TCP/IP protocols

TCP/IP is a family of communication protocols used to connect computer systems in a network. It is named after two of the protocols in the family: Transmission Control Protocol (TCP) and Internet Protocol (IP). Hypertext Transfer Protocol (HTTP) is a member of the TCP/IP family.

The protocols in the TCP/IP family correspond, in many cases, to the layers of the Open Systems Interconnection (OSI) model. Table 1 shows HTTP and the underlying layers of the TCP/IP family in terms of the OSI model. The Systems Network Architecture (SNA) layers, which approximately match the OSI layers, are also shown.

Table 1. The layers of the TCP/IP protocol family
7 Application Application HTTP
6 Presentation Presentation (empty)
5 Session Data flow (empty)
4 Transport Transmission TCP
3 Network Path control IP
2 Data link Data link Subnetwork
1 Physical Physical Subnetwork
Internet Protocol (IP)
IP is a network-layer protocol that provides a connectionless data transmission service that is used by TCP. Data is transmitted link by link; an end-to-end connection is never set up during the call. The unit of data transmission is the datagram.
Transmission Control Protocol (TCP)
TCP is a transport-layer protocol that provides a reliable, full duplex, connection-oriented data transmission service. Most Internet applications use TCP.
Hypertext Transfer Protocol (HTTP)
HTTP is an application-layer protocol that is used for distributed, collaborative, hypermedia information systems. HTTP is the protocol used between web clients and web servers.

Many TCP/IP implementations provide an application programming interface to the TCP protocol; that is, to the transport layer. This interface is commonly known as the Sockets interface. The TCP/IP Sockets interface for CICS is the z/OS® Communications Server IP CICS Sockets interface. It is supplied with z/OS Communications Server and is an integral part of z/OS. It is not part of CICS web support and does not use the CICS SO domain. z/OS Communications Server: IP CICS Sockets Guide, SC31-8807, describes the CICS Sockets interface.