Advanced socket concepts

Advanced socket concepts go beyond a general discussion of what sockets are and how they work. They provide ways to design socket applications for larger and more complex networks.

• Asynchronous I/O
  Asynchronous I/O APIs provide a method for threaded client server models to perform highly concurrent and memory efficient I/O.
• Secure sockets
  Currently, i5/OS™ supports two methods of creating secure socket applications on the iSeries™. The SSL_ APIs and Global Secure Toolkit (GSKit) APIs provide communications privacy over an open communications network, which in most cases is the Internet.
• Client SOCKS support
  iSeries™ uses SOCKS version 4 to enable programs that use the AF_INET address family with SOCK_STREAM socket type to communicate with server programs that run on systems outside a firewall.
• Thread safety
  A function is considered threadsafe if you can start it simultaneously in multiple threads within the same process.
• Nonblocking I/O
  When an application issues one of the socket input functions and there is no data to read, the function blocks and does not return until there is data to read.
• Signals
  An application program can request to be notified asynchronously (request that the system send a signal) when a condition that the application is interested in occurs.
• IP multicasting
  IP multicasting allows an application to send a single IP datagram that a group of hosts in a network can receive.
• File data transfer—send_file() and accept_and_recv()
  i5/OS™ sockets provide the send_file() and accept_and_recv() APIs that enable faster and easier file transfers over connected sockets.
• Out-of-band data
  Out-of-band (OOB) data is user-specific data that only has meaning for connection-oriented (stream) sockets.
• I/O multiplexing—select()
  Because asynchronous I/O provides a more efficient way to maximize your application resources, it is recommended that you use asynchronous I/O APIs rather than the select() API. However, your specific application design may allow select() to be used.
• Socket network functions
  Socket network functions allow application programs to obtain information from the host, protocol, service, and network files.
• Domain Name System support
  iSeries™ provides applications with access to the Domain Name System (DNS) through the resolver functions.
• Berkeley Software Distribution compatibility
  Sockets is a Berkeley Software Distribution (BSD) interface.
• UNIX 98 compatibility
  Created by The Open Group, a consortium of developers and venders, UNIX^® 98 improved the inter-operability of the UNIX^® operating system while incorporating much of the Internet-related function for which UNIX^® had become known.
• Descriptor passing between processes—sendmsg() and recvmsg()
  The ability to pass an open descriptor between jobs can lead to a new way of designing client/server applications.