Shulou(Shulou.com)06/03 Report--

the first chapter summarizes

1.1 The role of networks in modern times

Three modernizations in the 21st century: digitization (digital processing of sound signals for computer processing and transmission), networking, and informatization

Triple play: telecommunications networks (telephone), cable networks (coaxial cable, from cable company to subscriber), computer networks (Internet, other networks)

1.2 Important Functions of Computer Networks

Connectivity: communicating with each other and exchanging information·Remote desktop client: mstsc (Microsoft terminal services client)

Win10 and Win7 are single-user operating systems that allow only one user to operate simultaneously. Server is a multi-user operating system that allows multiple people to log in at the same time.

· \\ip address (or computer name) to access the computer remotely

Sharing: information sharing, software and hardware sharing

1.3 Internet Overview

(1) Network: Connecting computers with switches or hubs constitutes a network. Computers on the same network, on the same network segment.

(2) Internetwork: Multiple networks connected by hubs or switches (multiple networks connected together are an interconnected network)

(3) Routers: exchanging data (forwarding packets) between different network segments,

The World's Largest Network: Internet

(5) Computer history: (5.1) ARPANET to the Internet (TCP/IP protocol)(1960s-80s)

(5.2) Three-tiered Internet (backbone, campus, and LAN)(mid-1980s-early 1990s)

(5.3) Multi-tiered ISP (Internet Service Provider)

(6) Two-line access: one computer room is connected to the networks of two operators.

1.4 Composition of the Internet

(1) Communicating computers (edge)

Computer communication methods:

Client/Server (c/s)

Peer-to-peer: BT, P2P (data is obtained from different computers, and the process of uploading and downloading is peer to peer)

(2) Network (core part)

Core:

Circuit mode: establish connection before communication, bandwidth guaranteed, release connection after communication

(for voice, video, real-time communications)

Process: establish connection (apply for occupying communication resources), call (occupy resources all the time), release connection (release communication resources)

Message exchange: Data to be transmitted is sent together as a unit (address required)

Packet switching: sending data to be transmitted in segments (each packet requires an address)

Advantages: Efficient, flexible, fast, reliable

Disadvantages: Latency (store and forward)

The way the Internet uses packet switching

Communication time:

Circuit switching: connection establishment + data transmission + connection release

Message exchange: data transmission time + store-and-forward time

Packet switching:

1.5 Computer network type

Scope of action:

WAN (Wide Area Network) leased telecommunications lines, pay for bandwidth (Internet operator layout)

Metropolitan Area Network (MAN)

local area network (LAN)(Local Area Network) range for a few kilometers, spend money to buy equipment, maintain their own, fixed bandwidth

Personal local area network (PAN)

Twisted pair transmission distance of 100m

User:

public network

private network

Topologies: bus, ring, star (switch networking), tree, mesh

How it works: resource subnet (server providing services to others), communication subnet (network equipment), access network (computer requesting network resources)

1.6 computer network performance

(1) Rate: Number of bits transmitted per second (bit/s)(KB/S) 8bit=1B

(2) Throughput: the amount of data passing through in unit time (including all uploaded and downloaded traffic)

Simplex, half-duplex, full-duplex (twice nominal throughput)

(3) Bandwidth: maximum bit per second of NIC b/s, kb/s,Gb/s converted to 1000

(4) Delay

Transmission delay: data block length (bit)/channel bandwidth (bit/s)

propagation delay

processing delay

queuing delay

Total processing time = transmission delay + propagation delay + processing delay + queuing delay (not included)

Ping Command Time Round Trip Time

-lsize Specifies the size

(5) Delay bandwidth product: Calculate the number of bits on the link

(6) Channel utilization ratio: with data transit time/(with + without) data transit time

(7) Current network delay = network idle delay/(1-channel utilization)

Delay increases exponentially with utilization

(8) Non-performance indicators: cost, quality, standardization, reliability, scalability, upgradability, management and maintenance

1.7 OSI Reference Model (Open Systems Interconnection Reference Model), layers of computer networks

Layering: Changes in each layer do not cause changes in other layers

Standardization: different manufacturers, equipment can work together, the bottom layer provides services for the upper layer

Peer-to-peer protocols: encapsulated formats

7-Layer Layered Protocol:

Application Protocol Layer: Defined methods and specifications between server and client

Specification (method) of what requests clients can send to the server

Server sends corresponding status to client

interactive steps

Application: Browser...

Presentation layer: ASCⅡ, binary file (program picture..), Encryption, compression

Session Layer: The session established between the client and the server

Transport layer: capable of reliable transmission (packet loss retransmission buffer sorting)

Flow Control (Client Settings Server Send Window)

congestion avoidance

Network layer: Routers forward packets through network addresses (routers work at the network layer)

Choose the best transmission path based on the address of the packet (does not ensure reliable transmission, nor does it ensure that the data arrives in order)

Network layer addresses are ip addresses (packets)

Data link layer: data link layer address is mac address (frame)

responsible for encapsulating frames of data into the frame format of the link traversed

Physical layer: interface standard and voltage standard of network equipment

OSI Protocol and Network Troubleshooting

Layer-by-layer inspection: from the bottom to the top

Physical layer: network cable (failure of connection failure)

Data link layer: mac address, speed negotiation

Network layer: Gateway, routing, VLAN

Application layer: proxy server (garbled, configuration problems)

OSI Reference Model and Network Security

Physical layer security: WiFi physical layer is not secure

Data link layer security: WiFi password is not secure, mac conflict, ADSL account password, mac authentication

Network layer security: router, windows firewall (wf.msc)

Application Layer Security: Developers (SQL Injection Vulnerability)

Osi reference model and network data

Physical layer equipment: hub, network cable

Data link layer devices: switches, bridges

Network equipment: router

TCP/IP protocol stack

Application layer (HTTP\FTP\DNS\RDP\POP3\SMTP)

Transport Layer (TCP\UDP)

Network layer (IPV4 ARP\ICMP\IGMP)

Network Interface Layer (eTHERNet\ATM\FRAMERELAY\PPP\CSMA\CD)

The bottom layer provides services for the upper layer, the bottom layer encapsulates, and the upper layer unpacks:

Application Layer: Data Transfer Unit

Transport layer: message (segment)

Network layer: IP packets (packets)

Data link layer: data frames

Physical layer: binary bit stream (bits)

Switches: access layer switches (lower layer), aggregation layer switches (upper layer)

Author: xuan97916

References: [1] Han Ligang, Computer Network Principle Innovation Course [M], Water Conservancy and Hydropower Press, January 2017

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