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					HomePlug AV MAC

      R. Newman
  University of Florida
      What is HomePlug AV?
• Open industry standard
  – 4+ manufacturers (including Intellon/Atheros)
  – Compatible with HP1.0
• Developed 2003-2007 by Homeplug Powerline
  Alliance (HPA)
  – Consortium of chip designers, OEMs, PLC users
  – Products shipped in Q1 2006
• Most widely available ethernet class PLC
  – 150 Mbps coded PHY data rate
  – 0ver 40 million units shipped
• Comprises
  – PHY – modulation, coupling, FEC, etc.
  – MAC – medium access, ARQ, etc.
  – Bridging – to other PLC networks or to 803.3/11/etc.
Reference Model
Protocol Layer Architecture
              HPAV Challenges
• Backward compatibility with HP1.0
  • Delivered base of over 10 million chips
  • Return customers likely
• Take advantage of high speed PHY
  • Fixed time overheads for delimiters/VCS
  • MSDUs typically less than 1500 octets
• Provide QoS for video/audio/gaming/etc.
  • Latency and jitter control
  • Bandwidth “guarantees”
• Deal with PHY challenges
  • Channels change – can degrade, cause loss
  • Impulse noise may destroy 1-2 symbols per impulse
  • Hidden nodes, neighbor networks
           HPAV Challenges (2)
• Minimize overhead
   • Aim at 80% MAC efficiency for streams
   • Low efficiency expected with low data rate streams
• User-friendly security
   • Must be understandable
   • Must be convenient
   • Must be secure
• Stations may leave unexpectedly
   • Consumer electronic devices
   • Not dedicated to AVLN like AP is to WLAN
      HPAV Solution Approaches
• Backward compatibility with HP1.0
  • Maintain common VCS
• Take advantage of high speed PHY
  • Maximize PHY Body length for efficiency
• Provide QoS for video/audio/gaming/etc.
  •   Timestamp MSDUs with QoS needs
  •   Move on if MSDU can’t be delivered on time
  •   Admission control for new QoS streams
  •   Scheduled access
  HPAV Solution Approaches (2)
• Deal with PHY challenges
   •   Allow tone maps to vary with line cycle
   •   Maintain view of channel rates
   •   Maintain view of stream backlogs
   •   Allow partial reception of MPDU
   •   RTS/CTS for hidden nodes
   •   Repeating for hidden nodes
   •   Redundancy for scheduling information
   •   Neighbor network coordination
• User-friendly security
   •   Mental models
   •   Network password entry
   •   Device password entry
   •   Push-button authorization
  HPAV Solution Approaches (3)
• Minimize overhead
  •   Aggregation of MSDUs, management messages
  •   Minimize use of delimiters
  •   Small addresses – 8-bit Terminal Equipment IDs (TEIs)
  •   Allow for contention-free access
  •   Integrated encryption/IV derivation
• Stations may leave unexpectedly
  • Employ soft state
  • Use negotiation for determining coordinator
  • Allow for handover/recovery of responsibilities
                 HPAV Solutions
• Backward compatibility with HP1.0
   • Hybrid delimiters – allow for common VCS
• Central Coordinator
   • Allows admission control/scheduled access
   • Must be able to move CCo/recover from loss of CCo
   • Maintains authoritative network time base
• Central Beacon
   •   Provides common information
   •   Provides synchronization for access
   •   Advertises network time base (NTB) for QoS
   •   Includes persistence for redundancy
   •   Synchronized to line cycle
• Proxy Coordinator
   • Repeats Central Beacon for hidden nodes
              HPAV Solutions (2)
• Contention-Free Periods
  •   Managed by call admission through CCo
  •   Regions reserved for specific streams
  •   Reservations persist in same part of line cycle
  •   QoS stream creation negotiated by all parties
  •   Global link identifiers for efficient reference
  •   Expand/squeeze as needs/channels change
•Two-level Segmentation/Reassembly
  •   Aggregate MSDUs & MMs into MAC Frame stream
  •   Segment MF Stream for encryption/transmission
  •   Make segments unit of reliable delivery inside MAC
  •   CRC per segment
  •   Selective Acknowledgements for multiple segments
             HPAV Solutions (3)
• MPDU bursting to save on ACKs
  • Acknowledge all segments in multiple MPDUs in SACK
  • MPDU number to know when to send SACK
  • MPDU count to know burst duration
• AV Logical Networks based on cryptography
  •   Key hierarchy
  •   NMK needed to join logical network
  •   NEK used for data encryption
  •   Integrated segmentation/encryption
  •   IV derived from MPDU and segment information
  •   Push-button inherently insecure at time of join
  •   Two security levels
  •   Password parameter definition
              HPAV Networks
• Physical Network (PhyNet)
    •   Relative to a station (STA)
    •   All other STAs able to communicate
        with the reference STA
• Logical Network (AVLN)
    •   Has a Central Coordinator (CCo) STA
    •   Set of STAs with same
          •   Network ID (NID) and
          •   Network Membership Key (NMK)
             AV Logical Networks
                  CCo1    CCo2

         A                            E

              B                  D        F

    • Neighbor networks
    • Hidden nodes
    HPAV General Operation
• Each AVLN has a CCo
    •   CCo is determined dynamically
    •   CCo give general information in beacon
    •   CCo admits new STAs
• STAs join AVLN by requesting NEK
    •   STA must have Network Membership
        Key (NMK) to get Network Encryption
        Key (NEK)
    •   Unauthenticated STAs can do very little
    •   STA gets NEK from CCo
• Time divided into Beacon Periods (BPs)
    •   Access information based on BP
            HPAV STA Roles
• Level-0 CCo (no QoS support) – every STA
     •    Assoc/Authenticate new STA
     •    TEI provisioning
     •    CSMA operation
     •    Neighbor Network (NNW) passive
• Level-1 CCo = Level-0 plus:
     •    TDMA operation/scheduling/admission
     •    GLID provisioning
     •    Uncoordinated mode with NNWs
• Level-2 CCo = Level-1 plus:
     •    Coordinated mode with NNWs
HPAV Beacon Periods
              HPAV Beacon Timing
 LCTn     BTTm    LCTn+1             LCTn+2 BTTm+1   LCTn+3

    Beacon                              Beacon
     Offset                              Offset
                     Beacon Period

• Line Cycle Crossing Time (LCT)
  • PHY detection and digital phase lock loop (DPLL)
• Beacon Offset
  • Use to keep network time base (NTB)
  • Advertise future beacon transmit times
                HPAV Beacon
• Beacon Payload holds 136 octets
   • Uses mini-ROBO modulation
• Beacon sent periodically (once per BP)
   • Sent by Central Controller (CCo)
   • Provides reference Network Time Base (NTB)
   • Indicates offsets for future Beacons
• Three Beacon types
   • Central Beacon – issued by CCo
     • Provides scheduling information
  • Proxy Beacon – copy of central beacon repeated
    by Proxy Coordinator (PCo) when hidden nodes
  • Discovery Beacon – sent for network discovery
        Beacon Scheduling Info
• Non-Persistent Scheduling Information
  •   Can change from one Beacon Period to the next
  •   Extra allocations to backlogged QoS streams
  •   Extra CSMA region
  •   Discover beacons
• Persistent Scheduling Information
  •   Remains constant for advertised number of BPs
  •   Allows access even when Beacon is lost
  •   Persistence information included in Beacon
  •   Persistent CSMA allocations – for CSMA access
  •   Persistent TDMA allocations – contention-free
  •   May include preview schedule when changing
 Beacon Schedule Persistence

• CSCD – current schedule countdown
  • Minimum # BPs for which this schedule is valid
• PSCD – preview schedule countdown
  • # BPs in which this schedule will take effect
CSMA-Only Beacon Period
                    Uncoordinated Mode BP
            Fixed offset from AC
              Line Cycle Zero
                                                                    AC Line Cycle
                                                                                                                      

                                                   Beacon Period

               Beacon Period Start Time,
              synchornized to AC line cycle
                     CSMA Region                                        Reserved Region


Beacon             Persistent Shared
                                              Persistent and Non-Persistent Allocations for TDMA and CSMA/CA traffic
PPDU                 CSMA Alloc.

Beacon Region
 contains one
 Beacon Slot
                        Coordinated Mode BP
             Fixed offset from AC
               Line Cycle Zero
                    Cross                                                   AC Line Cycle
                                                                                                                                         

                                                            Beacon Period

                Beacon Period Start Time,
               synchornized to AC line cycle
                       CSMA Region                        Stayout Region                                   Reserved Region

Beacon    Beacon    Beacon     Persistent Shared                                              Persistent and Non-Persistent Allocations for
                                                   STAs in AVLN are not allowed to transmit
 Slot-1    Slot-2    Slot-3      CSMA Alloc.                                                          TDMA and CSMA/CA traffic

                                     Beacon Region contains multiple Beacon
                                      Slot, CCo transmits Beacon in one the
    Beacon                                         Beacon Slots

               Channel Access
• Beacons
  • In Beacon Slot (Coordinated and Uncoordinated)
  • CSMA (CSMA-Only mode, and Discovery Beacons)
• CSMA (Contention-based Access)
  •   Like HomePlug 1.0.1
  •   Two priority reservation slots (PRS0, PRS1)
  •   Contention window depending on priority, history
  •   May use RTS/CTS for hidden nodes
• TDMA (Contention-free Access)
  •   Must have global link identifier (GLID)
  •   CCo does admission control, scheduling
  •   Schedule advertised in central beacon
  •   Backlog advertised for non-persistent extra allocation
        Links and Connections
• Connections – higher layer abstraction
   • May be unidirectional unicast, bidirectional, or
   • Do not reflect the asymmetry of PLC channels
• Links - Used by Convergence Layer (CL)
   • Unidirectional (single source)
   • May be unicast or multicast/broadcast
   • Reflect underlying channel characteristics
   • Allow for scheduling based on channel
   • Local links for CSMA (source + link ID unique)
   • Global links for TDMA (assigned by CCo)
   • Connection Manager determines mapping to link
   • Connectionless traffic assigned a “priority link”
   • Priority Link IDs (PLIDs) only identify priority
         Links and Scheduling
• Priority Link IDs (PLIDs): 0x00-0x03
  • Only indicate priority of traffic
  • Compete in CP
• Local Link IDs (LLIDs): 0x04-0x7F
  • Assigned by local STA’s CM
  • Compete in CP
• Global Link IDs (GLIDs): 0x80-0xFF
  • Used in Beacon Entries for scheduling
  • Special values:
     • 0xFF = local CSMA allocation
     • 0xFE = shared CSMA allocation
     • 0xFD = Discover Beacon by designated STA
     • 0xFC = Contention Free Period Initiation region
  • 0x80-0xF7 = CCo-assigned global link IDs
  • Rest are reserved
  Connection IDs and CSPECs
• Connection ID (CID)
  • Assigned by initiating STA’s CM
  • 16-bit concatenation of TEI and initial LLID
  • Globally unique in AVLN
• Connection Specification (CSPEC)
  • Associated with each connection
  • Contains QoS parameters for connection
• Connection setup
  •   HLE gives Connection Manager (CM) CSPEC
  •   If feasible, CM contacts destination CM
  •   If destination CM/HLE agree, connection formed
  •   If GLID needed (based on CSPEC), then CCo asked
  •   If CCo agrees, assigns GLID and schedules cnx
  •   Release messages needed on failure
       HPAV Channel Estimation
• Performed using SOUND MPDUs
  • Predetermined pattern using all carriers
  • May also used ROBO modulated data MPDUs
• Determines Tone Map:
  •   Modulation method for each carrier
  •   FEC rate
  •   Cyclic Prefix (CP) duration
  •   Interval of line cycle in which TM applies
• TM and TMI reported to STA and to CCo
  • Sender uses for forming MPDUs and PPDUs
  • CCo uses for allocation algorithms
• Initial and Dynamic CE processes
  • TMs expire on demand or time-out in 30 sec.
HPAV MAC Protocol Data Units
• 4 MPDU Formats
   • AV-Only Short MPDU
     • Only HPAV preamble and Frame Control (FC)
  • AV-Only Long MPDU
     • Like above, but with (data) payload
  • Hybrid Short MPDU
     • Hybrid preamble, HP1.0 FC and HPAV FC
  • Hybrid Long MPDU
     • Like above, but with (data) payload
• HP1.0 FC is just to give HP1.0 nodes VCS
  • Need for backward compatibility
AV-Only MPDU Structure
Hybrid MPDU Structure
        HPAV MPDU Structure
• Delimiter
   • Hybrid or AV-mode
• HP1.0 FC is as in HomePlug 1.0.1 (25 bits)
   • FC_AV holds 128 bits
   • Mapped by PHY to preamble and coded FC(s)
   • 7 Delimiter Types
• Two sizes
   • Long MPDUs have payload
   • Short MPDUs have no payload (delimiter only)
• Payload (if present) consists of PHY Blocks (PBs)
   • 520 octet or 136 octet length
   • Encoded by PHY as FEC blocks
       HPAV Frame Control (FC)
• 3 bits Delimiter Type (DT)
  •   Beacon
  •   SOF, RSOF
  •   SACK
  •   Sound
  •   RTS/CTS
• 1 bit Access Field (ACCESS)
  • True iff MPDU transmitted on an Access NW
• 4 bits Short Network Identifier (SNID)
• 96 bits variant field (depends on DT)
• 24 bits Frame Control Check Sequence (FCCS)
    HPAV Start of Frame (SOF)
96-bit Variant Field includes
• Demodulation and Virtual Carrier Sense Info
   • Modulation (TMI) – indexes tone map (TM)
   • Length (for VCS) – number of OFDM symbols
   • PHY Block size (520 or 136 octet)
• Addressing
   • Source Terminal Equipment ID (STEI)
   • Destination TEI (DTEI)
   • Link Identifier (LID)
• Encryption Key Select (EKS) – for decryption
• Lots of other stuff (cover later)
   HPAV Selective ACK (SACK)
96-bit Variant Field includes
• Destination TEI (DTEI)
• Coordination information
• Encoded bitmap of correctly received PBs
   • Bits correspond to BP position in received
   • Custom compression capability
• A little other stuff (cover later)
   HPAV Reverse SOF (RSOF)
Carries SACK info plus a return payload
96-bit RSOF Variant Field includes
• SACK Information (like SACK)
• Demodulation and Virtual Carrier Sense Info
   • Modulation (TMI) – indexes tone map (TM)
   • Length (for VCS) – number of OFDM symbols
   • PHY Block size (520 or 136 octet)
• Addressing
   • DTEI only (why? Why not STEI/LID?)
•A little other stuff (cover later)
     HPAV Request/Clear to Send
Needed when hidden nodes present
96-bit Variant Field includes
• Addressing
•Source Terminal Equipment ID (STEI)
   • Destination TEI (DTEI)
   • Link Identifier (LID)
• Coordination information
• Duration
   • How long is medium busy
• A little other stuff (cover later)
BUT – only deals with one level of hidden nodes!
       HPAV Sound/SoundAck
Similar to SOF, but used for channel estimation
Fixed modulation (ROBO)
96-bit Variant Field includes
• Channel Estimation and Virtual Carrier Sense Info
   • Maximum TMs requested
   • Length (for VCS) – time of payload
   • PHY Block size (520 or 136 octet)
   • Last SOUND flag
   • Sound ACK flag – indicates this is an ACK
   • Reason for SOUND
• Addressing
• Some other stuff (cover later)
     HPAV Long MPDU Structure
• Delimiter
   • Determines length explicitly or implicitly
   • One or more PB-520s (length & TMI)
   • One PB-136 (if PB size indicates small PB)
• Beacon
   • One PB-136
• Sound
   • One 520 octet or one 136 octet length
Sizes can’t be mixed
Only one PB-136 per MPDU
Only one PB in last symbol
allow for processing time
             HPAV Data Plane

• Data carried
  • MSDUs or Management Messages
• Encapsulated in MAC Frames
  • For recovery and error checking
• MAC Frames aggregated into MF Stream
  • MF Stream segmented for delivery
                HPAV MAC Frames
   2 Octets      4 Octets            Variable number of Octets      4 Octets

  MAC Frame   ATS/Confounder
                               MSDU Payload or Management Message     ICV
   Header       (Optional)

• Delimit messages
   • Aggregation for efficient transmission at high speeds
   • Needed for disaggregation
• Provide timing information
   • Needed for jitter control, delivery guarantees
• Check correct reassembly, decryption
   • Integrity Check Value (ICV)
              MAC Frame Fields
• MF Header
  • MF Type (2 bits)
     •   Bit pad to end of segment
     •   MSDU without ATS
     •   MSDU with ATS
     •   Management Message with confounder
  • MF Length (14 bits)
• ATS/Confounder (0 or 32 bits)
  • Arrival timestamp for AV streams
  • Random confounder for Management Messages
• Body
  • MSDU from higher layer or Management Message
• Integrity Check Value (32 bit CRC)
• Total overhead = 6-10 octets
HPAV Segmentation
     HPAV PHY Block Structure
• PBs are mapped by PHY to FEC Blocks
  • FEC succeeds or fails
• PBs are basic unit of delivery by MAC internally
  • PB is ACKed or retransmitted using SR-ARQ
  • SACK specifies ACK/NAK
• PH Header (PBH) – 4 octets
  • Info for reassembly, disaggregation, recovery
• PB Body (PBB)
  • 512 octets or 128 octets long – not interpreted here
• PB Check Sequence (PBCS)
  • CRC-32 – not encrypted – for checking PB reception
  • PB discarded and NAKed if incorrect
HPAV PHY Block Structure
       HPAV PHY Block Header
• Segment Sequence Number (SSN)
  • 16 bits – segment # in MAC Frame stream
     • Init to 0, increment on each new segment sent
     • Discard duplicates
• MAC Frame Boundary Offset (MFBO)
  • 9 bits to indicate first octet of first MF in PB Body
  • Resynch if a segment is never received
• Flags (1 bit each)
  • Valid PB Flag – in case whole PB is padding
  • Management Message Queue Flag
     • reassemble in MM queue instead of message queue
  • MAC Frame Boundary Flag – is MFBO valid
  • Oldest Pending Segment Flag
     • No older segment will be sent again
            HPAV Reassembly
• MPDU Header
  • Provides STEI, DTEI, LID
  • These identify reassembly stream
• Segment Sequence Number (SSN)
  • Used to place segment in PBB into buffer position
  • Recreate MAC Frame Stream
• MAC Frame Boundary Offset + MFB Flag
  • If segment(s) never received, these allow next intact
    MAC frame to be found
• MAC Frame Header
  • Type and Length fields used to find next MAC Frame
  • Also used to locate MAC Frame Body
  • ATS (if present) determines when to deliver MSDU
        HPAV Data Encryption
• Cipher Suite used
  • AES in CBC mode
  • CRC-32 used as ICV for MIC
  • IV derived from MPDU SOF, PB Header, PB location
     • SOF variant field (12 octets)
     • 3 least significant octets of PBH
     • 1 octet of PB Count (location in MPDU)
• Encryption done on PB Body
  • PBB is multiple of cipher block size – no waste
  • PBB is encrypted anew each time it is sent
  • Once a MF Stream segment is placed in a PBB, it will
    always be sent as that PBB
         HPAV MPDU Bursting

• MPDU Bursting
  • Multiple MPDUs sent before SACK returned
  • Reduces delimiters and interframe space overhead
• MPDU Count
  • MPDUCnt counts down to zero
  • When MPDUCnt=0, time to send SACK
• Total time in CP <= 5 msec (including SACK)
• Sender may request SACK retransmission if lost
                HPAV SR-ARQ
• Selective ACK (SACK) expected after burst
  • SACK holds SACK Information fields for four MDPUs
  • Each SACKI can be
     • All Bad (default value)
     • All Good
     • Corresponding MPDU was not detected
     • Mixed results
        • One bit per PB in order (bit map)
        • One bit per pair of PBs (consolidated bit map)
        • Compressed bit map (custom compression)
• MPDU Count field
  • Used to detect entire missing MPDUs in burst
• Request SACK Retransmission
  • Only available for Global Links
           HPAV Retransmission
• SACK indicates lost PBs
  • Sender knows which segments have been received
  • May retransmit (may even duplicate in same MPDU)
• Number of retransmission attempts
  • Limited by AV parameter on maximum tries
  • Limited by delivery deadline for QoS streams
• Sender may develop backlog
  •   Pending PBs reported in SOF
  •   CCo can grant extra allocation if possible
  •   CF stream may use CP for retransmission also
  •   Sender may discard segment – receiver finds this out
      from oldest pending segment flag
    HPAV Bidirectional Bursting

• Allows data to be piggybacked on SACK
  • Reduces delimiters and interframe space overhead
• Must be requested and granted
  • SACK has RRTL field to specify length requested
  • SOF’s BBF flag and MRTFL field specify grant length
  • EKS is same as the forward transmission’s
• ACK field in SOF for reverse transmission
  CF Region Interframe Spacing
                      e o Pi d
                       a   r
                      B cn eo

e oR i n
 a   g
B cn e o   S Ri n
            M g
           C A eo                   ReeR i n
                                    e r d eo
                                     sv   g              e oR i n
                                                          a   g
                                                         B cn e o
                          F lo 1
                             l .
                          CA c#              F lo 2
                                                l .
                                             CA c#


  S K   O
        SF    S K
              AC       O
                       SF     AC
                              S K      S K
                                       AC      O
                                               SF     AC
                                                      S K   S K
                                                            AC      e o0
                                                                    B cn

 AS               I _
                   F A
                  RS V               IF
                                     AS                RS V
                                                        F A
                                                       I _           B
                                                                    B IS

                  oei - eL #
                   n to F   n
                  C t n n rei k 1               oei - eL #
                                                 n to F   n
                                                C t n n rei k 2

• CIFS, RIFS, EIFS similar to HP1.0.1
  • RIFS_AV may vary – set by receiver
• B2BIFS needed before/after each beacon
• AIFS needed before new CF allocation
      CSMA Interframe Spacing

• CIFS, RIFS, EIFS similar to HP1.0.1
• B2BIFS needed before/after each beacon
• AIFS needed before SOF of new CF allocation
  • Unless CF allocation is for contention period
        Burst Interframe Spacing
                        ec n e d
                       Bao Proi

 ecn e o
Bao R i n    SA e o
            CM R i n               ReeR i n
                                   e r d eo
                                    sv   g             ecn e o
                                                      Bao R i n
                            F lo #
                            CA c 1         F lo #
                                           CA c 2

               CI S                           I _V
                                              R SA

      SC       O
               SF      O
                       SF      SF
                               O      O
                                      SF      AK
                                              SC     O

                BS      BS
                        IF      IF

                        P Br
                         D  s
                        M Uut

• BIFS needed between burst MPDUs
   Extended Interframe Spacing
                      0 s
                     2. µ
     6 µ
     9 s
     16                               16
                                      6 µ
                                      9 s
                  mm L )
                   n MA
                    m x VF
                  (ii u a _

                           RA                    IS
      o b
       S l
     T yo                             wm
                                       o b
                                        S l
                                      T yo
  A                                V
     r Cl
     a o
     Fen ro       MPa
                  P ad
                   Ulo                r Cl
                                      a o
                                      Fen ro
 Pb                               rm
      ( F                              SO)
                                       ( F


• EIFS used when VCS is lost
  • Maximum long MPDU along with SACK and IFSs
      Central Coordinator (CCo)
• Issues central beacon
• Associates new stations
  • Issues TEI with lease, announces to AVLN
• Authenticates new stations
  • Verifies possession of NMK, issues NEK
  • Rotates NEK
• Performs admission control
  • Determines resource needs and availability
  • Issues Global LID
  • Performs scheduling
• May perform handover
  • Transfer CCo functions to another STA
• Performs neighbor network coordination
             Power-on Behavior
• State of STA
   • Has it ever been a member of an AVLN?
• Search for AVLNs
   • Listen for Central and Proxy Beacons
   • Listen for Discovery Beacons
   • Listen for Unassociated STA advertisements
• If find matching Network ID (NID)
   • Associate
   • Attempt to authenticate (get NEK)
   • End if successful, else continue (mark NID)
• If time runs out
   • If matching Unassociated STA NID, try to form AVLN
   • Else if AVLN present, advertise Unassociated STA
   • Else become Unassociated CCo (issue beacon)
             Unassociated STA
• Advertise infrequently
   • Issue Unassociated STA advertisements
   • Send once per Discovery Period, more or less
• Synchronize to an existing AVLN
   • Adopt mode (Hybrid or AV-Only) from Beacon
   • Use NTB of AVLN
   • Use SNID of AVLN in multi-network broadcasts
• If find matching Network ID (NID)
   • If beacon, try to join AVLN
   • If unassociated STA, try to form AVLN
• If AVLN disappears
   • Become Unassociated CCo
             Authenticated STA
• Determine whether should become CCo
   • If STA is a User-appointed CCo, and current CCo is not a
     User-appointed CCo, request handover
   • May also execute CCo Selection process, become CCo if
     more capable or better positioned
   • May become CCo if current CCo fails and STA is backup
• Adopt mode of operation from Beacon
   • Advertise detection of HP1.0/HP1.0.1 delimiters
   • Piggybacked in SOF, SACK, etc.
• If AVLN lost
   • No central/proxy beacon for timeout period
   • Start Power-on Procedure
• If asked to leave
   • Become Unassociated STA
                  CCo Behavior
• Perform CCo Duties
  • As long as there are other STAs in AVLN
• If all other STAs leave AVLN
  • Remain CCo for at least Discovery period
  • If no STA joins and another AVLN is present, become
    Unassociated STA
  • Else become Unassociated CCo
• If STA in AVLN should become CCo
  •   Other STA is User-appointed and this one is not
  •   Other STA is more capable or better positioned
  •   Execute handover procedure
  •   Become STA in AVLN
              Mode of Operation
• AV-Only Mode
  • Use AV-Only delimiters
• Hybrid Mode
  • Use Hybrid delimiters
• Deciding Mode
  •   STA adopts mode of AVLN
  •   All STAs listen for HP1.0/HP1.0.1 delimiters
  •   If seen often enough, advertise using flags
  •   CCo adopts mode based on detection
  •   Revert to AV-Only if HP1.0/HP1.0.1 delimiters no longer
• Have a CCo
  • CCo issues central beacon, acts as coordinator
  • May have Proxy Coordinator(s) also
• Share same Network ID (NID)
  • NID normally derived from NMK
  • Should uniquely identify AVLN
  • Remains constant regardless of CCo
• Share same Security Level
  • NMK associated with SL
  • SL must be the same throughout AVLN
• Share same NEK
  • CCo provides NEK during authentication using NMK
  • NEK used to encrypt traffic in AVLN
• One AVLN may have multiple sub-AVLNs
  • Share a single CCo
• Share same Network ID (NID)
  • NID not derived from NMK
  • CCo must use MAC address to decide which NMK to use
    for a given STA
   User-Friendly AVLN and STA IDs
• User-friendly name is printable ASCII string
  • Use for humans to identify conveniently
  • Not guaranteed to be unique
  • STA and AVLNs may have these assigned
• Assigning HFIDs
  • Use primitive over the H1 interface for either
  • Use Management Message to CCo for AVLN
• Getting HFIDs
  • Management Message to request from STA or CCo
  • Request not required to be encrypted
  • Response to non-encrypted request need not provide
    actual HFID
         Association with an AVLN
• Association provides a unique identifier
   • CCo assigns a valid TEI with lease on request
   • STA uses special TEI=0x00 before obtaining TEI
   • NID or SNID must be used to disambiguate TEIs
• Obtaining a TEI
   •   STA makes request
   •   CCo responds (decline or provide valid TEI/lease)
   •   If accepted, CCo advertises all TEI/MAC addresses
   •   TEI must be renewed before lease expires
• Leaving an AVLN
   • STA may leave voluntarily – send disassociate message
   • TEI lease may expire
   • CCo may ask STA to leave – send leave message
• Process Steps
  • Association is obtaining a valid TEI
  • Authorization is obtaining a valid NMK
  • Authentication is obtaining a valid NEK
• Obtaining a valid NEK
  • STA must have NMK first
  • STA requests NEK from CCo using NMK, provide nonce
  • If CCo decrypts, NMK is valid; provide NEK and nonce
    using NMK, else CCo indicates failure
• Updating NEK
  • NEK rotated at least once per hour
  • CCo requests nonce (NEK encrypted); STA responds
    with nonce (NEK encrypted)
  • CCo sends set key msg with nonce encrypted with NMK
    and old NEK; STA acknowledges using same keys
           Forming a New AVLN
• Circumstances for new AVLN formation
  •   Two Unassociated STAs with matching NID
  •   Two Unassociated STAs using DAK
  •   Two Unassociated STAs, one in Join, one in Add
  •   Two Unassociated STAs, both in Join
• Matching NID
  • Determine from Unassociated STA advertisements
  • Decide who becomes CCo from CCo capabilities and
    MAC address in Unassociated STA advertisements
  • Winner becomes Unassociated CCo, sends beacons
  • Other STA(s) join it by associating, authenticating
  • Loser(s) continue to send Unassociated STA
    advertisements until beacon with NID detected
  • Multiple AVLNs with same NID/NMK can merge
        Forming a New AVLN (2)
• DAK-based Protocol
  • STA with Device Access Key (DAK) of another STA
    broadcasts a set-key message encrypted with DAK holding
    a TEK
  • Any STA receiving a message like this tries to decrypt it
  • If it succeeds, then it replies (unicast) encrypting with the
    Temporary Encryption Key (TEK) the message held
  • If the initiating STA decrypts a response encrypted with the
    TEK, it sends a set-key message with the new NMK and
    the nonce in the reply encrypted with the DAK
  • If the new STA decrypts this message with its DAK and the
    nonce matches, it sets its NMK and NID
  • STAs decide who becomes the CCo from capabilities in
    the exchanged messages
  • CCo issues beacons, other STA associates, authenticates
         Forming a New AVLN (3)
• Push-button Mechanism
  • Button press causes STA in AVLN to admin another one
  • STA never in AVLN (or reset) will join an AVLN
• Two Unassociated STAs, one in Join, one in Add
  •   STA that has been in an AVLN will enter silent Add state
  •   STA in Join state will broadcast its desire to join an AVLN
  •   STA in Add state will respond unicast and become CCo
  •   STA in Join will associate with new AVLN
  •   STAs should perform channel adaptation
  •   STAs then start UKE protocol
       • Exchange hash keys
       • Hash these to form temporary encryption key (TEK)
       • Use TEK to send NMK from CCo to new STA
  • STA then authenticates using NMK
       Forming a New AVLN (4)
•Two Unassociated STAs, both in Join
  • STA in Join state will broadcast its desire to join an AVLN
  • STAs will see each other’s advertisements
  • STAs decide who should become CCo from capabilities
  • Winner becomes CCo, generates new random NMK,
    switches to Add state, sends confirmation to other STA
  • STA in Join will associate with new AVLN
  • STAs should perform channel adaptation
  • STAs then start UKE protocol
      • Exchange hash keys
      • Hash these to form temporary encryption key (TEK)
      • Use TEK to send NMK from CCo to new STA
  • STA then authenticates using NMK

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