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Using Tellabs Modal Adapter Cable

Introduction

Document Number

ENG-010618

Purpose

This document will outline the use cases and implementation of Tellabs SMF to MMF Adapter cable. The Modal Adapter cable is used to adapt Tellabs PON equipment to use MMF cables between the output of the splitter and the ONT. This allows cost savings with re-use of MMF cables in the horizontal rather than replacing them with SMF cables.

Applies To

This document applies to the Tellabs MMF Modal Adapter Cables.

Single Mode vs Multimode Fiber

There are two basic types of fiber. SMF or Single mode fiber, and MMF or multi-mode fiber.

MMF is a much older type of fiber with a much larger core diameter and typically manufactured at much lower tolerances. It is the primary type of fiber used within buildings and on short fiber runs. It has many shortcomings that limit the applications which it can serve. The picture below shows the common fiber core diameters of 62.5um and 50um for multi-mode and 9um for Single mode:
 

Multimode fiber due to its larger diameter, allows multiple modes of light (multiple beams) of light to emerge within the fiber. This can lead to a smearing out of the light at the other end of the fiber. Single mode is such a small core that only a single mode of light can form in the fiber.

The multiple modes of light result in the pulses being spread out and creates what is known as modal dispersion.

The received signal is much poorer and much harder to discern the 1’s and 0’s being sent on the fiber. The consequences are that a multimode has much shorter reach, and the maximum bandwidth over the fiber is limited.

Single mode, on the other hand, can support very high bandwidth (multi-terabit) and go very long distances. PON uses this capability to support 20km of reach or more.

The Tellabs Modal Adapter Cable performs mode cancelling within the fiber and allows the light to pass from the SMF to MMF domains with the best quality signal possible. Tellabs supports up to the maximum of 550m of MMF fiber for both GPON and XGS-PON signals.

Tellabs MMF Modal Adapter Use Cases

Tellabs has introduced a modal adapter cables which allow the re-use of MMF horizontal runs within the PON network on the splitter to ONT fiber runs. This technology should only be used for overlaying existing applications and all new installations should only use SMF fibers.

The modal adapter cable can be placed at two locations within the PON distribution network: 

• Between the Splitter and ONT
• Between the OLT and Splitter

Modal Adapter Cable between Splitter and ONT

These Modal Adapter Cable can be used in two basic applications:

• MMF reuse for Fiber to the Desktop
• MMF reuse for Fiber to the Closet

Fiber to the Desktop applications are where a lower port ONT, typically 2/4/8 ports, is placed on the end user’s desktop. The fiber goes all the way to the user's desktop. This application has a much higher fanout and the 2:16 or 2:32 splitters are appropriate for this application. This allows full re-use of the horizontal fiber lowering the cost of the installation for rehab of existing fiber to the desktop installations.

In the Fiber the closet application, the splitter is located at the building ingress re-uses the existing MMF fibers that are deployed within a building going to the data closets, or IDF rooms within the building. This allows the use of those existing fibers to implement PON allowing increased speeds over MMF fibers. The MMF modal adapter cable can support both GPON and XGS-PON on the MMF horizontal fibers. Typically, these are used in conjunction with Tellabs 24 and 48 port ONTs with copper distribution to end users. SMF or Single Mode Fiber is being used to bring traffic to a building or to a floor within a building, and the MMF fiber is being used in the horizontal to reach the data closets on that floor or within that building.

As there are most often lower numbers of data closets within a building/floor and from a network engineering standpoint, the user wants to optimize the bandwidth available to end users, the most appropriate choices are the 2x8 or 2x16 splitters. Tellabs typically recommends no more than 5x 24 port ONTs on a PON and no more than 10x 48 port ONTs on an XGS-PON. The lower count fiber splitters will allow more margin on the MMF fibers, allowing lower quality fiber to be used on the MMF fiber runs and still run error free.

Modal Adapter Cable between OLT to Splitter

The modal adapter cable has also been tested in the fiber run from the OLT to the Splitter. This can allow re-use of Multi-mode fiber that already exists and goes to the data closet or between buildings. The MMF fiber distances still must be constrained to the limits specified in the next section. The modal adapter cable should be placed on the splitter end of the cable and then plugged into the splitter.

Configuration Requirements

Forward Error Correction (FEC) must be enabled on any PON port connected to a cable segment with an MMF component.

Tellabs modal adapter technology allows existing infrastructure to be repurposed. However, the modal dispersion inherent in MMF fiber and potential degradation associated with aging cable plants can still result in data transmission errors. Without a mitigation strategy, the retransmission of errored packets can result in congestion affecting network performance.

Data transmission errors are dealt with using Forward Error Correction (FEC). FEC is a technique that uses error correction code (EEC) to encode messages with redundant data. This redundancy allows a receiver to detect errors in a message and correct them without requiring re-transmission.

To enable FEC on a PON port, use the following procedure:

1. Create a PON Profile with FEC enabled:
   
2. Apply the profile to the PON port:
    
   

Tellabs Modal Adapter Cables Distance

The following are some typical distances achievable with the MMF and cable plants. These distances have been validated to run error-free on good cables, but it is expected that possibly 5-10% of MMF cables may have bad enough connectors to have to re-terminate the MMF cables. Newer cables are likely to have higher tolerances and are likely to have fewer cables with issues. Since GPON uses a single cable, this often leaves two cables to most existing drops that can be utilized. Lowering the split ratio can also gain additional margin to prevent re-termination of cables.

The ODN should be specified for no more than 22dB of loss or an anticipated power of -20dB or more.

Distances when Modal Adapter Cable is in on the Splitter to ONT side of ODN
 

Distances when the Modal Adapter Cable is in the OLT to Splitter side of ODN

Tellabs SMF Modal Adapter Cable Types

Tellabs has two versions of the MMF Modal Adapter Cable and also sells the MMF to SMF jumper to be used on the ONT end of the fiber run:

• 81.SMFMMF-SCLC-3M - FlexSym SM SC/APC MM LC/UPC Fiber Jumper 3 Meter SC/APC(SMF) to LC/UPC(MMF) Modal Adapter Cable

  This attaches to the splitter and then typically goes over to the MMF patch panel.
  
  

  • 81.SMFMMF-SCST-3M - FlexSym SM SC/APC MM ST/UPC Fiber Jumper 3 Meter SC/APC(SMF) to ST/UPC(MMF) Modal Adapter Cable

• 81.SCAPC-LCUPC-3M - FlexSym SM SC/APC to LC/UPC 3M 10 Pack

  SC/APC to LC/UPC jumper cable used for going from wall plate to ONT and adapting the MMF to SMF at the ONT end of the circuit.

  

Tellabs Modal Adapter Cable Specifications

The Tellabs SMF to MMF splitter has the following specifications: