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And DynamicAccess does not suffer from the WINSOCK.DLL limitations because it works as a shim between the protocols and the NDIS (Network Driver Interface Specification) 3.1 drivers. Essentially, DynamicAccess monitors the packets coming in from the Layer 3 protocol (whether IP or IPX) and modifies the IP precedence and ToS bits before sending them on to the network adapter's driver, just as it does with the 802.1Q priority bits. This lets you prioritize the IP traffic at the end points, rather than on a per-hop basis within your network.

The Future of IP Prioritization

There are many opportunities and methods for implementing application-centric prioritization schemes across an IP network. These services can be tied to the priorities found on 802.1Q/802.1p networks, spoofed by infrastructure applications like 3Com's DynamicAccess, and even implemented by vendors directly (where the operating system supports this functionality).

But hold on to your hats! This area also is undergoing dramatic change. In an effort to provide better prioritization-management services to ISP networks, an IETF working group has convened to consider changing the fundamental nature of the ToS byte.

The name of the working group--Differential Services, or "diffserv" for short--is a good indication of the goal of this group: to provide customers with different classes of service (such as "silver" or "gold"). Current proposals the group is considering suggest replacing the ToS byte with a new set of values based on this goal.

If this comes to pass, network managers will lose the ability to define per-application prioritization services on an end-to-end basis, because whatever you put into the ToS byte will be overwritten by the ISP once it gets the packet. There are no facilities for preserving the existing data in the current proposals.

Whether or not this is a good thing depends entirely upon your perspective. ISPs love it, of course, since they get to charge for PVCs without having to build them. Furthermore, there's some benefit to being able to relay this information to other ISPs on a per-packet basis, which diffserv should allow.

However, if the current ToS byte is replaced--and there is no backward compatibility--managers of end-point networks will likely lose out. The prioritization schemes you implement for the benefit of your network and applications will only get discarded once they leave your local network. The only way to preserve the existing prioritization functionality will be to buy your own private WANs.

Eric Hall is president of EHS Co., a network technology research and testing firm in San Mateo, Calif. Send your comments to him at ehall@nwc.com.