now and then

THE ULTIMATE VISION FOR next-generation networks usually includes the consolidation of voice and data into a single, unified data and VoIP network. Class 5 circuit switches will be retired and IP-based, next-generation softswitches will take their place.

Every voice customer will be served by broadband access plant and all voice traffic will be converted in the access network to VoIP under softswitch control. Yet the ultimate vision of a unified data/VoIP network is far from being achieved.

What stands in the way of this vision? Timing, capital and technological incompatibilities, primarily.

New broadband access plant often is deployed far prior to softswitching, creating a timing mismatch and requiring carriers to implement Class 5 control of VoIP in the interim.

It may take decades to reach a majority of customers with new broadband access technologies, given the high capital costs and logistics of constructing new outside plant.

Softswitches by their nature are IP-based and not compatible with the circuit-based access plant upon which most voice traffic rides today, so replacing the Class 5 switches seems far off as well.

Today’s VoIP customers fall into roughly three main categories: customers served by new access plant such as FTTx and broadband loop carriers (BLCs); selected business customers; and residential customers wanting low-cost voice over broadband access. Left out of VoIP are the large majority of carriers’ customers on the millions of remaining residential and small business lines.

One reason VoIP is not more widespread is that it simply is different than POTS. Though VoIP provides benefits like new softswitch features, VoIP can have powering issues and often requires additional premises equipment. With POTS, you simply plug your phone into a wall jack — and line-powering comes from the line cards of a Class 5 or DSL. VoIP, however, rides on broadband and usually requires premises equipment like DSL modems, integrated access devices, Ethernet adapters or FTTP optical network terminals — all of which are usually house-powered and need to be backed up by batteries to ensure, for instance, an E911 call could be made during a power outage.

It is unrealistic to assume carriers will deploy this kind of VoIP quickly, incurring the expense and effort of installing battery systems or requiring new equipment in every home and business — and POTS customers certainly will need to be convinced of the benefits before changing anything about their existing service. On the other hand, BLCs typically provide line powering for POTS and also lack the premises equipment issues. However, with more than $300 billion (in yesterday’s dollars) of outside plant investment for incumbent telcos, it likely will be many years before legacy plant is replaced substantially by BLCs. But by using a universal media gateway (UMG) as the key network element in a three-phased approach, service providers can reach their goal of a unified network much faster, quickly gaining the benefits of Class 5 replacement, central office consolidation, and ubiquitous, softswitched VoIP.

In Phase 1, carriers use the UMG to accommodate their newly installed broadband access plant. The UMG links the Class 5 switch to this plant over standard DLC interfaces such as GR-303, TR-08 and V5.2. As a result, network timing mismatches are eliminated as carriers can deploy this new plant without having to implement immediately softswitching to control voice services.

In Phase 2, carriers deploy softswitched VoIP over broadband access and provide, for example, hosted IP PBX or residential second-line VoIP services. The UMG in this phase adds a new function to trunk calls between the softswitched VoIP network and the legacy circuit network.

In Phase 3, carriers use the UMG to connect their legacy, circuit-based DLCs and remotes to the softswitch. The UMG appears to the DLCs as the front end or “IDT” function of a Class 5 switch. By simultaneously supporting softswitching protocols and proxying the line-powered, circuit-based phone lines of the DLCs as “IP endpoints” to the softswitch, the UMG allows the softswitch to maintain control over the POTS phones.

Phase 3 gives carriers a timely relief valve. With more than 220,000 DLCs in the United States alone serving more than 40 million lines, roughly one-third of line-powered telephone lines can be converted immediately to softswitched VoIP. The POTS lines that remain can be accommodated by re-terminating them on high-density DLC in conjunction with the UMG, or by replacing them over time with new BLC and FTTx access plant.

The UMG allows carriers to use a single network element to enable the migration from circuit-based networks to a unified data and VoIP network. This makes significant strides toward the cost reduction initiatives associated with softswitched VoIP, and does so faster and at a lower cost than forcing upgrades in the outside plant.