Q: We want to scale up our WLAN to very many users over large areas. For example, complete coverage of a university campus - and without reducing the bandwidth per user to something very small. Each user should be able to at least receive a video conference at about 800 kbit/s - so a minimum bandwidth/user should be 1M bit/s. Users should be able to roam seamlessly and maintain their flow rates during handovers between wireless stations, and between network segments. Ideally, systems should allow for future upgrading - long term I envision that at least some users may wish to have at least 10 Mbit/s capability within such a network. Also, are there are any standards associated with such large enterprise configurations, or is all the present work done on specific installations by different vendors?
- David M.

The Wizards gaze into their crystal ball and respond:

Michael Montemurro, Chantry Networks
There are vendors that let you deploy large-scale WLAN networks that provide the bandwidth and coverage you require. These systems address the key issues with deploying large-scale wireless networks, which are management/ease-of-use, security and mobility.

As you deploy more access points, it makes more sense to deal with them more as a continuum rather than discrete network elements. Management needs to be done centrally and RF management becomes more important to maintain performance.

Offering network access on this scale becomes challenging from a network access perspective. Depending on the environment, it becomes more important to protect the users and the data flowing across the network. Security policy should be centralised and applied consistently over the entire network.

WLAN is a Layer 2 technology. As access points are deployed widely across a network, it generally needs to span across router boundaries. The wireless network needs to be provisioned in such a manner as to allow users to roam from access point to access point without having to renew their IP address as they pass across a router boundary.

The CAPWAP (Control and Provisioning of Wireless Access Points) architecture group in the IETF is working on a standard mechanism to manage large-scale WLAN installations. They are currently studying the architecture and requirements for these installations and their goal is to define a protocol to allow large, scalable WLAN deployments. Once such protocol - CTP (CAPWAP Tunneling Protocol) has been submitted for consideration.

Seth Goldhammer, Roving Planet
Bandwidth control on a wireless network becomes tricky. The access points themselves are essentially Layer 1 hubs, which means bandwidth is shared for all active devices associated to the access point. Setting a rate limit for a group or user therefore does not necessarily protect the bandwidth for that device, depending on the active traffic on the access point the device is associated.

For example, let's say I give all students a rate limit of 1 Mbit/s, and I give the professor 2 Mbit/s. In the lecture hall, the professor is outnumbered by the amount of students. The system will be working to protect the students' 1 Mbit/s per access, which will conflict with the professors allotted 2 Mbit/s. Any system you look at should be able to consider the bandwidth available at the access point, and allocate bandwidth according to the users active on the access point.

Furthermore, the solution needs to account for bandwidth not only to users, but for specific applications. In this case, the system needs to recognise that, while this is a student, the traffic from the student is targeted for the videoconference application and needs a different allocation of bandwidth.

Most firewall-type products with bandwidth shaping capabilities will only look at the service port level (e.g., port 80 or port 25). There are a few products that can actually determine the application type (HTTP, SMTP), but that might be more than you need.

Most likely, what you need is a product that can combine an IP address with a service port, so you can identify as the videoconferencing application, and provide the appropriate amount of bandwidth. The application definition should also have the capability of overriding the user's bandwidth allocation.

Greg Murphy, Airwave Wireless
You are correct in planning ahead for your university campus network. WLANs in university environments have unique challenges and requirements, as you pointed out in your example of videoconferencing and roaming. While it may be difficult for you to accurately project network size and usage, one thing is certain: your university wireless network will be substantially larger and more heavily used in the future than it is today. To position your organisation for successful growth, focus on:

  1. Manageability. Configuring access points and monitoring usage manually may be possible when you have a very small network. But when you have thousands of wireless access points covering an entire university campus, efficient centralized management will be essential. Buy wireless hardware that can be monitored and configured remotely via SNMP and other standard protocols. Low-cost SOHO access points may be cheaper than enterprise-grade products, but many cannot be managed remotely and will cost you far more in increased support costs than you save on the hardware.
  2. Heterogeneity. Like your wired Ethernet network, as your WLAN expands across multiple facilities and locations it is almost certain that you will have multiple hardware vendors. If you plan for this diversity and select standards-based hardware and vendor-agnostic management solutions, you will be able to control a multi-vendor network effectively. If you use proprietary systems, you may find yourself locked into an expensive dead-end technology.
  3. Monitoring. The key to managing network expansion successfully is to be fanatical about monitoring network usage and performance. Where is your wireless network overused? Where is it underused? How long is it taking users to connect to the network? How much bandwidth are people using? Is the system close to maximum capacity? Are there coverage gaps on the network? Wireless hardware is relatively inexpensive, so expanding network capacity is affordable for most organisations. The trick is in knowing where additional capacity is needed and in continuously reconfiguring the network to maintain optimal performance as it grows.