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