TCPIP in Z/OS

TCP/IP or Transmission Control Protocol/Internet Protocol:

• The TCP protocol is used to interconnect and transfer controls between interconnected peers whereas the IP protocol identifies a host on the internet with its IP address.
• The TCP/IP daemon implements the IP protocol stack which runs a number of IP applications.
• Even though Z/OS is running as an EBCDIC host, communication with ASCII based application is seamless. The primary goal of TCP/IP is to build an interconnection between same or different physical networks using Host, IP address, Router and many other components.
• TCP/IP started tasks drives all IP based activities in Z/OS.
• Once the IP protocol stack is enabled, the TCP/IP profile dataset and TCP/IP data file will utilize the parameters specified for the TCP/IP setup.

Functions of TCP/IP:

• When using TCP/IP, your network of machines share data, processing resources etc,.
• Logon to a remote Host
• Transfer of datasets
• Sending and Receiving Email
• Print on remote printers
• Authenticate network users
• Network monitoring
• Managing network resources

Elements of TCP/IP:

• Host: Every system that is interconnected in a TCP/IP environment is identified as Host.
• Router: A Router interconnects the remote system by sending and receiving data in the form of "Packets".
• Port: It is a 16-bit number which is used by Host-to-Host protocol to identify another process to send its result. Well-known ports range from 1 to 1023 and Ephemeral ports range from 1024 to 65535.
• IP address: An IP address is a 32-bit unsigned binary value but expressed in dotted decimal format. Each IP address is made up of 2 logical address. That is, Network Address(Represents a Physical network in the internet) and Host Address(Represents the individual Host within the physical network).

TCP/IP Layers:

• Physical Layer: It is responsible for the physical transmission of real data.
• Internet Layer: It provides the routing of Datagrams from one computer to anothet using IP protocol.
• Transport Layer: The data is sent as Byte Streams with fragmentation at one end and defragmentation at the other end. The appended bits are used for Packet or Datagram identification. It uses TCP and UDP protocols.
• Application Layer: The higher level protocol used to access internet applications.

Starting TCP/IP Subsystem:

• To start: S TCPIP
• The TCP/IP procedure "EZBTCPIP" is created as part of SYS1.PROCLIB or CPAC.PROCLIB. Now, the TCP/IP configuration files like TCPIVP.TCPPARMS(PROFILE) and TCPIVP.TCPPARMS(TCPDATA) are identified and invoked.
•  TCPIVP.TCPPARMS(PROFILE): It contains HOME and LINK( IP Link and Address Configuration), IPCONFIG (IP Configuration), TCPCONFIG (TCP Configuration), BEGINROUTES (Static Routing Information) and AUTOLOG (Automated IP application monitoring.
• TCPIVP.TCPPARMS(TCPDATA): The TCPDATA contains the name of the started procedure to start the TCP/IP address space, Hostname of the system, Resolver Address resolution etc,.