What is Backhaul? Wired vs Wireless, Fiber vs Ethernet

Backhaul transport provides a high-capacity bridge between wireless cell towers and wired fiber-optic infrastructure. This backhaul link is created through a combination of wireless microwave connections and wired dark fiber and Ethernet circuits.

Backhaul is the transport of voice, video, and data traffic, originating from a wireless carrier’s mobile base station, or cell tower, to its mobile switching center (MSC), or other central exchange point where the traffic is then switched onto a wireline telecommunications network.

Dgtl Infra provides an in-depth overview of backhaul, including its meaning, role in the broader telecommunications network, and differentiates between wired (dark fiber, Ethernet, and copper) and wireless (microwave) backhaul. Additionally, we outline the important demand drivers of backhaul, as well as identify the providers and customers of backhaul. Finally, Dgtl Infra answers critical questions including What is Backhauling?, What is the Difference Between Backhaul and Backbone?, and What is Wi-Fi Backhaul?

What is Backhaul?

Backhaul is the transport of voice, video, and data traffic, originating from a wireless carrier’s mobile base station, or cell tower, to its mobile switching center (MSC), or other central exchange point where the traffic is then switched onto a wireline telecommunications network. Wireless carriers, such as AT&T, Verizon, and T-Mobile, use the backhaul segment of wireless networks to transmit traffic towards their core network.

Backhaul Transport Methods

As shown below, the three primary transport methods to backhaul voice, video, and data traffic are optical fiber, microwave (via wireless spectrum), and legacy copper connections. Network connections utilizing fiber and copper are forms of wired backhaul, while microwave connections are a method of wireless backhaul.

These connections transport voice, video, and data traffic to a mobile switching center (MSC), which is a building where wireless carriers house their Internet routers and voice switching equipment.

Fiber connections are utilized for backhaul when economic, particularly in densely populated urban and suburban areas. While microwave connections are largely used to extend coverage in rural, remote, and difficult to reach areas (e.g., ski resorts, tops of mountains, and islands), where fiber deployments are cost prohibitive.

In developed markets, like the United States and UK, the majority of cell towers are connected by fiber networks. While in emerging markets, such as Brazil and India, the prevalence of copper connections for backhaul remains much higher.

Role of Backhaul in Network Architecture

As highlighted below, backhaul comprises the Transport network, that connects the Tower / Access Point (mobile base station), which is part of the Radio Access Network (RAN), to the Core Network, where most computing resources are located.

Backhaul Network Diagram

Cell towers are typically connected by a ring of fiber-optic cable (instead of a straight line) where several towers are looped together to hubs. This network architecture ensures redundancy, meaning that if one fiber-optic network is disrupted, then there is another network to seamlessly take its place, ensuring that customers will not be impacted.

From these rings, fiber-optic cable is extended to connect directly to the cell towers, which is often referred to as Fiber-to-the-Tower (FTTT). This is where laterals or spurs are built to connect cell towers to the wider terrestrial network via fiber-optic connections.

Why Do We Need Backhaul?

Backhaul transport bridges the distance between wireless cell towers and fixed line fiber-optic infrastructure. Below this concept is illustrated through a typical mobile call sequence.

Cellular devices transmit their signals wirelessly, via radio wave spectrum, to an antenna which resides on top of a cell tower. Through the cell tower’s base station, spectrum radio waves are translated into backhaul (#4) and the signal travels via a backhaul method (e.g., fiber) to market-level aggregation points (#5). Traffic is then aggregated and sent to the mobile core network.

Core networks are usually situated in central office locations of the wireless carrier and are located at a significant distance from the base station. Finally, the call signal converts from backhaul to spectrum at another base station (#8) and utilizes another cell tower to reach a different user’s device.

What is Wired Backhaul? (Fiber and Copper)

Wired backhaul transports the vast majority of backhaul traffic in the United States, primarily over fiber-optic networks (i.e., 90%+), but also legacy copper-based T-1 circuits. Fiber-optic networks are superior to copper in terms of speed, latency, and capacity, for the transport of voice, video, and data traffic.

Fiber Backhaul

Fiber backhaul services provide wireless carriers with a wired solution for their increasing traffic and, as a result, capacity demands, while delivering increased availability and reliability. Within wired backhaul, two primary fiber backhaul product offerings exist:

1. Dark fiber infrastructure leases, which are commonly referred to as fiber-to-the-tower (FTTT)
2. Lit (or enterprise) fiber services, which specifically utilize Ethernet circuits, and can be thought of as bandwidth-to-the-tower

Fiber Connects to Base Station / Radio Access Network (RAN) Equipment

Dark fiber provides dedicated high bandwidth, fixed network capacity but does not provide any communications services across the fiber. While lit (or enterprise) fiber is where a service provider “lights” the fiber and enables connectivity for the customer.

READ MORE: Dark Fiber and Enterprise Fiber Connect The Global Network

Historically, fiber-based backhaul has been delivered to wireless carriers through lit services, with the most widely used standard currently being high-bandwidth Ethernet circuits. However, wireless carriers are increasingly leasing dark fiber for backhaul purposes, rather than utilizing Ethernet circuits.

To this end, instead of purchasing progressively more bandwidth via Ethernet circuits as data traffic demand increases, wireless carriers are able to lease a dark fiber connection to the tower. In turn, these wireless carriers can then “light” and turn up as much bandwidth as they need.

What is Dark Fiber Backhaul?

Dark fiber backhaul is infrastructure for wireless carriers, allowing them to create their own services, control their own network, and deliver the performance levels for their unique needs. Specifically, dark fiber backhaul is sold through an indefeasible right of use (IRU) lease to a wireless carrier for newly laid fiber between the wireless carrier’s mobile switching center (MSC) and cell tower.

For example, dark fiber is leased in dedicated fiber pairs, usually consisting of 2 to 12 total fibers, to wireless carriers who “light” the fiber using their own optronics.

What is Ethernet Backhaul?

Ethernet backhaul is a fiber-based transport service which enables wireless carriers to gain the “last-mile” of connectivity to increase the reach of their network. Particularly, Ethernet circuits for backhaul are sold with high capacity bandwidth and are fully managed by network service providers.

For example, at present, bandwidth to lit cell towers generally ranges from speeds of 300 megabits per second (Mbps) to 1 gigabit per second (Gbps). At the same time, wireless carriers have ongoing capacity upgrades to bring 10 Gbps service to their cell towers.

In the future, wireless carriers will require further upgrades, to 25 Gbps and, subsequently, 100 Gbps, to support their 5G networks. To this end, Verizon expects backhaul requirements to increase by 10x current levels over the next few years.

Fiber-to-the-Small Cell (FTTS)

Dark fiber backhaul is necessary for the deployment of small cells and distributed antenna systems (DAS) in urban centers, which is often referred to as Fiber-to-the-Small Cell (FTTS) or Fiber-to-the-Cell (FTTC). Notably, the majority of the cost in deploying small cells relates to fiber and the construction of that fiber to the small cell.

READ MORE: What Are Small Cells and Distributed Antenna Systems (DAS)?

Using a C-RAN (cloud-Radio Access Network) architecture, wireless carriers are deploying small cells to supplement their cell towers for coverage and capacity. As shown below, high strand count dark fiber deployments are critical because every small cell requires two strands of dark fiber, one for backhaul and one for fronthaul.

C-RAN Architecture

What is Fronthaul?

In C-RAN architecture, fronthaul refers to the transmission of traffic, via dark fiber, from the centralized baseband unit (BBU) at a cell tower, out to a small cell, also known as a remote radio head (RRH). Fronthaul allows wireless carriers to use these detached baseband and radio units, avoiding the need to deploy and manage full-featured base stations or cells. In so doing, wireless carriers can reduce their network’s total cost of ownership.

Ultimately, the small cell fronthaul network is connected to mobile switching centers (MSCs) on the wireless carrier’s backhaul network.

What is Wireless Backhaul? (Microwave via Wireless Spectrum)

Wireless backhaul, also known as fixed wireless backhaul, utilizes microwave connections, via wireless spectrum, to transport voice, video, and data traffic. As highlighted below, on a cell tower, the wireless carrier owns a microwave dish for the purposes of backhaul. This microwave dish is a specific type of antenna, which is used in point-to-point data communications.

Microwave Connections on a Cell Tower

Microwave backhaul focuses on serving cell towers in rural, remote, and difficult to reach areas, which have lesser bandwidth needs. This is because microwave technology does not provide sufficient capacity for data traffic needs of densely populated urban and suburban areas.

At the same time, microwave backhaul serves these rural and remote areas more economically than the alternative, fiber, which has a much higher deployment cost. Therefore, these less populated areas can be served with less capital-intensive and less bandwidth-capable microwave solutions, at a lower total cost.

Spectrum – Frequencies Used for Wireless Backhaul

Wireless backhaul utilizes licensed wireless spectrum, particularly millimeter wave (mmWave) bands, to transport voice, video, and data traffic. For example, wireless spectrum in the 24 GHz and 39 GHz frequency bands are used in the United States for backhaul.

Demand Drivers of Backhaul

Demand for backhaul services is coming from wireless carriers seeking high-capacity connections, driven primarily by the nationwide roll-out of 5G, the continued rise in mobile video and data usage, and the geographic coverage and network capacity expansions of wireless carriers.

What is Backhaul for 5G?

For 5G wireless networks, fiber backhaul is replacing much of the microwave and legacy copper connections (used in 4G networks) in order to facilitate improvements to latency, speed, density, capacity, and costs.

• Latency: low-latency applications which require <10 milliseconds of one-way latency (<20 milliseconds of roundtrip latency)
• Speed: multi-gigabit per second speeds which can be realized with new 5G-enabled wireless devices and unlimited data offerings
• Density: ability to support more connected devices per square mile of network, which is important for the Internet of Things (IoT)
• Capacity: increases in network throughput, which is the amount of data that travels through a cell tower
• Costs: operating expense and capital expenditure savings of 15%+ from shared backhaul transport

Additionally, fiber backhaul is enabling 5G because new, high-capacity fiber is being built – with higher strand counts – which can support greater network demands. In turn, fiber backhaul can facilitate new architectures like software-defined networking (SDN) and network functions virtualization (NFV).

Providers of Backhaul

Providers of backhaul services include incumbent local exchange carriers (ILECs) & competitive local exchange carriers (CLECs), cable multiple system operators (MSOs), fiber service providers, and satellite service providers. Examples of these backhaul providers include:

• ILECs & CLECs: Frontier Communications, Lumen Technologies, and Windstream. Additionally, wireless carriers like AT&T and Verizon offer their fiber to third-parties for backhaul purposes
• Cable Multiple System Operators (MSOs): Cox Communications, Charter Communications, and Comcast
• Fiber Service Providers: Zayo, Crown Castle, Uniti Group, Segra (owned by Cox Communications), Everstream, Fatbeam, FirstLight, Consolidated Communications, BAI Communications (Mobilitie), Conterra Networks, ExteNet Systems, Lightpath (owned by Altice USA and Morgan Stanley), Astound Broadband
• Satellite Service Providers: Intelsat, SES, Eutelsat, OneWeb, and potentially Starlink (SpaceX) provide higher latency mobile backhaul services, particularly for rural and remote locations

Market Structure

The fiber backhaul market is extremely competitive in urban areas. For example, there are at least 7 fiber providers in each of Boston, Denver, and Los Angeles. While there are at least 10 fiber providers in each of New York City and Washington, D.C.

In turn, backhaul pricing is competitive and based on the quantity of dark fiber or lit bandwidth consumed and the number of locations served. As a general rule, backhaul becomes relatively less expensive, on price per bit basis, at higher bandwidths. Also, dark fiber leases generate lower monthly recurring revenue (MRR) than lit services, albeit dark fiber leases have a longer term.

As an example, Ethernet backhaul circuits could be priced in the range of $500 to $1,000 per month.

Backhaul contract terms vary based on the type of product being sold:

1. Dark Fiber: indefeasible right of use (IRU) leases normally range between 10 years and 20 years
2. Lit (or Enterprise) Fiber: Ethernet backhaul service contracts typically have a term of 5 years, but may vary in term from 18 months to 7 years

Customers of Backhaul

Customers of backhaul services include wireless carriers, fiber service providers, and government entities. Examples of these backhaul customers include:

• Wireless Carriers: AT&T, Verizon, T-Mobile, and DISH Network are anchor tenants for backhaul networks. At the same time, Verizon is an example of a wireless carrier that has insourced significant portions of its own backhaul requirements in certain geographic regions
• Fiber Service Providers: wholesale customers for transport services. Positioned as a cost-effective alternative to deploying fiber, for reaching towers that are either cost-prohibitive or difficult to reach with fiber
• Government Entities: first responder networks, municipal (school, hospital, local government) networks, commercial mobile networks

What is Backhauling?

Backhauling is the act of transporting voice, video, and data traffic, originating from a wireless carrier’s mobile base station, or cell tower, to its mobile switching center (MSC), or other central exchange point where the traffic is then switched onto a wireline telecommunications network.

What is the Difference Between Backhaul and Backbone?

The backbone network, also known as the core network, is a major fiber-optic network that interconnects smaller intermediate networks, including regional and metropolitan networks. Whereas the backhaul portion comprises the intermediate links that connect the backbone (core) network and the subnetworks, including a wireless carrier’s mobile base station, or cell tower, which is part of the Radio Access Network (RAN).

Core and Radio Access Network Architecture

What is Wi-Fi Backhaul?

Wi-Fi backhaul supports small cells at the edge of a wireless carrier’s network by placing a small cell (e.g., femtocell) in the consumer’s home to support both in- and out-of-home wireless connectivity services.

READ MORE: Small Cells – Microcell, Picocell and Femtocell Comparison

In turn, Wi-Fi backhaul provides an alternate form of connectivity for others, outside of the home, enabling wireless service to be provided in areas outside of a wireless carrier’s coverage area. This is implemented by utilizing the wired, Ethernet backhaul through the consumer’s gateway device, rather than a cell tower connection.

These remotely deployable access points provide cellular connectivity services at the network edge in combination with transport functions. As a result, Wi-Fi backhaul allows wireless carriers to more cost-effectively densify their networks while simultaneously improving coverage and capacity. Ultimately, Wi-Fi backhaul is a solution in areas where wired dark fiber or microwave connections are not available or are cost-prohibitive.