[Reprint] [computer network] Overview 00

[Computer network] Overview 00

HTTPS: // linianhui.github.io/computer-networking/00-overview/ 

original author to write very good.

 

2019-09-22 08:10, about  1622 words, reading of about  4 minutes  [computer network]  ARPNET   the IETF   the LAN   the WAN   the WLAN   a WiFi   packet switching   rate of   the bandwidth   delay   the RTT   the OSI   the TCP / the IP   channel utilization  559f516  the Add-Computer Networking 2019-09-22 11:25   Source

November 1969 US Department of Defense has established a packet-switched network called ARPANET (Internet of prototype), the current time is 2019, 50 years have passed, and now the network has been integrated into all aspects of society, its importance goes without saying Yu. This series of blog focusing on the core concepts of computer networks and architecture, does not involve the concept of network programming.

1 Standardization

Computer network by a node (node: a computer, a hub, switch or router) and the links connecting them (link) the composition. How many of the communication between these devices? Where the meaning is inseparable from a wide variety of standard, that standard uniform rules, you can follow the same standard interoperability between devices, in order to avoid some incompatibility problems. IETF (Internet Engineering Task Force) is an important institution in charge of standardization, IP, TCP, UDP, DNS , HTTP , and so many protocols are standardized by the IETF.

2 common classification

According to regional location geographically divided, we have the following classification:

1. LAN : Local Area Network (LAN), such as all devices connected to a home router on the formation of a LAN.
2. WAN : Wide Area Network (WAN), such as routers through the PPPoEconnection to the broadband operator's network environment.
3. WLAN : Wireless LAN (WLAN), such as WiFi or WAPI.

3 packet switching (Packet Switching)

The computer network does not use the traditional telephone networkCircuit SwitchedCommunication mode, instead of using packet switching. Understanding of computer network packet switching is to understand the most important step (no one).

1. Circuit Switched : The core principle is to establish a reliable and dedicated communication link for the two sides, the two sides for communication use.
2. Packet switching: the core principle is to split the original data into a small packets of data, then forwarding, then forwarding the communication is transmitted both ways.

It is also packet-switched this design, it was able to support the Internet's explosive growth.

4 Performance

Performance computer network's performance in it on several indicators.

4.1 rate (Bit Rate)

Rate is the bit rate of data transmission (bit rate): bit unit time (second) transmission (binary digit) number. Units bit/s, b/sor bps.

1. Kbps : 103 per bit.
2. Mbps : Per 106 bit.
3. Gbps : Per 109 bit.

4.2 Bandwidth (Bandwidth)

Refers to the bandwidth of the original signal bandwidth, such as 300Hz ~ 600Hz, this time is measured in hertz (Hz).

In computer networking, the bandwidth typically refers to the highest rate of the link, right, is the above-mentioned # 4.1 rate (Bit Rate) .

4.3 Throughput (Throughput)

Throughput is the actual amount of data through a link per unit time (seconds). It's usually the unit and # 4.1 rate (Bit Rate) is the same.

For example, for a 10Gb/snetwork, its actual throughput may be 100Mb/s, but can not exceed the maximum 10Gb/s.

4.4 Delay (Delay)

Is the time delay data from one end to the other end of the link is consumed. Delayed by several distinct parts:

1. Queuing delay: data frames queued at the node waiting time is consumed during processing.
2. Processing Delay: node processing time consumed by a data frame.
3. Transmission delay: a data frame transmission time consumed (such as a total of 100 bit, a first bit transmitted from the beginning to the completion of the 100 bit transmission time). = Transmission delay  数据帧长度(bit) / 发送速率(bit/s).
4. Propagation delay: the time required for the electromagnetic wave propagation in a channel. = Propagation delay  信道长度(m) / 传播速度(m/s). Electromagnetic wave propagation velocity in a vacuum is the speed of light 300000km/sin the fiber is about 200000km/s. For example the fiber 200km, then a delay of about 1ms =  (200000km/s) / 200km.

The total delay =  排队延迟 + 处理延迟 + 发送延迟 + 传播延迟 . At the same rate, the delay as low as possible. In the case of different rates, sometimes a low rate low-latency network is better than + a + high rate high latency network.

4.5 round trip time (RTT)

A round trip time required for the communication, roughly equal to 2 ( # 4.4 delay (Delay) ) time.

4.6 channel utilization (Channel Utilization)

Formula: = channel utilization  发送延迟 / (发送延迟 + 往返传播延迟). For example, to send 10kbdata, the transmission rate 1000kb/s, the fiber length 20km. Then:

1. Transmission delay =  10/1000 =  10ms.
2. Round-trip propagation delay =  (20mk / 200000km/s) * 2 =  20ms.
3. Channel utilization =  10ms / (10ms + 20ms) =  33.33%.

5 layered architecture

Solving complex problems in the computer field, there are two time-tested means of: abstract and layered. Today, the reality of the computer network is usually a hierarchy follows.