TCP/IP and OSI

Recently in the reading of TCP/IP, here are some simple summary introductions, first introduce some concepts:

TCP/IP protocol model : the TCP/IP model is a generic term for a series of network protocols that are designed to allow information exchange between computers. The so-called "protocol" can be understood as the language of conversation between machines, and each protocol has its own purpose. The TCP/IP model consists of hundreds of protocols that regulate all aspects of the exchange of information on the Internet. TCP/IP protocol corresponds to OSI

Internet Address (IP): Each node on the network must have a separate Internet address (also known as an IP address), and the IP address is a combination of network number + host number. Now, the commonly used IP address is a 32bit number, which is what we often call the IPV4 standard, this 32bit number is divided into four groups, that is, the common 255.255.255.255 style. IPV4 Standard, the address is divided into five categories, specific classification and reference http://blog.csdn.net/panjunnn/article/details/5653388, we commonly used is a class B address.

Domain Name System : The domain Name System is a distributed database that provides services that convert host names (URLs) to IP addresses.

RFC:RFC is a standard document for the TCP/IP protocol, now it has a total of more than 4,000 protocol definitions, generally we need to learn more than 10.

Port number : Note that this number is used on the tcp,udp of a logical number, not a hardware port, we usually say that a port is sealed off, but also only in the IP layer with this number of IP packets to filter out just. A port is a software structure that is used by client programs or service processes to send and receive information. One port corresponds to a 16-bit number. A service process typically uses a fixed port, for example, SMTP uses 25, Xwindows uses 6000. These port numbers are ' well-known ' because these and destination addresses are required to communicate when establishing a connection to a particular host or service.

application Programming Interface : Now the common programming interface has sockets and Tli. And the front is sometimes called the "Berkeley socket", can be seen Berkeley for the development of the network of how much contribution.

The OSI System Reference model and the TCP/IP system comparison:

OSI seven-layer model	TCP/IP four layer model	Corresponding network protocol
Application Layer (application)	Application Layer	Telnet,ftp,tftp,smtp,http,dns ...
Presentation Layer (Presentation)		Text: Ascii,ebcdic Graphics: tiff,jpeg,gif,pict sound: Midi,mpeg,quicktime ...
Conversation Layer (session)		NFS,SQL,RPC,ASP,SCP ...
Transport Layer (Transport)	Transport Layer	Tcp,udp ...
Networking Layer (Network)	Internet Layer	Ip,icmp,arp,rarp,akp
Data Link Layer	Network interface	SDLC,HDLC,PPP,STP, Frame Relay:
Physical Layer (physical)		Eia/tia rs-232,v.35 ...

As shown in the following examples:

Functional details of the OSI layers: see blog http://blog.csdn.net/htyurencaotang/article/details/11473015

(1) Physical layer:

Provides the mechanical, electrical, functional, and procedural characteristics required to establish, maintain, and dismantle physical links, and provides information on the transmission of non-structural bitstream and physical link fault detection instructions on the transmission medium. In this layer, the data is not yet organized, only as the original bit-stream or electrical voltage processing, in units of bits.

(2) Data link layer

responsible for the transmission of frame-based data on the line between two adjacent nodes without error, and flow control. Each frame includes a certain amount of data and some necessary control information. Similar to the physical layer, the data link layer is responsible for establishing, maintaining, and releasing connections to the data link. When transmitting data, if the receiving point detects errors in the transmitted data, it is necessary to notify the sender to re-send the frame.

(3) Network layer

It provides end-to-end switched network data transfer function for transport layer entities, so that the transport layer can get rid of network transmission details such as routing, switching mode, congestion control and so on, one or more communication paths may be established, maintained and dismantled for the transport layer entities, and the unrecoverable errors occurring in the network transmission will be reported. The network layer consists of a packet of frames provided by the data link layer, which encapsulates the network layer header, which contains the logical address information-the network address of the source site and destination site address.

(4) Transport layer

provide transparent and reliable data transmission service for the session layer entity, ensure end-to-end integrity, select the most appropriate service at the network layer, and provide the ability to establish, maintain and dismantle the transport connection. Based on the characteristics of the communication subnet, the transport layer provides the best use of network resources to provide the function of establishing, maintaining and canceling the transmission connection between the session layers of the two-terminal system and transmitting the data in a reliable and economical way. In this layer, the transmitting unit of information is the message.

(5) Session level

Provides the ability to establish, maintain, and end session connections for each other's presentation-level entities, and to complete the correspondence between the logical name of the communication process and the physical name; provides session management services.

(6) Presentation layer

Provides a set of services that interpret the meaning of the exchanged information for the application-layer process, converting the data to be exchanged from the abstract syntax appropriate for a user to the transfer syntax suitable for internal use within the OSI system, providing a formatted representation and transforming the data service. Data compression, decompression, encryption and decryption are the responsibility of the presentation layer.

(7) Application layer

OSI User Services are provided to determine the nature of communication between processes to meet user needs and to provide interface services between the network and the user application software.

In short, the roles of each layer are:

Physical Layer : transmits the raw data bitstream on the physical media.

Data Link Layer : Divides data into data frames and transmits them in a data frame. There should be a reply, the wrong re-hair.

Network layer : The data is divided into a certain length of grouping, will be grouped through the communication subnet, select a path from the source to upload to the message.

Transport Layer : an efficient, cost-effective, transparent, end-to-end data transfer service that provides no specific network.

Session Layer : Conversations between processes are also known as sessions, and the session layer manages conversations between processes on different hosts.

Presentation Layer : Provides a formatted representation and transformation Data service for the application-tier process.

Application Layer : Provides the means by which applications access the OSI environment.

The corresponding layers of TCP/IP can be summarized as follows:

Network Interface : Responsible for the establishment of circuit connection, is the physical basis of the entire network, the typical protocol includes Ethernet, ADSL and so on;

Internet Layer : responsible for assigning addresses and transmitting binary data, the main protocol is IP protocol;

Transport Layer : responsible for the transmission of text data, the main protocol is the TCP protocol;

Application Layer : Responsible for the transmission of various final forms of data, is directly related to the user layer, the typical protocol is HTTP, FTP and so on.

Common protocols and their port numbers:

Where the TCP/IP layer	Key words	Protocol Name	Port number
Application Layer	Ftp	File Transfer Protocol (TCP:FTP data transfer)	20
	HTTP	Hypertext Transfer Protocol (TCP: Access Web site)	80
	Dns	Domain Name Server protocol (UDP: Domain name resolution Service, Client for domain name query Tcp:domain name server, DNS inter-server domain name replication)	53
	Smtp	Simple Mail Transfer Protocol (TCP: Transport of messages)	25
	Nfs	Network File System protocol (file share TCP and UDP)	2049
Transport Layer	Tcp	Control Transfer Protocol	The port number is generally used to distinguish the various services of a single host, such as WEB,FTP services. Use the port number to find a Unique program in a single device. So if you need a Computer to establish a connection, you only need to know the IP address or domain name, but if you want to A program to Exchange data, you must also know that the program The port number used.
	Udp	User Datagram Protocol
Internet Layer	Ip	Internet Protocol
	Icmp	Internet Control Message Protocol
	Arp	Address Resolution Protocol
	RARP	Reverse Address Resolution Protocol
Network interface	Hdlc	Advanced Link Control Protocol
	Ppp	Point-to-Point protocol
	SLIP	Serial Line Interface Protocol

Reference Blog: http://www.ruanyifeng.com/blog/2009/03/tcp-ip_model.html

http://blog.csdn.net/htyurencaotang/article/details/11473015

TCP/IP and OSI