物理层在OSI模型中的功能| 计算机网络

什么是物理层？ (What is Physical Layer?)

The physical layer consists of all the functions required to transmit a bitstream over a Physical medium. The electrical and mechanical specifications of the interface and transmission medium deals by this layer.

物理层包括在物理介质上传输比特流所需的所有功能。 接口和传输介质的电气和机械规格由该层处理。

• This is the lowest layer of the OSI reference model.
  这是OSI参考模型的最低层。
• For transmission, it defines all the procedures and functions that physical devices and interfaces have to perform.
  对于传输，它定义了物理设备和接口必须执行的所有过程和功能。
• It is physical and tangible as well.
  它也是有形的和有形的。
• However, it does not deal with the actual physical medium (like fiber, copper).
  但是，它不处理实际的物理介质(如纤维，铜)。
• Physical Layer devices are Hub, Repeater, Modem, Cables.物理层设备是集线器，中继器，调制解调器，电缆。

This figure shows the position of the physical layer concerning the transmission medium and the data link layer.

该图显示了有关传输介质和数据链路层的物理层的位置。

Physical Layer

物理层

物理层的设计问题 (Design Issues with Physical Layer)

• Physical Layer is transmitted raw bits over a communication channel.物理层通过通信信道发送原始位。
• Making sure that when one side sends a 1 bit, it is received by the other side as a 1 bit and not as a 0 bit.
  确保当一侧发送1位时，另一侧以1位而不是0位接收它。
• The design issues here mostly deal with electrical, mechanical and timing interfaces.
  这里的设计问题主要涉及电气，机械和定时接口。

Physical Layer concerned with the following,

物理层涉及以下方面，

Physical characteristics of interfaces and media: It defines the characteristics of the interface between the devices and the transmission medium. It also defines the type of transmission medium.

接口和媒体的物理特性 ：它定义了设备和传输媒体之间接口的特性。 它还定义了传输介质的类型。

The capacity of transmission media is bandwidth. It defines transmission speed and communication methodology.

传输媒体的容量就是带宽。 它定义了传输速度和通信方法。

Representation of bits: The physical layer data involves a stream of bits (sequence of 0's and 1's) without any interpretation. To be transmitted bits must be encoded into the signals - electrical or optical.

比特表示 ： 物理层数据涉及比特流(0和1的序列)，没有任何解释。 要传输，必须将比特编码为电或光信号。

• physical layer defines the type of encoding (how 0's and 1's are changed in signals).物理层定义了编码的类型(信号中0和1的变化方式)。
• Physical layer obtains data in the form of signals or the radio signals or the optical signals.物理层以信号或无线电信号或光信号的形式获得数据。
• The physical layer is responsible for delivering those signals from a cable, a Wi-Fi router or an optical fiber.
  物理层负责从电缆，Wi-Fi路由器或光纤传送那些信号。

Data Rate (Transmission Rate): The number of bits sends each second is also defined by the physical layer. In other words, the physical layer defines the duration of a bit also.

数据速率(传输速率) ：每秒发送的位数也由物理层定义。 换句话说，物理层也定义了比特的持续时间。

Synchronization of bits: It is necessary to have synchronization between sender and receiver at the bit level that is the clocks of the sender and the receiver must be synchronized.

比特同步：在发送者和接收者之间的同步必须达到比特级别，即发送者和接收者的时钟必须同步。

Line configuration: The physical layer is responsible for the connection of devices to the medium. Two devices are connected through a dedicated link in a point-to-point configuration.

线路配置 ：物理层负责将设备连接到介质。 两个设备通过点对点配置中的专用链路连接。

• A single link is shared among several devices in a multipoint configuration,
  在多点配置中，多个设备之间共享一条链接，
• The computer generates data in the form of '0's and '1's. So, there are different varieties of cable that carry data from our computer to the switch or a nearby port.
  计算机生成“ 0”和“ 1”形式的数据。 因此，有各种各样的电缆将数据从我们的计算机传输到交换机或附近的端口。
• In this case, an encoder is responsible for the encoding of data before sending them on the different wires just like traffic police.
  在这种情况下，编码器负责数据的编码，然后再像交通警察一样在不同的线路上发送数据。
• Then, the decoder will similarly extract those data from the different wires and make them readable to the computers.
  然后，解码器将类似地从不同的导线中提取那些数据，并使它们对计算机可读。

Physical topology: The Physical topology determines how devices are connected to create a network. Devices can be using a mesh topology (every device can be connected to other devices), a star topology (all the devices are connected through a central device), a ring topology (devices are connected to the next forming a ring), or a bus topology (every device shared a common link). For digital and analog communication, data signaling encompasses timing and coding rules.

物理拓扑 ：物理拓扑确定如何连接设备以创建网络。 设备可以使用网状拓扑(每个设备都可以连接到其他设备)，星形拓扑(所有设备都通过中央设备连接)，环形拓扑(设备连接到下一个形成环的设备)或总线拓扑(每个设备共享一个公共链接)。 对于数字和模拟通信，数据信令包含时序和编码规则。

Transmission mode: The mechanism of transferring data or information between two linked devices connected over a network, is referred to as Transmission Modes.

传输模式 ：在通过网络连接的两个链接的设备之间传输数据或信息的机制，称为传输模式。

They are simplex, half-duplex, or full-duplex.

它们是单工，半双工或全双工。

• simplex mode, communication is unidirectional that is data can be sent only in one direction. This means you cannot send a message back to the sender just like a one-way street.单工模式下 ，通信是单向的，即数据只能在一个方向上发送。 这意味着您不能像单向街一样将消息发送回发件人。
• half-duplex mode, each station can transmit and receive the data as well.半双工模式下 ，每个站点也可以发送和接收数据。
• full-duplex (or simply duplex) mode, the communication is bi-directional, i.e., the data flow in both the directions at the same time.全双工 (或简单双工)模式下，通信是双向的，即，数据同时在两个方向上流动。

翻译自: https://www.includehelp.com/computer-networks/functions-of-physical-layer-in-the-osi-model.aspx