Frequency bands

Written on 10:33 AM by ooe

Allocations made for narrowband wireless local loop applications vary from country to country but in most cases they are in the 2 to 4 GHz band. Individual operators have been granted spectrum allocations of approximately 10 to 50 MHz within these bands, which is relatively small. There is increasing interest in using these frequencies for mid-band systems offering data services as well as voice. The advantage over higher frequencies is that these systems can work over greater distances and use less sophisticated and hence less expensive components. However, there is inherently less spectrum available and it is in demand for future wide area mobile systems.

Broadband systems require more spectrum and the allocations that have been made, or are being considered, lie within the 10 to 40 GHz band. indicates the major allocations in the US and Europe. Shown are both issued and proposed licences, with the UK shown separately from Europe to illustrate that even within one region there are still national differences. It can be seen that a number of past licences issued for fixed wireless access in the UK are under consideration for reallocation, due to lack of use.

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Spectrum trading

Written on 10:33 AM by ooe

A common licence condition for block allocations specifies whether or not spectrum trading is permitted. If it is, the winning operator may subsequently transfer their licence to another party for instance if they wish to sell it or merge their licence holdings with those of another operator. If trading is prohibited, an operator is not at liberty to sell their licence and if they no longer require it, it must be returned to the government for resale.

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Competitive tender or ‘beauty contest’

Written on 10:33 AM by ooe

An alternative method of awarding block licences is commonly known as a ‘beauty contest’. In most cases, an annual fee is charged for the licences, but this is an administrative charge, much lower than the likely auction price. The award is based not on which operator is willing to pay the most, but rather the operator who undertakes to make best use of the spectrum.

In a similar way to the minimum permitted performance licence conditions often imposed on auction winning operators, the beauty contest attempts to ensure that the government's original objectives in issuing the spectrum are met. While an auction process limits itself to specifying a minimum set of desirable parameters that the resultant network must exhibit, the beauty contest award decision is given to the operator whose proposed network offers the most desirable features. Exactly how these desirability criteria are judged will again depend on the original objectives.

One obvious flaw with this process is that an operator could over-promise in an attempt to secure a licence. For this reason, the promises usually form the basis of the winner's licence conditions. Additionally it is common for a detailed business plan to be required which shows achievable forecasts for revenue and expenditure.

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Auction

Written on 10:32 AM by ooe

Block spectrum allocations are often awarded using a competitive auction. Holders of such licences can use the spectrum wherever and as often as they like, within a given country or region. Such awards usually last for a set number of years, with the issuing authority then claiming back the spectrum for reissue or an alternative use.

There have been many successful auctions for FWA spectrum around the world with considerable income being generated, for instance the 1998 US LMDS auctions (spectrum in the 28–31 GHz range) raised $600 million. However, the UK 28 GHz auction held in 2000 illustrates the risk to governments of using this process – 26 of the 42 licences offered failed to attract any bids, leaving large parts of the UK without any broadband FWA operators to compete with existing access providers.

Other risks occur depending on the government's original motivation in offering the spectrum for FWA usage. In many cases the objective is to increase competition in the access market by using the potentially low cost of entry offered by wireless networks compared to wired networks. One possibility is that the licence winner will ‘cherry pick’, only offering service in the highest profit areas. This can mean that only the most densely populated business districts will obtain the benefit of increased access competition. Alternatively, the spectrum might be used for infrastructure connections, such as point-to-point backhaul connections within the operator's network, rather than for its intended application in access networks. Outcomes such as these can be guarded against by introducing licence conditions such as minimum coverage areas that must be achieved within a given time and strict definitions on the permitted use of the spectrum.

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‘Per link’ fees

Written on 10:32 AM by ooe

This type of spectrum licence charging tends to be applied to point-to-point systems, where dedicated spectrum is required for each customer connection. The operator must apply for the spectrum required for each radio link and the licence obtained is only valid for that frequency in that particular location. Generally, if the link is removed, the spectrum licence must be handed back to the issuing government. Charging may have temporal, capacity, usage and geographic elements.

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Free of charge

Written on 10:32 AM by ooe

Some spectrum can be used without payment to the government that owns it. Some such spectrum still requires the user to obtain a licence prior to use and some is set aside for use without any permissions at all, provided certain technical constraints are met. The main example of the latter are the internationally agreed ISM (industrial, scientific and medical) bands, this spectrum often being known as ‘licence-exempt’. Whilst the technical parameters vary by country, the aim is the same – to make spectrum available that may be used on an ad hoc basis without need for prior permission. Example applications include microwave ovens and industrial heaters, wireless LANs and remote control units. Another emerging use of these bands in many countries is for commercial fixed wireless access networks, often focused on delivering data services and based on existing wireless LAN technology.

Within the UK there is an unusual constraint on these bands which limits their licence-exempt use to ‘private self-provided communications’ in effect precluding their use for commercial access networks without a licence. Thus far the government has only issued one commercial use licence per region within the UK.

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Spectrum

Written on 10:32 AM by ooe

All fixed wireless access systems require a portion of the radio spectrum in which to operate. In almost all cases, a licence to use this spectrum must be purchased from the appropriate government agency before the system can be operated or even planned. The size of the radio spectrum is in theory infinite, extending from zero hertz through progressively high frequencies to light, x-rays and beyond. In practice only a very limited part of this spectrum is usable for commercial access systems. Demand for these frequencies is huge and growing all the time with competition to fixed terrestrial access systems coming from uses such as satellite communications, radio astronomy, industrial applications, emergency services, television broadcasting, telemetry, mobile communications, military and medical applications.

The large and ever changing appetite for such a scarce resource leads to a requirement for careful management on national, continental and global fronts, which in turn limits the amount of spectrum available for fixed wireless access use at any point in time. Suitable parts of the radio spectrum, or bands, are usually made available by a national government when agreement is reached with all other previous or potential users of the spectrum and there is judged to be significant interest from operators.

Would-be fixed wireless access operators therefore face the difficult situation where their ability to deploy a network is dependent on being able to obtain a licence for suitable spectrum from the local government, who may or may not make such licences available at some point in future. This makes spectrum an absolutely essential ingredient in any planning or operation of wireless networks.

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Fixed Wireless Access

Written on 10:31 AM by ooe

Mankind has been communicating via radio signals for a very long time, between neighbouring buildings, across oceans and even from one planet to another. Theoretically such technology can be used for the last mile of a telecommunications network to connect its customers. In practice, however, it is not well suited to such use and it is only over the last decade or two that tailored solutions have emerged, allowing large scale wireless access to become economically viable.

Wireless access splits into two classes – fixed and mobile. Fixed systems are known by many names including fixed wireless access (FWA), wireless local loop (WLL), multimedia wireless systems (MWS), broadband wireless access (BWA) and local multipoint distribution systems (LMDS). While mobile systems allow users to roam around the network, in fixed systems the radio units are permanently mounted in the same way as copper and optical fibre.

Using radio in the access network presents a unique set of engineering challenges, especially if service quality is to rival wired delivery. Securing suitable spectrum is a prerequisite to establishing a network. The transmission medium presents many challenges which are outside the direct control of the network operator, and those that are of particular importance for fixed applications have to be considered when selecting radio equipment. Careful planning of the network is required to ensure it meets initial and longer term market requirements and the initial technology and architecture choices are key to achieving success. When all these aspects have been considered, a network operator can assess the likely costs and revenue of a wireless system and can answer a more fundamental question – is wireless the best choice of access technology for this application? This chapter will explore each of these issues in more depth.

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Development of a portfolio of services

Written on 2:55 PM by ooe

The biggest barrier associated with deploying FTTH may not be due to technical or cost constraints but due to customer demand. However much the infrastructure and transmission equipment is developed and cost optimised, unless sufficient customers want the services that FTTH can deliver it will not be commercially viable. Most customers are interested only in the services that they have access to and not the network which provides them. As discussed earlier, services such as software delivery and High Definition TV require bandwidths that would greatly stretch the capabilities of most, if not all, technology options except FTTH. To drive FTTH deployment, one or more high bandwidth killer applications need to be developed which will increase the revenue per customer. Until such applications are found FTTH deployment is likely to continue at a more sedate, though no less stoppable, pace.

• The deployment of FTTH is largely constrained by commercial and not technology issues. What is needed is both a reduction in the cost of deployment and an increase in the perceived revenue that may be achieved. Once an acceptable profit margin can be seen the speed of deployment will accelerate. This may fuel further cost reductions associated with volume production which may sustain the acceleration.

• The development of a killer application, for which many customers would be prepared to pay a premium price, could generate a compelling commercial argument for deploying FTTH more quickly and as widespread as operationally possible.

• Even with a concerted commitment, universal deployment of FTTH across the whole of the UK is unlikely to be achieved in less than five to ten years even if it were started tomorrow.

• Current effort of the Broadband Network Engineering Network Modelling team is concentrated on understanding the costs involved and seeking ways to reduce these. Optimisation of the distribution network is seen as crucial for cost per customer reduction. Blown fibre is seen as a key enabler for FTTH.

• Infrastructure cost per customer is highly dependent upon customer take up. This tails off at 50%, so ideally active marketing should be undertaken to achieve take up of at least 50% in most geographical areas. 11
  
  
  

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Labour

Written on 2:55 PM by ooe

Labour costs, whether for direct employees or external contracts, form a significant part of the total deployment costs for any network. For FTTH a large amount of external network installation will be involved. The bulk of costs are attributable to this installation work, including duct build, cable installation and jointing/configuring cables. It is, however, important to consider the wider labour requirements associated with the whole lifetime of the FTTH network as shown in Figure 10.12. Not only does this add to the labour costs, it demonstrates the number of different functions required; these functions are usually carried out by different personnel.

Reduction of labour costs could be achieved by one or more of the following:

• making the best use of the existing infrastructure (particularly duct network);

• optimising network design;

• more efficient practices;

• more efficient processes;

• better utilisation of personnel;

• deskilling practices to enable lower paid personnel to be used.

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Infrastructure cost reduction

Written on 2:53 PM by ooe

It would be technically possible to use current commercially available fibre infrastructure for FTTH. However, much of this infrastructure has been designed for dedicated fibre feeds to business customers. It has been realised that this plant is likely to be over specified for wide scale FTTH provision. Similarly operational practices have been developed for providing fibre feeds to individual or small groups of customers and are not likely to be optimum for FTTH. It can be concluded that cost optimisation is required for both infrastructure stores and labour before FTTH could be seriously considered. It should be noted that a significant reduction in transmission system costs is also required. This is discussed elsewhere [2].

The largest single factor that affects the cost per customer of installed FTTH infrastructure is customer take up. High customer take up in a geographical area enables greater sharing of network segments and consequently greater sharing of the costs associated with those parts of the network. The effect for the town of Ipswich is demonstrated in Figure 10.11 for both a 32 way split PON and a dedicated fibre network. It can be seen that the cost reduction tails off above 50%. For a PON network the infrastructure cost per customer is halved by increasing the customer take up from 10 to 50%.

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FTTH infrastructure cost breakdown

Written on 2:53 PM by ooe

Detailed cost modelling of FTTH infrastructure has been performed for the town of Ipswich. This area includes five exchanges which serve a total of approximately 70 000 customers. The average cost per customer connected has been estimated by dimensioning a fibre network for an expected level of customer take up. The results of the modelling activity highlight the following cost trends.

Figures 10.9 and 10.10 show simple summary charts indicating the network infrastructure cost breakdowns for PON and point-to-point networks to serve an expected customer penetration of 20% (with no demographics applied). In both cases it can be seen that the distribution side of the network contributes the greatest cost per customer. This is because this network segment is shared between the least number of customers. Optimisation of the distribution network is therefore crucial in order to reduce overall costs. For both PON and dedicated fibre networks, labour costs contribute approximately 50% of the total infrastructure bill. A key part of this process is using NetMod to carry out cost sensitivity analysis and hence start to develop planning rules that ensure cost effective network deployment.

Figure 10.9: PON cost breakdown

Figure 10.10: Dedicated fibre cost breakdown

Detailed cost breakdowns have also been produced to identify those items of the network build that contribute most to the cost per customer connected. These individual items are now being targeted for potential cost reduction. For a PON network the highest cost items are distribution blown fibre and optical splitters. For dedicated fibre the highest cost items are primary cables and distribution blown fibre.

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Results output

Written on 2:52 PM by ooe

Results from NetMod can be either numerical or graphical. Figure 10.6 shows an example of a graphical summary output from the demographics module. It highlights the number of potential customers in East Anglia for a particular system service set. With no demographics applied (100% of population) customer take-up numbers are shown within predefined bands, whereas when demographics are applied only targeted customers are identified.

Figure 10.6: Demographics module output

These maps are useful for visualising the effect of varying estimated customer take-up of a particular service set/technology. They can also be used to develop strategies for cost effective network rollout based on targeting specific customer types that promise high potential revenue.

Simple networks designed by the E-side and D-side geography builders respectively are shown in Figures 10.7 and 10.8. Figure 10.7 shows a spine and spur network linking a number of primary nodes (positioned at PCPs) to their serving exchange. Figure 10.8 shows a network connecting secondary nodes (positioned at DPs) to their serving primary node (positioned at a PCP). By repeatedly running the geography builders for all the E-side and D-side networks within an exchange area the entire network within the exchange area can be designed. This can then be dimensioned and costed. This process can be repeated for all exchanges within the UK or for a representative sample of exchanges.

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Fibre to the Home Infrastructure Deployment Issues

Written on 3:52 PM by ooe

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Future point-to-point technologies

Written on 3:51 PM by ooe

A constant theme through this chapter is that technology is improving all the time and nowhere more so than in the access network space. It is clear that point-to-point technologies will improve with time, however, they tend to require concentrators in the access domain or long runs of optical fibre, both of which are non-optimal except for green field sites. Despite these limitations, many manufacturers and start-ups are active in this space and future upgrades to this type of equipment are certain.

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Future PON technologies

Written on 3:51 PM by ooe

Current PON technology is limited to 622 Mbit/s, however, this is not a practical limit for this technology, merely the highest agreed bit rate supported by the ITU-T. The IEEE and FSAN are already considering systems with 1.25 Gbit/s PON speeds, and higher bit rates are feasible.

Whilst the IEEE Ethernet PONs are rumoured to be a lot cheaper that APON technology, so far no systems have been produced to test this hypotheses. Time will tell whether this technology will actually prove to be cheaper although many components will be common between the two architectures leading to some doubt as to the reduced cost claims.

Already we have seen experimental Super-PON architectures from Alcatel [3,4] where the split ratios can be increased from the more usual 32 to over 100, with thousands or more being possible. Furthermore, optical amplifier technology is making possible PONs with a transmission reach of thousands of kilometres.

WDM technology will allow common infrastructure to serve both residential and business end users, even if those businesses require very high point-to-point data rates.

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Point-to-point applications

Written on 3:50 PM by ooe

Point-to-point systems generally utilise multiplexors at or near the street cabinet. This is not ideal for most ILEC applications although CLECs may find the technology useful in the longer term as this fits with their current architectures.

It is fair to say that point-to-point architectures usually compare favourably to PON architectures where there is a strong demand and a central site at which concentration can be achieved, and hence they are often used for campus environments.

Point-to-point technology has been used successfully where there is a need for fast Internet service, however, the systems tend to be poor at providing voice services. For that reason they seem best suited as an overlay technology, leaving existing services on copper. For the network operator, however, the costs of maintaining two parallel networks can prove highly undesirable.

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As core feeder technologies

Written on 3:50 PM by ooe

Most operators are rolling out ADSL systems and are considering the next step ahead. VDSL is considered a realistic future step for the access network. However, all DSL technologies have one major weakness, they require a metro-type transmission network to feed them. Some in the industry are experimenting with new feeder architectures based on PON designs. Current 155 or even 622 Mbit/s systems are not really powerful enough for these core feeder applications but future PONs based on 1.25 Gbit/s and higher seem to be well suited to these applications.

One could visualise an architecture where the access and metro/core networks could be rolled into one and served by powerful PON systems. Studies are already underway to examine the cost implications of such architectures and if successful, these could pave the way for the introduction of the technology in a much shorter timescale than would otherwise be possible. These systems would need greater split ratios and much longer reach than current PON technology would allow.

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As access devices

Written on 3:50 PM by ooe

As has been said many times, optical fibre in the access network would create the ultimate access network, although controlling the costs of implementing such architectures is key. PON technology has been shown to reduce the costs of access fibre network rollout for two reasons:

• It allows a reduction in the number of fibres back to the exchange giving better duct utilisation and shared head-end (OLT) costs.

• It inherently concentrates the traffic onto fewer data streams hence reducing the cost of metro equipment.

Given the increase in speed of computing devices, and the proliferation of the Internet, it is to be expected that the market for high-speed connections will continue to grow and will become ever more resource hungry, both in terms of bandwidth connectivity and service support. In this market it is to be expected that optical technology will outstrip other access network technologies to become the technology of choice.

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PON applications

Written on 3:49 PM by ooe

PON systems have never be deployed in quantity in Europe for several reasons. Whilst it is true that these systems need to be multi-service, it is also fair to say that most systems to date have not proven to be so with PSTN services missing from most designs. This situation is now changing and several manufacturers are showing PSTN on their PON product roadmaps, with delivery of such systems scheduled for mid 2003.

Despite the costs and lack of flexibility associated with current equipment designs, there are inherent advantages of PON technology and the next sections look at types of deployments for which PON systems are most suited.

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OAM specification

Written on 3:21 PM by ooe

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Protection

Written on 3:21 PM by ooe

It has been identified that PON systems might not give the level of reliability required for certain applications. Whilst the PON electro-optics are generally reliable, it has been found that a major cause of failure is the physical media, i.e. the optical fibres in the access network themselves, and in many cases faults are caused by external influences. Point-to-point systems can allow for protection using back up or standby fibre pairs.

It is not the aim of protection scenarios to restrict the architectures possible in a PON architecture but to support and enhance whatever architecture is chosen for a particular application. For this reason, the protection scenarios offered are not exhaustive, but are representative of those it is considered will be of interest. These must be carefully tailored to the applications for which they are required.

Generally it is only FSAN, and through them, the ITU-T that have considered protection of PON systems in some detail and an ITU-T recommendation is due shortly. This will be known as ‘G.983.5: A broadband optical access system with enhanced survivability’.

The main requirements of a protection system shall be that:

• It should be possible to have several C protection configurations on the same OLT.

• It should be possible to duplicate the OLT-PON-interface and the fibres between the OLT and splitter and to duplicate the entire fibre path between the OLT and ONU for a set of ONUs.

• It should be possible to have a mixture of protected and unprotected ONUs on one B-PON interface.

• The addition or removal of a protected ONU on a PON should not affect other ONUs on the same PON.

• It should be possible to have automatic switching, which would be triggered by a fault detection such as loss of signal, loss of cell delineation, signal degrade (e.g., BER becomes worse than the pre-determined threshold), etc.

• It should be possible to have forced switching, which would be activated by administrative events such as fibre re-routing, fibre replacement, etc.

• It is necessary to avoid unnecessary switching. Because unstable switching affects service quality, unnecessary protection switching and unnecessary revertive protection switching should not occur.

• It should be possible to realise switching without connection loss of the ATM connections.

• It should be possible for the operator to choose between a revertive and a nonrevertive switching mode.

• The service halt time should be less than 50 ms if the extra traffic option is not used.

• The events or conditions that trigger automatic switching should be chosen among the G.983.1 OAM parameters.

• The chosen protocols and mechanisms must apply to the B-PON section layer.

• Extra traffic should be carried over the protection entities while the working entity is active and would not be protected. This capability will provide effective usage of bandwidth on the protection entities.

• It must be possible for an operator not to activate the extra traffic option (e.g., to achieve a lower service interruption time).

Extra messages are introduced into the base set of PLOAM messages from G.983.1 to cope with the additional functionality required for protection switching but generally it is the OLT that initiates the switch-over.

There are two basic protection schemes that can be used and the authors do not attempt to judge failure mechanisms within this chapter and make no recommendations as to the better protection mechanism to use. The first is a partial protection scheme and is designated type B protection. It is useful when it is the feeder fibre(s) that are considered at most risk of failure. The more fully protected scheme is known as type C protection.

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Dynamic bandwidth assignment

Written on 3:21 PM by ooe

Most access network systems, with the exception of point-to-point systems, use fixed, or static, bandwidth assignment. Most point-to-point systems allow static multiplexing and therefore the following section does not directly apply to them. With PON access network Systems, the situation is somewhat different.

A typical APON system would run at a bit rate of 155 Mbit/s, allowing a total customer bandwidth of around 130 Mbit/s. If this were statically multiplexed, the bandwidth per customer on a 32 way PON would be in the order of 5 Mbit/s. Now 5 Mbit/s is not a lot and could be provided by alternative technologies such as DSL.

Dynamic bandwidth assignment relies on the fact that it is uncommon for each user on a PON to require their full bandwidth at any one time. In fact each user can have potential access to bandwidths in excess of their mean bandwidths for extended periods of time and this is what dynamic bandwidth assignments would allow.

Instead of bandwidth being assigned on a per user basis, bandwidth is provided on demand, with the user unaware during normal operation that their share of the overall bandwidth ‘pot’ has increased.

On an APON system, it is not too difficult to arrange this as the speed of transmission over the PON is quite fast and therefore latency issues are kept to a minimum. The user is unaware of the precise mechanism by which the ATM packets are queued and then transmitted across the PON.

The principle recommendation from the ITU-T that deals with dynamic bandwidth assignment is G.983.4 (‘A broadband optical access system with increased service capability using dynamic bandwidth assignment’). Dynamic bandwidth assignment is also known as DBA.

In the DBA recommendation, G.983.1 is modified to allow for extra messages required in order to support the DBA mechanism. The DBA standard is designed to include:

• Performance objectives (for example, bandwidth assignment delay, maximum waiting time).

• Application functionality (for example, dynamic bandwidth assignment for bursty traffic and for ONU/ONT aggregated traffic composed of different traffic classes).

• Fairness criteria and protocols (for example, dynamic bandwidth assignment based on ONU/ONT status reporting, dynamic bandwidth assignment based on OLT monitoring, dynamic bandwidth assignment based on a combination of reporting and monitoring).

• Backwards compatibility.

As a background to understanding the dynamic bandwidth principles, it is essential to understand the way an APON works, at the cell level.

The basic APON standard is the ITU-T Recommendation G.983.1 which specifies a flexible access platform to provide broadband services through passive optical networks. In this Recommendation, the upstream traffic from the ONUs/ONTs to the OLT is transferred in a frame of 53 time-slots (cell slots). Each time-slot consists of three bytes of PON layer overhead and an ATM cell or a PLOAM cell. The upstream bandwidth is shared among the associated ONUs/ONTs. The OLT controls each upstream transmission from the ONUs/ONTs on a time-slot-by-timeslot basis. This is accomplished by sending data grants in downstream PLOAM cells.

PLOAM data grant cells are sent in the downstream direction to all ONUs/ONTs. The data grants are addressed to specific ONUs/ONTs and contain parameters that include the number of upstream data grants and the time-slots for the grants that are assigned to the individual ONU/ONT. Originally the grants were assigned in a static manner and only updated when a new connection is provisioned on a PON or an existing connection is removed from a PON. Once the bandwidth is provisioned, the OLT would continuously send the assigned grants to the associated ONUs/ONTs; subsequently, the OLT would receive corresponding user cells in the upstream. This current granting mechanism was efficient for real-time traffic but lacked any dynamic assignment capability.

However, the above mechanism is not efficient for non-real-time traffic, or where bandwidths are increased beyond the norm. For non-real-time traffic types, the ability to assign bandwidth dynamically is expected to provide higher efficiency than the original static granting mechanisms.

In ITU-T G.983.1, the OLT grant generation and distribution was updated when a new connection is provisioned on a PON or an existing connection was removed from a PON. Once the bandwidth is provisioned, the OLT would continuously send the assigned grants to the associated ONUs subsequently, the OLT would receive corresponding user cells in the upstream.

However, ITU-T G.983.1 was intended to enable a wide range of broadband services, including those that do not have a constant bit rate. For example, the Internet connects to many bursty traffic sources, which are best accommodated by ATM SBR Class 2 or GFR, which have less rigid requirements on cell transfer delay and cell delay variation. Mapping these non-real-time services into a fixed bandwidth channel prevents the ONUs on a PON from dynamically sharing the upstream PON bandwidth. For these non-real-time traffic types, the ability to assign bandwidth dynamically is expected to provide higher efficiency than the current static granting mechanisms.

The DBA protocol consists of three strategies, referred to as non status reporting, status reporting and hybrid types. The non status reporting type strategy is invoked by monitoring traffic in the OLT where lengthening buffer queues can be viewed as a requirement for extra bandwidth. The status reporting type strategy is invoked by status reports sent from ONUs to the OLT, where requests for more bandwidth are explicitly given. The hybrid strategy is invoked by both monitoring traffic in the OLT and processing in the OLT the status reports from ONUs. The recommendation does not specify detailed mechanisms or algorithms for these strategies, but rather message requirements and the required interfaces at specified reference points.

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Bandwidth increases

Written on 3:20 PM by ooe

The most obvious change that can be made to a PON system is to increase its overall bandwidth. This would allow more bandwidth per customer on average which should mean that the cost per unit of bandwidth will decrease.

The early APON standards specified 155 Mbit/s to a maximum of 32 users. This results in a bandwidth per customer in the order of 5 Mbit/s. Whilst this can be considered a great improvement on current systems, and is symmetrical in nature, in practice this bandwidth is not a great deal and would not be capable of adequately supporting the ‘Triple Play’ of voice, data and video services. Furthermore, VDSL can be configured to give bandwidths in this range and therefore the base specification APON is probably not of tremendous interest.

More recently the APON standard has been extended to allow for 622 Mbit/s downstream and 155 Mbit/s upstream asymmetric bit rates as well as a 622 Mbit/s symmetrical option. These are seen as being of greater value, since with the same 32 way split specification these can deliver in the order of 20 Mbit/s to the user. This is closer to the sorts of bandwidth required for a wider mix of services.

Currently FSAN is considering a 1.25 Gbit/s and even a 2.5 Gbit/s PON option, using new architectures not based on their baseline which was G.983.1. These new PONs may have a use in the telecommunications arena probably only as a feeder/backhaul network for VDSL or other access network systems. The IEEE is also becoming active in this area and will soon specify a 1.25 Gbit/s PON, although details are sketchy at the time of writing this chapter.

Point-to-point Ethernet systems are also becoming more prevalent although the lack of standardisation is hindering the creation of consistent product offerings amongst different vendors. Systems comprising of a head-end and street electronic concentrators are being installed, i.e. in Sweden, where they are providing high speed Internet connections to multiple dwelling unit.

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Recent trends in PON system development

Written on 3:20 PM by ooe

Recent trends in PON specifications have been of a rather technical nature, looking at the many facets of PON architectures, and attempting to make the systems more efficient or easier to use in the real world where deployment issues can entrap the unwary. This section highlights recent trends in PON system specification but the reader should note that none of these new specifications are mandatory. Indeed they may or may not be used individually on a particular system implementation. This can lead to a myriad of systems, all incompatible with each other, but conforming to the ITU-T recommendations and originating from FSAN.

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The IEEE Ethernet in the First Mile group (EFM)

Written on 3:19 PM by ooe

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The FSAN group

Written on 3:19 PM by ooe

The FSAN group has been around for 17 years now and is split into optical systems and copper systems. This chapter will deal only with the optical systems. The basic FSAN recommendations were input into the ITU-T some time ago with the baseline documents being G.983.1 and G.983.2. Recent work has resulted in new standards which enhance the usefulness of the basic PON systems in certain circumstances. These will be discussed further in this chapter.

What is of interest is that work in the group is not coming to an end as one might expect. Rather the group are moving on to higher specification PON systems. Work is progressing on higher bit rate PONs although the technology underlying the new architectures (i.e. ATM or Ethernet) has yet to be agreed. Limited further information is included later within this chapter as the key agreements have yet to be reached.

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Developments in Optical Access Networks

Written on 3:18 PM by ooe

Optical fibre access network technology has become more complex over the last few years with bit rates steadily increasing. PON systems are available with bit rates in the range 155 Mbit/s to, currently, 622 Mbit/s. Newer systems, both PON and point-to-point, will allow this trend to continue with 2.5 Gbit/s systems becoming practicable in the near future. With this increase in technology has come an increase in the opportunities for fibre system to cost-reduce more of the network, including the metro space – a fact that increases the appeal of the technology. Some of the newer PON systems are being designed using Ethernet as the underlying technology with a promise of reducing the price of the technology still further. How this will occur in practice, however, is still unclear. What is certain is that optical access technologies are expanding and are sure to find an opening in real networks in the foreseeable future.

Developing equipment for the access network has always been a risk for the equipment manufacturers. The size of the network means that equipment volumes can be huge but the equipment is extremely cost sensitive. Furthermore, the sheer cost of equipment rollout means that network operators do not attempt such a major upgrade of their networks lightly. Indeed, to date there have been no ubiquitous upgrades of the UK access network, rather there have been many small, ad hoc changes. Things are now beginning to change with the introduction of ADSL, although this still utilises the most costly and fault-prone parts of the copper access network.

Whilst some new services are being rolled out to businesses that can afford them, these roll-outs are focused on those customers wanting to use the bandwidths immediately with little effort on overall network upgrades. In the UK, services such as the short haul data service can provide upto 2 Gbit/s to customers separated by no more than 40 km, whilst conventional data networks can supply in the order of an STM1's worth (155 Mbit/s) to high bandwidth customers, again mainly business related.

In terms of residential customers, progress in upgrading the network has been slow, mainly because of the perceived lack of value of bandwidth upgrades. The residential market has been getting ever more cost sensitive, with the restrictions in permitted price increases and a glut of bandwidth in the core now hurting many CLEC companies quite significantly. Against this backdrop comes ADSL, enabling users to get 500 kbit/s downstream and 256 kbit/s upstream at an extremely competitive price.

Back in 1989 people predicted the introduction of Passive Optical Network (PON) technology into the network [1]; however, this roll-out did not occur for several reasons, the main one being that there was no perceived market for the types of services that optical fibre technology could bring. This is now beginning to change.

Current bandwidth upgrades will not satisfy customers for ever. There is a question as to when residential customers will require more bandwidth than that offered by ADSL but it seems to be required sooner rather than later. During the last 10 years, there has been a step change in the computing power available to the average residential consumer. Processing power has increased from 8 Mbit/s systems to the current 2 Gbit/s systems (with 3 Gbit/s around the corner) and there is little sign of the pace of technological advancement slowing. This is already leading to customers being able to manipulate video images in real time. What they cannot do is transport this data, in real time, across the telecommunications network.

Following a similar line, point-to-point Ethernet technologies are also receiving attention with a variety of systems becoming available from different manufacturers.

If developments continue at the same pace, then there will be a need for affordable interconnections at speeds currently unattainable by ADSL. Whilst VDSL could cope in the medium term, questions are already being asked about its suitability, given the high operational costs of the required street located electronics and questions relating to radio interference from overhead copper cables.

Against this backdrop the future development of fibre systems for the access network seems to be important. Fibre access network products are already becoming available but most of these are expensive, difficult to implement and are not full service compatible.

Whilst fibre technology has yet to mature enough to make cheap access systems, the major problem is the lack of volume in the sector to date. It is against this backdrop that there is a need to develop affordable, flexible systems. A variety of companies and people, however, are rising to the challenge. It has become noticeable that there are more start-up companies designing and building equipment for this market sector than ever before and that existing major players are now moving into this field with mainstream products.

Whilst standardisation of systems has been shown to lead to a steep reduction in their price, along with increased availability, standardisation too early can lead to poor products. Hence pre-standards discussions in an open environment can be a useful first step. This can be brought about at specialist fora at which the associated problems and challenges can be discussed and indeed such fora have been created and are making good progress in setting initial requirements and solving technical problems.

The best known standards forum is FSAN. Until recently the FSAN group has been the mainstay of optical fibre access system development. Seven operators, including BT, first met in the spring of 1995 in order to begin the FSAN initiative. FSAN stands for Full Service access network and had an initial focus on passive optical network system (PONs). BT had previously been experimenting with ATM-based PON systems [2] but these systems remained largely in-house.

The network operators invited equipment providers to join the group in order to progress activities in a manner suited to the production and specification of such equipment. Using this mechanism the number of contributors to the FSAN forum could be controlled, preventing the organisation from becoming unwieldy. It is still the situation today that equipment vendors only join FSAN by invitation, although they are free to solicit such invitations.

The IEEE are also now active in this area and have their own forum, the Ethernet in the First Mile (EFM) group, trying to create access network standards around existing Ethernet standards.

These groups will now be discussed in some detail.

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Overbuilding

Written on 2:32 PM by ooe

Overbuilding refers to the situation where a new network is being provided in addition to established infrastructures such as twisted pair for telephony and coaxial cable for cable TV services. The incumbent networks may be old and the ability or will to deliver broadband data services is weak. The opportunity for the over-builder is to offer broadband data as an alternative or in addition to the other services. New-entrant operators are introducing point-to-point Ethernet systems to satisfy the demand for data in both residential and small to medium sized business sectors.

The standard PON is based upon ITU G983 series and is capable of delivering 622 Mbit/s symmetrical services by circuit emulation, or with ATM or Ethernet interfaces. These PONs are currently focused on the business market but work is in progress to widen the service set to include telephony and cable TV services for residential green field applications. The cost of fibre access is high, so it is a challenge for any fibre access solution to be profitable in the residential overbuilding scenario. A data-only solution is likely to be simpler and cost less than a full service access network but has fewer revenue streams available to pay for its introduction.

A data-centric approach is possible using point-to-point fibre and LAN technology to connect buildings and apartment blocks to service providers. An active node such as a hub, switch or router at the fibre entry point to the building is used to connect individual offices or residences via category 5 cable (one twisted pair for each direction of transmission). This type of network is gaining popularity but will struggle to deliver high quality telephony and real time video for residential applications because of the absence of circuits. Contention for bandwidth in such networks is difficult to control if the access protocol remains IP.

The G983 series PONs are able to deliver data-only services and multiple line digital telephony by circuit emulation. These systems can be considered as an alternative to SDH and PDH point-to-point rings for overbuilding in a business community where demand for telephony in blocks of up to 24 (T1) or 30 (E1) channels are commonly found.

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Green field

Written on 2:32 PM by ooe

As mentioned in, green field (new-build) is a key problem area, which gives a focus to the problem of FTTH. New homes will incur the costs of civil works (digging) and outside plant anyway so the issue is which technology to install: twisted pair, coaxial cable or fibre, or a mixture of all three.

Green field fibre construction has been neglected because of the advance of broadband over DSL, cable modems and UMTS. Nevertheless, on a worldwide basis, there are significant volumes of new homes being built and even more homes requiring basic telecommunications services in developing nations.

The problem for system designers is to provide multiple-service capability: telephony, video and data. A rich service set allows a single fibre network to compete more effectively in economic terms with twisted pair and coaxial cable as the traditional means of delivering each of these services. None of these competes with fibre in terms of capacity and fibre offers more resistance to water ingress, lightning damage and electrical or RF interference. The opportunity for fibre systems vendors and operators is to make a single fibre more profitable than a bundle of wire pairs and coaxial cable for the delivery of multiple services. The full services access networks (FSAN) group was set up with this as the final goal. The activities of this and other standards bodies will be described later.

Providing traditional telephony services is troublesome over fibre because of the absence of wire for power feeding. Fibre is dependent upon the local electricity supply and batteries for back-up. Nevertheless, since this problem has been solved for cellular telephony, similar solutions can be used for fibre without incurring the additional cost of a copper access network.

There are numerous ways of providing video services. Both broadcast and switched are possible via PONs. The fibre infrastructure may carry broadcast services in all legacy modulation formats but time division multiplexing (TDM) offers opto-electonic simplicity and high power budgets. Pure TDM unfortunately is not a format used for video services in the mass market yet, although digitally encoded channels in TDM ‘bouquets’ are found in FDM broadcast systems. Such systems may come a close second best for transmission of broadcast video over fibre. Base-band switched video services direct to a PC are emerging via the Internet.

In the UK, although the franchises for cable operators expired in 2001, most green field build has remained a combination of twisted pair and cable. Twisted pair is provided to almost all locations, while cable is typically provided in the less rural areas. Fibre to the home has remained a niche application because of the continuing success of ADSL and the higher cost of fibre as explained earlier. Only in a few select trial areas has fibre to the home been deployed.

For BT, green field build has been a relatively low volume offering a limited opportunity for new infrastructure. However, there is expected to be a need for around 1 M new homes in the UK over the next decade with large developments in SE England.

A green field solution used by BT is TPON (telecommunications over a passive optical network) in remote cabinets or buildings. It has been narrowband only because of restrictions on cable TV services and an uncertain market for interactive broadband. In most cases the feeder to customers is copper pair rather than fibre.

So, despite the competitive environment that has been opened up since 2001, fibre to the home systems have remained difficult to justify, even in green field where the infrastructure costs are always encountered. This may change in the future as homes require data rates in excess of ADSL capabilities and more broadband services become available.

In the USA, the situation is similar; Telcos are beginning to compete with cable for multiple service provision. This competition is making incumbent operators think about radical restructuring of the access network to offer FTTH particularly in newbuild situations and there are a number of trial areas where FTTH has been used.

In mainland Europe and Japan cable operators and Telcos have followed separate evolution paths with separate licenses for cable TV and telecommunications and little competition between the two.

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Deployment strategies

Written on 2:31 PM by ooe

The choice of deployment strategy will determine how much and at what stages capital is spent, the coverage and how much infrastructure is provided. The choice of strategy therefore represents a key economic consideration for fibre access. Three approaches are considered here: green field, overbuilding and upgrading an existing network.

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Resilient networks

Written on 2:31 PM by ooe

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Rings

Written on 2:31 PM by ooe

Rings are used extensively in core and metropolitan networks because they offer a means of interconnecting a number of nodes (cities, towns) in a way that enables large capacities to be transported with resilience. The opto-electronic technology is the same as that needed for point-to-point unless WDM is involved. If a route fails another route can be found by sending traffic in the opposite direction round the ring as shown in.

The amount of fibre needed is considerably less than point-to-point networks, however there may be more civil works involved in serving a community as two fibre entry points are needed if strict route diversity is required. Furthermore if the ring is to be used to provide resilience, two optical paths and two sets of transceivers are needed to offer loop-back protection which increases the cost. Without loop back protection a unidirectional ring is vulnerable, as a single failure causes all of the traffic to be lost.

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Passive star (tree and branch)

Written on 2:31 PM by ooe

Passive star architectures can be implemented with either passive power dividers or with wavelength division multiplexing (WDM) components. Both offer a one-to-many optical concentration function. The passive optical network (PON) approach, shown in, makes use of passive power dividers in the network and promises lower cost and more flexibility for early deployment. It may use any available multiplexing schemes in the equipment at either end of the network. WDM on the other hand promises a lower power budget and is therefore capable of giving more bandwidth per user on a dedicated basis, rather like a point-to-point fibre. The PON or tree architecture allows many signals to be combined onto a common bearer into the central node by suitable choice of multiplexing rather like conventional cable TV over coaxial cable. Traffic may be concentrated at any point in the network. In general, costs are minimised if the concentration point is near the customers. In the downstream direction, the multiplex is broadcast to all users. In the upstream direction broadcasting does not occur but a multiplex may be formed optically ‘on-the-fly’ using multiplexing such as WDM or TDM in the terminal equipment. The multiplex must be designed to avoid mutual interference, which would arise if channels are chosen at random.

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Active star/point-to-point

Written on 2:30 PM by ooe

Point-to-point systems use one or two fibres to connect a pair of nodes. The full bandwidth of the fibre is available for future upgrades and a high power budget is available for long-distance transmission. A drawback is that the network is not well-suited to broadcast services.

As the number of nodes in a network grows it is desirable to concentrate traffic to avoid the huge proliferation of fibre, which would arise with an unlimited mesh size. The choice of concentration point will affect the cost of the network. For example, if the concentration is nearer the customer the amount of fibre required can be reduced. However, point-to-point systems require a concentration point with active electronics. Consideration of environmental issues such as powering and temperature control and water ingress is then needed. These issues can be solved more easily if there is an existing building such as a central office offering environmental control. In the green field or overbuild situation these buildings may not exist and an external plant solution such as a pedestal or cabinet will be required at some cost.

The benign environment of an existing central office can perform this concentration function for point-to-point systems. The location of this building has been chosen to suit the needs of twisted-pair transmission. With fibre access using point-point technology, it is almost inconceivable to replace the wire pairs with fibre on a one-for-one basis because of disruption to existing services. Alternatively the installation of a new cables as an overlay containing massive numbers of fibres is very costly

For the mass market, operators are considering alternative architectures than traditional point-to-point for the local loop – the passive star that avoids the cost of active concentrators and can reduce opto-electronics costs by resource sharing.

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Fibre access topologies

Written on 2:30 PM by ooe

The choice of topology is critical because it affects the cost of the network, the services, and the reliability of the access network. Once installed it will be very difficult to change the physical configuration, so topology needs careful consideration. Here we examine the key candidate topologies: point-to-point, passive star, and ring.

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Service requirements

Written on 2:30 PM by ooe

Bearer service requirements include telephony, data (both guaranteed and best-effort) and broadcast TV. For business users high availability is a key requirement whereas a broadcast TV service may be of secondary importance. For the residential community a rich set of switched and broadcast video services will be attractive but lower availability will be acceptable if it saves cost.

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Fibre Access Networks

Written on 2:29 PM by ooe

Demand for bandwidth is the key driver for fibre in the access network. Fibre has served the large bandwidth needs of long-haul networks for 20 years. Businesses or buildings, which can concentrate many users' traffic onto a fibre, have also been directly connected. The fibre access systems used have much in common with core transmission techniques such as PDH or SDH and are configured as point-to-point or ring networks. Corporate access customers have traffic concentrations, security and reliability requirements similar to core networks.

The big challenge is to solve the problem of the mass-market with the ultimate goal of fibre to the home (FTTH). Much of the technology needed has been around since the mid-1980s, but until now FTTH has been achieved only in technology trials or small-scale deployments. For FTTH to become ubiquitous, costs need to fall to be comparable with alternatives such as twisted pair or hybrid fibre-coax. Three important costs are the technology, installation and ownership. For FTTH to succeed these costs must be lower than the expected income from services over the life of the system.

Green field (new-build) is a key problem area, which gives a focus to the problem of FTTH. The cost of providing any fixed access network is very high when the civil works are included. New homes will incur these costs anyway so the issue is whether to deploy twisted pair, coaxial cable or fibre, or a mixture of all three.

Fibre promises capacity far in excess of the alternatives and offers future-proofing as demand for broadband services grows. What is needed is an entry-level system, which is cost-effective to justify the investment in a fibre infrastructure, rather than an alternative. To do this it must be comparable in cost and carry a richer set of services than the alternatives. Once installed the return on investment of the fibre network over its whole life could be higher than the alternatives, which would not compete so well as the demand for bandwidth increases.

This chapter sets the scene for a mass-market product by focusing on fibre access technology choices that influence cost and/or service capability.

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Integration to backend OSS

Written on 4:17 PM by ooe

The development of automated interfaces between operators is only part of the OSS challenge. Many changes have to be made to the backend (back office) systems of both operators. It is well understood in the IT industry that changing legacy systems is complex, expensive and time-consuming.

The LLU systems development has had to support many new products types. Examples from the UK design include:

• exchange area data that relates exchange servicing areas to postcodes and makes the information available securely on a web server;

• collocation facilities – this requires the linking of BT forecasting and planning processes to LLU operators' plans so as to provide and reserve frame, tie cable and collocation capacity;

• appointment reservations systems for LLU service provisioning and repair including access to exchange buildings;

• provisioning rules for job management systems.

In some cases the customer may wish to transfer (or port) their telephone number. This required some integration of the processes and systems for number portability products with those for LLU products. The allocation of a line to a LLU operator requires the suppression of the automated billing which would otherwise be sent to the retail customer for an ‘in service’ access network path.

Considerable changes have been needed to the repair processes to cover demarcation of responsibilities between operators, co-ordination of testing, and escalation processes with the consequential impacts on the BT maintenance and repair systems. Substantial modification to the process and systems for testing of lines has been necessary.

New management information systems are needed to track statistics for LLU provisioning and repair. These are needed to monitor and track actual service performance and support the provision of information to the regulator. These requirements have resulted in significant new developments and hundreds of changes to existing legacy systems in an unprecedented short interval of time.

Several examples have been given derived mainly from the authors' experience in BT. These services, together with wholesale DSL products, allow competitive operators to use existing metallic access networks belonging to other operators without investing in building their own networks. Implementing LLU involves complex developments of technology, support systems and processes. The work requires agreement between network owners, regulators and representatives from other operators. BT was among the first operators to fully meet the challenge of the EU LLU regulation. The first collocation areas in the BT network were handed over to operators in late 2000, and in January 2001 BT released its first unbundled loop. The next few years will see a massive expansion in the availability of broadband access services and there may be volume demand for LLU products when the telecom sector recovers from the downturn which started during 2000. However, a wide range of broadband access technologies is available including DSL, broadband radio, satellite and cable TV. Only time will tell what role local loop unbundling will play in this expansion. The eventual extent and rate of unbundling depends to a very large extent on the commercial interests and firm orders received from new entrant operators.

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Technical approach to OSS

Written on 4:16 PM by ooe

The definition of industry processes for LLU was an essential precursor to the definition of the technical interfaces. The LLU Automation Forum (LLUAF), a working group established under the OPF, was set up to address this specific need. An innovative approach was adopted for the specification of these interfaces.

Rapid progress had been made in the development of business-to-business e-commerce technologies and supply chain integration. It was recognised that OSS integration might be simplified if they were employed. The ordering interfaces were based on the Commerce One Common Business Library CBL. This is a recognised e-commerce library that allows the specification of purchase orders and order status using the XML (extensible mark-up language). The library comprises a large number of definitions of general use in constructing ordering processes and messages. For example, CBL defines a structure of a purchase order and semantics for data types such as customer name, address, order reference codes and the semantics of delivery and order dates [8]. The Commerce One library needed some adaptation to make it suitable for use in telecommunications services. These extensions are based upon conclusions reached in a research study in an EURESCOM project P908 on business-to-business OSS gateways [9].

Publication of the LLU message sets for the agreed industry processes was completed in January 2001 and industry feedback and comment was solicited through the LLU Automation Forum and the UK Telco API Forum web sites [10]. Promotion of the work through the ITU-T, and the Tele Management Forum lead to world-wide acclaim of the leading-edge innovative approach being taken by BT and the UK industry.

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Inter-operator OSS interfaces

Written on 4:16 PM by ooe

The quality of service experienced by the end-user is highly dependent on the ability of all parties to provide, maintain and bill for LLU services in a cost-effective manner at high volume levels. Close co-operation between operators is required both at initial service provision and during any maintenance activity that may be required. It was recognised that a high degree of automation would be required to support large volumes of loops. This required that LLU operators be able to connect their operational support systems to BT's computer systems which were not designed to support LLU. Over 20 major computer systems were impacted and the integration task was one of the most complex undertaken since BT first installed customer care and billing systems in the 1980s.

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Line sharing and sub-loop unbundling process issues

Written on 4:16 PM by ooe

Processes were developed for line sharing and sub-loop LLU. Line sharing adds complexity to many LLU processes as two service providers use a single access line. New scenarios are introduced making the whole operational environment significantly more complex. Operators must now deal with requests for new shared lines, conversion of a telephony line to line sharing and reversion back to their original state, or a complete cease of all services. When a fault occurs there is potential for confusion. For example, it may be unclear whether the fault is on the network owner or LLU operator part of the line; the end-user may not know which operator to report the fault to and each operator may consider that the fault lies on the other's network. Processes and procedures are required to resolve any issue quickly.

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Fault handling

Written on 4:16 PM by ooe

Accurate and timely handling of customer's reported faults is fundamental to achieving customer satisfaction. LLU services rely on a combination of network elements including the metallic path provided by the network owner, additional components supplied by the LLU operator and perhaps some components supplied by the end-user. When the end-user experiences degraded service, it may be unclear which component is the cause.

In the UK, the OPF group developed processes to reduce the scope for multiple handing of the fault report and to support efficient and timely resolution of the fault report. In full unbundling the LLU operator is responsible for receiving fault reports from the end-user and should pass them to BT only if the LLU operator has reason to believe that a fault exists on the BT network. The situation is more complex where line sharing is used as both BT and the LLU operators are providing services to the enduser using the same metallic path. The end-user should report service degradation to the appropriate service provider in the first instance. Maintenance and repair activity on one service is likely to disrupt the other service so close co-operation between BT and LLU operator may be required. BT already has systems and processes to deal with problems affecting the narrowband (telephony) service due to network faults. These processes have been adapted to enable repair engineers to return the unbundled loop to specification based upon electrical performance. Once a repair is complete the unbundled loop is returned to the LLU operator with a report of the relevant electrical characteristics as proof of repair. Furthermore the LLU operator can purchase further test products to enable it to obtain additional information about a metallic pair. The LLU operator is, of course, solely responsible for dealing with faults caused by that operator's equipment or in the operation/configuration of the broadband service by the end-user.

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Unbundled loop provision

Written on 4:15 PM by ooe

Provision of metallic pairs is carried out in three stages: the pre-order enquiry, deliver customer order and order acceptance. At the pre-order enquiry stage the operator is provided with information about the customer access line. The operator may wish to have a new metallic pair or to take over an existing one. The line information enables the LLU operator to decide if its service will work over the metallic pair to be provided. The operator may decide not to go ahead with the order if its service will not work because of the distance of the end-user from the exchange. If the operator decides to proceed, BT provides the pair as requested and the operator has two days to decide to accept or reject the pair. This period provides sufficient time to enable the operator to test its service.

The provision of the pair is usually quite straight forward. However, a number of issues need to be considered. The end-user is now a customer of the LLU operator and BT has to rely on the operator to make arrangements for access to their premises. Further complications are introduced if an order is combined with other products such as number portability, carrier pre-selection and/or calls and access.

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Points of presence

Written on 4:15 PM by ooe

Once registration has been completed the LLU operator can order physical collocations or distant locations from the BT exchanges in the geographical areas in which they are interested. At each intended point of presence, a two-stage survey and building process with identified timescales was agreed. This was necessary to establish an audit trail should queries arise.

When LLU was initially launched more than 40 operators registered an interest and there was clearly potential for a large volume of collocation orders. The OPF group agreed that a process was required to manage this bow wave of orders before demand settled down and business as usual processes could be adopted. A demand management process was devised, which was to be operated by the Electoral Reform Society and Oftel, to decide in which order BT would tackle equipping its exchanges. This process was put in place in September 2000. In fact the volume of orders was massively below the industry forecast level and BT was able to handle them without using the bow wave. From December 2000, LLU operators were able to order distant location on a business-as-usual basis. Based on a fuller understanding of what was practicable, in February 2001, BT announced that it could handle demand for collocation space as business-as-usual.

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LLU registration

Written on 4:15 PM by ooe

The gain business process covers registration for LLU service with BT. New contracts have been developed which cover the provision of network information required to enable operators to develop their business plans, and the ordering and maintenance of new LLU products from BT. If operators decide to go ahead with their business cases then registration is completed and BT will set up service accounts for billing purposes.

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Process design

Written on 4:15 PM by ooe

Like any large network operator, BT has a large number of complex processes and systems which govern the operation of its access network.

However, it is a starting point from which to determine what would need to be modified. Typical examples of these changes include:

• how appointments are made with the end-user for equipment installation by BT;

• how faults are determined and resolved (that is, whether a fault is in the LLU operator's service area or on the network provided by BT);

• what to do if the end-user contacts BT directly rather than contacting the LLU operator.

These and similar issues were discussed at several OPF meetings which resulted in the interface between BT and the LLU operator being defined. Although this work was completed in April 2000, industry and Oftel requested numerous changes resulting in major reviews. A simplified end-to-end description of the unbundling process is shown below.

• Operator registers for LLU service with BT.

• LLU operator orders points of presence (collocation or distant location).

• BT or contractor builds points of presence.

• LLU operator installs equipment.

• LLU operator requests unbundled loop.

• BT provides unbundled loop.

• LLU operator provides service.

• LLU operator reports faults to BT.

• BT investigates problems.

A number of activities such as billing and field force control are inherent in these steps – threads running through every major process. Add to this the number of scenarios identified for unbundling (over 100) and the scale and complexity of the operational environment starts to be seen.

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Cageless collocation

Written on 4:14 PM by ooe

LLU operators in many countries have lobbied to be allowed to place equipment in the same rooms as the network owner. They argue that this is the best way to ensure parity of treatment between operators. This raises significant security concerns as local exchange buildings were almost always designed and built for sole use of a single network operator. Cageless collocation is no simpler to implement than physical collocation as provision must be made to connect power services, metallic pairs and backhaul services to the LLU operators equipment. Design calculations to ensure that sufficient air conditioning capacity are more complex in a cageless environment. Safety and security issues are more significant where the LLU operator shares a room with the network owner. In many cases the LLU operators' equipment and people have to satisfy more stringent testing or vetting before being allowed into the equipment rooms.

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Distant location

Written on 4:14 PM by ooe

Distant location was initially conceived to address the situation where some BT exchanges would offer insufficient accommodation to meet OLO demands for physical collocations. It uses an external tie cable from the BT MDF to premises or street furniture obtained by an LLU operator, near to the BT building. Providing accommodation for distant location is the responsibility of the LLU operator although BT may be sub-contracted to undertake the installation.

Distant location does not require the LLU operator to place equipment in or even to enter the BT building so there are many fewer restrictions on the design of the LLU operator equipment and operations. Distant locations have been built in nearby buildings and in self-contained street cabinets.

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Physical collocation

Written on 4:14 PM by ooe

Physical collocation allows LLU operators to place equipment in local exchange buildings and allows their authorised people to gain access to relevant parts of the buildings to operate their networks.

Providing collocation facilities means much more than simply making floor space available. Operators will require power, ventilation and related building services. For security reasons some degree of segregation is required between LLU operators' equipment and network owners' equipment. The agreed design criteria for physical collocation includes:

• LLU operators must be able to source their equipment from the global marketplace.

• A wide range of rack and cabinet sizes to be offered as well as differing power and environmental operating characteristics.

• Different and innovative deployment models were required as each LLU operator would be competing for business within each exchange area. These models might range from a small ‘toe in the water’ presence to an installation able to serve several thousand customer lines from the outset.

• No ‘one size fits all’ constraint.

• Recognition that some LLU operators would wish to have a dedicated room tailored to their stated need, offering a reasonable level of physical security.

• Some operators might wish to collaborate and share a collocation space in an area.

An LLU Hostel product was designed which formed the primary means of responding to demand and meeting the outlined criteria (Figure 7.6). In essence, the LLU Hostel enables an LLU operator to simply order one or more equipment bays – an area of floorspace suitable for equipment racks. Electricity is provided to each bay via an AC final distribution fuseboard providing a designated maximum power load. Expectations that LLU operator demand would be focused on exchange buildings serving the main population centres led to an initial minimum hostel size of two suites. This lower limit was subsequently dropped and a reduced version of the product was introduced to satisfy demand for hostel bays in smaller exchange buildings or where space constraints lead to the adaptation of rooms not originally designed for housing network equipment. Key design features of the LLU Hostel range of collocation spaces includes:

• The use of forced air cooling will generally be made.

• An HDF located at, or close to, the end of each bay. The HDF is used as the interface for internal tie cables provided by BT to the MDF.

• An initial provision of tie pairs to the exchange side of the MDF. Additional ties can be ordered separately.

• Fire/smoke detection.

• Access control. BT has modified its building security systems to allow the other operator's people to access the relevant parts of the buildings without needing to be escorted by BT people.

• An AC power distribution board from which LLU operators take their power feeds.

• A cable support system using ‘unistrut’ ironwork in a simple configuration. The end-product is a ‘ready to go’ environment into which an LLU operator can readily deploy and commission equipment.

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Collocation

Written on 4:13 PM by ooe

Collocation is considered to be one of the most important services in LLU. LLU operators must place equipment close to the MDF to which they wish to connect. There are three broad types of collocation which are physical collocation where the operator rents space inside the local exchange building, distant location where the operator's equipment is housed in a nearby building or street cabinet and cageless collocation where equipment belonging to the LLU operator is located in the same room as that of the network owner.

In the UK, BT has more than five thousand local exchange buildings and these were never designed or intended for third-party access. When designing collocation products BT studied the similar products offered by other incumbent operators in the USA and continental Europe and adopted the best practices from these operators.

The introduction of collocation requires that standards for equipment and operations be agreed. In the UK the standards for equipment and the inter operator processes for collocation were developed and trialled by BT and representatives of the LLU operators in a sub group of the Operator Policy Forum during 2000.

A key aim of the product design was to minimise the need for equipment specifically for designed or modified for LLU and wherever possible off the shelf hardware was used to minimise supply chain bottlenecks. Statutory requirements and customer affecting considerations such as safety, fire detection, planning law, security and risk management all had to be satisfied. In addition, BT's operating licence places it under an obligation to secure its network equipment.

The first collocation rooms and distant location facilities were completed in December 2000. At the completion of the collocation trial BT was well placed to design and build substantial volumes of collocation facilities in response to firm orders placed by LLU operators.

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Test equipment

Written on 4:13 PM by ooe

The technical specification of the unbundled line forms a part of the contract between network owner and the LLU operator. It is important that the network owner is able to test the lines before provision and during maintenance activities. BT has invested heavily in test equipment for use on its conventional telephone lines and it was logical that the same equipment should be used to test unbundled lines. The connection between the test equipment and the metallic line is a part of the local exchange concentrator but this is not connected to unbundled lines. The short term solution to this problem was to provide a physical test point connected to the unbundled metallic path near the point where the tie cables were connected to the MDF. When a test was needed on an unbundled line a BT engineer had to visit the MDF and make a manual connection between the line test systems and the metallic path test point. A further visit was required at the end of the test period. This solution was simple to implement but relatively slow and manually intensive to operate.

BT has decided that the longer term solution to the test problem is to connect all the unbundled lines through a specially provided test access switch matrix. This device simply automates the process of connecting the test equipment to the line. This could not be adopted at the initial launch of LLU products owing to the time taken to specify and procure a switch matrix and in particular to integrate it into BT support systems and processes. The test matrix will allow tests to be carried out more quickly than the manual test solution allows.

This test solution is appropriate for both full unbundling and line sharing. It is not appropriate for sub loop unbundled lines which do not connect to the local exchange site. A different approach must be developed if these lines are to be tested without manual intervention.

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