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HomePlug 1.0 MAC

(c) 2013 R. Newman University of Florida. HomePlug 1.0 MAC. What is HomePlug 1.0?. Broadband PLC for home networking Open industry standard 4 manufacturers (including Intellon) Developed in 2000 by Homeplug Powerline Alliance (HPA) Consortium of chip designers, OEMs, PLC users

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HomePlug 1.0 MAC

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  1. (c) 2013 R. Newman University of Florida HomePlug 1.0 MAC

  2. What is HomePlug 1.0? • Broadband PLC for home networking • Open industry standard • 4 manufacturers (including Intellon) • Developed in 2000 by Homeplug Powerline Alliance (HPA) • Consortium of chip designers, OEMs, PLC users • Products shipped in 2001 • First ethernet class PLC, most widely available • 11 Mbps coded PHY data rate • 0ver 10 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. HomePlug 1.0 MAC Overview • Frame Transport • Frame length = 46-1500 bytes/frame • IEEE 802.3 frames encapsulated • IEEE 802.3 48-bit addressing used • Bridging between PLC and other networks • Reliable Frame Delivery • Rate adaptive PHY • Channel estimation and tone map generation • Stop&Wait ARQ for unicast frames • “Partial ACK” for multicast frames • Segmentation to limit time exposed on wire

  4. HP 1.0 MAC Overview (con’t) • Quality of Service • 4 priority levels for differentiated service • Priority signaling slots enforce priority access • Segmentation bounds delay • Bursting for contention-free access • Privacy • 56-bit key DES encryption in CBC mode • Password-based key derivation supported • Management • Registered ethertype for management data

  5. HP1.0 MAC • CSMA/CA • Virtual Carrier Sense - length in FC • 4 levels of priority for differentiated service • Advanced contention resolution • Variable tone map, including code rate selection • Packets of ~0.5ms to ~2ms • Packet bursting to avoid contention • Stop&Wait ARQ • 56-bit DES in CBC mode for privacy • Bridging function

  6. HP1.0 PHY PDU • Preamble = 38.4 usec • Set pattern of 7.5 special symbols • Allows AGI, synchronization by receiver • Detection used for PCS • Frame Control (FC) = 33.6 usec. (4 symbols) • Heavily coded • Uses BPSK (low rate) modulation • Very robust • Very few (25) information bits • FC holds info for PHY • Tone Map Index- for demodulation of body • Frame duration (how long to demodulate)

  7. HP1.0 PHY Frame Format • Detect delimiter from preamble, correct FC • SOF FC indicates symbol count, tone map • Pad Frame Body to PHY Tx block boundary • EOF FC delimits end of data frame

  8. HP1.0 Delimiters • Delimiter • Preamble + frame control = 72.0 usec • FC holds 25 bits of information • 1 bit – contention control (CC) • 3 bits – delimiter type (DT) • 13 bits – variant field (depends on DT) • 8 bits – frame control check sequence (FCCS) • CC bit restricts next access • If set, only frames at same or higher priority allowed to contend • FCCS checks frame control • 8-bit CRC

  9. HP1.0 Delimiter Type • 000 = SOF, no response expected (mcast/bcast) • 001 = SOF, response expected • 010 = EOF, no response expected • 011 = EOF, response expected • 100 = ACK (frame received w/o errors) • 101 = NACK/FAIL • Variable field has Response Type (RT) • RT=0 – NACK if address recognized but errors • RT=1 – FAIL if frame error-free but receiver does not currently have resources to receive • 110-111 = Reserved

  10. HP1.0 SOF Variant Field • 8 bits Frame Length (FL) • In multiples of 20 symbols • Interpreted by PHY as PHY Transmit Blocks • 0x00 = 20 symbols • 0x07 = 160 symbols • 0x08-0xFF = reserved • 5 bits Tone Map Index (TMI) • 0x00 = ROBO (only 40-symbol PTBs allowed) • 0x01-0x0F = negotiated tone map • 0x10-0x1F = reserved

  11. HP1.0 EOF Variant Field • 2 bits Channel Access Priority (CAP) • 11 = highest, 00 = lowest • Used for bursting • 1 bit Invalid • Must be set to 0 or FC is invalid • 10 bits Reserved • Set to 0 on transmit, ignored on receive

  12. HP1.0 ACK Variant Field • 2 bits Channel Access Priority (CAP) • 11 = highest, 00 = lowest • Used for bursting • 11 bits Received Frame Check Sequence (RFCS) • Last 11 bits of CRC-16 of frame being acknowledged • If RFCS does not match, treated as collision

  13. HP1.0 NACK/FAIL Variant Field • 2 bits Channel Access Priority (CAP) • For NACK, copied from valid EOF, else segt ctl • 1 bit Response Type (RT) • RT=0 NACK • RT=1 FAIL • 10 bits Received Frame Check Sequence (RFCS) • Only used by FAIL – set to 0 by NACK • Last 10 bits of CRC-16 of frame being acknowledged • If RFCS does not match, treated as collision

  14. HP1.0 Medium Access • Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) • Maintain view of medium state • Don’t send when busy or if unsure • Use slotted contention window to avoid collisions • Recover from collisions by backoff process • Priority-based access • Four priority levels CA3>CA2>CA1>CA0 (30.72 us per slot)

  15. HP1.0 CSMA/CA • Carrier Sense • PCS by SYNC detection (SOF, EOF, ACK, NACK/FAIL) • VCS by delimiter type and fields Medium states when frame sent or detected during contention

  16. HP1.0 CSMA/CA (con’t) • Priority Slots (PRSs) • Two slots (PRS0, PRS1), 30.72 usec per slot • Assert “1” bits in CAP – shortened inverted preamble • Receive others’ “ORed” bits if “assert” 0 in a PRS • Defer if “1” detected Medium states when preempted in PRSs but no frame detected

  17. HP1.0 CSMA/CA (con’t) • Collisions • Inferred from absence of expected response or Frame Control errors Medium states when collision detected but no frame detected

  18. HP1.0 Interframe Space (IFS) • End of Frame Gap (EFG) • 1.5 usec between end of frame body and EOF • Contention IFS (CIFS) • 35.9usec between end of last transmission and PRS0 • Response IFS (RIFS) • 26.0usec between end of a transmission and start of its expected response (ACK, NACK/FAIL) • Delimiter indicates whether response is expected • If none expected, CIFS is used • Extended IFS (EIFS) • Used when station is unsure of medium state • Maximum busy time possible • EIFS = 3*delim + EFG + 2*PRS + CIFS + RIFS + Max frame size * symbol time

  19. HP1.0 CIFS and RIFS

  20. HP1.0 Collision Avoidance • Priority Resolution • Only frames of highest priority contend • Priority resolution slots enforce priority strictly • Contention Period • 35 usec slots to start transmission/detect sync • Initial number of slots depends on priority level • Randomly select a slot in initial contention window • Listen to earlier slots – defer if detect transmission • Resume countdown next available contention period • Random Backoff • Invoked if collision detected

  21. HP1.0 Random Backoff Procedure • Goal is to estimate number of contenders • Adjust contention window used to minimize time until successful transmission • Avoid collisions • Avoid extended idle times • Use information available • Collisions • Deferrals CA3 & CA2 CA1 & CA0 BPC=0 CW=7, DC=0 CW=7, DC=0 BPC=1 CW=15, DC=1 CW=15, DC=1 BPC=2 CW=15, DC=3 CW=31, DC=3 BPC=3 CW=31, DC=15 CW=63, DC=15

  22. HP1.0 Random Backoff Procedure Counters Used • BPC – Backoff Procedure Event Counter • TC – Transmit Counter – # times transmitted • BC – Backoff Counter – countdown to Tx • DC – Deferral Counter – # times deferred • CW – Contention Window – range for BC • Collision_Retries – when not in ROBO • NACK_Retries – when not in ROBO • FAIL_Retries • Collision_ROBO_Retries – when in ROBO • NACK_ROBO_Retries – when in ROBO

  23. HP1.0 Random Backoff Procedure • Initialize counters to 0, go to step 2 • Determine medium state • If Idle, transmit • If Busy, wait • If PRS0 or PRS1, resolve priority, go to step 3 • If priority contention lost, go to step 2

  24. HP1.0 Random Backoff Procedure • If priority contention won, then may contend If BPC=0 or BC=0 or DC=0 • Set CW to CW[BPC,priority] • Set DC to DC[BPC,priority] • Increment BPC • Set BC = Random(CW) • On each contention slot when BC>0, • If empty, decrement BC • If medium becomes busy, go to step 2 • If BC = 0, transmit, then go to step 5

  25. HP1.0 Random Backoff Procedure • After transmitting a frame • If no response expected, or if receive ACK with valid RFCS, then done. • If collision inferred, then increment proper collision counter, and - If robo retry max reached, discard frame, - else if regular retry max reached, switch to ROBO, - else try again – go to step 2

  26. HP1.0 Random Backoff Procedure • After transmitting a frame (con't) • If valid NACK received, then increment proper NACK counter, and Reset BPC to 0 - If NACK robo retry max reached, discard frame, - else if NACK regular retry max reached, switch to ROBO, - else try again – go to step 2

  27. HP1.0 Random Backoff Procedure • After transmitting a frame (con't) • If valid FAIL received with valid RFCS, then increment FAIL counter, and Reset BPC to 0 - If FAIL retry max reached, discard frame, - else wait for FAIL_DELAY then try again – go to step 2

  28. HP1.0 Random Backoff Procedure Key points: • Very conservative in avoiding collisions • Uses collisions to estimate number of contenders, like 802.3 and 802.11 • Also uses number of deferrals to estimate number of contenders • Eschewed the theoretically more efficient binary countdown approach to use more robust (against confusion) unary approach

  29. HP1.0 MAC Data Frame Format • Data frame has SOF, payload, EOF • Block pad (B-PAD) zero-fills last PHY Tx Block • Frame Check Sequence (FCS) – 16-bit CRC • EOF followed by end-of-frame gap (EFG) • Immediate response delimiter

  30. HP1.0 Frame Header • Frame Header is channel adapted • Only intended receiver demodulates it • 48-bit DA and SA • IEEE 802.3 MAC addresses • 40-bit Segment Control • Holds length of actual data along with flags, bursting info, CAP

  31. HP1.0 Segment Control Field • 3 bits Protocol Version Number (=1) • 2 bits reserved • 1 bit Multicast Flag (MCF) (=1 for mcast/bcast) • 2 bits Channel Access Priority (CAP) • 15 bits Segment Length (SL) • Length in bytes of Frame Body • Not including Segment Header, E-Pad, or ICV • 1 bit Last Segment Flag (LSF) • Set if last (or only) segment in Service Block • 6 bits Segment Count (SC) • Incremented with each new segment of a Service Block • 10 bits Sequence Number (SN) • Incremented with each new Service Block sent

  32. HP1.0 Segmentation

  33. HP1.0 Service Block • 9 bytes Encryption Control (EC) • 1 byte Encryption Key Select (EKS) • 8 bytes Initialization Vector (IV) • IV=0 means encryption is bypassed • 4 bytes Integrity Check Value (ICV) • 32-bit CRC of bytes following Encryption Control through E-PAD before encryption • EC and ICV are present in every Service Block

  34. HP1.0 Service Block Fields • 4 Bytes IEEE 802.1Q VLAN Tag (copied from MSDU) • Present iff present in MSDU frame • Variable length MAC Management Information • Indicated by ethertype 0x887B in first two bytes • MAC Control byte indicates # MAC data entries • Type/Length/Value (TLV) encoded on MAC Entries • 2 Bytes Type (copied from data frame) • Present only if Service Block carries MSDU • Variable length Frame Data (copied from data frame) • Present only if Service Block carries MSDU • Variable length Encryption Pad (E-PAD) • Pads encrypted bits to a multiple of 64 bits • Present even if encryption is bypassed

  35. HP1.0 MAC Management Entries • Channel estimation request/response • Tone Map Index (TMI) • Tone map • bit map of valid tones, FEC rate, Modulation method • Bridged addresses, etc. • Replace bridge address • Allows reconstruction of original MSDU with SA, DA • Set/confirm network encryption key • EKS, 64-bit NEK • Multicast with response • Holds MAC multicast address • DA in Frame Header indicates STA to respond • Request Parameters and Statistics • Vendor specific • Start with OUI

  36. HP1.0 MAC Parameters and Statistics • Transmit Counters • ACK • NACK • FAIL • Contention loss • Collisions • Tx latency counter for all priorities CA0-CA3 • Receive Counters • Bytes per 40-symbol packet • SNMP Compatible • Stored in MIBs

  37. HP1.0 Tone Maps • Tone Map is stale if • Expires (30 second lifetime) • Transmitter forced to go to ROBO • New link • Limits on how often TMs requested • Avoid too much computation at receiver • Avoid too much network traffic • Request Channel Estimation MME • Always sent using ROBO modulation • Channel Estimation Response • Within 1 second • Must change the TMI • May be sent unsolicited

  38. HP1.0 Privacy/Key Management • DES using CBC mode (64 bit blocks) • Data encrypted with Network Encryption Key (NEK) • NEK may be generated from password • Specifies method: PBKDF1 from PKCS#5v2.0 • Valid password is 4-24 printable ASCII chars • EKS = 0x01 in this case • NEK may be sent to a new STA over network • Set Key MME must be encrypted • “Default key” or password of new STA may be entered on STA already in network, used to encrypt MME • EKS for Set Key MME is 0x00 in this case

  39. HP1.0 Logical Networks

  40. HP1.0 Field Tests vs. 802.11b • 2700 Sq. ft., 10 year-old residence • interior walls hollow (not concrete) • two laptop computers with both interfaces Network Configurations ad hoc networkvery short distances with line of sight modified Infrastructure modeLaptop-2 through the Ethernet to base stationbase station talking to Laptop-1fixed location of base station (and Laptop-2)moved Laptop-1 to various locations

  41. HP1.0 Field Test Scenarios Scenario-1: FTP – • Transmit Buffer Size: 4096 Bytes • Receive Buffer Size: 4096 Bytes • File transfer size: 40 MbytesScenario-2: TCP – • Buffer Length: 4096 Bytes • Number of Buffers Sent: 5000 • Total data exchange: 20 Mbytes

  42. Field Tests Results vs. 802.11b

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