NS-2 NIST add-on IEEE model (MAC+PHY) Miray Kas 28 Jan 2008

Outline MAC Layer overview Basic Data about PHY Layer List of Available/Unavailable Features Available Features  Convergence Sublayer  MAC Common Part  PHY Layer Comments on Unavailable Features

Basic Data on IEEE Standards (1)

Basic Data on IEEE Standards (2)

Why NS-2 & WiMAX Ns-2:  De facto Standard for Simulation of Networks Not so many WiMAX modules available:  NIST Most reliable Only one that has mobility functionality  Chang Gung University Taiwan  State University of Campinas Brazil

ns-2 vs. ns-3 environment ns-2 since 1996 ns-3 in progress, no initial alpha release ns-3 : Rewrite of core simulator  PHY cleanup  ns-2 integration with ns-3  tools to parse output data (tcpdump and Ethereal)  (Dynamic) Calendar Queue  NIST WiMAX ns-2 port to ns-3

Main Features of WiMAX Module PHY: PHY:  OFDM MAC: MAC:  PMP mode  TDD Builds on ns2 legacy code Implemented in C++

Convergence Sublayer Classifying higher layer PDUs into appropriate connections Delivering resulting CS PDUs to MAC SAP associated with the service flow. Suppressing / Rebuilding payload header information Used for Internet Protocol (IP) Point-to-Point Protocol (PPP) Ethernet (IEEE 802.3)

Convergence Sublayer

MAC Sublayer - Addressing & Connection Initialization of BS Initialization of BS  Initial Ranging( )  Padding( )  Broadcast( )  Adaptive Antenna System( ) Initialization of SS Initialization of SS  Initial Ranging( )  Padding( )  Broadcast( ) During network entry, following are set up: During network entry, following are set up:  Basic CID( ) Exchange time urgent MAC mng. msg  Primary CID( ) Longer delay tolerant MAC mng. msg  Secondary CID( ) DHCP, TFTP, SNMP  Data CIDs Current model supports only one

MAC PDU Format 0 or more sub-headers 0 or more fragments Fixed Length  Virtual PHY header : Used to carry physical information such as frequency, modulation…

Mutually Exclusive HT = 1 HT = 0

Construction & Transmission of MAC PDUs 3 steps:  Receive, classify, put in the connection queue  Scheduling  Transmission Construction:  Fragmentation & Packing  CRC calculation

Scheduler Service Flow classes are implemented  UGS, nrtPS, rtPS, BE Current one does not use service classes  Best Effort Scheduler with Round-Robin algorithm Allows custom implementations  One default for SS and BS each Replace current one by a TCL command  $mac set-scheduler $scheduler

Scheduler

QoS Structure supports Service Flows  ertPS not implemented Scheduler does not use them No Admission Control during creation of flows  Accept all requests from MSs List of flows in each SS  Static  Stored by ServiceFlowHandler

Contention Resolution BS has full control on downlink Collisions possible in uplink  Initial Ranging Request  Bandwidth Request BS decides contention slots Binary exponential backoff window  SS decides how many minislots to defer

Contention Slot

Contention Request

TDD  Uplink transmissions occur after downlink transmissions at each frame

Frame Structure

Network Entry & Initialization Steps:  Scan downlink channel  Obtain transmit parameters  Initial ranging  Registration Following can be configured:  Timers to perform channel scanning  Frequency of the DCD/UCD messages  Parameters for initial ranging (backoff window size & # of slots per frame)  Channel allocation

Network Entry

Scanning Related to Handover procedure When link quality weakens MS scans to find another BS Send MOB-SCN_REQ to current BS to request scanning interval

Scanning

Scanning Modes Without association  MS attempts itself Association Level 0 – w.o. Coordination  Target BS has no information about scanning MS Association Level 1 – with Coordination  Serving BS negotiates with target BS Association Level 2 – Network Assisted  Not implemented yet.

Scanning WiMAXCtrlAgent  Extends Agent Has three functions:  Exchange DCD/UCD info btw. BSs  Trigger sending of NBR-ADV msg. to MSs  Synchronize BSs (serving & target)

Ranging Definition  A mechanism to allow an SS to maintain link quality by adjusting its 1-) Transmission power 2-) Modulation Uplink Ranging = Initial Ranging + Periodic Ranging Downlink Ranging = No periodic ranging

Ranging (Current Situation in the Module) No algorithm to make use of ranging capabilities Periodic ranging not implemented CDMA request not implemented Only to add latency to the network entry Mechanism implemented not applicable to OFDMA

Timers WimaxFrameTimer WimaxRxTimer WimaxDCDTimer WimaxUCDTimer WimaxRngIntTimer WimaxLostDLMAPTimer WimaxLostULMAPTimer DLTimer ULTimer WimaxT1Timer WimaxT2Timer WimaxT3Timer WimaxT6Timer WimaxT9Timer WimaxT12Timer WimaxT16Timer WimaxT17Timer WimaxT21Timer  WimaxMobNbrAdvTimer  WimaxScanIntervalTimer  WimaxRdvTimer  WimaxT44Timer MobilityExtensions

PHY Layer Only OFDM is implemented OFDMA WirelessMAN-SC WirelessMAN-SCa WirelessHUMAN Missing Yet!!!

PHY Layer Configurable parameters (TCL):  Transmission power  Cyclic Prefix  Frequency  Frequency bandwidth  Modulation Computed values:  Sampling frequency  OFDM symbol time duration  Xmission time of a packet acc. to its size and modulation  Max packet size for a given modulation and # of available OFDM symbols

PHY Layer Default: Default:  OFDM_BPSK_1_2 modulation  OFDM_IDLE Supported Modulations: Supported Modulations: States: States:  OFDM_IDLE  OFDM_SEND  OFDM_RECV  OFDM_RX2TX  OFDM_TX2RX

PHY Layer

Available/Unavailable Features

Open to Improvement WirelessMAN-OFDMA physical layer ARQ (Automatic Repeat Request) Error Correction Service Flow and QoS scheduling Call Admission Control Periodic ranging and power adjustments

Will be Still Missing… ATM Convergence Sublayer Mesh Mode Physical Layers  WirelessMAN-SC  WirelessMAN-SCa  WirelessHUMAN Frequency Division Duplexing (FDD) Authentication