Inside BT

We’ve all heard of BT, if you haven’t, British Telecommunications (BT for short) is a global communication operator, who inherited a nationwide copper landline network from the General Post Office back in the ’80’s, Providing a perfect network for telephone calls, however, when the first internet products were launched, the dial-up based network soon became congested. With competitors like Freeserve using Energis, another network competitor stealing valuable market share and sharing the same delivery network. Many of the 5500+ exchanges were running out of backhaul connectivity.

BT’s ATM network was originally built in the 1990’s to serve business ‘leased lines’ however greater bandwidths were needed for consumer broadband and with the introduction of DSL, the ATM was used for a new, massive IP based ‘Colossus’ Network, completed in the late 90’s and saw consumer narrowband speeds of 56k upgraded to 512kbps and beyond.

BT started deploying DSLAMs (Digital Subscriber Line Access Multiplexer) to exchanges nationwide to get people onto the higher speeds, connecting each with multiple 155 Mbps ‘virtual pipes’ to an authentication ‘BRAS’ (Broadband Remote Access Server) location. This is where the connection will be authenticated by the ISP and passed onto their network for internet provision.

Some smaller exchanges will use neighbouring exchanges backhaul to the ‘Colossus’ network and will have a smaller 30Mbps ‘Virtual Pipe’ capacity. These virtual pipes will inter-connect throughout the BT network until it reaches one of ten BRAS locations (Birmingham, Bletchley, Ealing, Edinburgh, Ilford, Kingston, Manchester, Reading, Sheffield, Faraday).

Each ISP will lease a number of 155Mbps virtual pipes from BT with a capacity of 8,000 per pipe, to handover customers connections from one of the BRAS locations to the ISP’s own internet point of presence. This move freed up the upgraded telephone capacity, making free evening and weekend calls cheaper and beginning unlimited call plans.

These BRAS locations are high concentrations points within the network and would typically be housed within a large telephone exchange. This worked well until the DSLAMs were upgraded to up to 8Mbps and virtual pipes became congested. Upgrades allowed 622 Mbps virtual pipes to be used, allowing 25,600 customers per pipe, and further upgrades allowed 30,000 customers per pipe adding to congestion at peak times.

A new network was needed with the old ‘separate voice/data’ network dubbed 20th-century network and the new ‘converged’ 21st-century network, which will renovate the ageing analogue public switched telephone network and onto a new ‘multi-service’ IP network which will cater for both calls and broadband.

The 21CN was born with over 4,400 sites with copper and fibre MSANs (multi-service access node) connecting to over 1,000 Tier 1 MSANs, which connect to approx 86 metro network locations and onto 20 core network locations (Birmingham, London North West, Bristol, Manchester, Cardiff, Milton Keynes, City of London, Newcastle, Clyde Valley, Peterborough, Derby, Preston, Docklands, Sheffield, Glasgow, Slough, Guildford, Southbank, Leeds & Wolverhampton) – By using a more distributed network means high concentrations points are evenly spread out causing less mass congestion.

This also enabled competitors to rent space for their own DSLAMs in exchanges and connect to their own nationwide fibre network (or leased fibres) and away from BT’s Colossus network. Providers like Sky & TalkTalk use this network configuration.

BT later abandoned the IP Telephone plan and is still using analogue public switched telephone network and focused on introducing FTTC and then G.FAST products, pushing DSLAM’s deeper into the street furniture, slightly increasing speeds over their copper network.

The new 21CN have seen 155Mbps and 622Mbps pipes upgraded to 2.5 Gbps or 10Gbps pipes and with FTTC & G.FAST pushing the pipes out from exchanges and into street-side cabinets. These upgrades have pushed broadband over their copper network from up to 8Mbps through to 24Mbps to 80Mbps and now 330Mbps. Pushing these speeds out caused massive congestion issues, being upgraded as and when needed.

BT’s lack of fibre to the door and focus on copper-based products opened the market for many competitors, who have secured billions in funding and are installing a patchy network nationwide, offering speeds of up to 1Gbps and stealing market share.

BT are slowly coming round to the fact FTTP is needed and we’re now seeing rollouts happening in pockets nationwide. With the limit in speed and others providing faster services for around the same cost, it won’t be long before the incumbent falls. If BT is to succeed, it needs to expand its fibre to the door rollout and start copying the new start-ups and stem the exodous.



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