Note: Descriptions are shown in the official language in which they were submitted.
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
WIRELESS COMMUNICATION SYSTEMS AND APPARATUS AND METHODS
AND PROTOCOLS FOR USE THEREIN
Field of the invention
This invention relates to wireless communication systems
and apparatus and methods for use therein. In
particular, the invention relates to utilising wireless
local area network (WLAN) technology by a wireless radio
communication system. The invention is applicable to,
but not limited to, facilitating and supporting WLAN
features in a TErrestrial Trunked RAdio (TETRA)
communication system.
Background of the Invention
Over recent years, the development in wireless
communication has been dramatic. A number of wireless
communications have been standardised, to facilitate
inter-operability of communications between different
manufacturers as well as ensure that all communication
units offer the same level of performance in a particular
communication field. One technology to undergo such
rapid development and standardisation is Wireless Local
Area Networks (WLANs). WLANs have been targeted to
provide wireless connectivity at bit rates higher than
100 Mbps. WLANs also offer the opportunity of enhanced
security, enhanced mobility management, inter-working
with cellular networks, etc. Thus, WLAN technology is
anticipated as playing a key role in the wireless data
market for many years to come.
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
2
Furthermore, WLANs are currently being enhanced to
provide a guaranteed quality of service (QoS), as can be
seen in IEEE Std. 802.11e/D6.0, "Part 11: Wireless Medium
Access Control (MAC) and physical layer (PHY)
specifications: Medium Access Control (MAC) Quality of
Service (QoS) Enhancements", November 2003. This is a
further reason as to why WLAN solutions for voice and
video services are quickly emerging in the data
marketplace.
Wireless communication systems, for example cellular
telephony or private mobile radio communication systems,
typically provide for radio telecommunication links to be
arranged between a system infrastructure including a
plurality of base transceiver stations (BTSs) and a
plurality of subscriber units or terminals, often termed
mobile stations (MSs). An example of a zone/cell-based
wireless communication system is a TETRA (TErrestrial
Trunked Radio) system, which is a system operating
according to TETRA standards and protocols as defined by
the European Telecommunications Standards Institute
(ETSI). A primary focus for TETRA equipment is use by
the emergency services, as TETRA provides dispatch and
control services. The system infrastructure in a TETRA
system is generally referred to as a switching and
management infrastructure (SwMI), which substantially
contains all of the communication elements apart from the
MSs.
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
3
The communication network may provide radio
communications between the infrastructure and MSs (or
between MSs via the infrastructure) of information in any
of the known forms in which such communications are
possible. In particular, information may represent
speech, sound, data, picture or video information. Data
information is usually digital information representing
written words, numbers etc, i.e. the type of user
information processed in a personal computer. In
addition, signalling messages are communicated. These
are messages relating to the communication system itself,
e.g. to control the manner in which user information is
communicated in compliance with the selected industry
protocol such as TETRA. Different channels may be used
for communication of the different forms of information.
For data to be transferred across communication networks
via a data communication channel, a communication
terminal addressing protocol is required. The
communication units are generally allocated addresses
that are read by a communication bridge, gateway and/or
router, in order to determine how to transfer the data to
the addressed destination communication unit. Such data
transfer needs to be effectively and efficiently provided
for, in order to optimise use of limited communication
resources. Currently, the most popular protocol used to
transfer data in communications systems is the Internet
Protocol (IP).
The Internet Protocol adds a data header on to the
information passed from the transport layer. The
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
4
resultant data packet is known as an Internet datagram.
The header of the datagram contains information such as
destination and source IP addresses, the version number
of the IP protocol etc. Each exchange of data typically
consists of sending one or more data packets on an uplink
channel and one or more data packets on a downlink
channel. A Packet Data CHannel (PDCH) in a TETRA. network
can serve several MSs at the same time. In this regard,
the resources of the PDCH are then shared between the MSs
on the channel on a statistical multiplex basis. This
enables the air interface resources to be used in an
optimal manner.
The TETRA known signalling procedure, used for accessing
the PDCH, requires a MS firstly to request access to the
PDCH via the main control channel (MCCH) on which control
signalling messages are mainly sent. Following access
approval by the SwMI and sending of an appropriate
signalling message to the MS, the MS is then moved by
receipt of the signalling message to the PDCH, where data
packets are exchanged.
In TETRA packet data communication, physical data
channels carry both system control signalling and data
payload (user communicated information). These two types
of traffic may be given different priorities, with
control signalling usually being allocated a higher
priority. TETRA packet data communication currently
operates at a maximum of 28.8kbits/sec, which is
significantly less than some other wireless communication
technologies, such as WLAN.
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
The inventor has recognised therefore that a need exists
for an improved mechanism and associated apparatuses,
methods and communication protocols for enhancing the
5 data rate to be provided to TETRA-capable communication
units, wherein the abovementioned disadvantages/
limitations may be alleviated.
Summary of the invention
In accordance with a first aspect of the present
invention, there is provided a wireless communication
system. The wireless communication system comprises a
wireless local area network (WLAN) operably coupled to a
private mobile radio system and arranged such that a
wireless communication unit is capable of private mobile
communication with the private mobile radio system over
the wireless local area network.
In accordance with second, third and fourth aspects of
the present invention, there is provided respectively a
wireless local area network (WLAN) access gateway (WAG),
an InterWorking Function (IWF) and a wireless terminal
adapted to facilitate communication over a private mobile
radio system such as a TETRA system and the wireless
local area network (WLAN) in the aforementioned wireless
communication system.
In accordance with a fifth aspect of the present
invention, there is provided a method of communicating
between a wireless local area network (WLAN) and a
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
6
private mobile radio system by a dual-mode terminal
capable of operating over the WLAN and the private mobile
radio system. The method comprises the steps of
receiving a message from the dual-mode terminal
requesting an association with the WLAN using the
identified (SSID); creating a tunnel to route private
mobile radio communications to or from the terminal via
the WLAN and assigning an address to route communications
to or from the terminal. The method further comprises
the steps of processing communicated packets comprising
extracting the assigned address; and routing packets to
or from the terminal in response to the extracted
assigned address.
In accordance with a sixth aspect of the present
invention, there is provided a protocol for facilitating
the aforementioned communications between a wireless
local area network (WLAN) and a private mobile radio
system.
Further features of the present invention are defined in
the dependent Claims.
Brief Description of the accompanying drawings
Embodiments of the present invention will now be
described by way of example only, with reference to the
accompanying drawings, in which:
FIG. 1 illustrates a schematic block diagram of a WLAN
inter-operating with a TETRA Switching and Management
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
7
Infrastructure (SwMI) adapted in accordance with the
preferred embodiment of the present invention;
FIG. 2 illustrates a further schematic block diagram of a
WLAN inter-operating with a TETRA Switching and
Management Infrastructure (SwMI), which contains the
various logical interfaces;
FIG. 3 illustrates a mechanism of traffic flow between
ToW terminals tunnelled through the IP network;
FIG. 4 illustrates a protocol architecture of a ToW
terminal according to the preferred embodiment of the
present invention;
FIG. 5 illustrates a preferred packet structure employed
in the TETRA over WLAN architecture;
FIG. 6 illustrates a preferred packet structure of a
control-plane packet transmitted by an IWF that contains
a D-SETUP message; and
FIG. 7 and FIG. 8 illustrate example signalling flows of
TETRA over WLAN system, according to the preferred
embodiments of the present invention.
Description of embodiments of the invention
In summary, the preferred embodiment of the present
invention proposes to integrate WLAN technology with a
private mobile radio system, such as a TErrestrial
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
8
Trunked RAdio system, as defined by the European
Telecommunication Standards Institute (ETSI). A proposed
system configuration of both a WLAN inter-operating with
a TETRA switching and management infrastructure (SwMI) is
illustrated in the schematic block diagram of FIG. 1.
The preferred embodiment of the present invention
proposes a dual-mode wireless communication unit. The
dual-mode operation utilises a first private (or public)
mobile radio technology, such as TETRA, and a second WLAN
technology. The wireless communication terminals,
hereinafter referred to as a TETRA over WLAN (ToW)
terminal 116, interface with the TETRA. Switching and
Management Infrastructure (SwMI) 160 over a WLAN radio
interface 115. This is in contrast to a conventional
TETRA terminal 132 interfacing with the TETRA SwMI 160
via a conventional TETRA enhanced base transceiver
station (EBTS) 134 over a conventional TETRA radio
interface and communication link 135. Thus, a dual-mode
TETRA and WLAN supported terminal is described.
In the context of the present invention, a Tetra-over-
WLAN (ToW) terminal 116 is any WLAN terminal that is
configured to be able to interface with the TETRA SwMI
160 and employ TETRA services by means of the protocols
and functions specified herein. ToW terminals 116
preferably associate with the WLAN by using a special
Service Set IDentifier (SSID).
A preferred example of an SSID is described in IEEE
standard 802.11, edition 1999, titled "Wireless LAN
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
9
Medium Access Control (MAC) and Physical Layer (PHY)
Specification". By means of this special SSID, the WLAN
is able to differentiate between ToW terminals and non-
ToW terminals and therefore apply different routeing
and/or access control policies.
The WLAN preferably implements a special routeing
enforcement policy for ToW terminals 116. That is, the
WLAN tunnels uplink packets from all ToW terminals 116 to
an Interworking function (IWF) 150 over a Ft tunnel.
Thus, a Ft interface preferably operates between the WAG
142 and the IWF 150, and is used to implement a
tunnelling scheme that tunnels IP packets through an IP
network 140 between the WAG 142 and the IWF 150.
Although the preferred embodiment utilises a'Ft Tunnel',
as known in the art, it is envisaged that any possible
tunnelling scheme could be used, e.g. IP encapsulation,
GRE, etc. In a case when the IWF 150 interconnects with
a WAG 142 over a leased line, tunnelling can be
eliminated. Thus, packets originating from any ToW
terminal 116 are routed to the IWF 150 via the Ft tunnel.
FIG. 3 depicts a preferred mechanism of how traffic from
ToW terminals is tunnelled to the IWF 150 and how traffic
from all other terminals can be routed to the Internet or
an Intranet.
Every ToW terminal preferably implements the protocol
architecture and the procedures specified below, in order
to support TETRA services over WLAN. Physically, it is
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
envisaged that a ToW 116 may be any kind of wireless
communication device with a WLAN interface, namely, a
personal computer (PC), laptop, PDA, dual-mode WLAN/TETRA
terminal, etc.
5
From a SwMI perspective, ToW terminals 116 may be
considered as any TETRA terminal. That is, ToW terminals
116 are preferably assigned a TETRA Individual Short
Subscriber Identity (ISSI), and thus able to initiate and
10 participate in group calls, able to receive/send Short
Data Service (SDS) messages, and, in general, able to
utilise all authorized services provided by the TETRA
SwMI 160. A ToW terminal 116 is therefore able to
communicate with other ToW terminals, with conventional
TETRA terminals, with dispatchers, PSTN users, and other
TETRA entities in accordance with their subscription
profile in the SwMI 160.
The ToW terminals 116 preferably employ all of the known
TETRA services, including group calls, short data service
(SDS) messaging, packet services, etc. From a SwMI
perspective, the ToW terminal 116 is no different to any
other conventional TETRA terminal 132.
Advantageously, the characteristics of the WLAN radio
interface 115 enable extended capabilities and new
features, such as high-speed data services, simultaneous
voice and data, improved voice quality, reduced call set-
up and voice transmission delays, simultaneous reception
of many group calls, monitoring of Main Control Channel
(MCCH) traffic while receiving voice and/or data, etc.
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
11
Thus, TETRA terminals (e.g. ToW terminals 116) benefit
from known advantages of WLAN technology.
The ToW terminals 116 operate ori a WLAN site, which can
be considered as a geographical area wherein WLAN
coverage is provided and it is controlled by a single
WLAN Access Gateway 142. A WLAN site typically comprises
one or more APs. The ToW terminals 116 have a wireless
interface to a WLAN access point 114. The WLAN Access
Point 114 interfaces with WLAN terminals over any kind of
WLAN interface, for example using IEEE 802.11 WLAN
technology, as published by IEEE in the document titled
"Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) Specification , IEEE standard 802.11, edition
1999. The WLAN access point has an interface 115 to the
Internet Protocol (IP) network 140 via one or more WLAN
Access Gateways 142. The IP network 140 is operably
coupled to the TETRA SwMI 160 via key component of the
proposed system, i.e. the Interworking Function (IWF)
150.
The IWF 150 is configured to interface 155 to the SwMI in
a similar manner to a TETRA conventional base station
134. The IWF 150 interfaces also with one or more WLAN
Access Gateways (WAGs) 142. In effect, the WAG 142 is a
router, or a combination of router and Ethernet Switches
to control a single WLAN site. The WAG interfaces with
one or more APs 114 typically through an Ethernet
100BaseT medium. Preferably, one WAG is assigned for
each WLAN site. The WAG 142 is preferably creating a Ft
tunnel with the IWF 150 when there are ToW terminals in
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
12
its WLAN site. It is envisaged that any known tunnel
establishment protocol can be used, e.g. PPTP, L2TP,
IPsec. The WAG 142 then applies the appropriate routeing
enforcement policy, a preferred example of which is
illustrated in FIG. 3. In addition, the WAG 142 is
preferably releasing the Ft tunnel when there are no ToW
terminals in its WLAN site, in order to free up capacity.
It is envisaged that there may also be a static Ft tunnel
that is not created/released dynamically.
Notably, both WAG and AP are off-the-shelf devices and
their configuration is typical to known WAGs and APs,
save for a signal processing function that has been
adapted to support TETRA SSIDs, and route such TETRA
communication according to a determination of the SSID.
The IWF 150 uses known IP multicasting technology to
transfer control packet data units (PDUs) and voice
packets to the TETRA-over-WLAN (ToW) terminals 116.
Thus, in this manner, mobile or fixed ToW terminals 116
are able to access the typical services provided by the
TETRA. SwMI 160 by means of a WLAN network interface 115
and corresponding software drivers and applications, as
will be appreciated by a skilled artisan. The ToW
terminals 116 re-use the majority of TETRA air interface
protocols, as illustrated in the European
Telecommunication Standards Institute's (ETSI) document -
EN 300 392-2 v2.3.10, "Terrestrial Trunked Radio (TETRA);
Voice plus Data (V+D); Part 2: Air Interface (AI)", ETSI,
June 2003. Notably, the ToW terminals 116 re-use the
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
13
majority of TETRA air interface protocols on top of the
WLAN radio interface. The TETRA SwMI 160 is preferably
built on IP multicast and Voice-over-IP (VoIP)
technologies, such that interfacing with IWF 150 is
relatively straightforward, as will also be appreciated
by a skilled artisan.
The InterWorking Function (IWF) 150 is a key functional
element that interfaces with the TETRA SwMI 160 over any
suitable interface, such as a proprietary interface, and
also interfaces with one or more WAGs 142 over the Ft
interface. Notably, one function of the IWF 150 is to
hide from the SwMI 160 the peculiarities of the WLANs,
and thus make it easier to integrate them with the SwMI
160.
Referring now to FIG. 2, a further schematic block
diagram of a WLAN inter-operating with a TETRA Switching
and Management Infrastructure (SwMI) is illustrated,
which contains the logical interfaces of the system of
FIG. 1. As can be seen, a number of
system/infrastructure elements are comparable to similar
elements described with reference to FIG. 1. As such,
they will not be described further here.
Again, the WLAN preferably implements a special routeing
enforcement policy for ToW terminals by tunnelling uplink
packets from all ToW terminals to an Interworking
function (IWF) 150 over, preferably, a Ft tunnel. Thus,
a Ft interface preferably operates between the WAG 142,
225 and the IWF 150. A proprietary interface 155 is
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
14
illustrated between the TETRA SwMI 160 and the IWF 150.
It is envisaged that the IWF 150 may also employ a
logical link to ToW terminals 112, 116 over an Ut
interface 210. In this regard, the Ut interface 210
supports the protocols and procedures that govern the
communication between a ToW 112, 116 and the IWF 150. As
discussed later, a new protocol operates on this logical
interface 210.
Also, logical interface Wt is applied to the
communication link between the WAG 142, 225 and the ToW
terminals. The Wt interface supports the protocols and
procedures that govern the communication between a ToW
terminal (fixed or mobile) and an AP. This interface is
preferably compliant with the IEEE 802.11 basic
specification.
Referring now to FIG. 3, a preferred mechanism of traffic
flow between ToW terminals tunnelled through the IP
network is illustrated, in accordance with the preferred
embodiment of the present invention. As illustrated in
FIG. 3, a ToW terminal 116 wishes to communicate with the
TETRA SwMI 160 and transmits an association request with
SSID=TETRA to an access point 114, which relays the
request to an associated WAG 142.
As mentioned above, the SSID of a ToW terminal is
preferably a well-known predefined one, for example
"TETRA", "Dimetra", "TETRAoverWLAN", etc. Similarly, the
SSID used by a non-ToW could be something like "Public",
"MotorolaTM", "Wireless-HotSpot", "ANY", "Operator-A",
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
etc. In this regard, the only difference between a ToW
SSID and a non-ToW SSID is that the WLAN is configured to
treat them differently. Apart from that, they are both
alphanumeric strings preferably compliant with the 802.11
5 spec. The WLAN service provider is preferably free to
select his preferred ToW SSID and inform his customers of
the SSID. The customers would then configure this ToW
into the terminals.
10 Typically, an AP would map traffic from/to terminals with
different SSIDs to different WLANs on the Ethernet
interface.
The WAG 142 tunnels all such traffic from ToW terminals
15 from the WLAN (i.e. the one associated with the ToW SSID)
to the IWF 150 and sends them over the IP network 140 via
the Ft tunnel. The IWF 150 then forwards them to the
TETRA SwMI 160, preferably over a proprietary interface
155, as shown.
Referring now to FIG. 4, an overview of the communication
layers associated with TETRA communication over a WLAN
system is illustrated. The preferred communication
architecture is comparable with the ETSI EN 300 392-2
TETRA specification. That is, control plane 410
information comprises SNDCP 415, mobility management (MM)
420 and a call management control entity (CMCE) 425. A
mobile link entity (MLE) 430 and a logical link control
(LLC) layer 435 are also supported.
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
16
In the user plane 440 the Real Time Protocol (RTP) or the
Compressed RTP protocol 450 is used to transport TETRA
adaptive code excited linear predicted (ACELP) encoded
voice blocks 445 according to ETS 300 395, between the
ToW and the IWF. Normally, one voice block is generated
every 30 msec. On the Control Plane, all TETRA air
interface protocols are re-used, except the TETRA MAC and
Physical layer protocols, which are not applicable to a
WLAN radio access. The LLC layer supports both the Basic
Link services and the Advanced Link services, as
described in ETSI, EN 300 392-2 v2.3.10, "Terrestrial
Trunked Radio (TETRA); Voice plus Data (V+D); Part 2: Air
Interface (AI)", ETSI, June 2003. The LLC layer runs in
the ToW and in the IWF (or partially in the SwMI).
Notably, a new layer of communication is specified in a
TETRA over WLAN system, namely, an Adaptation Layer 460.
The Adaptation Layer 460 provides the necessary
adaptation functionality required to operate the TETRA
air interface protocols over a WLAN. The Adaptation
Layer 460 is implemented in a ToW and in an IWF and
provides services that include a subset of the services
provided by the TETRA MAC layer. In particular, it
supports TETRA-compliant encryption and addressing using
TETRA SSIs.
The Adaptation Layer interfaces with the UDP layer
through a Control-Plane-Service Access Point (CP-SAP) 465
and one or more User-Plane-Service Access Points (UP-
SAPs) 470. The CP-SAP 465 is always present and is used
to carry control-plane traffic that is not associated
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
17
with an ongoing call, i.e. control traffic normally
transmitted on a TETRA MCCH or SCCH.
A well-known (predefined) multicast IP address and Port
number, referred to as MCCH-multicast and MCCH-port,
respectively, are used to transport such kind of traffic.
Conversely, user plane traffic is carried on a UP-SAP
470. At the beginning of a new call, a new UP-SAP 470
instance is created to support that particular call. A
UP-SAP 470 instance is using a dynamically assigned
multicast IP address and port number. As discussed
below, this multicast IP address and port number are
assigned by the IWF and are communicated to the ToW in
the packet that signals the start of the new call. A UP-
SAP 470 is dynamically created to support user data,
traffic and call associated control traffic. Notably,
the UP-SAP 470 also supports control-plane traffic 410
that is associated with an ongoing call (e.g. a D-TX-
CEASED PDU). The Adaptation Layer is used to
differentiate between the user-plane traffic and the
call-associate control traffic on the same UP-SAP.
The Adaptation Layer 460 in the ToW analyses every
received packet and identifies (based on the indicated
SSI) if it should further be processed or be dropped. If
it requires further processing, the Adaptation layer
dictates whether decryption should be applied (i.e. if
the received message is encrypted) and, if it was
received over a UP-SAP, it forwards it either to an LLC
entity or to an RTP entity.
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
18
FIG. 4 illustrates further aspects of the protocol
architecture of a ToW terminal. The WLAN Physical layer
490 and WLAN MAC layer 485 are used for establishing
wideband wireless connectivity with an AP. These layers
are preferably compliant with the IEEE 802.11
specification, as described in the document titled:
"Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) Specification", and published in the IEEE
standard 802.11, edition 1999. However, it is envisaged
that any WLAN can be used.
These layers are also compliant with the Quality of
Service (QoS) enhancements specified in IEEE Std.
802.11e/D6.0, "Part 11: Wireless Medium Access Control
(MAC) and physical layer (PHY) specifications: Medium
Access Control (MAC) Quality of Service (QoS)
Enhancements", November 2003.
It is envisaged that these layers may also support the
security features specified in IEEE, "Port-Based Network
Access Control", IEEE standard 802.1X, edition 2001 and
IEEE Std 802.11i/D7.0, "Part 11: Wireless Medium Access
Control (MAC) and physical layer (PHY) specifications:
Medium Access Control (MAC) Security Enhancements",
October 2003.
Connectivity with the IWF is provided with the IP layer,
by means of its routing and addressing services, as
described in J. Postel's paper, titled "Internet
Protocol", and published in RFC 791 in September 1981.
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
19
The UDP layer provides error detection and multiplexing
services, as specified in J. Postel's paper, titled "User
Datagram Protocol", and published in RFC 0768, 1980.
The IP layer is implemented in the ToW terminal, the IWF
and the intermediate IP Network (as shown FIG. 1). The
IP layer ensures that all IP datagrams from/to ToWs are
routed to/from the IWF. If necessary, it may also enable
different quality of service (QoS) routing to different
kinds of IP datagrams, according to the Type of Service
(ToS) field in their respective IP headers. Such QoS
services may be required to provide preferential
transportation services to IP datagrams carrying voice
packets.
Referring now to FIG. 5, a preferred packet structure 500
employed in the TETRA over WLAN architecture is
illustrated. In FIG. 5, the general format of control-
plane 510 and user-plane 550 packets exchanged over the
Ut interface (i.e. transmitted between the IWF and the
ToW terminals) are illustrated.
The control-plane packets 510 carry normal TETRA LLC PDUs
530 encapsulated into IP/UDP. The structure of the
Adaptation Layer header is a key component of the
inventive concepts herein described. The structure of all
other protocol fields (e.g. IP 515, UDP 520, RTP, LLC,
CMCE, MLE, MM, SNDCP 535) is designed to comply with
known protocol specifications.
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
That is, the LLC, CMCE, MLE, MM, and SNDCP protocol
fields are described further in the document ETSI, EN 300
392-2 v2.3.10, "Terrestrial Trunked Radio (TETRA); Voice
plus Data (V+D); Part 2: Air Interface (AI)", ETSI, June
5 2003. The IP protocol field is described further in the
document by J. Postel, "Internet Protocol", RFC 791, Sep.
1981. The UDP protocol field is described further in the
document by J. Postel, "User Datagram Protocol", and RFC
0768, 1980.
It is envisaged that other kind of TETRA PDUs might also
be encapsulated in the control-plane packets, e.g. for
broadcasting security related information such as a
Common Cipher Key (CCK) identifier or a Static Cipher Key
(SCK) version number.
The Adaptation Layer header 525, 565 is populated with
critical information that is normally included in the
TETRA MAC header. More specifically, the Adaptation
Layer header 525, 565 preferably includes a TETRA SSI and
an Encryption Mode field, which indicates whether the
embedded LLC or RTP PDU is encrypted or not. In a
downlink direction the TETRA SSI identifies the TETRA
address of the packet recipient(s), whereas in the uplink
direction, it identifies the TETRA address of the packet
originator.
In addition, the Adaptation Layer 525, 565 preferably
includes more information in packets that signal the
origination of a new call (of any kind). In this case,
the Adaptation Layer 525, 565 preferably includes also
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
21
the Multicast address and the Port Number that are used
to transport the voice packets of the upcoming call.
Finally, the Adaptation Layer header 525, 565 preferably
includes an information field that indicates if there is
an LLC PDU or an RTP PDU encapsulated in the packet.
Referring now to FIG. 6, an example of how the various
headers are populated in a packet 600 carrying a known
TETRA D-SETUP message is illustrated.
A packet 610 is, for example, sent by the IWF. The
packet 610 indicates that a terminal with SSI=46
originates a group call to GSSI=8388888. The IP address
615 of IWF is x.y.z.w and the multicast address and port
corresponding to the well-known MCCH address and MCCH
port 620, are designated as MCCH-mcast and MCCH-port,
respectively. This packet is sent by the IWF to all WAGs
that have previously established a Ft tunnel. Thus, the
packet will ultimately be broadcast to all WLAN sites
controlled by this IWF. Therefore, all ToW terminals in
these sites will receive and decode the packet. The ToW
terminals affiliated with the GSSI=8388888 will thus be
configured to receive the upcoming user-plane information
for this group call by creating a new UP-SAP instance.
The new UP-SAP of the adaptation layer header 620 is
bound to the multicast address g1.g2.g3.g4 and port Gp.
Also a packet 650 is, for example, sent by a ToW. The
packet 650 indicates that a ToW terminal has a SSI=46, in
order to affiliate to group with GSSI=8388888. The IP
address 655 of the ToW is designated as a.b.c.d. It is
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
22
noteworthy that in this packet 650, the Adaptation Layer
665 does not include a multicast IP address and port
pair, since the packet does not originate a new call.
Referring now to FIG. 7 and FIG. 8, example signalling
flows of TETRA over WLAN system are illustrated,
according to the preferred embodiments of the present
invention. In particular, FIG. 7 illustrates a
signalling flow 700 comprising a WLAN association and
location update.
The signalling flow 700 illustrates communication between
a ToW terminal 710, an AP and WAG of a WLAN 715 and an
IWF 720. The message sequence that takes place when a
WLAN terminal requests an association with the WLAN using
the SSID="TETRA", in step 725. This happens either when
the WLAN terminal powers up or when it chooses to change
radio access technology, i.e. to leave a TETRA site and
join a WLAN site. The WLAN preferably acknowledges the
request in step 730.
At point 1 735, the WAG 715 creates an Ft tunnel with the
predefined address of the IWF 720, if there is no such
tunnel already in place. The WAG 715 also sets up its
forwarding function in order to forward subsequent
packets from the ToW 710 to the IWF 720 via the Ft
tunnel. Next, the ToW 710 initiates a DCHP procedure to
obtain an IP address, as shown in step 740 and step 745.
This IP address in typically assigned in step 745 by the
IWF 720, using an internal DCHP server or possibly an
external DHCP server.
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
23
At point 2 750, the ToW 710 enables its CP-SAP and starts
receiving packets with destination IP equal to MCCH-
multicast and UPD port equal to MCCH-port. The values of
MCCH-multicast and MCCH-port are assumed to be pre-
configured in the ToW 710. However, it is envisaged that
other means could also be developed for sending these
parameters to the ToW 710, if necessary.
After point 2 750, the Adaptation Layer in the ToW 710
starts receiving and processing packets 755, 760, 765
that include TETRA traffic normally transmitted on the
MCCH channel.
At point 3 770, the ToW 710 sends to the IWF 720 a U-
LOCATION-UPDATE-DEMAND PDU 775 to request the SwMI to
update its location. This PDU 775 is transmitted on the
CP-SAP and therefore the destination IP address is equal
to MCCH-multicast and the destination UDP port is equal
to MCCH-port. A D-LOCATION-UPDATE ACCEPT PDU 775 is sent
from the IWF 720 to the ToW terminal 710.
A skilled artisan will appreciate that FIG. 7 represents
only a simple example of an association request and
location update message, and does not aim to show every
possible communication.
Referring now to FIG. 8, a signalling flow 800 comprising
a message sequence for group call initiation and
participation is illustrated. The signalling flow 800
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
24
illustrates communication between a ToW terminal 805, an
AP and WAG of a WLAN 810 and an IWF 815.
An indication of a new Group call 820 is received at IWF
815, for ToW terminals affiliated to group 18388888'.
The destination multicast address of a packet 825 and the
destination UDP port (relating to the new group call) are
the well-known MCCH-mcast and MCCH-port, respectively.
The Adaptation Layer header in this packet indicates that
the new group call will use an IP multicast address
g1.g2.g3.g4 and the UDP port Gp. This is illustrated in
the MCCH D-SETUP message 825 transmitted from the IWF 815
to the ToW terminal 805. All ToW terminals in the WLAN
area of the IWF receive this packet, irrespective of
whether they are engaged in a call or not. ToW terminals
affiliated to group 18388888' and willing to participate
in this group call, will create a new UP-SAP instance and
will bind it to the designated multicast address and UDP
port (i.e. g1.g2.g3.g4/Gp). ToW terminal 805, with
SSI='90', receives this group call.
After receiving the MCCH D-SETUP message 825, a series of
IP multicast datagrams are transmitted from the IWF 815
to the ToW 805. Each datagram 830, 835 carries a voice
packet from the originator. The datagrams 830, 835, and
possibly subsequent datagrams, indicate in the Adaptation
Layer header that they carry encrypted RTP PDUs for the
group with GSSI=8388888.
Datagram message 840 is a call-associated control packet,
carrying a D-TX Ceased PDU. The Adaptation Layer in the
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
ToW 805 understands that this carries an LLC PDU (as
opposed to an RTP PDU) and thus forwards it to the LLC
layer as indicated in the Info field. After datagram
message 840, the considered ToW 805 decides to take
5 control of the group call and thus sends an uplink call-
associated control packet 845. The uplink call-
associated control packet 845 carries a U-TX Request PDU
that requests from the SwMI permission to transmit.
10 In response, the SwMI grants transmit permission to ToW
805 with a D-Tx Granted message 850. Thus, starting from
message 855, the ToW 805 transmits a series of user-plane
packet that contain encrypted RTP PDUs.
15 In an enhanced embodiment of the present invention,
security and authentication procedures can be readily
incorporated into the TETRA over WLAN system. The
authentication procedure can be readily supported by
exchanging the appropriate layer-3 messages between the
20 ToW and the IWF, e.g. a D-AUTHENTICATION DEMAND and a
U-/D-AUTHENTICATION RESPONSE, as described in ETSI, EN
300 392-7 v2.1.1, "Terrestrial Trunked Radio (TETRA);
Voice plus Data (V+D); Part 7: Security", Feb. 2001.
25 During this procedure, the Adaptation Layer in the ToW is
responsible to run the appropriate security algorithms
and create a Derived Ciphering Key (DCK). This key is
subsequently used by the Adaptation Layer to encrypt and
decrypt all LLC and RTP PDUs over the Ut interface.
Support of Static and Common Cipher Keys (SCK, CCK) is
also possible. The CCK is generated by the SwMI to
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
26
protect group addressed signalling and traffic, as well
as also protecting SSI identities.
In addition, it is envisaged that a yet further enhanced
embodiment of the present invention will support
individual and telephone interconnect calls in a similar
manner to the signalling flow for group calls described
above. A skilled artisan will appreciate that other
procedures and corresponding signalling flows, e.g. for
SDS and packet data transmission/reception, can be easily
adapted and incorporated using the principles and the
protocols hereinbefore described.
Thus, the inventive concept has proposed a mechanism for
incorporating WLAN technology in TETRA networks, thereby
providing the advantages of such WLAN.technology in TETRA
products and services. The proposed mechanism is based
on IP multicast and VoIP technology.
It will be understood that the aforementioned
architecture, devices, functional elements, protocol and
signalling flows, embodying the inventive concepts
described above, tend to provide at least one or more of
the following advantages:
(i) The integration of WLANs with TETRA networks
provides a wide range of new capabilities and benefits,
which will result to product differentiation and
competitive advantages.
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
27
(ii) Officers and other business users are able to
use dual-mode TETRA/WLAN terminals in the field as well
as in the office environment and/or over a private WLAN.
(iii) In strategic locations, such as airports,
hotels, shopping precincts, etc, TETRA services can be
provided over WLAN. This will enable better indoors
coverage,, increased capacity, new services, etc. in a
cost effective manner.
(iv) Over the WLAN, enhanced services can be
provided to the end user. For example:
(a) Enhanced voice encoding schemes to
provide much improved voice quality
(i.e. no need to restrict to the 7.2
kbps capacity offered by the TETRA
TCH/S);
(b) Wideband data services could be
supported;
(c) Voice and data services could be
simultaneously provided;
(v) Control traffic normally transmitted on the
TETRA. MCCH can now be received while there are voice
and/or data sessions active. In conventional TETRA, a
terminal in a voice session cannot also receive the
control traffic on a main control channel (MCCH), because
voice and MCCH traffic are transmitted on different
channels. However, in accordance with the preferred
embodiment of the present invention with TETRA
communication over a WLAN, this is now feasible.
(vi) A skilled artisan will appreciate that, by
means of IP multicast, many Group Calls can be monitored
simultaneously by a single user, etc.
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
28
(vii) WLANs feature large air interface capacity and
can therefore support many simultaneous TETRA voice/data
calls in an efficient and cost effective manner.
(viii) A skilled artisan will also appreciate that
call set up delays and voice transmission delays can be
considerably reduced. Thus, since the WLAN supports
higher bit rates, the control messages and the voice
datagrams are transmitted faster.
(ix) Inexpensive subscriber devices can be supported
- any PC, PDA, or Cellular with a WLAN adapter can be
used.
(x) Dual-mode WLAN/Cellular mobile terminals are
quickly emerging in the marketplace and these terminals
could also support TETRA services over WLAN.
(xi) Ability to support seamless roaming between
WLAN access and conventional TETRA access: i.e. mobiles
entering a WLAN area are treated in a similar manner to
them entering a new TETRA location area in that they use
the typical TETRA. mobility management procedures to
update the SwMI with their new location.
(xii) Supplementary TETRA features (e.g. Late Entry,
etc) can be readily supported - some of them with less
SwMI processing or intervention (e.g. Priority
Monitoring).
(xiii) TETRA terminals can participate
simultaneously in group call(s), data session(s) and also
receive information normally sent on MCCH. This creates
new capabilities not available on conventional TETRA
radio systems.
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
29
(xiv) The WLAN is primarily used as a new wireless
access scheme for the transportation of TETRA control and
user data PDUs.
(xv) The preferred architecture has minimum impact
on the TETRA SwMI. The IWF can be considered as a
special kind of TETRA Base Station Controller, which can
easily interface with the SwMI core.
(xvi) Local Site Trunking in a WLAN area can be
easily supported by proper engineering of the IWF.
(xvii) ToW terminals can be managed in the same way
as any other TETRA terminal, i.e. there is no need for
new subscriber profiles.
(xviii) Full compatibility between ToW terminals and
conventional TETRA terminals is maintained.
Whilst specific implementations of the present invention
have been described, it is clear that one skilled in the
art could readily apply further variations and
modifications of such implementations within the scope of
the accompanying claims.
Thus, a wireless communication system, a wireless local
area network (WLAN) access gateway (WAG), an InterWorking
Function (IWF) and a wireless terminal adapted to
facilitate communication over a private mobile radio
system such as a TETRA system and the wireless local area
network (WLAN) in the aforementioned wireless
communication system have been described.
Furthermore, a method of communicating between a wireless
local area network (WLAN) and a private mobile radio
CA 02599007 2007-08-23
WO 2006/094088 PCT/US2006/007355
system by a dual-mode terminal capable of operating over
the WLAN and the private mobile radio system and a
protocol therefor have been provided by the invention
that tend to alleviate the disadvantages of such
5 scheduling when carried out according to prior art
procedures.
