Introduction

 

In the last few years passive optical networks became the most needed access networks. They meet the increasing demand of wavelengths, and their passive construction does not require any upgrade after conversion into the next generation PON. Using fibers as the transmission medium, allow for Triple-Play services of very high quality. This type of situation hasled to mass production by active devices manufacturers.

 

There are many PON supporters and opponents. Some experts believe that when it comes to the topology the point-to-point outrival the PON because of the flexibility, scalability and economic. However, more people believe that passive optical networks, using point-to-multipoint architecture are next step in the evolution of access networks. They allow to tjoin a larger number of subscribers without laying additional fiber from the switching to the user.

 

Nowadays the dominant solution of passive optical networks is GPON technology, based on ITU-T G.984 standard. With higher bitrate, interoperability and transmission efficienty is better than older GEPON (IEEE 802.3ah standard), which price is not much cheaper than GPON.

 

As it turns out, GPON market is growing at a very high peace. Dell’Oro Group reported that GPON devices sales in 2002 increased by 34% in comparison to last year.

 

In Poland you can see dozens of GPON introductions. Thanks to EU grants (POIG 8.4. Last mail access), many operators see an opportunity to gain competitive advantage. Besides the possibility of obtaining grants, the rapid development of teleinformatic networks in last ten years generates significant growth of transmitted data. Multinational backbones supports enormous bitrates but development of teleinformatic networks caused a significant increase of the amount of transmitted data.. For years, the critical point is last mail connection, between end of WAN and LAN. Given bitrates obtained in this part of network are often inadequate to bitrate of both LAN and WAN what result is bottleneck effect. From the solution of this problem will depend the pace of teleinformatic services development for the end customer which is way it is now given a lot of attention.

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PON architecture

 

Main division each of access networks is: point-to-point (P2P) and point-to-multipoint (P2MP). xPON networks are consist of:

• OLT (Optical Line Termination) central device (distributing), which is e.g. controlling data transmission and customer access through MAC adresses.

• ONT (Optical Network Termination)  subscriber terminal. Ensure access to ISP services.

• ONU (Optical Network Unit) - end device. Difference between ONU and ONT is the placement od them in end point. ONU signal is splitting to customers, ONT is ending device in subscriber.
  

• ODN (Optical Distribution Network) is distribution network between OLT and ONU/ONT. Consist of passive elements: splitters etc.

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GPON standard

GPON using 3 wavelengths:

• 1310nm - upstream
• 1490nm - downstream
• 1550nm - CATV

Discussing standard allows to bitrates: 2,5 Gbit/s downlink and 1,25 Gbit/s uplink. GPON uses TMDA (Time Division Multiple Access) technology, which allows for access subscribers due to time slots. Technique responsible for bandwith allocation for subscriber to improve efficient of optical networks is DBA (Dynamic Bandwith Allocation). This algorithm besides the improvement of  wavelength productivity, allows to add more end users which  enable to generate grater profits by ISP’s.

 

More about GPON technology and samples solution can be found on: www.xpon.com.pl

 

 

Patryk Pobłocki