Howto:Rules for successful IP1200 deployment

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There are a few things to watch out for when deploying multi-cell IP1200 DECT systems.

Here they are.

Contents

Applies To

This information applies to

  • IP1200

More Information

Preface

In general, as with all DECT systems (IP600, IP1500, IP1200, single-cell, multi-cell) you need to perform a professional deployment to successfully install and run a DECT system. Use innovaphone’s deployment kit and apply what you have learned in the iCE advanced training.

Keep in mind that a possibly existing previous installation of a 3rd party DECT system will at best give you some hints as of how and where to position your radios. Just removing the old radios and installing the new ones in place of the old ones will likely not produce a good result. It is you who will need to go on-site again if initial deployment is not done carefully.

Also, we are often asked if or if not a particular 3rd party DECT handset will work with the installation. The answer is: we don’t know. Honestly. If the customer insists of using “old” handsets, then you need to do a proper installation and have the customer try his handsets on her own risk.

Deployment Preconditions

Deployment is done before the system is installed. The special deployment handset available is useful (as it can be locked to a particular radio without trying handover), but not strictly required.

When you do the deployment, and also when you do the final corrections once the system went life, you need to make sure the system operates under “real life conditions”. In an office environment, just any conditions are probably real life. However, in an industrial environment, make sure you have worst case conditions. Especially watch out for large electrical machines or heavy vehicle traffic. This may influence deployment heavily.

Deployment Overview

There are 3 major goals to achieve with proper deployment

  1. Find spots to install IP1200 such that there is a proper, redundant synchronization chain
  2. Make sure that there is good radio coverage wherever calls shall be made
  3. Make sure overlap is sufficient and properly layed out so that handover performance meets the requirements

How to determine Voice Quality

At the end of the day, the deployments goal is to make sure DECT users can make phone calls everywhere they want to with good voice quality and not disturbed when moving.

The good question now is: how to make sure voice quality is “good”? The answer is: listen to the calls voice performance as the users would do.

For this it is critical to perform real calls, both during pre- and post-deployment. Using innovaphone’s deployment kit, you can place calls to the deployment base. In previous versions, this was done by connecting the call to the internal music on hold. Unfortunately, when there are deployment problems, voice performance is often asymmetric. That is, it may well be that (seen from the handset) the receive channel is good while the transmission is not. Moreover, when there are problems in the receive channel, the handset will try a handover to a better channel. However, if there are problems in the transmit channel, then the handset wouldn’t know and thus not try handover to fix the situation.

It is thus critical not only to listen to the music on hold, but perform real conversations to verify both directions.

We have thus changed the firmware so that you will be connected to a loop-back instead (one of the rare conditions where self discussions are helpful). Of course you can also use 2 handsets and do a real conversation...

When doing the calls and walking around, look at the handsets deployment mode display and verify the data shown. This implies that you use a headset!

As a rule of thumb, an RSSI with less than 80 is a good reason to look for better alternatives. But there is no strict rule here (such as “81 is good and 80 is not”). Instead, you have to observe Q value and voice performance carefully. This is much more important.

When the data shows frequent handovers even when not moving, then make sure this does not compromise voice quality. Handover is not bad, but if there are frequent handovers then you need to make sure they go smoothly. See the separate article Howto:Understanding DECT handover with IP1200 about handover.

Issues particular to the IP1200 in a multi-cell installation

There is a big difference between an IP1200-based installation and an IP1500-based installation when it comes to multi-cell: DECT radios need to be synchronized when handover happens. If not, handover will fail.

Surprisingly, handover may even happen although the handset is not moved at all. This may e.g. happen if some other handset is moved out-of or in-to the coverage area of the radio serving your handset. So if you perceive “quality issues” like noise or lost calls, then it may be handover issues although you would not expect one.

So how is the synchronization done?

In an IP1500 it is quite simple. All bases are linked to the controller (a.k.a CCFP or wireless server) and receiver their synchronization through the wire.

In an IP1200, synchronization for the bases must be done through the air, just like for the repeaters in an IP1500 installation. This implies that all IP1200s need to form a “synchronization chain” where each IP1200 receives the sync from another IP1200 and all these chains ultimately end up in the “synchronization master” which has no primary or alternate sync source configured. Practically this means that each IP1200 at least needs to “see” one other IP1200 receive sync from (ideally it sees 2 IP1200 to guarantee a good primary and alternate sync source). The coverage areas of the 2 IP1200s (the one providing and the one receiving the sync) must overlap thus.

If need be, you can also have an IP1200 receive its sync from a repeater instead of an IP1200. However, it is best to avoid this as a repeater has only a single sync source. If it fails, then the remaining sync chain of all IP1200s receiving their sync directly or indirectly from this repeater is broken, making for an unreliable system setup.

Rules for a successful IP1200 multi-cell deployment

1. Do not use half-slot repeaters
IP1200 is a “full-slot” system, that is, it uses 12 channels(max.10 channels for voice calls) on the air. A full-slot system can only work with full-slot repeaters. So half-slot repeaters will not work with an IP1200. The symptoms if you install half-slot repeaters with IP1200 (either single-cell or multi-cell) are lost sync and failing hand-overs. On a residential (or single-cell) system, you may use residential-full-slot-repeaters (order code 02334611 on the label), but then you will not be able to upgrade to a multi-cell systems. Or you may use multi-cell-full-slot-repeaters (order code 02334621 on the label). This will work both in single-cell and multi-cell installations.

2. If avoidable, do not sync an IP1200 on a repeater
See above for an explanation.

3. If avoidable, do not sync an IP1200 on repeater chains
You can configure repeater chains in an IP1200 system. This is when a repeater synchronizes on a repeater again (and again …). This is fine; If one of the repeater looses the sync source all repeaters behind will loose the sync. If now the IP1200 has no alternate sync source configured (e.g another IP1200) then it will loose the sync also.

4. Create repeater chains correctly
If you create repeater chains, make sure the chains radio IDs are configured properly. Each repeater in the chain must have a radio id of its predecessor (the one it is synced to) plus 64. So if you attach a chain to base with ID 2, then the repeaters shall have IDs 66 ,130 and 194. Also, you need to set the sysmask parameter in the radios to 0x3f. This parameter will normally be replicated from the master to the radios. For more information on the sysmask parameter see a separate article. Howto:Understanding DECT handover with IP1200

5. Put the sync master in the center
The sync master is the IP1200 which has no sync source configured at all. All other IP1200 and repeaters shall be directly or indirectly synchronized on the sync master. For this to work best, select an IP1200 in the geographic centre of your installation. This will ensure that the resulting synchronization chains are as short as possible. The shorter the better! Please note that the synchronization master is not the DECT master. In other words, you need not use the DECT master as a sync master. Just any IP1200 can be the sync master. A repeater cannot.

6. Ensure a sync signal of at least 80
Make sure that when deploying the IP1200, the signal strength of the base intended to serve as a sync source for another IP1200 is at least between 80 and 85 on a handset in RSSI indicator mode (this assumes that the handset shows approx. 96 when used next to an IP1200, normal handsets are not calibrated and thus may vary a bit). In the OtherBasesReq (see below) this is equivalent to a signal strength indicated as 25 (decimal).

Debugging

  • Once you installed the system according to the layout determined during deployment, do a verification on-site. You will need to walk around and verify the signal strength and voice quality wherever calls shall be done.
  • verify the handover performance

You may well have proper signal strengths all over the campus and still have no handover. This is because handover takes time (up to 10 seconds). When you move, the handset will perform a handover as soon as the Q52 values falls below 52 or becomes unstable or it falls below 58 and there is a better radio available. Then it will search the best base (with highest RSSI) and will try a handover. If the handset completely looses its current radio because it is moved too fast, then handover will fail and the call will drop. Even if the call is not dropped, the signal may drop to a level where uncomfortable noise is experienced in the call.

This behavior implies that you must ensure enough overlap between radio coverage areas. To verify, make a call and move as your customers would move. If they walk, it’s fine to walk. If they use vehicles, use the vehicle too.

  • Verify sync source field strength

therefore go to Administration/Dect/Radio. In any IP1200, use this view to verify the signal strength of the sync sources for this IP1200. This will output the next best bases along with their ID and RSSI value.

image:Howto-Rules_for_successful_IP1200_deployment_Dect1.PNG

Make sure any sync source has at least a decimal RSSI of 25 (the value in brackets are decimal although they begin with 0). Verify over a period of time under normal (that is, worst case) environmental conditions. Be sure to verify both sides (i.e. strength of sync source at device and strength of device at sync source)!

  • Monitor the systems behavior for a while

Have a look at the sync status on the master and also at the statistic page.

image:Rules_for_successful_IP1200_deployment_Dect2.PNG

In this page 2 values are of special importance:

1. Handover failed shows the number of failed handovers in all the radios.
This value should not exceed 20% of the number of calls connected (both in and out). Failed handovers are not always a problem, as they may be followed by a successful handover later on.

2. Abnormal call Release should be very small or ideally 0.
This counter is incremented when a call is released because a radio (or repeater) lost its handset. This will of course also happen if a user just removes the battery or walks out of the coverage area during a call. As these are rare situations though, the counter should be near to zero.

If users complain or the number of failed handovers becomes large, do appropriate corrections.

Base or repeater?

It is sometimes difficult to decide if to put a repeater or a base in a certain place. Generally, a base provides real voice channels thus allowing more concurrent calls, whereas a repeater just provides coverage as voice calls need channels on the repeater AND on the base. So the number of concurrent calls not only is not extended, each call actually takes twice as many channels in the air. However, repeater can – if configured properly – do bearer handover, which is faster and less noisy. See the separate article on handover. Howto:Understanding DECT handover with IP1200

Things to avoid

There are certainly a lot of things to watch out for when doing a dect deployment, so do not expect a exhaustive list of things here. However, here are a few that are easily forgotten:

  • When you place a radio (base or repeater), do not place it near to reflective material.
    This can create all kind of distortion and must be avoided. While it is obvious not to install a radio on a steel surface, there are less obvious situations which are nevertheless similar from a radios point of view.
  • You should not install a radio directly underneath the ceiling.
    The reason is that there is a good chance that there is steel armour in the ceiling even though you can’t see it. Especially in industrial environments, a buildings layout is often changed using sheet metal walls. As they may be painted like other (e.g. wooden) walls, they are sometimes not easily recognized. So watch out.
  • Even normal walls can contain a lot of metal.
    Consider a plant where a wall bears the electrical supply for a huge machine. The cables required to cover the power consumption may behave like a steel wall. To fix the problem if you can’t avoid to place the radio in such a position, mount it with 30cm or more and you should be fine. The metal will still degrade your coverage, but there will be less distortion.
  • We have seen installations where handover performance was poor although coverage and overlap was fine. It turned out that there were several other DECT systems running in parallel causing noise and excessive handover rates. In this cases, try to switch off these systems (often, people have such systems in place although they are not even used any more). If this is not feasible, make sure that you place the IP1200 with “enough” distance to the existing DECT radio. “Enough” in that case means: keep a distance so that the alien DECT signal at this position is at least 20dB less then directly next to the alien base. Unfortunately, to determine the exact signal loss, you will need appropriate measurement equipment, such as the special “deployment handset” available from Kirk.
  • When you need to provide for many simultaneous calls in an area, then you need to install several bases in that area. However, too many bases next to each other create problems where the bases influence each other and ultimately render all radios unusable (a phenomenon known as “hot spot”). To work around that, you need to make sure no more than 3 radios sit next to each other. If more are needed, make sure that the next radio is placed such that the signal loss of the first 3 radios is at least 20dB


Protective Housing

Especially in industrial environments, users will not handle the DECT equipment with care. This is not only true for the handsets (which are pretty robust), but also for the bases and repeaters. So make sure you protect the devices itself, their power supply in case of repeaters and the cabling against any damage.

In rough conditions (rain, wind, dirt etc.) provide protective housing for the radios.

As an example, google for “hensel kg9003”.

Proper Installation

Pre-deployment will usually be done by the reseller whereas the physical installation then is done by the customer or its electrician.

This is fine, however, in many cases the actual installer then has no sufficient knowledge of the peculiarities of DECT deployment. It might well happen thus that the installer for practical reasons (or perhaps a certain amount of laziness) installs the radios only roughly at the spots they ought to be installed at. Things like not mounting radios on a metal surface or keeping them away from the wall surface are easily ignored then. To help, we recommend to clearly mark the spots where radios are to be installed during deployment. This can be done using little red adhesive stickers for example. Take a bunch with you on a deployment.

Also, make the installer aware of the tools available for proper mounting of the radios. This includes protective housings as well as the radio mounting kits available from innovaphone.

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