Lag

From Wikipedia, the free encyclopedia

For other uses, see Lag (disambiguation).

Lag is a common term used to describe a symptom often encountered in computing and especially networked systems, where results of actions appear much later than expected. While different kinds of latency are well defined technical terms, lag is not and should be used to describe the symptom, not the cause.

Communications latency is the time taken for a packet of data from the sending application to the receiving application. This includes both transit time over the network, and computer processing time at both the source and destination computers. Also known as one way latency this includes the time it requires to encode the packet for transmission and transmit it, the time it takes that serial data to traverse the network equipment between the nodes, and the time it takes to get the data off the circuit. The absolute minimum bound on latency is determined by the distance between communicating devices and the fraction of the speed of light (typically 70-95%) that the signal propagates within the circuits. However, packet processing in networking equipment and other traffic can increase latency significantly from this minimum.

Whilst in the strictest sense every packet experiences lag, the term lag is implied to refer to noticeable delays to the user caused as a result of extended or unexpected delay. As the time taken for a packet to travel from a server in Europe to a client nearby in the same region is likely to differ from a trip from Europe to the Americas or Asia, it is possible that two users may experience connections to the same server with a different extent of network lag. As latency is directly related to distance this tends to be the case. However well written code and protocols which avoid "application turns" or unnecessary chattiness are less effected by the inherent latency in a network. Modern corporate networks have devices to cache frequently requested data and accelerate protocols, thus reducing application response time, the cumulative effect of latency.

[edit] Causes of abnormal delay

Lag may be traced to three main sources:

Inadequate network performance: The packets are either interrupted along their path by faulty routers, the network cannot handle the number of packets sent/required (see: bandwidth) or the packets pass through an unusually large number of routers before reaching their destination.
Inadequate server processing power: Lag may be experienced where the user submits an unusual request which is not yet cached, or where the reply requires a large amount of processing before it can be sent. This affects multiplayer gaming. The bandwidth of an area which the packets would normally pass through quickly may be disrupted during working hours (for example), thus the packet would need to 'queue' at each router before being sent onwards. A suitable analogy would be the effects of rush hour on everyday road traffic. LAG stands for Latency Assimulation Gathering. Not very descripted, but that is what the techs say.
Inadequate computer processing power: Even on a fast connection, a slow computer may have a difficult time to process all the data being sent and received while other applications are running (ex.: online games and Internet browsers). Spyware and Peer-to-peer programs hamper the efficiency of both computer and connection integrity, reliability and efficiency in a timely manner.; Slow computers can usually be upgraded very easily in both hardware and software to improve efficiency. Stopping other programs such as spyware, trojans, viruses, and Peer-to-peer programs help as well.
Packet reordering and retries: Many communications protocols, especially those involved in on-line real-time gaming, require packets to be reassembled in order. If the network reorders the packets (which it is allowed to do), some protocols (as well as some protocol implementations) drop the out-of-order packets and rely on packet retries. This causes a delay in communications that is much greater than the network latency.

[edit] See also

Bandwidth - Measure of a connection's maximum data transfer capacity.
Ping - Tool for determining network latency with regard to another system.
Avalon - Movie by Mamoru Oshii, in which large parts of the portrayed society play an immense online virtual reality game, features lag as a phenomenon to which players react with bodily symptoms (convulsions, nausea).
Lagometer - A 'device' that measures lag.
Input lag
Counter-Strike culture