takes message, breakws message into smaller packets. Transmits packet into access network at transmissin rate of R.

Packet transmission delay = time needed to transmit L-bit packet into link = L (bits) / R(bits / sec)

bit progates between transmitter / receiver pairs physical link - what lies between transmitter and receiver

guided media = something that you can physically touch unguided media = signals that travel freely. radio, wifi etc.

twisted pair cables are twisted because it minimises the noise in the cable. You have way less noise with twisted pair.

Cat-6 have a more twisted cable than cat-5.

cable television uses coaxial cables. two concentric copper conductors, a mesh around i.

fiber optic cable

has lower error rate 2 mirrors inside of it which bounce

packt switching

its where it stores and forwards a packet. first we need to receive the whole packet, and then send it again. we use packet switching because one network edge device cannot send it all the way.

sometimes routers get more packets than they can send so they just recover from those.

circuit switching

non persistant connections

whenever you send a request for an object you have ot initiate tcp connection, get object, tcp connection will be closed. non persistant HTTP. every object you have ot initiate a TCP connection. One way to work around is just to open many tcp connections in paraell.

With persistant HTTP you just leave it open. You open a tcp connection, ask for the object and the server does not close the connection.

is there anyway to send a HTTP response without getting a request first?

cookies

header line of HTTP response message Cookie geader line in net http request message

Trans[ort layer

The transport layer provides a logical communication between app processes running on different hosts. We don’t have to care how the network looks like. If we send it out this layer it’ll come onthe other side.

how demultiplexing works

host receives IP datagrams each datagram has source IP address, detination IP address each datagram carries on transport layer segment each segment has source destination portnumber