Combination of IP address and port number (e.g., 192.0.2.10:80) uniquely identifying one end of a transport-layer conversation.

Socket Pair

Two sockets (source and destination) that together identify a unique TCP or UDP session.

Three-Way Handshake

TCP connection-establishment process using SYN, SYN-ACK, and ACK segments to synchronize sequence numbers and confirm readiness.

SYN Flag

TCP control bit used to synchronize sequence numbers and initiate a connection.

ACK Flag

TCP control bit indicating the Acknowledgment field is significant; used in connection setup and normal data transfer.

FIN Flag

TCP control bit indicating that a sender has finished sending data and wants to terminate the session.

RST Flag

TCP control bit that immediately resets a connection due to error or refusal.

PSH Flag

TCP control bit requesting that data be pushed promptly to the receiving application.

URG Flag

TCP control bit indicating that the Urgent pointer field contains valid data that should be prioritized.

Window Size

16-bit TCP header field advertising how many bytes the receiver can accept without acknowledgment.

TCP Header

Segment header containing source and destination ports, sequence and acknowledgment numbers, flags, window size, checksum, and more; minimum 20 bytes.

UDP Header

Simple 8-byte header containing source port, destination port, length, and checksum fields.

Source Port

Port number identifying the originating application on the sending host in TCP/UDP headers.

Destination Port

Port number identifying the target application on the receiving host in TCP/UDP headers.

netstat

Command-line tool that displays active TCP/UDP connections and listening ports to help diagnose network issues.

Conversation

A single, logical flow of data between two devices identified by a unique socket pair.

Reliability (TCP)

Capability of TCP to ensure complete, accurate data delivery through acknowledgments, retransmissions, and ordered reassembly.

Datagram Reassembly (UDP)

Process by which UDP delivers payload to an application in the order received, without reordering lost or out-of-sequence datagrams.

Best-Effort Delivery

Characteristic of UDP indicating no guarantees of delivery, ordering, or error recovery.