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AEC

1-2-3 Revit: BIM on a WAN

6 Jul, 2006 By: AIA ,Rick Rundell

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Hardware and software solutions make distributing a building information model across a wide-area network fast.

Most building design tools are based on legacy drafting or object-oriented CAD technology -- file-based applications with computational or practical limits constraining the size of the output files. A purpose-built BIM solution such as Autodesk Revit uses a completely different technology to define a building project; it uses an interconnected database of building information. Globalization dictates that these data-intensive BIMs must be shared between distributed design teams as well as clients and contractors. New BIM applications that serve engineering disciplines (such as Autodesk Revit Structure and Revit Systems, have further underscored the need for design collaboration across distributed teams.

If project teams are in the same company, everyone can work together on a single shared model. With multiple teams or disciplines working in different organizations, the Revit platform approach lets each cross-link their models -- creating a shared, distributed BIM.

In some cases, teams swapping or sharing models are networked together in a LAN (local area network). But in all likelihood, they're separated by geography or organizations and use a WAN (wide area network). This month's article explores a specific technology that is used to support BIM across a WAN.

Network 101
LANs are computer networks that span a relatively small area. Computers within a LAN can access data and devices anywhere on the LAN. Many users can share data, applications and resources such as printers. Most LANs are confined to a single building or group of buildings.

WANs are computer networks that cover a wide geographic area. Computers connected in a WAN often use public networks such as the telephone system. They also can be connected through leased lines or satellites.

LANs can transmit data at very fast rates, much faster than data can be transmitted over a WAN. Bandwidth, also called throughput, and latency together determine the perceived speed of a network connection. The bandwidth (the amount of information that can be transferred over a connection in a given period of time) of a WAN is much smaller than a LAN, perhaps 1% to 0.05%. Making matters worse, the latency of a WAN (the amount of time it takes for a response to return from a request) is much higher than a LAN, typically 100 to 1,000 times higher. These numbers mean that moving large files across a LAN is fast but can be painfully slow across a WAN.

Networked BIM
Getting back to BIM, for firms with widely distributed teams using a WAN, the LAN-to-WAN bottleneck encumbers sharing of the BIM in an easy and fluid way.

Revit Worksharing offers team members a range of collaboration modes, all of which hinge on access to a shared master BIM that acts as the distribution point for publishing work to the rest of the team. To begin worksharing, users get a copy of the central BIM and save it as a local file on their own hard drive or LAN network. As they modify the model, they save their changes to this local copy, and then at certain points publish their work to the central file (Save to Central in Revit terminology).

When this saving happens, the changes in a local file are copied across the network to wherever the central file is located and incorporated into the master BIM, allowing all other team members to then reload those changes into their own local file. At the same time, changes that the rest of the team has Saved to Central are downloaded to the user's local building model.

The discipline-specific portions of a distributed BIM can range from fifty to a few hundred megabytes, depending on the size and complexity of the project. Moving this much data across a LAN isn't an issue, but it can pose problems across a WAN.

Firms with team members located in far flung offices have tried various workarounds to avoid WANs; for example, using Windows Remote Desktop to access a computer on the same LAN as the central file, burning CDs/DVDs and sending these via overnight delivery services back and forth between offices or actually a flying team members to different offices. All of these tactics defeat the purpose of a central building model.

Making WANs Seem Like LANs
Our global economy has made WAN performance ripe for improvement, so in recent years we've seen the introduction of network appliances: hardware and software solutions that speed up the performance of applications and data across WANs and make a WAN perform more like a LAN without upgrading bandwidth. Riverbed Technology is a pioneer in this field. Its Steelhead appliances can accelerate applications over WANs by as much as 100 times and can reduce WAN traffic by as much as 95%.

Riverbed appliances are being used successfully by companies sharing large Revit building information models -- allowing disparate workers to more easily collaborate on a building project.

Little
Little is a national architecture and design firm headquartered in Charlotte, North Carolina. It has eight locations with almost 350 employees. Chris France, the CIO of Little, installed its first Steelhead appliances in December 2004. The original motive for deploying them was to enable collaboration on AutoCAD-based building projects with architects in different cities. Not only was this goal achieved, but Little also was able to centralize and accelerate its data backup in remote branch offices.

Little is in the process of converting from AutoCAD to Revit Building and in early 2006 decided to use Revit Building over its Steelhead-enabled WAN links on an existing Revit project -- a three-story office building, approximately 83,000 sq. ft., slated for construction in Florida. Project team members are located in three different offices -- Washington, DC; Charlotte, North Carolina; and Orlando, Florida. The 62MB central file resides in its Washington office.

France reports, "The results have been excellent. With Steelhead appliances deployed, our architects in Charlotte and Orlando can open and save this Revit Building file from our DC office in a few minutes -- only about twice the time that would be required over a LAN. The Riverbed-enabled link was getting pretty close to LAN-like performance, even from a remote office." In another example, France reported close to a 10x increase in speed when saving changes to the central file across a WAN using Riverbed appliances.

Saving and reloading changes to the central file are completed a few times a day, so these time savings may seem mundane. But with the larger the project and the scope of the changes, not to mention network traffic, the wait times made collaboration across a WAN extremely frustrating. As France puts it, "Revit Building is critical for us; we see it as the next step to helping us deliver better designs faster to our clients. Now with our Steelhead appliances we can involve the right people in our organization -- regardless of their location -- in a project whenever and wherever they're needed."

Don't be Limited by WAN
The building industry's adoption of BIM is pushing the limits of the existing network infrastructure. Using appliances such as those offered by Riverbed solves the problem of shared access to a BIM across a WAN. By providing optimizations that are orders of magnitude greater than what users experience today, Riverbed's appliances are changing the way project teams work -- enabling a distributed BIM and allowing a workforce located around the world to collaborate as if they were next door to each other.