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1. Since 1992, the remit of the Granta Backbone Network Management Committee (GBNMC) has been to oversee, on behalf of the University and the Colleges, the operation, maintenance, and development of the physical network of ducts and cables. The GBNMC reports annually to the Finance Committee and the Bursars' Committee; this is the eleventh Report and covers the period from 1 August 2002 to 31 July 2003.
2. The Granta Backbone Network (GBN), which stretches from Girton College to the New Addenbrooke's Site, consists of ducts and cabling in more than 32 km of trenches connecting over 90 separate sites. The GBN's design brief was to be capable of meeting the communications infrastructure needs of the University and the Colleges for at least 25 years; the network as installed has done so easily for the last eleven years and seems set fair to continue. While most GBN traffic is for data communications, it also carries video transmissions, pictures from security cameras and signals from remote alarms and performance monitors. The basic network of 58 sites was financed corporately on a formula basis (University 60%, Colleges 40%), but additional connections were and are still being provided at the request and expense of individual University institutions or Colleges.
3. Professor R. M. Needham, who continued as Chairman until his death in the Lent Term, has been replaced by Professor A. Hopper. Dr R. Hanka resigned at the start of the year and was replaced by Mr S. W. Hedley. Dr J. R. Seagrave, Dr R. D. H. Walker, and Mrs J. M. Womack continued as members of the GBNMC with Dr M. D. Sayers, Dr B. A. Westwood, and Mr C. J. Cheney from the Computing Service and Mr M. J. Dowling from the Estate Management and Building Service in attendance. Apart from one face-to-face meeting in October 2002, the Committee's business was routine and was satisfactorily conducted by electronic mail.
4. At the Addenbrooke's Site, the re-routing and temporary resplicing of the GBN cables on the route across the old Downing College playing fields was completed by November; discussions then began about a route into the new building being constructed there to house Cancer Research UK and some University staff. At Homerton, the existing cables were re-routed and respliced for the construction of a new access road. Later in the year, in a co-ordinated operation, one GBN cable was re-routed around both a pavilion extension at St Catharine's Sports Ground and Downing's new pavilion at the adjacent Trinity New Field.
5. At Fenner's, the GBN routes are affected by the construction of new accommodation for Hughes Hall at one part of the site and the University's new Cricket School at another. Since one of the existing routes runs too close to the first to be adequately protected against the builders, its cables have been temporarily disconnected and drawn back (leaving Hughes Hall, Anglia Polytechnic, and Local Examinations on a spur rather than a ring) ready to be re-installed in their ducts once the building has been completed. The GBN cabinet and cables have been temporarily removed from a Magdalene College hostel while the building is being refurbished.
6. Early in the year, the installation of a new gas pipe at the Library resulted in a damaged GBN duct and loss of part of the building entry gland. In April, all three ducts running along Downing Street appeared be damaged in the vicinity of the service entrance to a public house at the Emmanuel end of the street and the Estate Management and Building Service (EMBS) was called in to investigate. Diversions have been completed to isolate a section of the GBN through Downing College, in order to permit the investigation, during Autumn 2003, of possible damage where the ducts run under a hedge.
7. The University plans to sell off the buildings at 17 and 19 Brookside once Education have moved out; this will badly affect the GBN because its main route south goes through them on its way to the New Addenbrooke's Site. In October 2002 the GBNMC informed EMBS that it will be essential, before the site is sold, both to modify the carriageway duct runs by adding a short section at the corner of Brookside (which needs approval from the City Council) and to install a new GBN cable all the way from Chemistry to the Botanic Garden. Plans have also been made to install a GBN mini-node in the West Cambridge Residences in Spring 2004.
8. Although the decision to install the GBN was taken corporately by the University and all the Colleges, joint ownership proved impracticable for legal reasons and it was agreed both that the University should own the network and that the wayleaves needed where the GBN runs over College land should be both identical and provided at only nominal cost. In recent years, it has become increasingly apparent that, because there have been so many changes among Bursars and other personnel since 1992, these arrangements are now not well known and can come as a considerable surprise to College staff and/or land agents. To provide a first point of reference in future negotiations, a page containing the relevant historical information has been added to the GBN section of the Computing Service website.
9. GBN routes in the initial installation normally have three ducts, of which one is primarily for the voice telephone network. The standard GBN fibre-optic cable is specially made and contains 48 fibres in all, of which 8 are 50 μm multimode, 16 are 62.5 μm multimode and the remaining 24 are single mode, although cables with other combinations of fibre capacities have also been installed in parts of the GBN to meet particular requirements. In addition, there are direct cables from the New Museums Site to the Cavendish Laboratory, Chemistry, Engineering, and the New Addenbrooke's Site (each with 16 62.5 μm fibres) and one of 16 50 μm fibre from the New Museums Site to the Sidgwick Site.
10. The GBNMC does not itself provide end-user services but rather allocates individual fibres in GBN cables for the University Data Network, for security uses and for private links between physically separated sites of individual institutions and space in the GBN ducts for local wiring for the voice network. The following table summarizes fibre allocations at July 2003 (with allocations at July 2002 in brackets):
| Type of use | Type of fibre | No of fibres | Total length (km) | ||
| University Data Network | 62.5 µm | 141 | (153) | 170 | (182) |
| 50 µm | 18 | (20) | 16 | (17) | |
| singlemode | 58 | (52) | 152 | (145) | |
| Security | 62.5 µm | 5 | (5) | 7 | (7) |
| singlemode | 23 | (23) | 63 | (63) | |
| Private fibres | 62.5 µm | 106 | (99) | 122 | (116) |
| 50 µm | 6 | (6) | 9 | (9) | |
| singlemode | 53 | (41) | 166 | (139) | |
| Total | 410 | (399) | 704 | (676) | |
The allocations shown in the table represent the following proportions of the total fibre length available in the network (with the 2002 proportions in brackets): 62.5 µm 75% (76%); 50 µm 12% (13%); single mode 59% (58%).
11. Some of the main uses to which the GBN is being put at present are:
(a) Cambridge University Data Network
The gigabit ethernet (1000 Mbps) backbone infrastructure which interconnects the eight area routers and central switches and the ethernet connections from the area routers to the local area networks in just about every University institution and College both rely on using the GBN. At the end of July 2003, the total numbers and bandwidths of ethernet connections were 46 at 10 Mbps or less, 76 at 100 Mbps and 35 at 1000 Mbps (compared to 55, 72, and 26 in July 2002).
(b) Security
A mixture of fibre and copper connections transmits information to the Security Control Room on the New Museums Site, including pictures from remote security cameras, signals from remote intruder entry, and security loop alarms and monitoring information for building services equipment such as boilers and air-conditioning plant.
(c) Private fibres
Links between physically separate sites may be rented by individual institutions for various purposes. During the year, new private fibre links were installed for Clare College, Corpus Christi College, the Department of Earth Sciences, the Management Information Services Division, the Department of Plant Sciences, and Sidney Sussex College.
(d) University Telephone Network
Although GBN fibres are no longer used for trunk voice connections, there is widespread use of fairly short runs of multi-pair copper cables in GBN ducts to distribute individual telephone circuits from network nodes to nearby sites.
12. The Network Division of the Computing Service continued to carry out all GBN operations on behalf of the GBNMC. Fibre allocations and general administration were handled by Dr C. A. Robinson (a part-time Computer Associate) while the Network Installation team were responsible for either carrying out the technical installation and maintenance work themselves or supervising the employment of outside contractors.
13. The GBN rental charges, which are pro rata to the total length of fibre in each connection, are intended to cover the running costs of the network, including the capital cost of installing additional fibres as required. Rental rates have remained unchanged since 1995 and for some years past all rentals have been at the standard rental rate, with none at the cheaper research rate for short term research or similar projects. The Computing Service (in respect of the CUDN) is by far the largest single contributor to the rental income.
14. While maintaining the existing network is comparatively cheap because of the passive nature of the ducts and cables, there is usually a moderate amount of expenditure each year on repairing damage due to unknown causes. The costs of route diversions on account of new building work can be quite large but are normally recoverable under the provisions of the wayleaves. The most variable factor affecting recurrent expenditure is the installation of additional cables in heavily used parts of the network, which tends to be much more expensive than other maintenance but usually only becomes necessary every few years.
15. In 2000-01 there was an overall surplus of £21,500 on the year's activities, but in 2001-02, because of the need to install a considerable amount of additional network capacity, the overall deficit was £22,167. In 2002-03, with a return to needing no expenditure on additional capacity, there was an overall surplus of £20,535 and the accumulated balance rose to £66,622. While the Committee welcomed the return to being in surplus on the year's operations, it decided to leave the GBN rental rates unchanged for the time being.
| October 2003 | A. HOPPER Chairman |
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Cambridge University Reporter, 23 January 2004
Copyright © 2003 The Chancellor, Masters and Scholars
of the University of Cambridge.