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3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 1 Multimedia Clock Synchronization over 802.11 WLAN Javier del Prado and Sai Shankar.

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Presentation on theme: "3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 1 Multimedia Clock Synchronization over 802.11 WLAN Javier del Prado and Sai Shankar."— Presentation transcript:

1 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 1 Multimedia Clock Synchronization over 802.11 WLAN Javier del Prado and Sai Shankar N Wireless Communications and Networking Dept. Philips Research-USA Briarcliff Manor, New York E-mail: {javier.delprado,sai.shankar}@philips.com and Sunghyun Choi Multimedia & Wireless Networking Lab. (MWNL) School of Electrical Engineering Seoul National University, Korea E-mail: schoi@snu.ac.kr

2 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 2 Outline Introduction Multimedia Clock Synchronization over IEEE 802.11 IEEE 802.11e MLME Higher Layer Synchronization Primitives Conclusions

3 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 3 Introduction In an IEEE 802.11 WLAN network, stringent clock synchronization is required to enable audio and video applications For instance, in an audio application, trained ears can hear the clock jitter of  1.5  s [5][6] To support a wide variety of applications, including professional audio, IEEE 1394 over IEEE 802.11e WLAN. (Eg: 1394 achieves the clock jitter of less than  41 ns (I.e., one clock tick) [4])

4 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 4 In-home Streaming Scenario RG Access Point DVD Recorder HDTV SDTV PDA Bridge Internet Internet Access Content Server

5 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 5 Synchronization Requirements

6 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 6 Wireless 1394 Scenario (Virtual 1394 Bus) CM

7 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 7 Our Solution – CM transmits directly <= 10 ms a(n) n n' 1394 synchronization frame sent by CM Cycle Master CTR a(n) Cycle Slave CTR b(n) a(n)  adjust Last_Symbol_on_Air PHY_TXEND.confirm PHY_RXEND.indication 1394 synchronization frame sent by CM n Frame Sequence Number PHY_TXEND.confirm PHY_RXEND.indication

8 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 8 Our solution – CM transmits through HC Cycle Master CTR a(n) Cycle Slave CTR b(n) a(n)  adjust HC/ QAP Last_Symbol_on_Air CM sends synchronization frame to HC HC forwards the frame to the BSS PHY_RXEND.indication CM sends synchronization frame to HC with a(n) PHY_RXEND.indication 1394 synchronization frame sent by HC n Frame Sequence Number HC forwards the frame to the BSS a(n) n n' 1394 synchronization frame sent by HC

9 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 9 How It Works At Cycle Master –a(n) = CTR_Value (at observed Last_Symbol_On_Air event) – offset –Multicasts a(n) and n in synchronization frame at a semi- regular interval (e.g. 10 ms) At Cycle Slave –b(n) = CTR_Value (at observed Last_Symbol_On_Air event) – offset –Receive synchronization frames and retrieve a(n) and n –Compare b(n) and a(n) and use  to adjust CTR appropriately offset: delay from the end of the last symbol on the air to when capturing of the CTR value takes place

10 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 10 Changes required in 802.11 No major change required! Only three new primitives need to be defined to support the synchronization The primitives will pass the 1394 synchronization frame information from the MAC to the SME The communication between the SME and the 1394 PAL Layer is out of the scope of this submission

11 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 11 Synchronization Primitives MLME-HL-SYNC.request MLME-HL-SYNC.confirm MLME-HL-SYNC.indication

12 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 12 MLME-HL-SYNC.request This primitive requests activating the higher layer synchronization support mechanism It is generated by the SME when a higher layer protocol, which requires a stringent synchronization, such as the 1394 PAL, is active in the STA Semantics: MLME-HL-SYNC.request( RxAddress ) Name Type Valid Range Description RxAddress MACAddress A multicast MAC address Specifies themulticast MAC address that the synchronization frames are addressedat.

13 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 13 MLME-HL-SYNC.confirm This primitive confirms the activation of the higher layer synchronization support mechanism It is generated by the MLME as a result of an MLME-HL- SYNC.request to activate the mechanism for the higher layer synchronization support Semantics: MLME-HL-SYNC.confirm( ResultCode ) Name Type Valid Range Description ResultCode Enumeration SUCCESS, NOT_SUPPORTED Indicates the result of the MLME-HL-SYNC.request

14 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 14 MLME-HL-SYNC.indication This primitive reports completed transmission or reception of a higher layer synchronization frame This primitive is generated by the MLME when the successful reception/transmission of a synchronization frame is detected. The synchronization frame is identified by the multicast MAC address indicated by the MLME-HL-SYNC.request primitive, in Address 1 field of the synchronization frame. Semantics: MLME-HL-SYNC.indication( SourceAddress SequenceNumber ProcDelay )

15 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 15 MLME-HL-SYNC.indication (II) Parameters: NameTypeValid RangeDescription SourceAddressMACAddressAny valid individual MAC address Specifies the Source Address of the synchronization frame. In the case of the STA sending the frame, it will be its own MAC address. SequenceNumberEnumerationAs defined in the frame format Specifies the sequence number of the synchronization frame received/transmitted. ProcDelayEnumeration  0 0 Specifies the estimated time between the generation of this primitive and the time at which the end of the last symbol of the frame that generated this primitive was detected on the air.

16 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 16 Conclusion (I) A new clock synchronization mechanism defined for timing critical multimedia application –Relies on a higher-layer clock in each node and the Last_Symbol_On_Air timing that occurs simultaneously across 802.11 WLAN –Does not rely on TSF Timer, which may not be accessible, reliable, or accurate enough Mechanism already approved by the 1394 WWG! Any node can become the Cycle Master!!! Not require any significant change in 802.11 –PHY_TXEND & PHY_RXEND are readily available –Only three new primitives need to be defined

17 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 17 Conclusion (II) The MAC change is essentially optional !!! –Look at MLME-HL-SYNC.confirm (Not Supported) –E.g., no need to implement it if no plan to support timing-critical applications Can be used for any higher layer protocol that requires stringent clock synchronization!!!

18 3rd NYMAN Javier, Sai and Sunghyun Sept. 2003 Philips Research USA Slide 18 References [1] IEEE P1394.1 High Performance Serial Bus Bridge, Draft standard. [2] ETSI TS 101 493-3 Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Packet Based Convergence Layer; Part 3: IEEE 1394 Service Specific Convergence Sublayer (SSCS), ETSI 200-09. [3] IEEE Std 802.11-1999, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications, Reference number ISO/IEC 8802-11:1999(E), IEEE Std 802.11, 1999 edition, 1999. [4] IEEE Std 1394-1995, High Performance Serial Bus [5] F. Wightman, D. Kistler: Hearing in three Dimensions: Sound Localization, AES 8th Int. Conference [6] W. Hartmann: Localization of a Source of Sound in a Room, AES 8 th Int. Conference

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