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Converged design for FTTH and Wireless Access networks

Virtualization and Disaggregation are few of the most widely discussed topics in technology world today. Emergence of open systems for both fixed line and wireless is disrupting entire network architecture. However, the success of new architecture is heavily dependent on underlying Optical fiber infrastructure. In this article, we have tried to decipher few important aspects of Converged Network design.

What is Converged network?

In earlier days, a typical communication network was divided between two distinct segments – Transport and Access. Transport network was characterized by high capacity optical fiber based communication supported by high-speed transmission technologies like DWDM and MPLS. The access technologies were meant for extending connectivity from Transport edge to the small to medium capacity end user. The popular access media were copper and wireless. The OFC medium was also used at very limited scale for Mobile Backhaul and Enterprise connectivity in access networks. The situation changed drastically during last decade after adoption of FTTH picked up in different geographies. However, the term “convergence” gained prominence after virtualization of Radio Access Technologies (VRAN) started gaining traction. Post virtualization, RAN connectivity will be disaggregated between multiple segments like Mid-Haul and Front-haul, collectively referred to as X-Haul. The medium for Mid-haul and Front-haul will be Optical fiber. In 5G era, Cell sites will be located very close to end users. Hence, in practical sense, the fiber path of both FTTH and X-Haul will fall on the same path leading to “Convergence” of Wireless and Fixed line access network.

What are the design considerations for Converged Access Network?

Highly densified network: In 5G era, large number of cell sites with small coverage footprint will be deployed. In the serving area of a single Macro sites, typically 20 to 50 small cell sites will be deployed depending upon traffic consideration. All these small cell sites will have to be connected on fiber. This will lead to highly densified FTTx network.

High fiber Count: FTTH network using Point to multi-Point (P2MP) technologies like GPON, EPON etc., used to have moderate consumption of fiber. The fiber consumption in P2MP tech is optimized using multi-stage splitting. However, in 5G era, every cell site will require multiple pairs of fiber drop. Let us assume that two antennae installed at every cell site located 50 meters apart. Along the street, every Km of road will require 40 pair of fiber only for Cell site backhaul. Also, along the street, there will be homes and shops that will need to be connected using FTTP / FTTH. Considering both the requirements combined together, typical requirement along the street may go beyond few hundreds of fiber strand. Hence any new network designed in urban area will need to deploy high fiber count cable.

Provision of large number of fiber tapping points: Future networks will require a lot of elements along the street, to be connected on fiber. In legacy designs of fiber access networks, chambers / cabinets for extending end point connectivity used to be deployed few hundred meters apart. However, in densified and converged fiber access network, provision of tapping fiber will be required every 50 – 100 meters. Though initial cost of providing so many tapping points at shorter intervals may look expensive, but it may prove beneficial in saving future capex. It will also help in connecting a new site rapidly giving competitive advantages.

Use of Specialized fiber and cable design: Traditional fiber and cable design was primarily meant for supporting long distance and intracity transport network only. Example of such legacy fiber design was governed by ITU G.652D standards. Such cable has very poor bend and tapping characteristics and hence not suitable for supporting next generations of converged access networks. For supporting converged and densified networks, specialized design with very good bend performance of fiber will be needed. One of the most popular recommended fiber specification for such networks is ITU 657 A2. Most of the leading operators across the globe has started using modern specification in Converged access design. This also helps in future proofing of the network and eliminates the need of highly skilled resources for deployment of FTTx networks.

Specialized Connectivity Solution: Optical connectors, Joint closures and cabinets are critical components of any converged FTTx network. Since Optical fiber carries light as signal, it is very important to have dust free, kink free, moisture proof, proper bending space, low loss splicing / connectorization etc. in outdoor environment. There have been standard cabinets, joint closures, fiber management system in wide deployment. However, increasing scale has made it important to design customized products based on constraints like space, permission, flexibility to operate, cost optimization etc.

Emergence of new network architecture has necessitated to opt for very different approach for designing fiber infrastructure. In Future, common fiber infrastructure is expected to support the requirements of different layers of the network for both fixed line and wireless. Hence, converged design approach is the key requirement while working on any future Fiber network design.

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