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In a hierarchical
telecommunications network A telecommunications network is a group of nodes interconnected by telecommunications links that are used to exchange messages between the nodes. The links may use a variety of technologies based on the methodologies of circuit switching, mes ...
, the backhaul portion of the network comprises the intermediate links between the core network, or
backbone network A backbone or core network is a part of a computer network which interconnects networks, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same buildin ...
, and the small subnetworks at the ''edge'' of the network. The most common network type in which backhaul is implemented is a mobile network. A backhaul of a mobile network, also referred to as mobile-backhaul connects a
cell site A cell site, cell tower, or cellular base station is a cellular-enabled mobile device site where antennas and electronic communications equipment are placed (typically on a radio mast, tower, or other raised structure) to create a cell, or adj ...
towards the core network. The two main methods of mobile backhaul implementations are fiber-based backhaul and wireless point-to-point backhaul. Other methods, such as copper-based wireline, satellite communications and point-to-multipoint wireless technologies are being phased out as capacity and latency requirements become higher in 4G and 5G networks. In both the technical and commercial definitions, ''backhaul'' generally refers to the side of the network that communicates with the global Internet, paid for at wholesale commercial access rates to or at an Internet exchange point or other
core network A backbone or core network is a part of a computer network which interconnects networks, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same buildin ...
access location. Sometimes
middle mile Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek ( ...
networks exist between the customer's own
LAN Lan or LAN may also refer to: Science and technology * Local asymptotic normality, a fundamental property of regular models in statistics * Longitude of the ascending node, one of the orbital elements used to specify the orbit of an object in spa ...
and those exchanges. This can be a local WAN connection. Cell phones communicating with a single cell tower constitute a local subnetwork; the connection between the cell tower and the rest of the world begins with a backhaul link to the core of the
internet service provider An Internet service provider (ISP) is an organization that provides services for accessing, using, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, non-profit, or otherwise priva ...
's network (via a point of presence). A backhaul may include wired, fiber optic and wireless components. Wireless sections may include using
microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...
bands and mesh and
edge Edge or EDGE may refer to: Technology Computing * Edge computing, a network load-balancing system * Edge device, an entry point to a computer network * Adobe Edge, a graphical development application * Microsoft Edge, a web browser developed ...
network topologies that may use a high-capacity wireless channel to get packets to the microwave or fiber links.


Definition

Visualizing the entire hierarchical network as a human skeleton, the
core network A backbone or core network is a part of a computer network which interconnects networks, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same buildin ...
would represent the spine, the backhaul links would be the limbs, the edge networks would be the hands and feet, and the individual links within those edge networks would be the fingers and toes. Other examples include: *Connecting wireless
base station Base station (or base radio station) is – according to the International Telecommunication Union's (ITU) Radio Regulations (RR) – a "land station in the land mobile service." The term is used in the context of mobile telephony, wireless c ...
s to the corresponding base station controllers. *Connecting
DSLAM A digital subscriber line access multiplexer (DSLAM, often pronounced ''DEE-slam'') is a network device, often located in telephone exchanges, that connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital co ...
s to the nearest ATM or
Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1 ...
aggregation node. *Connecting a large company's site to a metro Ethernet network. *Connecting a
submarine communications cable A submarine communications cable is a cable laid on the sea bed between land-based stations to carry telecommunication signals across stretches of ocean and sea. The first submarine communications cables laid beginning in the 1850s carried tel ...
system landing point (which is usually in a remote location) with the main terrestrial telecommunications network of the country that the cable serves.


National broadband plans

A
telephone company A telephone company, also known as a telco, telephone service provider, or telecommunications operator, is a kind of communications service provider (CSP), more precisely a telecommunications service provider (TSP), that provides telecommunicat ...
is very often the internet service provider providing backhaul, although for academic research and education networks, large commercial networks or municipal networks, it is increasingly common to connect to public broadband backhaul. See national broadband plans from around the world, many of which were motivated by the perceived need to break the monopoly of incumbent commercial providers. The US plan for instance, specifies that all community anchor institutions should be connected by gigabit fiber optics before the end of 2020.


Available backhaul technologies

The choice of backhaul technology must take account of such parameters as capacity, cost, reach, and the need for such resources as frequency spectrum,
optical fiber An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass ( silica) or plastic to a diameter slightly thicker than that of a human hair Hair is a protein filament that grows ...
, wiring, or rights of way. Generally, backhaul solutions can largely be categorized into wired (
leased line A leased line is a private telecommunications circuit between two or more locations provided according to a commercial contract. It is sometimes also known as a private circuit, and as a data line in the UK. Typically, leased lines are used by ...
s or copper/fiber) or
wireless Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points without the use of an electrical conductor, optical fiber or other continuous guided medium for the transfer. The most ...
( point-to-point, point-to-multipoint over high-capacity radio links). Wired is usually a very expensive solution and often impossible to deploy in remote areas, hence making wireless a more suitable and/or a viable option. Multi-hop wireless architecture can overcome the hurdles of wired solutions to create efficient large coverage areas and with growing demand in
emerging markets An emerging market (or an emerging country or an emerging economy) is a market that has some characteristics of a developed market, but does not fully meet its standards. This includes markets that may become developed markets in the future or wer ...
where often cost is a major factor in deciding technologies, a wireless backhaul solution is able to offer 'carrier-grade' services, whereas this is not easily feasible with wired backhaul connectivity. Backhaul technologies include: * Free-space optical (FSO) *Point-to-point
microwave radio relay Microwave transmission is the transmission of information by electromagnetic waves with wavelengths in the microwave frequency range of 300MHz to 300GHz(1 m - 1 mm wavelength) of the electromagnetic spectrum. Microwave signals are normally lim ...
transmission (terrestrial or, in some cases, by satellite) * Point-to-multipoint microwave-access technologies, such as LMDS,
Wi-Fi Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio waves ...
,
WiMAX Worldwide Interoperability for Microwave Access (WiMAX) is a family of wireless broadband communication standards based on the IEEE 802.16 set of standards, which provide physical layer (PHY) and media access control (MAC) options. The WiMAX ...
, etc., can also function for backhauling purposes * DSL variants, such as
ADSL Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ...
,
VDSL Very high-speed digital subscriber line (VDSL) and very high-speed digital subscriber line 2 (VDSL2) are digital subscriber line (DSL) technologies providing data transmission faster than the earlier standards of asymmetric digital subscriber line ...
and
SHDSL Single-pair high-speed digital subscriber line (SHDSL) is a form of symmetric digital subscriber line (SDSL), a data communications technology for equal transmit and receive (i.e. symmetric) data rate over copper telephone lines, faster than a con ...
* PDH and SDH/SONET interfaces, such as (fractional) E1/T1, E3, T3, STM-1/OC-3, etc. *
Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1 ...
* VoIP telephony over dedicated and public IP networks Backhaul capacity can also be leased from another network operator, in which case that other network operator generally selects the technology being used, though this can be limited to fewer technologies if the requirement is very specific such as short-term links for emergency/disaster relief or for public events, where cost and time would be major factors and would immediately rule out wired solutions, unless pre-existing infrastructure was readily accessible or available.


Wireless vs. wireline backhaul

Wireless backhaul is easy to deploy, cost efficient and can provide high capacity connectivity (multiple Gbps (Gigabit per second) and even 10s of Gbps). Wireline fiber backhaul, on the other hand, can provide practically endless capacity, but requires investment in deploying fiber as well as in optical equipment. The abovementioned tradeoff is considered when planning. The type of backhaul for each site is determined taking into consideration the capacity requirement (current and future), deployment timeline, fiber availability and feasibility and budget constraints.


WiFi mesh networks for wireless backhaul

As data rates increase, the range of wireless network coverage is reduced, raising investment costs for building infrastructure with access points to cover service areas. Mesh networks are unique enablers that can reduce this cost due to their flexible architecture. With mesh networking, access points are connected wirelessly and exchange data frames with each other to forward to/from a gateway point. Since a mesh requires no costly cable constructions for its backhaul network, it reduces total investment cost. Mesh technology’s capabilities can boost extending coverage of service areas easily and flexibly. For further cost reduction, a large-scale high-capacity mesh is desirable. For instance, Kyushu University's Mimo-Mesh Project, based in Fukuoka City,
Fukuoka Prefecture is a prefecture of Japan located on the island of Kyūshū. Fukuoka Prefecture has a population of 5,109,323 (1 June 2019) and has a geographic area of 4,986 km2 (1,925 sq mi). Fukuoka Prefecture borders Saga Prefecture to the southwest, K ...
, Japan, has developed and put into use new technology for building high capacity mesh infrastructure. A key component is called IPT, intermittent periodic transmit, a proprietary packet-forwarding scheme that is designed to reduce radio interference in the forwarding path of mesh networks. In 2010, hundreds of wireless LAN access points incorporating the technology were installed in the commercial shopping and entertainment complex, Canal City Hakata, resulting in the successful operation of one of the world's largest indoor wireless multi-hop backhauls. That network uses a wireless multi-hop relay of up to 11 access points while delivering high bandwidth to end users. Actual throughput is double that of standard mesh network systems using conventional packet forwarding. Latency, as in all multi-hop relays, suffers, but not to the degree that it compromises
voice over IP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...
communications.


Open solutions: using many connections as a backhaul

Many common wireless mesh network hotspot solutions are supported in
open source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized so ...
router firmware including
DD-WRT DD-WRT is Linux-based firmware for wireless routers and access points. Originally designed for the Linksys WRT54G series, it now runs on a wide variety of models. DD-WRT is one of a handful of third-party firmware projects designed to replace ...
, OpenWRT and derivatives. The
IEEE 802.21 The IEEE 802.21 refers to Media Independent Handoff (MIH) and is an IEEE standard published in 2008. The standard supports algorithms enabling seamless handover between wired and wireless networks of the same type as well as handover between differe ...
standard specifies basic capabilities for such systems including
802.11u IEEE 802.11u-2011 is an amendment to the IEEE 802.11-2007 standard to add features that improve interworking with external networks. 802.11 is a family of IEEE technical standards for mobile communication devices such as laptop computers or multi- ...
unknown user authentication and 802.11s ad hoc wireless mesh networking support. Effectively these allow arbitrary wired net connections to be teamed or ganged into what appears to be a single backhaul – a "
virtual private cloud A virtual private cloud (VPC) is an on-demand configurable pool of shared resources allocated within a public cloud environment, providing a certain level of isolation between the different organizations (denoted as ''users'' hereafter) using t ...
". Proprietary networks from Meraki follow similar principles. The use of the term backhaul to describe this type of connectivity may be controversial technically. They invert the business definition, as it is the customer who is providing the connectivity to the open Internet while the vendor is providing authentication and management services.


Very long range (including submarine) networks

On very large scale long range networks, including transcontinental, submarine telecommunications cables are used. Sometimes these are laid alongside
HVDC A high-voltage direct current (HVDC) electric power transmission system (also called a power superhighway or an electrical superhighway) uses direct current (DC) for electric power transmission, in contrast with the more common alternating curre ...
cables on the same route. Several companies, including
Prysmian Prysmian S.p.A. is an Italian company with headquarters in Milan, specialising in the production of electrical cable for use in the energy and telecom sectors and for optical fibres. Prysmian is present in North America with 23 plants, 48 in Eu ...
, run both HVDC power cables and telecommunications cables as far as
FTTx Fiber to the ''x'' (FTTX; also spelled "fibre") or fiber in the loop is a generic term for any broadband network architecture using optical fiber to provide all or part of the local loop used for last mile telecommunications. As fiber optic ...
. This reflects the fact that telecommunications backhaul and long range high voltage electricity transmission have many technologies in common, and are almost identical in terms of route clearing, liability in outages, and other legal aspects.


See also

* Access network * Free Space Optics (FSO) * Last mile *
Middle mile Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek ( ...
*
Optical fiber An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass ( silica) or plastic to a diameter slightly thicker than that of a human hair Hair is a protein filament that grows ...
* Point-to-multipoint * Point-to-point * Return channel *
Wireless LAN A wireless LAN (WLAN) is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, or office buildi ...


References


Bibliography

* * Hilt, Attila (2022). ''Throughput Estimation of K-zone Gbps Radio Links Operating in the E-band'', Informacije MIDEM, Journal of Microelectronics, Electronic Components and Materials, Vol.52, No.1, pp.29-39, {{ISSN, 2232-6979, Slovenia, 2022. DOI: 10.33180/InfMIDEM2022.104.
PDF)
Telecommunications infrastructure Network architecture Wireless networking