Posted by arlene

TCP/IP was built using a layered approach. You may have heard about the OSI (Open Systems Interconnect or Open Systems Interconnection) Reference model that is used mostly as a framework around which a discussion of network protocols can be discussed. Developed in 1984 by the International Organization for Standardization (ISO), this model defines a protocol stack in a modular fashion, specifying what functions are performed by each module.

For the purposes, it should be noted that development of TCP/IP began long before the OSI model, and, as can be expected, TCP/IP protocols don’t always neatly match up to the seven layers of the OSI model.

The ISO used this model to develop a set of open network protocols, but these were never widely adopted. This was due to several factors. First, at that time many computer vendors held market share by keeping customers locked into proprietary hardware/software solutions. Second, the OSI protocols required a considerable amount of system resources, so it was impractical to try to implement them on smaller computers, such as minicomputers, much less the now-standard PC. However, the OSI networking model is still used today when discussing network protocols, and it is a good idea to become familiar with it if you will be working in this field. TCP/IP was developed based on a similar, though less modular, reference model, the DOD (Department of Defense) or DARPA model.

As you can see, TCP/IP doesn’t exactly fit into the OSI model, but it is still possible to refer to the model when discussing certain aspects of the protocols and services that TCP/IP provides.

TCP/IP Is a Collection of Protocols, Services, and Applications

The acronym TCP/IP stands for Transmission Control Protocol/Internet Protocol. In addition to these two important protocols, many other related protocols and utilities are commonly grouped together and called the TCP/IP protocol suite. This “suite” of protocols includes such things as the User Datagram Protocol (UDP) and the Internet Control Message Protocol (ICMP).

TCP/IP, IP, and UDP

The main workhorses of this protocol suite are IP, TCP, and UDP:

• IP—The Internet Protocol is an unreliable, connectionless protocol that provides the means to get a datagram from one computer or device to another and for internetwork addressing.

• TCP—The Transmission Control Protocol uses IP but provides a higher-level functionality that checks to be sure that the packets that IP manages actually get to and from their intended destinations. TCP is a reliable, connection-oriented protocol, requiring that a session be established to manage communications between two points in the network so that errors can be detected and, if possible, corrected.

• UDP—The User Datagram Protocol also uses IP to move data through a network. Whereas TCP uses an acknowledgment mechanism to ensure reliable delivery, UDP does not. UDP is intended for use in applications that don’t necessarily need the guaranteed delivery service provided by TCP. The Domain Name System (DNS) service is an example of an application that uses UDP. Applications that make use of UDP are responsible for taking on the functions of checking for reliable delivery that is provided by TCP.

IP is the basic protocol used in the TCP/IP suite to get datagrams delivered.

TCP/IP and its related protocols work above the physical components of the network. Therefore, it is easy to adapt TCP/IP to different types of networks, such as Ethernet and Token-Ring. When you talk about using TCP/IP on the network, what it all boils down to is that you’re packaging your data into an IP packet that is passed down to the actual network hardware for delivery. Because IP is the common denominator of the TCP/IP suite, after that shows how the remaining protocols build on the functions provided by IP.

Other Miscellaneous Protocols

In addition to TCP and IP, many other protocols are part of the TCP/IP suite. IGMP and ICMP protocols are included. IGMP is the Internet Group Management Protocol, which is used to manage groups of systems that are members of multicast groups. Multicasting is a technique that allows a datagram to be delivered to more than one destination. Internet Control Message Protocol (ICMP), which performs many functions to help control traffic on a network. In addition to these protocols, other protocols usually considered as part of or associated with the TCP/IP protocol suite include the following:

• ARP—The Address Resolution Protocol. ARP is used by a computer to determine what hardware address is associated with an IP address. This is necessary because IP addresses are used to route data between networks, while communications on the local network segment are done using the burned-in hardware address of the network cards.
• RARP—The Reverse Address Resolution Protocol is similar to ARP but works in reverse. This is an older protocol that was developed to allow a computer to find out what IP address it should use, based on a table stored on a device such as a router. This functionality has generally been replaced by other protocols, such as BOOTP and DHCP. However, you can still find this protocol in use on many networks that contain older legacy equipment that has yet to reach the end of its useful life, such as diskless X-Windows terminals.

• DNS—The Domain Name System is the hierarchical naming system used by the Internet and most TCP/IP networks.

• BOOTP—The Bootstrap Protocol is also an older protocol that has generally been replaced by DHCP. In fact, most DHCP servers can act as BOOTP servers as well. BOOTP was created to allow a diskless workstation to download configuration information, such as an IP address and the name of a server that can be used to download an operating system. Because the diskless workstation has no local storage (other than memory), it can’t store this information itself between boots.

• DHCP—The Dynamic Host Configuration Protocol relieves the network administrator of the task of having to manually configure each computer on the network with static addressing and other information.

• SNMP—TheSimple Network Management Protocol was developed to make managing network devices and computers from a central location easier.
• RMON—TheRemote Monitoring protocol was developed to further enhance the administrator’s ability to manage computers and network devices remotely.

• SMTP—TheSimple Mail Transfer Protocol is the protocol that gets your email from here to there.

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