Network Knowledge complementing

Integrated Service Digital Network: ISDN, a dial-up connection. isdn bri provides 2B + D data channels. Each B channel has a rate of 64 Kbps, and the maximum rate is kbps. isdnp has 2 standard; European Standard

Quasi (30B + d) and North American Standard (23B + d). ISDN is a digital transmission mode with fast connection and reliable transmission, and supports peer number identification.

Leased Line: leasedline, known as DDN in China, is a point-to-point connection mode with a speed of 64 kbps-2.048kbps. the advantage of a leased line is that data transmission is well guaranteed, and the bandwidth is constant: But it is expensive and

The point-to-point structure is not flexible enough.

The circuit mode is based on the principle of telephone network circuit switching. When a user requests to send data, the switch connects a physical data transmission path between the caller and the called user. it features low latency and "Transparent" Transmission

(That is, the transmission path does not modify or interpret user data), and the information transmission throughput is high. The disadvantage is that the usage of fixed bandwidth resources is low.

The traditional PSTN/ISDN network is based on the circuit switching mode.
Grouping is a storage and forwarding exchange method. It divides the information to be transmitted into packets (groups) of a certain length (ATM) or variable length, and stores and forwards data in groups. Each group information is loaded

The identifier of the Receiving address and Sending address. On the Way of grouping, dynamic multiplexing technology is used to transmit each group, bandwidth can be reused, and network resource utilization is high. The disadvantage is poor real-time performance.

A modem is a device for signal conversion between the end system and the communication system. It is an indispensable device in the wide area network. Modem can be divided into two types: synchronous and asynchronous.

Ports are connected. Synchronization Can Be Used for leased lines, frame relay, and X.25, and asynchronous is used for PSTN connections.

The Session Layer allows users on different machines to establish, manage, and terminate the session relationships between applications. The session layer is required to coordinate communications between different applications. this layer allows each application to know the status of other applications

The Session Layer also provides duplex negotiation, session synchronization, and so on.

The Session Layer establishes between applications by executing multiple mechanisms to maintain and terminate sessions. the Session Layer includes billing, traffic control, and session parameter negotiation. common session-layer protocols: Structured Query Language (SQL) network text

File System (NFS). Remote Procedure Call (RPC), xwindows system, etc.

The presentation layer focuses on the syntax and meaning of the transmitted information. It processes computer-related data formats from the application layer into computer-independent formats. this ensures that the Peer device can accurately understand the sender data. same

The presentation layer is also responsible for data encryption.

The presentation layer ensures that the source data can be understood and recognized by the target presentation layer. transparent to applications. the presentation layer provides the data format conversion service. data encryption. services such as data representation standards. the presentation layer determines

Organization method. Common presentation layer protocols include: Data Structure standard, ASCII, image standard JPEG, GIF, Midi, MPEG, QuickTime, etc.

The application layer is the layer closest to the user of the OSI reference model. It provides network services for applications. The application layer identifies and verifies the availability of the target communication party and synchronizes the applications that work collaboratively.

The Wan Physical Layer Protocol describes the interfaces between the data terminal device (DTE) and the data circuit terminal device (DCE. DTE is located on the user's network interface client device; DCE provides physical connection interfaces to the network, providing

Clock signal for data transmission between step DTE and DCE devices. in short, the DTE device is close to the user side, and the DCE device is close to the network. commonly Used for DTE devices: terminal hosts and routers; commonly used for DCE devices: Wan Switching

Machine, moderm, CSU/DSU.

EIA/TIA-232, also known as RS-232, is a public physical layer standard, used to support signal rate up to 64 Kbps of non-balanced circuit.

V.24 standard: interfaces between DTE and DCE defined by ITU-T. the cable can work in both synchronous and asynchronous modes. in asynchronous mode, the link layer protocol is encapsulated to support IP addresses and IPX, while the highest transmission rate is

115200bps. In synchronous mode, link layer protocols such as X.25 Frame Relay PPP, HDLc, slip, and lapb can be encapsulated. IP and IPX are supported, and the highest transmission rate is 64000bps.

V.35 standard: the standard used to describe the physical layer protocol for synchronous communication between network access devices and group networks. v.35 is widely used in the United States and Europe. v.35 cable transmission (in synchronous mode) is recognized as the highest speed

2048000bps.

 

The LLC sub-layer is located between the network layer and the MAC Sub-layer. It is the management layer of the upper and lower layers, responsible for traffic control and synchronization. the LLC sublayer communicates with the network layer protocol through SSAP (Source Access Node) and DSAP (destination Access Node.

The MAC Sub-layer is responsible for building the "0" and "1" bits of the physical layer into frames. the child segment is detected by CRC at the end of the frame (cyclic redundancy check. in short, the MAC Sub-layer defines network access to shared media.