BitWithBiteCCNA Networking · Quick Reference
Module 14 — Transport Layer Cheat Sheet
In one line: The Transport Layer (Layer 4) sits between the Application Layer and the Network Layer. Its job is to manage the actual transport of data between applications running on source ...
Key Ideas
1Role of the Transport Layer. The Transport Layer (Layer 4) sits between the Application Layer and the Network Layer. Its job is to manage the actual transport of data between applications running ...
2TCP Overview. TCP (Transmission Control Protocol) is a connection-oriented protocol that guarantees reliable, ordered, and error-checked delivery. It is used whenever data integrity...
3UDP Overview. UDP (User Datagram Protocol) is connectionless and provides no reliability, ordering, or flow control. It simply sends datagrams and moves on — making it far faster an...
4Port Numbers. Port numbers let a single IP address support many simultaneous conversations. Combined with the IP address, a port number forms a socket — and a pair of sockets (sourc...
5TCP Communication Process. Before any data flows, TCP establishes a session with the three-way handshake — a synchronized exchange that confirms both sides are ready and agrees on starting seque...
Code Examples
Key TCP header fields:
Source Port 16 bits — identifies sending application
Destination Port 16 bits — identifies receiving application
Sequence Number 32 bits — tracks byte order for reassembly
Acknowledgment Number 32 bits — next byte the ...
UDP header — only 4 fields, 8 bytes total:
Source Port 16 bits
Destination Port 16 bits
Length 16 bits — size of header + data
Checksum 16 bits — error detection only, no recovery
Socket = IP address : Port number
192.168.1.10:51422 (client socket — random high port)
93.184.216.34:443 (server socket — well-known HTTPS port)
Socket Pair = source socket + destination socket — uniquely identifies ONE conversation
192.168.1.10...