Ranger and Wireless Networks

Question

Can Ranger work over wireless Networks?

Cause

This article covers some of the problems schools have encountered when trailing Ranger over a wireless network and includes the suggestions we made to the schools in an attempt to resolve their issues. In addition this article discusses some general advice with regards to the design of a wireless network in particular what changes can be made to improve the logon speeds in an attempt to reduce the logon times and therefore the number of Ranger logon failures.

Wireless Technology

Wireless technology is an ideal solution for many use cases however in a school environment with large dispersed networks, high bandwidth requirements designing a wireless solution requires a good understanding of the hardware capabilities, the hardware limitations and most importantly having a realistic expectation of what to expect and what changes might be needed in order to support a wireless network.

Network Requirements

The design and implementation of a wireless network requires careful consideration to ensure that the infrastructure is capable of meeting the high demands placed on a school network. School networks generally require large bandwidth in order to support large numbers of users logging in and out during each class, allow applications to be run across the network and cope with file transfers to user's home areas. It's important to remember that in order to satisfy these high demands schools have had to increase the network bandwidth in many instances to as much as gigabit backbones with 100 Mbs connections to the workstation.

Wireless Speeds

According to the specification wireless speeds on the client should be comparable to wired network speeds for example figures like 125Mbs are available. The problem is the actual speeds are normally much slower than the maximum speed but instead reduced to a fraction of the speed maybe as low as 1-5mbs in order to maintain connectivity.

There can be a number of reasons why wireless speeds are much slower than those rated in the specification. The distance between the computer and the access point will affect the speed as the card and access point negotiate for a reliable connection. Interference from lights and physical obstacles i.e. walls, ceilings will reduce the speeds further. In addition access points share network bandwidth between connections therefore the actual speed the computers has to the server maybe very limited.

Depending on the demands placed on the connection users may not even be aware of this limitation for example web browsing would be fine however for network applications such as media streaming, transferring large files and coping with and large numbers of users logging in and out with their network profiles wireless is not suitable.

An example of Speed difference

To give some idea of what the speeds differences are between wireless and wired networks and what affect this has on logon time here is a basic calculation.

Given that 100 Mb/s and 54 Mb/s devices are fairly new many of the existing installations have been performed with 11 Mb/s devices.?

Assuming the following setup:

This would then mean that the computers would get a transfer speed of approximately 78 kb/s if 8 computers where on and 156Kb/s if 4 were on.

Now consider a typical network logon, first the domain authentication, logon scripts and then the users profile. The amount of data transferred for a new user could be as much as 1MB in size. The logon time would approximately take between 12 and 20 seconds. In some cases user profiles can be as large as 10MB in size which would mean just downloading the profile you are looking upwards of 2 minutes.

If Ranger is installed in addition to the normal logon process, Ranger will download a small amount of configuration data about 250k, it may also redirect the users start menus and desktops to locations on the network, it may also download package data to the machine during logon. All of which mean the amount of data transferred between the client and server will increase. If you now multiply the demand on the access points and servers to allow a whole classroom to logon simultaneously the network utilisation will increase substantially, the bandwidth will reduce and resulting in data transfer times increase further still.

Why do slow logons affect Ranger?

Ranger is designed for a wired network, therefore the communication protocols established reflect the speeds available from a wired network. Ranger itself adds approximately 250K to a users logon which is not a problem in a wired network whereas over a wireless connection every byte adds to the overall time it takes for the user to logon and if the logon takes too long the logon session will time out causing the logon to fail.

Resolution

The solution therefore is to take all these points into account including the reliably and limited speeds and try to reduce the amount of data transferred during the client logon. This can be archived by:

Hopefully the logon times can be reduced to a level where the Ranger logon failure messages are no longer reported.

Planning your Wireless Network

In addition to making configuration changes to affect logon speeds also consider the following.

Access Points are essentially wireless hubs sharing the available bandwidth between users. This is different to most schools network infrastructures where network switches are used which provides each connection with a dedicated connection speed. This means it is important to get the balance right between number of access points and number of wireless computers.

The physical positioning of the access point affects the connection speeds and the available coverage. For example you shouldn't place access points at the base of a wall, next to large metal objects or near devices that generate large electromagnetic fields. Try to place them in a open environment with ideally a line of sight, any obstacle in the way will reduce the signal strength and therefore the speed.

The hardware by default is automatically set to adjust its speed to reduce data transmission errors but sometimes you can get speed improvement without reducing connectivity by manually setting the connection speeds.

With planning and consideration of the issues raised you can significantly improve coverage and connectivity speeds without any additional cost.

Instructions

Our recommendation therefore is test your wireless network without Ranger installed to begin with. Start small testing connectivity and perform speed tests as you go. Then gradually increase the number of Access Points and clients as you go.