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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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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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:
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LLU operators must be able to source their equipment from the global marketplace.
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A wide range of rack and cabinet sizes to be offered as well as differing power and environmental operating characteristics.
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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.
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No ‘one size fits all’ constraint.
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Recognition that some LLU operators would wish to have a dedicated room tailored to their stated need, offering a reasonable level of physical security.
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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:
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The use of forced air cooling will generally be made.
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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.
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An initial provision of tie pairs to the exchange side of the MDF. Additional ties can be ordered separately.
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Fire/smoke detection.
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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.
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An AC power distribution board from which LLU operators take their power feeds.
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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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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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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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Written on 4:13 PM by ooe
Cost effective and timely maintenance is an important component of any telecommunications product. This can be difficult to achieve in the LLU situation as responsibility for maintenance is divided between two or more operators. Clear demarcation points between areas of responsibility are crucial to effective transparent processes and to ensure a good customer experience. In the UK the NICC DSL Task Group addressed this concern early in the development of LLU. The unbundled loop is defined between two demarcation points located at the network termination point in the customer premises (usually a telephone socket) and at the handover distribution frame in the LLU operator room or distant location. A clear and unequivocal specification of the performance of the unbundled pair was written and agreed by the DSL task group. It was expressed in terms that could be measured by either BT or the LLU operator and took account of the skills and tools available to the workforce. The specification provided a base from which DSL Task Group developed a code of practice for maintenance activities that allowed each operator to understand their responsibilities under fault conditions.
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Written on 4:13 PM by ooe
LLU will often be used in conjunction with DSL technology to provide data services. BT has, for many years, been a leader in research into DSL crosstalk interference and in the formulation of deployment rules to control it [4,5]. Before LLU was introduced to the UK, BT was solely responsible for ensuring that its transmission systems were used in a way that avoided excessive crosstalk on its network. With the introduction of LLU, it was no longer appropriate nor possible for BT alone to control system deployments. A new set of rules was required that all operators could follow. The new rules had to be clear, easy to implement, fair and had to take account of likely future developments in the access network.
The NICC DSL Task Group [7] was the cross-industry technical forum that was tasked by Oftel to design an access network frequency plan to meet these requirements. The task group was chaired by BT and was open to all interested parties. A wide range of telecommunications operators and equipment vendors actively participated with BT and Oftel. The access network frequency plan (ANFP) for the BT network is described in detail in Chapter 4.
The ANFP for the BT network controls crosstalk by defining limits on the power, frequency and location of DSL systems. The ANFP works by placing limits on the worst-case crosstalk noise in the network. By ensuring that new developments in the access network are no more harmful to their neighbours than current systems, the ANFP provides the stability that allows all operators to plan for the future with confidence. The ANFP places the onus on individual operators to ensure that their DSL deployments are compliant and remain so. The DSL task group designed a code of practice to be used when investigating allegations of interference.
When the ANFP was first mooted, line sharing and sub-loop LLU were not required so the first issue of the ANFP made no specific provision for them. Similarly, international standards for VDSL technology were at that time not agreed and the first plan excluded VDSL. At the time of writing the DSL task group is extending the plan to accommodate VDSL and sub loop unbundling.
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