Anyone who has to test hardware and software designed to operate in a Wide Area Network (WAN) environment will be familiar with the problems.

Internet and intranet applications differ from classical applications in the variety of networks they are expected to support at any one time. For instance, IP applications have to support cable modems, satellite links, high-speed backbones and analogue modems, and once you introduce Internet connectivity, any chance you had of predicting performance and reliability goes out of the window.

Making sure that an application or piece of hardware functions well and enjoys reasonable response times over these various connections is a difficult task. Parameters such as physical distance, time of day, connection speed and the Internet Service Provider (ISP) can all greatly affect a network’s behaviour, thus affecting the application’s performance and stability.

The Cloud – from US-based Shunra Software (distributed in the UK by Trend Communications) – simulates a WAN accessed by two gateways. All three components are simulated on a single machine which can have one or more network cards installed. With one network card it is possible to simulate single server to multiple clients. With two NICs, The Cloud can act as a router and allow any number of hosts on the two separate subnets to communicate via the simulated WAN.

Installation couldn’t be simpler, and during the process a new service is installed in NT that allows The Cloud to assume control of packets passing through the protocol stack. This service is used to simulate latency, packet loss, abnormal packet effects and bandwidth conditions of any IP WAN without the IP traffic ever leaving the LAN.

The user interface presents the WAN configuration pictorially, with an East and West gateway separated by the WAN “cloud” (hence the name). The gateways simulate the access points to the WAN, and double clicking on them allows you to define their characteristics. The bandwidth of each gateway can be configured as symmetrical or asymmetrical (to simulate 56Kbps modems, ADSL or satellite links), and you can simulate bandwidth from 300bps (or less, if you are really masochistic) to 2Mbps or 10Mbps (depending on which version you have). It is also possible to define the size of the gateway’s buffer. Both gateways can be defined independently from each other, allowing you to simulate a user’s modem at one end of the link and an ISP router at the other. Simply by reducing the bandwidth of one gateway from “unrestricted” to 64Kbps, you will immediately see the traffic passing through The Cloud experience significant delays as the simulation comes into effect.

Double clicking on the cloud allows you to set the conditions of the WAN, and this is where it gets slightly more complicated. There are obviously many possible variations that can apply in a true WAN scenario, and The Cloud attempts to simulate most of them. One of the most important is latency, which is the delay experienced by a packet of data as it travels through the WAN – quite often this is the key figure in any Service Level Agreement (SLA) with your ISP. This can be defined as a fixed value, or as a variable value with either a uniform or normal distribution. Other effects can also be defined, including packet loss (periodic, random, or burst), abnormal packet effects (duplicate packets, out of order packets and fragmentation), link faults (bit errors and disconnections) and congestion.

Whilst some of these factors may be known on a private network, setting them can be a nightmare on that “moveable feast”, the Internet. For that reason, Shunra also provides the Cloud Catcher. This allows you to record the latency and packet loss parameters in real time on a live WAN link and incorporate these “real life” settings into subsequent simulations, making The Cloud even more realistic.

Once you have all your simulated WAN settings as you want them, they can be saved in a template file for use over and over again. This allows you to build up a library of different configurations and situations (perhaps different times of the day on the Internet), and recall them instantly for replay. As you start the simulation, the packets flowing through The Cloud are affected in accordance with your settings. A number of real-time report screens allow you to monitor traffic throughput, and all the recorded data can be saved for replay and analysis at your leisure.

During testing I set a simple continuous Ping going between two devices on either side of The Cloud. It was great fun playing with the various settings and then observing the effects on the round trip time of the ICMP packets. If you have delay-sensitive applications, you can initiate these then and increase the latency or reduce bandwidth in The Cloud to observe the point at which the application becomes unusable. This sort of thing can help you in defining SLA’s with your ISP, since you can finally prove exactly how much bandwidth you require, or how little latency you can permit, before your applications begin to fail.

The Cloud can also be used to test hardware devices in certain circumstances too. For instance, we recently has a requirement to test Web cache devices, and the only way we could do this properly was to use a live Internet connection. Testing in a pure lab environment would be no good, since cache devices are designed to alleviate a bottleneck, and a 10/100Mbit LAN connection provides no such bottleneck. The Cloud enabled us to introduce a bottleneck artificially on our LAN, using parameters taken from real-life Internet sessions captured using Cloud Catcher. Thus we could run the same tests time after time with different devices, safe in the knowledge that our poor “Internet” response would be identical for every run and every device.

The more we use it, the more applications we can think of. The Cloud has already become an essential tool in our test armoury.

Verdict

The Cloud is the only software-based WAN simulation tool we have seen to date, and it is offered at a very reasonable price. Anyone who needs to examine the effects of various WAN configurations on their hardware and software should get a copy.

Contact: Trend Communications Ltd.��
Telephone:�� 01628 524977��

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