Telco fixed access networks are “the last mile” to homes and commercial buildings. They play a key role in the delivery of OTT Video, and are undergoing big changes to support its growth. Telco fixed access networks were originally built in the 19th century to deliver telegraph services, evolving during the 20th century into telephone services. Today they provide vital telecommunications services supporting all aspects of a nation’s life including government, business, education and entertainment. Companies in this sector include the likes of British Telecom, Telecom Italia and AT&T. Over the last 30 years, the voice-first PSTN network has evolved to support data services over broadband, and today telco’s are deploying new data-first access networks.
In contrast to Telco networks are “Cable networks” – think Virgin Media, Comcast and UPC. These businesses were created to support video and data delivery. This article focuses on Telco fixed access networks which generally serve the vast majority of any country’s population with broadband and voice services. So, what are the technology evolutions or revolutions underway in telco access networks, and how do they support the growth of OTT Video?
Telco Access Network Technology
Today there are two primary types of Telco access network technology:
- “Legacy” that includes a level of copper network and includes solutions like ADSL (Asymmetric Digital Subscriber Line), VDSL (Very high bit-rate DSL) and FTTC (Fiber To The Cabinet)
- “Next-gen” that is fully fiber-based and is called FTTP (Fiber to The Premises) or FTTH (Fiber To The Home)
The future of OTT Video delivery needs next-gen access networks. These networks will deliver greater bandwidth and reliability. For legacy networks, the copper cable itself is the limiting factor for both performance metrics. Over recent decades there have been multiple upgrades to the electronics attached to the copper network which have increased bandwidth while routine network maintenance activities have maintained reliability, but copper has effectively reached its limit.
To go faster needs fiber. Next-gen FTTP networks are based on GPON (Gigabit Passive Optical Network) technology. A typical deployment for a residential property today supports a single connection with up to 2.4Gbps downstream. As the current deployable architecture for GPON can split a signal up to 32 ways this delivers a theoretical limit of 80Mbps per home, enough to support at least 10 simultaneous HD video streams.
The 2.4Gbps speed is only the starting point of GPON technologies that will be rolled out over the course of the 21st century. There are already field-proven deployments of 10Gbps fiber technologies called XG-PON, and 100Gbps GPON is now at the experimental phase.
These speed enhancements will be achieved by advances in the electronics attached to the fiber – the ONTs (optical network units) and OLTs (optical line terminals) – to utilize more of the fiber-optical network capacity over time. These electronic upgrades are expected to enable fiber networks to significantly increase bandwidth for many decades to come.
The Need For Speed?
An HD video typically streams to an IP-connected device at a maximum of 8Mbps. A UHD stream is up to 14Mbps. But what applications will utilize all the bandwidth being made available by >1Gbps bandwidth connections?
The use of live services such as video streaming, video conferencing and gaming is expected to expand dramatically over time. In an average household with multiple connected devices being used for work, school, gaming, entertainment and socializing it’s easy to imagine using over 100Mbps.
Non-live services are where the bandwidth is heavily consumed. Downloading files, such as video, photographs and documents will use all available bandwidth. Generally, a file download will squeeze a live stream and could potentially disrupt the live stream quality. This is one reason why OTT video operators are increasingly looking for CDN solutions that prioritize live video streaming over VOD downloads.
Looking further to the future, higher bandwidth will be needed for virtual reality and augmented reality experiences. How far these types of services will penetrate in the near future is unclear, but technology advances will create the option for these types of applications to become commonly used.
Combining these various use cases, and accounting for the growth in video file sizes (e.g. UHD formats are 2-4 times bigger than HD formats depending on compression) it is clear that the total quantity of content that will be downloaded and streamed to the home will increase over time, even if the number of users remains constant. However, with general population growth and increasing numbers of IP-connected devices, not only will content-per-person increase but so will the number of people using the internet. Cisco’s Annual Internet Report 2018-2023 forecasts that global internet users will increase from 3.9 billion in 2018 to 5.3 billion in 2023. And while more saturated regions like Western Europe are not growing as fast, 87% of the population is expected to be internet-connected by 2023, up from 82% in 2018, while the number of IP-connected devices per capita will grow from 5.6 to 9.4. All this by 2023, so what will the situation be in 2030?
At the same time, specifically for video streaming, we can also see that encoding technology is focused on delivering equal quality at lower bitrates. For example, HEVC encodes and streams at 66% of the bitrate of the older H.264 codec. This sort of change could reduce some of the bandwidth consumption but is likely to be offset by customers choosing to stream at higher bitrates because they can, and because they want to benefit from their 4K Smart TVs which are rapidly growing in volume deployed each year.
Access network operators see this large and general demand for increased bandwidth. In advanced markets, copper networks have reached their limits. FTTP is the choice for the future and today’s large-scale network upgrade investments will provide many decades of support for bandwidth-hungry applications to grow.
For video streaming services, reliability is as important as speed. After decades of reliable terrestrial and satellite video services, and with ever-growing pressure on internet capacity, we can be easily frustrated by poor quality OTT video (and videoconferencing). And the more serious network service outages, while relatively rare, can be very disruptive. FTTP has various features that provide higher levels of performance and reliability than legacy networks.
Most broadband networks today have sections of copper networks which were originally deployed for conducting voice signals. With FTTC, VDSL and ADSL, copper wires connect the street cabinet to the premises. Copper wires are susceptible to rain as they can erode and rust, affecting the quality of the electrical signal being carried over them. FTTP is much less weather-sensitive which is important if we are to rely on it consistently delivering 100s of Mbps of content and data to our homes.
Put simply, FTTP has an “on/off” performance status because it is based on transporting light, instead of electricity. This avoids the very challenging service degradation problems that affect the electricity-based delivery format of legacy networks and cause the various performance and intermittent fault problems each of us has experienced at some point.
In addition, while FTTP networks have fiber joints and splices like copper networks, the network architecture removes points of connectivity which are potential points of failure. For example, FTTP architectures do not include street cabinets, which will gradually become extinct. Instead, the fiber network runs underground from major exchange buildings to termination points near or at the premises. This network simplification directly improves reliability.
FTTP also removes points of intervention when compared to legacy networks. If a household changes broadband provider in a legacy network, a technical intervention is required at the street cabinet. This creates a risk of interrupting an existing service to another premise connected through the same cabinet. With FTTP, broadband provider changes will be controlled through the central exchange locations where ISP services meet the access network, dramatically reducing the level of intervention-caused network faults.
Overall, the FTTP architecture is more centralized than legacy networks. For example, BT Openreach’s FTTP deployment will require 1000 telephone exchanges, while the legacy network requires 5500. While FTTP is less-distributed, it is more quality-controllable.
Moving The Bottleneck
Historically, access networks have been a well-publicized bottleneck to performance because of contention on last-mile networks. But with FTTP, the dynamics will shift.
Figure 2: Relative capacities of E2E network elements over time. Note that in some countries, Access and Core Network relative capacities are reversed.
It is worth noting that FTTP capacity is still “oversold” based on estimates of normal and peak-time usage, much like airplane seats. The 2.4Gbps connection serving up to 32 homes will allow each home to have up to 80Mbps uncontested, but it is often sold at speeds of “up to” 1 Gbps. There could be peak moments when a home wants to have 1Gbps and cannot have it, but the expectation is that 80Mbps will work well in most situations for now.
But even if a house can receive 80Mbps uncontested, can this be sustained to the receiving devices? One new dynamic with FTTP is that it pushes today’s intermittent and performance-sensitive issues from the legacy access network to the home network, which is often not designed for high-performance broadband delivery, and to the on-premises equipment
It is well understood that WiFi speed reduces as you move further away from the home router. It is also true that most homes are not fitted with CAT5 or CAT6 ethernet networks, and in new homes builders will often install the FTTP termination equipment in a location that is out of sight, which is aesthetically pleasing but sub-optimal for wireless network performance. We then find ourselves trying to strengthen performance through in-home network extensions. So, while access network speeds expand dramatically with FTTP, can the home network can keep up? Because the answer is “probably not”, it is conceivable that professional AV deployments will become more commonplace in homes of the future to assure performance to the end devices.
Caching Deeper In The Network
Low latency OTT video delivery for Live and VOD relies on caching content close to the consumer. Generally, this means the place where the network speed will ensure low latency. Today, caches for OTT video are deployed in a small number of POPs in the ISP Core Networks. Network operators themselves deploy caches throughout their core networks to serve large populations over the last-mile access network without consuming unnecessary core network capacity.
ISPs deploy their own Edge sites in Exchange buildings. This is where an ISP network termination point (like the DSLAM and MSAN) will connect to the access network operator’s infrastructure. Not all countries have the same corporate and/or State ownership of core and access network operators, but network architecture designs are generally consistent.
In the Openreach example, it is conceivable in the future that the UK’s 1000 Exchange buildings will be the target for Edge Cache deployment, including the potential for deploying private caches for the largest content providers. ISPs will most likely decide these deployment plans based on business cases related to content provider bandwidth requirements and core network capacity expansion costs.
Openreach, like other access network operators, sees high-quality live OTT content delivery for the largest prime-time audiences as a major challenge for content providers in future.
Every country has a different situation to manage based on population and geography, but if we calculate that a large live OTT event today can attract 1 million viewers in a single country, and we calculate that by the end of the 2020s most households will watch their evening and prime-time TV on an OTT service, then the access network in the UK must be ready for 25x-30x the volume of traffic, at least based on today’s average bit-rates.
Access network upgrades to next-gen architectures are therefore a critical enabler for large audiences of the future that will expect reliable OTT video delivery, whatever the weather.
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