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 [phone], Fax [phone],
  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

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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
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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

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Characteristics WLAN vs. WiMAX
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IEEE 802.16 Broadband Wireless Access System
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802.16 Network Architecture
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802.16 Deployment
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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)

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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

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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).

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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

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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

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Medium Access Control (MAC Layer)
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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.

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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

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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.

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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)

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IEEE Std 802.16 MAC Protocol Layering
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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)

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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

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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)

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Packet Convergence Sublayer

• used for all packet-based protocols,
• such as IPv4, IPv6, Ethernet, and VLAN
• Similar functions as ATM convergence
• sublayer, including PHS

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MAC Common Part Sublayer

• Defines multiple-access mechanism
• Functions system access, bandwidth allocation,
  connection establishment, and connection
  maintenance

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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

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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).

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DL-MAP and UL-MAP
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Uplink Subframe
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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.

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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

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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

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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

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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

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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

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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)
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IEEE 802.16 MAC Layer Connection Management
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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

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Network entry process
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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

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

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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

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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

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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

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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.

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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

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IEEE 802.16 QoS Architecture
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IEEE 802.16 Service Provisioning
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Network management reference model
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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.

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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.

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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.

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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.

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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.

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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.

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Main MAC Innovations
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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

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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.