01TCP/IP Foundation

Iso/osi Reference Model: OSI (open System Interconnection) Open Systems Interconnect model is made up of ISO (international Organization for Standardization) a network layering model defined by the International Organization for Standardization, a total of seven layers. Detailed action of each layer: physical layer (physical layer): Physical layer defines all electronic and physical equipment specifications, for the transmission of the upper layer provides a physical medium, the unit of data transmission in this tier is bit (bit). The specifications belonging to the definition of this layer are Eia/tia RS-232, Eia/tia RS-449, v.35, RJ-45, etc., the actual use of equipment such as network cards belong to this layer. Data Link layer: Data is framed for the bit streams received by the physical layer. Provide reliable data transfer service for error-free data transmission. The units of data in the data link layer are frames (frame). The specifications that are defined in this layer are SDLC, HDLC, PPP, STP, Frame relay, etc., and the device in use, such as a switch switch, belongs to this layer. Network layer: The network layer is responsible for routing, grouping, and reorganizing data between subnets. The unit of data transfer in this layer is a packet (packet). The specifications that belong to this layer are IP, IPX, RIP, OSPF, ICMP, IGMP, and so on. Devices that are actually in use, such as routers, belong to this layer. Transport Layer (Transport layer): Provides a reliable data transfer service that detects packets dropped by the router, and then generates a retransmission request that can reorder the packets received by the order. Session Layer: Manages the session process between hosts, including session creation, termination, and management during sessions. The presentation layer (Presentation layer): The presentation layer transforms the data transmitted over the network, allowing the information transmitted between multiple hosts to understand each other, including data compression, encryption, and format conversion. Application layer (Application layer): The application layer communicates with the application interface to achieve the purpose that is presented to the user. In this common agreement are: HTTP,HTTPS,FTP,TELNET,SSH,SMTP,POP3 and so on the role of seven layers and a vivid description of each other: The above is an idealized model, but in the practical application of a wide range of: tcp/ IP four layer model: Below is a comparison of the seven layers:

Application Tier Application Layer		Application Tier Application Layer
Presentation Layer Presentation Layers
Conversation Layer Session Layers
Transport Layer Transport Layers		Transport Layer Transport Layers
Network tier Internet Layer		Network tier Internet Layer
Data Link Layer		Link Layer Link Layers
Physical layers Physical Layer

The following are the representative agreements in each layer:

Peer communication: The same layer, such as the transport layer and the transport layer of communication seems to be direct communication, that is, the peer communication, in fact, based on the other layer of communication collaboration.

Packaging:

Package data after sending .....

After receiving the data .....

Divided by:

Below is the classification, scope, meaning of the port:

Known ports (well known Ports): from 0 to 1023, these ports are assigned and controlled by the IANA tightly bound to some services. Usually the communication of these ports clearly indicates the protocol of a certain service. For example, Port 21 is the FTP service port. Register port (registered Ports): from 1024 to 49151. Some of its ports are not controlled by the IANA but are registered by the IANA and provide a list of usage. They are loosely tied to some services. This means that there are many services bound to these ports, which are also used for many other purposes. For example: 1433 Microsoft SQL Service port dynamic or private port (dynamics or Private Ports): from 49152 to 65535. IANA regardless of these ports. In fact, machines typically allocate dynamic ports from 1024 onwards. But there are exceptions: Sun's RPC port starts at 32768.

01TCP/IP Foundation