Thursday, December 20, 2018


FIBER ACCESS NETWORKS TOPOLOGIES AND ARCHITECTURES: Fiber is already the dominant medium in metro and long-distance networks. Today, fiber is also succeeding in the access networks, matching user bandwidth demands with the cost decrease of available optical devices and technologies.

Today I will explain about the fiber access network topology one by one.The main role of fiber access networks is the connection of the end-users, along with the authentication, authorization and accounting of the connection. All over the world fiber access network increasing very rapidly for users bandwidth demands.
Role of fiber access network in our life


1.POINT-TO-POINT (P2P) Fiber Access Network
The most straightforward and simple way to deploy a fiber fixed access network is using a physical Point-to-Point (P2P) fiber access network architecture to connect the Access Node directly to each user. This architecture does not require a Remote Node.
Point-to-point fiber access network Architecture
Point-to-point fiber access network

Point-to-Point P2P fiber access network technologies can use either a dedicated single fiber, if both transmission directions are supported in a single fiber, or two dedicated fibers, if each direction goes in a separated fiber. Active network elements are not needed along the path.

Point-to-Point (P2P) fiber access network architectures are ideal in terms of isolation between passive infrastructure and active equipment, providing technical neutrality to any protocol and modulation format. However, physical P2P fiber access network architectures are not cost-efficient in most cases.

Point-to-Point P2P fiber access network technologies are mainly based in Ethernet switching technology, with a high density Ethernet ports installed in the Access Node. The used network termination at the user site is then realized with Ethernet media converters.

Point-to-Point P2P fiber access network architectures are considered appropriate for high-demanding customers, large business and demanding applications such as mobile backhaul. However the overall cost of running and managing P2P architectures is prohibitive for most of the cases in the residential market. Instead, shared-network approaches such as Point-to-Multipoint (P2MP) architectures provide cost savings and, thus, are the favored option for residential market by most operators worldwide.

Point-to-point Fiber Access Network Architecture

Point-to-Multipoint (P2MP) fiber access network architectures allow reducing the number of fibers in access networks. In the simplest form of P2MP fiber access network architecture, a single fiber is extended from the Access Node (AN) to reach the Remote Node (RN). There, the RN performs a 1:N function (where N represents a splitting ratio), fanning out N single fiber drops to the service end-points. N usually ranges between 4 and 64.

Point-to-Multipoint P2MP fiber access network architectures reduce the number of used fibers because a single feeder fiber is shared by N users. Moreover,Point-to-Multipoint  P2MP fiber access network architectures have a reduced footprint and power consumption compared to P2P.

Two P2MP architectures can be distinguished:

➤Active Optical Network (AON)
Active Optical Networks (AON) are operated with active aggregation equipment in the Remote Node. The location of the Remote Node device can be a street cabinet or the communication room at the end user building.
➤Passive Optical Network (PON)
Passive Optical Networks (PON) are operated with no active devices in any intermediate point. The elements at the Remote Node are less expensive and longer-lived optical passive components, such as optical splitters.
Active and passive optical access network
Active and passive optical access network

The main advantages of Passive Optical Networks (PON) versus Active Optical Networks (AON) are:

PON incurs in lower capital expenditures.
PON has a higher reliability because no electronic components are located in the harsh outside plant environment, which are prone to failure. PON do not need to be powered, except at the end points.
PON incurs lower operational expenditures, since there is no need to provide and monitor electrical power in the field or maintain backup batteries. Supply and maintenance of electrical power in outside plant is considered as one of the key operational costs in access networks.
PON don’t introduce bandwidth dependent technologies in the fiber path, substantially increasing the options for future upgrades.
PON provide rate and signal format transparency which becomes a sort of insurance policy that the access network could flexibly be upgraded as new technologies mature or new standards evolve.


PON consists of three main parts, generally known by the names-

OLT, for Optical Line Termination. Located at the Access Node (AN)
ONU/ONT, for Optical Network Unit/ Optical Network Terminal. Located at user’s
ODN, for Optical Distribution Network. It is the all-optical passive segment of the network connecting the OLT to ONU/ONTs.

The OLT and the ONUs/ONTs are the only active elements and are located at the serviceable endpoints of the PON.

The OLT provides the network operator’s interface to the aggregation/core network. The equipment behind the OLT can include switches, servers, routers, etc. The OLT also supports management functions and is capable of managing links to many ONU/ONTs.

The ONU/ONTs provide service interfaces to end users, converting signals from optical to electrical and delivering traffic. Several ONUs or ONTs are associated to a single OLT.

Generally, the PON remote unit is called ONU. However, when fibers terminate at the user´s premises, the remote unit is then called ONT, combining ONU and terminal equipment functionalities in the same device. In order to simplify the terminology, ONU and ONT will not be distinguished any longer in this guideline and ONT will be the single term to refer both PON end-user devices.

ONTs support their own links to the OLT. For economic reasons, ONTs don’t use top-performance optics and their internal components are capable of operating without any sophisticated temperature control. The OLT equipment can be somewhat more sophisticated, since it resides in a controlled environment, and its cost can be shared over many users served out of a single OLT port. As a result, a single ONT device is relatively inexpensive, while the OLT device tends to be more capable and thus more expensive.

Tree topology is the most common topology in fiber access networks. The ODN forms a tree structure with the OLT as the root of the tree and the ONTs as leaves of this tree. Remote Nodes (RN) are located in intermediate points between the OLT and the ONTs and contain passive optical aggregation devices (in practice optical splitters). In more complex architectures, two or even three Remote Nodes stages might be present in the path from the OLT to the ONTs.


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