Multimedia services through ftth

ONT
Fibre
Copper
Copper
Fibre
Fibre
NT
ONU
NT
ONU
OLT
FTTH
FTTB/C
FTTCab
UNI
SNI
Home
Network
Access Network
UNI: User Network Interface 
SNI: Service Node Interface 
ONT: Optical Network Terminal 
ONU: Optical Network Unit 
NT: Network Terminal 
OLT: Optical Line Terminal 
FFTB: Fiber to the Building 
FTTC: Fiber to the Curb 
Figure 1 
Different architectures that use fiber in the access network.

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Figure 1 shows different architectures that employ optical fiber in the local access part. 
FTTH has optical fiber all the way from the OLT at the local exchange end where we 
have SNI (Service Node Interface) to the user premises where we have ONT. In FTTB/C 
we don’t have fiber going directly to the user but it is terminated before that in the 
building or some other mid way where there is an ONU. The purpose of ONU is to have 
optical electrical interface for conversion of signals in the two domains. In FTTCab the 
ONU is in the street cabinet where this optical to electrical and electrical to optical 
conversion is carried out.
3. 
FTTH Architecture 
In FTTH fiber cable is laid directly from the local switching office to the customers. The 
interface equipment at central office is not only connected to PSTN (Public Switched 
Telephone Network) but also to ISP (Internet Service Provider), CATV (Cable TV) head-
end, digital video head-end or even to satellite or radio. Different signals gathered from 
different sources and services are combined together using WDM (Wavelength Division 
Multiplexing) techniques. The customer can obtain all the services like circuit switched 
telephony for voice, high-speed data, video broadcast etc over a single strand of fiber. 
The optical electrical converter at the user end provides different electrical interfaces like 
RJ11 jacks for telephony, RJ45 jacks for high-speed data and 75 ohm coax ports for 
CATV. 
Figure 2 
A typical layout of PON based FTTH architecture.
Figure 2 shows a typical FTTH layout. All the elements in the optical distribution are 
passive components. This includes single mode fiber optic cable, Passive optical 
splitters/couplers, connectors and splices. Active components are placed at the end points. 
The network is built up in point to multipoint tree and branch configuration. This should 
not be taken as some restriction as the layout architecture can be protected ring or bus 
architecture depending upon the needs and importance of the network.

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Passive optical networks employ no active components in the local access network 
whereas active optical networks employ the active components requiring power in the 
local access network. Active optical networks are not very commonly used in access 
networks, as active networks are difficult to maintain.
A number of topologies can be employed for PON where a central office is serving a 
number of subscribers. These include tree, bus and ring. There can be certain 
modifications to these topologies to increase the redundancy or protection. Some of the 
most commonly used topologies are shown in the figure 3.