In computers, lag is delay (latency) between the action of the user (input) and the reaction of the server supporting the task, which has to be sent back to the client. The player's ability to tolerate lag depends on the type of game being played. For instance, a strategy game or a turn-based game with a slow pace may have a high threshold or even be mostly unaffected by high lag. A game with twitch gameplay such as a first-person shooter or a fighting game with a considerably faster pace may require a significantly lower lag to provide satisfying gameplay. Lag is mostly measured in milliseconds (ms) and may be displayed in-game (sometimes called a lagometer). The most common causes of lag are expressed as ping time (or simply ping) and the frame rate (fps). Generally a lag below 100 ms (10 hz or fps) is considered to be necessary for playability. The lowest ping physically possible for a connection between opposite points on Earth crossing half of the planet is 133 ms. Other causes of lag result commonly in a lag below a playable 20 ms (50 Hz or fps), or in the loss, corruption or jitter of the game.
Causes
While a single-player game maintains the main game state on the local machine, an online game requires it to be maintained on a central server in order to avoid inconsistencies between individual clients. As such, the client has no direct control over the central game state and may only send change requests to the server, and can only update the local game state by receiving updates from the server. This need to communicate causes a delay between the clients and the server, and is the fundamental cause behind lag. While there may be numerous underlying reasons for why a player experiences lag, most common reasons are poor connection between the client and server, or insufficient processing in either the client or the server.
Connection Perhaps the most common type of lag is caused by network performance problems. Losses, corruption or jitter (an outdated packet is in effect a loss) may all cause problems, but these problems are relatively rare in a network with sufficient bandwidth and no or little congestion. Instead, the latency involved in transmitting data between clients and server plays a significant role. Latency varies depending on a number of factors, such as the physical distance between the end-systems, as a longer distance means additional transmission length and routing required and therefore higher latency. Routing over the Internet may be extremely indirect, resulting in far more transmission length (and consequent latency) than a direct route, although the cloud gaming service OnLive has developed a solution to this issue by establishing peering relationships with multiple Tier 1 network Internet Service Providers and choosing an optimal route between server and user. –====Ping time==== Ping time, or simply ping, is the main measure of connection lag. Ping time is the network delay for a round trip between a player's client and the game server as measured with the ping utility or equivalent. Ping time is an average time measured in milliseconds (ms). The lower one's ping is, the lower the latency is and the less lag the player will experience. High ping and low ping are commonly used terms in online gaming, where high ping refers to a ping that causes a severe amount of lag; while any level of ping may cause lag, severe lag is usually indicated by a ping of over 100 ms. This usage is a gaming cultural colloquialism and is not commonly found or used in professional computer networking circles. Some factors that might particularly affect ping include: communication protocol used, Internet throughput (connection speed), the quality of a user's Internet service provider and the configuration of firewalls. Ping is also affected by geographical location. For instance, if someone is in India, playing on a server located in the United States, the distance between the two is greater than it would be for players located within the US, and therefore it takes longer for data to be transmitted, resulting at 90,000 km (halfway around the Earth) in a ping of 0 ms. However, the amount of packet-switching and network hardware in between the two computers is often more significant. For instance, wireless network interface cards must modulate digital signals into radio signals, which is often more costly than the time it takes an electrical signal to traverse a typical span of cable. As such, lower ping can result in faster Internet download and upload rates.
Interface
Input-lag Input-lag or input latency is the lag produced by the input device, such as a mouse, keyboard or other controller, and its connection. Wireless devices are particularly affected by this kind of lag. Some people claim to notice extra lag when using a wireless controller, while other people claim that the 0–1 milliseconds of lag is negligible. The refresh rate is a type or part of input-lag that is the rate of a display to produce distinct picture, measured in Hz (e.g. 60, 240 or 360, that is 16.7, 4.2 or 2.8 ms respectively).
Display lag
This is the lag caused by the television or monitor (also called output lag). In addition to the latency imposed by the screen's pixel response time, any image processing (such as upscaling, motion smoothing, or edge smoothing) takes time and therefore adds more input lag. An input lag below 60 ms is generally considered unnoticeable in a television. Once the frame has been processed, the final step is the updating the pixels to display the correct color for the new frame. The time this takes is called the pixel response time.
… excerpt ends here. Continue reading the full article.
