Quality of Service: Directing Data through the Network - Industry Trend or Event

ENT, Oct 6, 1999 by David B. Miller

Much has been made recently of quality of service (QoS) technology. QoS promises to mitigate bandwidth problems by prioritizing traffic so the most important data gets through first. Microsoft Corp. plans to include QoS technology in Windows 2000 and Windows 98. Despite the early stages of the technology, Microsoft is pushing QoS hard. Network equipment vendors are also preaching QoS to meet the demands of multimedia applications and the convergence of voice and data. Therefore, now is the time to become familiar with QoS and how it can manage bandwidth across your enterprise.

Quality -- At Your Service

The key goal of QoS is to help network managers establish bandwidth policies that ensure the data a company considers most important gets through first. For example, a company running a large SAP application might want SAP transactions to execute ahead of an FTP file transfer; or company executives might deem that a videoconference running over their newly converged voice/data network gets priority. Characteristics such as tolerance for delay, throughput and jitter are taken into consideration by a QoS-enabled network to determine what applications get precedence.

Several mechanisms, backed by emerging Internet Engineering Task Force (IETF, www.ietf.org) standards, work in harmony to ensure priorities. An application on a Windows 98 workstation, for example, uses protocols such as the resource reservation protocol (RSVP) to request network resources. Policies defined by the network group reside in network devices, such as switches and routers, that get information from policy servers running common open policy service (COPS) and LDAPv3-complaint policy repositories. As application traffic traverses the network, the policies are consulted and an ordering is applied to the data. On the LAN, class of service (CoS) bits are set at the media access control (MAC) layer and the IEEE 802.1p protocol ensures that data arrives in the correct order. Across IP networks, above Layer 2, protocols such as DiffServ map the CoS bits to the never-before-used DiffServ field -- previously known as the TOS field -- in the IP header. The end result is that application usage of network reso urces gets smoothed out, with mission-critical applications getting priority.

Let's Get Started

Network vendors will make this effort seem absolutely necessary and trivial, but you know better. "While QoS sounds great in theory, it truly approaches rocket science in reality," says David Passmore, research director and founder of NetReference (www.netreference.com), a networking consulting firm. "The learning curve is steep. Take for example, the idea of directory-enabled networks and the storing of policy information in LDAP directories. Now, network managers have to start tackling concepts such as schemas, stuff that they thought only database types had to worry about. The list of new concepts is pretty big," he explains.

In addition to complexity, Passmore cites three more reasons why QoS implementations still have a way to go. The first is interoperability, which "is non-existent right now," Passmore notes. "It's hard enough for vendors to handle QoS in their own equipment let alone someone else's. Furthermore, for true end-to-end QoS, components ranging from the application itself, the network interface card, switch and router will all have to participate, requiring the cooperation of a host of vendors."

The second reason is the issue of emerging standards. "For example, COPS isn't handled by most switches and routers yet. RSVP [which Microsoft is implementing in Windows 2000 and Windows 98] is very resource intensive," Passmore notes.

The third big obstacle is office priorities. "Perhaps the greatest challenge revolves around the politics of QoS. Who gets to divvy up the bandwidth and to who's benefit? Imagine the meeting with your company's business unit directors and asking them to figure out who's application is the most important and deserves the best treatment."

Pressing Onward

While bandwidth management via QoS faces some impediments, these haven't stopped vendors from forging ahead with policy management systems. And it's not just the networking equipment giants. Other vendors are investing heavily into QoS product development, citing the nonproprietary nature as a major reason to consider them.

"We see the acceptance of QoS technology occurring in phases," notes Charles Muirhead, founder and president of Orchestream (www.orchestream.com), a QoS technology vendor. "The first critical need is to manage application availability. QoS implementations will focus on increasing application uptime by insulating the application from changes in network congestion, such as frame relay problems."

After companies invest in QoS for its insurance policy aspects, Muirhead believes more serious attention will be paid to the cost-optimization benefits. QoS has the ability to steer traffic into appropriate queues, thus providing better network utilization. Network executives will be better armed to make decisions on potential bandwidth upgrades and will make better use of the bandwidth they already have.