NS default values and PCLP

1
NS default values and PCLP

• Thomas King ltking_at_rtna.daimlerchrysler.comgt
• Marc Torrent Moreno lttorrent_at_rtna.daimlerchrysler.
  comgt

2
NS default values

• ns/tcl/lib/ns-default.tclphysical wireless
  default values
• ns/tcl/lan/ns-mac.tcl802.11 mac default values
• ns/mac/mac-802_11.h802.11 mac default values
• ns/tcl/lan/ns-ll.tcldsrc link layer default
  values

3
ns-2.26/tcl/lib/ns-default.tcl
4
ns-2.26/tcl/lan/ns-mac.tcl

• IEEE 802.11 MAC settings
• if TclObject is-class Mac/802_11
• Mac/802_11 set delay_ 64us
• Mac/802_11 set ifs_ 16us
• Mac/802_11 set slotTime_ 16us
• Mac/802_11 set cwmin_ 16
• Mac/802_11 set cwmax_ 1024
• Mac/802_11 set rtxLimit_ 16
• Mac/802_11 set bssId_ -1
• Mac/802_11 set sifs_ 8us
• Mac/802_11 set pifs_ 12us
• Mac/802_11 set difs_ 16us
• Mac/802_11 set rtxAckLimit_ 1
• Mac/802_11 set rtxRtsLimit_ 3
• Mac/802_11 set basicRate_ 1Mb set this to 0
  if want to use bandwidth_ for
• Mac/802_11 set dataRate_ 1Mb both control
  and data pkts

5
ns-2.26/mac/mac-802_11.h

• Default values for the DSSS PHY MIB 802.11a
  OFDM
• define DSSS_CWMin 31 15
• define DSSS_CWMax 1023 1023
• define DSSS_SlotTime 0.000020 0.000009
• define DSSS_CCATime 0.000015 lt0.000004
• define DSSS_RxTxTurnaroundTime 0.000005
  lt0.000002
• define DSSS_SIFSTime 0.000010 0.000016
• define DSSS_PreambleLength 144 0.000016
  (sec)
• define DSSS_PLCPHeaderLength 48 40
• define DSSS_PLCPDataRate 1.0e6 6.0e6
• define DSSS_MaxPropagationDelay 0.000002
  // 2us XXXX
• / IEEE 802.11 Spec, section 11.4.4.2 default
  values for the MAC Attributes /
• //define MAC_RTSThreshold 3000 // bytes
• define MAC_RTSThreshold 0 // bytes
• define MAC_ShortRetryLimit 7 //
  retransmittions
• define MAC_LongRetryLimit 4 //
  retransmissions
• define MAC_FragmentationThreshold 2346 //
  bytes
• define MAC_MaxTransmitMSDULifetime 512 // time
  units

6
NS default values

• Most of the values are described in the
  IEEE802.11a standard
• Some are hardware and driver specific (Atheros,
  Stellcom)

7
PLCP PPDU Frame Format
PLCP Preamble 16 us SIGNAL 4 us
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PLCP Receive State Machine
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NS implementation

• PLCP recieve state machine not implemented.
• BER depending on modulation (BSK)
• 2 receiving Thresholds
• No accumulative Interference but at least
  comparison of 2 received signals (10 dB)
• No management mechanisms (No beacons)
• Some MAC layer bugs

10
NS MAC Layer Bugs

• Additon of random time (0,cw) at the initial
  Defer timer (difs_)(fixed)
• If channel becames busy while deferring (difs_)
  the timer doesnt get cancelled nor start the
  backoff timer. (No need to be changed)
• It doesnt reset the SSRC after receiving CTS
  !!!(fixed)
• No NAV reset if no activity (Simplification?,
  Atheros?)
• No Fragmentation (Simpl?)
• ?sec (time x 106) 0,5 (?)
• No reset retry counters when broadcast sent.(no
  need, Atheros?)

11
NS modifications to do

• 802.11a values
• Atheros chip phy values
• Stellcom API
• Get power incoming packets
• Control transmision power in a packet basis
• Control modulation in a packet basis