FOA Guide 


Topic: FTTH PON Types 

Table of Contents: The FOA Reference Guide To Fiber Optics




FTTH PON: Passive Optical Network
  A PON system utilizes a passive splitter that takes one input and splits it to "broadcast" signals downstream to many users. This reduces the cost of the system substantially by sharing one set of electronics and an expensive laser with up to 32 homes. Upstream, the passive splitter acts as a combiner to connect all users to the same shared PON port. An inexpensive laser is used for the home to send signals back to the FTTH system in the central office.

FTTX PON architecutre


Triple Play Systems
   Most FTTH systems are so-called "triple play" systems offering voice (telephone), video (TV) and data (Internet access.) To provide all three services over one fiber, signals are sent bidirectionally over a single fiber using several wavelengths of light.
 
   BPON, or broadband PON, was the most popular PON application in the beginning. BPON uses ATM as the protocol. ATM is widely used for telephone networks and the methods of transporting all data types (voice, Internet, video, etc.) are well known. BPON digital signals operate at ATM rates of 155, 622 and 1244 Mb/s.    

   Downstream digital signals from the CO through the splitter to the home are sent at 1490 nm. This signal carries both voice and data to the home. Video on the first systems used the same technology as CATV, an analog modulated signal, broadcast separately using a 1550 nm laser which may require a fiber amplifier to provide enough signal strength to overcome the loss of the optical splitter. Video could be upgraded to digital using IPTV, negating the need for the separate wavelength for video. Upstream digital signals for voice and data are sent back to the CO from the home using an inexpensive 1310 nm laser. WDM couplers separate the signals at both the home and the CO.

FTTH PON services from Central Office

BPON architecture with analog TV

   GPON, or gigabit-capable PON, uses an IP-based protocol and either ATM or GEM (GPON encapsulation method) encoding. Data rates of up to 2.5 Gb/s are specified and it is very flexible in what types of traffic it carries. GPON enables “triple play” (voice-data-video) and is the basis of most planned FTTP applications in the near future. In the diagram above, one merely drops the AM Video at the CO and carries digital video over the downstream digital link.

   EPON or Ethernet PON is based on the IEEE standard for Ethernet in the First Mile. It uses packet-based transmission at 1 Gb/s with 10 Gb/s under discussion. EPON is widely deployed in Asia. The system architecture is the same as GPON but data protocols are differenet.

PON System Specification Summary

BPON GPON EPON
Standard ITU-T G.983 ITU-T G.984 IEEE 802.3ah (1 Gb/s)
IEEE 802.3av (10Gb/s)
Downstream Bitrate 155, 622 Mb/s, 1.2 Gb/s 155, 622 Mb/s, 1.2, 2.5 Gb/s 1.25 Gb/s, 10.3 Gb/s
Upstream Bitrate 155, 622 Mb/s 155, 622 Mb/s, 1.2, 2.5 Gb/s 1.25 Gb/s, 1.25 or 10.3 Gb/s
Downstream Wavelength 1490, 1550 1490 1490, 1550
Upstream Wavelength 1310 1310 1310
Protocol ATM Ethernet over ATM/IP or TDM Ethernet
Video RF at 1550 or IP at 1490 RF at 1550 or IP at 1490 IP Video
Max PON Splits 32 64 16
Transmitter Power*
OLT: ~0 to +6 dBm, ONT: ~ -4 to +2 dBm

Power Budget*
~13dB (min) to 28dB (max) w/32 split ~13dB (min) to 28dB (max) w/32 split

Coverage <20 km <60 km <20 km
  * There are several versions of each type that vary so these are typical ranges.

RFOG: CATV's FTTH
CATV operators were the first broadband providers using a HFC (hybrid fiber coax) system with cable modems using RF signals. Today, some CATV operators see a need for a system to provide fiber to the home, which has lead to the development of RFOG (RF over Glass.) CATV standards have looked at PON architectures and the SCTE has proposed a standard for deploying a broadcast architecture of analog signals similar to PONs called RFoG for RF (radio frequency - i.e. FM) over Glass. RFOG is basically nothing more than an all-fiber HFC/cable modem system built with less expensive components now available thanks to the volume pricing of components used in FTTH. It’s designed to operate over a standard telco PON (passive optical network) fiber architecture with short fiber lengths and including the losses of a FTTH PON splitter.

RFOG

There is one interesting aspect of this approach. Now telcos and CATV companies can deliver the same services over the same cable plant using totally different technologies. But that means that office or apartment building owners, developers or even whole towns that might be considering installing FTTH infrastructure themselves and leasing the fiber to a service provider can have a choice of service providers. One cable network can support either CATV or telco systems – or even someone else for that matter. That opens up a big market for private fiber optic systems.

WDM and PON
Obviously, PON networks use WDM (wavelength-division multiplexing) with different wavelengths upstream and downstream. But the PON architecture can easily support more wavelengths, allowing greater bandwidth to the user but allocating one wavelength to a user or a group of users or greater security by having each user have their own wavelength. WDM PON architectures are being developed by many companies but no standards exist for them yet.

Other Uses For PONs
PONs offer low cost connectivity for a large number of users with high security and relatively low management needs. Some PON suppliers have been promoting PONs as an alternative to LANs (Local Area Networks), which are especially attractive to organizations with large numbers of users. Passive Optical LANs are claimed to be less expensive than traditional copper cabling for LANs but offer virtually unlimited future expansion. See Premises/Networks for more information on POLs.

PON Upgrades - Speed, Split & Distance
As is common with all communications networks, work on upgradeing network capability and speed starts as soon as a network is introduced and PONs are no exception. GPON has been the most widely used PON scheme for both FTTx netowrks and passive optical LANs (OLANs) and GPON has been upgraded to several versions with higher transmission speeds and higher power budgets to allow greater distance, higher split capability, or both.
The assumption is that a fiber network has a lifetime of up to 40 years, so upgrades to GPON have assumed that they will use the same passive optical network architecture and fiber type (G.652 singlemode.) Furthermore, upgrades have been designed around coexistence with current GPON networks. By utilizing different wavelengths, it is possible to have these newer, faster networks sharing the same passive optical network as the original GPON system, allowing offering higher speeds to users while continuing to serve current users without disruption. Some commercial users can take advantage of higher speeds while typical consumers are well served by GPON. One of the big advantages of the PON upgrade standards is the ability to overlay networks. Thus a city could operate one regular GPON network for consumer FTTH use and have another, faster network operating on the same cable plant independently, offering a higher level of service and security.

Upgrade PON System Specification Summary

NG-PON2 XG-PON XGS-PON
Standard ITU-T G.989 ITU-T G.987 ITU-T G.9807
Downstream/Upstream Bitrate
10/2.5, 10/10, 2.5/2.5 Gb/s 10/2.5, 10/10 Gb/s 10/10 Gb/s
Downstream Wavelength ~1596-1603 nm ~1575-1580 Either same as GPON if no current GPON or XG-PON for overlay
Upstream Wavelength ~1524-1544 ~1260-1280 Either same as GPON if no current GPON or XG-PON for overlay
Max PON Splits 64,128, 256 64,128, 256 64, 128, 256+
Power Budget*
14-29 dB (min - max) up to
20-35 dB
(min - max) in 4 versions with up to 15 dB differential optical path loss
14-29 dB (min - max) up to
20-35 dB
(min - max) in 4 versions with up to 20 dB differential optical path loss
13-28 dB (min - max) up to
20-35 dB
(min - max) in 6 versions with up to 20 or 40 dB differential optical path loss in 2 versions
Coverage 20 and 40 km versions  60 km 60 km

Technical Information on FTTX  From The FOA Online Reference Guide
FTTH  
FTTH ArchitecturesMDUs (Multiple Dwelling Units)  
FTTH PON Protocols 
FTTH Installation 
Customer Premises Installation  
Testing FTTH Networks  
FTTx Online Tutorial
Here's links for more information on FTTx

Case Studies: Do-It-Yourself FTTH  

Training & Certification
Fiber U Online FTTx Self Study Program (free)
FOA Certification Overview
FOA FTTx Certification Requirements
FOA-Approved Training Programs


 Table of Contents: The FOA Reference Guide To Fiber Optics





 


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