# The copper loop: From barbed wire to broadband

Bhawani Shankar

If xDSL technology is the answer to the current bandwidth dilemma, why aren’t vendors and service providers beating down the developers’ door?

In the operator and service provider world, it is now an accepted, inescapable conclusion that xDSL technologies will one day be installed on a global basis, in vast quantities. Despite other technology developments-not excluding recent announcements about the commercial viability of sending data down power lines-it is still the only viable technology capable of substantially increasing bandwidth on the local access loop without a substantial overhaul. These copper loops are ubiquitous over every home in Europe and it is unlikely that any mass scale upgrade to fiber will happen within the next 15 years.

The primary driver for xDSL is high speed Internet service deployment to residential customers. So far, there have been two small commercial deployments and no less than 55 trials around the world, trying to prove that asynchronous DSL (ADSL) can provide a downstream connection of up to 8 Mbps and upstream connection of up to 1 Mbps over the existing telephony copper pair.

Both IP and ATM network architectures are currently being trialled. ATM is considered the probable choice in the future, although initial trials have used stand-along ADSL modems with discrete IP interfaces for reasons of time-to-market and availability and these are evolving to highly integrate digital subscriber loop access multiplexers (DSLAM) solutions.

The complete network typically consists of a core which is based around SDH, wrapped with broadband ATM switches, ATM access switches and DSLAMs. The DSLAMs provide the individual xDSL lines out to the customer premises and integrate with the existing POTS network connections. But even after having been in trial for more than 18 months, few operators seem close to commercial rollouts. What is taking them so long? Rob Brading, marketing director for Atlantech technologies, which is helping telcos to manage some of the world’s leading xDSL trials, has some answers to the question.

‘Some of the main barriers to large-scale adoption include the continuing standards battle and the lack of interoperability’, he told Telecommunications®
International. The existence of two de facto standards, namely DMT and CAP,
provides network operators with a dilemma; deciding which to adopt before a leader is clearly identifiable in case the choice ends up as the Betamax of the standards. There are two ‘standard’ camps, one apparently led by Israel’s Amati, which has developed modems using discrete multitone technology (DMT) for the line coding. Motorola and Alcatel are among the major manufacturers who have developed DMT modems. The second camp has adopted a technology developed by the former AT&T Paradyne, which championed carrierless amplitude
Modulation/ phase modulation (CAP) for the line coding. Westell, the company that made the ADSL modems being used in Bell Atlantic’s Virginia trial uses CAP. With no clear stance being taken, a general ‘wait and see’ attitude is developing.

Lack of interoperability is also becoming a matter of concern. ‘The current xDSL units on the market, from a variety of vendors, supporting different standards, do not interoperate,’ Brading said. Interoperability between vendors’ equipment is key to mass roll out and provisioning. The ultimate goal is for the end customer to be able to purchase their own ADSL termination units, much the same people buy off-the-shelf analogue modems today. For this to happen, the ADSL termination unit technology needs to mature to the point were it is as simple as a modem to install and operate.

Figure1: ADSL: set for stupendous growth

Source: Telechoice.

Operators are still deciding on suitable end-to-end architectures. Once these infrastructures have been agreed upon, the business and technology in place, service can then be rolled out in volume. These new architectures need to address the integration of network, service and business management of these new broadband services. ‘Without these seamless, end-to-end management systems in place, it is difficult to see how operators will be able to make any profit on broadband services’, said Brading.

The management challenge

The new broadband services being deployed by network operators and service providers are typically delivered over very complex network environments which include legacy equipment with primitive management capabilities and newer systems incorporating sophisticated TMN-based element management. New network management infrastructures are required to mould these disparate
information sources into a cohesive view of the end-to-end service being delivered. This can be complicated by the large scale of such service-typically involving hundreds-of-thousands or millions of network elements.

The major requirements can be summarized as follows:

Cost-effective, performance scale ability-a system with the ability to manage small pilot networks and expand as the network grows without performance degradation;

Multiple protocol support-standards-based and proprietary management protocols must be supported in a transparent manner to the network applications;

Powerful event management-as the network grows, the number of events grows exponentially. The ability to manage this volume of events in a way that helps the operator make sense of the status of the network is mandatory;

Seamless application interworking-operators will use a number of different applications to manage aspects of the network, but they require the ability to move easily between applications, to investigate problems or configure service for a particular customer, for example.

User access management-the information within the management system must be protected, but it must also be feasible to partition the data, and the access to it, in a way that supports operational processes.

xDSL network architecture

Some of the key management challenges when installing xDSL networks include potential element volumes. xDSL network elements are extremely complex devices that require real time management. As element volumes increase exponentially, operators are faced with the challenges of implementing end-to-end systems that can manage millions of highly complex access elements.
As an example, the 1994 BT video-on-demand (VOD) trial supported 2,000 ADSL lines, equating to 4,000 access elements. Although this was classified as a small marketing trial, it is still the largest single xDSL installation in the world. This network generated a tremendous amount of management traffic, primarily with SNMP and performance monitoring information, all of which had to be processed in real time by the central management workstation.

Additionally, xDSL equipment, by virtue of its inherent built-in intelligence, generates a tremendous amount of management traffic. This information, be it alarms, performance monitoring information, configuration data, diagnostic commands or inventory data, has to be processed, stored, prioritised, formatted, and displayed by the central management console. A single element management workstation cannot scale to support any major network growth.

Element and network complexity is also an issue that operators need to prepare for. xDSL equipment is becoming more complex with each generation. The latest generation uses rate-adaptive transmission which causes a myriad of possible upstream and downstream speed permutation. Remote equipment now incorporates xDSL transmission hardware, IP routing equipment and IP or ATM CPE interfaces into a single unit. In addition, it has to be seamlessly integrated with the existing POTS network leading to a wealth of configuration permutations, performance monitoring information, alarm and event reports, diagnostic functions and inventory data being available to the network operator.
A typical end-to-end network capable of delivering high speed Internet, and on demand services, data and voice from multiple service providers is extremely complex. Many issues can only be resolved with the use of integrated management applications and systems. This often results in a number of non-compatible element management systems being installed to manage different parts of the network, then integrated together to provide a ‘zero touch’ system to allow the end customer to control and manage a large part of their own service offering in real time.

xDSL equipment is normally installed over existing telephony circuits but the devices at each end of the connection contain POTS splitters that allow both the telephony circuit and the xDSL circle to use a single copper pair. This requires the integration of a new xDSL management system with existing POTS systems.

A range of issues also cloud on the most efficient interface for the customer premises equipment. The two protocols in question are IP and ATM. Network operators are installing complex networking equipment into residential environments for the first time. This can lead to a multiplicity of new problems ranging from units being tampered with and cables being disconnected, to PCs being reconfigured, resulting in a huge increase in the number of service related calls and queries directed at the network operator who has to be able to diagnose, isolate, and analyse problems from the central management system. Only when this type of network and system management and control is achieved will broadband services become commercially viable.

Commercial viability

‘The density of the technology must increase dramatically to enable operators to fit all the required ADSL termination units into their existing exchange real estate,’ said grading. xDSL technologies are still costly, and this is holding back general acceptance due to the costs of equipment investment and the ongoing line rental charge. Price in the range of US$150 to US$300 would start to approach an acceptable level for the benefits of this new broadband technology.

But in most European countries, high capacity broadband ATM backbone networks have yet to be deployed. Without this backbone infrastructure there is little benefit to be gained from introducing an upgraded access network. In the infrastructure context, the questions of how some major European operators will play-off ADSL against their substantial ISDN services will be an interesting debate. As it now stands, current versions of ADSL can not co-exist with ISDN BRI lines. New versions of ADSL are being developed that will co-exist with ISDN but as yet are only available in small trial volumes from one or two vendors.

Telcos such as Deutsche telekom, which bet its future on ISDN, are now involved in desperately trying to increase ISDN usage before ADSL establishes itself. The situation it faces-in common with many other operators in Europe-is that too much emphasis and keenly-priced ISDN will undermine ADSL; but, at the same time, not investing an adequate amount of resource on ADSL now might undermine its future as a broadband services provider.

ADSL outlook

From the point of view of commercial (profitable-both for provider and user) service provision, xDSL can be considered an immature technology. ‘xDSL has been proven an effective, reliable solution in many international trials,’ said brading. ‘however, it is developing and progressing continually. This adds to the xDSL management complexities requiring the facilities for operators to download new algorithms on a regular basis.’
xDSL standards are relatively new and are therefore, prone to change on a regular basis. This involves regular, programmable equipment upgrade such as software download of new versions of xDSL transmission and application code from a central management station.

As with all new technologies, technical and cost issues do get resolved in subsequent generations. xDSL is no different. The market demand for high-speed, broadband communications will drive the development of the technology
and will produce an economic, reliable solution for end users. For network operator, xDSL is the most cost effective way of upgrading the copper infrastructure and competing against fibre and cable competitors. Another factor in determining market direction is a move for European PTTs from monopoly to deregulation and free competition. This will force network operators to unbundle their loops in a similar way to what has happened in the UK and US. These new competitors will aggressively target end customers with offers of high-speed, broadband data communications, tempting them from the traditional service providers who may not be moving as quickly towards new service provision.

So, using the existing copper networks, xDSL will be made available which will motivate PTTs to respond, leading to a critical mass and explosion in xDSL deployments. While network operators, service providers and vendors debate the standards, technology and cost issues of deploying ads networks, costumer demand is growing for cost-effective, high speed, broadband networks that unless new services and new business potential for them. ‘Looking at the rapid development of internet and intranet business and services over the last 2 years, I think you can expect resolutions to the main issues and mass ads deployment within the next 2-4 years’, Brading predicts.

Source: Bhawani Shankar, The copper loop: from barbed wire to broadband, Telecommunications (International Edition), November 1997, pp.79-82.