July 2001

Thinking Outside The Network -- Better Service Delivery

BY SUKETU PANDYA

Service providers are also actively looking for ways to profitably deliver lucrative new services that increase average revenue per user (ARPU), without requiring the replacement of existing infrastructure. Simply overbuilding the network has proven to be impractical and unprofitable. And attempts at packet classification, with their costly infrastructure changes and excessive management complexity, have not delivered convincing results. Providers and their customers are asking for solutions that can scale to support tens of thousands of subscribers, do not require hundreds of man-hours to implement and maintain, and provide effective service delivery without disturbing their existing infrastructure.

Application Prioritization -- Starting With The Subscriber
Today, providers are evaluating a new approach that prioritizes and controls applications and services precisely where they are used -- at the subscriber end station. This approach differs from QoS because it focuses on aligning network resources directly with subscriber demands and revenue opportunities. By implementing control and prioritization at the end user device (e.g., PC, palmtop, IP phone), providers can now effectively and profitably address the distributed nature of subscribers and applications.

This distributed approach applies and enforces business-driven policies at the session layer (layer 5) of the OSI model, between the application and the network. Session layer implementation provides the ability to "see" traffic flows in terms of the originating application or service. Policies are therefore targeted at high-level entities such as users, applications, and groups. This approach makes management a much simpler task, as policies are based on intuitive business concepts. The need to deal with messy packet definitions or router configurations is eliminated. In addition, the billing of services based on usage becomes much easier, because a direct correlation exists between the policy and the entity or service being billed.

Solutions based on session layer prioritization use an architecture consisting of centralized policy management and distributed policy enforcement. Policies based on users, applications, and services are managed centrally at a policy management engine. These policies are distributed to agents at the end devices for local session layer enforcement. This unique design provides holistic visibility into users, applications, and resources throughout the network, while leveraging the power and performance of end devices.

Getting Results With Existing Networks
Among the biggest problems of QoS has been the need for complex implementations. QoS technologies such as Differentiated Services (DiffServ), Multi-protocol Label Switching (MPLS), Resource Reservation Protocol (RSVP), and proprietary QoS appliances require router updates or replacements, or the addition of new gear. Managers therefore must visit and reconfigure virtually every WAN, which is an effort that is simply impractical on most large networks. In many cases, applications must also be upgraded or modified to take advantage of the QoS capabilities of the new equipment. And managers must be diligent about interoperability among all QoS devices, which are extremely sensitive to firmware revisions.

Application prioritization resolves this dilemma by removing the need to touch the existing network infrastructure. These new systems transparently overlay onto networks with no configuration requirements or considerations. Managers can deploy these solutions even as their networks continue to run at full capacity. Desktop agents are distributed to client devices through Web-based installations or management systems such as Microsoft SMS, and can be rolled out at a pace to meet any schedule.

The Scalability Challenge
Another challenge for traditional QoS is scalability. Standard QoS solutions require that traffic reach a central router or QoS appliance before any control or shaping takes place. As the network grows, or traffic loads increase, a classic bottleneck occurs as too many packets attempt to pass through the now overloaded QoS device. Once the bottleneck occurs, packets are either queued for delayed delivery, or dropped completely, forcing costly retransmissions. This is a bad outcome for all users, and particularly negative for delay-sensitive applications, such as VoIP and streaming media.

The focus on application prioritization offers an important breakthrough for implementing truly scalable service delivery. The enforcement agents efficiently use the power of each desktop CPU to carry out the service delivery workload. This means that as the network grows to tens of thousands of users, additional resources become available to help ensure reliable delivery for everyone. The agents also help enhance the performance of existing routers, by moving the prioritization workload off the network, and allowing routers to focus on their primary task of routing.

The session layer control of application prioritization has another positive effect on scalability -- the elimination of costly congestion. A "hidden" drawback to traditional QoS has been the lack of congestion control. Because traffic runs unrestrained until it reaches the first QoS device, congestion is a permanent artifact of the network. With the session layer approach to prioritization, traffic is sorted and prioritized before it ever enters the network. This results in smoother and more predictable delivery for all applications and users, regardless of their priority, and keeps bandwidth working at maximum efficiency.

Focusing On Service Revenue And Profitability
In addition to scalability and greater efficiency, application prioritization can directly generate new revenue for providers. For example, VoIP service is a powerful companion offering to business customers signing up for VPNs. After all, why shouldn't customers leverage their VPN investment to reduce their voice costs? This has proven to have been an awkward sales strategy, because providers have had no way to ensure the delivery of time-sensitive VoIP on VPNs. The process of data encryption prevents the effectiveness of traditional QoS. The new prioritization systems control VPN traffic at the session layer, prior to data encryption. So, providers can now offer VoIP as an add-on sale to VPN customers with the confidence that they can ensure adequate delivery.

Distributed service prioritization offers value well beyond ensuring and controlling delivery. With services initiated right at the subscriber's device, providers can deliver new capabilities that go well beyond the traditional bounds of QoS. For example, providers can now include such services as billing by application or usage, built-in level one customer support, desktop provisioning, and encryption services. Simply distributing the agent to subscriber desktops enables each of these add-on services. The add-on service then resides quietly at the desktop until the provider is ready to put the capability into action.

Conclusion
Distributed service prioritization provides a profitable new focus on the application and subscriber. With its non-invasive implementation and distributed scalability, this new approach helps providers ensure the efficiency of their networks and reliable delivery for customers, while expanding revenue opportunities with a new generation of services.

Suketu Pandya is co-founder and CTO of Centricity Software. Centricity Software provides solutions that uniquely enable distributed service providers and enterprises to deliver and differentiate application services to their users, partners, and customers.

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