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HomePlug AV MAC

(c) 2013 R. Newman University of Florida. HomePlug AV MAC. 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

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HomePlug AV MAC

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  1. (c) 2013 R. Newman University of Florida HomePlug AV MAC

  2. 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.

  3. Reference Model

  4. Protocol Layer Architecture

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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) (usually)

  14. AV Logical Networks • Neighbor networks • Hidden nodes

  15. 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

  16. HPAV STA Roles • Level-0 CCo (no QoS support) – every STA • Assoc/Authenticate new STA • TEI provisioning • CSMA operation • Neighbor Network (NNW) passive coordination • Level-1 CCo = Level-0 plus: • TDMA operation/scheduling/admission control • GLID provisioning • Uncoordinated mode with NNWs • Level-2 CCo = Level-1 plus: • Coordinated mode with NNWs

  17. HPAV Beacon Periods

  18. HPAV Beacon Timing • 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

  19. 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

  20. 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

  21. 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

  22. CSMA-Only Beacon Period

  23. Uncoordinated Mode BP

  24. Coordinated Mode BP

  25. 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

  26. Links and Connections • Connections – higher layer abstraction • May be unidirectional unicast, bidirectional, or multicast • 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

  27. 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

  28. 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

  29. 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.

  30. 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

  31. AV-Only MPDU Structure

  32. Hybrid MPDU Structure

  33. 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

  34. 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)

  35. 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)

  36. 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 transmission • Custom compression capability • A little other stuff (cover later)

  37. 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)

  38. HPAV Request/Clear to Send (RTS/CTS) 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!

  39. 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 • STEI, DTEI, LID • Some other stuff (cover later)

  40. HPAV Long MPDU Structure • Delimiter • Determines length explicitly or implicitly • SOF or RSOF • 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

  41. 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

  42. HPAV MAC Frames • 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)

  43. 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

  44. HPAV Segmentation

  45. 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

  46. HPAV PHY Block Structure

  47. 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

  48. 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

  49. 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

  50. 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

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