Mike Shorthose, Nikos Fistas Eurocontrol

Transcription

1 Mike Shorthose, Nikos Fistas Eurocontrol AMCP WG-M 5th meeting St Petersburg, 20 August 2002 Slide 1

2 Background limitations of current protocol benefits of new protocol Process Eurocontrol funded development Validation details Technical details of new protocol Slide 2

3 Process Validation details Technical details of new protocol Slide 3

4 VDL Mode 4: status in WGM AMCP/7 meeting approved SARPs and TM for VDL Mode 4 for surveillance applications only WGM is considering the use of VM4 for point to point communications Some deficiencies exist with the currently specified VM4 DLS protocol Slide 4

5 Closely based on VDL Mode 2 (AVLC) Allows transfer of 4 frames before an acknowledgement is required BUT: does not provide support for message priority does not allow fragmentation of longer messages problem with leave event generation protocol adds unnecessary complexity errors and duplication inconsistencies and ambiguities in references to VDL Mode 2 Slide 5

6 New DLS provides explicit acknowledgement of each DATA packet mechanisms to make maximum use of reserved slots for DATA transfer ability to link sequences of messages in reserved slots packet fragmentation with minimum overhead, optimally matched to link conditions duplicate detection and suppression support for 15 priority levels supports pre-emption by higher priority message Slide 6

7 Benefits of new DLS protocol removes errors, duplication, inconsistencies and ambiguities reduces protocol complexity handles priority messages in an efficient way provides fragmentation reduce overhead optimal match of fragment size to link conditions extends performance benefits of previous DLS protocol greatly extends ability to combine successive messages between peers achieves high channel utilisation through maximum possible use of reserved access protocols Slide 7

8 LME Interface with DLS updated to take account of revised DLS services beneficial removal of special LME transport protocol Import of text previously called up from Mode 2 standard no functional change text is much clearer these changes highlighted in yellow Modification of parameter content rationalisation of parameters no change in functionality VSS consequential changes main impact is support for 15 priority levels Slide 8

9 Background Validation details Technical details of new protocol Slide 9

10 The basic principles of a new DLS proposal were presented to WGM/2 by Eurocontrol WGM agreed that this is a good direction and requested to advance the work and make a complete proposal for a new DLS protocol Eurocontrol established (Nov. 2001) a team to complete DLS proposal and validate the new DLS Slide 10

11 Drafting carried out by Mike Shorthose (Helios) and Tony Whyman (MWA) assisted by Steve Friedman (ADSI) and Marcus Gustafsson (SAAB) development team Other inputs from WG-M members Validation carried out by independent validation team at Helios Co-ordination maintained between the development team and VM4 radio manufactures (ADSI, SAAB), LFV, FAA, DFS and other WG-M members Slide 11

12 Define a complete proposal for a new DLS Resolution of issues review of initial DLS outline proposal with analysis of outstanding issues Produce outline design specification Design of burst types Produce first draft for technical manual Review after first phase of validation Produce second draft for technical manual response to validation issues drafting of LME interface Review after second stage of validation Final update and presentation to WG-M (this meeting) Slide 12

13 Validation of new DLS First stage inspection and analysis of DLS protocol Identification of protocol states Identification of state diagrams and associated events Protocol walk through: Step through of data transfer protocol including special transfer protocols Output: Validation report Slide 13

14 Validation of new DLS (c td) Second stage simulation of DLS and inspection of LME changes Carried out after update by development team Implementation of single aircraft test simulator Investigation of protocol performance in presence of disruption (lost messages, out of sequence messages etc) Inspection of LME changes Output: Simulation report containing open issues Third stage review of validation activities carried out after final update by development team and review by WG-M members Output: Updated simulation report (no open issues) Slide 14

15 Production of Implementation Manual entry to replace previous DLS text contains estimate of link utilisation provides guidance on use of short and long transmission protocols and ground reservation protocols Change proposal brings together and introduces all documentation Slide 15

16 The following are submitted for consideration by WG-M Covering paper Revision-marked text of the VM4 Technical Manual Validation report Simulation report Revision-marked text of the VM4 Implementation Manual Slide 16

17 Background Process Technical details of new protocol Slide 17

18 Validation carried out by independent team Initial process inspection derivation of state diagrams Connection Establishment Data Transmission Data Reception report of initial findings (validation report) Slide 18

19 Rx Data, Notifications Tx Data LME DLS DLS User SZOM CTRL(IB=1) Invalid T-bit Tx Data Disconnected Connected Reset Rx Data, Failure Notifications Timer Expires FRMR_ACK Received Tx DLPDUs, VSS Rx DLPDUs, Failure Notifications Slide 19

20 INFO, CTRL Start RTS Type? UDATA Receive processing (long transmission) T-Bit? Correct T-bit Incorrect T-bit Send CTS INFO, CTRL Data Type? UDATA Correct T-bit T-bit? Incorrect T-bit None Received Send ACK Forward to Receive Array Send NACK Discard DATA Forward To DLS User END Slide 20

21 No fundamental problems found A number of logical errors discovered Corrective action suggested by the validation team Slide 21

22 Validation Stage 2 Stage 2 consisted of: inspection and analysis of v0.4 simulation of protocols using simple test harness inspection of LME interface production of simulation report Stage 2 results simulations show that protocol is robust development of simulator demonstrates that text is clear a number of open issues left for resolution which were addressed and closed in Stage 3 Slide 22

23 Control Physical Station 1 Station 2 Data Control Slide 23

24 Slide 24

25 Input input script configuration file inputs includes modifier which makes it possible to disrupt the data flow Output output file Slide 25

26 Background Process Validation details Slide 26

27 Provides services to external users for point-to-point comm to the LME to support link management between peer DLSs both air/ground and air/air for broadcast Uses services of VSS to send/receive messages LME DLS User DLS VSS Peer DLS Slide 27

28 DLS provides: simple transmit/acknowledge protocol duplicate suppression via toggle bit message fragmentation via M bit 15 message priority levels pre-emption of lower priority messages short and long transmission protocols includes linking of successive messages make best use of reservation protocols provided by VSS minimises use of random access protocol re-transmission based on knowledge of when ack is expected removes dependence on timers Slide 28

29 DLS User LME Directed Data (INFO, CTRL) Broadcast Data (UDATA) Connection Management (IB/SZOM) Message Segmentation (M-bit) Delivery Order (T-bit) DLS Short Acknowledged Long Acknowledged Short Unacknowledged Long Unacknowledged Unicast Request Reservation General Response Protocol Information Transfer Request Retransmission VSS Slide 29

30 Data link protocol data unit (DLPDU) Burst id + one or two DLS frames DATA frames transfer of user information CTRL (LME packets), INFO (point to point user data) and UDATA (broadcast user data or broadcast LME data) ACK frames acknowledge transfer of user information CTRL_ACK and INFO_ACK Slide 30

31 RTS frames request reservation of slots for DATA transfer CTRL_RTS, INFO_RTS, UDATA_RTS CTS frames provide reserved slots for DATA transfer CTRL_CTS, INFO_CTS, UDATA_CTS Other link control frames FRMR, FRMR_ACK for link reset DM/DISC for air/ground link disconnection SZOM for air/air link initialisation Slide 31

32 Toggle bit (T) alternatively set to 1 and 0 on each successive data transmission A B DATA T = 1 ACK T = 1 DATA T = 0 ACK T = 0 Slide 32

33 More Bit (M) set to zero to indicate end of message. Message fragmentation/concatenation If the length of the burst is longer than N4 slots the sending station will fragment the message. For single fragment messages: M bit is zero For multiple fragment messages: The M bit is set to 1 except the last segment, which is set to zero Slide 33

34 Initialise bit (IB) - used to initialise T bit Priority (p) absolute priority Length (lg) length of the data Negotiation subfield (neg) indicates link parameters for air/air link Slide 34

35 DATA sent (M = 0, pr = 2, T = 0, unicast reservation) A B DATA received (M = 0, pr = 2, T = 0) ACK sent (T = 0) ACK received (T = 0) Key Transmission sent by random access) Transmission sent in unicast reservation Slide 35

36 RTS Sent (lg = 4, pr = 2, T = 0, unicast reservation) CTS received (T = 0) A B RTS received (lg = 4, pr = 2, T = 0) CTS sent (T = 0, info transfer request reservation) DATA sent (M = 0, pr = 2, T = 0) Data received (M = 0, pr = 2, T = 0) ACK received (T = 0) ACK sent (T = 0) Key Transmission sent by random access Transmission sent by unicast reservation Transmission sent by info reservation Transmission sent by info reservation Slide 36

37 Up to two DLS frames can be contained in a single DLS burst enables protocols to be linked so as to avoid use of random access protocol The following combinations are possible: DATA/RTS and ACK/CTS links a stream of messages or fragments sent from one peer to another ACK/DATA allows receiving station to send back a single slot response ACK/RTS allows a receiving station to reserved slots for multi-slot response eg subsequent transport ACK Slide 37

38 A B RTS CTS DATA / RTS ACK / CTS Slide 38

39 TD1 and TD2: control the air/air link ND1: Maximum number of octets in any frame ND2: The maximum length of the message to be sent as a short protocol ND3: The maximum length of a segment Slide 39

40 The services offered to the LME will be: transfer of LME packets encoded within CTRL frames using the T bit protocol (duplicate suppression) at the highest priority T-bit initialisation via flag setting within CTRL frame fragmentation for long LME packets provision of short and long transmission protocols for CTRL frames pre-emption of lower priority INFO frames transfer of broadcast LME packets using modified short and long transmission protocols ability to disconnect link via DM/DISC frame Slide 40

41 The services offered for air/ground INFO transfer are: disconnect mode indication if INFO transfer is attempted before a link is established operation on a full 4 bit priority basis duplicate suppression pre-emption fragmentation provision of short and long transmission protocols for INFO frames transfer of broadcast INFO packets using modified short and long transmission protocols Slide 41

42 The services offered for air/air INFO exchange are: T-bit initialisation via an SZOM frame which is combined with the first INFO frame Link parameter negotiation via version number Link maintenance via send and receive timers Operation on a full 4 bit priority basis Transfer of information encoded within INFO frames using the T-bit protocol pre-emption fragmentation provision of short and long transmission protocols Slide 42

43 Protocol provides minimisation of use of random access protocol protection against hidden and exposed terminals priority handling including pre-emption use of ground reserved slots to protect transmissions Slide 43