Multisite Capacity Plus

MOTOTRBO Multisite Capacity Plus is a multisite trunked radio system, partially based on ETSI DMR. It supports up to fifteen RF sites with a maximum of 140 peers across all sites and up to twelve repeaters per site. At any given site, there can be up to eight trunked repeaters and up to eleven - optional - data revert repeaters. Unlike other trunked systems like Capacity Max, Multisite Capacity Plus does not require a site controller. nor does it use a dedicated control channel to set up calls.

Since a single site might serve a large area, having 15 sites could potentially cover an entire region or city. With eight trunked repeaters at each site, a system could also support around 3600 radio users.

Multisite Capacity Plus does not require any additional hardware. CfS licenses are required in all repeaters though - even on data revert repeaters. The below system, for example, would require 17 MSCP CfS licenses.

Trunked Channel Operation

With Multisite Capacity Plus, either timeslot of one repeater at each site will serve as a rest channel. Radios which are not party to a call will monitor the rest channel. When a voice call is established, this is done on the rest channel which becomes a voice channel. At the same time, the next available timeslot will become the new rest channel. Radios not party to that call will move to the new rest channel.

The call setup mechanism on a Multisite Capacity Plus is a combination of IP Site Connect and Capacity Plus Single Site with the following differences:

• In an IP Site Connect system, a customer can configure a logical channel as either a local channel or a wide area channel. A call over a local channel is repeated only over the local site, whereas a call over a wide area channel is repeated over all the sites if the slot is free. Instead of local and wide-area channels of IP Site Connect, Multisite Capacity Plus supports both local and wide area talkgroups. A repeater handles a local talkgroup call using same method used in (Single Site) Capacity Plus. However, a wide area talkgroup call is repeated over all the associated sites where at least one timeslot is idle.
• In an IP Site Connect system, a call starts at all sites. This is often called “All sites Light-Up". An advantage of this is the simplicity in implementation because repeaters are not required to know the list of radios present at its site. A disadvantage is that a multi-site configuration does not increase the capacity of a system but only the coverage. Multisite Capacity Plus allows defining a talkgroup as a wide area talkgroup. A wide area talkgroup call "lights-up" only the sites which are statically associated with the talkgroup. The call is rejected when a radio tries to initiate a wide area Talkgroup Call from a site not associated with the talkgroup. The talkgroups not defined as wide-area are local talkgroups. A local call "lights-up" only one site where the initiating radio is located. Private Call initially “lights-up” all the sites but after approximately 400 milliseconds, the call continues only at the sites where the source and destination radio are present.
• A wide area non-Emergency talkgroup call starts only if all the associated sites have idle timeslots. This is defined as “All Start”. Additionally, Multisite Capacity Plus allows a customer to reserve a number of logical channels for wide-area talkgroup calls only. This improves the success of “All Start” for wide-area talkgroup calls.
• An exception to the "All Start: rule (for all wide-area talkgroup calls) is when all channels at the destination site(s) are unusable (due to interference, BSI transmission or HW failure). In this case, the call source site is able to continue the wide-area call setup process excluding unusable site(s).
• Just like Capacity Plus (single Site), a Multisite Capacity Plus system has no controller. Repeaters of one site trunk the logical channels available at that site. Also, repeaters from one site do not participate in trunking the RF resources of another site. Each site trunks its channel but arbitrates calls between them.

Data Revert Channel

A Data Revert Channel is useful to offload large volumes of (radio-to-server) data from the trunked channels thereby increasing the overall system capacity. When configured for this, instead of sending data to the application over a trunked channel, the radio momentarily drops off the trunked system and sends the required data on a predefined conventional channel, then returns to the trunked channel once the data has been sent.

Server-to-radio data is still sent over the trunked channel. However, the number of server-originated messages will usually be minimal.

A Data Revert Channel could be either an Enhanced GPS Revert Channel or a normal Data Revert Channel. Each logical channel of a Data Revert Repeater can be independently configured either as an Enhanced GPS Revert Channel or as a normal Data Revert Channel.

The radios are configured with a list of all Trunked Channels and Data Revert Channels for each site.

System Operation

In an IP Site Connect system, a customer can configure a logical channel as either a local channel or a wide area channel. A call over a local channel is repeated only over the local site, whereas a call over a wide area channel is repeated over all the sites where at least a channel is idle. Instead of local and wide area channels of IP Site Connect, CPMS supports both local and wide area talkgroups. A repeater handles a local talkgroup call in the same method as in a Capacity Plus Single Site configuration. However, a wide area talkgroup call is repeated over all the associated sites where at least one logical channel is idle.

In an IP Site Connect system, a call is streamed to all connected (wide area channel) sites. This concept is sometimes called All sites Light-Up. This simplifies the architecture since repeaters do not need to know whether any radios are present at its site. The disadvantage is, that a multi-site configuration does not increase the capacity of a system. Potentially, a talkgroup call could be streamed to a site with no parties on it.

Multisite Capacity Plus allows a talkgroup to be streamed/routed to predefined sites. A wide area talkgroup call is only streamed the sites which are statically associated with the talkgroup. The call is rejected when a radio tries to initiate a wide area Group Call from a site not associated with the talkgroup.

The talkgroups not defined as wide-area are local talkgroups. A local call "lights-up" only one site where the initiating radio is located.

The CPMS Private Call initially “lights-up” all the sites but after approximately 400 milliseconds, the call continues only at the sites (at most two) where the source radio or destination radio are present.

In CPMS, a wide area non-Emergency talkgroup call starts only if all the associated sites have idle channels. This is defined as “All Start.” Additionally, CPMS allows a customer to reserve a number

of logical channels for wide area talkgroup calls only. This improves the success of “All Start” for the wide area talkgroup calls.

Just like a Capacity Plus Single Site system, an CPMS system has no controller. Repeaters of a site trunk the logical channels available at the site. The trunking process in CPMS is similar to that of Capacity Plus Single Site. Repeaters of a site do not participate in trunking the RF resources of another site. Each site trunks their channels.

Design Considerations

Although all sites can support up to eight trunked and up to eleven data revert repeaters, it is not recommended to exceed a total of twelve repeaters. For example, if there are six trunked repeater at a site, then up to six data revert repeaters can be added.

Erlang B should be used for calculating the required number of repeaters in a Multisite Capacity Plus system. This is because when all channels are busy, a call setup will fail. Transmit Interrupt can be used to free up a channel to pass (an urgent) call. Erlang C can only be used when designing a Capacity Max system.

It is not necessary to have the same number of repeaters at each site but careful attention must be made on the Talkgroups-Site table in the Master Repeater as well as the Reserved Wide Area Channel settings in CPS2/Radio Management.

If an existing network makes use of any DR3000 repeaters, only the 32MB version will support Multisite Capacity Plus.

Multisite Capacity Plus uses All Start for talkgroup calls. It also does not support call queueing. In a system with a different number of repeaters at each site, there may be situations where a call fails

All the repeaters at the same site must be on the same software version. Ideally, all the repeaters in the system should be on the same software version.

A Multisite Capacity Plus Repeater is configured either for Trunking or Data Revert capabilities. It is therefore not possible to use one slot for data and the other for voice - even if it renders the other slot superfluous.

A Multisite Capacity Plus system may have several applications like RDAC and MNIS connected. These are seen as repeaters by the Master. Satellite Receivers however are not treated as repeaters and do not count towards the total. When the number of repeaters and applications in a system exceed 140, a dedicated non-trunked Master repeater must be used. This dedicated Master must be configured as a Data Revert repeater. Adding it does not reduce the number of Data Revert repeaters that can be normally deployed at that site. This dedicated Master repeater should have no voice or data activities (this includes CWID).

Networking

Repeaters in a Multisite Capacity Plus system use multiple individual messages to communicate with other repeaters in the system. The rest channel host repeater will also send a broadcast message to IP address 255.255.255.255. These broadcast messages may have undesired effects on any other devices present on the LAN. Therefore, repeaters should not hare the LAN with other, non-MOTOTRBO, devices such as printers or smart-home equipment.

All repeaters at a site must be on the same LAN, in other words, they must be behind the same router and plugged into the same network switch. It is strongly recommended that no other device be present on the LAN. For Multisite Capacity Plus software versions R02.10.00 and prior, the router at the Master repeater’s site should be capable of hairpinning.

In software versions R02.20.00 onwards, Multisite Capacity Plus can work with - or without - a hairpinning router at the Master-repeater site. When a non-hair-pinning router is utilized, each Multisite Capacity Plus repeater at same site as the Master, must be configured with a unique static IP address and a unique UDP port. The Rest Channel/Site IP address must also be configured as a unique static IP address and a unique UDP port for the site. If a non-hairpinning router is utilized, port address translation/port preservation for UDP must be disabled.

If a shared network will be used to link sites, or if security is a concern, a router VPN capabilities should be used. Using VPN doubles the required bandwidth so appropriate trade-offs need to be considered between the available bandwidth and the desired level of system security.

Like IP Site Connect, a Multisite Capacity Plus system needs one repeater to act as the Master. The Master repeater must have a static IP address, while other repeaters can have static IP addresses or obtain them dynamically from a DHCP server. All the repeaters in a Multisite Capacity Plus configuration register with the Master using the static IP address of the Master. This IP address is provisioned in all repeaters when the system is assembled during staging.

Emergency Mode

Multisite Capacity Plus supports emergency calls and uses an impolite channel access method.

A radio user on a Multisite Capacity Plus system can leave a Talkgroup Call and start an emergency or control call (e.g. Call Alert, Radio Check, Radio Disable etc.). When this happens, the radio moves to the current Rest Channel and starts a new call on the Rest Channel. If a user starts a non-Emergency Call when all channels are busy, then the call fails, and the radio stays on the traffic (voice) channel and call.

Unlike IP Site Connect and Single Site, Multisite Capacity Plus does not support a revert channel for emergency. Instead, the start of an Emergency Call is announced over all busy channels. This allows any listening radios that are to join the Emergency Call, to leave their current channel and monitor the Emergency Call. A radio will join an Emergency Call if the emergency talkgroup is either the TX-Contact or is in the RX-Group list for that personality.

A radio listening to an Emergency Call (e.g. E01) joins another Emergency Call (e.g. E02), only if the E02 group has a higher priority than the E01 group. The first priority is the TX-Contact, followed by any Talkgroup in the RX Group List of the radio.

Transmit Interrupt

Transmit Interrupt allows a radio to shut down an ongoing interruptible voice transmission, and potentially initiate a new transmission. Transmit Interrupt is independent of call type, therefore it applies to Group Calls, Private Calls, Emergency Calls and All Calls. This feature also applies to Private Calls that are initiated through remote monitor command, and Group Calls that are initiated via emergency remote monitor. This feature is supported on Capacity Plus Single Site and Multi Site system configurations from software version R01.07.00 onwards.

For Transmit Interrupt to operate consistently, all radios using the system should be provisioned with the ability to be interrupted. If some radios are provisioned without the ability to be interrupted (e.g. a supervisor’s radio), then those radios’ transmissions cannot be interrupted.

Channel Blocked Override

Channel Blocked Override improves the user experience in wide-area talkgroup call setups, in that these calls can now be set up successfully, even when some of the associated sites have no repeaters with free slots available due to interference; CWID transmission or a Major Alarm.

Unlike Capacity Max, talkgroup calls in a Multisite Capacity Plus system are statically streamed to RF sites - even to ones where there are no talkgroup members present. The sites to which a call must be streamed is defined in the Master Repeater codeplug/configuration, under Talkgroups.

No configuration is required to enable Channel Blocked Override, the only requirement is that all radios and repeaters are on M2022.01

Care needs to exercised when setting the number of Reserved Wide Area Channels. Setting this value too high will negate any advantage Channel Blocked Override brings in that the above setting reserves a certain number of timeslots purely for wide-area talkgroups which then causes local area talkgroups (i.e. talkgroups going out on just one site) to fail.

Reserved Wide Area Channels

This is a system feature that will make the repeaters in each site, reserve a certain number of timeslots solely to pass wide area talkgroup calls.

Care needs to exercised when setting the number of Reserved Wide Area Channels as this will restrict the number of concurrent private and single-site calls the system can handle. For example, if the number is set too high and all the non-reserved slots are occupied will non-wide-area calls, any further non-wide-area call setups will fail, even if the site(s) have free wide area slots.

See Also

MOTOTRBO