Integrated Access Devices Give ATM New Life in Local Loop

But Good Old TDM Assures Voice Quality and CLASS Features

The solution to that inefficiency, some say, lies with asynchronous transfer mode (ATM) cell switching. It was designed from the start to answer the now-urgent service provider demand for equipment that integrates voice, data and video over a single, broadband access connection, while also provisioning and policing quality of service (QoS) for each of those services in that single pipe.

The central pitch: ATM Layer 2 transport enables service providers to provision a virtual circuit (VC) for each traffic type, and each VC can be assigned a QoS performance level to accommodate the demands of Layer 3 services such as data virtual private network (VPN) or delay-sensitive packet voice service.

In turn, QoS mechanisms enable service providers to offer specific, network performance-based service level agreements (SLAs) to their customers, a key to premium service differentiation in the bewildering clutter of competitive local exchange carriers (CLECs), incumbent LECs (ILECs) and Internet service providers (ISPs).

"CLECs can only compete with ILECs using technology that is both cheaper and more capable than traditional, fixed-bandwidth, TDM (time-division multiplexing) technology," says Tom Barsi, marketing vice president for VINA Technologies Inc., Fremont, Calif. VINA supplies ATM-based Multiservice xchange integrated access devices (IADs) to Tampa, Fla.-based CLEC 2nd Century Communications Inc. "It's natural for CLECs to go to packet voice, because a 40 [percent] to 50 percent cost reduction will lower their entry barrier by eliminating TDM cross-connects and Class 5 switches, and gain dynamic bandwidth in the access segment," he adds.

In 2nd Century's case, VINA's access device will work with Boca Raton, Fla.-based Siemens Communication and Information Networks' ATM switches to deliver data VCs to a customer's ISP and voice VCs to a customer's long distance telephone carrier.

Naysayers to this vision doubt the abilities of either ATM transport of packets or direct Layer 3 Internet protocol (IP) packet switching to support the call-control features that customers expect from their TDM, Class 5 and 4 voice switches--features ranging from call waiting to private branch exchange (PBX) to 800-number translation.

Yet ATM IAD makers such as VINA say they'll bring increasing support for enhanced Centrex, unified messaging and other voice applications into their packet- and cell-based products this year. Similarly, Sonoma Systems Inc., Marina del Rey, Calif., intends to deliver circuit emulation software for voice support to its ATM platform "soon." This could enable it to pass packet voice traffic through gateways and TR-303 and TR-008 interfaces to Class voice switches.

IAD Model

To fuel service-provider differentiation, dozens of new and established integrated access equipment suppliers are offering lightning in a pair of bottles: one, designed as customer premises equipment (CPE), is the IAD; the second, sitting at the central office (CO) or point of presence (POP), is the multiservice access (MSA) device.

In general, the IAD includes ports for phones, PBXs, routers and modems--a single box integrating all traffic over one, rather than many, access lines. Fed by the IAD, the MSA grooms each data or voice service type out of the aggregate flow, combines it with other like traffic, and passes it to the appropriate backbone provider. All agree: This architecture reduces cost by "collapsing" multiple physical lines into one physical line, and by unifying network management onto a single platform.

Combined with advancing high-capacity, local-loop technologies such as digital subscriber line (DSL), the IAD-MSA architecture promises to make access networks more future-proof.

"There's a big opportunity for high-bandwidth community and aggregation of high-bandwidth traffic," says John Stormer, vice president of marketing for national DSL CLEC NorthPoint Communi-cations Inc., San Francisco. "The application side is just beginning to realize the possibilities of broadband."

Although NorthPoint has "no intention of ever owning a Class 5" voice switch, it could pass packet-voice traffic to either circuit-voice or packet-voice carriers and is now "in the thick of developing" integrated data and voice transport over DSL, Stormer says. "There are both cost and performance issues, such as how to handle voice or video without a way to negotiate my way through the Internet. That is a QoS issue."

Adding VC-based transport to broadband integrated access promises to enable not only QoS, but also "oversubscription" of bandwidth by dynamically allocating capacity to services as needed, rather than preconfiguring permanent TDM circuits, the bandwidth of which lies unused and wasted when phones or modems are inactive.

"TDM is very rigid, requiring that you actually touch wires and ports and devices to turn up a new service," says Kevin Walsh, marketing vice president for Accelerated Networks Inc., Moore Park, Calif., another maker of VC-based integrated access equipment for service providers and customers. "You need something that virtualizes the network, which means using ATM VCs or IP flows to turn off a VC to one ISP and turn on a VC to another ISP with a single software command."

To offer bona fide voice services, the IAD will have to become mighty complex, incorporating "Layer 2 VCs, Layer 3 routing and bridging, software PBX and voice interfaces," Walsh says. "We will have a voice over IP (VoIP) gateway connection to the Class switch, but it's not here yet for a pragmatic reason: 99 percent of voice calls remain circuit-switched."

Delivering Voice and Data Services over End-to-End ATM

Virgin Market

For now, the window of opportunity for VC-based integrated access lies with the largely untapped small- to medium-sized business market for integrated data and voice access, particularly in the deployment of DSL services. For small businesses and consumers, DSL promises broadband, integrated access over a single copper loop.

Both regional Bell operating companies (RBOCs) and CLECs have deployed ATM and, in some cases, frame relay (which also is capable of provisioning VCs for each data or voice or video session) in their DSL access networks, all the way to the customer premises.

With their 1996 joint purchase of Plano, Texas-based Alcatel USA's asymmetric DSL (ADSL) equipment, BellSouth Corp. and SBC Communications Inc. adopted ATM transport from modem to CO. Although "always-on," high-speed data plus is driving ADSL so far, Alcatel will add "voice-over-X" capabilities to its ADSL system by the third quarter of this year, says Steve Makgill, the company's director of DSL products. "Our whole ADSL infrastructure is ATM, so voice directly over ATM is a simple matter, and we can carry IP traffic, so voice over IP over ATM is not a problem for us either."

Further, last year, long distance carriers AT&T Corp. and Sprint Corp. also endorsed multiservice ATM access, and DSL CLECs Covad Communications Co. (an AT&T partner), Santa Clara, Calif.; Rhythms NetConnections Inc. (an MCI WorldCom Inc. partner), Englewood, Colo.; and NorthPoint adopted ADSL and symmetric DSL (SDSL) that employ either ATM or frame relay transport.

To advance the cause of integrated access over DSL by the second quarter of this year, DSL router makers including FlowPoint Corp., Los Gatos, Calif., and Netopia Inc., Alameda, Calif., will combine forces with packet-voice gateway makers CopperCom Inc., Santa Clara, Calif., and Jetstream Communications Inc., San Jose, Calif., to create IADs that will accommodate up to 16 toll-quality voice VCs, along with a high-speed data VC, over single copper pair. Thanks to ATM statistical multiplexing, whenever any of those virtual voice circuits is unused, the bandwidth is reallocated to the data VC.

With 1.2 million high-speed DSL (xDSL) lines installed worldwide, PairGain Technologies Inc., Tustin, Calif., has developed the ATM-based Avidia System IAD and MSA. "Our IAD follows the model of putting more intelligence at the customer premises--for PBX, voice management, data aggregation, routing--setting up VCs from CPE to CO," says Kevin Woods, director of Megabit Access product marketing at PairGain.

"Installing dumb DSL access multiplexers is expensive and won't handle large-scale IP voice and other advanced services," Woods says. "Why put up a permanent 64-kilobit analog voice circuit when quality voice can be delivered with about 8- to 10-kilobit ATM variable bit-rate VCs and some compression?"

For larger businesses and multiple-tenant units unable to justify the cost of 45 megabits-per-second (mbps) T3 optical network access, IAD vendors including ADC Telecommunications Inc., Minneapolis; Sentient Networks Inc., Milpitas, Calif.; Sonoma and VINA also expect to deliver inverse multiplexing over ATM (IMA), which can "bond" multiple 1.5mbps, T1 access lines together as if they were one, broadband pipe.

For example, the Sonoma Access multiservice ATM access device, combined with Vienna, Va.-based Advanced Switching Communications Inc.'s Multiservice Aggregator, is optimized for multiplexed services over three to four bonded T1s. Shipping since last June at less than $10,000, Sonoma Access supports Ethernet, fast Ethernet, token ring, dial-up modem and other customer interfaces, while delivering T1, IMA, T3 or OC-3 (155mbps) access to the carrier.

"All this allows service providers to offer new, profitable services--grooming voice from data, Internet access, telemedicine, distance learning--that you couldn't do at high-access facility price points," says John Mazzaferro, Sonoma's marketing vice president. "The key is oversubscription to save on facilities costs and QoS. Service providers are offering SLAs, and they can't do that without QoS."

Not So Fast

By pulling CLASS (customer local area signaling service) voice feature software off of Class 4 and 5 switch hardware and storing it in call-control servers, ATM integrated services would use the servers to apply features to packet-voice traffic, then pass the traffic directly to packet backbones or through gateways to the public switched telephone network (PSTN).

However, many industry players question the speed with which robust call-feature sets can be developed for the call-control server model.

"With voice, you need to be rich with features, most of which are generated by Class 5 and Class 4 switches," says John Marble, vice president of Telco Systems Inc., Norwood, Mass. Telco Systems' EdgeLink 300 IAD supports Internet and transparent local area network (LAN) services (TLS) via packet transport, but it also supports up to 30 voice circuits via standard TDM.

"Packet-to-circuit gateway makers are seeking to replace Class 4 switches with packet switches, where the port volumes are highest, but it will take a long time to replicate all Class 5 features on the packet side," Marble says. "Initially, like any technology, packet voice will be feature-poor, which is where carriers make all their money. And while packet in the long term may prove most efficient, there are a lot of interim steps first to protect that TDM feature investment."

According to frame relay equipment makers, the better near-term solution is to support both TDM voice circuits and packet data over integrated access links. That way, voice features are maintained. At the same time, frame relay vendors including Adtran Inc., Huntsville, Ala.; Paradyne Corp., Largo, Fla.; and Sync Research, Irvine, Calif., are adding to their equipment "probes" designed to report frame relay permanent VC (PVC) performance and so to support data SLAs.

"It could be 10 TDM circuits dedicated to the PBX and six DS-0s that look like one pipe with one or 100 PVCs for data," says Scott Eudy, vice president of Paradyne's network access division. "In the past, packet data over frame could be sold as riding for free over the extra DS-0s in your voice network, and now with data growth, the message is analog voice rides for free on your data network."

Consequently, ADC; Carrier Access Corp., Boulder, Colo.; Paradyne; Premisys Communications Inc., Fremont, Calif.; Telco Systems and other access vendors continue to offer a mix of packet and circuit transport over an integrated access link, as do frame relay-based DSL equipment makers, including Fujitsu Network Communications Inc., Richardson, Texas.

Still, some of those vendors say their equipment will accommodate migration to packetized and/or cell-based integrated access. Currently, for example, Paradyne's SuperLine IAD combines dedicated TDM circuits with frame relay data transport to the CO, but "well before the end of the year, we'll unveil multiline voice over IP-over-DSL," says Ron Stein, DSL marketing director.

The leading makers of Class switches themselves may help such efforts. In February, Lucent Technologies Inc., Murray Hill, N.J., delivered its AnyMedia MultiService Module packet-switching enhancement software to ICG Communi-cations Inc.'s Class 5 switches. The module combines remote access concentrators with ATM switching to terminate either TDM or packet traffic on any Lucent 5ESS switch.

Also in February, SBC Communications began beta testing Richardson, Texas-based Nortel Networks' Succession Network, a complex of distributed ATM switches, multiservice gateways and call-control servers.

"Carriers want to cut costs by collapsing Class 5 and 4 into one layer, and they're realizing that, if you want to offer voice services, you have to have ATM, because you have to offer the same quality of service that enterprises get today," says Graham Rance, Nortel's vice president. "It's no longer a nodal system; it's the distribution of ATM switching fabric for the purposes of distributing both access and call control."

Nortel and Lucent enjoy at least a slight edge over startup players in maintaining those TDM call-control services in the packet world. "Competitors will have to create the services," Rance notes. "We can just move them over from our switches."

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