May 1999

Packetizing The Local Loop With
BROADBAND LOOP EMULATION SERVICES

BY STEFAN KNIGHT

The word of the day is broadband. Cable companies team up with long-distance carriers to bypass the copper infrastructure, Competitive Local Exchange Carriers (CLECs) rent unbundled copper from the incumbent LECs (ILECs) to offer high-speed Internet services, Regional Bell Operating Companies (RBOCs) and independents look to form partnerships with ISPs to gain marketshare - all in the name of broadband. Current broadband deployments - mainly Digital Subscriber Line (DSL) and cable modems - have focused on Internet access as the key service being deployed. Technological and regulatory paths are merging to facilitate the creation of the next major broadband application: Broadband Loop Emulation Services (BLES).

Simply put, BLES is the delivery of local telephone services (along with high-speed Internet access) in a packetized form over a broadband network. Since the invention of the telephone, local loop voice services have been delivered by ILECs, including independents, RBOCs, and PTTs in Europe. With telecommunications deregulation and the advent of new technologies, we are on the verge of a local loop revolution that is as dramatic as the invention of the telephone.

FROM THE CORE TO THE LOCAL LOOP
Network convergence has been happening deeper in the PSTN (public switched telephone network) for trunking applications between switches and PBXs, as well as in toll bypass applications in the long-distance network, but to date, not much attention has been paid to delivering combined data and voice in the local loop. BLES delivers POTS (Plain Old Telephone Services) from a Class 5 switch across a digital network as packet-based voice plus packet-based signaling over many physical transport mediums, including wireless, cable, and DSL.

A wave of new integrated access products are emerging on the market to make it possible for all of these service providers to deliver integrated local voice and high-speed data services at compelling price points in the local loop. This is good news for small businesses and residences that were previously unapproachable given the state of technology. Now competition will take hold in the local loop to provide these new integrated voice and data services at competitive rates.

Existing packet technologies have addressed the integration of data and voice deeper in the network. Toll bypass and trunking generally deal with large volumes of calls over long distance backhaul facilities. These applications are ideal for packet voice technologies; many calls can be multiplexed inside of large packets with low overhead and delay. However, the technological demands for voice in the local loop are fundamentally different. Local loop voice applications are much more dynamic and involve far fewer calls, which results in the need for more effective bandwidth and delay management. Let's examine the technical requirements for this new application in more detail. While the requirements are transport independent, we will illustrate these requirements based on DSL transport.

The requirements for an analog POTS service are very strict and present many technical challenges. For in fact, local loop voice as an application goes beyond just voice. A local loop voice service also includes all of the features that a voice subscriber has come to expect. These features include advanced calling features like caller ID and call back, which are a source of significant value added revenues for carriers. The Class 5 switch still enjoys a position of prominence even in competitive service providers' networks because its features add substantially to revenues. The first challenge is to connect the Class 5 switch to the broadband access network, in this case the DSL network.

BRIDGING A CHASM
The vast majority of DSL vendors and service providers implementing DSL are rolling out ATM-based DSL networks. ATM was designed to deliver voice, video, and data services with support for real-time Quality of Service (QoS) guarantees. For years now ATM has been deployed in the backbone network because it can distinguish between different types of traffic and priorities for the traffic being sent over it.

Getting voice from a Class 5 switch onto the ATM network for delivery as ATM over DSL to subscribers is not an entirely straightforward affair. There are ways of trunking voice calls over an ATM backhaul network, but there are no solutions for connecting a Class 5 switch's lineside interfaces to an ATM network for the purpose of delivering POTS across the access network to analog phones.

The local loop networks for voice and broadband data services are entirely separate today. Voice and data services arrive on separate copper pairs to independent voice and data Customer Premises Equipment (CPE). ADSL can deliver a single POTS line in the baseband of a DSL line as well as high speed data but that is the extent of voice and data integration for DSL. HDSL and SDSL have been deployed as T1 replacements or for non-channelized high speed data.

To enable the delivery of integrated voice and data services, two new devices are needed in the network. Traditional DSL CPE has been designed to connect data devices such as LANs and PCs to the DSL network. First, a new voice plus data CPE device is required to connect analog phones, key systems, and PBXs as well as high-speed LANs and PCs. This device is needed to convert analog voice to packetized format before it can be sent into the DSL network.

Second, in the network, a voice gateway is needed to connect the Class 5 switch to the ATM network. This gateway will need to bridge the PSTN to the ATM network using traditional line-side connections. Line-side connections for local loop voice are usually analog loops or T1 trunks to Digital Loop Carriers that deliver analog loops to subscribers.

Integrated voice and data is certainly a compelling application with tremendous benefits for both incumbent and competitive carriers. As stated earlier, the upside can only be realized if true local loop voice services can be delivered with all of their features. Additionally, this application will only be successful if the strict requirements for local loop voice services can be met by packet voice solutions. The system requirements for voice over data products can be summed up in brief as:

True Telephony
New voice services in the local loop must be held to as high a standard if not an even higher standard than traditional POTS telephony services. New carriers will be compared against the incumbent carriers for quality of voice services. This means that delays introduced by packetization or compression cannot have an adverse effect on voice quality.

Flexible and Efficient
Even with broadband access like DSL, there is still no bandwidth to waste. Digitizing voice gives the carrier the opportunity to offer compressed voice services that can be toll quality. Compressing voice to reasonable levels allows for more lines to be delivered. But beware: compressing fax or modem traffic that is delivered over derived POTS slows down transmission speeds noticeably.

Seamless Integration
DSL data networks are being deployed and gathering momentum worldwide. Voice is an incremental application that should be able to be deployed as an overlay to the existing DSL rollout. New DSL CPE that integrate both voice and data ports will be required, but it is important to leverage deployed DSLAMs and voice switches by introducing standards based, interoperable products. It is equally important to leverage existing CPE such as analog phones, PBXs, key systems, fax machines and POS devices.

Easy to Provision and Manage
This application for DSL does require some new network equipment. New network equipment should have as little impact on the existing network as possible. To this end it is important that existing billing and provisioning systems be leveraged for the provisioning and management of the voice gateway. The easiest way to accomplish this is for the gateway to appear to the Class 5 switch as a DLC would. This has different implications for ILECs and CLECs.

Reliability
The voice network is designed to an exacting standard: 99.999% reliability. Residential POTS services are required to be lifeline service, which means that phone service is always available to report life-threatening emergencies, even in the event of power outage. Data networks are being built to ever more exacting standards for availability and reliability, but still not to the standards of the voice network. The packetized voice network must be designed to the same rigid "five-nines" of reliability.

Packet voice today is perceived to be of lesser quality than traditional analog voice, which may cause some to hesitate when considering "packetizng" the local loop. This perception is mostly due to early implementations that traded off quality for aggressive compression algorithms to reduce the impact of packet header overhead. Additionally, early packet voice gateways were not designed with the strict guidelines for network equipment that carriers require. Packet voice, and broadband loop emulation services, can meet the strict requirements of the traditional carrier network if the system requirements for such networks are understood and acted upon.

Stefan Knight is director of Product Marketing at CopperCom. CopperCom manufactures an integrated voice and data CPE device called the CopperCom MXR as well as a voice gateway called the CopperCom Gateway. CopperCom is leading the industry in defining Complete DSL, the implementation of Broadband Loop Emulation Services for the DSL network. For more information, please visit the company's Web site at www.coppercom.com.