1. Communications in Client-Server Systems the details…

2. Communications in Client-Server Systems  Sockets (IPC)  Remote Procedure Calls (RPC)  Pipes (ordinary & named)

3. Communications in Client-Server Systems  Sockets - an endpoint for communication Uses TCP/IP Protocol 2 processes - 2 sockets socket identified as IP address concatenated with port number  telnet: port 23  ftp: port 21 (or 22 secure)  http: port 80 client calls on known port (under 1024) host establishes return port >1024 but <1625 Common/efficient low level communication  unstructured stream of bytes (data) 127.0.0.1 - loopback (used when client & server are on same host)

4. Communications in Client-Server Systems  Remote Procedure Calls (RPC) higher level communication well structured data packet sent to a RPC daemon listening on a specific port output sent back as a separate message utilizes stub (small piece of code that indicates how to locate or load the remote library routine) External Data Representation (XDR) instead of…  big-endian (most significant byte first)  little-endian (least significant byte first) Implementation of call  at most once (time-stamp history – ignore message with later stamp  exactly once (at most once, plus ACK message from server to client)

5. Communications in Client-Server Systems  Pipes a conduit for two processes to communicate Higher level communication file-like (read/write) two types  ordinary  access within parent/child relationship of processes  unidirectional  two pipes are used for bi-directional communication  file closed by both ends – to mark end of file  end of process == end of pipe  named  can exist beyond a process  usually more than 1 “writer”  ½ duplex (UNIX) full duplex (Windows) data transmission