DCN

Data Info

Data is a collection of values, symbols, or characters that represents information

Two kinds of data

• Qualitative data (Non-numerical data) 定类数据
• Quantitative data 定量数据
  • Discrete data
    • Binary data
    • Limited values(finite values)
  • Continuous data^[1]

Communication

Message

the information (data) to be communicated(text, numbers, pictures, audio, and video,...)

Sender

the device that sends the data message(a computer, workstation, telephone handset,video camera, and so on)

Receiver

the device that receives the message.

Transmission medium

the physical path by which a message travels from sender to receiver. (twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves)

Protocol

a set of rules that govern data communications :::success expample Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese. :::

network protocol

Info

TIP

A protocol is an agreement between the communicating parties on how communication is to proceed

• Communication node is machine
• All communication is controlled by protocols
• Protocols define formats, order of sending and receiving of messages, and the actions that the reception initiates

For example -HTTP

HTTP (HyperText Transfer Protocol) specifies rules by which the client and the server interact so as to retrieve a document. The protocol assumes the client and the server can exchange messages directly. The client software needs to set up a two-way connection prior to the HTTP request.

Elements of a Protocol

Syntax

• Structure or format of the data
• Indicates how to read the bits - field delineation

Semantics(语义)

• Interprets the meaning of the bits
• Knows which fields define what action

Timing

• When data should be sent
• Speed at which data should be sent or speed at which it is being received.

Data flow

simplex

Keyboards and traditional monitors are examples of simplex devices. The keyboard can only introduce input; the monitor can only accept output

half-duplex

The half-duplex mode is used in cases where there is no need for communication in both directions at the same time; the entire capacity of the channel can be utilized for each direction

full-duplex

One common example of full-duplex communication is the telephone network

Signals

Analog signal(模拟信号)

Analog signals are continuous electrical signals that vary in time.

Digital signal(数字信号)

Digital signals are non-continuous. They consist of pulses or digits with discrete levels or values. Digital signals usually have two amplitude levels such as 1 or -1, HIGH or LOW

Advantages of Digital Signals

Less sensitive to the interferences (e.g., noise, magnetic field) Easier for further processing (e.g., error correction, storage, etc.)

Digital Encoding Schemes

非归零 (NRZ)

• 优点：
  1. 实现简单，易于理解。
  2. 对于高速数据传输来说，能够最大程度地利用可用带宽。
• 缺点：
  1. 缺乏时钟恢复机制。
  2. 无法检测数据中的错误。

曼彻斯特 (Manchester)

• 优点：
  1. 提供时钟恢复机制，确保可以从传输信号中恢复数据。
  2. 每个数据比特都与一个信号过渡相关联，因此可以进行错误检测。
• 缺点：
  1. 带宽利用不够充分，因为过渡消耗了一半的可用带宽。
  2. 实现相对于NRZ而言更为复杂。

4B/5B编码

• 优点：
  1. 每个码字是唯一的，因此可以进行错误检测。
  2. 提供时钟恢复机制。
  3. 与曼彻斯特相比，带宽利用更佳。
• 缺点：
  1. 相对于NRZ和曼彻斯特，实现更为复杂。
  2. 需要额外的硬件和处理能力。

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1. This means Any value in a certain range AND it is a unlimited values, infinite values ↩︎