A, OSI reference model
Open Systems Interconnection (OSI) reference model by the International Organization for Standardization (OSI) in 1984 proposed a layered network architecture hunger constitutive model, is designed to support heterogeneous network system interoperability.
It is divided into seven layers: an application layer, presentation layer, session layer, transport layer, network layer, data link layer, physical layer.
Two, OSI reference model for data communication process with the package
Each layer is encapsulated in the data, until the physical layer transmission bits.
Q: Why data package?
A: increasing the control information, the control configuration of the protocol unit (PDU)
Control information including:
- An address (Address): identifies the transmitting / receiving ends
- Acronym coding error (Error-detecting code): used for error detection or correction
- Control protocol (Protocol control): implement the protocol function of additional information, such as: priority (priority), quality of service (QoS), security control
Third, the physical layer function
Function: the transmission of each bit on the specific physical media.
specific:
- Definition and specification of the interface characteristics :
mechanical properties: the geometry of the interfaces, which side of the plug socket in
electrical characteristics: Battery voltage selection
feature: the number of pins and functional interface
protocol characteristics: Working Process Interface - Resolve bit coding problem
- Data Rate
- Bit synchronization
- Transmission mode : simplex, half duplex, duplex
Fourth, the data link layer
- Responsible node - the node (node-to-node) data transfer (data transfer to solve two neighboring nodes directly connected to the physical link).
- Framing (Framing): generally increase tailing head, the main purpose is to enable the receiver to receive one end of a series of bits from the physical layer when the flow can be cut successfully separated a data frame, thereby separating header and trailer information complete the data link layer protocol in accordance with a predetermined header and trailer information related functions.
- In the physical data link layer address (Physical addressing): increase the transmission end and / or the physical address of the receiving end, the transmitting end of a data frame identification and / or a receiver in the header.
Application example:
when the shared physical medium, 20 to 62 transmits, the other host can receive the data frame, but they are not to receive, only 62 will be to receive.
- Flow Control (Flow control): a receiving end to avoid flooding
- Error control (Error control): Detection and retransmits the corrupted or missing frames, repeating frames and avoid
- Access (Access) control (Access control): any given time to determine which device has a link (physical medium) controls the right to use
5, the network layer functions
- Responsible source to destination, data packets are delivered across multiple networks possible
- Logical addressing (Logical addressing): globally unique logical addresses, no matter how many are unique across the network, to ensure that the data packet is the destination host service, such as IP address
- Routing (Routing): routers (or gateway) network, and routes the packet to the destination host. Path selection.
- A packet forwarding
network layer address globally unique logical FIG red letters represent, green letters represent the physical address, can see the source and destination network addresses are the same
Sixth, a transport layer function
Responsible source - Purpose - (interprocess) (terminal end) complete packet transmission.
- Fragmentation and Reassembly : The session is transmitted over the transport layer level complete message into a data segment, and then delivered to the network layer.
- SAP Addressing : Be sure to submit a complete message to the correct process , such as port number.
Protocol data unit (PDU) received a session layer, transport layer, the transport layer will then be divided to form a transport layer protocol data unit, where x and y for the source and destination address of the SAP. The data further to the network layer, S and D for the source and destination network address. Data to the data link layer, a physical address is added.
- Connection Control : This is the logical connection
- flow control
- Error Control
Seven, session layer functions
- Dialogue control (dialog controlling): establish, maintain
- Synchronization (synchronization): Insert "synchronization point" in the data stream, once the purpose of data transmission in a control point near the interruption, the next time to recover as long as the recovery in the last control point
- Functional thin, no such actual Internet network layer
Eight, the presentation layer function
Between two processing systems to exchange information syntax and semantics of the problem.
- Data represents the conversion : Conversion of a host independent coding, regardless of the particular system
- encrypt and decode
- Compression / decompression
- No such layer in the actual development, application layer will undertake this work layer
Nine, the application layer functions
- User support by user agents (such as a browser) or network interface using network (service)
- Typical application layer services: file transfer (FTP), email (SMTP), Web (HTTP), etc.
Ten, TCP / IP reference model
TCP / IP reference model for a total of four. Network interface layer protocols and is not specifically defined, as long as the Internet layer encapsulating IP packets, i.e., IP packets capable of transmission from one point to another point on it.
Eleven, five reference model
Integrated OSI and TCP / IP advantages of
the application layer : support a variety of network applications (FTP, SMTP, HTTP)
transport layer : Process - data transfer process (TCP, UDP)
Network layer : routing of data packets to the source host and the destination host forwarding (IP protocol, etc. routing protocol)
link layer : a neighboring network elements (hosts, switches, routers, etc.) of the data transmission (Ethernet, WiFi, PPP)
physical layer : bit transfer
