This document discusses network communication and server architecture. It covers TCP/IP protocols like IP, UDP, and TCP. It describes how TCP connections are established and terminated. Sockets are introduced as the interface for processes to communicate over TCP. Simple client and server code is shown using sockets. Common server models like prefork and threads with select are explained. The concepts of wait states, I/O multiplexing, server load, and throughput are defined in relation to handling multiple connections efficiently.

1. June 2016
NETWORK
COMMUNICATION

2. NETWORK COMMUNICATION
TCP/IP
SOCKETS
CLIENTS AND SERVERS
WAIT STATES
MULTIPLEXING
SERVER LOAD AND THROUGHPUT

3. TCP/IP
TCP/IP comprises multiple protocols
Link Layer
IP – Internet Protocol
UDP – User Datagram Protocol
TCP – Transmission Control Protocol

4. Transport Layer TCP and UDP
UDP – Connectionless Datagram Protocol
(used for DNS, BOOTP and others)
TCP – Connection Oriented Protocol
(HTTP, HTTPS, MySQL, etc)

5. TCP Connections
Connection Establishment
Client SYN ; Sever SYN + ACK ; Client ACK
ISNs – packet sequencing
Inbuilt checksums
Connection Termination
FIN ; FIN + ACK

6. Sockets
Sockets are how processes communicate over
TCP
Similar to Files: read(), write()
Sockets can be passed like file descriptors
Socket creation handled by kernel

7. Simple TCP Client
Create Socket
Connect
Read / Write
Close

8. Simple TCP Server
Create Socket
Bind
Listen
Accept
Read / Write
Close

9. TCP Server Models
Listen, Accept, Read and Write are all Blocking
Handling Multiple Blocking I/O Calls:
Fork
Prefork
Threads with Select

10. Process Models
Apache httpd and MySQL with Prefork

11. Process Models
Nginx with threads, php-fpm

12. I/O and Wait States
Shh! Don't wake them!
CPUs are faster than I/O

13. I/O Multiplexing
On a process scale: 1 process, many sockets
On a server scale: 1 server, many sockets
Kernel: Distribute active connections to
processes
Processes: Handle requests, make calculations,
return responses, close sockets

14. I/O Multiplexing
There must be enough processes to handle the
I/O
There must be enough CPU to handle the
processes

15. Server Load
CPU Load
=
Number of processes running
+
Number of processes waiting for CPU

16. Throughput
Number of requests handled per minute
=
Function of
server load,
processing efficiency,
related I/O,
connection overhead

17. Bibliography
TCP/IP Illustrated
(2 volumes)
Unix Network Programming
(2 volumes)
W. Richard Stevens