Hi,
I am sending back to back IP packets from a server and receiving them on my laptop. Laptop has windows XP installed and uses IP over PPP over 3G wireless protocols for Internet connectivity. Since the bandwidth of the connection from the base station to the laptop is about 2 Mbps and packet size is 1500 Bytes, I expect the time between two received packets to be at least 6 ms. However, when I use ethereal to capture the arriving packets the time between packets is zero. When I send 10 back to back UDP packets in a burst from the server (once every second), the time between the packets received at the laptop are either 0 sec or
0.015625 sec. Queuing in the network can explain the 0.015625 sec inter-arrival time, but 0 sec inter-arrival time does not make sense. Moreover, I keep seeing the same inter-arrival time 0.015625 (can't be queuing - there has to be some randomness). Here is a sample: -
Frame 38 (1514 bytes on wire, 1514 bytes captured)
Arrival Time: Mar 19, 2006 16:25:14.734375000
Time delta from previous packet: 0.890625000 seconds
Time since reference or first frame: 5.453125000
seconds
Frame Number: 38
Packet Length: 1514 bytes
Capture Length: 1514 bytes
Protocols in frame: eth:ip:udp:data
Ethernet II, Src: a4:45:20:00:02:00 (a4:45:20:00:02:00), Dst: 02:00:02:00:00:00 (02:00:02:00:00:00)
Internet Protocol, Src: x.y.z.3 (x.y.z.3), Dst: x.y.z.170 (x.y.z.170)
User Datagram Protocol, Src Port: 39996 (39996), Dst Port: 1257 (1257)
Data (1472 bytes)
Frame 39 (1514 bytes on wire, 1514 bytes captured)
Arrival Time: Mar 19, 2006 16:25:14.750000000
Time delta from previous packet: 0.015625000 seconds
Frame 40 (1514 bytes on wire, 1514 bytes captured)
Arrival Time: Mar 19, 2006 16:25:14.765625000
Time delta from previous packet: 0.015625000 seconds
Frame 41 (1514 bytes on wire, 1514 bytes captured)
Arrival Time: Mar 19, 2006 16:25:14.781250000
Time delta from previous packet: 0.015625000 seconds
Frame 42 (1514 bytes on wire, 1514 bytes captured)
Arrival Time: Mar 19, 2006 16:25:14.796875000
Time delta from previous packet: 0.015625000 seconds
Frame 43 (1514 bytes on wire, 1514 bytes captured)
Arrival Time: Mar 19, 2006 16:25:14.812500000
Time delta from previous packet: 0.015625000 seconds
Frame 44 (1514 bytes on wire, 1514 bytes captured)
Arrival Time: Mar 19, 2006 16:25:14.828125000
Time delta from previous packet: 0.015625000 seconds
Frame 45 (1514 bytes on wire, 1514 bytes captured)
Arrival Time: Mar 19, 2006 16:25:14.828125000
Time delta from previous packet: 0.000000000 seconds
When I use the same client-server over standard ehternet, the inter-arrival times are very accurate (of the order of a few microseconds). Is this a problem with PPP? (maybe windows is processing the PPP packets once every
0.015625 ms to save processor cycles). Does anybody know of any workarounds to increase the timing accuracy in this case?
Thanks