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gbn-shieldThe Granta Backbone Network (GBN) is a network of underground ducts and cables providing an advanced communications infrastructure for the University and Colleges of Cambridge, capable of lasting well into the 21st century. The £3.6M cost of installing the GBN was shared between the University and Colleges, with contributions from the Cambridge Foundation and some non-University institutions which have direct GBN connections. 

The project, completed in March 1992, involved the excavation of some 30 kilometres of trenching linking 80 University and College sites stretching from Girton College in the north-west of the city through the central and western parts of Cambridge to Addenbrooke's Hospital in the south-east. A small number of non-University sites are directly connected to the GBN; these sites have close contacts with the University. Since 1992, the duct network has more than doubled and has been extended to Madingley Hall in the northwest and Hinxton to the south.  

A termination cabinet or tray (known as a "node") at each site provides the point of access between the GBN and local site networks. The fibre-optic cables are installed site to site; splicing of fibres at individual nodes allows circuits to be added or removed as the need arises and gives a high degree of flexibility in implementing different types of network topology. Connections into the GBN are made only at these nodes; it is not possible to connect by breaking into ducts or routeing chambers between nodes. Circuits, made up of sections of fibre spliced together, can be rented to network service providers or to individual institutions. 

End-user services are not provided directly by the GBN itself but by existing service providers, for example, University Information Services for data network services, the University Telephone Network for voice services. Current uses of the GBN infrastructure include private links for multi-site Departments and Colleges; communications research by the Computer Laboratory and Department of Engineering; security services such as alarms and CCTV surveillance; and for the various requirements of the Cambridge University Data Network (CUDN) - electronic mail, file transfer, remote computer access, access to national and international networks and so on.

The network is managed by the GBN Management Committee which comprises both University and College representatives. The day-to-day administration of the network is undertaken on behalf of the Management Committee by University Information Services.1

Formally, the GBN is owned by the University on behalf of all the participating bodies. As a result, where GBN plant crosses non-University land there is a wayleave agreement2 between the individual landowner concerned and the University. Amongst other terms and conditions in the wayleave agreement between the University and individual Colleges, a College's repositioning of any element of the network within College land should be carried out by the University with costs for doing so borne by the College. The University is also given the right to enter College land on reasonable notice except in the case of emergency for the purpose of repairing, maintaining, renewing and re-laying the parts of the network.

The onus is on the landowner, whether University, a College or other, to ensure that the GBN infrastructure is not damaged, either by day-to-day activities or by building works. Therefore, when an activity is likely to conflict with the GBN, the landowner must contact the UIS to negotiate a resolution of the conflict; Information Services will liaise with Estates Management on relevant civil engineering matters. Landowners contemplating sale or lease of land which is subject to a Granta wayleave must draw the attention of the purchaser to the wayleave and its terms. If the sale or lease is to a third party (outside the University and Colleges), the landowner must consult Information Services first, and it may be necessary to arrange for diversion of the Granta ducts and cables, at the landowner's expense, before the sale or lease.

1. All matters concerning the GBN, be it requests for dark-fibre circuits, extending the GBN to serve other buildings or new building works conflicting with the GBN, should be directed in the first instance to the Granta Backbone Network team, gbn-enquiries@uis.cam.ac.uk.

2. Colleges will have signed copies of their executed wayleave agreements. At the completion of the original project maps were sent to each College indicating where GBN plant crosses land owned by that College. Copies of the terms and conditions in the wayleave and replacement maps may be obtained from the Granta Backbone Network Manager.

Last updated: 30 June 2022

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