Wang computer network study notes - Chapter One (continuously updated ......)

Section

1.1.1 The composition of a function and classification

The network contains a computer network
Computer network: a dispersion having a function independent computer system , via a communication device with a line connected, sharing resources and information transfer system by a fully functional software.
Computer networks are interconnected , the computer autonomous collection.

Interconnection - Interconnection communications link
Self - master-slave relationship

Computer networks function

1.数据通信（连通性）
2.资源共享 （硬件 软件 数据）
3.分布式处理 多台计算机各自承担统一工作任务的不同部分
4.提高可靠性

Up a computer network

Part of
the hardware, software, protocols
Way of working

section	use
Edge portions	User directly -c / s mode, p2p mode
core part	An edge portion of the service

Functional components

Subnet	Features
Subnetworks	Realize data communication
Resources subnet	Realize resource sharing , data processing

Classification of computer networks

range
distribution area	WAN WAN LAN WAN MAN MAN PAN Personal Area Network
user	Shared network-private network
Switching technology	Circuit switching exchange packet-switched messages
Topology	Bus · star · ring-type network (WAN)
Transmission technology	· Broadcast networks share a common communication channel, using the ad hoc network- packet forwarding storage and routing mechanisms

1.1.2 Standardization and related organizations

Standardization

standard	Explanation
Statutory criteria	Designated by the authority of formal legal criteria	OSI
De facto standard	Some of the company's products occupy the mainstream in the competition, a long time for these products has become standard protocols and technology	TCP、IP

RFC - Internet standard form:

RFC to rise as the official Internet standard of four stages :
1) a draft Internet (Internet Draft) at this stage is not the RFC documents.
2) proposed standard (Proposed Standard) from the stage became RFC documents.
~~3) draft standard (Draft Standard)~~
4) Internet standards (Internet Standard)

Standardization organizations

organization	Responsibility
International Organization for Standardization iso	OSI reference model, HDLC protocol
International Telecommunication Union ITU	Develop communication rules
International Association of Electrical and Electronics Engineers (IEEE)	Academic institutions · IEEE802 series of standards · 5G
Internet Engineering Task Force (IETF)	Responsible for Internet-related standards RFC

1.1.3 rate related performance indicators

rate

Both the rate of the bit rate or said data transmission rate or bit rate .

Bits: 1/0 bit

Connected to a computer network, host transmit data in the digital channel bits and rate

Unit: B / S, kB / S, MB / S, GB / S, TB / S

rate	storage capacity
One thousand 1KB / S = 10 ^{. 3} B / S	1KB=2¹⁰B=1024B=1024 * 8b
兆1Mb/s=10³kb/s= 10⁹b/s	1MB= 2¹⁰KB=1024KB
吉1Gb/s=10³Mb/s= 10⁶kb/s=10⁹b/s	1 GB=2¹⁰MB=1024MB
太1Tb/s=10³Gb/s=10⁶Mb/s=10⁹kb/s=10¹²b/s	1TB= 2¹⁰GB= 1024GB

bandwidth

" Bandwidth " originally refers to a difference signal having a frequency bandwidth, both the highest frequency and the lowest frequency, in Hertz (HZ)
Computer network, the bandwidth for data transmission capability of the communication network line expression, a point generally refers to "per unit time from the network to another point that can be adopted by the highest data rate ." Unit is "bits per second", b / s, kb / s, mb / s, gb / s

Network device supports a maximum speed

The columns: link bandwidth = 1Mb / s within 1us host may send data to the link 1bit

Throughput

Definition: represents the amount through a network (or a channel, the interface) of data per unit time

Throughput rate is limited by the rated bandwidth of the network or networks.

1.1.4 delay, delay-bandwidth product, RTT, and utilization

Delay

Definition: data transfer from one network to the other end of the time required, also known as delay or delay unit is s.

Transmission delay (propagation delay) : counted from the first bit of the transmission packet. The last bit of the packet transmission time required for completion (= data length / channel bandwidth (transmission rate))
Propagation delay : it depends on the electromagnetic wave propagation velocity and the length of the link (= channel length / channel electromagnetic wave propagation speed)
Queuing delay : Wait Input / output link is available
Processing delay : error detection, looking for export

Delay-bandwidth product

Definition: delay bandwidth product (bit) = the propagation delay (s) X Bandwidth (b / s)

Also called toLink length in units of bits, Is a " certain link How many bits "

Round-trip time RTT

Starts to send data from the sender to the sender receives acknowledgment receiving side (immediately after the receiver receives the data acknowledgment transmission), total delay experienced .

RTT larger, until confirmation is received, the more data can be transmitted.

RTT comprising: round-trip propagation delay 2 * = propagation delay , and the end of the processing time .

Utilization

$ Channel utilization = \ frac {} {data by time (no + n)} $ Time data
Network utilization - a weighted average channel utilization

Section II

1.2.1 hierarchical structure, protocols, interfaces, services

Why layered?

Before sending the file to be done:

The computer will initiate communication via the communication must be activated .
To tell the network how to identify the destination host.
To find a computer to initiate communication with the host whether the purpose of the boot, and the network is normal.
Computer to initiate communication to figure out whether the other computer file management application is ready to work.
Ensure that errors and accidents can be resolved.

……

How stratification?

Task : 82 years of Lafite mail to them.

Between the layers mutually independently , each implement only a relatively independent function.
Between each interface naturally clear , easy to understand, communicate with each other as little as possible.
Separable structure cut on each floor are used the most appropriate technology to achieve.
Remain lower on the upper independence, the upper one-way use the services provided by the lower layer .
The entire hierarchy should promote standardization.

Officially recognized hierarchy

Entity : the active element is referred to as n-th layer in the n-layer entity . The same layer entity is called peer entities .
Protocol : rules for network entities in the peer data exchange established standards or conventions called network protocol level []
- Provision of data transmission format: Syntax
- Semantics: provisions must complete function
- Synchronization: a predetermined sequence of the various operations
Interface (service access point SAP) : use the upper entrance of the underlying services.
Services : lower call to the function provided adjacent the upper. 【vertical】

SDU service data unit: completion data requested by the user and to be transmitted.

PCI Protocol Control Information: Control Message Protocol operation.

PDU protocol data unit: a unit of data transfer between peer level.

The concept summary

From the network architecture is functional description of the computer network architecture.

Structure referred to as network architecture computer network system is a hierarchical structure .

Each follow a / some network protocols to accomplish this layer functions.

Computer Network Architecture is a computer network layers and protocols set.

The n + 1 layer in the layer to provide service, which includes not only a function of n-th to n layer itself, further comprising a function provided by the underlying service.

Only in an interface between adjacent layers on the specific implementation details and the services provided by a layer completely shielded.

Architecture is abstract , while the realization refers to the number of software and hardware that can run.

1.2.2 OSI Reference Model

Computer network hierarchy:

7-layer OSI reference model ^{legal standards}
Layer 4 TCP, IP reference model ^{de facto standard}

ISO / OSI reference model - how come?

In order to solve the problem of large complex computer networks - hierarchical structure ( by function )

Purpose: To support a heterogeneous network system interoperability.

International Organization for Standardization (ISO) proposed OSI (OSI) reference model in 1984.

Note: The theory is successful, market failure.

ISO / OSI reference model

OSI layer	The number of layers	effect
Application layer	7 \|	DATA header plus control information
Presentation layer	6 \| Resource subnet (data processing)	7----PDU
Session Layer	5 _\|	6-------PDU
Transport Layer	4	5----------PDU
Network layer	3 \|	4------------PDU
data link layer	2 \| subnetworks (data communication)	T2--3---------------PDU
Physical Layer	1 _\|	010100011111000……

Doggerel:Things Suki trial。

Completion of a particular function of each layer

ISO / OSI reference model explains the communication process

Application layer

Definition: All programs can generate network traffic and user interaction

Typical application layer services:

File transfer (FTP)
E-mail (SMTP)
World Wide Web (HTTP)

……

Presentation layer

Definition: a communication system for processing a two way exchange of information indicating (syntax and semantics)

Function 1: data exchange format ^translator

Function II: data encryption and decryption

Function Three: data compression and recovery

Session Layer

Definition: providing presentation entities / user process to establish a link and the connecting order to transmit data.

This is the session, but also to establish synchronization (SYN)

A function: to create, manage, terminate a session

Two functions: a checkpoint can use the communication session failure / recovery to continue communication synchronization points from the check point, data synchronization. (Applicable to transfer large files)

Transport Layer

Definition: The host is responsible for the two processes to communicate that to-end communications. Transmission unit is a segment or User Datagram

Function 1:canBy transmission, unreliable delivery

Function II:differenceWrong control

Function Three:flowVolume control

Function 4: ComplexuseDemultiplexing

Doggerel: can be retained difference?