1.Introduced.
1.1. Causes
The IP protocol is used for multiple packet switching network connected, it in the source and destination addresses before transmission address called data submitted to things, it also provides for data size reassemble function, to meet the different network of packet size requirements.
IP duty is to transmit data from source to the destination. It is not responsible for ensuring that transmit reliability, flow control, packet sequence and other for hosts to host protocol is very ordinary service.
130. Interface
This agreement by the host to host protocol calls, and this agreement is responsible for call native network protocol data submitted to transmit the following a gateway or its destination. For example TCP can call the IP protocol, when the function is called transmit the destination address and the source address as parameters, IP forming data submitted to and call the local network (protocol) interface transmit data reported.
1.4. Operation
IP achieve two basic functions: addressing and subsection. IP may, according to data submitted to the destination address of its header including data submitted to teleport to the destination address, during the course of IP is responsible for the choice of the delivery of the road, this choice road called routing functions. If some network inside can transmit small data reported, IP can be submitted to reassemble data in header field indicate. IP modules including these basic functions, these modules exists in the network hosts and gateway on each machine, and these modules (especially in the gateway has a routing and other service functions. Data submitted to IP speaking, between no connection, what to say to IP connection or logical link.
TCP/IP USES four key technology to provide service: service type, survival time, options and header check code. Service type refers to hope to get the service quality. Service type is a parameter set, these parameters is Internet can provide service representative. This service by the gateway, used to use type in a specific network, or used for another next to go through the network, or the next to the data submitted to the gateway routed on selecting actual transmission parameters. Survival was data submitted to the time limit can survive. It consists of the sender Settings, by a routing place processing. If not arrived survival time for zero, discard the data reported. For controlling function for option is important, but for usually communications it no longer necessary. Options including timestamp, safety and special routing. Header check code to ensure that the data of correct transmission. If calibration error, abandon the whole data reported.
IP does not provide reliable transmission service, it does not provide end-to-end or (routing) node to (routing) node confirmed, for data without error-controlling, it only use header check code, it does not provide retransmission and flow control. If something goes wrong by ICMP reports, ICMP in IP modules realize.
2.Overview
2.1. Contact with other agreement
The following figure displays the IP protocol agreement in system of the position.
IP fluctuation two interfaces, and one is from the host with the host protocol interfaces, the other is a local and network interface, the local network can be a small networks can also large network, perhaps.
2.2. Operating mode
The following example can see operating model is what. We assume that the transmission should pass between gateways. Transmit process call native IP module transmit data simultaneously transmit the destination address and other parameters as call parameters. IP layer to prepare data header and add it to need data transmitted before. IP module for this network address decided to a local network addresses, here is the gateway to address. IP transmit data report and the local network address to the network interface. The local network interface to create a local network head, then add in data newspaper to send the local network.
Add the local network headjoint data submitted to reach gateway, local network interface get rid of the head, will send (gateway results on) IP module. This IP module decided purpose of local network addresses, then as mentioned above process data transmission report local network interface. The local network interface to create a local network head upon data, the data submitted to the newspaper teleport to its destination. In its destination, the local network interface to remove data of the newspaper local network head, results to IP module. IP module decision data submitted to the data submitted should which an application, the system will send transfer system call modules, IP address and other parameters return to the source.
2.3. Functional description
IP is the ability to send data reported on interconnected network transmission, through the data reported in each IP module is sent between until purpose module to achieve a goal. Network in each host and gateway has IP module. Data reported in each between modules by routing processing network address teleport to the destination address. Therefore network address for the IP protocol is very important. As mentioned above, because each network data on a newspaper size may be different, so it is necessary to large data reported on section.
Name, address and routing is a difference, name is we want to point out the name, address, routing where solve the problem how to get there. IP address issues mainly handling. The name and address by mapping work completed by upper agreement. IP address and module will be to your local network address mapping, and local network address and routing by mapping is low-rise agreement task.
The address is 32 bits long, by the network number and local address two parts. Address into three categories: A kind of the top bits to zero, seven said the network number, other 24 bits said local address; Class B before two 10, after 14 says network addresses, other 16 said local address; Class C three for 110, after 21 is a network number, and the other eight representative local address.
In the network address and local network address by mapping must note that some hosts may use several different IP address (we can put the local network address understanding as a MAC address). We must be able to handle a host has several processing port, and each port has several logic IP address.
For different network which is transmitted packet size may be different, so the 1200w points small function is a must. Data submitted to also can be marked as "not fragment, if a data submitted to be how to mark, then in any circumstances prohibit to it and section. If unsegmented could not reach my destination, then put your bag in the halfway abandoned. Within the again within the segment and reorganization on IP module is not visible, this method can also be used.
Also the restructuring and reorganization of subsection, marking the receiving party sub-waveforms by using these markers that distinguish different section. Section offset domain told the recipient should this paragraph is put in what place, more paragraphs marker instructions last section, using different domains can completely restructuring a data reported. Mark domain is used to only quote mark data, it is original sender Settings, but also to ensure that the data reported in network transmission in the whole process of the it the only. Original sender put more paragraphs flag set to zero, zero offset Settings section.
We hypothesized that a large data IP module newspaper is divided into two small, IP module first obtained data header, again space data for two copies, will add in two copies data header data. Space data with 8 bytes for the unit, the second period is not necessarily 8 bytes, but first must be. We put the first section of the eight bytes called segments KuaiShu (NFB). The new generation of the first data submitted to within a generation of the first section data, setting multistratum marked as 1; Newly generated a second data submitted to the second paragraph within is to generate data, more paragraphs marker is equal to the original data submitted to the value of the paragraph within the offset is equal to the original data submitted to the value plus NFB. The above process can be extended to N from 2.
The restructuring of the requirements to segment the following four domain have the same value, marking, the source address, the target address and protocols. Will different data reported according to bring their own offset retooling for new section, the first paragraph offset 0, last one segment of multistratum marker for 0.
2.4. Gateways
Gateway in different network data transmission between reported, gateway also realization gateway to gateway protocol (GGP), it used to transmit routing and other control information. Gateway of high-level agreement no realization, GGP functionality can be realized in IP module.
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