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DSRC (Dedicated Short Range Communication) IEEE 1609 + IEEE 802.11p

DSRC (Dedicated Short Range Communication) IEEE 1609 + IEEE 802.11p. Secure Vehicular Communications System. Source: P. Papadimitratos et al ., "Securing Vehicular Communications - Assumptions, Requirements, and Principles", in ESCAR 2006. Background.

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DSRC (Dedicated Short Range Communication) IEEE 1609 + IEEE 802.11p

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  1. DSRC (Dedicated Short Range Communication)IEEE 1609 + IEEE 802.11p

  2. Secure Vehicular Communications System Source: P. Papadimitratos et al., "Securing Vehicular Communications - Assumptions, Requirements, and Principles", in ESCAR 2006

  3. Background • IEEE 802.11p可視為實現 Dedicated Short Range Communication (DSRC) 的底層標準規範 • IEEE 802.11p主要著眼在MAC (Medium Access Control) 層 • 另可能實作DSRC的技術為 RFID、bluetooth …

  4. Critical Safety of Life High Power Public Safety Control Channel Ch 172 Ch 174 Ch 176 Ch 178 Ch 180 Ch 182 Ch 184 5.860 5.870 5.880 5.890 5.900 5.910 5.920 5.850 Frequency (GHz) Service Channels Service Channels Background • DSRC • ITS重要建置之一，用於短距離之單向或雙向通訊無線通訊 • 路側系統(Road Side Unit，RSU)與車輛單元(On-Board Unit，OBU)之通訊，或車輛單元與車輛單元之間的通訊 • Spectrum @ 5.9 GHz, 7 licensed channels • Data rate: 6 – 27 Mbps • To save lives and improve traffic flow, and also to provide value through private applications

  5. Background • Spectrum (各國有些差異)

  6. DSRC in North America • IEEE 802.11p protocol • Vehicle speeds up to 100 mph (=160.9 km/h) • Low latency: 50 ms • Application priority: 8 levels • Short range radio: 300m (~1000m) • Data rate: 6-27 Mbps • Half duplex • Channel 172: vehicle safety only • Security • Encrypt using Public Key Infrastructure (PKI) • Road Side Unit (RSU) Authentication • On Board Unit (OBU) Privacy

  7. DSRC in North America • How DSRC works? • Road-Side Unit • Announces to OBUs 10 times per second • Applications it supports on which channel • On-Board Unit • Listens on Channel 178 • Authenticates RSU digital signature • Executes safety applications first • Then switches channels • Executes non-safety applications • Returns to Channel 178 and listens

  8. DSRC in North America • IP address • Long-lived IP address would only happen when stationary • All devices change IP address when OBU moves from one RSU to another • MAC address • Generate random MAC address out of local space (?) • When to change? • At startup? • Allows tracking for individual trips • When the signing key changes? • Every 5-10 minutes • Close monitoring can follow transitions

  9. IEEE 802.11p vs. IEEE 1609 • IEEE 802.11p (又稱WAVE) • WAVE = wireless access in vehicular environments • 一個由IEEE 802.11標準擴充的通訊協定，主要用於車用電子的無線通訊，以符合智慧型運輸系統的相關應用 • 應用的層面包括高速率的車輛之間以及車輛與5.9GHz (5.85-5.925GHz) 波段的標準ITS路邊基礎設施之間的資料數據交換 • 2010年7月正式定案 • IEEE 1609是以IEEE 802.11p通訊協定為基礎的高層標準 • IEEE 1609提供能將車輛的主要系統資訊(包含引擎、傳動系統、煞車、懸吊系統等)與道路的基礎架構兩者相互溝通的機制 • 使用IEEE 802.11無線區域網路通訊標準802.11p(由IEEE 802.11a發展而來)作為底層的通訊技術，同時採用IPv6作為上層的通訊協定

  10. IEEE 1609 • IEEE 1609包括四個部份，技術內容皆已審核通過，進入測試使用的階段 • IEEE 1609.1: WAVE Resource Manager，規範多個遠程應用和資源管理間的控制互換流程 • IEEE 1609.2: WAVE Security Services for Applications and Management Messages，包括WAVE訊息安全、抵制竊聽、電子欺詐和其他襲擊的方法 • IEEE 1609.3: WAVE Networking Services，規範通信協議的網路層與傳輸層 • IEEE 1609.4: WAVE Multi-Channel Operations，提供IEEE 802.11p MAC對WAVE的支援

  11. 取得IEEE 1609規範文件 (圖書館的西文電子資料庫，進到IEL作查詢即可取得)

  12. Protocol Stack (Relating to ISO/OSI Ref. Model)

  13. Protocol Stack OSI Reference Model Application ApplicationPresentationSession Security Services 1609.1 WME UDP/TCP WSMP Transport IETF MIB IPv6 1609.2 Network 1609.3 LLC Data Link 802.2 MLME WAVE MAC 802.11 Multi-channel operation 1609.4 802.11p PLME WAVE Physical Physical 1609.3 Data plane Management plane A message sent over WSMP (WAVE short message protocol) and routed to a receiving application using an ACID (application class identifier) and an ACM (application context mark) rather than an IP address and port.

  14. IEEE 802.11p — WAVE • WAVE (wireless access in vehicular environments) • A mode of operation used by IEEE 802.11 devices in environments where physical channel properties are rapidly changing and short-duration communications exchanges are required • Interoperability and transactions must be completed in time frames much shorter than the minimum possible with infrastructure or ad hoc 802.11 networks • Time frames shorter that required for standard authentication and association to join a BSS (Basic Service Set) are accommodated in IEEE 802.11p • No scanning • No authentication and association

  15. WAVE Components

  16. IEEE 1609.4 • Provides frequency band coordination and management within the MAC layer • Supplements 802.11 MAC features • Coordinates operation on the Control Channel (CCH) and Service Channels (SCH) • CCH for broadcast, high priority, and single-use messages • SCH for ongoing transactions • 提供頻帶的協調及MAC子層的管理功能，它針對 802.11 MAC 層的特色進行增補，協調控制頻道 (CCH)與服務頻道的操作 (SCH)

  17. IEEE 1609.3 • Provides WAVE networking services to WAVE devices and systems • Defines WAVE networking services that operate at the network and transport layers • Represents roughly layers 3 and 4 of the OSI model and the IP, UDP, and TCP elements of the Internet model

  18. IEEE 1609.2 • Defines secure message formats • Specifies methods for securing WAVE management messages and application messages • Processes secure messages of DSRC/WAVE systems • Exception of vehicle-originating safety messages • Provides administrative functions necessary to support core security functions

  19. IEEE 1609.1 • Resource management • Specifies a DSRC application overlying WAVE • Allows remote site applications to communicate with OBUs or RSUs • Acts like an application layer • To conduct application-level information interchanges

  20. IEEE 1609.4: Multi-Channel Operation 1609.4

  21. Terminology (1/2) • Control channel (CCH) • 用於管理訊息和 WSM (WAVE short message) 訊息交換的通道 • Used for broadcast transmission and to establish communications • Service channel (SCH) • 使用在應用程式的資訊交換 • Transmitter profile • 一個資料物件(data object)用以描述進行傳輸時所用通訊參數，包含SCH number、通訊能力等級、資料速率、適合的通訊能力狀態、網際網路通訊協定應用程式的資料速率等 • Provider • WBSS的創建者(initiator)或WSMs (WAVE short messages)的寄送者

  22. Terminology(2/2) • User • 一個裝置，依收到的WAVE announcement action frames作動作 • Onboard unit (OBU) • 一個移動的WAVE裝置，能與RSU或其他OBU之間作資料交換 • Roadside unit (RSU) • 一個固定式的WAVE裝置，能與OBU之間作資料交換 • Only RSU can broadcast on the Control Channel • WAVE short message (WSM) • A message specifically designed to operate in the WAVE band. Itcan be exchanged directly among WAVE devices without the overhead of IP or management associatedwith initiating a WBSS • WAVE short message protocol (WSMP) • WAVE short messages 所使用的通訊協定

  23. IEEE 1609.4 的主要工作 • Channel routing • Routing for WSMP data • Routing for IP datagram • User priority (UP) • Channel coordination • MAC service data unit (MSDU) data transfer

  24. Channel Routing: Routing for WSMP Data (1/2) • WSMP header contains the channel, power level, and data rate associated with the data packet as specified in IEEE 1609.3 Portion of the WSMP header used to control PHY transmit parameters

  25. Channel Routing: Routing for WSMP Data (2/2) • Procedure • WSMP data is passed from LLC to MAC • MAC shall route the packet to a proper buffer (queue) corresponding to the channel number contained in the WSMP header • Data packet shall be discarded when the channel number contained is not a valid channel number • A channel number is invalid if it does not correspond to the CCH number or the current SCH number (defined by dot4JoinedServiceChannelNumber)

  26. Channel Routing: Routing for IP Datagrams • Procedure • Before initializing IP data exchanges, the transmitter profile shall be registered to the MAC layer management entity (MLME) • Transmitter profile contains an SCH number, power level, data rate, and the adaptable status of power level and data rate • Only one transmitter profile may be active at any given time • When IP data is passed from LLC to MAC, the MAC shall route the packet to a data buffer that corresponds to the current SCH • If there is no transmitter profile registered or the transmitting WAVE device is not a member of any WBSS, data is discarded

  27. Channel Routing and Coordination • Two 802.11p MAC entities Transmit Queue Pre-queue channel access function

  28. User Priority • Using IEEE 802.11e Enhanced Distributed Channel Access mechanism (EDCA) to contend for medium access • MAC buffers the data by mapping its user priority to access category index (ACI) as defined in IEEE 802.11 • EDCA parameters • Arbitration inter-frame space (AIFS) • Contention window (CW) • Transmit opportunity (TXOP) limit • (附錄一)

  29. Channel Types • Two types of radio channels: a single control channel (CCH) and multiple service channels (SCH) • By default, WAVE devices operate on the CCH reserved for short, high-priority application and system control messages • CCH to transmit WSMs and announce WAVE services • SCHs for application interactions/transmissions • Transmit/receive operation on CCH and SCH is coordinated based on sync intervals that are synchronized using a commonly external system time base (e.g. UTC/GPS) • A sync interval = a CCH interval + a SCH interval Guard interval

  30. Channel Coordination • Channel coordination (續) • 當CCH在運作時 (CCH interval)，每一個 WAVE 裝置都會去監督CCH • All WAVE devices monitor the CCH during a common time interval (e.g., CCH interval) during which high-priority WSMs with the CCH number indicated in the WSMP header and WSAs (WAVE service advertisements) shall be transmitted • These messages may also be transmitted on the CCH during the SCH interval • WSA: WME-collected configuration data, identifying WAVE applications and associated network parameters • For devices remaining on CCH during the SCH interval, low-priority frames may be transmitted at any time

  31. Frame Format • MSDU vs. MPDU • MAC accepts MSDU (MAC service data unit) from higher layer and adds headers and trailers to create a MAC protocol data unit (MPDU) • MPDU (i.e. MAC frame) is then passed to PHY and sent over the medium • MAC may fragment MSDU into several frames to increase the probability of successful delivery

  32. Frame Format (WAVE) • Using EtherType • MAC shall identify the type of a data packet (WSMP or IP) indicated by its EtherType • For WSMs, the channel, transmit power, and data rate are specified in the WSMP header and may be modified on a per-message basis (EtherType = 0x88DC) • For IP datagrams, the channel, transmit power, and data rate to be used are stored in a transmitter profile (EtherType = 0x86DD) • MSDU format

  33. Layer Management • SAP (Service Access Point) interfaces relevant to IEEE 1609.4 (WAVE Management Entity)

  34. MAC Management Extension • Relationship between MLME-WSA and MLME-WAVEANNOUNCEMENT service primitives • WBSS provider: a WAVE station advertising the presence of a WBSS • WBSS user: a WAVE station that elects to join a WBSS advertised by a WBSS provider

  35. Transmit Operations (1/5) 1 2 3 4 5 6 7

  36. Transmit Operations (2/5) • Procedure 1. LLC passes an MSDU to MAC. 2. Channel router examines the EtherType field of the MSDU: 1) If EtherType indicates WSMP, the channel router looks up the channel number in the WSMP header and designates the MSDU to the AC based on the channel and the user priority. (The MSDU is discarded if the channel number is invalid.) 2) If EtherType indicates IP, the channel router designates the MSDU to the AC assigned to the SCH and user priority. 3. Through channel coordination, data buffers allocated to the current channel are served.

  37. Transmit Operations (3/5) • Procedure (續) 4. MAC selects the MSDU that wins the internal contention on the current channel. The EtherType field of the MSDU is examined again: 1) If the data unit is a WSM, the transmit power and data rate stored in the WSMP header are used for transmission. 2) If the data unit is an IP datagram, the transmit power and data rate stored in the registered transmitter profile are used for transmission. 5. The values of the power level and data rate are set in the TXVECTOR. The procedure between MAC and PHY to transfer an MPDU is summarized below: 1) PHY reports a clear channel to MAC by issuing a PHY-CCA.indication(IDLE).

  38. Transmit Operations (4/5) • Procedure (續) 5. The values of the power level and data rate are set in the TXVECTOR. The procedure between MAC/PHY to transfer an MPDU is summarized below: 1) PHY reports a clear channel to MAC by issuing a PHY-CCA.indication(IDLE). 2) MAC issues a PHY-TXSTART.request(TXVECTOR) to PHY. A confirmation is issued back to MAC after PHY sets the desired power level and data rate. 3) The data is then exchanged between MAC/PHY through a series of PHYDATA.request(DATA) primitives issued by MAC, and PHY-DATA.confirm primitives issued by PHY. 4) After transmitting the final bit of the last MPDU octet, the transmission is terminated by MAC through the primitive PHY-TXEND.request.

  39. Transmit Operations (5/5) • Procedure (續) 6. If transmission of an MPDU is not completed at the scheduled guard interval, the transmission shall be canceled by MAC through the primitive PHY-TXEND.request. 7. LLC waits for a status indication from MAC if required.

  40. MSDU Data Transfer • Control channel data transfer • WSMs conforming to WSMP can be exchanged directly • Transmission of IP datagrams is not permitted • Service channel data transfer • Provider • To initiate communication on an SCH, an RSU or an OBU transmits WAVE announcement action frames on CCH to advertise offered services available on that SCH • User • An OBU receives the announcement on CCH and generally establishes communications

  41. IEEE 802.11p: MAC and PHY Operations

  42. Background • IEEE 802.11p • Supports data exchange between stations without first establishing a BSS • Stations transmit data to other stations having any valid MAC address (including group addresses) without being part of a BSS. These data exchanges cannot be transmitted directly toa MAC address on a DS (distribution system) • Terminology • WAVE basic service set (WBSS): A set of cooperating stations operating in WAVE mode consisting of a single WAVE service provider and none or more WAVE service users • WAVE service information element (WSIE): An information element that contains information specified by the upper layers. It may be included as a field in a WAVE Advertisement frame using the on-demand management frame

  43. Recall: Radio Spectrum Dedicated Public Safety Dedicated Public Safety Shared Pub.Safety/Private Medium Range Serv. Shared Pub.Safety/Private Medium Range Serv. Ch 172 Ch 174 Ch 176 Ch 178 Ch 180 Ch 182 Ch 184 Public Safety V2V Public Safety / private Public Safety / private Control Channel Public Safety / private Public Safety / private Public Safety Intersections 10MHz 5MHz 10MHz 10MHz 10MHz 10MHz 10MHz 10MHz 5.850 5.925 (GHz) Ch 175 Ch 181 Optionally Combined Service channel Optionally Combined Service channel Reserved 75 MHz 10MHz for one channel 20MHz 20MHz

  44. IEEE 802.11p MAC Layer • Quality of Service (QoS) — 802.11e • This amendment defines MAC procedures to support LAN applications with QoS requirements • Reduction of interference — 802.11h • This amendment is added to the IEEE 802.11 standard for Spectrum and Transmit Power Management Extensions • Service — IEEE 1609 family • IEEE 1609.1, IEEE 1609.2 , IEEE 1609.3 , IEEE 1609.4

  45. MAC Layer and Frame Format (1/3) (附錄一) • Current MAC Header • Data frame format as in IEEE 802.11 • Current MAC frame format • Adds extra 34 (28) bytes to each packet Vehicle Communication Networks and Protocols Vehicle Communication Networks and Protocols

  46. MAC Layer and Frame Format (2/3) • New MAC header • Different frame formats (Frame Control field) • Type: 2 bits • Subtype: 4 bits • New MAC frame format • Adds extra 20 bytes to each packet (Only 1 of the 4 available subtypes) (Only 8 of the 16 available subtypes) Vehicle Communication Networks and Protocols

  47. MAC Layer and Frame Format (3/3) • Random MAC addresses • No one should be able to explicitly identify a particular vehicle by its DSRC transmissions • Short header for vehicle safety messages • IPv6 • 車載通訊的環境經常變動，車子由一個區域到另一個區域勢必要有handoff機制 • 在此使用IPv6來達到seamless handoff

  48. Channel Switching (1/2) • 目的：確保安全性(safety)訊息的傳輸及最大化服務時間 • Ensure safety • Check for ongoing events • Send routine messages • Update the context • Maximize the service usage time • 802.11p尚未明確定義channel switching機制 • 但MAC層已有許多channel switching的方法，例如：global synchronization, distributed synchronization, independent channel switching, … (附錄二) • 或參考交大曾煜棋教授所整理的教材：http://www.csie.nctu.edu.tw/~yctseng/WirelessNet05-02/manet-multi-channel.ppt

  49. Channel Switching (2/2) • Assumed channel requirements • Channel can handle a message every 2 - 4 milliseconds • An average safety message is around 300 bytes • Average transmission time of a safety message of about 400 microseconds • Major problems • Deterministic channel model cannot be assumed in the fast changing topology • Hidden terminal collisions cannot be avoided efficiently

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