Here's all you need to know on TCP/IP

Here's all you need to know on TCP/IP

Mail's in'and the transport protocols delivered it and doublechecked that it arrived uncorrupted

By Carlos A. Soto

GCN Staff

TCP/IP. It stands for Transmission Control Protocol/Internet Protocol. You've heard of it. You probably use it every day. But do you know how TCP/IP works?

To get on and navigate the Internet, your computer needs an IP address. Once you have an IP address, you use TCP/IP to surf the Web. But how?

A thorough explanation requires a little background. So, let's go back a few decades.

In 1969 and 1970, programmers created the first computer language that let computers communicate. The Defense Advanced Research Projects Agency came up with the Network Control Protocol. It used NCP in the Internet's prototype, the Advanced Research Projects Agency Network, which is better known as Arpanet.

Cold War baby



Arpanet was the first major WAN to link large universities, research labs and Defense Department facilities. It's no surprise that Arpanet was born during the Cold War. Its creators wanted a resilient form of communication, something that could survive a nuclear attack.

From Arpanet came an Internet test bed comprised of researchers at the University of California at Los Angeles, Stanford University and the University of Utah.

Around that time, DARPA began issuing requests for comments on a host of new technologies.

The results of the RFCs quickly formed the basis for the standards that would define the Internet as we know it today.

Every standard received an RFC number. For example, the File Transfer Protocol, which in 1973 established a method for the transport of large data files across a network, is RFC-454.

Today things work a bit differently. The Internet Engineering Task Force, formed in 1990 as an international group that creates and maintains Internet rules and standards as part of the Internet Society and the Internet Architecture Board, uses RFCs to create rules and standards for the Net.

The task force, society and board consist of designers, vendors, network engineers and programmers in the computer industry from around the world. They review RFCs constantly and consider them for adoption as Internet standards.

But how did TCP/IP evolve from Arpanet, RFCs and the Internet test bed?

In 1974, DARPA implemented the Transmission Control Protocol, RFC-793, as a durable and reliable method to connect two hosts or computers across Arpanet to transmit information.

TCP is one of two Internet transport protocols. The second is the User Datagram Protocol, RFC-768. TCP and UDP serve different purposes. TCP is reliable, more intricate and good for communications across vast heterogeneous networks.

UDP is not as reliable, less complex and better for use across LANs and Ethernet infrastructures.

After TCP creates a bridge between the computer sending the data and the computer receiving the data, the protocol cuts the data into segments.

TCP categorizes the segments by assigning each one a number. Assigning numbers increases the likelihood of the data being received. The receiving computer sends an acknowledgment message confirming the successful delivery of all of the segments.

If some segments don't arrive, the receiving computer doesn't send an acknowledgement and the sending computer retransmits the package.

Likewise, if the receiving computer gets corrupted data, it withholds the acknowledgement and the sending computer retransmits the data.

UDP doesn't perform segmenting or acknowledgement functions. As a result, UDP is a lot simpler and sometimes a lot quicker than TCP. Two applications that use UDP are the Networking Basic Input Output System and the Simple Network Management Protocol.


What's in the OSI stack?
'Layer 7: The applications layer includes functions for specific services such as file transfer and remote file access.

'Layer 6: The presentation layer manages the way data looks and how it is encoded from one system to another.

'Layer 5: The session layer manages the dialogue for the transport layer.

'Layer 4: The transport layer establishes rules for information exchange and provides error detection and recovery.

'Layer 3: The network layer establishes routes between stations across networks.

'Layer 2: The data link layer handles node-to-node transfers, putting data into frames.

'Layer 1: The physical layer deals with the electrical, mechanical and functional aspects of the physical medium.


I think of TCP as comparable to the FedEx or UPS delivery person. TCP is out in the field taking the packages of data from one place to another.

TCP communicates across a WAN effectively. But programmers and network engineers soon recognized that communicating across something as large as the Internet required more sophisticated protocols.

In 1981, a group of programmers developed the Internet Protocol, RFC-791, as a simple way to package information for Internet transfer.

IP is not as reliable as TCP; it does not guarantee delivery or acknowledge whether data has been received or corrupted. Instead, IP deals with routing and addressing.

IP is one of four major networking protocols. It doesn't establish a connection with the receiving computer before sending out data; it relies on finding the computer's IP address, a set of four numbers equaling 32 bits'you've seen these numbers'such as 123.45.67.8.

IP searches for the target address in routers or centralized devices that contain other LANs' IP addresses.

Three partners

The three other major network protocols have easier jobs than IP. The Address Resolution Protocol (ARP) obtains the hardware addresses of computers on the same network. The Internet Control Message Protocol (ICMP) focuses on relaying reports regarding data deliveries. And the Internet Group Management Protocol supports multicast routing.

Think of IP as the shipping service representative who processes and establishes a connection between the address of where the package is coming from and the address of where the package is going.

You could use this UPS or FedEx analogy when describing both TCP and IP, but it is a little more complicated, especially when it comes to describing how the two work together.

TCP and IP make up two of the seven layers of Internet communications topology that comprise the Open Systems Interconnection model.

The OSI model is simple to understand. After you write an e-mail message and click Send, for example, the data goes through seven layers, or steps, on the way to its destination.

The TCP/IP suites are in layers 3 and 4. These are the only Internet-specific layers of OSI. Layers 1 and 2 involve physical and node information. Layers 5 and 6 deal with messaging dialogues and data presentation. Finally, Layer 7 handles specific services such as remote file transfer.

As mentioned already, TCP and UDP are transport protocols and lie in OSI's transport layer, Layer 4. IP, ARP and ICMP handle Internet routing and so lie in the network layer, Layer 3.

TCP and IP are clumped together because they are the only layers of the OSI model that specifically deal with Internet transmissions. These protocols are essential to making data mesh and systems interact. But when it comes down to it, without TCP and IP, there is no Internet.

Because of the crucial nature of layers 3 and 4, work on TCP/IP enhancements has continued practically unabated since the Net's earliest days. The Internet Engineering Task Force has repeatedly upgraded TCP/IP and approved new versions.

Most recently, the task force has had to deal with the rapid growth of Net traffic. And more growth is likely as wireless technologies seek to use the Internet as a communications medium.

All the 32-bit number combinations to delineate computers on the Internet are running out, the same problem many telephone companies have had with phone numbers.

Net developers also want to bolster the security of transactions to protect them from hackers and viruses.

To deal with these issues, the Internet Society has created a new IP version. IP Version 6, RFC-1752, features an enhanced 128-bit addressing scheme and includes the Autoconfiguration Protocol.

The new 128-bit addresses will enhance security and create billions of new numbering combinations.

The autoconfiguration will assign computers and other devices permanent IP addresses automatically.

But it will take some time for users to convert to the IPv6 because of the costs of migrating to new software and hardware. For now, many users will stick with the earlier version, IP Version 4.

Essentially, the components of TCP/IP make communication over an immense, virtually heterogeneous environment possible. The protocols represent the language of the Internet.

inside gcn

  • When cybersecurity capabilities are paid for, but untapped

Reader Comments

Please post your comments here. Comments are moderated, so they may not appear immediately after submitting. We will not post comments that we consider abusive or off-topic.

Please type the letters/numbers you see above