FTTX NETWORK ARCHITECTURES AND APPLICATIONS

FTTX  NETWORK ARCHITECTURES AND  APPLICATIONS: FTTX is a generic term used to describe several access networks architectures using optical fiber. The different flavors of FTTX depend on how close the fiber comes to the end user.

A fiber-based PON access network connects a large number of end users to an Access Node (AN). Main service points are:

➥Mobile network base stations.

➥Subscribers in SDUs (Single Dwelling Units) or MDUs (Multi Dwelling Units).

➥Larger buildings such as schools, hospitals, businesses and government.

Optical Fiber Network Architecture

FTTX NETWORK ARCHITECTURES

COPPER XDSL ARCHITECTURES

Direct replacement of the old copper pair with fiber is a huge investment, and thus the introduction of fiber in the access networks has been phased progressively in time to match user bandwidth demands with the cost decrease of available optical devices.

However, the existing copper infrastructure is unable to meet the future demand of bandwidth in both residential and business customers. These demands will only be met by the deepest penetration of optical fiber in access networks up to user’s premises.

The different flavors of FTTX depend on how close the fiber comes to the end user & terminology used for them.

FTTN – Fiber to the Node

Fiber is terminated in an Active Remote Node, called Multiservice Access Node (MSAN), usually housed in an outdoor cabinet. The access multiplexer housed there carries the aggregated traffic of the neighborhood. The Access Node is connected to the Remote Node via optical cable and then from the Remote Node to the end-user premises via existing distribution network based on copper infrastructure and VDSL technology.

FTTC – Fiber to the Curb / FTTdp – Fiber to the Distribution Point

This is very similar to FTTN, but the cabinet is closer to the user's premises, typically within 300 m. Connection to the users is based upon advanced copper based technologies, such as VDSL2 or VDSL2 Vectoring.

FTTB – Fiber to the Building

Fiber is terminated at the boundary of the building, such as the basement in a multi-dwelling unit. The connections between users and the building switch are not fiber but can be copper based and involve some form of transport suited to the medium available in the vertical.

FTTH – Fiber to the Home

Fiber reaches the user’s living. Each user is connected by a dedicated fiber to a port on the equipment in the Access Node (AN), or to the passive optical splitter in the Remote Node (RN) using a shared feeder and P2MP topology.

The development of progressive generations of ever more sophisticated signal processing xDSL technologies transported on copper pair, such as ADSL, VDSL, VDSL2 has allowed to get more bit rate from the last segment of copper pair. However those technologies force to shorten the cooper loop length.

To get interesting bit rates in those xDSL dialects, distances are quite modest, and progressively shorter, up to the point where the access line is built almost entirely of fiber. Those solutions also require interposing active remote equipment in the outside plant to make the optical-electrical conversion, which may be an inconvenience in terms of operational issues.

During the recent years, network operators are facing challenges concerning the strategy to update the access networks. While some have opted to upgrade to those aforementioned xDSL solutions, most see this as a temporary “fix” that will only delay the inevitable road to FTTH and, thus, prefer to skip that step to future-proof their networks with an all-fiber solution. While xDSL involve some cunning and interesting technology innovations, it hardly represents an adequate response to the near-future demands of access networks.

For that reason, Telecom operators has adopted FTTH architectures and GPON technology as the preferred broadband solution in access networks, in line with global trends to face the anticipated challenges in terms of bandwidth required for various services in a competitive market.

There are several reasons for claiming that all-fiber access networks (FTTH), once installed, are unlikely to require any re-engineering for decades:

➥Fiber’s enormous and scalable bandwidth.

➥Fiber’s low attenuation, which translates into rate-independent transmission over longer distances (tenths of Km), whereas attenuation in copper poses many serious problems even at spans lengths of 1 km.

➥Fiber’s low-power transmission which yields energy consumption savings. Optical transmission is considered green and environmental friendly.

➥Fiber’s passive nature. The absence of intermediate electronics reduces provisioning and repairing times compared with systems embodying electronics along the path-of-way.

➥Fiber’s transparency and protocol-insensitivity with respect to legacy or future traffic types. Thus, as new bit rates, formats, higher protocol levels, and services are introduced, no major changes are needed in the outside plant. Instead, protocol-sensitive electronics intervene in xDSL technologies.

➥Fiber’s improved capability to handle symmetric traffic compared with the high degree of capacity asymmetry dictated by xDSL technologies.

APPLICATIONS OF THE OPTICAL ACCESS

FIBER TO THE HOME (FTTH)

FTTH is the most ambitious option to provide highest broadband to residential homes. The growing bandwidth demand in the residential market is mainly driven by the evolution of video services. Linear TV, video on demand, and peer to peer will represent 90% of the global consumer traffic today. More video content will be provided over unicast platforms which will increase the traffic volume dramatically. Moreover, video bandwidths will also increase due to the evolution from today’s SDTV formats towards Super HD (4k), Ultra HD (8K), Hugh Dynamic Range, Virtual Reality and 3D formats.

The predominance of traditional video distribution services means that residential traffic will remain asymmetric. However, this may change if direct distribution is adopted, for instance, to offer live video streaming.

Moreover, there are some further trends driving the bandwidth demand such as the increasing number of connected devices in a fully integrated digital home, the rise of on-line gaming and the accessibility of a wide range of on-demand cloud services.

Bandwidth growth will be driven by future video formats availability, but the bandwidth demand might increase dramatically during the upcoming years. Some studies forecast a sustainable bandwidth between 200 Mbps to 500 Mbps by 2020, with peak rates above 1 Gbps for the residential market.

FIBER TO THE BUSINESS

Business services will also indeed benefit from the symmetric and high bit rate connectivity available in optical access networks. Connectivity services from a few hundreds of Mbps up to 10 Gbps may be available to fit industry needs from different sizes and requirements.

Other factors to consider in the business market are data security and integrity and strong Service Level Agreement (SLA).

FIBER TO THE MOBILE

Passive Optical Networks (PON) has the potential to increase the number of supported services, beyond provisioning broadband access to residential and business. Services that are currently delivered over different, and sometimes, dedicated networks could migrate on ubiquitous PON access systems, which are able to deliver high capacity. In fact, one of the main applications considered for upcoming PON architectures is to provide transport for wireless access networks, and beyond that, to build a real converged fixed-wireless network.

With the progressive introduction of LTE and LTE Advanced, also referred to as 4G radio access technology, wireless networks are evolving to next-generation packet architectures capable of supporting enhanced broadband connections. The introduction of 4G promises a whole new mobile broadband experience for private and business users, with short latency and data rates up to 1 Gbps. However, this advanced performance will only be experienced when supported by a reliable and high-capacity optical backhaul network and therefore, the deployment of a cost-efficient, reliable and ubiquitous backhaul transport for the Radio Access Network (RAN) is critical.

Microwave links has been so far the most used option, but the idea of using a shared, low-cost and ubiquitous PON becomes very attractive by offering large capacity, good synchronization capabilities, bandwidth flexibility, protected architectures, encryption transmission and scalability to grow.