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IEEE 802.16 Medium AccessControl and Service Provisioning Chien Chen Department of Computer and Information Science National Chiao Tung University Hsin-Chu, Taiwan Tel: (03) 573-1768, Fax: (03) 572-1490, firstname.lastname@example.org
Outline • IEEE 802.16 Broadband Wireless Access System • Medium Access Control (MAC) Layer • IEEE 802.16 MAC Layer Connection Management • IEEE 802.16 Quality of Service (QoS) • IEEE 802.16 Service Provisioning
Wireless Technologies Bandwidth IEEE 802.15 IEEE 802.11 IEEE 802.16 3GPP 1 Gbps 802.15.3 High Speed Wireless PAN 100 Mbps Wi-Fi 802.11a/g Wi-Fi 802.11b Wi-MAX 802.16 (802.16-2004 & 802.16e) 10 Mbps 4G 3G 2.5G 1 Mbps 802.15.1 Bluetooth <1m 10m 100m Up to 50Km Up to 80Km PAN LAN MAN WAN PAN: Personal area networks MAN: Metropolitan area networks LAN: Local area networks Wide area networks
IEEE 802.16 • Scope : • Specifies the air interface, MAC (Medium Access Control), PHY(Physical layer) • Purpose : • Enable rapid worldwide deployment of cost-effective broadband wireless access products • Facilitate competition in broadband access by providing alternatives to wireline broadband access • Main advantage : • Fast deployment, dynamic sharing of radio resources and low cost
IEEE 802.16 Extension • 802.16a • Use the licensed and license-exempt frequencies from 2 to 11Ghz • Support Mesh-Network • 802.16b • Increase spectrum to 5 and 6GHz • Provide QoS (for real-time voice and video service) • 802.16c • Represents a 10 to 66GHz system profile • 802.16d • Improvement and fixes for 802.16a • 802.16e • Addresses on mobility • Enable high-speed signal handoffs necessary for communications with users moving at vehicular speeds
IEEE 802.16 Components and Data Path • IEEE 802.16 architecture consists of two kinds of fixed (non-mobile) stations • Subscriber stations (SS) • Base station (BS) • The communication path between SS and BS has two directions • Uplink(from SS to BS) • Downlink (from BS to SS)
When the system uses time-division multiplexing (TDM), for uplink and downlink transmissions, the frame is subdivided into an uplink subframe and a downlink subframe IEEE 802.16 TDM frame structure
MAC Frame Structure and PDU • Each MAC packet consists of the three components, • a) A MAC header, which contains frame control information. • b) A variable length frame body, which contains information specific to the frame type. • c) A frame check sequence(FCS), which contains an IEEE 32-bit cyclic redundancy code (CRC).
Downlink vs. Uplink • Downlink (from BS to SS) The data packets are broadcasted to all SSs and an SS only picks up the packets destined to it • Uplink (from SS to BS) • BS determines the number of time slots that each SS will be allowed to transmit in an uplink subframe • This information is broadcasted by the BS through the uplink map message (UL-MAP) at the beginning of each frame • UL-MAP contains information element (IE) which include the transmission opportunities
Two BW-request modes in uplink • The BS uplink scheduling module determines the IEs using BW-request sent from SSs to BS • In IEEE 802.16 standard, there are two modes of transmitting the BW-Request • Contention mode • SSs send BW-Request during the contention period. Contention is resolved using back-off resolution • Contention-free mode (polling) • BS polls each SS and SSs reply by sending BW-request. • Due to the predictable signaling delay of the polling scheme, contention-free mode is suitable for real time applications
IEEE 802.16 MAC Layer • Objective : to manage the resources of the air-link in an efficient manner and provide Quality of Service (QoS) differentiation. • Supporting Point to Multipoint (PMP) and Mesh network models. • To perform link adaptation and Automatic Repeat Request (ARQ) functions to maintain target Bit Error Rates (BER) while maximizing the data throughput.
802.16 MAC Header Types • A generic frame : be used to transmit data or MAC messages • A bandwidth request frame : be used by the SS to request BW on the UL
IEEE 802.16 MAC Layer Functions • Transmission scheduling • Controls up and downlink transmissions so that different QoS can be provided to each user • Admission control • Ensures that resources to support QoS requirements of a new flow are available • Link initialization • Scans for a channel, synchronizes the SS with the BS, performs registration, and various security issues.
IEEE 802.16 MAC Layer Functions (Contd.) • Support for integrated voice/data connections • Provide various levels of bandwidth allocation, error rates, delay and jitter • Fragmentation • Sequence number in the MAC header is used to reassemble at the receiver • Retransmission • Implement an ARQ (Automatic Repeat Request)
Service Specific Convergence Sublayer • The service specific convergence sublayer (CS) provides any transformation or mapping of external network data, received through the CS service access point (SAP) • Object : classifying external network service data units (SDU) and associating them to the proper service flow identified by the connection identifier (CID)
MAC Convergence Sublayer • Functions: • Classification, possible processing of higher-layer PDUs • Delivery to proper MAC SAP • Receives CS PDUs from peer • Two sublayers specified: ATM and packet convergence sublayer
ATM Convergence Sublayer • ATM cells mapped to MAC frames • Differentiates Virtual Path switched / Virtual Channel switched ATM connections • Assigns channel ID (CID) • Can perform Payload Header Suppression (PHS)
Packet Convergence Sublayer • used for all packet-based protocols, such as IPv4, IPv6, Ethernet, and VLAN • Similar functions as ATM convergence sublayer, including PHS
Defines multiple-access mechanism Functions :system access, bandwidth allocation, connection establishment, and connection maintenance MAC Common Part Sublayer
Security Sublayer • The MAC security sublayer has two component protocols: • Encapsulation protocol for data encryption • defines cryptographic suites i.e. pairings of data encryption and authentication algorithms • the rules for applying those algorithms to a MAC payload • Privacy key management (PKM) • describes how the BS distributes keys to client SS
Media Acces Control (MAC) • Connection orienteded • Service Flow(SF) • Connection ID (CID) • Channel access: • UL-MAP • Defines uplink channel access • Defines uplink data burst profiles • DL-MAP • Defines downlink data burst profiles • UL-MAP and DL-MAP are both transmitted in the beginning of each downlink subframe (FDD and TDD).
Uplink Periods • Initial Maintenance opportunities • Ranging • To determine network delay and to request power or downlink burst profile changes • Collisions may occur in this interval • Request opportunities • SSs request bandwith in response to polling from BS • Collisions may occur in this interval aswell • Data grants period • SSs transmit data bursts in the intervals granted by the BS • Transition gaps between data intervals forsynchronization purposes.
Bandwidth Request Mechanisms • The standard defines various mechanisms for the SS to access the shared uplink and request transmission opportunities (bandwidth) and for the BS to grant such transmission opportunities • The key mechanisms of the request-grant process are the bandwidth request and the bandwidth allocation
Bandwidth Request • SSs may request bandwidth in 3 ways: • Use the ”contention request opportunities” interval upon being polled by the BS (unicast, multicast or broadcast poll) • Send a standalone MAC message called ”BW request” in an already granted slot • Piggyback a BW request message on a data packet
BS grants/allocates bandwidth in one of two modes Grant Per Subscriber Station (GPSS) Grant Per Connection (GPC) Decision based on requested BW, QoS parameters and available resources Grants are realized through the UL-MAP Bandwidth Allocation
Polling • Polling is the process by which the BS allocates to the SSs bandwidth specifically for the purpose of making bandwidth requests • These allocations may be to individual SSs or to groups of SSs • Allocations to groups of connections and/or SSs actually define bandwidth request contention IEs • The allocations are not in the form of an explicit message, but are contained as a series of IEs within the UL-MAP
Polling Way • Unicast • When an SS is polled individually, no explicit message is transmitted to poll the SS. Rather, the SS is allocated bandwidth sufficient to respond with a Bandwidth (BW) Request (in the UL-MAP) • Multicast and broadcast • If insufficient bandwidth is available to individually poll many inactive SSs, some SSs may be polled in multicast groups or a broadcast poll may be issued • Certain CIDs are reserved for multicast groups and for broadcast messages
BS SS 1 Poll(UL-MAP) 2 3 4 Data Unicast Polling • BS polls for the SS in the uplink subframe via the IEs in UL-MAP • SS receives poll message to send a BW request • BS allocates available next frame time slots via UL-MAP in respond to the SS’s request • SS uses allocated time slots to send data Request Allocate(UL-MAP)
Network Entry • In order to communicate on the network an SS needs to successfully complete the network entry process with the desired BS. The network entry process is divided into : (1) DL channel synchronization (2) initial ranging (3) capabilities negotiation (4) authentication message exchange (5) Registration (6) IP connectivity
Protocol Data Unit (PDU) Creation and Automatic Repeat Request (ARQ) • The 802.16 MAC performs the standard PDU creation functions. It applies the MAC header and optionally calculates the CRC. • ARQ processing is the process of retransmitting MAC SDU blocks (“ARQ blocks”) that have been lost or garbled
Service Classes • Unsolicited Grant Services (UGS): UGS is designed to support Constant Bit Rate (CBR) services, such as T1/E1 emulation, and Voice Over IP (VoIP) without silence suppression. • Real-Time Polling Services (rtPS): rtPS is designed to support real-time services that generate variable size data packets on a periodic basis, such as MPEG video or VoIP with silence suppression. • Non-Real-Time Polling Services (nrtPS): nrtPS is designed to support non-real-time services that require variable size data grant burst types on a regular basis. • Best Effort (BE) Services: BE services are typically provided by the Internet today for Web surfing.
QoS mechanisms • Classification • Mapping from MAC SDU fields (e.g destination IP address or TOS field to CID and SFID • Scheduling • Downlink scheduling module • Uplink scheduling module • Call admission Control • No algorithms defined in standard
Classification in IEEE 802.16 • All packets generated by active applications are tagged with CID (connection ID) and SFID (Service Flow ID) • Classification modules map MAC SDU fields (e.g. Destination IP address or TOS field) to CID and SFID
Scheduling in IEEE 802.16 • Downlink scheduling module • Simple, all queues in BS • Uplink scheduling module • Queues are distributed among SSs • Queue states and QoS requirements are obtained through BW requests • Scheduling algorithms are not defineded in standard
Scheduling and Link Adaptation • The goal of scheduling and link adaptation : provide the desired QoS treatment to the traffic traversing the air-link, while optimally utilizing the resources of the air-link. • Scheduling in the 802.16 MAC is divided into two related scheduling tasks: • GPSS (Grant Per Subscriber Station) : scheduling the usage of the airlink among the SS’s • GPC (Grant Per Connection) : scheduling individual packets at the BSs and SS’s.
Call Admission Control in IEEE 802.16 • Admission control • To ensure required QoS is guaranteed while admit a new connection • Assessment of admission connection • Usually use traffic descriptor and effective bandwidth • But… • Traffic descriptors may not reflect the real traffic • Traffic descriptors is very simple (peak rate, avg. rate, etc…) • Users may overestimate their requirements • QoS is uneasy to guarantee