TCP/IP and sockets

• ATNL - Application, Transport, Network, Link
• Transport/TCP/IP: the 'handler' - Tracks receipt validity and order, resending etc.
• Network/IP: Deals with the routing
• TCP and IP both add headers to the packets for the respectibe layers on the otherside
• There are limited amount of sockets. Some are public service designated but eg. port 80 - HTTP is outdated due to HTTPS
• MAC addresses are globally unique, permanent for each device/NIC
• IP addresses are assigned by the network
• ports/sockets are used so an application doesn't have to deal with coms that are irrelevant to it
• IP class A: N.X.X.X - 16mil hosts (50% overall)
• IP class B: N.N.X.X - 25% of all, 65k hosts
• IP class C: N.N.N.X - 16+mil availble, only 254 hosts
• Home broadband - uses reusable IP addresses from which the traffic is combined into one channel to the outside world, but these can only be used in local networks
• Server socket - sets a socket on which to wait for some coms serverside
• Use print streams and buffered readers to generate output and read input raw across sockets
• Once server socket senses request, generate a socket connection based on the client socket (Socket object as ServerSocket.accept() in java)
• The server will listen on a specific port. When a server is listening on a port it is bound to it. Only one server (or process) on a machine can be listening on a certain port.

  The client will connect to a machine via a client socket, which will specify the the port to send to (the same one).
• Use threads to handle requests simultaneosly and not have to wait
• Threads cause the typical expected side effects - race conditions, bad interleaving interactions
• socket = IP and port#