latency

The latency assumption seems to be that data should be transmitted instantly between one point and 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 place and another at the speed of light.
• Transmission: The medium itself (whether optical fiber, wireless, or some other) introduces some delay. The size of the packet introduces delay in a round trip since a larger packet will take longer to receive and return than a short one.
• Router and other processing: Each gateway node takes time to examine and possibly change the header in a packet (for example, changing the hop count in the time-to-live field).
• Other computer and storage delays: Within networks at each end of the journey, a packet may be subject to storage and hard disk access delays at intermediate devices such as switches and bridges. (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 real or perceived response time beyond the response time desired. Specific contributors to computer latency include mismatches 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 parallelism across 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 the appropriate image.

Getting started with latency

To explore how latency is used in the enterprise, here is an additional resource:

Storage network bandwidth planning: How to avoid network latency: Learn how to take storage network bandwidth into account to avoid network latency and maximize your clients' application performance.

Server virtualization and the network: Site consolidation's impact on latency: Server virtualization holds exciting promise for companies in reducing overall administrative costs, consolidating their physical infrastructure, and improving the ability to dynamically roll out new services. It also presents new challenges for network managers. This tip explores the implications of some of these issues and looks at some of the strategies for keeping the network humming along in the face of these new challenges.

What correlation does ping latency have with high server activity?: A network administration expert explains which metrics provide visibility into what's going on at peak activity levels in order to optimize network performance in this Q&A.

Will different wireless card link speeds cause network latency?: A wireless networking expert explains how to avoid network latency when wireless network cards with different maximum link speeds slow down your WLAN.

Assessing WAN connectivity, identifying latency for centralized application access: When assessing the WAN connectivity network learn to identify latency and low response times for centralized application access from a WAN optimization expert.

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