What is the difference between MPT1327 and Capacity Max?

MPT1327

MPT1327 was a technical standard for trunked radio communications, developed by the (then) UK Ministry of Posts and Telecommunications and Department of Trade and Industry (now OFCOM). The first version of the standard was published in 1987.

Although not an international standard, a number of manufactures produced both fixed equipment and radios that supported this - including Motorola. There have been MPT1327 systems in almost all countries at one time or another - with the majority in EMEA and Asia.

There are actually two additional standards which are used in conjunction with MPT1327:

MPT1343 described a numbering system that allows radio and talkgroup identities to divided into ranges known as fleets together with some specifications relating to the man-machine-interface(sic).

There were other country/manufacturer-specific dialling schemes out there - such as egionnet43; Dutch PTT and Nokia Actionet - which meant radio vendors had to be able to support all of these in order to support such systems.

The MAP27 supplement described a mechanism that allowed (circuit-switched) data transfer between data terminals connected to the radio.

DMR Tier 3

Outside of the Motorola-world, Capacity Max is known as DMR Tier 3 (sometimes written as DMR Tier III). It is described in ETSI Technical Specification 102 361-1 to -4, with the latter specification focusing on the trunking aspects.

Like MPT1327, the specification was developed by a number of industry players who formed the DMR MoU (now DMRA) and there is a large number of manufacturers who offer DMR fixed and radio equipment as well as applications. Outside of TETRA and P25, DMR has become the dominant technology used in LMR systems.

The high level (obvious) differences.

DMR is digital whereas MPT1327 is analogue. 

DMR Tier 3 uses one timeslot on one of the channels for control channel. Both technologies require one continuous control channel signal on each site - this allows radios to identify the network and make ongoing signal quality measurements.

Capacity Max is able to allow the 2nd timeslot of a control channel host to be used for mass registration. This is particularly useful for situations where you have a large number of radios turning on at the same time.

Although MPT1327 and MPT1343 were very specific about how each function worked, there was no interoperability testing required. Despite this, there was a very high level of interoperability between vendors. Which meant that a MPT1327 radio from vendor A, would, in all cases be able to work on a system from Vendor B.

There are a number of services described in the DMR Tier 3 standard, which are not well defined. The standard itself allows manufacturers some degree of market specialisation which some features and services are not able to interoperate with each other. There is the DMRA IOP but this does not cover all features and services. This means that there is a limited level of interoperability between vendors - though this will improve with time.*

Some similarities

Capacity Max also uses the terms OACSU and FOACSU to describe the mechanism to set up private (individual) voice calls.

With OACSU, the called radio rings until the user answers the call. When they do, a private call will be setup between both parties. This is better than FOACSU in that a traffic timeslot is not wasted one a user who potentially isn't there.

With FOACSU, a private call is automatically setup between the called and calling radios without any intervention from the called radio user.

Like MPT1327, DMR Tier 3 supports dialled call modifiers:

In MPT1327, adding *9* in front of the dialled number would make the radio sset up an emergency call with that radio/group. Similarly, adding *8* would give the call a higher priority.

DMR Tier 3 borrowed a lot of technical terminology and compects from MPT1327, for example, the System Identity Code bears some resemblance to the MPT1327 System Identity in that both are 16 bits and transmitted continuously on the control channel. Read more about that here.

Like MPT1327, radios on a Capacity Max system go through a hunting and registration process. Once registered on the system they will occasionally have the chance to carry out a Vote Now process. In this case, while not in a call, the system will inform all radios on a particular control channel that for the next few frames they can leave the current control channel and go off to sample the signal strength and quality of control channels from neighboring sites. While this happens, the system will queue any calls intended for the radio(s) carrying this out.

Depending on the results of this exercise, the radio may roam to another site and attempt to register there.

Voice Calls

Capacity Max supports all of the voice call types that MPT1327 did. However, Capacity Max also supports the following call types that were not available in MPT1327:

System-Wide All Call

Site-Wide Call Call.

Emergency Call 

Things must have been safer then or people just didn't care but MPT1327 didn't offer much in terms of emergency call handling. The best you could do was to have the radio start an emergency talkgroup call. Capacity Max, however is able to support many useful features for critical situations:

1. Although not really a system feature, Mandown functionality is standard in all -e series radios. This allows a radio to automatically trigger emergency if a portable radio is tilted for more than a certain time or if the radio does not move.
2. An emergency call is given priority 1 in the system. This means, amongst others, that the call does not get placed into a queue, like other calls - even high priority ones.
3. Call preemption is supported. This tears down an ongoing low priority call, to pass the emergency call, if all channels at the site are busy.
4. Emergency Voice Interrupt can be used. If, for example, an emergency call goes through on a talkgroup and someone else talking on that talkgroup, their call will be interrupted to pass the emergency transmission.
5. Also not really a system feature, all MOTOTRO radios support Lone Worker. When enabled, the radio will wait (and operate normally) for a set amount of time. After this time, the radio will sound a continuous alert. The user must respond to this alert or else the radio will trigger emergency. Responding to this alert will reset the timer and return the radio to normal operation. The user can respond to the alert by pressing any button.
6. Hot Mic and Remote Monitor are two features used with emergency. When an emergency is triggered, the radio can be configured to automatically PTT and allow the dispatcher to listen in on the radio's microphone without any indication to the user. Additionally, Remote Monitor is a feature that can be optionally enabled in radios to allow a dispatcher to remotely control the radio's PTT thus allowing them (the dispatcher) to hear what is going on.
7. Another radio feature is Emergency Search Tone. This allows the position of the radio to be found when visibility is a problem. If the user triggers emergency, the radio can be set up to also emit a beeping tone. Rescuers can use this sound to find the position of the radio - and user.

Emergency calls can be made to a talkgroup or individual radio. My suggestion is to direct all emergency calls to a dedicated talkgroup and have a radio setup in the control room (or wherever it is needed) with the volume cranked all the way up, so that when someone triggers emergency, many users are made aware.

Data

DMR (and DMR Tier 3) inherently supports IP paket data. MPT1327 had data capabilities but only circuit switched data which meant it was only possible to have a data call between two radios - any data exiting the radio system would require some additional and high-level conversion.

In DMR, voice and data are packetised in the same way: that is both are sent as IP packets complete with source and destination addresses.

Location

MPT1327 predates commercially available GPS by a few years so for many years location tracking was not possible. Eventually, a few hardware solutions became available which - for example - allowed the location of a vehicle to be tracked. In most cases, the location updates were sent using Short Data Messaging (SDM).

Certain MOTOTRBO radios both support GPS and MPT1327. On a MPT1327 system, the radio's location can be queried and sent to an application using SDM.

The trouble here is that SDM calls are comparatively slow and rely on the availability of a free traffic channel.

In Capacity Max, location is processed using Motorola's LRRP protocol. This only requires the tracking application to send a single location request after which the radio(s) will send regular updates.

Location, like all data in DMR is sent using the same protocol/format as voice and is inherently IP. 

For customers who need to track a large fleet of radios with a small cadence, Data Revert and Single CSBK data can be used.

Data Revert is a system level feature that reserves one or more TDMA timeslots on a site for radio-to-system-data only traffic. Whenever a radio needs to send a location update, it will go to the statically assigned channel/timeslot send the data there, then return to the control channel.

Single CSBK data reduces the location update down to a single data burst thus reducing the amount of time the channel is occupied for a location update - this free up the channel for more location updates from other radios.

Embedded GPS allows a location update to be sent while the radio is transmitting. When doing this, some bits in each frame are used to send the location data. It is not as fast as a standalone location update but alleviates some delays from busy radios.

A radio will not send a location update while monitoring a call. Doing so would make the radio user miss part of the transmission.

Telephony

MPT1343 had some unusual characteristics in that it was not possible to have a talkgroup ident of 999. The reason for this, is that in the UK, 999 is the emergency number. The designers of MPT1343 wanted to have radio calls made to 999 to be sent to the telephone network. For this to work, the radio system would require a telephone interconnect. Since MPT1327 predates SIP, the telephone interconnect would into an analogue POTS or FXO line.

Similarly, idents starting with 8 were supposed to be PABX calls and numbers starting with 0 external PSTN calls.

In other European countries, the emergency telephone number is (was) 112. To address this requirement, adaptions were made to the MPT1343 standard to allow for calls made to this - and other - number to be directed to the correct telephone line/number. Hence variations like Regionet43 and Dutch PTT were created.

Capacity Max allows voice calls to be directed to a SIP PBX via a telephone gateway. The gateway is essentially an application that acts as a SIP client and handles the transcoding between ABME+2 and G729.

Each radio on the system can be assigned a unique direct-dial telephone number, such that calls made from a telephone to a radio user can be dialled without requiring any additional overdialling. 

Radio and Talkgroup Identities.

Capacity Max uses the numbering scheme defined in ETSI TS 102 361-1 -3. This means that Radio 1 will have ID 1 and Talkgroup 1 will have ID 1.

MPT13343 defined a mechanism that allowed a MPT1327 number to be converted into a Prefix; Fleet and Individual. This made sense when radios were not as sophisticated or for shared public systems.

For example, with MPT1343, a radio with (MPT1327) ID would have a MPT1343 number of 200 2001 201. Another radio could have 200 2001 202. In order to call the latter radio, the user would only have to dial 202. This could be useful in that the system owner could prevent users from dialing a radio ID that is not in the 200 2001 XXX range.

The same numbering scheme was used on Talkgroup IDs except that the last three digits start with 9xx.

Migration

Customers who currently have a MPT1327 system need to urgently consider migration plans. Many key hardware manufacturers no longer exist or no longer produce important items like site controllers.

A number of MOTOTRBO portable and mobile radios are available with a MPT1327 option board which allows them to be used on MPT1327 systems while the move to digital is underway.

The SLR series repeaters support connection to an external MPT1327 site controller. This allows the replacement of old (analogue-only) repeaters while maintaining MPT operation. The SLR repeaters can then be programmed for digital operation at a later date.

Post Scriptum

As always, the more interesting part is the questions I get via the comments. So if you think I've missed something, please do ask below.

* Edit 04.02.22