Socket type

The second parameter on a socket call determines the socket type. Socket type provides the type identification and characteristics of the connection that are enabled for data transportation from one machine or process to another.

The system supports the following socket types:

Stream (SOCK_STREAM)

This type of socket is connection-oriented. Establish an end-to-end connection by using the bind(), listen(), accept(), and connect() APIs. SOCK_STREAM sends data without errors or duplication, and receives the data in the sending order. SOCK_STREAM builds flow control to avoid data overruns. It does not impose record boundaries on the data. SOCK_STREAM considers the data to be a stream of bytes. In the IBM i implementation, you can use stream sockets over Transmission Control Protocol (TCP), AF_UNIX, and AF_UNIX_CCSID. You can also use stream sockets to communicate with systems outside a secure host (firewall).

Datagram (SOCK_DGRAM)

In Internet Protocol terminology, the basic unit of data transfer is a datagram. This is basically a header followed by some data. The datagram socket is connectionless. It establishes no end-to-end connection with the transport provider (protocol). The socket sends datagrams as independent packets with no guarantee of delivery. You might lose or duplicate data. Datagrams might arrive out of order. The size of the datagram is limited to the data size that you can send in a single transaction. For some transport providers, each datagram can use a different route through the network. You can issue a connect() API on this type of socket. However, on the connect() API, you must specify the destination address that the program sends to and receives from. In the IBM i implementation, you can use datagram sockets over User Datagram Protocol (UDP), AF_UNIX, and AF_UNIX_CCSID.

Raw (SOCK_RAW)

This type of socket allows direct access to lower-layer protocols, such as Internet Protocol (IPv4 or IPv6) and Internet Control Message Protocol (ICMP or ICMP6). SOCK_RAW requires more programming expertise because you manage the protocol header information used by the transport provider. At this level, the transport provider can dictate the format of the data and the semantics that are transport-provider specific.