Software Designer review notes _ computer network Basics

This note is based on <software designer tutorial> (2010.7.

1. Concepts of computer networks.

(1) concept: A computer network is a large-scale and functional computer application system that connects computers distributed in different geographic regions with dedicated external devices using communication lines. so that many computers can easily transmit information to each other and share hardware, software, data information, and other resources.

(2) objective: to share resources

(3) three aspects: A. At least two computers are interconnected. B. Communication Equipment and line medium. C. network software, including communication protocols and network operating systems.

2. Composition of computer networks.

(1) hardware composition.

<1> computer devices: Host and front-end processors.

<2> communication lines: wired lines and wireless lines.

* 1. Wired media.

A. Twisted Pair wires: Shielded twisted pair wires (suitable for networks with low network traffic) and unshielded twisted pair wires.

B. coaxial cable: baseband coaxial cable and broadband coaxial cable

C. Optical Fiber

* 2. Wireless media.

A. Microwave

B. Infrared and laser.

C. Satellite Communication

<3> network connection device: vro and vswitch. The vswitch form a network of computers, and the vro form a larger network.

(2) software composition.

<1> system-level network operating system.

<2> network communication protocol.

<3> application-level dedicated software that provides network services

(3) Function composition

Data communication and data processing are divided:

<1> Communication Subnet: corresponds to the Lower Layer 3 (physical layer, data link layer, and network layer) of the model)

<2> resource subnet. It corresponds to the Layer 3 (Session Layer, presentation layer, and application layer) of the model)

This division extracts tasks of the Communication Subnet from the host. devices in the Communication Subnet specifically solve data transmission and communication control problems. Computers in the resource subnet can process data in several ways. this improves the sentence efficiency and overall network performance.

3. Computer Network Classification

(1) According to the computer network coverage and the distance between the communication terminals:

<1> LAN)

<2> man)

<3> Wan)

4. network interconnection devices.

(1) physical layer interconnection device.

<1> repeater: Used to interconnect lan network segments on the physical layer. Used to extend the length of lan network segments.

Advantages: easy to install, easy to use, and inexpensive.

Disadvantages: high latency and Attenuation

<2> hub: a special multi-channel repeater. It has the signal amplification function.

It can be divided into: Active hub, passive hub and smart hub.

(2) interconnection devices at the data link layer.

<1> Bridge: used to connect two local network segments.

Principle: The Bridge checks the source address and destination address of the frame. If the source address and destination address are not in the same CIDR Block, the frame is forwarded to another CIDR block. If the source address and destination address are the same, the frame is not forwarded.

Purpose: Filter frames to improve network reliability and transmission rate.

For example, when a network suffers a heavy load and its performance degrades, you can use a bridge to divide it into two network segments and minimize the traffic between these segments.

<2> vswitch: forwards relatively simple decision information based on the MAC address in each package.

Features: simplified, low price, high performance, and high port density. in addition, the forwarding data delay is very small, far exceeding the forwarding performance of common bridging. you can also adjust the bandwidth of shared and dedicated LAN segments. to reduce the bottleneck of information flow between local networks.

Principle: After a vswitch receives an Ethernet frame from a node, it immediately searches for the address table in its memory (the storage port corresponds to the MAC address, you have confirmed the node address where the Mac Nic is connected. then, it is forwarded to the frame node. if the packet does not exist, the switch broadcasts the packet to all nodes. the NIC that owns the MAC address immediately responds after receiving the broadcast frame, so that the switch adds the MAC address of its node to the address table.

The switch uses three types of switching technologies: port switching, frame switching, and Token switching.

(3) interconnection devices at the network layer: Routers

Purpose: connect multiple independent subnet networks.

Features:

A. Strong heterogeneous network interconnection capabilities.

The minimum two layers of interconnected networks can be different. use the driver software to unify it to the third layer. if the layer-3 protocol is the same. you can use a single-protocol router for interconnection. If different, you need to use a multi-protocol router. (multi-protocol routing: routes that support multiple protocols do not refer to mutual conversion before different protocols)

B. Select the path.

A path table is maintained in the vro. the logical addresses of each network are recorded in the table. it can be used to identify other networks. In an Internet connection, when a vro receives a message from the network to another network. first, discard the outer layer of the information package and interpret the data in the information package to obtain the Logical Address of the destination network. next we will use xing'anling RoadProgramDetermine the information forwarding path. repackage the forwarding.

C. Because routers work at the network layer and process more data than bridges, the processing speed is slower than that of bridges.

(4) interconnection devices at the application layer: Gateways

Role: protocol conversion.

5. Architecture of network protocols.

LAN Standard: 802.3 (CSMA/CD, Ethernet) 802.4 (Token Bus) 802.5 (Licensing ring)

Three factors that determine LAN features: the transmission media for data transmission, the topology of various devices connected and the Media Access Control for shared resources.

(1) LAN topology and protocol.

<1> bus structure

Advantages:

A. There is only one two-way connection to facilitate broadcasting.

B. Distributed Control. No central processor is required.

C. Good system scalability.

D. Use passive lines for interfaces. high reliability.

E. Few devices, low prices, and convenient installation.

Disadvantages:

When the load is heavy, the line utilization rate is low, the information delay on the internet is uncertain, and fault isolation and detection are difficult.

<2> Star Structure

Advantages: Easy maintenance and management, flexible reconfiguration, easy fault isolation and detection, low network latency.

Disadvantages: each node must communicate with each other through a central processor, with poor network sharing, low line utilization, and heavy load on the central unit.

<3> Ring Structure

Each node is connected to the network through the first line of the repeater.

Advantages: The Path Control is simple, and bypass equipment is available. In the event of a fault, the system automatically bypasses and the reliability is high.

Disadvantages: low transmission rate and slow response speed. expansion is difficult due to closed loops.

<4> tree structure.

It is used in a hierarchical structure composed of multiple networks.

<5> wide area networks are generally distributed or tree-like, and common LAN bus-type, ring-shaped, star-shaped, or tree-like structures are used.

(2) LAN model.

<1> Physical Layer

Like the OSI physical layer, it processes bit streams on physical links, including channel distribution of bandwidth and signal modulation of baseband.

<2> media access layer.

The network topology is related to the transmission media type, as long as the access control and channel resource allocation of the media are included.

<3> Logical Link control layer.

Provides connection-oriented and non-connection-oriented services, encapsulates and removes data frames, and provides logical interfaces for network services for the high-level management to implement Error Control and traffic control.

(3) Ethernet

The media access control method adopted is a multi-channel access protocol (CSMA/CD) technology for carrier listeners with conflict detection.

Three main types:

A. Standard LAN defined in. Speed: 10 Mbps. Transmission Medium: coaxial cable.

B. Fast Ethernet as defined in 802.3u, with a speed of Mbps. Transmission Medium: twisted pair wires.

C. Gigabit Ethernet defined in 802.3z. The transmission speed is Mbps. The transmission medium is optical brazing or twisted pair cable.

<1> media access technology.

Working Process: First listen to the channel, if the channel is idle, it will be sent. if the channel is busy, listen again until the channel is idle and send immediately. start sending for a period of time before detecting the conflict. the method is to receive and compare the received and sent messages while sending them. if the results are different, it indicates that the sent information encounters a collision, so immediately stop sending the message and send a genetic blocking signal to the bus to notify the stations on the channel that the conflict has been sent. wait for a while and try again. wait timeAlgorithm: Binary Index backoff algorithm.

(4) Ling card ring network

Transmission Medium: Mainly shielded twisted pair wires and unshielded twisted pair wires.

Topology: ring, Star (maximum), bus

Encoding method: Differential Manchester encoding.

Media Access: card ring control technology.

6. Wan protocol.

(1) Point-to-Point Protocol (PPP): used for Dial-Up Over-the-Internet WAN connection.

It has the advantages of simplicity, user authentication capability, and IP Address allocation.

(2) asymmetric data user line asdl/pppoe

(3) digital user line: XDSL: Asymmetric Digital user line ADSL.

(4) digital data network.

(5) frame interruption

It provides a simple connection-oriented virtual circuit grouping service. including switching virtual circuit connection and permanent virtual circuit connection. it has the advantages of reducing network interconnection costs, simplifying network functions, improving network performance, and adopting international standards.

(6) asynchronous transmission mode (ATM)

It is a group-oriented fast group switching mode. It uses asynchronous time division multiplexing technology to divide information flows into fixed-length cells. use a unified unit of information. it can easily achieve multimedia communication that combines various information flows and dynamically allocate valid capacity based on service type and speed requirements. in an ATM network, data is transmitted in units of fixed-length cells. A cell consists of a header and a letter body. Each cell contains 53 bytes, including the first five bytes of the cell, the cell body contains 48 bytes.

(7) X.25 Protocol

7. ISO/OSI reference model

(1) layer-7 protocol:

Application Layer: provides users with interfaces such as network management programs, emails, and FTP.

Presentation Layer: data compression, encryption and decryption

Session Layer: provides the ability to establish, maintain, and end session connections for the presentation layer.

Transport Layer: TCP/UDP

Network Layer: vro, IP, ICMP, ARP, and RARP.

Data link layer: Frame

Physical Layer: bit stream

(2) TCP/IP protocol family

Features: Logical addressing, route selection, domain name resolution, error detection, traffic control, and support for applications.

<1> layer-4 Structure: Application Layer/Transport Layer/Internet Layer/Network Interface Layer

<2> Network Interface Layer Protocol: Ethernet

<3> Internet Protocol: IP protocol (unreliable and connectionless)

ARP and RARP protocols. ICMP protocol.

<4> Transport Layer Protocol: connection-oriented reliable TCP protocol (SYN/ACK): ftp

For connectionless UDP protocols: DNS and SNMP

8. Internet and Applications

(1) Internet address.

<1> Domain Name: Host Name. local place name. group name. top-level domain name

<2> ip address.

A: 1.0.0.0-126.0.0.0 indicates 127 subnets.

10.0.0.0-10.255.255.255 is retained, and 127.0.0.0 is used in closed loop.

B: 128.1.0.0-192.254.0.0 where 172.16.0.0-172.31.255.255 is retained

C: 192.0.1.0 to 223.255.254.0, where 192.168.0.0 and 192.168.255.255 are retained

D: The multicast address is 224.0.0.0 to 239. 255. 255.254.

E: Reserved address: 240.0.0.0 to 255.255.255.255

<3> subnet mask.

<4> NAT technology

(2) Internet services

<1> Domain Name Service <DNS>

Domain Name Server: master server, cache Domain Name Server, and forwarding server.

<2> remote login service <Telnet protocol>

<3> email service

<4> World Wide Web Services

<5> File Transfer Service <FTP protocol>

9. Common network management commands.

(1) ipconfig

(2) Ping

(3) ARP

(4) netstat

(5) tracert