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What is TCP/IP and the Internet Protocol Suite

TCP/IP is a communications protocol that is used on packet switching computer networks. The creation of TCP/IP was funded by DARPA; DARPA was an agency of the U.S. Department of Defense. TCP/IP was coinvented by Bob Kahn and Vint Cerf, who worked for DARPA in the 1970's. TCP/IP became a U.S. Department of Defense standard in 1980, and was originally called: DoD TCP/IP.

DARPA created the Internet Architecture Board (IAB) in 1983 to oversee the evolution of TCP/IP. TCP/IP was applied to a range of U.S. federally funded computer networks in the 1980's, such as: ARPANET, NSFNET, MILNET, ESNET, amongst others. TCP/IP was also used by a range of commercially funded computer networks in the 1980's, such as: CERFnet, PSInet and UUnet.

When TCP/IP computer networks were interconnected in the 1980's, they became the Internet (interconnected networks). From 1992-2014 (present day), oversight and leadership of the Internet Architecture Board (IAB) changed hands: previously DARPA (U.S. federal government), presently the Internet Society (international organisation). TCP and IP are now the core protocols of the Internet protocol suite, and the Internet protocol suite is openly engineered by organisations under charter from the Internet Society.

Development of TCP/IP

ARPA funded the creation of the first American wide area computer networks (ARPANET) in the late 1960's. ARPA were renamed to DARPA in the early 1970's. ARPANET used the Network Control Program (NCP) to traffic data between it's nodes (locations). The Network Control Program (NCP) was written by the computer scientists who created ARPANET, and, therefore, the creation of the Network Control Program (NCP) was funded by DARPA.

Vint Cerf had collaborated in the creation of the Network Control Program (NCP), and Bob Kahn was part of the BBN team which built the routers (IMPs) for ARPANET. DARPA employed Bob Kahn (he previously worked at BBN) in 1972, and Bob Kahn had an idea for a new 'open' network architecture which could replace the Network Control Program (NCP). In 1973, Bob Kahn invited Vint Cerf to help develop his idea into a working protocol. In May, 1974, Bob Kahn and Vinton Cerf published a paper outlining a protocol for packet switching. This paper was a seminal moment in computer networking, and was named: A Protocol for Packet Network Intercommunication.

The first working protocol that Kahn and Cerf developed was called the Transmission Control Program; like it's predecessor, the Network Control Program, it was a single protocol program. Only later was it decided that a fragmented suite of interlinking protocols would be preferable. TCP/IP evolved slowly, being tested on a number of computer networks. TCP/IP eventually became a Department of Defense (DoD) standard in 1980, and was named DoD TCP/IP. While TCP/IP was funded by DARPA and the U.S. Department of Defense, it was implemented on a variety of U.S. federal and commercial networks in the 1980's. TCP/IP was implemented onto ARPANET (replacing NCP) on the 1st of January, 1983.

As the number of TCP/IP computer networks grew in the 1980's, the importance of it's continuing development was apparent. In 1983, DARPA created the Internet Activities Board (IAB) to oversee the development of TCP/IP. The Internet Activities Board (IAB) continue (as of 2014) to oversee the development of TCP/IP, but, leadership of the IAB is no longer provided by DARPA: instead it is provided by the Internet Society. TCP and IP (TCP/IP) are now the core protocols of the Internet protocol suite.

What are TCP and IP

The Internet is basically a system of computer networks that interconnect using a software system named TCP/IP. TCP/IP is comprised of two protocols:

  1. IP - Internet Protocol
  2. TCP - Transmission Control Protocol

The Internet Protocol (IP) defines the structure of data packets (blocks of data sent from one location to another), and creates an address system that can route a data packet from it's host to it's destination. Every device connected to a computer network - that uses TCP/IP - is assigned an IP address. The method of assigning an IP address varies across computer networks; but the format of IP addresses is defined by the Internet Protocol (IP). Data packets sent across these computer networks are formatted by the Internet Protocol. Packets have two sections: a header and it's content. The header includes: the IP address of it's source (host); the IP address of it's destination; and other information that is required to route the packet from it's source to it's destination.

The Transmission Control Protocol (TCP) is classified as a transportation protocol. Services that are designed for the Internet use a range of application protocols, such as: HTTP (World Wide Web), SMTP (Email), POP3 (Email), IMAP (Email), and FTP (Downloading). TCP is the "bridge" or "middle man" between these application protocols and the IP Protocol (IP). TCP helps application protocols send and receive packets of data in a accurate manner: it does this through an ordered transportation procedure that includes error-checking the delivery. While the data will by delivered by the Internet Protocol (IP), TCP ensures the delivery takes place without error.

TCP/IP evolves into the Internet protocol suite

When TCP/IP was developed in the 1970's, the number of Internet protocols was fairly modest. While protocols, like FTP (File Transfer Protocol), had been created to send files across ARPANET, the amount of protocols (services) on the Internet was limited. In the 1980's, when TCP/IP networks began to interconnect - NSFNET, ARPANET, CSNET - more protocols were developed to create gateways and route data between these networks. The DNS protocol was created in the 1980's to more easily locate resources on TCP/IP networks. By the 1990's, due to the popularity of the Internet, new services began to be designed for the Internet, most notable the World Wide Web (e-tailing). By 2000, even more protocols, like Voice-over-Internet Protocols for Voice 2.0 application were designed.

Therefore, there came a point in time that TCP and IP, while being the core protocols of the Internet, did not accurately describe the full collection of Internet protocols. Therefore, instead of being referred to as the TCP/IP protocol suite, the protocols of the Internet were named the Internet protocol suite. Present day (2014), the Internet protocol suite is engineered by the Internet Engineering Task Force (IETF); leadership of the IEFT is provided by the IAB and Internet Society. TCP and IP are still the "core" protocols of the Internet protocol suite; the Internet could not function without them. TCP and IP protocols deal with the "nuts and bolts" processes of the Internet: creating a technical architecture where data can be routed from one address to another.

Core protocols of the Internet protocol suite

  • IP - The Internet Protocol is a network layer protocol that moves data between host computers.
  • TCP - The Transport Control Protocol is a transport layer protocol that moves multiple packet data between applications.
  • UDP - The User Datagram Protocol is a transport layer protocol - like TCP - but is less complex and more reliable than TCP.
  • ICMP - The Internet Control Message Protocol: carries network error messages and other network software requirements.

A computer network does not need to implement all the protocols of the Internet protocol suite to access the Internet, but, at a minimum, it should support the following protocols:

  1. Address Resolution Protocol (ARP)
  2. Internet Protocol (IP)
  3. Internet Control Message Protocol (ICMP)
  4. Internet Group Management Protocol (IGMP)
  5. Transmission Control Protocol (TCP)
  6. User Datagram Protocol (UDP)

Every device that is connected to the Internet is assigned an IP address; the Domain Name System is used to locate IP addresses via domain names. Management of IP address blocks and the Domain Name System is managed by the Internet Assigned Numbers Authority (IANA). Jon Postel, while working at the Information Sciences Institute (ISI), created IANA in 1990 (although it had unofficially operated for over a decade).

TCP and IP (TCP/IP) are the core protocols of the Internet protocol suite. Other Internet protocols - like Telnet, FTP and SMTP - which were originally developed for ARPANET - are also a part of the Internet protocol suite. The Internet protocol suite is based upon a four layer networking model. The Internet's four layer model should not be confused with the OSI seven layer networking model; while there are similarities between the two models, they are different models. For more information about computer networking models: ANSI; Daisy Chain; Extranet's, Intranet's and VPNs.

Four layer model of the Internet protocol suite

The various protocols included in the Internet protocol suite have been classified into four "loosely" defined layers. The four layers are:

  1. Application layer: protocols used by applications designed for users services.
  2. Transport layer: creates a data channel for a specific application.
  3. Internet layer: sends data(packets) across computer networks.
  4. Link layer: moves data between the Internet layers of linked hosts.

The four layers listed above are listed within the correct hierarchy. The application layer refers to the software programs that end-users use on the Internet. For example, HTTP is in the application layer, this is the protocol used on the World Wide Web. The transportation layer helps these applications send and receive data packets across the Internet. Data packets are to sent from, and to, IP addresses. The Internet layer defines the structure of these packets, and the format of IP addresses. The Internet layer also sends the packet with the aid of the transport layer; the transport layer ensures the packets are sent correctly. The link layer moves packets across the physical infrastructure; and supports the physical transmission of the data. Encapsulation is used between the different layers so that they can communicate. TCP, for example, will often encapsulate: HTTP, POP3 and FTP.

Application layer:


Transport layer:


Internet layer:


Link layer:



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