TCP/IP Protocol Suite Facts

Groups of protocols (called protocol suites or protocol stacks) are designed to interact and be used together. The TCP/IP protocol suite is used on the Internet and on most networks. The TCP/IP protocol suite was developed to work independently of the Physical layer implementation. When learning about TCP/IP protocols, it is common to use a theoretical layered model called the TCP/IP model (also known as the Department of Defense (DoD) model). The layers of the DoD model are as follows:

• The Application layer (also called the Process layer) corresponds to the Session, Presentation, and Application layers of the OSI model.


• The Host-to-host layer is comparable to the Transport layer of the OSI model and is responsible for error checking and reliable packet delivery. Here, the data stream is broken into segments that must be assigned sequence numbers so that the segments can be reassembled correctly on the remote side after they are transported.


• The Internet layer is comparable to the Network layer of the OSI model. It is responsible for moving packets through a network. This involves addressing of hosts and making routing decisions to identify how the packet transverses the network.


• The Network Access layer corresponds to the functions of the Physical and Data Link layers of the OSI model. It is responsible for describing the physical layout of the network and how messages are formatted on the transmission medium. Sometimes this layer is divided into the Network Access and the Physical layer.

The following table lists several protocols in the TCP/IP protocol suite.

Protocol	Description	OSI Model Layer(s)	DoD Model Layer
File Transfer Protocol (FTP)	provides a generic method of transferring files. It can include file security through usernames and passwords, and it allows file transfer between dissimilar computer systems.	Application, Presentation, Session	Application Process
Trivial File Transfer Protocol (TFTP)	Transfer files between a host and an FTP server. However, it provides no user authentication and uses UDP instead of TCP as the transport protocol.	Application, Presentation, Session	Application Process
Hypertext Transfer Protocol (HTTP)	Used by Web browsers and Web servers to exchange files (such as Web pages) through the World Wide Web and intranets. HTTP can be described as an information requesting and responding protocol. It is typically used to request and send Web documents, but is also used as the protocol for communication between agents using different TCP/IP protocols.	Application, Presentation, Session	Application Process
Simple Mail Transfer Protocol (SMTP)	Route electronic mail through the internetwork. E-mail applications provide the interface to communicate with SMTP or mail servers.	Application, Presentation, Session	Application Process
Simple Network Management Protocol (SNMP)	Managing complex networks. SNMP lets network hosts exchange configuration and status information. This information can be gathered by management software and used to monitor and manage the network.	Application, Presentation, Session	Application Process
Telnet Remote Terminal Emulation (Telnet)	allows an attached computer to act as a dumb terminal, with data processing taking place on the TCP/IP host computer. It is still widely used to provide connectivity between dissimilar systems.	Application, Presentation, Session	Application Process
Network File System (NFS)	developed by Sun Microsystems. It consists of several protocols that enable users on various platforms to seamlessly access files from remote file systems.	Application, Presentation, Session	Application Process
Voice Over Internet Protocol (VoIP)	optimized for the transmission of voice through the Internet or other packet switched networks. Voice over IP protocols carry telephony signals as digital audio encapsulated in a data packet stream over IP.	Application, Presentation, Session	Application Process
Domain Name System (DNS)	A system that is distributed throughout the internetwork to provide address/name resolution.	Application, Presentation, Session	Application Process
Transmission Control Protocol (TCP)	Provides connection-oriented services and performs segment sequencing and service addressing. It also performs important error-checking functions and is considered a host-to-host protocol.	Transport	Host-to-Host (Transport)
User Datagram Protocol (UDP)	Not connection-oriented like TCP. Because of less overhead, it transfers data faster, but is not as reliable.	Transport	Host-to-Host (Transport)
Internet Protocol (IP)	The main TCP/IP protocol. A connectionless protocol that makes routing path decisions, based on the information it receives from ARP. It also handles logical addressing issues through the use of IP addresses.	Network	Internet
Internet Control Message Protocol (ICMP)	ICMP works closely with IP in providing error and control information that helps move data packets through the internetwork.	Network	Internet
Internet Group Membership Protocol (IGMP)	Define host groups. All group members can receive broadcast messages intended for the group (called multicasts). Multicast groups can be composed of devices within the same network or across networks (connected with a router).	Network	Internet
Address Resolution Protocol (ARP)	used to get the MAC address of a host from a known IP address. ARP is used within a subnet to get the MAC address of a device on the same subnet as the requesting device.	Network	Internet
Reverse Address Resolution Protocol (RARP) Bootstrap Protocol (BOOTP)	Both BOOTP (Bootstrap Protocol) and RARP are used to discover the IP address of a device with a known MAC address. BOOTP is an enhancement to RARP, and is more commonly implemented than RARP. As its name implies, BOOTP is used by computers as they boot to receive an IP address from a BOOTP server. The BOOTP address request packet sent by the host is answered by the server.	Network	Internet
Dynamic Host Configuration Protocol (DHCP)	simplifies address administration. DHCP servers maintain a list of available and assigned addresses, and communicate configuration information to requesting hosts. DHCP has the following two components. * A protocol for delivering IP configuration parameters from a DHCP server to a host * A protocol specifying how IP addresses are assigned	Network	Internet
Open Shortest Path First (OSPF)	A route discovery protocol that uses the link-state method. It is more efficient than RIP in updating routing tables, especially on large networks.	Network	Internet
Routing Information Protocol (RIP)	A route discovery protocol that uses the distance-vector method. If the network is large and complex, OSPF should be used instead of RIP.	Network	Internet