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IEEE 802'16 Medium Access Control and Service Provisioning

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Title: IEEE 802'16 Medium Access Control and Service Provisioning


1
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,
    cchen_at_cis.nctu.edu.tw

2
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

3
IEEE 802.16 Broadband Wireless Access System
4
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
lt1m 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
5
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

6
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

7
Characteristics WLAN vs. WiMAX
8
IEEE 802.16 Broadband Wireless Access System
9
802.16 Deployment
10
802.16 Network Architecture
11
Medium Access Control (MAC Layer)
12
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)

13
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).

14
IEEE 802.16 TDM frame structure
  • 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

15
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

16
DL-MAP and UL-MAP
17
Downlink Subframe
18
Uplink Subframe
19
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 as well
  • Data grants period
  • SSs transmit data bursts in the intervals granted
    by the BS
  • Transition gaps between data intervals for
    synchronization purposes.

20
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

21
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.

22
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

23
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.

24
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)

25
IEEE Std 802.16 MAC Protocol Layering
26
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)

27
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

28
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)

29
Packet Convergence Sublayer
  • Used for all packet-based protocols,
  • such as IPv4, IPv6, Ethernet, and VLAN
  • Similar functions as ATM convergence
  • sublayer, including PHS

30
MAC Common Part Sublayer
  • Defines multiple-access mechanism
  • Functions system access, bandwidth allocation,
    connection establishment, and connection
    maintenance

31
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

32
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).

33
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

34
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

35
Bandwidth Allocation
  • 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

36
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

37
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

38
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 SSs request
  • SS uses allocated time slots to send data

Request
Allocate(UL-MAP)
39
IEEE 802.16 MAC Layer Connection Management
40
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

41
Network entry process
42
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

43
PDU and SDU in protocol stack
44
IEEE 802.16 Quality of Service (QoS)
45
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.

46
Unsolicited Grant Service (UGS)
  • The UGS supports real-time service flows that
    generate fixed size periodic data packets, such
    as T1
  • This service provides periodic, fixed size grants
    that avoid the overhead and latency of frequent
    SS redundant requests
  • It ensures that grants are available to meet the
    continuous needs of the service flow

47
Real-Time Polling Service (rtPS)
  • The rtPS supports real-time service flows that
    have periodic data packets of various sizes, such
    as MPEG streams
  • This service provides periodic, unicast request
    opportunities through polling, to respond to the
    needs of the service flows
  • It allows the SS to dynamically specify the size
    of the requested grant
  • Compared to UGS, this service has additional
    overhead due to the polling process. However, it
    can handle variable grant sizes compared to UGS
    that can handle only fixed grant sizes

48
Non-Real-Time Polling Service (nrtPS)
  • The nrtPS supports non-real-time service flows
    that have data packets of various sizes, such as
    FTP
  • The service provides consistent unicast request
    opportunities even during network congestion (SS
    can simultaneously send unicast request packets
    in response to the BS Poll and content for
    request opportunities )
  • The standard specifies that a BS needs to poll
    the SS on a regular basis (periodically or
    non-periodically) and allow it to send unicast
    request opportunities

49
Best Effort Service (BE)
  • The Best Effort (BE) Service supports service
    flows that do not require QoS support and provide
    efficient service for best effort traffic
  • The SS issues its requests in a contention period
  • BE Service flow is allowed to piggyback a BW
    Request on a data packet

50
Scheduling Services and Usage Rules
51
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

52
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

53
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

54
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 SSs
  • GPC (Grant Per Connection) scheduling
    individual packets at the BSs and SSs.

55
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

56
IEEE 802.16 QoS Architecture
57
IEEE 802.16 Service Provisioning
58
Network management reference model
59
Management reference model of BWA networks
  • The model consists of a Network Management System
    (NMS), managed nodes, and a Service Flow
    Database. BS and SS managed nodes collect and
    store the managed objects in an 802.16 MIB
    format.
  • Managed objects are made available to NMSs using
    the Simple Network Management Protocol (SNMP).
  • The Service Flow Database contains the service
    flow and the associated QoS information that
    directs the BS and SS in the creation of
    transport connections when a service is
    provisioned or an SS enters the network.

60
Objects contained by wmanIfmib
  • The MIB structure of wmanIfMib for 802.16.
    wmanIfMib is composed of three groups
  • wmanIfBsObjects This group contains managed
    objects to be implemented in the BS.
  • wmanIfSsObjects This group contains managed
    objects to be implemented in the SS.
  • wmanIfCommonObjects This group contains common
    managed objects to be implemented in the BS and
    SS.

61
Tables maintained by wmanIfmib
  • wmanIfBsProvisionedSfTable
  • contains the pre-provisioned service flow
    information to be used to create connections when
    a user enters the network.
  • wmanIfBsServiceClassTable
  • contains the QoS parameters that are associated
    with service flows.
  • wmanBsClassifierRuleTable
  • contains rules for the packet classifier to
    map DL and UL packets to the service flow.

62
wmanIfBsProvisionedSfTable
  • SS MAC address a unique SS identifier to
    associate the service flow with an SS.
  • Direction the direction of this service flow
    (e.g., UL or DL).
  • Service class index a pointer to the QoS
    parameter set for such service flow.
  • Service flow state there are three states
    indicating whether the resource is provisioned,
    admitted, or active.

63
wmanIfBsServiceClassTable
  • Traffic priority The value (0 .. 7) specifies
    the priority assigned to a service flow.
  • Maximum sustained rate Specifies the peak
    information rate of the service flow in bits per
    second.
  • Maximum traffic burst Specifies the maximum
    burst size that can be transported.
  • Minimum reserved rate The rate in bits per
    second specifies the minimum amount of data to be
    transported on the service flow when averaged
    over time.
  • Tolerated jitter Specifies the maximum delay
    variation (jitter) for the service flow.
  • Maximum latency Specifies the maximum latency
    between the reception of a packet by the BS or SS
    on its network interface and the forwarding of
    the packet to its RF interface.

64
wmanBsClassifierRuleTable
  • In the DL/UL direction
  • The classifier in the BS/SS may use the MAC
    address or IP address to determine which packet
    shall be forwarded to, and may use Type of
    Service (TOS) or Differentiated Service Code
    Point (DSCP) parameters to select the service
    flow with suitable QoS.

65
Service Provisioning Example
66
Main MAC Innovations
67
Summary
  • IEEE 802.16 is uniquely positioned to extend
    broadband wireless beyond the small islands of
    service offered by Wi-Fi systems today.
  • IEEE 802.16 PHY and MAC layer specification that
    unites the market behind a common set of
    standards, a flexible end-to-end network
    architecture that is coupled with a coherent
    service vision, and an efficient certification
    process that enables interoperability, are key
    enablers for realizing the WiMAX vision

68
Summary (Contd.)
  • The IEEE 802.16 group realized the need for
    multimedia applications and the required QoS
    support. Therefore, IEEE 802.16 has included a
    number of QoS signaling mechanisms.
  • However, the algorithms that use such signaling
    mechanisms in order to provide QoS support are
    vendor specific and are left out of the standard.
    This allows vendors to differentiate their
    products but still be interoperable.

69
Reference
  • 1 IEEE recommended practice for local and
    metropolitan area networks. Coexistence of fixed
    broadband wireless access systems IEEE Std
    802.16.2-2004 (Revision of IEEE Std
    802.16.2-2001) 2004
  • 2 IEEE standard 802.16 a technical overview
    of the WirelessMAN air interface for broadband
    wireless access, Eklund, C. Marks, R.B.
    Stanwood, K.L. Wang, S.Communications
    Magazine, IEEE Volume 40,  Issue 6,  June 2002
    Page(s)98 - 107
  • 3 IEEE 802.16-REVd/D5-2004 Air Interface for
    Fixed Broadband Wireless Access Systems
  • 4 IEEE 802.16 Working Group on Broadband
    Wireless Access, http//wirelessman.org
  • 5 IEEE 802.16 Medium Access Control and
    Service Provisioning, Nair, G, etc., Intel
    Technology Journal, Vol. 8, Issue 3, 2004
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