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Thin client requires a brawny, agile WAN

The WAN that supports the emerging era of mainframe computing is totally different from the WAN that supported the previous era.

By Jim Metzler and Steve Taylor
July 6, 2010 10:10 AM ET

Network World - This is the fourth in a series of newsletters that is exploring our premise that we are returning to a new era of mainframe computing. Previous newsletters showed how today's thin client approach to computing is analogous to the dumb terminals and 3270 terminals of the previous mainframe era. This newsletter will describe how the WAN that supports the emerging era of mainframe computing is totally different than the WAN that supported the previous era.

The biggest difference between the WAN of the previous era of mainframe computing and the present era is raw capacity. For example, the bandwidth requirements of server based computing (SBC) generally fall in the range of between 20K and 30Kbps per simultaneous user.

Hence, if there are 50 simultaneous users in a hypothetical office, that requires between 1M and 1.5Mbps just to support desktop virtualization. That is roughly 100 times the capacity of the 9600 baud WAN link that supported a branch office during the previous era of mainframe computing. It is important to realize that this estimate of WAN bandwidth, like the one below, is just for illustrative purposes. They are intended to highlight the potential impact of desktop virtualization on the WAN. Any IT organization that is evaluating the implementation of desktop virtualization needs to do a careful analysis of the impact that that implementation would have on their WAN.

The bandwidth requirements of other forms of desktop virtualization are notably higher than are the requirements for SBC. For example, it is common for a VDI user to require at least 200Kbps of bandwidth per simultaneous user.

Hence, if the 50 users in the previously referenced hypothetical office are all using VDI, the office will need at least a 10Mbps WAN link just to support the VDI traffic. That is roughly 1000 times the capacity of the 9600 baud WAN link that supported a branch office during the previous era of mainframe computing.

The impact of desktop virtualization, however, is about more than just raw bandwidth. Citrix's Independent Computing Architecture (ICA) and Microsoft's Remote Desktop Protocol (RDP) protocols that are employed by many hosted virtualization solutions are somewhat efficient in their use of the WAN because they incorporate a number of compression techniques including bitmap image compression, screen refresh compression and general data compression. However, if a user were to quickly move their mouse, it could appear jerky on the screen. As a result, many IT organizations that have deployed these protocols have also deployed WAN compression techniques to overcome some of the WAN latency challenges.

While protocols such as ICA and RDP can often provide adequate performance for traditional data applications, they have limitations with graphics-intensive applications, 3D applications, and applications that require audio-video synchronization. A number of protocols have been developed to support transmitting graphics and 3D images over the WAN. One example of that new generation of protocols is the PC-over-IP (PCoIP) protocol from Teradici. We will discuss that protocol in more detail in the next newsletter and will also begin our discussion of the new generation of mainframe computers.

Read more about lans & wans in Network World's LANs & WANs section.

Steve Taylor is president of Distributed Networking Associates and publisher/editor-in-chief of Webtorials. Jim Metzler is vice president of Ashton, Metzler & Associates.

Reprinted with permission from NetworkWorld.com. Story copyright 2012 Network World, Inc. All rights reserved.
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