什么是 Latency

1) In a network, latency, a synonym for delay, is an expression of how much time it takesfor a packet ofdata to get from one designated point to another. In some usages (for example, AT&T), latencyis measured by sending a packet that is returned to the sender and the round-trip time isconsidered the latency.

The latency assumption seems to be that data should be transmitted instantly between one pointand another (that is, with no delay at all). The contributors to network latency include:

• Propagation: This is simply the time it takes for a packet to travel between one placeand another at the speed of light.
• Transmission: The medium itself (whether opticalfiber, wireless,or some other) introduces some delay. The size

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• of the packet introduces delay in a round trip sincea larger packet will take longer to receive and return than a short one.
• Router and other processing: Each gateway node takestime to examine and possibly change the header in a packet (for example, changing the hopcount in the time-to-livefield).
• Other computer and storage delays: Within networks at each end of the journey, a packetmay be subject to storage and hard disk access delays at intermediate devices such as switches andbridges.(In backbone statistics, however, this kind of latency is probably not considered.)

2) In a computer system, latency is often used to mean any delay or waiting that increases realor perceived responsetime beyond the response time desired. Specific contributors to computer latency includemismatches in data speed between the microprocessor and input/output devices and inadequate data buffers.

Within a computer, latency can be removed or "hidden" by such techniques as prefetching(anticipating the need for data input requests) and multithreading, or using parallelismacross multiple execution threads.

3) In 3D simulation, in describing a helmet that provides stereoscopic vision and head tracking,latency is the time between the computer detecting head motion to the time it displays theappropriate image.

Contributor(s): Ed Blair

This was last updated in June 1997

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PING ——网络延时，目前比较正规的叫法为“Latency”，是指您的机器和总服务器之间的连接速度，Latency 是在您发出的指令在经过多少单位时间后，服务器才做出反应的
这段延时时间。
PING值越高（数值越大）速度越慢，反之越快。
PING 值的高低主要和网络连接方式有关。
比如ADSL连接一个当地的服务器，PING 值在20-80 之间；用56kmodem 连接，PING 值是在200-300 之间。

FPS —— frames per second 每秒钟显示的图像帧数。FPS 反映的是机器在运行该游戏和程序的“快与慢”的问题，
FPS 越高（值大）速度越快；反之，则速度越慢。
FPS主要和您的机器配置（其中与显卡和CPU关系最大）、config 设置（游戏设置，比如使用高质量画质显示等）相关，
和ping 基本上没有关系。基本上，有高PING 必有LAG，但是有LAG不一定表示PING值高。FPS和PING，LAG没有直接关系，高FPS 下也偶然会出现LAG。

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ping来检查网络时，如下 Reply from 119.75.218.45：bytes=32 time=28ms TTL=55

1、默认32 ，可以在命令行修改
2、网速快慢
3、TTL是IP协议包中的一个值，它告诉网络,数据包在网络中的时间是否太长而应被丢弃。TTL的最初设想是确定一个时间范围，超过此时间就把包丢弃。由于每个路由器都至少要把TTL域一，TTL通常表示包在被丢弃前最多能经过的路由器个数。当记数到0时，路由器决定丢弃该包，并发送一个ICMP报文给最初的发送者。