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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 fifteenth report and covers the period from 1 August 2006 to 31 July 2007.
2. The Granta Backbone Network (GBN), which stretches from Girton College to New Addenbrooke's, 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 for the last fourteen years and seems likely to continue. While most GBN traffic is for data communications, it also carries telephony, 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 A. Hopper was reappointed as Chairman and Mr J. K. Milner, Mr A. M. Reid, and Dr R. D. H. Walker continued as members. Dr J. R. Seagrave left the committee and was replaced by Mr I. M. Du Quesnay. Mr C. J. Cheney retired in February and was replaced as secretary by Dr J. D. Hornsby. Mr M. J. Dowling from the Estate Management and Building Service and Dr C. A. Robinson from the University Computing Service were in attendance at meetings. Apart from one face-to-face meeting in February 2007, the Committee's business was routine and was satisfactorily conducted by electronic mail.
4. Additional security covers have been installed in a number of chambers in remote locations.
5. GBN mini-nodes were installed at the new CR-UK building for the Clinical School and at Scroope Terrace for Architecture.
6. GBN mini-nodes were installed at Storey's Way for Trinity Hall and 38 Newnham Road for Clare College.
7. Additional single-mode cables, totalling 1.5km, have been installed to increase capacity on certain routes.
8. A major re-routing of all GBN cables and active services was required as part of the preparatory works for two building projects; the Physics of Medicine building at West Cambridge and a theatre in Downing College. The cables running through both sites carry a large number of active services.
9. The work to overlay the GBN route onto the University Press's map of Cambridge is progressing.
10. Most GBN routes 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. New cables are now tending to contain single-mode fibres only because this is the preferred type of fibre for most new uses. New cables are often installed between two non-adjacent nodes without visiting all intermediate nodes, so that there are now a number of 'direct' single mode cables as well as the original five: New Museums Site to the Cavendish Laboratory, to Chemistry, to Engineering and to New Addenbrooke's, each with sixteen 62.5 μm fibres, and one of sixteen 50 μm fibres from the New Museums Site to the Sidgwick Site.
11. The GBNMC does not itself provide end-user services but rather allocates individual fibres in GBN cables for the University Data Network, for the University Telephone 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 2007 (with the corresponding July 2006 statistics in brackets):
No of fibres
Total length (km)
|Type of use||Type of fibre|
|University Data Network||62.5μm|
|University Telephone Network||single-mode|
|Private fibres||62.5 μm|| |
The allocations shown in the table represent the following proportions of the total fibre length available in the network (with the 2005-06 proportions in brackets): 62.5 μm 29% (28%); 50 μm 7.5% (7.5%); single mode 47% (49%).
12. Some of the main uses to which the GBN is being put at present are:
The 10 Gbps ethernet backbone infrastructure that interconnects the eight area routers/switches 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 2007, the total numbers and bandwidths of ethernet connections were 16 at 10 Mbps or less, 76 at 100 Mbps and 69 at 1,000 Mbps (July 2006: 18, 77, and 63 respectively).
(b) University Telephone Network
The JTMC makes use of GBN single-mode fibre for their time-division multiplexor (TDM) network and also makes 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.
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.
(d) Private fibres
Links between physically separate sites are rented by individual institutions for various purposes. During the year, new private fibre links were installed for the Management Information Services Division (MISD), Clare College, Trinity Hall, the Fitzwilliam Museum, and Anglia Ruskin University.
Staffing and finance
13. 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, who calls on the Network Installation team for either carrying out the technical installation and maintenance work or supervising external contractors. Civil engineering works for the GBN, carried out for the University, are supervised by the Estate Management and Building Service (EMBS), liaising as appropriate with Dr Robinson.
14. 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. For some years past all rentals have been at the standard rental rate, with none at the previously cheaper rate for short-term research or similar projects.
15. While maintaining the existing network is comparatively low-cost 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 way-leaves. The most variable factor affecting recurrent expenditure is the installation of additional cables in heavily used parts of the network. There has been major investment in new cables over the past few years, and will probably continue so for several more.
16. In the previous year, 2005-06, expenditure exceeded income by £28,674, largely due to cable installation and increased external labour costs, and the accumulated balance fell to £48,744. In 2006-07 expenditure again exceeded income, by £16,739, and the accumulated balance fell to £20,830. In February 2007, the Committee decided to raise the GBN rental charges from 1 August 2007 to £10.00 per 100 metres or part thereof. The installation charges will remain the same at a minimum of £110 per site with £30 per individual splice and a £60 per fibre per circuit administration charge. The committee noted that there had been a large excess of expenditure over income for the last two years that needed to be redressed and also felt that it is necessary to build up a reserve for repairs and refurbishments to the duct network that are anticipated in the future because of the growing age of the network. The new rental rate is roughly equivalent to that which was charged at the outset of the GBN. The rental rate remained constant at £7.50 between 1997-98 and 2003-04 when it was reduced to £6.00, and then raised to the current rate of £6.50 in 2005-06. The Committee envisaged that further modest increases to the rental charges would be needed in subsequent years.
|A. HOPPER Chairman||November 2007|
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Cambridge University Reporter 25 October 2008
Copyright © 2011 The Chancellor, Masters and Scholars of the University of Cambridge.