I am trying to calculate ethernet throughput using python (by creating UDP socket). I got throughput in 10-15 MBps range. When I cross verified using iperf, iperf is showing throughput as 35 MBps.
what logic does iperf use to calculate throughput?
does it use UDP or TCP protocol?
For iperf2 and UDP (-u) the value is the number of packets * udp payload / time. If -i is used then interval reports will report per that. A final report gives the -t value. For TCP, it's the bytes read / time.
Bob
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Most articles are about how to increase a UDP socket's receive buffer size to handle more packets, but I need a solution to decrease the UDP receive buffer to accept only 1 packet at a time and discard/drop all other packets until that packet is read.
I'm trying to do this for Linux, and did some network stack tuning, like setting the RCVBUFF and RCVBUFFFORCE socket options, but that didn't work. I cannot reduce RCVBUFF lower than 2046B (maybe 1 memory page), even when setting the udp_rmem_min to 0.
Why i can’t set UDP RCVBUF lower than 2046?
Does UDP packet loss percentage might increase considering packet size? For example if I send 100'000 packets, in first try byte[] size is 30, but second 300. Could packet size play role in it's drop ability or packet loss percentage is not its size dependent?
The packet loss is depending on the size of the packet. This has several reasons.
IP packets can go up to 64k approximately, but they are fragmented up to the MTU of ethernet and if one of those packets gets lost , the whole IP packet is dropped. For larger packets if the traffic is high the probability is higher that the larger packet will be dropped. The MTU is around 1500 bytes.
There is more to it than just that. Internally a protocol stack is implemented using internal buffers that are a lot smaller than the mtu, this can vary from 300 bytes and larger. But the point is that these buffers are also a limited resource. If the network device runs out of buffers, then the packet will be dropped as well.
If you don't know the MTU on the network in question according to the link below a 512-byte UDP payload is considered reasonable to allow a margin for other header information that you may not have anticipated.
What is the largest Safe UDP Packet Size on the Internet
Because you're sending larger packets, yes it could increase the chances that packets are dropped.
Now if you compare sending 100000 packets of 30 bytes or 10000 packets of 300 bytes, even though the user data is the same the total size of the packets is larger due to the headers.
I'm experimenting on an LTE connection for checking the maximum rate of bandwidth can be achieved in the uplink.While creating iperf sessions i observed that i'm not able to go beyond 100Kbps in the uplink when the UDP packet size is set as 1400.Apparently when i increased the packet size to 50000 i was able to achieve 2 Mbps in the same link.
Can someone guide me why this performance difference is observed ?When i tried this in a wired channel there i was able to achieve 10Mbps with UDP packet size set as 1400 itself.
What could be the reason for this?
Will trying TCP/IP instead of UDP increase the data throughput?
It probably matters where fragmentation is done - application or IP stack. Your observations show you that IP stack is more efficient.
TCP will be slower. TCP's built-in congestion control will not allow you to send packets until some of already sent have been ACK-ed. That adds round-trip time to performance considerations.
UDP has no such restrictions. It can (ab)use the network to its full potential.
a little info on what i'm trying to achieve here first. I'm using a Texas Instrument board EVM6678LE, and what i am trying to do is to increase the UDP transfer rate between the board and my PC.
I've increased the MTU on my PC through netsh>interface>ipv4 to 15,000. But when i ping the board from my PC i am only able to ping up to "ping 192.168.2.100 -l 10194", if i ping with 195bytes onwards i'll receive a request timeout. Is this a limitation of my PC or something?
Does anyone have any idea what could be the possible cause of this? Any advice or suggestions at all would be welcome. As the only way to increase the transfer rate i could think of it increasing the per packet size which reduces overhead. And at 10k i have a rate of around 9.1MB/s, and i'm trying to attain 25MB/s.
Thanks!
Increasing the MTU on your PC may not prevent fragmentation. I don't know exactly what is controlling this, but your network card or driver can fragment the packet even when MTU is not reached. Use a sniffer like Wireshark to see how the packets are sent.
About the timeout, it is possible that your board rejects fragmented pings (because of Ping of Death protection). There is also a possibility that its packet buffer is 10kB (10240) bytes long, and can't receive larger packets. Also, make sure that the receiving endpoint have a matching MTU.
Anyway, if you are trying to increase transfer rate, you are on the wrong track. The overhead for UDP is 8 bytes, IP 20 bytes, Ethernet 18 bytes, which make a total of 46 bytes (oh, coincidence, 46+10194 is exactly 10240). 46 bytes overhead for 1024 MTU is 95.5%. 46 bytes for 4096 is 98.9%, 46 bytes for 16384 is 99.7%. That means you gain +3.5% transfer rate from 1024 to 4096 MTU, and another +0.8% from 4096 to 16384. The gain is just ridiculous, and you should just let the MTU to the common default 1500.
Anyway, going from 9.1MB/s to 25MB/s just by changing the MTU is IMPOSSIBLE (if it was, why the PC default is not higher ?). Here I guess you are using Fast Ethernet (100BASE-T), and you are already transferring near full bandwidth. To get higher rates, you would need to have Gigabit Ethernet (1000BASE‑T). That means you need both hardware endpoints to support 1000BASE-T.
I've been tinkering around with the BLE (Bluetooth Low Energy) connectivity classes quiet a bit lately and haven't been able to make it transfer data any faster than 1KB / 5 seconds. I believe, in the documentation, it says the max speed is 60 bytes per 20 milliseconds. With data transfer and counting the Ack transfer after each set of packets, I believe we should be able to go as fast as 1.5KB per second. So my code is around 7-8 times slower than it should be.
I'm just wondering if anyone has been able to do data transfer in BLE as fast as the documentation says it should be able to do. What sort of speed are you getting if faster than mine?
Thanks a lot
see at the guidlines of apple and you will see that a connection update request is required to speed up your connection.
https://developer.apple.com/hardwaredrivers/BluetoothDesignGuidelines.pdf
I have min=20ms max 40 ms
I hope I could help
Roman
If you are able to use higher MTU size (negotiated by the iOS) then you would be able to increase the bandwidth even more, because there is a 4 byte L2CAP header and a 3 byte ATT header that wouldn't be transmitted more than in one packet.
If you are able to transmit 6 packets pr connection interval, then you would be able to put in 35 byte extra per connection interval (the 7 byte header would still be there for the first packet) The MTU size could also be split over several connection intervals, increasing the throughput with 7 more bytes pr connection interval. (Just takes longer time to assemble the packet again.) The max MTU size allowed by ATT is 515 bytes (Max size of att is 512 bytes + 3 byte header for opcode + handle)