Aircraft data link network routing

(54) Title: METHOD FOR ROUTING MESSAGES FROM AIRCRAFT DATA LINK ABOUT A PLURALITY OF NETWORKS OF

COMMUNICATIONS, COMPUTER PROGRAM PRODUCT, AND AIRCRAFT COMMUNICATION SYSTEM (30) Unionist Priority: 08/08/2007 usn / 835.864 (73) Holder (s): honeywell International inc.

(72) Inventor (s): Alfonso Malaga, Matt E. Larsen, Richard J. Eckert, Willard R. True (57) Summary: method for routing messages from AIRCRAFT DATA LINK ABOUT COMMUNICATION NETWORK PLURALITY, PRODUCT FROM COMPUTER PROGRAM, AND AIRCRAFT COMMUNICATION SYSTEM. A method for routing messages from the aircraft data link over a plurality of communications networks is disclosed. The method assigns at least one data link message router service to an aircraft having a first application for processing messages at predetermined criteria, the predetermined criteria comprising preferred networks of the plurality of communications networks. When a first communications network becomes available, the method selects a first message route, from the assigned routing service, and transmits each of the data link messages on the first message route, as long as the first message route satisfies predetermined criteria. When the predetermined criteria change over a plurality of flight phases of the aircraft, the method reassigns at least one data link message route to continue transmitting the data link messages to and from the aircraft, based on the last predetermined criteria.

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Ρ 0803325-5

METHOD FOR ROUTING MESSAGES FROM THE AIRCRAFT DATA LINK ABOUT COMMUNICATION NETWORK PLURALITY,

COMPUTER PROGRAM PRODUCT, AND MA COMMUNICATION SYSTEM

OF AVIONICS

BACKGROUND OF THE INVENTION

Flight phase measurements are already used normally in communication with aircraft. A specific flight phase is often used to trigger certain communication messages. For example, many aircraft maintenance systems send their reports via an aerial data link network, when an aircraft is in the final approach, or immediately after landing. In addition, air data links transmit information between an aircraft and air traffic control services, when the aircraft is too far from an air traffic control tower, to make voice radio and radar communication possible. For example, aircraft data link systems are used for long-haul flights operating on any considerable land or sea routes.

Recurring costs with aircraft data link messages are significant. For example, message transmission rates (ie loading and unloading speeds) vary considerably during certain phases of flight between network service providers, the aircraft's location, and any applicable networks and aerial subnets within the network. aircraft. Since connection fees for a specific aerial (subnet) network vary with the service provider, any further improvement in the routing of aircraft data link networks between various extreme points represents an important cost benefit.

For the reasons mentioned above and for other reasons mentioned below, which will become clear to people skilled in the art, after reading and understanding this specification, there is a need in the technique for improvements in the routing of aircraft data link networks.

SUMMARY OF THE INVENTION

The following descriptive report discusses the routing of aircraft data link networks in an avionics communication system. This summary was prepared for purposes of example, not limitation. It is presented simply to assist the reader in understanding some aspects of one or more modalities described in the following specification.

In particular, in one embodiment, a method is presented for routing messages from the aircraft data link through a plurality of communications networks. The method assigns at least one data link message routing service to an aircraft having a first message processing application based on predetermined criteria, the predetermined criteria comprising preferred networks of the plurality of communications networks. When a first preferred communications network becomes available, the method selects a first message route from the assigned routing service, and transmits each of the data link messages on the first message route, when the first message route satisfies predetermined criteria. When the predetermined criteria change over a plurality of aircraft flight phases, the method reassigns at least one data link message route to continue transmitting the data link messages to and from the aircraft, based on last predetermined criteria.

DRAWINGS

These and other features, aspects, and advantages are best understood with respect to the following description, attached claims, and attached drawings, where:

fig. 1 is a block diagram of an avionics communication system;

fig. 2 is a block diagram of an embodiment of a message routing portion of an avionics communication system;

is fig. 3 is a block diagram of a mode ί.

a network managing and selecting portion of an avionics communication system;

fig. 4 is a flow chart illustrating a modality of a method for routing data link networks for aircraft; and fig. 5 is a flow chart illustrating a modality of a method for network selection and management in an avionics communication system.

The different resources described are designed to emphasize resources relevant to the disclosed modalities.

Reference characters indicate similar elements throughout the figures and text of the specification.

DETAILED DESCRIPTION

Modalities of the present invention describe routing of data link networks for aircraft on various service provider networks through an aircraft communications management unit (CMU). In at least one modality, a plurality of wireless networks covering local, metropolitan and remote areas (collectively, global or continental scales) is used based on an expanded set of programmable message routing rules to select at any time , the appropriate network (s). The network routing discussed here provides appropriate data link services based on application needs and availability of networks for various aircraft data link applications. In addition, network selections and message routing are based on current flight phases and aircraft status.

As discussed in more detail below, the rules for network selection and message routing are separate from specific network protocol interfaces.

Programmable rules can be customized to meet the requirements of individual customers of (for example) commercial airlines or aircraft manufacturers, as described in detail below. In addition, the network routing discussed here provides an application framework, which is independent of any present (or future) network protocol architecture, including any wireless networks with efficient bandwidth (ie, non-distributed spectrum) ), as discussed in detail below.

In one implementation, a message routing function block provides a uniform service interface for converging data link applications trying to communicate over the plurality of wireless networks. Any specific data link application requests are analyzed, and message routing rules are defined based on network availability. A network selection and management function block monitors and selects the various wireless networks and subnets for the message routing function block service interface. The network selection and management function block analyzes various

Aircraft Status and applies the rules for network selection and message routing. The network routing discussed here combines information about network availability, user preferences (as specified in the network selection rules and programmable message routing), and the various requirements of the data link applications to select preferred communications networks for any routing of data link messages to aircraft.

Examples of applicable aircraft data link processing applications suitable for use with the network routing discussed here include, but are not limited to, information about flight management system (FMS) databases, data loads for display avionics, aircraft turbine data, electronic flight package (EFB) data,

Quick Access, data on Quality Assurance of

Flight Operations (FOQA), in-flight entertainment data, data for Aeronautical Operational Control (AOC), data for Air Traffic Control (ATC), data on

Aeronautical Telecommunications (ATN), and data from the.

Aircraft Communications Notification and Addressing (ACARS).

Fig. 1 is a block diagram of an avionics communication system 100. System 100 comprises a CMU 102 having a processing unit 104. In the exemplary embodiment of fig. 1, processing unit 104 is at least one of 'a programmable microprocessor, a field programmable port set (FPGA), a field programmable object set (FPOA), an application specific integrated circuit (ASIC), and a programmable logic device (PLD). Communicatively coupled to the processing unit 104 within the CMU 102 is a converged service interface 106 and a network adaptation interface 108. The converged service interface 106 serves as an on-board routing function for data link messages to (from) message processing applications 110. In one implementation, the converged service interface 106 transmits data link messages between the appropriate messaging applications 110.

In addition, the converged service interface 106 performs the conversion between various types of data from message processing applications 110 to a plurality of routers (discussed below with respect to fig. 2), to establish connectivity between the aircraft and any extreme points requested. The network adaptation interface 108 provides functions for adapting specific networks, to transmit information from specific applications through certain communication networks, as discussed below with respect to fig. 3.

System 100 still comprises applications for processing messages 110i to 110_K, communicatively coupled to the CMU 102. It should be clear that the system 100 is capable of accommodating any appropriate number of applications for processing messages 110 (for example,

<td>example,</td><td>fur</td><td>least one application</td><td>for</td><td>Processing</td>

<td>posts</td><td> 110)</td><td>in a single system</td><td> 100.</td><td>As below</td>

<td>discussed</td><td>with</td><td>with respect to fig. 2,</td><td>the</td><td>applications for</td>

110 message processing_Σ to 110_K include, but are not limited to, an FMS, aircraft traffic services, an aircraft condition monitoring system, an EFB, and similar combinations of its CMU-hosted message processing applications. In addition, system 110 comprises a plurality of network interfaces 112_T to 112_K communicatively linked to the CMU

102. It should be clear that system 100 is capable of accommodating any appropriate number of network interfaces 112 (for example, at least one network interface 112) in a single system 100. As discussed below with respect to fig.

2, each of the network interfaces 112i to 112_K is reactive to at least one wireless communication network, including, but not limited to, a very high frequency data link (VHF), a high frequency data link (HF), a satellite communication data link (SATCOM), a local area network (LAN), such as a Wi-Fi network, a remote network (WAN), such as a cellular radio network, a metropolitan network (MAN), such as a network

Worldwide Interoperability for Microwave Access (WiMAX), and wireless communication networks with similar efficient bandwidth employing, among others, Orthogonal Frequency Division Multiplexing (OFDM) based on 802.llg, 802.11η, 802.16d network protocols ,

802.16e.

In operation, processing unit 104 assigns at least one data link message routing service to a first message processing application 110 based on predetermined criteria (for example, from at least one set of rules for routing data). programmable messages). When a first communications network becomes available, processing unit 104 selects a first message route on at least one of the network interfaces 112 via the assigned routing service. In one implementation, the processing unit 104 detects the available wireless communication networks through the plurality of efficient bandwidth communication networks supported by the CMU 102 that meets the predetermined criteria. In addition, processing unit 104 dynamically allocates any necessary bandwidth to the converged service interface 106, to support any requirements for extreme communication points, regardless of the transport medium and data format for routing the network. data link discussed here.

When instructed by processing unit 104, at least one network interface 112 transmits messages from the data link to the first application for processing messages 110 on the first message route that meets the predetermined criteria. In one implementation, processing unit 104 activates at least one network interface 112 to transmit each message, according to a set of rules for selecting programmable networks. If the availability of the network changes over a plurality of the flight phases of the aircraft, the processing unit 104 reassigns at least one data link message route to continue transmitting the data link messages to and from the aircraft. , based on predetermined criteria for each of the applications for processing messages 110. In one implementation, processing unit 104 reassigns the first message route to select at least a second preferred network from the plurality of networks reactive to network interfaces 112.

Fig. 2 is a block diagram of a message routing portion of an avionics communication system 200, similar to system 100 in fig. 1. The message routing portion of the system shown in fig. 2 comprises processing unit 104, network adaptation interface 108, message processing applications 110, and network interfaces 112. Processing unit 104 further comprises a message routing function block 202 communicatively coupled to an ATN router 204, an ACARS 206 router, and an Internet Protocol (IP) router 208. It should be made clear that additional routers for additional network protocols are possible, and that the network routing discussed here is not limited to any specific network protocols.

In at least one alternative implementation, routers

204 to 208 form at least a portion of the processing unit 104.

In the exemplary embodiment of fig. 2, message routing function block 202 is still reactive to 110i to 110 message processing applications₅. Applications for message processing 110 comprise a flight management system 110i, air traffic services IIO2, an aircraft condition monitoring system

IIO3, an electronic flight package (EFB) 110₄, and a messaging application hosted at CMU

IIO5. As discussed above with respect to fig. 1, there are 25 possible applications for processing 110 alternative messages. The message routing function block

202 it is still operable to receive a plurality of rules for routing programmable messages through the CMU

102. As discussed below with respect to fig. 3, the rules for message routing comprise selection of networks based on the current configurations of the aircraft equipment, aircraft flight phase, current aircraft position and trajectory, message priority, availability of networks in relation to other networks, relative cost of networks at a given time, and the like.

Routers 204 through 208 are still reactive to network interfaces 112i through 112₆ through a plurality of adaptation and control blocks 212i to 212₈ of the network adaptation interface 108, as shown in fig. 2. The network interfaces 112_χ to 112₆ comprise at least one of a radio interface of the VHF 112i data link, a radio interface of the HF 1122 data link, a radio interface of the SATCOM 112 data link₃, a LAN 112 interface₄, a WAN 112 interface₅, and a MAN 1126 interface. Οθ adaptation and control blocks 200i to 2006 include a radio adaptation and control block of the VHF data link (VDL) 212i, an adaptation and radio control block of the HF data link (HDL) ) 2122, a radio control and adaptation block of the SATCOM 212 data link₃, a LAN 212 adapter and control block₄, a WAN 212 $ adapter and control block, and a MAN 212 adapter and control block₆.

In operation, the rules for routing messages from CMU 102 are analyzed by the message routing function block 202. When data link messages from the message processing applications 110 are received in the message routing function block 202, the message routing function block 202 determines which of the routers 204 to 208 will transmit the message over the applicable network interface 112. In the exemplary embodiment of fig. 2, the rules for routing messages from CMU 102 are evaluated by the message routing function block 202 and each of the data link messages passes through network adaptation interface 108 for any additional selection adaptation functions. of networks, which may be necessary to complete the transmission of the data link, as discussed below with respect to fig. 3.

Fig. 3 is a block diagram of a management and network selection portion of an avionics communication system 300, similar to system 100 in fig. 1. The network selection and management portion of the system shown in fig. 3 comprises the processing unit 104, the network interfaces 112, and the adaptation and control blocks 212i to 2126 of the network adaptation interface 108. The processing unit 104 further comprises a network selection and management function block 302 reactive to the message routing function block 202 of fig. 2. In the exemplary embodiment of fig. 3, the network selection and management function block 302 is operable to receive a plurality of Aircraft State Entries based on a current flight phase of an aircraft hosting system 100, as described below with respect to fig.

5. In an implementation, the plurality of

Aircraft Status comprises the aircraft's flight phase, aircraft location, network access level, message priority level, and the like.

In operation, each of the 212 adaptation and control blocks routes messages from the aircraft's data link through a preferred network interface 112, based on network selection rules and programmable message routing managed by the management and selection function block. of 302 networks. The network selection and management function block 302 monitors and controls network interfaces 112, based on message routing decisions provided by message routing function block 202 and the Aircraft Status Entries received by CMU 102. As shown in Tables 1 below, the network selection and management function block 302 selects the appropriate network based on the Aircraft Status Inputs and informs the 212χ to 212β adaptation and control blocks to perform the additional selection adaptation functions. of networks needed to complete the transmission of the data link through the appropriate network interfaces 112i to 112₆. For example, the WiMAX 212β control and adaptation block will format a message

ACARS to be transmitted as an IP message over the WiMAX 1126 network interface ·

Aircraft State Entries

A partial listing of the State Entries of the

Aircraft from CMU 202, including examples, appear below with respect to Table 1.

<td>Aircraft State Entries</td><td>Examples</td>

<td>Flight Phase</td><td>Pre-flight; Climb; Cruise; Descent, Takeoff; Approximation; Circulation and Arrival</td>

<td>Flight Event</td><td>End; Out; Connected and Inside (OOOI)</td>

<td>Aircraft Position and Trajectory</td><td>latitude coordinates; longitude; mapping</td>

<td>Aircraft Status</td><td>Derived from sensors on board, including, but not limited to, amount / weight key on the wheels; parking brake; turbine speed; pressure of turbine oil; airspeed; ground speed; altitude of radio altimeter; altitude barometric</td>

<td>Aircraft distance from stations soil specific</td><td>Distance to an ACARS VDL station in the soil; Distance to points WiMAX or Wi-Fi access</td>

<td>Application Network Type</td><td>High Availability ACARS; ATN ATC communications; High IP Availability</td>

<td>Access Level and Relative Cost from the Web</td><td>Low Cost ACARS; ACARS of Low Latency; Low Cost IP</td>

<td>Message Priority Level</td><td>High, Urgent, Low</td>

Table 1 - Aircraft State Entries

As shown in Table 1 above, each of the Aircraft State Entries is evaluated together with the network selection rules and the programmable message routing rules, to route each of the 5 link messages, of data to the correct network . Routing rules are evaluated dynamically when

Aircraft Status Entries are updated by CMU

102. It should be made clear that Aircraft Status Entries presented here are not intended to be a complete listing, and that any aircraft status entries, which may affect the routing of messages on the aircraft's data link, may be used. In one implementation, the flight phase and flight event entries are adapted through Aeronautical Radio, Incorporated (ARINC) and

ATC.

Network Selection Rules and Message Routing

Programmable

A partial listing of programmable message routing rules through CMU 102, including examples, appears below with respect to Table 2.

<td>Rules for Routing</td><td rowspan="2">Examples</td>

<td>posts</td>

<td>Messages from application 1, type 1, can use any IP subnet or ACARS</td><td>High priority AOC messages</td>

<td>Messages from application 1, type 2, can only use ACH VHF or IP</td><td>Medium priority AOC messages</td>

<td>Messages from application 1, type 3, are maintained until detection of Wifi network</td><td>Low-priority AOC messages</td>

<td>Messages from application 2, type 1, use only ATN network, VHF subnet</td><td>ATN messages ATC</td>

<td>Messages from application 2, type 2, use only ACARS network, subnets VHF or SATCOM</td><td>FANS messages</td>

<td>All types of messages from</td><td>External user of the service (s)</td>

<td>application 3 can use networks ACARS or IP, and any subnets</td><td>converged network (s)</td>

<td>All types of messages from application 4 can use ACARS network and any ACARS subnet</td><td>External ACARS application (s)</td>

<td>Messages from application 5, type 1,</td><td>High priority EFB messages</td>

<td>can use any IP subnet</td><td></td>

<td>Messages from application 5, type 2, _:can only use IP subnets of low cost</td><td>Low priority EFB messages</td>

Table 2 - Rules for Programmable Message Routing

As shown in Table 2 above, each of the rules for routing programmable messages is dynamically evaluated when the aircraft status inputs are updated by CMU 102. It should be clear that the rules for routing messages presented here are not intended to constitute a complete list, and that any rules for routing programmable messages can be used. For example, the rules for routing programmable messages illustrated in Table 2 apply to routing applications, which implement AOC messaging and Air Navigation System standards.

Future (FANS). In order to route the data link messages using programmable message routing rules described in Table 2, system 300 actively manages network stacks (protocols) and subnets in the network selection and management function block 302. The network selection and management function block 302 uses the programmable network selection rules, which are also dynamically executed as changes in the network and aircraft status. Examples of network selection rules are shown below with respect to the Table

3.

<td>Network Selection Rules</td><td>Examples</td>

<td>Selection based on network types</td><td>Enable ACARS VHF subnets using</td>

<td>supported by aircraft</td><td>always existing rules for network selection</td>

<td>Selection based on the current state of</td><td>Enable ACARS SATCOM subnet on</td>

<td>aircraft And in another</td><td>(0001 OFF state) OR (when</td>

<td>network availability</td><td>no other ACARS subnets being available)</td>

<td>Selection based on the flight phase of</td><td>Enable Wi-Fi when state 0001</td>

<td>aircraft</td><td>for IN</td>

<td>Selection based on the flight phase of</td><td>(Enable WiMAX, when the</td>

<td>aircraft and other availability</td><td>flight NOT FOR Cruzeiro) E (Wi-Fi</td>

<td>network</td><td>is not available)</td>

<td>Selection based on the flight phase of</td><td>(Enable Cellular WAN when the</td>

<td>aircraft and other availability</td><td>state 0001 for IN) E (Wi-Fi not</td>

<td>network</td><td>available) AND (WiMAX does not being available)</td>

<td>Selection based on the flight phase of</td><td>Disable WiMAX during the</td>

<td>aircraft</td><td>flight in Cruzeiro</td>

<td>Selection based on the flight phase of</td><td>(Enable WiMAX when flight phase</td>

<td>aircraft AND selection based on</td><td>is Descending) E (within 15 ·</td>

<td>current position and trajectory of aircraft</td><td>miles from destination airport)</td>

<td>Selection based on position and</td><td>Activate ATN in an airspace</td>

<td>current trajectory of the aircraft</td><td>defined by the latitude /</td>

<td></td><td>longitude</td>

Table 3 - Rules for Selection of Programmable Networks

It should be clear that the rules for selecting networks in Table 3 are not intended to be a complete list, and that any rules for selecting programmable networks can be used. The rules for selecting programmable networks within the scope of user data link messages can be defined by the customer and loaded into CMU 102, regardless of the software that implements the network protocols. In an implementation, each set of rules for network selection and programmable message routing form at least a portion of a set of customizable features of known aircraft communication management systems. The rule sets for selecting networks and routing programmable messages, which belong to specific air traffic services, can also be loaded independently of the operational software on CMU 102, but will be controlled by standard aircraft certification processes.

Fig. 4 is a flow chart illustrating a method 400 for routing messages from the aircraft data link over a plurality of wireless communication networks. The method

400 addresses the provision of appropriate data link services based on application needs and network availability for various onboard applications for aircraft message routing discussed above with respect to figs. 1 to 3. Method 400 routes the appropriate data link services over the plurality of wireless communication networks, including wireless networks with efficient bandwidth, discussed above with respect to figs. 1 to 3.

0 method of fig. 4 assigns at least one data link message routing service to an aircraft having a first message processing application, based on predetermined criteria in the block

402. In one implementation, at least one data link message routing service receives instructions from a group of programmable message routing rules and a group of network selection rules (similar to the rules discussed above with respect to figs.

to 3), as the predetermined criteria. In addition, the method of fig. 4 incorporates each group of message routing rules and network selection rules as functions of an aircraft CMU.

If a first (ie preferred) communications network is available in block 404, method 400 20 selects a first message route from the routing service assigned in block 406 to the preferred network, based on at least one input aircraft status. Method 400 detects available networks from a plurality of wireless communications networks with efficient bandwidth, which meet the predetermined criteria defined in block 402. In one implementation, method 400 converts at least one data type into the first message processing application, for at least one router to establish connectivity between the aircraft and any requested end points using the first message route. In addition, method 400 uses a converged service interface to dynamically allocate any bandwidth required for at least the first message route.

As long as the preferred network is available, method 400 transmits each of the data link messages on the first message route that meets the predetermined criteria in block 410. When the predetermined criteria change over a plurality of the aircraft's flight phases (block 408), method 400 reassigns at least one data link message route in block 402 to at least one second preferred network selected from the plurality of wireless communications networks with efficient bandwidth. The reassigned data link message route continues transmitting data link messages to and from the aircraft, based on the latest predetermined criteria. For example, when the preferred network is changed over the plurality of the aircraft's flight phases, one or more network application interfaces are activated (deactivated), as discussed below with respect to fig. 5.

Fig. 5 is a flowchart illustrating a modality of a 500 method for managing and selecting networks in an avionics communication system. Method 500 manages the different interfaces of the network applications discussed above with respect to fig. 4, based on application service needs and network availability (for example, current aircraft status). The method of fig. 5 periodically evaluates at least one state of the aircraft in block 502. If at least one state of the aircraft has changed since a previous assessment (block

504), each of the programmable network selection rules (for example, rules 1 to N for selecting networks) is individually evaluated in blocks 506χ to 506_N. Periodic monitoring of programmable network selection rules ensures that the predetermined criteria for routing messages in a network management and selection function block (for example, the network management and selection function block 302) continue to be met . In an implementation, a current network interface (for example, network interfaces 112i through 112_K) is enabled (disabled) in blocks 508χ to 508n based on the programmable rule being evaluated. The method of fig. 5 resumes, after a certain period of time has passed in block 510.

The methods and techniques described here can be implemented in a combination of digital electronic circuits and software residing in a programmable processor (for example, a special processor, or a common processor in a computer). An apparatus incorporating these techniques may include suitable input and output devices, a programmable processor, and a storage medium, evidently incorporating program instructions for execution by the programmed processor. A process incorporating these techniques can be performed by a programmable processor running an instruction program, which operates on the input data and generates appropriate output data. The techniques can be implemented in one or more programs, which are executable in a programmable system, including at least one programmable processor coupled to receive data and instructions from (and to transmit data and instructions to) a data storage system, at least one input device, and at least one output device. In general, a processor should receive instructions and data from at least one of a read-only memory (ROM) and a random access memory (RAM).

Storage media suitable for incorporating, in an evident manner, data and instructions from computer programs include all forms of non-volatile memory, and include, for example, semiconductor memory devices; flash memory and ROM devices; magnetic disks, such as internal hard drives and removable disks; magnetic optical discs; optical discs, such as compact discs (CDs), digital video discs (DVDs), and other computer-readable media. Any of the above can be complemented, or incorporated, with a specially designed ASIC. When information is transferred or provided over a network or other communication connection (wired, wireless, or a combination of wired or wireless) to a computer, the computer views

<td>correctly</td><td>the connection</td><td>as</td><td>an</td><td>media</td><td>readable</td><td>per</td>

<td>10 computer.</td><td colspan="2">So any</td><td>an</td><td>of these</td><td>connections</td><td>is</td>

<td>correctly</td><td>named</td><td>in</td><td>an</td><td>media</td><td>readable</td><td>per</td>

<td>computer.</td><td>Combinations of</td><td colspan="2">above are</td><td>also</td><td>included</td><td>at the</td>

scope of computer-readable media

<td>That</td><td>description was</td><td colspan="2">presented</td><td>for purposes</td><td>in</td>

<td>15 illustration,</td><td>and do not intend</td><td>to be</td><td>complete</td><td>or limited</td><td>at</td>

<td>modalities</td><td colspan="2">disclosed. They may</td><td>to occur</td><td>variations</td><td>and</td>

modifications that affect the scope of the following claims.

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