LANs are big, fast and reliable networks normally found within an organisation's main site or building (or the test lab). They can be rightly viewed as being super fast highways. The amount of data they carry is light relative to their capacity and the distances this data travels is relatively short. In contrast, WANs are geographically disbursed networks of often lower capacity which are required to carry a high volume of data compared with their capacity, over much greater distances.
There are three network key characteristics that influence an application's performance:
Available Bandwidth
WANs tend to have a much lower bandwidth than LANs which means that individual applications have to compete for space. This lower bandwidth can have a detrimental affect on software performance. Additionally, network administrators can set up their networks to favour certain applications like Voice over IP (VoIP) over 'conventional' applications, so once in the production environment the application is again competing for supremacy over others.
Latency
Latency is the delay encountered when running an application between two networks. It occurs because standard TCP/IP networks do not do not send data in a continuous stream, instead breaking it down into packets (like envelopes in the post) and sending it in batches. They also wait for confirmation that the packets have arrived safely before sending more, causing further delay. Also, the journey itself is not direct and various network devices will be encountered along the way, which all add their own additional delay. As a result, it can take 90ms to complete a round trip journey and an application transaction will consist of many such trips.
Packet Loss, Error and Reordering
As the packets of data travel over the network they can be lost, errored or reordered so that they arrive out of sequence, or don't arrive at all. It's like sending a bus down the road that either doesn't arrive or doesn't arrive entirely intact and is therefore probably useless when it reaches its destination. Wireless WAN, Satellite and 3G/Mobile Phone networks are generally subject to higher loss and error rates than wired networks. The increased use of wireless networks within buildings and as a way of allowing mobile 'on-the-road' members of the workforce to receive data means that applications need to be developed to cope with this potential for loss, erroring or reordering.
WAN emulation / network simulation
Reproducing these three network conditions is impossible if testing is confined to the internal LAN. However, WAN emulation / network simulation technology can be deployed in the same room as a normal test rig or even on a desktop. It allows the user to recreate a wide variety of different WAN or Wireless conditions and enables testing during prototype, development, quality assurance and pre-deployment stages.
A WAN emulator also gives complete control over the conditions in a single test in and also has the ability to reproduce these conditions time and again. This cannot be guaranteed if using a live network and additionally testing on a live network can interfere with existing mission-critical business applications already running.
This article is condensed from the iTrinegy Networks white paper "The Importance of Testing in Realistic Network Conditions". You can request a copy of the full white paper by emailing info@itrinegy.com.
To find out more about how iTrinegy's WAN emulation solutions can help you please visit www.itrinegy.com.
About the Author
Written by Phil Bull from iTrinegy, developers of sophisticated, yet easy-to-use, application response time monitoring, network traffic analysis and WAN/Network emulation technology to help organizations address networked application performance issues.
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