DCN | Queuing models in data link networks

Ergodic process:As nothing is neither generated or lost in the queuing system, the arrival rate of packages equals to the departure rate.Little's LawStochastic processes and Markov chainsGiven appropriate state space and time variable, a stochastic process can be properly described. If the time variable is discrete, the process is called discrete-time process; otherwise, it's called continuous-time process.$\mu$ is the number of customers that can be served at one time (serving rate) $\lambda$

Data communication networks · 2024-10-25

EAWC | Acknowledgement, citation, paraphrasing and summary writing

Acknowledgement writingAcknowledgement is the last section of the body. It is set to express the author appreciation. This part is quite emotional and subjective.Components for acknowledgement: most important teachers, financial aids, financial support from foundation, research group (grant, fellowship, scholarship), other helps, friends, colleagues, families (but no boyfriend/girlfriend)Linguistic features of acknowledgement: being brief, polite, specific, first person, active voice, titles and

English for academic writing and communication · 2024-10-25

DCN | Data link layer: Framing & error detection

Data link layer is responsible for delivering data from one node to another node, which means that the duty scope of data link layer is only node-to-node. A packet at the data link layer is called a frame. Any mistakes made in physical layer is supposed to be solved in data link layer.Types of data link layer:Point to point link: it consists of a single sender at one end of the link and a single receiver at the other end.Broadcast link: it can have multiple sending and receiving nodes all connec

Data communication networks · 2024-10-08

DCN | Switching in data networks

Circuit switchingCircuit switching approaches are used in traditional telephone networksFrequency-Division Multiplexing (FDM)Time-Division Multiplexing (TDM)Three phases are needed for communication in a circuit-switched network:Setup: dial the phone numberData transfer: communicationTeardownDelay in circuit-switched networks is the sum of times needed to setup the connection (connection delay, propagation delay), transfer the data and disconnect the circuitPacket-switched networksDefinition: No

Data communication networks · 2024-09-29

EAWC | How to be a scholar - the basic

Critical thinkingbuild your own academic vocabulary for academic writing.Try to be a reviewer. RAS: reliable, acceptable (authority), sufficiencyCultivate your ability of critical thinking at anytime.How to write a literature reviewdescribe the procedures accurately and assure their replicability, making other researchers able to repeat your experimentsHow to read research papersPreparationbe acquainted with the fieldsbe criticalget newest research papers through different ways (google scholar,

English for academic writing and communication · 2024-09-20

信息论基础 | 信道编码

第6章 信道编码噪声信道中的编码前言平均互信息（信息传输率）为$I(X;Y)=H(X)-H(X|Y)$信道容量为$C=\max I(X;Y)$通过调整信源的概率分布，使得信息传输率尽量接近信道容量，也就是让信息传输率尽可能大，这一过程称为信源和信道匹配信源编码的目的：增加信源熵$H(X)$，理解为信源发出的所有符号中每个符号带有的平均信息量，实现符号匹配，压缩冗余信道编码的目的：减少损失熵$H(X|Y)$，提高传输信号的抗干扰能力避免少量差错信号对信息内容的影响：使用纠错编码（纠错、检错）信道编码的研究对象：信息序列（即码元间彼此无关且等概率出现）基本思路：在传输的信息码中按照一定规律产生一些附加码元，经过信道传输，在传输中若码字出现错误，接收端则利用编码规律发现码的内在相关性被破坏，从而按照一定的译码规则自动纠正或发现错误，降低误码率基本方法前向纠错(FEC)纠错过程在接收端独立进行，没有反馈，信息一直朝着前面的方向传播，因此叫前向译码设备复杂，适用于实时性高容错能力强的场合反馈重发(ARQ)在接收端判断收到的序列是否符合编码规则，如果不符合就通知重发如循环冗余校验码(CRC)混合纠

Informatics·General Learning · 2022-12-16

信息论基础 | 信源编码

第5章 信源编码前言编码方式信源编码信道编码信源编码原因由于信源符号之间存在分布不均匀和相关性，使得信源存在冗余度目的通过信源编码减少冗余，提高编码效率，提高通信的有效性方法解除相关性概率均匀化定理无失真编码定理（针对离散信源）限失真编码定理（针对连续信源）编码的概念定义分组码将信源消息分成若干组，用符号序列$\mathbf {x_i}=(x_{i_1},x_{i_2},\cdots,x_{i_l},\cdots,x_{i_L})$表示，序列中每个符号都取自于符号集$A$，$x_{i_L}\in A=\{a_1,a_2,\cdots,a_i,\cdots,a_n\}$，每个$x_i$依照固定的码表映射成一个码字$y_i$按照码表映射编码的码称为分组码，有时也叫做块码，只有分组码才有对应的码表，非分组码不存在码表码字每个码符号序列称为码字，如编码后的${0001,0010,1100}$$D$元码由$D$个符号组成的码字集合，如${0,1}$对应二源码，${0,1,2}$对应三元码理解根据编码方式的不同，同一个信源符号可以有不同的码符号序列将信源符号变换成由码元符号组成的码符号序列的过程就

Informatics·General Learning · 2022-12-13

信息论基础 | 信息率失真函数

第4章 信息率失真函数前言对于失真的合理与可行性分析实际信息处理过程允许一定程度的失真连续信源编码必定存在失真一定范围内的失真可以大幅提高编码效率本章的研究对象允许一定失真的离散信源编码和连续信源编码失真函数定义设某一信源$X$，输出样值为$x_i$，经过有失真的信源编码器，输出$Y$，样值为$y_j$，满足以下关系$$ x_i\in \{a_1,\cdots,a_n\},y_j\in \{b_1,\cdots,b_m\} $$如果$x_i$=$y_j$，则认为没有失真，反之认为产生失真失真函数表示为$d(x_i,y_i)$，是用来表示失真的大小的量，能衡量用$y_i$代替$x_i$所引起的失真程度，一般的失真函数可定义为$$ d(x_i,y_j)=\left \{ \begin {matrix} 0,&x_i=y_j\\ \alpha,&\alpha>0,x_i\neq y_j \end {matrix} \right. $$如果把所有的失真函数值排列起来，则可以用矩阵表示，构成失真矩阵$$ \mathbf d=\begin {bmatrix} d(a_1,b

Informatics·General Learning · 2022-12-05