The Network Interface layer also called the Network Access layer that handles
placing TCP/IP packets on the network medium and receiving TCP/IP packets off the
network medium. TCP/IP was designed to be independent of the network access
method, frame format, and medium. In this fashion, TCP/IP can be used to connect
differing network types and these include local area network (LAN) media such as
Ethernet and Token Ring and also WAN technologies such as X.25 and Frame Relay.
The network interface layer encompasses the data link and physical layers of the OSI
model.
Internet Layer
The Internet layer handles addressing, packaging, and routing functions. The core
protocols of the Internet layer are IP, ARP, ICMP, and IGMP.
• The Internet Protocol (IP) is a routing protocol that handles IP addressing,
routing, and the fragmentation and reassembly of packets.
• The Address Resolution Protocol (ARP) handles resolution of an Internet layer
address to a Network Interface layer address, such as a hardware address.
• The Internet Control Message Protocol (ICMP) handles providing diagnostic
functions and reporting errors due to the unsuccessful delivery of IP packets.
• The Internet Group Management Protocol (IGMP) handles management of IP
multicast group membership.
The Internet layer is similar to the Network layer of the OSI model.
Transport Layer
The Transport layer handles and provides session and datagram communication
services to Application layer. The core protocols of the Transport layer are
Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP).
• TCP provides a one-to-one, connection-oriented, reliable communications
service. TCP handles the establishment of a TCP connection, the sequencing and
acknowledgment of packets sent, and the recovery of packets lost during
transmission.
• UDP provides a one-to-one or one-to-many, connectionless, unreliable
communications service. UDP is used when the amount of data to be transmitted
is small (such as data that fits into a single packet), when you do not want the
overhead of establishing a TCP connection, or when the applications or upper
layer protocols provide reliable delivery.
The TCP/IP Transport layer is similar to the Transport layer of OSI model.
Application Layer
The application layer provides services for an application program to ensure that
effective communication with another application program in a network is possible.
The application layer is not the application itself that is doing the communication, but
with various application layer protocols.
The most widely known Application layer protocols are those used for the exchange
of user information:
• The Hypertext Transfer Protocol (HTTP) is used to transfer files that make up the
Web pages of the World Wide Web.
• The File Transfer Protocol (FTP) is used for interactive file transfer.
• The Simple Mail Transfer Protocol (SMTP) is used for the transfer of mail
messages and attachments.
• Telnet, a terminal emulation protocol, is used for logging on remotely to network
hosts.
Additionally, the following Application layer protocols help facilitate the use and
management of TCP/IP networks:
• The Domain Name System (DNS) is used to resolve a host name to an IP address.
• The Routing Information Protocol (RIP) is a routing protocol that routers use to
exchange routing information on an IP internetwork.
• The Simple Network Management Protocol (SNMP) is used between a network
management console and network devices (routers, bridges, intelligent hubs) to
collect and exchange network management information.
The TCP/IP Application layer encompasses the responsibilities of the Session,
Presentation, and Application layers of OSI model.
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