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Measure of file size: KBps

File size i.e. how big the file or how much space a file occupies in the hard disk measured in terms of Kilo Bytes (KB upper case “K” and upper case “B”). In computing terms the upper case “K” stands for 1024. 1024 is computed from 210. (2 power 10). 2 denote the number of characters in the binary system which is used to store data in the disc (ones and zeroes).
Other abbreviations like mega, giga and terra also use the base as 1024,

1KB (Kilo Byte) = 1024 Bytes (approximately 1000 Bytes)
1MB (Mega Byte) = 1024 KB (approximately 1000 Kilo Bytes or 1 million Bytes)
1GB (Gigabyte) = 1024 MB (approximately 1000 Mega Bytes or 1 billion Bytes)
1TB (Terra Byte) = 1024 GB (approximately 1000 Gigabytes or 1 trillion Bytes)

Measure of data transfer speeds: kbps

Data transfer speed over the networks (including the internet) is calculated in terms of bits per second: kilobits (kb small case “k” and small case “b”). The higher the kbps i.e. more the bits transferred per second, more the speed, faster the network/connection. Here k stands for 1000 (103 )

1 kbps (kilo bits per second) = 1000 bits per second
1 Mbps (mega bits per second) = 1000 kilo bits per second.
1 Gbps (giga bits per second) = 1,000 mega bits per second.

ISP bandwidth and download speeds

The most common confusion caused by the similarity of KBps and kbps is when it comes to internet bandwidth and download speeds. People often complain that their ISP promised 512kbps connectivity but they are seldom able to download any file at 512 KBps. They fail to notice the difference in cases of the units and hence think their ISP is cheating them or offering them poor quality service. As mentioned earlier data transfer speeds are always calculated in terms of kilo bits per second (kbps) so an ISP connectivity of 512 kbps promises of transfer of at the max 512 kilo bits per second.

On the other hand, file size measure is always in Kilo Bytes and thus download speeds are always calculated based on how many Bytes per second are downloaded and hence Kilo Bytes per second (KBps). KBps and kbps are not interchangeable.

So an internet connectivity of say 512kbps can never achieve a download speed of 512 KBps. To calculate the maximum download speed of a “X kbps” connection, we need to use a simple formula as below.

Download KBPS speed = (Kbps value*1000) /8)) / 1024.

I.e. For a connectivity of 512 kbps

kbps value 1000 = 512 1000 = 512000

512000 / 8 = 64000

64000 / 1024 = 62.5 KBps

Therefore theoretically an internet connection of 512kbps bandwidth can download at a speed of 62.5 KBps.

If you don’t want to go through all the hassles of the above formula, just multiply the kbps value with 0.1220703125 to get the KBps value.

512 kbps * 0.1220703125 = 62.5 KBps. Simple!

Internet connectivity

Download speed (approx) ( Marked in Italics)

256 kbps

31.3 KBps

384 kbps

46.9 KBps

512 kbps

62.5 KBps

768 kbps

93.8 KBps

1 mbps ~ 1000kbps

122.1 KBps

I have mentioned download speed as approximate because they will vary (always reduce) by 15 – 20% due to network signal loss, computer hardware overheads etc. So for realistic, real world figures always reduce 15 – 20% from the computed KBPS download speeds
Now I guess the confusion of kbps and KBps has cleared away. Just remember when you talk in terms of network it’s always bites per second (bps) and when you talk in terms of storage and files its always Bytes per second (Bps). And next time you won’t complain when your 512 kbps connection does not give you download speeds of 512KBps because now you know why .

from: https://www.quora.com/What-is-the-difference-between-kbps-and-KBPS

Q1: What's meaning of PAN, LAN, MAN, WAN and internet



  1. PANs(Personal Area Network) let devices communicate over the range of a person. A little example are wireless mouse, wireless keyboard that based on Bluetooth.
  2. LAN(Local Area Network) is a privately owned network that operates within and nearby a single building like a home, office or factory. When LANs are used by companies, the are called enterprise networks". AP, wireless router, base station are LAN devices.
  3. MAN(Metropolitan Area Network) covers a city.
  4. WAN(Wide Area Network) spans a large geographical area, often a country or continent.
  5. Internetwork(also called internet) is a collection of interconnected networks.

Q2: what's the difference of layer and interface.


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

A list of the protocols used by a certain system, one protocol per layer, is called a protocol stack.

Between each pair of adjacent layers is an interface.The interface defines which primitive operations and services the lower layer makes available to the upper one.

Q3: what are design issues for the layers


  1. Reliability

    1. error detection
    2. finding a working path through a network
  2. the evolution of the network
  3. resource allocation
  4. security

一. 网络中的7层模型是指哪些?他们的作用和职责分别是什么?


  • 应用层
  • 表示层
  • 会话层
  • 传输层
  • 网络层
  • 数据链路层
  • 物理层

2. 四层网络模型指的又是什么?他们的作用和职责指的是什么?分别和7层模型的对应关系是什么?


  • 应用层(application layer)
    每一个应用层(TCP/IP参考模型的最高层)协议一般都会使用到两个传输层协议之一: 面向连接的TCP传输控制协议和无连接的包传输的UDP用户数据报文协议。
  • 传输层(transport layer)
  • 网络互联层(internet layer)
    TCP/IP协议族中的网络互连层(internet layer)在OSI模型中叫做网络层(network layer)。
  • 网络接口层(link layer)



3. TCP/UDP分别是指什么?他们的区别是什么?

4. TCP新建连接的3次握手是指什么?为什么会有3次握手?

5. TCP关闭连接的时候的4次握手是指什么?为什么要4次握手?

6. IP地址是什么?什么是IP段,如何区分?

7. IP的A,B,C,D类地址指什么什么?

八. 什么是网桥?2层交换机,4层交换机,7层交换机是什么?分别用途是拿来做什么的?

1. 中继器


2. 网桥/2层交换机


3. 路由器/3层交换机


4. 4~7层交换机


5. 网关


常用的网关有“互联网邮件和手机邮件之间的转换服务”,以及WWW服务中的"Proxy Server"。


1. 关于单播,广播,多播,任播


  1. 单播就是主播想和一个人私聊了,然后说,谁送我火箭最多,我就和谁私聊,于是土豪的你一下买了1000个火箭送给主播,于是主播么么哒和你私聊
  2. 广播就是所有人,只要进了那个APP,就能看到一堆主播在那儿搔首弄姿,免费滴
  3. 多播就是,主播说,宝宝们,来点火箭,我把你们拉到一个单独的群里面看不一样的东西。
  4. 任播就是,主播想和某个粉丝私聊了,然后随便选了一个粉丝私聊



  1. 维基百科对TCPIP协议的说明,蛮不错的


A domain-specific language (DSL) is a computer language specialized to a particular application domain. This is in contrast to a general-purpose language (GPL), which is broadly applicable across domains. ... Simpler DSLs, particularly ones used by a single application, are sometimes informally called mini-languages