client must contact server
client contacts server by creating TCP socket, specifying IP, port number of server.
When client creates socket, TCP client establishes connection to TCP server.
When contacted by client, TCP server creates new socket for server process to communicate with that particular client.
Allows server to talk with multiple clients.
source port number used to distinguish clients.
application viewpoint TCP provides reliable, in-order byte-stream transfer (“pipe”) between client and server.