So – what is GPON? We are supplying GPON technology to many operators and feel that many operators are buzzing about it, but sometimes it happen that facts are mixed and often there are some misunderstandings. In this article we will try to take a look on technology again and we will try to answer this question in structured way – What is GPON?
What is GPON? – One of PON Technologies
PON (Passive Optical Network) as a concept started somewhere around 1995. Simply talking – it is optical access network where between Operators Central Office and Customers Premises is no active equipment – that is why it is Passive.
As we can see in following picture – all active nodes used in Active Optical Network are exchanged to Passive Optical Splitters – with are simple physical devices:
The main benefit of PON Networks:
They are passive, no active devices between Customer and Operator premises, with need power supply, configuration, maintenance. It results in stability – PON equipment usually are 99.999% or 99.9999% available (around 5min downtime/year), Ethernet switching devices used on AON scenario – 99.961% (more than 3h downtime/year).
When concept about PON is clear, we may proceed to different technologies used to run PON network. Over the years, there were many different implementations of network protocols:
GPON is just one of PON Network Protocols, but currently it is dominating world market. Mass adaptation of PON started from 2004 by wide implementation of EPON (or GEPON) technology in Asia – Japan, China and Korea. GPON started in both, USA and European markets from 2008, when traditional incumbent operators started to upgrade their DSL based cooper access networks to Fiber To The Home/Building (FTTH/FTTB). Why GPON was their choice – at that moment, it was latest standardized PON technology with highest bandwidth and it has several advantages if compared to EPON. GPON from beginning has been designed as Point-to-Multipoint Access Technology and has special frame structure allowing implementing various types of services. EPON is adaptation of IEEE 802 Ethernet for use in Point-to-Multipoint scenario and has its weaknesses and limitations. In 2015 we can see following PON technology panorama calculated by global spending:
What is GPON? – What about new PON Technologies?
10G EPON, XG-PON1 are currently in beginning phase of mass-market adaptation. They are now adopted by Telco’s with has implemented EPON/GPON several years ago and need to increase bandwidth on existing PON passive network branches. Both technologies can co-exist with legacy EPON/GPON. As currently cost of 10G EPON, XG-PON1 network terminals are relatively high – they are used on very dense network segments or to provide VIP or Corporate customer services. TWDM-PON now has ITU standard and several vendors claim that they have technology, but it’s far from mainstream implementation – it is question of 3 to 5 years.
What is GPON? – Main Principles:
GPON network consists of two main parts – OLT (Optical Line Terminal) usually capable of servicing few 1000 of optical network customers and located at operator premises, passive optical network and ONT/ONU (Optical Network Terminal/Unit) home gateway. One GPON OLT port can service up to 128 ONT’s. OLT and ONT’s are connected by using single-mode fiber, where WDM technology is used to separate Uplink and Downlink communication. For Uplink is used 1310 nm wavelength and for Downlink 1490 nm wavelength. GPON port has by default 28 db (B+) with reach up to 20 km or 31 db (C+) with reach up to 40 km power budget.
Uplink data are transmitted using TDMA technology – meaning that each ONT has separate time-slot to send data to OLT. Downlink data are broadcast – each ONT receives all data with are sent to all ONT’s in same branch. All data in GPON are encrypted using AES 128 encryption.
In GPON network OLT identifies ONT by it’s ID. To each ONT is allocated one or more T-CON’s or Traffic Containers. T-CON is group of logical connections (GEM Ports) and usually in one T-CON is grouped one kind of traffic type. T-CON is used for QoS purposes on upstream direction. GEM Port (GPON Encapsulation Method) is virtual container used for various kind of traffic encapsulation and represents logical connection between ONT and OLT. By using this structure, operators can provide granular QoS and different services to different customers and physical ports of ONT devices.
Dynamic Bandwidth Allocation (DBA) is mechanism, where GPON system sets SLA for each ONU – maximum and minimum bandwidths and provides different priorities for different services to each ONU – voice, video and Data based on overall traffic load and actual condition of ONT.
OMCI (ONT Management Control Interface) is protocol used to provide management channel between OLT and ONT for ONT configuration. This protocol is standardized by ITU-T in order to facilitate vendor inter-operability, however many vendors using proprietary fields in OMCI protocol and in practical cases it’s hard to enshore smooth interoperability between different vendors OLT and ONT.
What is GPON? – Main Vendors:
Data Q1:2015 – Broadbandtrends.com
What is GPON? – Summary:
We hope that we managed to answer question “What is GPON?” and this article was helpful. In the end of the day we have our two main arguments, why we strongly encourage operators / ISP consider PON technology:
Stability – PON technologies is much more stable and requires much less maintenance. In PON networks is much less points of failure resulting in higher MTBF parameters, and this is often missed – Customer Satisfaction. All ISP’s know – customers are very hard to acquire and when acquired, they are relatively stable.
Future Prove – besides GPON there are next generation technologies, with allows to increase access network bandwidth in a moment. When business cases are calculated, this is usually forgotten. Lifetime period of PON systems are much longer if compared to Ethernet Switch networks. More on this – in some future articles.