Guide for FTTH Deployment Options

FTTH (Fiber To The Home) has been proven to be the shining star of the NGA (next generation access) family, and provides an excellent platform for high or ultra-high speed access technologies. Not only do fixed access networks benefit from FTTH solutions, but advanced wireless networks do as well especially in regard to increased backhaul capacity. This tutorial details FTTH deployment options available for the operators.

FTTH Architectures

There are two commonly used FTTH architectures for FTTH deployment—active and passive. Active architecture is also called as Point 2 Point (P2P), and passive optical network (PON) architecture is called Point to Multi Point (P2M). Choice of active or passive architectures for deployment depends on the type of services to be delivered, cost of the infrastructure, current infrastructure and future plans for migrating to the new technologies.

Active Technology

Active Ethernet also called Ethernet Switched Optical Network (ESON) or Point to Point (P2P) network architecture provides a dedicated fiber to the side from the central office exchange shown in the picture below. A P2P architecture is a very simple network design.

P2P architecture

Since the fiber is dedicated, operation, administration and maintenance of the content and trouble shooting become easy. Active FTTH solutions are implemented in many different ways, through both standard and proprietary methods. As the distances of the central node and remote sites are known, estimation of power budget, trouble shooting the faults in the network would be easier. Transmission in P2P configuration, is more secure, since all transmissions are physically separated by fiber. Only the end points will transmit and receive information, which is not mixed with that of any other customer.

Active Network Architecture and Components

Core switch, aggregation switch and optical network terminal (ONT) are main building blocks of P2P network. The core switch is a high capacity Ethernet switch that communicates to aggregator switches using standard GbE optical signals. The aggregator switch interfaces this data stream to multiple premises gateways called optical network terminals (ONT). The core switch interfaces multiple content and service providers over an MPLS-based metro or regional network to deliver data, video, and voice services to the users on the access network. Aggregator switch resides in both standard CO and in building entrance and in outside plant cabinets to meet the environmental needs of the network provider. The aggregator switch delivers traffic to the subscriber in accordance with the specific bandwidth requirements from 1 Mb/s to 100 Mb/s (symmetrical) per subscriber. A typical connectivity diagram of active technology in the access network is show in the following picture.

active architecture

PON Technology

PON is a point to multipoint (P2M) network. Each customer is connected into the optical network via a passive optical splitter, therefore, no active electronics in the distribution network and bandwidth is shared from the feeder to the drop. The advantage of FTTH PON is the fact that they use purely optical passive components that can withstand severe and demanding outside plant environment conditions without the need to consumer energy between in the central office exchange and the customer premises. The benefit to telecom operators is that low maintenance requirements of these passive optical components will significantly reduce of the cost of upgrades and operating expenditures. PON architecture uses unidirectional splitters. And it can reduce the cable cost as it enables sharing of each fiber by many users. Typical PON architecture is shown below.

PON architecture

PON Architecture and Components

The optical line terminal (OLT) is the main element of the network and it is usually placed in the local exchange and it’s the engine that drives FTTH system. Optical network terminals (ONTs) are deployed at customer’s premises. ONTs are connected to the OLT by means of optical fiber and no active elements are present in the link. A single ONT can serve as point of access for one (Fiber to the Home) or multiple (Fiber to the Block or Curb) customers and be deployed either at customer’s premises (Fiber to the Home or Block) or on the street in a cabinet (Fiber to the Curb).

Splitters in outside plant are important in signal distribution. The ITU G.983.1 standard recommends splitting the signal up to 32 users. In PON, the transceiver in the ONT is the physical connection between the customer premises and the central office OLT. The following picture shows the typical PON architecture connectivity.

Fs pon-network-architecture.jpg

Comparison Between Active and PON Architectures

The similarities and differences between active and PON architectures are as follows.

Parameter ACTIVE (Point to Point /P2P) PON (Point to Multi Point /P2M)
Ethernet Switched Optical Networks (ESONs) contain an active electronic element, a switch aggregator, between the central office (CO) or head-end switch and the Customer Premise Equipment (CPE).
Passive Optical Networks (PONs) do not contain any electronics between the CO switch and the CPE. In a PON, the active optoelectronics are situated on either ends of the passive network .
It is based on IEEE 802.3 standard The recent completion of the 10 Gigabit Ethernet standards (802.3ae) provides a seamless transition from 1 Gigabit to 10 Gigabits.
There are three main varieties of PON today. APON/BPON : ITU-T G.983, EPON : IEEE 802.3ah, GPON : ITU-T G.984
Networks Supported
No. of Homes Served
ESON systems can serve up to 48 homes, on each fiber run, and isolate information streams and faults to each subscriber. As more homes are served additional bandwidth is added and up to 50,000 homes can be served from a single core switch centrally located.
Conserves fiber resources. It uses a technique called power splitting and can only serve 32 homes from one fiber run with BPON and EPON. 64 homes with GPON technology.
Only the content destined for a particular CPE is delivered to that subscriber. Even if a rogue CPE device is installed in an active network, no content is delivered to it.
In a PON the entire downstream bandwidth is transmitted to the power splitter, and a portion of the optical power is delivered to each subscriber. Since bandwidth in a passive system is not dedicated to each subscriber, each user shares the total capacity of the system.
Content Distribution and backhaul bandwidth utilization
Video stream is launched from the core switch to the aggregation switch when a service is ordered. If multiple subscribers order the same service, it is electrically split at the aggregation switch and delivered to the second subscriber – and only to the second subscriber. Thus, backhaul bandwidth is more efficiently used and content is not delivered to unintended CPE devices.
All subscribers are exposed to all downstream content, however, the OLT communicates with valid ONT only by verifying the password. When a subscriber orders a video service of 5 Mbps, for example, a separate information stream is launched from the OLT to each subscriber. Therefore, 10 orders for the same content spawn 10 streams of 5 Mbps down to all subscribers.
Ethernet to the Subscriber platforms can be located up to 120 km from each other without any geographic restrictions, or variations in the platforms. Active Ethernet use standard-based Small Form Factor Pluggable (SFP) optical transceivers.
Two main factors restrict the total reach of PON deployments. The first is the total available optical power budget, which is a factor of the OLT laser port and the total loss budget, including the fiber feeder and splitters. Secondly, because ONUs share the optical feeder and OLT port, a sophisticated algorithm is required within all the devices to prevent more than one ONU from transmitting at the same time, which would cause traffic collisions rendering applications like video unusable. APON and EPON are limited to a maximum of 20 km between the OLT and the ONU.
ESONs can be initially provisioned to deliver 20 Mbps to each subscriber and later remotely upgraded to 100 Mbps.
PONs must physically restrict the number of subscribers on a power splitter to achieve higher throughputs. If the total network capacity is exhausted, then the electronics at each end (CO and CPE) must be upgraded to a newer technology.



Two FTTH deployment options are illustrated in this paper. And both the two have their own features. You can choose the one that best suits your network demands.



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