TCP

TCP Flow and Congestion Control

Distinguish TCP's receiver-driven flow control from its network-driven congestion control mechanisms.

The TCP/IP Model

Learn the 4-layer TCP/IP model and how it maps to the 7 OSI layers.

The TCP Three-Way Handshake

Trace how TCP establishes a reliable connection using the SYN, SYN-ACK, and ACK exchange.

TCP vs UDP

Compare TCP and UDP across reliability, ordering, connection state, overhead, and typical use cases.

Difference Between TCP and UDP

TCP is a connection-oriented transport protocol that guarantees reliable, ordered, error-checked delivery through a handshake and acknowledgements, while UDP i…

What is the TCP Three-Way Handshake?

The TCP three-way handshake is the process a client and server use to establish a reliable connection before exchanging data: the client sends a SYN, the serve…

What is a Socket?

A socket is an endpoint for network communication, uniquely identified by the combination of an IP address, a port number, and a transport protocol (TCP or UDP…

What is a Port in Networking?

A port is a 16-bit number (0–65535) that identifies a specific process or service on a device, letting a single IP address handle many simultaneous network con…

What is the Transport Layer (OSI Layer 4)?

The Transport layer is OSI Layer 4 — it manages end-to-end communication between applications on two hosts, using port numbers to distinguish processes and pro…

What is Telnet?

Telnet is an application-layer protocol that provides a text-based, interactive terminal session to a remote host over TCP port 23, sending everything — includ…

What is TCP Flow Control and How Does It Work?

TCP flow control prevents a fast sender from overwhelming a slower receiver by having the receiver advertise how much buffer space it currently has left, via t…

What is TCP Congestion Control?

TCP congestion control is the set of sender-side algorithms that limit how much data is put into the network at once, using a congestion window (cwnd) that gro…

What is TCP Slow Start?

TCP slow start is the initial phase of congestion control where a new (or recovering) connection begins sending with a small congestion window and roughly doub…

What is TCP Window Scaling?

TCP window scaling is a negotiated option (RFC 7323) that lets both endpoints multiply the 16-bit window size field by a power of two, expanding the effectivel…

What is the Nagle Algorithm and When Should You Disable It?

Nagle’s algorithm is a TCP send-side optimization that buffers small outgoing segments and coalesces them into one larger segment instead of firing off many ti…

What is TCP Fast Retransmit?

TCP fast retransmit is a loss-recovery mechanism where a sender resends a segment as soon as it receives three duplicate ACKs for it, instead of waiting for th…

What is the TCP FIN Handshake (Connection Teardown)?

The TCP FIN handshake is the four-step process used to gracefully close a connection: each side independently sends a FIN to signal it has no more data, and th…

What is TCP Keepalive and How Does It Work?

TCP keepalive is an optional mechanism where an idle connection periodically sends a small probe segment to check whether the peer is still reachable and the c…

What is a SYN Flood Attack?

A SYN flood is a denial-of-service attack that sends a large number of TCP SYN segments, often with spoofed source addresses, to exhaust a server's connection…

TCP vs SCTP: What Is the Difference?

TCP is a single-stream, byte-oriented, reliable transport protocol, while SCTP (Stream Control Transmission Protocol) is a message-oriented transport that supp…

What is HTTP Keep-Alive?

HTTP Keep-Alive is a mechanism that reuses a single TCP connection for multiple HTTP requests and responses instead of opening a new connection for every reque…

What is Port Scanning?

Port scanning is the technique of systematically probing a target host’s TCP or UDP ports to discover which ones are open, closed, or filtered, revealing what…

Bandwidth vs Throughput: What is the Difference?

Bandwidth is the theoretical maximum data rate a link can carry, usually stated in bits per second, while throughput is the actual data rate achieved in practi…

What is Packet Loss?

Packet loss is the failure of one or more transmitted packets to reach their destination, caused by congestion, faulty hardware, signal interference, or a rout…

What is netstat?

netstat is a command-line utility that displays active network connections, listening ports, routing tables, and per-protocol statistics on a host, making it a…

What is Wireshark?

Wireshark is a free, open-source network protocol analyzer that captures traffic passing through a network interface and lets an engineer inspect every packet…

What is a Network Socket vs a Port?

A port is just a 16-bit number (0-65535) identifying an application or service on a host, while a socket is the full combination of protocol, source IP, source…

What Are Ephemeral Ports?

Ephemeral ports are short-lived, dynamically assigned source port numbers, typically drawn from the range 49152-65535 (or 32768-60999 on Linux), that an operat…