< Previous page ^ Table of Contents Next page >

Report of the Granta Backbone Network Management Committee for 2000-2001


1. The Granta Backbone Network Management Committee (GBNMC) was established in 1992. Its remit is to oversee the operation, maintenance, and development of the physical network of ducts and cables on behalf of the University and the Colleges and to report annually to the Finance Committee and the Bursars' Committee. This is the ninth annual report and covers the period from 1 August 2000 to 31 July 2001.

Granta Backbone Network

2. The Granta Backbone Network (GBN) consists of ducts and cabling in over 25 km of trenches which stretch from Girton College to New Addenbrooke's and interlink over eighty separate sites. The initial installation took place in 1992, with the intention that it should provide a suitable communications infrastructure to meet the needs of the University and the Colleges for at least twenty-five years. The traffic carried by the GBN includes that from data communications networks, the telephone network, video transmissions, security cameras, and remote alarm monitoring. The basic network (fifty-eight sites) was financed jointly on a formula basis (University 60%, Colleges 40%); additional connections to other sites have been provided when requested, both then and since, at the expense of individual institutions.


3. During the year, Professor R. M. Needham was reappointed as Chairman, while the other members continued to be Dr R. Hanka, Dr J. R. Seagrave, Dr R. D. H. Walker and Mrs J. M. Womack. Meetings were regularly attended by Dr M. D. Sayers, Dr B. A. Westwood, and Mr C. J. Cheney (with Dr C. A. Robinson as deputy) from the Computing Service and by Mr M. J. Dowling (with Mr J. Richardson as deputy) from the Estate Management and Building Service.

Maintaining the existing Network

4. Following completion of the new Unilever Centre, ducts and cables were installed on a new route into the Chemistry building from a chamber in Union Road. All connections using the new route were in use by the Easter Term and reinstatement of the services which had been diverted due to the works on the Unilever building took place during the following summer.

5. At West Cambridge, installing new GBN ducts and cables for the upgrading of the access road went smoothly; by February, all the existing services had been successfully moved over and cables were in place on part of the route to the new node in the Computer Laboratory. Later in the year, planning was put in hand for the next stage of expansion of the GBN ducts for the site as a whole. At Clarkson Road, although the second phase of work on the Mathematics building would be taking place near to the route to the GBN node, it was agreed, after considering the risks, that no diversions would be installed in advance.

6. As part of a major refurbishment of the buildings around it, the GBN cabinet at New Hall was relocated to the opposite end of the College. After the builders had installed ducts between the old and new locations and the Computing Service had installed a new cabinet and cables, the transfer early in the summer went very smoothly, with the CUDN connection being disrupted for only a few minutes. As part of the landscaping around the new building at Earth Sciences (Madingley Rise) the GBN ducts were lowered into a brick chase.

7. Much time was spent planning diversions of the GBN in connections with proposals for new buildings. Since plans by the University for further development of the Sidgwick Site and by Gonville and Caius for a new residential block at 4 West Road will both impact the GBN, it is clearly desirable to deal with the necessary routings as a whole rather than piecemeal. Unfortunately the first attempt at a solution was rejected by the City Council's Tree Officer, but discussions are in progress with the services consultants to produce an alternative route. A similar approach is planned once more details are known about the proposals at Fenners, which involve a new cricket school, and a residential development for Hughes Hall.

New Connections

8. During the year, Homerton was connected to the EastNet regional network via the GBN, using ducts which had been installed from a chamber at the railway to a building on the site as part of an earlier building project. The actual installation differed from the plans that had been approved and, contrary to normal GBN practice, included a section where its fibres shared a chamber both with other data cables and with electric power cables. Since correcting these problems would be very expensive, the Committee reluctantly agreed that, most exceptionally, Homerton should be responsible for the future maintenance of this route.

9. Although the installation of new ducts across farm land from existing ducts at Rifle Range Road to provide a GBN connection for EMBS engineering services staff at Laundry Farm went smoothly, agreeing the relevant easements over College land went less well until the Committee reminded those concerned that it had been agreed right at the beginning that since the GBN was a corporate project between the University and Colleges all its wayleaves should both be as identical as possible and also involve only a peppercorn rent.

10. In establishing the new GBN site node at the Computer Laboratory and providing the latter with connections for the CUDN, security, and a private link to the new Museums Site, problems arose because the building contractors had installed different ducts from those specified as the GBN standard, making it impossible to fit the glands caulking at the building entries. This is only one example of the difficulties experienced when detailed specifications provided to architects or services consultants at the planning stage fail to get carried through to the sub-contractors and clerk of works who are responsible for the actual work at a later date.

Network Allocations

11. Most GBN routes in the initial installation have three ducts, one of which is primarily for the voice telephone network, one which carries fibre-optic cables and one which is spare for future expansion. The standard GBN fibre-optic cable is specially made and has a total of 48 fibres of three types: 50 μm multi-mode (8 fibres), 62.5 μm multimode (16 fibres), and singlemode (24 fibres). A few busy routes have either a second similar cable or one with 24 62.5 μm fibres. There are also direct cables with 16 62.5 μm fibres each from the New Museums Site to the Cavendish Laboratory, Chemistry, Engineering, and New Addenbrooke's, and a 16 50 μm fibre direct cable from the New Museums Site to the Sidgwick Site.

12. The GBNMC does not itself provide end-user services but allocates space in GBN ducts and fibres in GBN cables for University-wide service providers such as the Computing Service (data network) and the Joint Telecommunications Management Committee (telephone network), for security uses, and to meet the needs of individual institutions for private links between physically separated sites. The table above summarizes fibre allocations at July 2001 (with allocations at July 2000 in brackets).

The allocations shown in the table represent the following proportions of the total fibre length available in the network (with the 2,000 proportions in brackets): 62.5 μm 80% (77%); 50 μm 18% (18%); singlemode 50% (35%).

13. Some of the main uses to which the GBN is being put at present are:

(a) Cambridge University Data Network

The GBN is used both to interconnect the eight area routers to the central switches and to link the area routers to local area networks in just about every University institution and College. During the year, the use of the ATM protocol was phased out from the main network and Gigabit (1000 Mbps) Ethernet trunk links were installed between all the area routers. The end connections to user institutions are now almost exclusively ethernet and between July 2000 and July 2001 the number of fast lines (with a bandwidth of 100 Mbps or more, including a handful at 1000 Mbps) increased from 48 to 76 while that of the slow ones (10 Mbps or less) fell from 94 to 73.

(b) University Telephone Network

Although GBN fibres provide the main voice connections for Jesus and Robinson Colleges, most use in connection with the telephone network involves fairly short runs of multi-pair copper cables in GBN ducts to distribute individual telephone circuits from network nodes to nearby sites.

(c) Security

The GBN transports information to the Security Control Room on the New Museums Site via both fibre and copper connections, including pictures from remote cameras, signals from remote intruder entry and security loop alarms, and monitoring information for building services equipment such as boilers and air-conditioning plant.

(d) Private Fibres

Institutions use these to link networks on two or more physically separate sites. During the year, institutions with new private fibre links included Corpus Christi, Darwin, and King's Colleges, the Commonwealth Trust, the Computer Laboratory, the Department of Geography, and the University Offices.

Type of Use Type of Fibre No of Fibres Total Length (km)
University Data Network 62.5μm 164 (154) 200 (194)
  50 μm 16 (12) 16 (16)
  singlemode 38 (20) 126 (92)
Telephone network 50 μm 6 (6) 15 (15)
Security 62.5 μm 5 (5) 7 (7)
  singlemode 21 (11) 51 (23)
Private fibres 62.5 μm 93 (87) 115 (109)
  50 μm 6 (4) 8 (5)
  singlemode 39 (29) 124 (98)
Total   388 (328) 662 (558)

Staffing and Finance

14. The Network Division of the Computing Service continued to carry out all GBN operations, with all fibre allocations and general administration being handled by Dr C. A. Robinson (a part-time Computer Associate) while other staff either carried out the necessary technical installation and maintenance work or supervised the use of outside contractors.

15. Because of the passive nature of the ducts and fibres, the running costs of the GBN are comparatively modest. They are met from rental charges (depending on the total length of fibre in each connection) which also provide for the capital cost of installing additional fibres as required. While the standard rental rate applies in most cases, there is a cheaper research rate for short-term projects; both have remained unchanged since 1995. The Computing Service (in respect of the CUDN) is by far the largest single contributor to this source of income.

16. Most of the GBN ducts and cable work carried out during the year was in response to, and so was funded by, new building projects or refurbishment programmes. As a result, apart from staff costs, expenditure was very modest and for the first time in several years there was a net surplus (of £19,877) on the year's operations. The GBN rental rates were left unchanged for 2001-02.

October 2001

R. M. Needham, Chairman

< Previous page ^ Table of Contents Next page >

Copyright © 2002 The Chancellor, Masters and Scholars of the University of Cambridge.
Comments should be sent to webmaster@admin.cam.ac.uk