Why a VDSL Upgrade Required Moving Access Equipment Closer to Subscribers?

Published: August 13, 2026 | Last Technically Reviewed: August 13, 2026

Quick Answer

In this 2017 Bulgaria Vivacom broadband modernization project, we could not simply replace every aging MSAN at its existing location and expect the VDSL Vectoring upgrade to meet the intended broadband objective. The original access network used ADSL/ADSL2+ over copper, but the project documentation identified VDSL2/VDSL Vectoring as having a substantially shorter usable transmission distance. For residential areas beyond the project's planned copper-loop limits, part of the broadband access equipment therefore had to move downstream, closer to subscribers.

At first glance, the work looked like a conventional replacement project: remove aging fixed-broadband equipment and install newer, higher-capacity hardware. The metro-network portion largely followed that pattern. The access network did not. Once the broadband technology changed, the physical location of the access equipment became part of the service design.

The key question was no longer simply, "What replaces the old MSAN?" It became:

The Upgrade Was Not Just a Hardware Replacement

Vivacom's fixed-broadband network at the time was divided into access, metro and backbone domains. This project covered the FBB access network and FBB metro network; the backbone upgrade was handled separately.

The existing access architecture used xDSL modems connected through MSANs. Those MSANs carried both broadband and traditional residential voice services. Broadband downlinks were based on ADSL/ADSL2+, and the project document records that the existing bandwidth had become insufficient for subscriber upgrade requirements. Vivacom selected VDSL Vectoring for the broadband modernization.

The existing physical relationship was approximately:

Original MSAN
     |
Long copper distribution
     |
    MDF
     |
Residential areas
     |
Subscribers

If this had remained purely an equipment-refresh project, the new equipment could have been installed at the same MSAN sites and connected to the same long copper distribution.

But the technology change introduced a new constraint.

The project documentation states that the transmission distance supported by VDSL2 and VDSL Vectoring was significantly shorter than that of the previous ADSL/ADSL2+ service. As a result, VDSL equipment had to be deployed closer to end users, requiring new remote sites.

The resulting concept became:

Existing MSAN / central site
          |
        Fiber
          |
   New remote VDSL site
          |
     Shorter copper
          |
      Subscribers

That was the engineering reason a one-for-one replacement at the original sites was not sufficient.

Existing Copper Routes Determined Where We Could Place the New Sites

Moving access equipment closer to subscribers did not mean choosing arbitrary new cabinet locations on a map.

The existing copper plant already defined how subscribers were physically reached.

The original project records that twisted-pair copper leaving an MSAN could pass through two or more levels of MDF distribution, branching in different directions toward different residential areas. In the example documented in the project, a 512-pair copper route from an MSAN reached an intermediate MDF and then split toward several residential areas, with different pair counts assigned according to the number of users served.

The site-selection process therefore followed the actual copper distribution path.

Before deciding whether an MDF could become a new VDSL remote site, the engineering team needed to understand:

• where the existing MSAN was located;
• how its copper routes left the site;
• which MDFs formed the distribution hierarchy;
• which residential areas were served by each branch;
• and how much copper remained between a candidate MDF and the subscribers.

The logic can be simplified as:

Original MSAN
      |
    Copper
      |
    MDF X
   /  |  \
MDF A MDF B MDF C
 |     |     |
Users Users Users

If MDF A was close enough to the users behind it, the upgraded architecture could place the new access equipment there:

       Fiber
         |
       MDF A
    [New VDSL]
         |
    Short Copper
         |
       Users

The project explicitly states that remote-site selection followed the copper route from the MSAN and selected suitable MDF locations along that route.

This is what made the activity a topology redesign rather than a simple hardware swap.

The Distance Threshold Became a Site-Selection Constraint

The historical project used two important planning values:

• within approximately 300 m, planned access bandwidth could reach about 100 Mb/s;
• within approximately 500 m, planned access bandwidth could reach about 80 Mb/s.

Those numbers directly affected where new remote sites could be placed.

A candidate MDF was useful only if the remaining copper distance from that MDF to its subscribers was short enough for the project's VDSL Vectoring objective. In other words, the MDF hierarchy was not merely documentation of the old network; it became the set of candidate locations for the new physical access layer.

Actual DSL performance can vary with copper quality, pair condition, crosstalk, vectoring implementation, profile and subscriber equipment. The historical values should therefore be read as project design thresholds, not contemporary performance specifications.

For this case study, the important point is not the absolute DSL rate.

It is that remaining copper-loop length became a hard site-selection constraint.

Not Every Residential Area Needed a New Remote Site

The project did not respond to the distance issue by moving every broadband subscriber onto newly built remote equipment.

That would have been unnecessary.

The original design states that residential areas already located within the VDSL Vectoring-supported distance from the existing MSAN site did not require a new remote site. Those subscribers could continue to receive broadband from the replacement MSAN at the original location.

This created two different outcomes from the same upgrade:

Residential area close enough to MSAN
            
Remain served from replacement MSAN

Residential area too far from MSAN
            
Select suitable downstream MDF
            
Build new remote VDSL site
            
Shorten subscriber copper loop

That distinction is important.

This is where the actual access topology and subscriber distribution mattered more than a generic equipment-replacement list.

The Engineering Decision

After remote sites were selected and surveyed, the project called for fiber to be installed from the new VDSL equipment back toward the metro-network site.

This table describes the design logic of this specific 2017 project. It is not a current universal DSL deployment template.

In modern refresh projects where new remote or access equipment also requires fiber connectivity, the corresponding optical transceivers for fiber uplinks should be validated against interface speed, fiber type, transmission distance and device compatibility before the BOM is finalized.

What This Project Taught Us

The engineering lesson from this case is broader than VDSL but still very specific:

Subscribers were still buying fixed broadband. But changing the access technology altered the acceptable relationship between the electronics and the copper plant.

The planning sequence therefore had to be:

Service target
      
Physical medium
      
Distance / site constraints
      
Existing infrastructure
      
Equipment location
      
Hardware selection

Not:

New hardware
      
Try to fit it into the old topology

The Vivacom project illustrates why infrastructure should be evaluated before replacement hardware is treated as a drop-in substitute.

Applying the Same Planning Discipline to Business Network Upgrades

This Vivacom project was a carrier fixed-broadband migration, not an SMB Wi-Fi or office-switching deployment. The technologies, scale and operational requirements are very different.

One planning discipline does carry over: start with the existing infrastructure and required service outcome, not with a product list.

In current hotel, café, restaurant, retail, coworking and SMB office projects, that means checking existing cabling, floor layout, endpoint count, wireless requirements, PoE demand, switch-port capacity, uplink bandwidth, optical compatibility and expected growth before recommending replacement equipment.

Our high-traffic business network solutions workflow follows that approach. If an existing topology is unclear, a floor plan, device list or current BOM can be reviewed before APs, switches, uplinks or optics are selected.

The scale is different from the 2017 Vivacom migration, but the engineering principle is the same: understand the constraints first, then decide where the new equipment belongs.