November 1999

QoS-BASED BILLING FOR ITSPs

BY JAMES SHEN

While IP telephony is leading the way to network convergence, utilizing an IP network to transport voice from phone to phone and phone to PC has also created serious Quality of Service (QoS) issues. The challenges are threefold: the IP network shares bandwidth, experiences bursts of heavy traffic, and was built to meet escalating needs without an overall design. These three factors result in an IP network that today experiences congestion, delay, and packet loss, and that cannot guarantee Quality of Service to its customers. The interconnection of many individual networks also makes the implementation of end-to-end solutions difficult. IP Telephony Service Providers (ITSPs) must learn how to manage these QoS issues and use them to develop their services and networks.

Managing the QoS of an IP network allows services providers to create new and differentiated services. QoS measurements can be used to define Service Level Agreements (SLAs) and to implement QoS-based management techniques such as QoS-based billing.

IP CALL QUALITY
The quality of an IP telephony call can be defined as a product of both signaling and voice quality: the ease with which a call is made and the quality of voice experienced by the caller. Voice and signaling quality are the result of network and external factors. The measurements of voice and call quality can be broken down as follows:

Voice Quality

• Interaction — the ability of a person to communicate with another person or device in real time, full duplex mode.
• Intelligibility — voice clarity.
• Echo — return speech.
• Volume — voice audibility.

Signaling Quality

• Call setup — the call setup success rate and call setup time.
• Call completion — call hang-up time, call completion rate, and the ability to complete post-call actions.
• DTMF — Dual tone multi-frequency detection, notch out during transmission, and resume.

QoS METRICS AND INDEX
Quality of Service standards can be established by measuring certain aspects of the IP network. A single index based on these measures can establish an easily manageable and identifiable QoS threshold. The measures include:

• Jitter — Distortion of voice due to consecutive packets arriving at irregular intervals. Severe jitter causes jittery or shaky voice quality, reducing intelligibility.
• Latency/Delay — Determined by factors such as bandwidth, processing times at nodes and endpoints, congestion, and queuing, delay causes a lack of speaker interaction, conversation overlap, and echo. Due to its real time delivery, IP telephony is delay intolerant.
• Throughput — Each IP telephony call requires a minimum quantity of bandwidth. If the network throughput does not meet the minimum requirements, the call cannot be established and any ongoing calls will be discontinued.
• Lost Packets — Network congestion results in the loss of voice and data packets across the network, disrupting speech and creating signaling problems.
• Availability — Availability of bandwidth impacts accessibility of the network and call completion.

QoS MONITORING AND MEASURING
Monitoring and measuring the QoS of an IP telephony network is the first step towards QoS-based management. Measurement of the network should be done in real time to allow QoS-based call routing, billing, and provisioning so that a historical record of the QoS can be established. Measurements can be recorded to establish daily, weekly, or monthly calling patterns.

QoS-BASED BILLING PROCESS
The QoS-based billing process is multi-dimensional, collecting network and transmission data to differentiate levels of QoS. The CDR (Call Detail Recording) of each transmission needs to be extended to include additional data such as byte usage, type, protocol, flow priority, and ID. SLAs can be established by applying different rates and discounts on calls with different levels of QoS. QoS-based billing can be conducted in real time, incorporating customer requested services and billing according to the QoS of each call.

SERVICE LEVEL AGREEMENTS
The SLA is an integral part of the billing process and can be defined according to QoS. Through monitoring and measuring QoS, service providers are able to offer differentiated SLAs according to service description, availability, and guarantees of the network. Through QoS-based SLAs, service providers are able to better manage the traffic across their network and provide customers with guarantees and boundaries for services and quality.

QoS-based billing ensures that customers get the level of service that they pay for. Before end-to-end QoS technologies such as RSVP and DiffServ can be implemented, network managers must be able to measure the QoS of their network and charge callers accordingly. The measures of QoS can be used to manage the timing of traffic and the geographic route it takes, so customers pay more to use the network in peak times and for selecting a certain geographic route.

OUTLOOK
Billing methods for next-generation networks are moving from a time and distance-based model to a priority and bandwidth-based multi-dimensional model. Billing according to QoS enables improved management of traffic flow, growth in the customer base, and more accurate and timely billing, all of which mean a better bottom line for the ITSP. Service providers can bill for the real cost of each call, assessing the priority of the transmission, the bandwidth of the network required to support it, the time and day of the transmission, and the final quality on the receiving end. For IP telephony customers, QoS-based billing means paying for the quality and services received.

Most important, QoS-based billing allows service providers to create a new revenue center outside of subscription-based revenue and enables voice carriers to go beyond price competition by offering differentiated services. The ability to create new services and implement multiple billing methods enhances profitability for both providers and customers, and it takes the IP telephony network one step closer to becoming the new public network.

James Shen is the CEO of NeTrue Communications, a provider of carrier-scale IP telephony solutions to worldwide communication service providers. For more information, please visit their Web site at www.netrue.com.