Mạng và viễn thông P43

Chia sẻ: Hug Go Go | Ngày: | Loại File: PDF | Số trang:13

lượt xem

Mạng và viễn thông P43

Mô tả tài liệu
  Download Vui lòng tải xuống để xem tài liệu đầy đủ

Tham khảo tài liệu 'mạng và viễn thông p43', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả

Chủ đề:

Nội dung Text: Mạng và viễn thông P43

  1. Networks and Telecommunications: Design and Operation, Second Edition. Martin P. Clark Copyright © 1991, 1997 John Wiley & Sons Ltd ISBNs: 0-471-97346-7 (Hardback); 0-470-84158-3 (Electronic) 42 Selecting and Procuring Equipment The preceding chapter described the factors in outline equipment design whichare crucial to the success of the network evolution plan. Having a good plan is one thing; executing it is another, andinthisrespecttheorderinganddelivery of theequipmentshouldreceiveconsiderable attention. This is an activity often referred to as ‘procurement’, and it can be carried out very successfullyhighly by mechanistic management methods. Various‘project management’ techniques are available which tackle network design as if it were the input of a procurement ‘process’, much as ‘raw material’ is the input to a manufacturing ‘process’. In production-line fashion, project management techniques lead the project through its design and checking stages, and on to ordering, installation, and testing. However, in the same way as a poor raw material has an effect right through to the end productof a manufacturing chain,so the defects of a poor network design cannot be made good during implementation. This chapter describes a typical methodology for selecting and procuring equipment, starting from the outline equipment design. 42.1 TENDERING FOR EQUIPMENT Except for some of the largest corporations, very few companies that operatenetworks also manufacture the equipment that goes to make them up; everything from personal computer links upwards needs to be bought from other manufacturers. small pieces For of equipment like modems the purchase may be straightforward, because a range of itemsmeetinga standard specification(say, an ITU-T V-series recommendation) is available from a number of manufacturers. The purchaser then has timeto concentrate on the finer differences (size, price, reliability, ease of maintenance, etc.) of the various equipments, and to choose what suits them best. More costly equipment, like major transmission systems or large exchanges, can seldom be bought ‘off-the-shelf. Instead, the differing circumstance of each network and application means that a considerable amount of ‘adaptive engineering’ is required in each case, to modify or upgrade the manufacturer’sown ‘basic’ equipmentdesign.Selectingsuitableequipment is then 763
  2. 764 SELECTING AND PROCURING EQUIPMENT much more difficult, because at the time of order it may be that none has yet been developed. Under these circumstances, the normal method of equipment selection is by an invitation to tender ( I T T ) ,request f o r proposal ( R F P ) or request f o r quotation ( R F Q ) and procurement follows after a contract has been placed with the manufacturer who has tendered a price and a technical conformance nearest to the specification. As well as a technical specification, an invitation to tender includes a number of commercial and other contract conditions. The specification itself either lays out in precise detail the individual electrical componentsand connections to be made, or it is a functional specijication which lays out only which general functions must be performed and which external interfaces are required. Functional speclJications are preferred by tenderers and manufacturers alike because they place fewer constraints on the internal design of the equipment. They permit a wider range of manufacturers to consider adaptation oftheirproducts to meettheexternalinterfacerequirements. Forthe purchaser, the larger the number of equipment manufacturers kept in competition and providing ‘standard’ equipment, lower tendered the the prices will be. For the manufacturer the benefit is the larger market. Each tender sets out the degree to which the equipment can be adapted to conform with the specification, the degree to which the commercial conditions are considered acceptable, and the quoted price. Even if none of the tenders meet the specifications and commercial conditions in every respect, purchasers can at least gain an understanding of each piece of equipment and decide on their owntrade-offs between various factors, which are e price and conditions for payment m amount of further technical development required by an existing product, and how much confidence there is that it can be achieved e ease of equipment maintenance e time required for installation, and whether the in-service date is early enough m quality of product and installation e modularity of kit; the ease of with which parts may be replaced or with which a subsequent equipment extension may be carried out m warranty and after-sales service m the area and standard of accommodation required m robustness and reliability of equipment m political factors (nationality and financial liquidity of manufacturer, etc.) m software licence and conditions The process of invitation-to-tender and response is illustrated in Figure 42.1 and is much the same, no matter what type of equipment is being purchased. The length of each of the working documents (specification, tender, etc.) depends on the complexity of therequirementandthe confidence gainedfromprevious experience, the but contract itselfneedsonly to be ashortdocumentcommittingthemanufacturerto
  3. TENDERING FOR 765 Outline network 'vision' - Detailed network design c Equipment specification and preparation of the invitation to tender document I I Manufacturers tenders I I E v a l u a t i o n of t e n d e r s , a n df u r t h e r n e g o t l a t t o n l P l a c e m e n t o f contract with chosen manufacturer I P r o j e c ti m p l e m e n t a t i o n Figure 42.1 Procuring equipment conformwiththetenderresponse.Intheeventofafailure to conformwiththe requirements of the contract, a number of penal clauses usually cover each of the possible eventualities. For example, failure on the part of the manufacturer to develop a given function may result in no payment, while failure on the part of the purchaser to pay a given instalment, or to provide some detailed information on a given date may nullify the contractual obligation placed on the supplier.
  4. 766 SELECTING AND PROCURING EQUIPMENT 42.2 PROJECT MANAGEMENT Even before the equipment goes out to tender, the job of project management must have commenced, to coordinate all the separate aspects associated with the provision. Equipment room accommodationwill be needed (someto a clinical standard) - built or refurbished by a separatelycontractedcompany; power andstandby generator equipment may need to be purchased and installed; and all sorts of changes in the network may need to be undertaken. During tendering,sound a project management keeps task schedule, each on extracting prompt replies from manufacturers, insisting on rigorous evaluation and timely contract placement. At the next stage the job becomes one of overseeing the manufacturer’s work and quality, andof coordinating the supporting in-house other or contractors’ activities. Later on in the process, prior to the contract completion date (CCD), purchaser the should test the equipment, especially any new developments, to check conformance with the specification before final acceptance and payment. The key to successful project management is early project planning. This must be thorough and realistic. Forgetting some activities, programming too much or too little or time for other activities, can seriously upset thesmooth running of the entire project. It is valuable during the project planning stage to undertake a critical path analysis. Thissets out the relationship betweeneach of thesub-projects,laying out the full sequence of events (or sub-projects) and the dependency of any individual event start date on the completionof an earlier event. For example, it would not be possible to fit- out a building before it had been built, but it might not matter whether the electrical wiring or theplumbing were to be carriedout first.Thisconsecutivesequence of interdependent sub-projects determines the earliest date at which the project could be completed. If any of the sub-projects were to take longer than scheduled, then the earliest possible project completiondate would slip by at least the same number of days. Figure 42.2 illustrates a simple critical path analysis project schedule. A number of computer software packages are available for this purpose (e.g. Microsoft Project). The exchange installation project depicted in Figure 42.2 comprises ten sub-projects or events. Four of these events make up the critical path of the project. These are the building and fitting out of the accommodation, followed by the exchange installation, the exchange testing, and the wiring-up of the network. None of these activities can commence before the previous one has been completed, so that the consecutive time period required for their completion determines the minimum overall project length. Slippage in any of these four sub-projects delays the project’s earliest completion date (i.e. the exchange opening). In contrast, the other six events do not lie on the critical path. This means that a degree of slack time is available. For example, a total of 29 months is available to recruit and train maintenancestaff, but only 10 months are required. These tasks could therefore be delayed for 19 months after the project start date without affecting the project end date. In fact, the only constraint in this case is that the training of staff cannot commence before January 1991, after the exchange installation, otherwise there is no equipment to be trained on. This relationship is shown by the dotted line arrow on Figure 42.2, indicating a dependent event. The use of a dotted line arrow indicates that it is only a one-way dependency, rather than two-way. In other words, the exchange
  5. PROJECT MANAGEMENT 767 U C O x \ '. v Y Q tolt
  6. 768 SELECTING AND PROCURING EQUIPMENT must be installed before training can commence, but in our example it is not the case that the maintenance staff need to have been recruited before exchange testing can commence. Other events which arenot time-critical are ordering circuits the the of and installation of transmission equipment. The ordering must precede the installation, but the ten months needed for the work are far less than the 26 months available. The transmission equipment installation cannot commence until July 1990 at the earliest, after the accommodation has been prepared. Not onlydoesacritical path analysisprovideachecklist of allthetasks to be undertaken, itprovidesastraightforwardandmechanisticmethodformarshalling resources and ensuring the timely completion of critical path events. Furthermore, it allows the scheduling of non-critical events in the most efficient and convenient manner possible within the timescale. For example, staff training in Figure 42.2 could start at any time between January and February 1991, according to convenience. 42.3 PROCUREMENT POLICY Before purchasing items of equipment, it is prudent for any company to determine a properprocurement policy. A procurement policyprotects interests the of the purchaser.Itisnogoodalwaysbuyingthecheapestequipment if thismeansthe eventual acquisition of a diverse range of slightly incompatible equipment, each piece requiring different spares and differently trained maintenance staff, and with insoluble compatibility problems should the equipments ever need to be integrated. On the other hand, if a company alwayspurchases equipment a from single supplier, then dependency creeps the in; supplier’sprices escalate may to give a better profit margin; worse still, the supplier may go out of business or become unreliable or un- cooperative. Using even a range small of differentsuppliers helps to maintain competition between them. An example of a complete equipment purchasing policy might be that ‘new equipment purchasedshould be compatible an with IBM equipment’. At the time of tendering for equipment, due account should be taken of the company procurement policy. It makes poorsense to write a specification which precludes all but onesupplier, when the company procurement policy is topromote competitive tendering,withalongtermobjective of maintaining at leasttwosuppliers.Over- worded and complicated specifications tend to havethe effect of precluding suppliers, so that in general it is best to try to keep conditions of tender and contract as simple as possible. 42.4 PLANNING DOCUMENTATION Before commencing any major project, whether it involves procurement or not, the network operator must determine the long term network strategy or ‘vision’ of which theprojectformsa part.The strategyshouldset outthelong termobjectives for network development, and against the backdrop of short term constraints, it should
  7. PLANNING DOCUMENTATION 769 map out a series of projects to achieve the long term goal. Typically, the strategic goal may be reachedinanumber of different ways, and theanalysisleading up toa recommendation of a particular plan should consider and reject a number of alternative options. Having laid out the long term strategy and mapped it into a series of component projects,theplanning,coordination, anddocumentation of eachindividualproject must commence. Any project is best documented in a controlled and layered structure toensure easy reference to detailed information while retaining consistency and oversight across the whole job. Figure 42.3 shows a schematic documentation structure of three layers, oriented in a triangular fashion. At the top or ‘strategy’ layer the documentation is light, laying out the overall objectives, the end goal, the resources to be used, and in outline the major component projects of the strategy. At the second or ‘plan’ layer a number of separate planning documents exist, each comprehensively describing an individual project. The plan needs to covereverything: service and project timescales, staff responsibilities, networktopology,maintenanceprocedures,customer service arrangements,accom- modation requirements, sales, procurement,customer billing, training and all other conceivable aspects. Ideally, the document refers to the strategy that it supports, and also explains the existence and inter-relationship of any more detailed specifications which exist to support it. The third and layer of documents, ‘specifications’, covers last the detailed technical definitions and procedures. Specification documents are the meat of the project. It is documents at this level of detail that are tendered to prospective manufacturers and are subsequently used for definitive reference. That is notto say that layer 1 and 2 documentsareany less important, because they hold the entire project and strategy together. Given a proper document structure, a document registration procedure should be set up toensure proper quality inspection of documents. Documents should be checked for Layer 1 Layer 2 Layer 3 Figure 42.3 A layered documentation structure
  8. 770 SELECTING AND PROCURING EQUIPMENT accuracy, comprehensiveness, and clarity by persons other than their original authors. To ensure that there is no confusion over discrepancies between differently updated or amendedversions of thesamedocument,a proper re-issuing andchange-control procedure should be adopted. 42.5 THE TENDER DOCUMENT The tender document orinvitation to tender describes the equipment to be supplied. It is prepared by thenetwork-operator wheneveramajoritem of equipment is to be procured. It describes which technical functions the equipment is expected to perform and it includes any commercial conditions which apply to the supply contract. Once prepared,thetenderdocument is sent tooneormore prospectivesuppliers,who consider the requirements and send back formal replies, stating what they are able to offer and the price to be charged if their offer is taken up. Thetenderdocument the and chosenmanufacturer’s response to it formthe documentation of contract. Any subsequent contractual dispute between the network operator and the supplier is resolved by reference to this documentation. From the network operator’s point of view, it is important to ensure that the tender document makes the obligations on any contracted supplier absolutely clear. The supplier on his side aims to make it clear in the response, which of the specified items can be supplied and which are not included in the offer. The most harmonious business relationships and the most successful projects are based on accurate understanding. In the remainder of the chapter we describe items that should to be included in the tender document. 42.5.1 CommercialConditions of Contract In the opening section of the tender document a general introduction should be given, explaining briefly the type of equipment required and in what timescales. This prevents any‘no-hope’supplierfromwastingfurthertime by analysingallthedetail.The commercial conditions of contract should go on explain in detail what items of work to are the obligation of the supplier, the timescales for delivery each item, and the terms of on which payment is to be made (for example, installments as each part is delivered, or ‘only when the whole job is done’). The commercial conditions also need to lay out the penalties for failure to conformwiththerequirements of contract. Thesepenalties sometimes include an obligation on the supplier to correct errors and may call for a sum of money to be paid to the network operator as compensation for liquidated damage. 42.5.2 OtherGeneralConditions of Contract The general conditions of contract may clarify any other legal or general constraints which thenetworkoperatormight wish to impose. This sectionmightcoverthe ownership of any document copyright, the ownership of patent rights and intellectual
  9. THE TENDER DOCUMENT 771 property rights (IPRs) of any new items that may be developed, and may cover general conditions pertaining to the disclosure of information. The section may constrain the supplier not to make press releases and should cover the procedure for resolution of contract disputes. It could cover both parties’ rights to terminate the contract, and (if relevant) the privilege of one party in the event of the other’s bankruptcy. Finally, the section may clarify how particular legal constraints on one of the parties affects the contract. For example, let us imagine that the network operator obliged by law not to is release information to aparticularthirdparty.Thisinformationmay,however, be required by the supplier in order that the contract can be fulfilled. In such an instance the supplier should be obliged by contract not to release the information to the third party. This type of situation caneasily arise. Imagine a telephonecompany A buying an exchange from company B, where company B is both a telephone network operating companyandan exchangesupplier.Nowcompany A mayneed to reveal to its exchange supplier details of its network configuration, and this may include details pertinent to network business held jointly with one of company B’s network operating competitors.Inthisinstancecompany A needs to release detailstotheexchange supplier part of company B, but with the proviso that this information is not passed backtocompany B’s networkadministrators,whomightgainunfaircompetitive advantage from it. 42.5.3 Technical Conditions The technical part of the specification sets out the type of equipment required and its detailedfunctions.Onceuponatime,manyofthelarge publictelecommunications operators (PTOs) had a hand in designing the equipment. In those days the specifica- tion was at a level of detail of an actual equipment design, almost a detailed circuit and componentdesign, so thatcontracts were principallyformanufacture.Nowadays, however, it is more common for purchasers (including PTOs) to provide a functional speczjication, laying out no more than the broad functions the equipment expected to is perform, together with the details of any external interfaces enabling thenew device to interwork correctly with other network components. As we have already noted, the use of a functional specification as opposed to an equipment design speclJication promotes competition among prospective suppliers, with a long term benefit of lower costs and higher quality. Items which may be pertinent in the specification are explained below 0 accommodationandenvironment 0 networkconfigurationandtopology 0 operationandmaintenance 0 equipment size andperformance 0 functions 0 control interfaces 0 power supply
  10. 772 SELECTING AND PROCURING EQUIPMENT Figure 42.4 A modern ISDN exchange (Courtesy of Siemens A G ) The accommodation and environment in which the equipment is to be installed: any constraining floor layouts, temperature considerations or other adverse conditions (e.g. siting of equipment in a manhole). -* The network configuration and topology in which the equipment is to work, include the specification of any interfaces to other network components. The operation and maintenance requirements: whether remote control or monitoring of equipment is required; which test points and test equipment is required; whether internal diagnostic programmes are required; what failure alarms are required. The equipment size and expected performance; for an exchange, the total daily traffic throughput in calls, and the peak hour traffic intensity (number of simultaneous calls) should quoted, be together with performance expectations underoverload. The number of busy hour call attempts (BHCA for circuit switched networks) or packets (packet switched) may be important to the dimensioning of the exchange processing capacity, and the total number of daily call attempts may govern how much storage capacity is required for any statistical information which may be required from the exchange. For a transmission system, the bandwidth of the system or the bit rate needs to be quoted, along with its jitter performance, sensitivity to noise, and other relevant information.
  11. THE TENDER DOCUMENT 773 The functions of theequipment. For an exchangethisincludes defining the call control, call routingcapabilities and services thatare required,together with the method of switching, the method of changing routing data held in the exchange, and the signalling systems to be provided. In addition, recorded announcements may be required, along with particular methods or formats for output traffic recording, call of charging and accounting information. Transmission equipment may need to provide maintenance staff with means some of remotemonitoring failures, and of reconfiguring equipment.An automatic switchover to an alternative line system may be required. The control interfaces. It is increasingly common for network operators to expect to be able to control, monitor and reconfigure the equipment within their network from a single computerized‘control centre’. Anyequipmentdestinedfor such a network requires the necessary computer interfaces to be built in. These must be covered by the specification. Conversely,theequipmentsuppliedmay be controllingother devices, and so it too must conform to a defined control interface. (An exchange, for example, mayhave to control externalechosuppressors or circuitmultiplicationequipment, and a computer may be required to monitor and control any of awholerange of devices.) The type of power supply. The supplier may need to provide equipment for working at a given voltage. Alternatively, the power equipment (including batteries and back-up generators)may need to be provided by thesupplier.Oftenelectronicequipment demands uninterruptable power supply ( U P S ) , because computer data canbe lost as the result of instantaneous breaks in power. 42.5.4 Reliability Conditions Reliability expectations should be quoted as a series of measurable parameters, quoted with reasonable target values. Measures such as ‘the number of separate instances of failure, measured month on month, shall not exceed. . . ’ are much better than more vague parameters like ‘the mean time between failures ( M T B F ) shall be greater than three years’, even if MTBF is an oft-quoted parameter. The problem with the latter statistic (MTBF) is that the long measurement period that is involved makes it virtually unenforceable. (If two failures happen in the first six months, does this mean that the next failure will nothappenforat least five-and-a-half years?) Obligations of the supplier on failing to meet the reliability conditions should also be laid out. For systems like publictelephoneexchanges or high grade computer control systems, where no break in service is acceptable to customers, availability values as high as (or even better than) 99.9% are common, though even more stringent measures may be appropriate. (It is sometimes not hard to meet a 99.9% availability for a network as a whole, even if some individual ports are outof service for days orweeks at a time, because the overall incidence of failure is nowadays usually very low.) Other considerations of reliability are the conditions and prices for the supply of spares and for after-sales support, ideally lasting for the lifetime of the equipment. The network operator does not want to be left in the position, a short time after equipment purchase, where the supplier changes the product range, and stops producing spares for the now obsolescent equipment.
  12. 774 SELECTING AND PROCURING EQUIPMENT 42.5.5 ProjectManagementConditions The tender document should lay out any special procedures for project management. The purchaser, for instance may make conditions on the work practices of the supplier, constraining noise, mess, access to site or health and safety. In addition it may be necessary to clarify responsibilities: whether for instance the supplier or the purchaser is to wire-up the equipment on site. Particular installation work practices may need to be adopted. Also, for a large and lengthy project, the purchaser may wish the supplier to build check points into the development and installation, so that the rate of progress through the project can be fairly closely monitored. 42.5.6 Quality Assurance The tender document should set down the particular measures that will be applied by the purchaser during acceptance testing to determine whether the equipment is fit-for- purpose. Usually a fair proportion of the monies are withheld until these tests have been completed. The tender document may also mandate the supplier to carry out internalinspections at variousstages of development andmanufacture,and may demand adherence to a quality work practice methodology such as those laid out the in I S 0 9000-series standards. 42.5.7 Documentation Training and In some cases, particularly when an open tender is undertaken between a number of competing suppliers, the purchaser may choose a type of equipment that is new to the network. this the In case purchaser requires training the for maintenance and administration staff, and full documentation for later reference. This should be stated in the tender document, so that the price for it receives full consideration. Alternatively, it could be the subject of a separate contract. 42.5.8 Definitions Finally, it is usual to include a glossary of definitions within the tender document, as a ready reference for terms of jargon or unfamiliar abbreviations. This is merely good documentation practice. The following list illustrates the parts of a complete tender document, butof course the size of it and the omission of any irrelevant parts arepurely at the purchaser’s discretion. 0 Commercial conditions 0 Other general conditions 0 Technical conditions 0 Reliability conditions
  13. SUMMARY 775 0 Projectmanagementconditions 0 Quality assurance 0 Documentationandtraining 0 Definitionsandglossary 42.6 SUMMARY In summary, the procurement of equipment can be a relatively straightforward and mechanistic process provided that the necessary planning is undertaken at an early date, and provided that care taken in preparing the documentation. The commonest causes is of project failure stem from faults in the very early stages. The cost of rectification can be enormous.
Đồng bộ tài khoản