ns-2 nist add-on ieee 802.16 model (mac+phy) miray kas 28 jan 2008
TRANSCRIPT
NS-2 NIST add-onIEEE 802.16 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 SublayerMAC Common PartPHY Layer
Comments on Unavailable Features
Basic Data on IEEE 802.16 Standards (1)
Basic Data on IEEE 802.16 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 TaiwanState 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
802.11 PHY cleanupns-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 modeTDD
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
Convergence Sublayer
Convergence Sublayer
MAC Sublayer - Addressing & Connection
Initialization of BSInitialization of BS Initial Ranging( ) Padding( ) Broadcast( ) Adaptive Antenna System( )
Initialization of SSInitialization 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-headers0 or more sub-headers
0 or more fragments0 or more fragments
Fixed LengthFixed Length
Virtual PHY header : Used to carry physical information such as frequency, modulation…
Mutually ExclusiveMutually Exclusive
HT = 1
HT = 0
Construction & Transmission of MAC PDUs 3 steps:
Receive, classify, put in the connection queueSchedulingTransmission
Construction:Fragmentation & PackingCRC 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 FlowsertPS 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
StaticStored by ServiceFlowHandler
Contention Resolution BS has full control on downlink Collisions possible in uplink
Initial Ranging RequestBandwidth 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 transmissionsat 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
DefinitionA 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
WimaxMobNbrAdvTimerWimaxScanIntervalTimerWimaxRdvTimerWimaxT44Timer
Mobility Mobility ExtensionsExtensions
PHY Layer
Only OFDM is implemented
OFDMA WirelessMAN-SC WirelessMAN-SCa WirelessHUMAN
Missing Yet!!!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