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FTTH(Fibre to the Home) basic tutorial

The FTTH tutorial covers basics of FTTH (fibre to the home) configurations and architectures viz. Active Optical Network(AON) and Passive Optical Network(PON). It covers PON standards EPON and GPON etc.

Earlier telecommunication networks were using optic fibre cables for connectivity between exchanges across sea. This has been replaced with all fibre network. This concept provides connectivity between user premises and the service provider using fibre optic. It has become more popular because of higher bandwidth and cheap cost. Moreover it is reliable and secure way of communication compare to wireless networks.

Fibre optic networks have been evolved very quickly and service providers are deploying different fibre configurations based on different applications. It is designed as FTTx. Here 'x' stands for final terminating point on the user side. 'x' can be Home or Premise or Building, Curb or Node. Based on this there are different terminologies of fibre optic deployment configurations. They are FTTH (Fibre to the Home), FTTP (Fibre to the Premise), FTTB(Fibre to the Building) FTTN(Fibre to the Node) and FTTC (Fibre to the Curb).

Following diagram depicts FTTH configuration.

Fibre Access Network Configurations

FTTH

As shown in the figure-1, there are two basic elements in the fibre optical network viz. OLT and ONU. OLT(Optical Line Terminal) is located at the telecom service provider side. ONU(Optical Network Unit) is located at the user premises. In this FTTH configuration modem is used at the user premises which converts optical signal to the electrical signal and vice versa. User computer is connected with the network using ethernet card.

FTTH Architectures

The major deployment consideration for telecom service provider is to decide on FTTH architecture. There are two categories of architectures. They are active optical network(AON) and passive optical network(PON). These AON and PON have been explained below.

AON vs PON

Active Optical Network

AON is a point to point FTTH architecture. This type uses active devices and connects OLT (Optical Line Terminal) placed at central office with ONT (Optical Network Terminal) placed at user premises using dedicated cable. Distance can be about 80 Km and the fibre cable provides full bi-directional communication. Figure-2 depicts typical active star ethernet (ASE) architecture which is a point to point architecture. This ASE architecture reduces cost due to sharing of the fibre cable.


Passive Optical Network

PON is a point to multipoint FTTH architecture. This configuration is used for various applications. It includes voice, video, data etc. This configuration uses optical splitter to connect OLT located at service provider side with multiple ONUs located at user premises. Optical splitters are available in different configurations viz. 1:4, 1:8, 1:16, 1:32, 1:64 etc. As the name suggests this architecture uses all the passive components between OLT and ONUs. No electronic or electrical active components are used. There are two benefits to this type of architecture; easy maintanance and lower cost. Typical distance between OLT and ONU is about 35Km.

As shown in the figure-3, transmission from user premises to service provider is referred as uplink and from service provider to user premises is referred as downlink. In the uplink TDMA is used and in the downlink TDM is used. TDMA stands for Time Division Multiple Access and TDM stands for Time Division Multiplexing.

PON standards

There are different standards which are evolving under PON based on ethernet technology advancement. They are EPON(Ethernet PON) and GPON(Gigabit Ethernet PON).

Specifications Basic PON(BPON) EPON GPON
Standard FSAN, ITU-T SG25, G-983 IEEE 802.3ah FSAN & ITU-T SG15, G984
Downstream wavelength 1490nm, 1550nm 1490nm 1490nm,1550nm
Download Speed 622Mbps 1.25Gbps 2.5Gbps
Upstream wavelength 1310nm 1310nm 1310nm
Upload speed 155.52Mbps 1.25Gbps 2.5Gbps
L2 protocol ATM Ethernet ATM, Ethernet, TDM over GEM
Distance between OLT and ONU 20Km 10Km, 20Km 20Km, upto max.60Km logically
Split ratio 1:16, 1:32, 1:64 1:16, 1:32 1:16, 1:32, 1:64
Security in the downlink direction AES Not specified yet AES
FEC technique Not provided Available Available
Protection switching Supports Does not support Supports

RELATED LINKS

SONET versus SDH
What is PDMA?
What is WDM?
SONET SDH tutorial
DWDM system basics
Fibre optic communication
Types of WDM
PDH versus SDH


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