2.2 Architecture of TCP / IP Protocol
TCP / IP level
l application layer
l Host to the host layer or transportation layer
l interconnect mesh
l Network access layer
l Physical layer
Physical Layer defines interfaces between data transmission devices and transport media or networks. This layer involves determination of transmission medium characteristics, signal characteristics, data rate, and related content.
The network access layer is concerned about the data exchange between a terminal system and the network it connects to.
Internet Layer Internet Protocol (IP) is used to provide selection functions over multiple networks at this layer. This protocol is not only implemented in the end system, but also in the router.
Host-to-host layer or transport layer ensures that all data can reach the destination application, and the order of data arrival is the same as the order of transmission. The mechanism to achieve reliable transmission is substantially independent of the characteristics of the application. Therefore, this mechanism is concentrated in a common level so that all applications can be shared. Transmission Control Protocol TCP (Transmission Control Protocol) is the most common protocol that provides this feature.
Application Layer includes the logical functions required to support a variety of user applications. Each of the different types of applications, such as file transfer, requires a separate module dedicated to this application.
TCP / IP work mode
In order to successfully communicate, each entity in the entire system must have a unique address. In fact, we need two levels of addressing. Each of the hosts on the subnet has a unique address in the full internet; this can make the data to the correct host. This address is used for IP selection and delivery of data. Each application on the host must have a unique address on this host; this address enables the host to the Host Protocol (TCP) to deliver data to the correct process. The latter address is called a port.
We can track a simple working process. It is assumed that there is a process to communicate with port 1 on host A, it wants to send a message to a process that communicates with port 2 on host B. The process on the host A is given the packet to the TCP below and allows it to send port 2 on the host B. TCP handed this packet to the following IP and let it send it to host B. We noticed that IP does not have to know the identity of the destination port. IP is just that the data is sent to host B. Next IP will give this message to the network access layer and tell it to send it to the router.
Assume that the transmission process produces a piece of data and handed it over to TCP. TCP may divide this data block into many smaller data blocks to make it easier to manage. For each such small block, you must add a TCP header containing control information, which forms a TCP message section. These control information is used by TCP protocol entities in host B.
The contained possibilities in the TCP head are:
l Dedicated port: When the TCP entity on the host B receives this message, it must know who this report is given.
l Serial number: TCP sequentially collected numbers on a message segment sent to a specific destination port so that the TCP entity on the host B can restore their original order when the report segment is unacceptable.
l Check and: The sender TCP also includes a piece of code, which is a function of the rest of the report. The acceptor TCP entity performs one of the same calculations and compares the results with the received code. If both are inconsistent, it will illustrate an error in the transmission process.
Next, TCP hand over each message section to IP and let IP transfer it to host B. These report segments should pass through one or more subnets and pass through one or more routers. This operation also uses control information. Because the IP entity adds the first part of the control information to each message segment, this forms an IP Datip (IP DataGram). There is a destination host address in the IP header included. Finally, each IP datagram is given to the network access layer to transmit it through it through it in the way to the destination. The network access layer adds its head to the IP packet, constitutes a packet (or a frame). This packet is sent through the subnet to the router. The packet first contains information that the subnet needs to transmit data.
The first part of the group includes, for example,:
l Purpose Subnet Address: The subnet must know which device to be delivered to the end to the end.
l Required equipment: Network access protocols may be used to use some subnet facilities, such as priority.
At the router, the first part of the group is removed, the router will later check the IP head. The IP module in the router will be sent to the host B by the IP module in the router according to the destination address information included in the IP header. In order to do this, the datagram has been added to a network access header.
Host
B
After receiving the above data, you have to complete an opposite process. The corresponding headers on each layer are removed, and the remaining part is handed over to the next layer of the adjacent, and this process continues until the original data delivered to the destination process.
