Using Overlay Networks
Introduction
This application note will outline the technology and applications for PON overlay Networks.
Document Number
ENG-10676
Applies To
This applies to all Tellabs OLTs. XGS-PON is only a feature of the OIU8, OIU2, and newer OLT products.
Overview
PON or passive optical networks were originally designed for use in service provider networks. In order to support seamless upgrades with little to no outages for customers, all PON technology is designed to enable co-existence of previous PON modes and future PON modes.
This is achieved by using wavelengths that do not interfere so that they can co-exist on a single PON Optical Distribution Network (ODN). This means that a single fiber can simultaneously carry GPON, XGS-PON, and NGPON2.
Figure 1: Distribution Network
This enables multiple advantages:
- Protects the cabling infrastructure investment - Fiber never needs to be replaced.
- Allows for upgrades to new technology with minimal service interruption.
- Enables Pay as you go by allowing upgrade of ONLY the users who need the higher speeds without affecting the existing lower-speed users.
Protection of Cabling Infrastructure Investment
PON technology is implemented around a single-mode fiber cabling plant. Single-mode fiber brings multiple advantages. The first is that it works well over long distances, up to 20km or more depending on the installed lasers. In addition, Single Mode fiber supports very high speeds and multi-terabit throughput has been demonstrated on a single mode fiber. This ensures that once the cabling is placed into the building, it can be re-used in subsequent upgrades to go to higher speeds and additional features with no changes to the cabling infrastructure.
Minimal Service Impacts during Network Upgrade
The ability to add additional wavelengths to the network with minimal interruption to the existing network is one of the key features that allows the user to upgrade with minimal impact on the users. Most upgrades can be performed with outages of a minute or less.
Pay As you Go Architecture
Since the Architecture supports multiple wavelengths on a fiber this allows you to upgrade users one by one as needed without service interruptions.
Figure 2: Mixing GPON and XGS-PON in Pay-as-You Go Architecture
The user simply upgrades the network with the procedure above, then, one by one, upgrades individual users by changing out their ONT to one that supports the new wavelength and higher speeds. Only users that need additional speed are moved to the new wavelength/higher speed ONTs. All other users who have adequate bandwidth can continue to use the existing ONTs and infrastructure.
Overlay Network Applications
Overlay networks have many applications that make use of the architecture to provide compelling features:
- Network Separation - Allows two or more separate networks to co-exist on the same fiber.
- Separation of Data and Payment systems - Both are isolated on the fiber and cannot see each other's traffic.
- Separation of Patient data from back office systems - Systems carrying patient data and other systems can be kept separate while riding on the same fiber.
- Separate Hospitality Back of House and Guest Services - Use a single fiber network to serve both front and back of house.
- Separation of Power Users from normal network users - Ensures that power users needing high network speeds are on a different wavelength so that typical corporate users are not affected. Power users can often monopolize network resources, starving access for other users.
- Multi-tenant - Allows two different tenants to share a fiber without being able to see each other's traffic.
- Seamless Upgrade - Upgrade with minimal impact on other users.
- Bandwidth Upgrade - Allow upgrade from GPON rates 2.5G to 10G XGS-PON rates.
XGS-PON Combiner Description
The XGS-PON combiner has three connections.
Figure 3: Input/Output Connections
- GPON - Should be attached to the GPON OLT PON laser.
- NGA - Should be connected to the XGS-PON OLT PON laser. (NGA stands for Next Generation Access.)
- COM - Common Connection, includes the combined XGS-PON and GPON signals.
Overlay Network Installation
This section will outline the details for the overlay network installation. Figure 4 below shows the implementation of a standard overlay network where PPGs are not involved.
Figure 4: Overlay Network Installation
Adding another wavelength only involves the following steps:
- Mount the Combiner or WDM near the existing splitter or near the OLT(s).
- Cable up the new XGS-PON/GPON OLT laser to the combiner input (NGA).
- Unplug the existing GPON fiber from the splitter and plug it into the combiner input (GPON).
- Plug in a new fiber going from the Combiner Common output (COM) to the input of the splitter.
- Add New ONTs or replace ONTs utilizing either PON type.
The system is now ready to implement the new wavelength.
Each PON can support both the GPON and XGS-PON wavelengths. One PON port is equipped with an XGS-PON laser. Another PON port is equipped with a GPON laser. These are both plugged into a wdm/combiner to combine the two wavelengths onto a single fiber. This fiber is then plugged into the splitter. From there, the installation follows normal practices.
Once both of the wavelengths have been placed onto the same fiber, either XGS-PON or GPON ONTs can be installed on the same fiber with no limitations.
To upgrade a user from GPON to XGS-PON, simply unplug their GPON ONT, plug in the XGS-PON ONT and they ONT if configured on the XGS-PON port, immediately comes into service and the user now has availability to the full 10G PON bandwidth.
The GPON and XGS-PON ONTs cannot see each other's traffic and are totally isolated.
Overlay Networks with PPGs
Overlay networks are also supported for PPG-based networks. PPG or PON Protection Groups utilize type B PON protection to enable protection from OLT and Uplink network failures. PPG can be combined with Overlay networks but requires some additional equipment to implement.
Figure 5: Overlay Networks with PPGs
Overlay Networks with PPG require a combiner for both the Primary and Secondary OLTs. This allows the XGS-PON and GPON signals to be combined. The common output of each combiner is then connected to the two inputs of the 2:N splitter.
This allows the GPON and XGS-PON signals to operate completely independent of each other from a protection status. XGS-PON might be active on the Primary OLT, and GPON can be active on the Secondary OLT.
Once this is cabled up, it can, for the most part, be treated as any other PPG, with the one exception that you must be aware of both XGS-PON and GPON signals on the fiber and force both onto the same OLT prior to performing any maintenance or upgrades to prevent service from being affected.
Optical Network Planning
When utilizing Overlay networks, you must ensure that you account for the losses within the combiner in the total network budget.
- The XGS-PON combiner introduces 1.2dB of insertion loss into the optical budget.
- The XGS-PON combiner datasheet can be found here.
Video
On this page