What happened to all that throughput?

• A typical 802.11b TCP data frame:
  • 18 byte preamble (sent at 1mbps) : 144us
  • 6 byte header (sent at 1mbps) : 74us (oops, this should be 48)
  • 32 (oops, this should be 34) bytes additional header for addressing and FCS (sent at 11mbps or best speed) : 23.27us
  • 48 (oops, this should be 52) bytes TCP/IP header, timestamp (sent at 11mbps or best speed) : 34.91us
  • 1448 bytes of data (sent at 11mbps or best speed) : 1053.09us
  • Interframe space : 10us
  • Total : 1339.27us
• The reciever will send an immediate 802.11 ACK:
  • 18 byte preamble : 144us
  • 6 byte header : 48us
  • 14 bytes ACK data : 10.18us
  • Interframe space : 10us
  • Total : 212.18us
• The reciever will also eventually send a TCP ACK:
  • Preamble, header, mac addressing as before : 215.27us
  • 52 bytes for TCP/IP header, ACK data : 37.82us
  • Interframe space : 10us
  • Total : 263.09
• The 802.11 layer must acknowledge the TCP ACK:
  • Another 212.18us
• Therefore, 1 TCP packet of 1448 bytes requires at least 2026.72us
• Maximum throughput : 5,715,639 bps
• Random backoff and occasional collisions will decrease this number further