Cambridge University Reporter


Report of the Granta Backbone Network Management Committee for 2004-05

Introduction

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 thirteenth report and covers the period from 1 August 2004 to 31 July 2005.

Granta Backbone Network

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 easily for the last twelve years and seems set fair 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.

Membership

3. Professor A. Hopper was reappointed as Chairman and Mr J. K. Milner, Mr A. M. Reid, Dr J. R. Seagrave, and Dr R. D. H. Walker continued as members. Mr C. J. Cheney continued as secretary. 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 2005, the Committee's business was routine and was satisfactorily conducted by electronic mail.

Extensions, building work, and other incidents affecting the GBN

4. There were no unplanned incidents affecting service delivered by the GBN during the year.

5. At the Addenbrooke's Site, the duct route to the new CR-UK building from the existing ducts serving the Clinical School is not yet complete. It is anticipated that the new route will be ready for cabling at the end of 2005.

6. At Homerton, the new Faculty of Education building was connected to the GBN.

7. At Fenner's, the new Hughes Hall building was connected to the GBN and, adjacent, a new mini-node was installed in the Gonville and Caius Mortimer Road hostels.

8. Building work at the Magdalene College hostel in Chesterton Road was completed and the GBN cabinet and cables were reinstalled.

9. The diversion of the GBN to bypass 17-19 Brookside prior to the sale of the property was completed.

10. A GBN mini-node for the West Cambridge Residences was installed.

11. An alternative duct route at New Hall to bypass their new building was agreed, installed, and is now in use.

12. The work to overlay the GBN route onto the University Press's map of Cambridge has unfortunately not progressed because of an issue with the software system used to hold all the GBN data. This issue should be resolved soon.

Network Allocations

13. 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. There are also five 'direct' cables from the 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.

14. 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 2005 (with the corresponding July 2004 statistics in brackets):
Type of useType of fibreNo of fibresTotal length (km)
  2004-05(2003-04)2004-05 (2003-04)
University Data Network62.5 μm130(141)166(170)
 50 μm18(18)18(16)
 single-mode72(58)169(153)
University Telephone Networksingle-mode45(6)404(29)
Security62.5 μm5(5)7(7)
 single-mode27(25)86(75)
Private fibres62.5 μm109(99)122(118)
 50 μm8(8)10(10)
 single-mode71(63)231(217)
Total 485(423)1,213 (795)

The allocations shown in the table represent the following proportions of the total fibre length available in the network (with the 2003-04 proportions in brackets): 62.5 μm 25% (30%); 50 μm 7.5% (7%); single mode 57% (45%).

graph showing fibre usage in kilometres by year

Fibre usage (km) by year

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

(a) Cambridge University Data Network (CUDN)

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 2005, the total numbers and bandwidths of ethernet connections were 22 at 10 Mbps or less, 78 at 100 Mbps and 54 at 1000 Mbps (July 2004: 35, 80, and 43 respectively).

(b) University Telephone Network

A large number of GBN single-mode fibre circuits were installed for the JTMC for their TDM multiplexor network to generate substantial savings in rental of external telecommunication circuits. The JTMC also make 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.

(c) 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 plants.

(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 Gonville and Caius College, Hughes Hall, Clare Hall, Anglia Ruskin University, Cambridge Assessment, and the Department of Plant Sciences.

Staffing and Finance

16. 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, liaising as appropriate with Dr Robinson.

17. 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. Whereas, in the past, the Computing Service (in respect of the CUDN) was by far the largest single contributor to the rental income, it has now been overtaken by the JTMC.

18. 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 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.

19. In the previous year, 2003-04, income exceeded expenditure by £7,204, and the accumulated balance fell to £64,732, as a result of needing to provide 25% matching SRIF funding for expenditure on cables, In 2004-05, expenditure exceeded income by £23,841 largely as a result of cable installation although, as a result of the excess of income over expenditure in the previous year, the accumulated balance stood at £72,089. In February 2005, the Committee decided to raise the GBN rental charge from 1 August 2005 to £6.50 per 100 metres or part thereof and expected to make a further similar increase after 12 months. The cost of GBN fibre rental is still greatly below that which the University would need to pay in the commercial marketplace.

 

A. HOPPER ChairmanNovember 2005