WO2018105024A1

WO2018105024A1 - Communication system

Info

Publication number: WO2018105024A1
Application number: PCT/JP2016/086115
Authority: WO
Inventors: Suan Yee TAN; Tien Ming Benjamin Koh; Takako Hori; Toyoki Ue
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2016-12-05
Filing date: 2016-12-05
Publication date: 2018-06-14
Anticipated expiration: 2019-06-05

Abstract

This invention describes the operation of an interfacing node that enables how the 3GPP system is set up to be interfaced with TETRA system to enable coverage extension, where the 3GPP system targeted is a private network. The second embodiment describes an alternative interworking solution where the targeted 3GPP system is a commercial network where no changes to the 3GPP system are made. A third embodiment describes how the interwork node based on the main embodiment can assist the user to select the correct terminal for usage.

Description

COMMUNICATION SYSTEM

The invention pertains to terminals equipped with multiple radio interfaces. More specifically, it relates to the operation of such terminals in a network assisted manner.

The modern day urban environment is dense with overlapping coverage of ubiquitous wireless networks. Heterogeneous digital radio networks of varying capability, range and usage pepper the typical urban landscape. Amongst the most notable include the 3GPP defined networks (including GSM, UMTS and LTE) used for cellular communications and TETRA that is used in many public safety outfits.

With the widespread proliferation of smartphones and wireless devices, the emphasis naturally shifts from the type of network to the service the user expects to receive regardless of the underlying network technology or device. Likewise, it is foreseeable that public safety personnel would expect communications to be accessible, whether the underlying communications is being carried over TETRA, LTE or some other platform. Similarly, devices can be expected to be switched out, dependent on available networks, with minimal service disruption.

Earlier teachings such as PTL 1 proposes a gateway to interconnect the Public Safety and Security (PSS) communication network and public cellular communication network. The gateway converts between PSS and cellular data protocols. However such a solution employs a voice transcoder to convert the voice signals from one format to another, required by the destination network. This results in additional network delay. The solution extends the range of Push-to-Talk (PTT) however it does not provide seamless transition from PTT coverage to cellular coverage.

Another similar teaching PTL 2 uses a dispatch gateway (DG) or real time exchange (RTX) that interfaces to the wireless communications system to provide advanced voice services. However such a solution is based on the older generation of cellular communication where circuit channels are used to provide reliable connections. However, in order to handle the longer circuit switch setup up time, the first talk burst uses pre-established Internet Packet (IP) data session. This complicated setup mechanism is no longer required in today's LTE system. Additionally, the proposed scheme is unable to provide true seamless service.

Yet in another possible method of extending 3GPP or TETRA service coverage, is by deploying more eNodeBs or TETRA switching management interfaces (SwMI). This is the most straight forward method but will result in high capital expenditure and operation expenditure which is undesirable. Another method is to include interworking functionality to TETRA server and private LTE service server. Through a new interface, TETRA service could be extended to use the LTE network. However this requires the existing TETRA network to be changed or upgraded and this might not be realistic.

[PTL 1] US20080171533A1
[PTL 2] US20100142414A1

It is an object of the invention to solve the above discussed problems. In particular this invention teaches a way to interwork between 3GPP user equipment and TETRA terminals to provide extension to voice communication coverage. A method is also disclosed for network-assisted information for device selection.

Figure 1 is a system configuration figure of the main embodiment; Figure 2 shows the modules in the TETRA application that enables UE(s) in 3GPP network to be capable of receiving TETRA related traffic; Figure 3 shows the modules in the interwork node configured for private 3GPP network; Figure 4 shows the frame format to be used for encapsulating TETRA voice frame in 3GPP defined network; Figure 5 is a sequence flow for the main embodiment; Figure 6 is the UE attachment procedure to be used in the main embodiment which is used for private LTE network; Figure 7 illustrates the establishment of the EPS bearers from UE to the interwork node; Figure 8 shows how a filter module is used to route the TETRA traffic, bypassing the P-GW; Figure 9 is a sequence flow for QCI setting for the EPS bearers; Figure 10 is a sequence flow that illustrates how TETRA related data is being conveyed in the 3GPP defined network; Figure 11 is a system configuration of the interwork node when used in commercial 3GPP defined network; Figure 12 shows the modules in the interwork node configured for commercial 3GPP network; Figure 13 is the sequence flow for the second embodiment; and Figure 14 illustrates the scenario where a user is carrying 2 devices with different network capabilities.

In the following description, for the purpose of explanation, specific numbers, times, structures, protocols, and other parameters are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to anyone skilled in the art that the present invention may be practiced without these specific details.

(Embodiment 1)
In the following description of the preferred embodiment, reference is made to the accompanying drawings from which the invention may be practiced. Figure 1 shows the interconnection of the invention that allows TETRA services extension. Within the diagram, 210 and 211 are TETRA SwMI which are connected to the TETRA network 230. 200 and 201 are TETRA terminals that are attached to the TETRA network. The interwork node 240 provides the functionalities of TETRA radio and the evolved packet core (EPC). The interwork node 240 could be attached to the TETRA network acting as a terminal and all incoming and outgoing 3GPP traffic to and from TETRA network is transferred via this node. It is also possible that the interwork node comprises of multiple TETRA radios to support concurrent frequency pairs (one for uplink and the other for downlink) such that each radio could be tuned to each carrier pairs. Traditionally, each TETRA base station supports a maximum of 8 carrier pairs (uplink and downlink) thus the interwork node 240 needs only to support maximum of 8 radios with the assumption that each radio can support both uplink and downlink. In the event that multiple radios are used, each radio will be serviced as if it is a terminal. In this manner, the 3GPP network is able to utilize the maximum capacity of the TETRA network through the interwork node 240. In short, more talk groups can be supported concurrently. The interwork node 240 is connected to the 3GPP base station or

eNodeB

220, 221 as it also serves as an EPC.

A Long Term Evaluation (LTE) user equipment (UE) 202 is attached to the 3GPP LTE network. In the LTE UE 202, a TETRA application comprising of reduced TETRA stack resides on top of the LTE radio and protocol stack. Figure 2 shows the architecture of the LTE UE 202 which is referred to as 300 in this diagram. As 300 is a LTE UE, it operates using a LTE radio and LTE protocol stack 330. Running on top of this stack is the TETRA application 310 comprising of a control 311, a reduced TETRA stack 313 and a frame buffering and jitter management module 312 that interfaces to the algebraic code-excited linear prediction (ACELP) codec 320. Even though in the figure the codec is not shown to be part of the TETRA application, it could be implemented as one. ACELP is the codec used by TETRA for encoding and decoding voice frames and the frame buffering and jitter management module 312 in the UE regulates the voice frames to the decoder so that voice can be played out smoothly. The control 311 receives commands from the user and maps them to corresponding instructions of the reduced TETRA stack 313. Requesting for permission to talk in a talk group by the pressing of a button on the UE is an example of a command from the user. The reduced TETRA stack 313 is in fact a full TETRA stack but with its radio and part of the mac layer functionalities related to the radio removed. Data conveyed between the reduced TETRA stack 313 and the LTE protocol stack 330 will be based on the TETRA mac frame format. The protocol stack 330 is made up of LTE radio layer 1 up to the RTP layer. Depending on the TETRA frame type received from the reduced TETRA stack, different encapsulation shall be used. TETRA commands or signalling frames shall be encapsulated using the TCP/IP or UDP/IP datagram. Voice frame on the other hand needs to be encapsulated in RTP/UDP/IP datagram.

Figure 3 shows the main components or functionalities present in the interwork node 240 which is referred to as 400 in this diagram. The interwork node 400 contains a TETRA radio module 450 that supports connection to a TETRA network. The TETRA radio module 450 may support concurrent transmission/reception on multiple frequency carriers. This allows more LTE UEs to use the PTT services concurrently and TETRA SwMI capabilities shall be the limiting factor. This radio module provides the interface and is the bridge to the TETRA network. The mapping function 410 provides a means to map Individual TETRA subscriber identity (ITSI) to group TETRA subscriber identity (GTSI) to individual mobile subscriber identity (IMSI) and vice versa. Using this mapping, data could be directed to the correct individual or user group. The registration of this mapping information could be performed through graphical user interface (GUI) application. LTE UE presence monitor 420 on the other hand is responsible for determining whether a UE is attached to the PTT service via LTE. If it is, PTT data destined for the UE will be forwarded to it. The interwork node 400 on receiving TETRA voice frames from the TETRA network via the TETRA radio module 450 in the interwork node, will encapsulate them as IP/UDP/RTP format which is referred to as 500 in Figure 4 via the encapsulation module 460. For TETRA signalling frames, IP/UDP or IP/TCP format could be used. Following this procedure, the encapsulated messages will be sent to the Evolved Packet Core (EPC) 440 which resides within the interwork node 400. The EPC comprises of the serving gateway (S-GW), packet data network gateway (P-GW), mobility and management entity (MME) and other sub-modules e.g. home subscriber server (HSS) and etc, may be connected to multiple eNodeB(s). This EPC like other normal EPCs can be connected to external networks and identification of a network is via the access point name identifier. The forwarding module 430 forwards the received LTE PTT frames back to the LTE network as there could be other LTE UEs using the PTT services in the LTE network. For frames from LTE network and destined for the TETRA network, the de-capsulation module 470, will retain the content of the LTE frame and repackage them using TETRA mac frame format. The interwork node 400 besides supporting TETRA group/individual calls also supports TETRA device-to-device mode where one end is a TETRA device and the other end a LTE UE, enabling it to act like a walkie talkie.

With this type of network configuration, LTE UE 202 and TETRA devices/

terminals

200 and 201 can communicate with one another using the advanced voice service or also known as the TETRA voice service.

Figure 5 summarizes the start-up behaviour of the proposed system. The system comprises of SwMI 601, UE under TETRA coverage 600, interwork node 602 connected to the eNB/eNodeB 603 and UE under the LTE coverage 604.The interwork node 602 as described earlier comprises of the TETRA radio and EPC. The TETRA radio helps link up the TETRA network while the EPC provides LTE core network functionalities and is connected to the eNodeB(s). At start-up, the interwork node 602 is assigned an identity e.g. access point name (APN) 620 so that LTE UE(s) can establish EPS bearer(s) for the TETRA services e.g. PTT. In order to start a group call, talk-groups need to be set up and ITSI, GTSI and IMSI of the allowed UEs are either pre-registered or dynamically registered into the system. Through this registration, the interwork node will be able to map the traffic to the corresponding UEs in the networks. For UEs/devices in the TETRA network, registration to the network with authentication is required 631. Likewise for UEs in the LTE network, registration and attachment procedure is needed 640.

Figure 6 shows the attachment procedure. UE first establishes a RRC connection 641. Then it sends the ATTACH REQUEST message together with a PDN CONNECTIVITY REQUEST 642 for the packet data network (PDN) connectivity on the established RRC Connection. The NAS common procedure of NAS identity, authentication and security mode procedure 643 is used if the network is unable to identify the UE. The MME updates the location of the UE and also requests the subscriber profile from the HSS 644. The MME establishes an eGTP User Tunnel to establish the default bearer at the SGW which sends a Create Session Request toward the SGW. The SGW creates the default bearer for this UE and requests the P-GW to create a bearer for this UE between the SGW and the P-GW to provide end-to end bearer connectivity. The P-GW then creates the bearer and allocates an IP Address for the UE 645. Upon receiving the Initial Context Setup Request, eNodeB reconfigures the resources to the UE by sending an RRC Connection Reconfiguration Request to the UE and it responds back with an RRC Connection Reconfiguration Complete. The eNodeB then responds with an Initial Context Setup Response 646. The MME updates the eNodeB tunnel ID for the default bearer using Modify Bearer Request 647.Finally the attachment procedure is completed 648 and a default bearer is established for the TETRA network.

After attachment, dedicated uplink and downlink channels are established 650 for the TETRA PTT traffic and the established dedicated bearers are linked to the earlier default bearer that is set up. This forms the virtual connection, EPS bearer, up to the interwork node 602.

Figure 7 shows the establishment of the EPS bearer from the UE to the interwork node.

For TETRA data (e.g. PTT data) transmission from the LTE network to the TETRA network, the P-GW could be bypass through routing of this traffic at the S-GW or eNodeB. The S-GW/eNodeB is able to identify a traffic is of TETRA type through determining EPS bearers that will lead up to the TETRA external network or other equivalent means. At the S-GW, the routed traffic is directed to the forwarding function module 430 in Figure 3.

Figure 8 shows the placement of a filter module 649 at the S-GW to direct TETRA traffic to/from the forwarding function module 430/ encapsulation module 460. This filter module 649 can be based on the EPS bearer id as discussed earlier. This mechanism will improve the packet delay budget by a couple of milliseconds. It should be highlighted that the EPC in Figure 3 with the optimization explained earlier, will not be the standard EPC but one that can quickly route traffic from the S-GW or other entity bypassing the P-GW for TETRA traffic.

For private LTE network, this type of customization is possible since there is full control of the LTE modules and their interconnections. In the event that multimedia broadcast multicast service (MBMS) is used, multicast service needs to be activated 660, 670. Interwork node is made known of a UE's connection to TETRA service via LTE through the use of Session Initiated Protocol (SIP) or any other equivalent protocol 680. On knowing that channels have been established between TETRA and LTE networks, TETRA traffic e.g. PTT could be directed to and from the networks for the concerned UEs.

Subsequent procedures

690, 692 and 691 are used to set up (join), terminate group calls and transmit data respectively. TETRA commands and voice frames destined for LTE network are encapsulated in IP/UDP or IP/TCP format and IP/UDP/RTP format respectively as shown in Figure 6.

As TETRA is generally deployed for public safety scenario (PSS) and when LTE is used to extend its coverage, there is a requirement to give TETRA services particularly PTT a higher priority as compared to the existing LTE services, since it is used in mission critical operations.

Figure 9 is an illustration of how the QoS class identifier (QCI) could be set for the PTT service over LTE. QCI 1 could be used for PTT however allocation and retention priority (ARP) should be given a lower value than VoLTE 800 so that the latter is of lower priority and could be pre-empted in times of congestion. Alternatively, QCI 65 which has been assigned for mission critical applications could also be used.

Figure 9 shows the QCI setting for the EPS bearer which is from the UE up to the P-GW. In this proposed invention, it should be noted that for TETRA related data, the P-GW can be skipped and the data is directed to the S-GW. For outgoing TETRA data from the LTE network, S-GW directs the frames to the forwarding module that checks whether forwarding back to the LTE network is necessary and also to the de-capsulation module 470 where it repackages the packet into TETRA mac frame format for transmission in the TETRA network. For incoming TETRA data, the encapsulation module 460 will direct the traffic into EPC and within it, the filter module 649 in Figure 8 will direct it to the corresponding S-GW and then the targeted eNodeB based on the EPS bearer information which is made up of the data bearer, S1 bearer and S5 bearer. Alternatively, TETRA traffic re-routing could also be performed at the eNodeB. Modification proposal is not made to this procedure as it is still applicable and to minimize customization required to the existing LTE core network stack.

Figure 10 shows LTE UE 703 transmitting PTT voice and signalling frames. The interwork node 704 when received the frames, will determine whether there are any PTT individual/group users in the LTE network. If there are e.g.

LTE users

710, 711, 712, the frames will be rerouted back to the LTE network. As a general rule, TETRA signalling frames are rerouted however if voice frames from a particular group has no user in the LTE network, rerouting is unnecessary.

The approach described in this embodiment is used for private LTE network scenario however it is also applicable to mobile virtual network operator (MVNO) scenario where the wireless communications services provider does not own the wireless network infrastructure. The MVNO could request the mobile network operator to customize their network such traffic traversing on certain EPS bearers be re-routed to some external ports instead of to the P-GW. The interwork node minus the EPC capabilities can be connected to the ports and in this manner, TETRA PTT services could be extended using LTE infrastructure. Similarly this concept could also be extended for MBMS. The mobile network operator provides the MBMS service while the interwork node provides the broadcast multicast service centre (BM-SC).

(Embodiment 2)
In the second embodiment, a description on how the 3GPP system is set up to be interfaced with TETRA system to enable coverage extension, where the targeted 3GPP system is a commercial network where no changes to the 3GPP system are made.

Figure 11 shows the setup of the interwork node 910. In this setup, the interwork node 910 is connected to the commercial LTE network (LTE Core Network) 920 via the internet 930 where the LTE network 920 is connected through the P-GW 921. The P-GW 921 is connected to the eNodeB 922. The interwork node 910 at the other end is connected to the TETRA infrastructure (TETRA Network) 900 via the TETRA radio module 450. Using this configuration for TETRA network 900 and commercial LTE network 920, TETRA services could be extended into the LTE network. LTE UE 923 installed with a TETRA application will be able use TETRA PTT over LTE and communicate with

TETRA devices

904, 903 which are connected to the

TETRA base stations

902 and 901 respectively.

Figure 12 shows the main modules present in the interwork node 910 which is referred to as 1000 in this diagram. The interwork node 1000 contains a TETRA radio module 1040 that supports connection to a TETRA network. The TETRA radio module 1040 may support concurrent transmission/reception on multiple frequency carriers and is the interface to the TETRA network. The mapping function 1010 provides a means to map Individual TETRA subscriber identity (ITSI) to group TETRA subscriber identity (GTSI) to individual mobile subscriber identity (IMSI) and vice versa. Using this mapping, data could be directed to the correct individual or user group. LTE UE presence monitor 1020 is a session manager and based on the session established by the UE, it is able to determining whether the UE is attached to the PTT service via LTE. Protocols like session initiated protocol (SIP), HTTP session and etc are examples of protocols that could be used for session management, Besides being equipped with UE presence detection capability, the monitor 1020 maintains the virtual channel or session for TETRA traffic to flow from the interwork to the UE via the EPC and vice versa. The interwork node 1000 upon receiving TETRA voice frames from the TETRA network via the TETRA radio module 1040 in the interwork node, will encapsulate them as IP/UDP/RTP format which is referred to as 500 in Figure 4 via the encapsulation module 1050. For TETRA signalling frames, IP/UDP or IP/TCP format could be used. The forwarding function module 1030 enables other UEs in the LTE network to receive TETRA related frames send from a UE, through forwarding the frames at the interwork node back to the LTE network on knowing the presence of other UEs in the network using the TETRA services. For frames from LTE network and destined for the TETRA network, the de-capsulation module 1060, will retain the content of the LTE frame and repackage them using TETRA mac frame format.

The same TETRA application shown in Figure 2 could also be used in this TETRA and commercial LTE network configurations.

The operations of the second embodiment are described in the flow/sequence chart found in Figure 13. The attach procedure 1100 registers the UE to the network that provides the internet service. The default bearer which is of non-guaranteed bit rate (UGBR) type usually is assigned for internet usage and this is decided by the network operator. The UE then establishes a session 1101 with the interwork node using the internet service set up earlier. LTE TETRA traffic will have to transverse through the P-GW as opposed to the main embodiment where P-GW could be bypassed. The protocol used by this session could be based on session layer protocol, SIP or application layer protocol, http session or the likes. One of the objectives is for the presence monitor to keep track of UEs currently using the TETRA services over LTE network. The remaining procedure is similar to the preferred embodiment.

The second embodiment can be easily integrated with any existing LTE network as it assumes no changes are required while the main embodiment enables a lower delay budget and is achieved via EPC optimization and setting QCI for EPS bearers carrying TETRA related data.

(Embodiment 3)
In the following description, the operation of the interwork node in assisting the user in device selection for service continuity is disclosed.

Figure 14 shows a scenario where a user carries on his person two mobile devices with different network capabilities. The first mobile device is the TETRA terminal 160 and the other device is a 3GPP user equipment (UE) 170. The user should have registered with an interwork node 150 accessible database that both devices belong to the same user. The interwork node 150 is connected to the TETRA network 130 and EPC 100 via the internet 120. The TETRA network 130 is connected to the TETRA base stations 140. EPC 100 is connected to the eNodeB 110.

For optimal operation, a switch application should be installed on the mobile devices. The primary function of the switch application would be to send periodic notification messages to the interwork node 150 from the respective mobile devices. The TETRA terminal 160 may use the TETRA SDS (Short Data Service) messages for efficiency purposes. The 3GPP UE 170 may use generic data communications to communicate with the interwork node 150.

In one particular deployment, should the interwork node 150 detect that the TETRA terminal 160 has not sent any notification messages after some pre-determined time, it may choose to initiate establishment of another connection to a different device registered with the same user. In this case, 3GPP UE 170 may start receiving TETRA messages or voice communications from the relevant groups that terminal 160 was registered to.

Some factors that may influence the selection of a terminal from the user list include location (i.e. near currently active device), pre-configured selection priority value of device, device status (for example, battery level, signal strength, device capabilities such as voice or text-only).

Depending on the policies or network limitations, it is possible that connection establishment may involve a text or voice message to the user so that the user can initiate establishment procedures or take action on the active terminal.

Additionally, it is possible that the connection establishment take place pre-emptively based on predicted disconnection due to poor signal strength or low battery power of the device.

Claims

A communication system used to extend TETRA services to 3GPP user equipment, the system comprising:
the 3GPP user equipment (UE) have an application installed that enabled the transmission and reception of TETRA related data; and
an interwork node connected to 3GPP capable network and TETRA network with the 3GPP user equipment or TETRA terminals registered to the networks,
wherein the interwork node enables the 3GPP user equipment or TETRA terminals to communicate with one another using different radios,
wherein the interwork node comprises UE presence monitor, mapping function module, encapsulation module, de-capsulation module, forwarding LTE TETRA frames module and the TETRA radio module.
The communication system according to claim 1, wherein, when configured as a private 3GPP network, the communication system comprises an additional module, the Evolved Packet Core (EPC).
The communication system according to claim 1, wherein, when configured as a commercial 3GPP network, the communication system does not require an Evolved Packet Core (EPC) in the interwork node as the EPC is provided by the network operator.
The communication system according to claim 1, wherein the TETRA radio module which is part of the interwork node is capable of connecting to the TETRA network thus allowing 3GPP user equipment to communicate with TETRA terminals.
The communication system according to claim 4, wherein the TETRA radio module used by the interwork node to connect to the TETRA network may concurrently support the maximum number of carriers supported by the TETRA base station.
The communication system according to claim 1, wherein the interwork node has a mapping or lookup function module or equivalent that is able to relate ITSI to GTSI to IMSI or ITSI to IMSI or GTSI to IMSI and vice versa.
The communication system according to claim 1, wherein, when the forwarding module in the interwork node, receives encapsulated TETRA voice or control or data frames from 3GPP user equipment connected to the 3GPP defined network, the forwarding module will be able to forward these received frames back to the 3GPP defined network and/or to the TETRA network.
The communication system according to claim 7, wherein the forwarding module of interwork node has the capability to determine which frames need to be forwarded back to 3GPP defined network and/or TETRA network.
The communication system according to claim 1, wherein, when the de-capsulation module in the interwork node receives voice, data or control frames from the 3GPP network, the de-capsulation module will be able to de-capsulate the frames of IP/UDP or IP/TCP or IP/UDP/RTP format and forward de-capsulated frames to the TETRA network.
The communication system according to claim 1, wherein, when the encapsulation module in the interwork node receives TETRA frames from the TETRA network, the encapsulation module is capable of encapsulating the frames into IP/UDP or IP/TCP frame format if the received TETRA frames are not voice frames and encapsulate the TETRA voice frames into IP/UDP/RTP format.
The communication system according to claim 2, wherein the EPC is customized such that the EPC is capable of routing incoming/outgoing TETRA related traffic in the 3GPP network bypassing the P-GW.
The communication system according to claim 11, wherein the interwork node which has a customized EPC will also act like an external network in which the customized EPC has its own APN wherein the 3GPP user equipment needing to use the TETRA services will need to attach to the customized EPC by establishing a default bearer first, followed by dedicated bearers.
The communication system according to claim 12, wherein the interwork node is capable of assigning IP address to the 3GPP user equipment.
The communication system according to claim 11, wherein the routing of incoming/outgoing TETRA related traffic in the EPC may be performed at the S-GW or eNodeB wherein there exists a filter module or its equivalent to support this routing.
The communication system according to claim 14, wherein the filter module determines the packets that need to be re-routed based on the EPS bearer identity which contains radio bearer identity, S1 bearer and S5/S8 bearer identity.
The communication system according to claim 14, wherein the filter module determines the destination nodes e.g. S-GW and/or eNodeB which the packets need to be directed based on the information derived from the EPS bearer identity.
The communication system according to claim 2, wherein the UE presence monitor in the interwork node is capable of acting as a session manager using session layer protocol e.g. SIP or application layer protocol e.g. http session or the likes to detect and monitor UEs' activity status regarding LTE TETRA services usage although TETRA data is not carried within the session.
The communication system according to claim 2, wherein the EPC is capable of configuring EPS bearer(s) carrying PTT voice frames with QCI 65 which is used for mission critical operations.
The communication system according to claim 2, wherein the EPC is capable of configuring EPS bearer(s) carrying PTT voice frames with QCI 1 and a higher ARP (lower value) than EPS bearer(s) carrying VoLTE.
The communication system according to claim 2, wherein, when the interwork node is connected to a 3GPP defined network capable of broadcasting and multicasting, the interwork node is able to serve as a broadcast multicast service centre (BM-SC) or interface with a BM-SC in the network wherein the downlink TETRA related data originally scheduled for transmission in the dedicated GBR bearers may be transmitted using the broadcast channels.
The communication system according to claim 3, wherein, when the interwork node is reachable by the 3GPP user equipment with an IP address, the interwork node is capable of allowing the 3GPP user equipment to establish sessions with the interwork node via internet, wherein TETRA data may be carried within the sessions.
The communication system according to claim 3, wherein, when the interwork node is connected to a 3GPP defined network capable of broadcasting and multicasting, the interwork node is able to serve as a broadcast multicast service centre (BM-SC) or interface with a BM-SC in the network wherein the downlink TETRA related data originally scheduled for transmission in the session(s) may be transmitted using the broadcast channels.
The communication system according to claim 1, wherein the interwork node is capable of operating with a TETRA terminal which is operating in direct mode operation wherein the 3GPP user equipment in the 3GPP network and installed with the TETRA application, can communicate with the TETRA terminal, in the absence of the TETRA infrastructure.
The communication system according to claim 1, wherein the interwork node with access to information regarding multiple devices belonging to the same user, may receive periodic status notifications from the devices, in order to initiate connection establishment and service continuity in the event the currently active device is disconnected.
The communication system according to claim 24, wherein the interwork node is a node where the alternate device selection may be made on the criteria of co-location with active device, device status or device capabilities.
The communication system according to claim 24, wherein the interwork node is a node where the connection establishment may be pre-emptive based on probability of disconnection of active device.
The communication system according to claim 1, wherein the installed application comprises a reduced TETRA stack, a control module, a frame buffering and jitter management module and optionally ACELP codec.
The communication system according to claim 27, wherein the reduced TETRA stack is a full TETRA stack minus the TETRA radio and part of the medium access control layer wherein the reduced TETRA stack is capable of processing TETRA signalling and data messages accordingly.
The communication system according to claim 27, wherein the control module is capable of receiving user command and act upon based on the user command.
The communication system according to claim 27, wherein the frame buffering and jitter management module is capable of buffering the received voice frames and playing out the frames in constant manner.
The communication system according to claim 27, wherein the installed application has the capability to perform ACELP encoding and decoding.
The communication system according to claim 1, wherein the 3GPP user equipment is capable of indicating a TETRA-private 3GPP network APN to the installed application when the 3GPP user equipment established a PDN connection to the interwork node.
The communication system according to claim 32, wherein the 3GPP user equipment is capable of obtaining an IP address from the interwork node i.e. while initiating the attachment to the interwork node which acts as an APN for the private 3GPP network scenario.