local area networks (LANs) in a city into a single larger network which may then also offer efficient connection to a wide area network. The term is also used to describe the interconnection of several LANs in a metropolitan area through the use of point-to-point connections between them.[1][2]
History
By 1999,
telephone exchanges were ill-designed to cope with the traffic spikes that LANs tended to produce.[4]
: 11
To interconnect local area networks more effectively, it was suggested that office buildings are connected using the single-mode optical fiber lines, which were by that time widely used in long-haul telephone trunks. Such dark fibre links were in some cases already installed on customer premises and telephone companies started to offer their dark fibre within their subscriber packages. Fibre optic metropolitan area networks were operated by telephone companies as private networks for their customers and did not necessarily have full integration with the public wide area network (WAN) through gateways.[4]: 12
Besides the larger companies that connected their offices across metropolitan areas, universities and research institutions also adopted dark fibre as their metropolitan area network backbone. In
mainframe computers that publicly funded universities and research institutions in the city housed. The BERCOM MAN project could progress at speed because the Deutsche Bundespost had already installed hundreds of miles of fibre optic cable in West Berlin. Like other metropolitan dark fibre networks at the time, the dark fibre network in West Berlin had a star topology with a hub somewhere in the city centre.[4]: 56 The backbone of the dedicated BERCOM MAN for universities and research institutions was an optical fibre double ring that used a high-speed slotted ring protocol developed by the GMD Research Centre for Innovative Computer Systems and Telephony. The BERCOM MAN backbone could thus support two times 280 Mbit/s data transfer.[4]
dense wavelength-division multiplexing (DWDM) provided another impetus for the development of metropolitan area networks in the 2000s. Long haul DWDM, with ranges from 0 to 3000+ km, had been developed so that companies that stored large amounts of data on different sites could exchange data or establish mirrors of their file server. With the use of DWDM on the existing fibre optic MANs of carriers, companies no longer needed to connect their LANs with a dedicated fibre optic link.[5]: 14 With DWDM companies could build dedicated MANs using the existing dark fibre network of a provider in a city. MANs thus became cheaper to build and maintain.[5]: 15 The DWDM platforms provided by dark fibre providers in cities allow for a single fibre pair to be divided into 32 wavelengths. One wavelength could support between 10 Mbit/s and 10 Gbit/s. Thus companies that paid for a MAN to connect different office sites within a city could increase the bandwidths of their MAN backbone as part of their subscription. DWDM platforms also alleviated the need for protocol conversion to connect LANs in a city, because any protocol and any traffic type could be transmitted using DWDM. Effectively it gave companies wishing to establish a MAN choice of protocol.[5]
The metro Ethernet rings that did not route IP traffic instead used one of the various proprietary
layer 2 switching can not operate if there is a loop in the network, the protocols to support L2 MAN rings all need to block redundant links and thus block part of the ring.[5]: 41 Capsuling protocols, such as Multiprotocol Label Switching (MPLS), were also deployed to address the drawbacks of operating L2 metro Ethernet rings.[5]
: 43
Metro Ethernet was effectively the extension of
Metro Ethernet Forum (MEF) in defining best practice and standards for metropolitan area networks thus also defined carrier Ethernet.[9] While the IEEE tried to standardise the emerging Ethernet-based proprietary protocols, industry forums such as the MEF filled the gap and in January 2013 launched a certification for network equipment that can be configured to meet Carrier Ethernet 2.0 specifications.[10]
In larger cities several local providers may have built a dark fibre MAN backbone. In London, the metro Ethernet rings of several providers make up the London MAN infrastructure. Like other MANs, the London MAN primarily serves the needs of its urban customers, who typically need a high number of connections with low bandwidth, a fast transit to other MAN providers, as well as high bandwidth access to national and international long-haul providers. Within the MAN of larger cities, metropolitan exchange points now play a vital role. The London Internet Exchange (LINX) had by 2005 built up several exchange points across the Greater London region.[13]
Cities that host one of the international Internet exchanges have become a preferred location for companies and
data centres. The Amsterdam Internet Exchange (AMS-IX) is the world's second-largest Internet exchange and has attracted companies to Amsterdam that are dependent on high-speed internet access. The Amsterdam metropolitan area network has benefited too from high-speed Internet access.[14]: 105 Similarly Frankfurt has become a magnet for data centres of international companies because it hosts the non-profit DE-CIX, the largest Internet exchange in the world.[14]: 116 The business model of the metro DE-CIX is to reduce the transit cost for local carriers by keeping data in the metropolitan area or region, while at the same time allowing long-haul low-latency peering globally with other major MANs.[15]
^802 IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture, IEEE Computer Society, 2002, p. 1, A MAN is optimized for a larger geographical area than is a LAN, ranging from several blocks of buildings to entire cities.
^"Quotes in 1999". Cafe au Lait Java News and Resources. Archived from the original on April 14, 2016. Retrieved December 25, 2022. Then one day, hardware was ridiculously cheap, software knew about the hardware, and you could actually plug a couple of machines together and they'd talk to each other. The real year of the LAN had quietly happened.
