TCP Servers - andrewkyllo-401-advanced-javascript/seattle-javascript-401d34 GitHub Wiki

Event Queues

• All objects that emit events in NodeJS are instances of the EventEmitter constructor
• Functions can be registered as listeners for an event on instances of the EventEmitter class

OSI Model

• Open Systems Interconnection Reference Model
• A seven layer model developed to describe the different processes in computer networking

Internet Protocol Suite

• A conceptual model for the protocols used by the internet.
• Also known as TCP/IP. Described using 4 layers: Link, Internet, transport, and application.

TCP (Transmission Control Protocol)

• Widely used by application layer protocols in the internet protocol suite.
• Creates a two way communication between two hosts and procides reliable, ordered, and error checked byte streams between applications
• Data transfers manage network congestion and use flow control to limit the rate a sender transfers data to guarantee reliable delivery.
• Each IP packet between the hosts carries a single TCP segment
• A TCP segment is made up of header and data sections

TCP Header

Used at each end to control the type of interaction being sent.

Byte 0: Source port
Byte 3: Destination port
Byte 4: Sequence number
Byte 8: Acknowledgement number
Byte 12: Data Offset, NS flag, and 3 undefined bits
Byte 13: CWR, ECE, URG, ACK, PSH, RST, SYN, and FYN flags
Byte 14: Window size
Byte 16: Checksum
Byte 18: Urgent pointer
Byte 20: Options

Connection Establishment

• The client sends a SYN packet with a random initial sequence number.
• The server sends a SYNACK packet with the acknowledgment number set to one more than the initial sequence number
• The client responds with an ACK and an acknowledgment number increment by one

Connection Termination

• One end sends a FIN Segment and the other sends an ACK segment followed by a FIN segment.
• The termination initiation will then respond with an Ack segment