Wireless networks - Lecture 43: IEEE 802.16 MAC/QoS. The main topics covered in this chapter include: reference model; burst profiles; convergence sublayers; MAC PDU format; MAC PDU transmission; fragmentation/packing; request/grant scheme; classes of uplink service; power management/handoff;...
Wireless Networks Lecture 43 IEEE 802.16 MAC/QoS Dr Ghalib A Shah Outlines Reference Model Burst profiles Convergence sublayers MAC PDU format MAC PDU Transmission Fragmentation / Packing Request/Grant Scheme Classes of Uplink service Power management/Handoff Outlines WiMAX Basics 802.16 Evolution Characteristics of 802.16 Why not 802.11 / 802.11 vs 802.16 Network Architecture Phy Layer ► Multiple Access technique ► HARQ ► MIMO MAC Layer ► QoS ► Power Management ► Handoff Reference Model Scope of standard MAC Service Specific Convergence Sublayer (CS) MAC SAP MAC Common Part Sublayer (MAC CPS) Privacy Sublayer PHY PHY SAP PHY Layer (PHY) Data/Control Plane Management Entity Service Specific Convergence Sublayer Management Entity MAC Common Part Sublayer Security Sublayer Management Entity PHY Layer Management Plane Network Management System CS SAP Adaptive Burst Profiles Burst profile ► Dynamically assigned according to link conditions ► ► Modulation and FEC Burst by burst, per subscriber station Trade-off capacity vs robustness in re al time Roughly doubled capacity for the same cell area Burst profile for downlink broadcast channel is well-known ATM Convergence Sublayer Support for: ► VP (Virtual Path) switched connections ► VC (Virtual Channel) switched connections Support for end-to-end signaling of dynamically created connections: ► SVCs ► soft PVCs ATM header suppression Full QoS support Packet Convergence Sublayer Initial support for Ethernet, IPv4, and IPv6 Payload header suppression Full QoS support Possible future support for: ► PPP ► MPLS ► etc Upon entering the network, the SS is assigned three management connections in each direction These three connections reflect the three different QoS requirements used by different management levels ► ► ► basic connection, which is used for the transfer of short, time-critical MAC and radio link control (RLC) messages The primary management connection is used to transfer longer, more delay-tolerant messages such as those used for authentication and connection setup The secondary management connection is used for the transfer of standards-based management messages such as DHCP, Trivial FTP, and SNMP In addition to these management connections, SSs are allocated transport connections for the contracted services Transport connections are unidirectional to facilitate different uplink and downlink QoS and traffic parameters; Definitions S e rvic e Data Unit (S DU) ► Data units exchanged between adjacent layers Pro to c o l Data Unit (PDU) ► Data units exchanged between peer entities Co nne c tio n and Co nne c tio n ID ► a unidirectional mapping between MAC peers over the airlink (uniquely identified by a CID) S e rvic e Flo w and S e rvic e Flo w ID ► a unidirectional flow of MAC PDUs on a connection that provides a particular QoS (Uniquely identified by a SFID) MAC PDU format msb ► the generic header ► bandwidth request header One or more MAC sub-headers may be part of the payload The presence of sub-headers is indicated by a Type field in the Generic MAC header field Generic MAC Header Payload (optional) Isb A MAC PDU consists of a fixed-length MAC header, a variable-length payload, and an optional cyclic redundancy check (CRC) Two header formats, distinguished by the HT field, are defined: CRC (optional) 10 Packing Fixed-Length SDUs MAC Header LEN = n*k+j A MAC SDUs fixed length MAC SDU length = n fixed length MAC SDU length = n fixed length MAC SDU length = n fixed length MAC SDU length = n 17 Packing Variable-Length SDUs variable length MAC SDU length = b PSH Length = c+2 variable length MAC SDU length = a PSH Length = b+2 PSH Length = a+2 MAC Header LEN = f Type = 00001xb A MAC SDUs variable length MAC SDU length = c Bytes Packing Sub-Header before each SDU ► ► ► Length of SDU: 11 bits fragmentation control (FS): bits fragmentation sequence number (FS): bits 18 Downlink transmissions Two kinds of bursts: TDM and TDMA All bursts are identified by a DIUC ► TDMA bursts have resync preamble ► Downlink Interval Usage Code allows for more flexible scheduling Each burst may contain data for several terminals SS must recognize the PDUs with known CIDs DL-MAP message signals downlink usage 19 Burst profiles C/(N+I) (dB) Burst Profile Z Overlap Burst Profile Y Each burst profile has mandatory exit threshold and minimum entry threshold SS allowed to request a less robust DIUC once above the minimum entry level SS must request fall back to more robust DIUC once at mandatory exit threshold Requests to change DIUC done with DBPC-REQ or RNG-REQ messages Overlap Burst Burst Profile Profile 20 Transition to a more robust profile SS BS DL data at DIUC n RNG-REQ or DBPC-REQ change to DIUC k C/ (N+1) Too Low for DIUC n Yes Continue monitoring DL data through DIUC n Send DL data at DIUC k DL data at DIUC k No RNG-RSP or DBPC-RSP Monitor DL data only through DIUC k DL data at DIUC k 21 Request/Grant Scheme Self Correcting Bandwidth Requests are always per Connection Grants are either per Connection (GPC) or per Subscriber Station (GPSS) 22 GPSS vs GPC Bandwidth Grant per Subscriber Station (GPSS) ► ► Base station grants bandwidth to the subscriber station Subscriber station may re-distribute bandwidth among its connections, maintaining QoS and service-level agreements Bandwidth Grant per Connection (GPC) ► ► Base station grants bandwidth to a connection Higher overhead, but allows simpler subscriber station 23 Classes of Uplink Service Unsolicited Grant Services (UGS) Real-time Polling Services (rtPS) Non-real-time Polling Services (nrtPS) Best Effort (BE) ► for best-effort traffic 24 [1] QoS Category Applications QoS Specifications UGS Unsolicited Grant Service VoIP Maximum Sustained Rate Maximum Latency Tolerance Jitter Tolerance rtPS RealTime Polling Service Streaming Audio or Video Minimum Reserved Rate Maximum Sustained Rate Maximum Latency Tolerance Traffic Priority ErtPS Extended RealTime Polling Service Voice with Activity Detection (VoIP) Minimum Reserved Rate Maximum Sustained Rate Maximum Latency Tolerance Jitter Tolerance Traffic Priority nrtPS Non RealTime Polling Service File Transfer Protocol (FTP) Minimum Reserved Rate Maximum Sustained Rate Traffic Priority BE BestEffort Service Data Transfer, Web Browsing, etc Maximum Sustained Rate Traffic Priority 25 Uplink Services - UGS No explicit bandwidth requests issued by SS Prohibited from using any contention requests No unicast request opportunity provided May include a Grant Management (GM) sub-header containing ► Slip indicator: indicates that there is an backlog in the buffer due to clock skew or loss of maps ► Poll-me bit: indicates that the terminal needs to be polled (allows for not polling terminals with UGS-only services) 26 Uplink Services - RTPS Intended for rt-VBR-like service flows such as MPEG video Prohibited from using any contention requests Terminals polled frequently enough to meet the delay requirements of the SFs Bandwidth requested with BW request messages (a special MAC PDU header) May use Grant Management sub-header 27 Uplink Service - NRTPS Intended for non-real-time service flows with better than best effort service Works like rt-polling except that polls are issued less frequently Allowed to use contention requests May use Grant Management sub-header 28 Uplink Service - BE No QoS guarantees Allowed to use contention requests May use Grant Management sub-header 29 Power Management Sleep and Idle modes enable power-efficient MS operation Sleep mode Idle mode ► Allows MS to become periodically available for broadcast messages without registering at a BS 30 Handoff handoff methods supported ► Hard Handoff (HHO) – required • “Break-before-make” • Optimized to keep handoff delays below 50 milliseconds ► Fast Base Station Switching (FBSS) - optional ► Macro Diversity Handover (MDHO) - optional 31 ... maps ► Poll-me bit: indicates that the terminal needs to be polled (allows for not polling terminals with UGS-only services) 26 Uplink Services - RTPS Intended for rt-VBR-like service... header) May use Grant Management sub-header 27 Uplink Service - NRTPS Intended for non-real-time service flows with better than best effort service Works like rt-polling except that polls are... Service Unsolicited Grant Services (UGS) Real-time Polling Services (rtPS) Non-real-time Polling Services (nrtPS) Best Effort (BE) ► for best-effort traffic 24 [1] QoS Category Applications