Chorus’ new Service Delivery Point (SDP). What is it?

By Steve Biddle, in , posted: 2-Sep-2010 20:50

One of the biggest issues affecting Digital Subscriber Line (DSL) broadband is the quality of the copper wiring it is delivered over. The quality of wiring hasn’t caused significant impact in the past with slower first generation ADSL services, but as Chorus along with other providers such as Vodafone, Orcon, and TelstraClear upgrade their networks to support faster ADSL2+ and VDSL2 speeds, wiring quality becomes a major issue.

Overall the quality of the wiring within the Chorus network is typically good, however poor quality wiring in your home or workplace is common, and has the ability to have significant impact on both speeds and the stability of your connection. Many homes have poorly installed wiring or jackpoints, or jackpoints that have suffered corrosion damage over time due to the damp climate in parts of New Zealand. If your home wiring has not been upgraded since the late 1990’s it probably uses older 3 wire jackpoints (with a master and extension unit) which also have the ability that play havoc with DSL signals. Many people have simply blamed their ISP for their speed or stability issues in the past, without understanding that their issues could well be as a result of wiring within the premises.

The SDP is the result of many hours of work spent developing a device that can be installed in a home or business to improve broadband speeds without having to replace all existing wiring within the premises to comply with modern wiring guidelines. The SDP also future proofs the house for a move to Voice Over Internet Protocol (VoIP) based phone services and can also simplify the setup of a home network to PC’s or network devices located in other locations around the house. To really understand why the SDP is so important however, we firstly need to look at the current state of broadband infrastructure in New Zealand.

Right now Chorus are past the halfway mark deploying a Fibre To The Node (FTTN) network in New Zealand consisting of 3600 new roadside cabinets. Previously most DSL based broadband services were provided from phone exchanges that may have been some distance from your home or business. Because the DSL signal degrades the further it has to travel, the further you were located from an exchange, the slower your broadband would be. These new roadside cabinets contain fibre optic cable to link them to the existing exchange, and a piece of equipment known as an Intelligent Service Access Manager (ISAM) or Digital Subscriber Line Access Multiplexer (DSLAM) to deliver your broadband connection directly from the cabinet over the existing copper wiring to your house. By the end of 2011 when this project is complete approximately 80% of New Zealanders will be located within approximately 2km of a phone exchange or roadside cabinet and will have access to broadband connections with a minimum speed of 10Mbps – the vast majority however will find that their speeds are closer to 18Mbps with current ADSL2+ technology, and with the upcoming launch of the VDSL2 technology many could see download speeds in the vicinity of 50Mbps over their existing copper wiring.

While Chorus are upgrading their network, in many cases the broadband speed bottleneck will now be the wiring in your home or business. DSL technologies use frequencies over your copper phone line that are much higher than those used by your normal voice services. To ensure that voice and DSL services can coexist on the same line and do not interfere with each other, filter(s) are required to be installed in your premises to split the two. There are two options available – a professionally installed master filter, or DIY plug in filters that are required for every phone in the home, as as well as other devices plugged into your phone line such as your Sky TV box, fax machine or medical alarm.

Most people choose to use plug in filters because it enables a them to perform a self install of their modem, and avoid the cost of a visit by a technician. Plug in filters are not a the perfect solution however – not only are they cumbersome, but they also don’t eliminate issues such as reflections on the line, nor can they compensate for poor quality wiring, connectors or jackpoints. As I mentioned earlier, damaged wiring or jackpoints, or even the use of older 3 wire jackpoints will cause a significant impact on DSL performance. Installing more than 4 plug in filters on a line can also cause the DSL signal to be degraded. These all have the ability to become a significant bottleneck with faster ADSL2+ and VDSL services which will suffer significant speed degradation or stability issues from any interference caused by your internal wiring.

Poor quality internal house wiring is an issue that is widely known, and is an issue that the industry has strugged to solve. Despite Telecom releasing guidelines in the late 90’s advising that a structured wiring solution be installed in all new homes, many new homes still don’t have one. Around the same time Telecom also advised of a move away from wiring phone jackpoints in a daisy chain configuration, but many electricians and phone installers still continue to this day to install jackpoints in this way. The daisy chain configuration involves connecting jackpoints in a “looped” configuration from one to the other, and causes impedance fluctuations or reflections on the line which in turn impacts on DSL signals, and ultimately broadband speeds.

A professionally installed master filter will split your broadband and voice signals as close as possible to where the cabling enters your house (a location known as the ETP or External Termination Point) and will give you a dedicated jackpoint to plug your DSL modem into. Because the DSL and voice signals are isolated It means that poor quality wiring can’t interfere with the DSL connection and in most cases will deliver faster speeds than what can be obtained using plug in filters. While it’s not possible to put an exact figure on this, for somebody who is connected to new equipment in an exchange or roadside cabinet and already gets good sync speeds  (ie in the 12000kbps – 15000kbps range) it could possibly deliver an increase of around 10%. Somebody connected to a new cabinet or exchange who has very poor quality house wiring could see speed increases of several hundred percent. A master filter is certainly recommend for anybody who uses DSL based broadband, and for VDSL services a professionally installed master filter is essential as existing ADSL plug in filters are unsuitable and can’t be used. Uptake of master filters has been low, in part because many people are unwilling to pay the costs associated with installation.

So on to the SDP. What exactly does it look like?



The SDP in it’s basic form is a very simple patch panel. The faceplate contains a number of RJ45 keystones and inside the unit there is a VDSL rated master splitter and a terminal block for interfacing with a house alarm. Ports 5 and 6 can be fitted and connected to RJ45 faceplates elsewhere in the house using cat5e or cat6 cable for connecting other PC’s or devices to your router to form a home network.

Your incoming phoneline is terminated to a VDSL rated master filter that is located inside the unit and your modem is now connected to port 1 of the SDP. Port 2 is the voice output from the VDSL filter, while port 3 is connected internally to existing phone jackpoints in your house. Port 4 is connected to port 3 and allows you to plug a phone in directly to the SDP. The PSTN jumper clip (shown in the image above) bridges your incoming voice services to your internal house wiring. Removing this and plugging a phone directly into port 2 allows a simple isolation test to be performed to establish very quickly check if a fault (such as no dialtone) is an internal wiring fault or is located between the premises and the cabinet or exchange.

The following images show a typical SDP installation:

Clean Pair1

The SDP itself is unpowered and requires no power to operate. Under development however is a battery backup module that allows home networking equipment to stay powered during a power cut. This is particularly important as we move into the fibre world with Fibre To The Home (FTTH) deployments and move towards using VoIP as a primary voice line replacement.  With FTTH all voice services use VoIP as analogue phone services can’t be carried over fibre optic cabling. The loss of power to your home will mean a loss of all phone and internet services, as unlike Telecom’s existing copper network which has batteries and generators at both cabinets and exchanges to maintain power during an outage, the equipment in your house can only be powered by your own electricity. The battery backup will allow you to keep your equipment powered so phone calls can still be made during a power cut.

It’s worth noting that while a lot of media attention has focussed on the battery backup issue and the potential inability of people to contact emergency services during a power cut if they use VoIP services, that a large number of New Zealand homes currently only use cordless phones that are rendered unusable in a power cut anyway. People should  ensure that they have at least one corded phone in their house that will allow them to make calls during a power cut.

There are two primary methods of connecting a SDP – one with a phone service delivered over POTS (as is the case for most people now), and one where a VoIP service is used as a primary voice line. The following example shows a typical SDP installation where a customer has voice (POTS) and DSL services provided over copper.

Diag 2


One of the great things about the SDP is that it allows a very simple transition process to a VoIP based phone service. Right now a large number people have installed their own analogue telephone adapter (ATA) at home and use VoIP services such as VFX or 2talk for their phone line. Many have also opted for Vodafone Home Phone Wireless boxes which use Vodafone’s mobile network. In both cases many people choose to simply plug a phone into the port on their ATA or Home Phone Wireless box because hooking this up to their existing house wiring is a process that is beyond many people’s capabilities. With the SDP, delivering a dial tone to any existing jackpoint in your home is a simple two step process – simply remove the PSTN clip and run a cable from your ATA or At Home box into port 3. Every jackpoint in your home that is connected to the SDP will now be connected to the ATA.

Diag 3

The SDP isn’t magical but it’s certainly a very cool little unit. Poor internal wiring is an issue that affects a large number of DSL customers, many of whom are totally oblivious to the issues and put up with speed related issues and problems such as frequent disconnections that can be directly attributed to poor internal wiring. To deliver optimum performance on ADSL2+, users should really have a central splitter installed, and for VDSL this will be mandatory. The SDP becomes a logical replacement for a master filter installation – rather than just install a basic filter the SDP fills a void that exists where people don’t want to spend significant amounts of money to replace wiring in their house, but want a cost effective way to be able to take advantage of faster broadband speeds and also future proof themselves for the arrival of fibre and VoIP services.

It is not a replacement for a proper structured cabling solution such as those recommended by the TCF, and if you are building a new home or upgrading your home then a structured cabling system should be seen as a key requirement.

If you’re wondering where you can sign up for one you’ll just have to wait a little while yet still. Chorus will be responsible for the installation but will not take orders directly - you will be able to request an installation through your ISP. The launch is not far away, and I’m sure we will see plenty of publicity surrounding the rollout when it does happen.

Other related posts:
Is the TCF mobile blacklist fuelling New Zealand’s latest crime fad?
Spark Paging network shutdown – the event nobody cares about? Not quite.
UFB voice, power cuts, copper invincibility and mainstream media FUD.

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sbiddle's profile

Steve Biddle
New Zealand

I'm an engineer who loves building solutions to solve problems. I'll also a co-founder of the travel site. 

I also love sharing my views and analysis of the tech world on this blog, along with the odd story about aviation and the travel industry.

My interests and skillset include:

*VoIP (Voice over IP). I work with various brands of hardware and PBX's on a daily basis
  -Asterisk (incl PiaF, FreePBX, Elastix)

  -xDSL deployments

*Structured cabling
  -Home/office cabling
  -Phone & Data

*Computer networking
  -Mikrotik hardware
  -WAN/LAN solutions

*Wireless solutions
  -Motel/Hotel hotspot deployments
  -Outdoor wireless deployments, both small and large scale
  -Temporary wireless deployments
*CCTV solutions
  -Analogue and IP

I'm an #avgeek who loves to travel the world (preferably in seat 1A) and stay in nice hotels.

+My views do no represent my employer. I'm sure they'll be happy to give their own if you ask them.

You can contact me here or by email at