HomeIndustry NewsTfL Connect Network Upgrade

TfL Connect Network Upgrade

Listen to this article

In the 1990s, London Underground (LU) embarked on a project to provide a new communications system across its entire network including provision of high fibre count cables, digital transmission, and track-to-train radio using the Tetra (Terrestrial Trunked Radio) standard. This was at the time when Private Finance Initiative (PFI) deals were in vogue and a contract was duly let to Racal Electronics for the design, installation, testing, commissioning and maintenance of the telecoms and radio network on a 20-year finance lease.

Known as the Connect project, the network was duly provided and introduced into service gradually in the years up to 2008. Racal was eventually acquired by Thales which continued to honour the contract until in 2019 when the lease period expired and the assets duly transferred to Transport for London (TfL). Thales continued to provide a maintenance service following that.

The Connect transmission network serves as a universal ‘digital pipe’ and is referred to as the Multi Services Network (MSN), with many of the services it supports being regarded as mission critical. Now some 25 years later, the insatiable demand for data and the progress in technology has meant that the network requires an upgrade to satisfy ongoing requirements and the replacement of obsolete technology.

Growing demand

With changing work patterns and people moving more around London, providing the travelling public with details of the tube network and updates on the current state of train services is ever more important. Equally, LU’s own needs are growing, particularly in the fields of surveillance and security. As such, being able to accurately monitor train and station operations on a minute-by-minute basis is evermore essential and this demands the appropriate technology to facilitate this.

Credit: Clive Kessell

To progress this communications upgrade, a partnership has been formed between TfL, Thales Ground Transportation Systems, and Nokia to design and implement an upgrade and renewal of elements within the existing Connect system.


One important factor since the announcement of the partnership is that Thales Ground Transportation Systems has subsequently been acquired by Hitachi Rail, combining both companies’ expertise in rolling stock, digital signalling, communications, and supervision systems. The company, which has its headquarters in London, now has 24,000 employees with a footprint across more than 50 countries, including major centres in Italy, Germany, Japan, and North America.


New network

The core of the Connect network is its fibre cable and transmission bearers. The latter was supplied by Ericsson using Synchronous Digital Hierarchy (SDH) with a core ring configuration of 2.5Gbit/s supplemented by a number of outer rings for each LU Line, each having a 155 Mbit/s capacity. An extensive high count fibre cable is provided on all routes with a configuration to ensure that any cut or damage to the cable will not cause communication to cease as traffic can be routed around the ring(s) in another direction. This type of technology has been commonplace for telecom networks for a number of years. The existing network achieves high levels of reliability.

So why the change? SDH is now outdated and is being replaced with Internet Protocol / Multi Protocol Label Switching (IP/MPLS) technology. This means that all devices connected to the network must have an IP address which will facilitate the addition of new requirements as well as enhancing cyber security.

The existing fibre cables are being retained but will be tested to ensure they remain in specification. A few additional cables will be provided primarily to enhance the ring configuration security. The ring layout will remain but will be changed slightly to create greater meshing of the primary and secondary networks.

The transmission equipment will be completely renewed but this will be carried out as a staged process. Nokia will be the provider of the IP/MPLS transmission kit which at first will be integrated into the existing Ericsson equipment on the existing fibre pairs. This will ensure continuity of service with reversion to the previous condition if any problems are encountered. Once the new equipment is fully proven the old SDH will be powered off, which will take a period of months. As part of this renewal, the digital capacity will be increased. The new equipment will be more environmentally friendly, consuming less power and able to work at higher temperatures up to 40°C.

Connected devices

The most significant requirement is universal CCTV coverage, and LU has thousands of cameras positioned at its stations and platforms. The important interchange stations may each have a hundred-plus cameras, and this constant monitoring of the situation is vital for safe operation. The majority of cameras remain analogue, and this will not change since they still have useful life. For the time being, analogue to digital convertors will be required to connect the cameras to the new transmission network, much as what happens already with SDH. In time, cameras will be replaced with digital devices with a direct IP feed but this is not part of the present contract. As an aside, the Docklands Light Railway (DLR), also part of TfL, is already changing over from analogue to digital cameras and the experience gained will be transferable to LU.

Other devices that will use the Connect backbone are tunnel telephones, long line public address, passenger help points, and the internal LU telephone system, as well as many LU data systems for planning, personnel resourcing, ticketing, and fares management. All of these already exist but will benefit from the enhanced speed of the new transmission network.

Credit: Clive Kessell

The radio network

The other major part of the original Connect contract was the provision of a new radio communication for both train crew and station staff. Based on the Tetra standard, this has provided good service over the life of the PFI contract, but again the network components were ageing.

In advance of the Connect renewal contract, a major upgrade of the radio network has taken place. This involved the replacement of 295 transceiver (base) stations with new Motorola products that offered enhanced functionality but retained the same frequency band within the Tetra specification. The coverage by both radiating cable and low mounted yagi aerials has been unchanged except where building work has necessitated revisions to aerial locations. New radio dispatcher terminals have been provided at control centres, depots, and major stations.

The Emergency Services Airwave network which uses the same technology, has separate base stations but uses the same radiating cable and aerial bearers. Airwave has end-to-end encryption for added security. It is possible that this will need to change to the proposed Emergency Services Network (ESM) as part of a national initiative, but this is still in the design stage and is many years off.
Another part of the radio contract awarded in 2023 is to provide new hand portable radios for a number of train crew and station staff. These are now coming on stream and will be issued when the existing radios become faulty or are damaged. Smaller than the current radios, they should prove popular with staff.

Project control and management

Hitachi Rail’s responsibility and a project director has been appointed. Going under the acronym of Renewal of Operational Network (RON), the Hitachi Rail project team is based in offices at Waterloo. London Underground managers will keep a watching brief on progress and Nokia engineers will be part of the integration team.

To ensure successful development and deployment, a reference network is being installed at Waterloo so that changes and additions can be fully tested before being installed and commissioned at the various node sites across LU. Since Hitachi Rail (as Thales) was the incumbent maintainer of the existing network, it will be retained to maintain the new equipment under a service level contract. All Hitachi Rail staff must be certified as competent under LU conditions and have to be fully compliant with the rules for access and safety. Around 220 people are involved in the contract to design and deliver the new system, covering design, installation, testing, commissioning, operations, and maintenance.

Two Network Management Centres exist at present and these will remain. These are needed to provide the necessary security and continued operation in the event of any incident.

The new network will be completed around 2027 and will be seamless in terms of user experience. Progressive changeover and updating will take place over the next three years. TfL, Hitachi Rail and Nokia will work as a partnership using the ISO 44001 Collaboration standard.

A media roundtable was recently held in London to explain the project and thanks are expressed to Rebecca Bissell from TfL, Andy Bell from Hitachi Rail, and Matthieu Bourguignon from Nokia for sharing their collective expertise. A subsequent conversation with Peter Gaylor, the Hitachi Rail programme director, helped to better understand the technical aspects.

Credit: iStockphoto.com/MattStansfield

The future

The upgraded Connect network is capable of being a bearer for all LU applications and will have the capacity to fulfil that. One potential future application could be in connection with the Communications-Based Train Control (CBTC) systems that increasingly use radio as the communication between track and train. The 4LM project covering the sub surface lines is using WiFi for connectivity, based on low power tunnel and surface mounted aerials. Provision of these is a substantial element of the project and the availability of a ready-made bearer for future projects has to be a consideration.

CBTC is a SIL4 (Safety Integrity Level) system so the designers and operators of the system are wary of using an independent communication network for the transfer of data. The designers of Connect are reluctant to give the network a SIL rating as it is essentially just a reliable and secure comms link. In time, the thought processes on how CBTC is structured might change, which has potential benefits for all.

The huge data capacity that the Connect network has to offer will lead to other opportunities and applications that will emerge over time. The media roundtable was entitled ‘Levelling up Communications’ so it is clearly the intention to make the most use of this digital backbone for whatever TfL requires. Rail Engineer will keep an eye on progress and developments.

Image credit: iStockphoto.com

LEAVE A REPLY

Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.