Analogue circuit, electrical bits of information diversion by switches
if the communication is not frequent, packetise the communication/ everything we do almost packetised technology
what inside of packet:
address, information, size, number of packet
In the past, switching happened in physical layer yet we nowadays happen in server clients layers.
physical layer analyser for SPI:
physical layer sends always pulse and convert into ascii etc..
Public Switch Telephone network:PSTN
Session= agreed …HTTP/ session happens over socket
network connections: what port we connect to? port No.
if we see a mail, socket can be like 442, program listening inbound message
Serial ; only one to one communication