Layered TCP / IP protocol

TCP / IP protocol family is a family of protocols with different protocol combinations thereof. Although commonly referred to as the protocol suite TCP / IP, but TCP and IP is just one of only two protocols (another name for the protocol suite is I nternet protocol suite (Internet Protocol Suite)).

TCP / IP is generally considered to be a four-layer protocol system as 1--1 in FIG.




Each layer is responsible for different functions:

1) Link layer , sometimes called the data link layer or the network interface layer, typically includes an operating system, device drivers and a corresponding computer network interface card. They are processed together with details of the physical interface cable (or any other transmission medium) is.

2) the network layer , sometimes called the Internet layer processes the packet in the network, for example, routing of the packet. In the TCP / IP protocol suite, including the network layer protocol IP protocol (Internet Protocol), ICMP protocol (I nternet Internet Control Message Protocol), and IGMP protocol (I nternet Group Management Protocol).

3) transport layer mainly provides end to end communication application on both hosts. In the TCP / IP protocol suite, there are two different transmission protocols: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

          TCP provides a highly reliable data communication to two hosts. All it does it comprises the application to the appropriate data into small blocks to the network layer below, acknowledgment packets received, provided the final confirmation packet transmission timeout clock or the like. Since the end of the transport layer provides a highly reliable communication, the application layer can ignore all these details. On the other hand, UDP, compared with the application layer provides a very simple service. It just transmitted packet is called datagrams from one host to another host, but does not guarantee that the packets reach the other end. Any required reliability must be provided by the application layer.

4) The application layer is responsible for handling specific application details. Almost a variety of TCP / IP implementation The following are some common applications:

• Telnet remote login.

• FTP file transfer protocol.

• SMTP Simple Mail Transfer Protocol.

• SNMP Simple Network Management Association.



Suppose there are two hosts in a local area network (LAN) such as Ethernet, both running FTP protocol, Figure 1 - 2 lists all the protocols involved in the process.


Here, we list a FTP client and FTP server to another program. Most web applications are designed to the client - server model. Server to provide customers with a service, is the file server resides on the host access in this case. In the telnet application Te lnet, the service is offered to customers log on to the server host.

On the same layer, or a plurality of protocols on both sides corresponding to communicate. For example, a TCP layer protocol to allow communication, while the other two IP protocol allows a communication layer.

In Figure 1 - Right 2, we note that the application process is usually a user, and the next three are generally executed (OS) kernel. Although this is not required, but usually are handled this way, for example, the UNIX operating system.

In Figure 1 - 2, there is another key difference between the top and the next three. The application layer is concerned with the details of the application, rather than the data transfer activity in the network. Under the three-tier application ignorant, but they want to deal with all the

Communication details.

It lists the four different protocol levels in 2 - 1 in FIG. FTP is an application layer protocol, TCP is a transport layer protocol, IP is a network layer protocol, and an Ethernet link layer protocol is applied. 


Network layer and the transport layer

Figure 1 - Internet 3 is a network comprising two of: an Ethernet and a token ring network, interconnected by a router. While there are only two hosts communicate through a router, virtually any host Ethernet network can communicate with any host in the token ring.

In Figure 1 - 3, we can divide the end-system (End system) (both sides of the two hosts) and intermediate systems (Intermediate system) (an intermediate router). Application layer and the transport layer is formed using end (En d - to - end) protocol. In the figure, only the end systems need two layers protocol. However, the network layer is provided hop (Ho p - by - hop) protocol, each of the two end systems and intermediate systems have to use it.


In the TCP / IP protocol suite, IP network layer provides an unreliable service. That is, it is only as fast as the packet from the source node to the destination node, but does not provide any guarantee reliability. On the other hand, TCP provides a reliable transport layer on the unreliable IP layer. To provide this reliable service, TCP retransmission timeout mechanism uses a transmission and reception end acknowledgment packet or the like. Thus, the transport and network layers are responsible for different functions.


TCP / IP protocol suite of protocols:


        Send and receive UDP datagrams application. It refers to a datagram one information unit (e.g., a certain number of bytes of information specified by the sender) transmitted from the sender to the recipient. But the difference is that TCP, UDP is not reliable, it can not guarantee that packets reach their ultimate goal of safe and correct manner. SNMP also uses the UDP protocol.

        IP is the main protocol on the network layer, while being TCP and UDP. Each TCP and UDP data are transmitted via the Internet in the terminal and IP layers of each intermediate router. In Figure 1 - 4, we present an application to directly access the IP. This is rare, but it is also possible (some older routing protocol is implemented in this way. Of course, the new transport layer protocol is also possible to use in this way).

        ICMP protocol IP protocol is a subsidiary. IP layer it with other hosts or routers to exchange error messages and other important information. Although ICMP mainly use IP, but the application is also possible to access it. We will analyze two popular diagnostic tool, P ing and Tr aceroute, they all use ICMP.

        IGMP is I nternet Group Management Protocol. It is used to a UDP datagram multicasting to multiple hosts.

        ARP (Address Resolution Protocol) and the RARP (Reverse Address Resolution Protocol) protocol is a certain special network interface (such as Ethernet and Token Ring) used for converting the IP layer address and network interface layer used.

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