Great resources on Congestion can be found by googling for Sally Floyd. Common reasons are DuplexMismatches or Congestion. And a lot of it is highly dependent on what protocols you're using and what software/firmware is implementing it. If the network is configured correctly, there's not much that can be done against packet loss as this is a somewhat "intended" behaviour.įor TCP based protocols this is often reasonably easy to detect and analysis of PacketLossPatterns can often give a hint of what is causing the problem. Packet loss and other related metrics like bit error rate (BER) can be hard or impossible to empirically see by looking at dumps in Wireshark, depending on what layer you're wanting to look at. Sometimes, defective hardware/software simply "forgets" packets. If you're looking for packet loss in TCP conversations you'll see that Wireshark will mark some packets as 'previous segment not captured' followed by 'Duplicate ACKs' from the other side, and finally a 'retransmission'. this will happen if a Router is receiving more data than it can transmit. There are some indicators that may help, depending on what the protocols in use are. Protocols above UDP would be the ones whose implementations detect packet loss and retransmit packets.) Reasonsįor most networks, packet loss is a typical behaviour, e.g. (UDP includes no acknowledgment information, so PacketLoss can't be detected by UDP implementations, and UDP implementations won't Retransmit the packet. (Which is easy once one has figured out WHY the packets are being lost, and where they are lost) ((The art of determining this information is often seen as BlackMagic))ĬonnectionOrientedProtocols such as TCP will detect a packet loss, and try to Retransmit the packet data.ĬonnectionlessProtocols such as UDP won't detect a packet loss, the data in that packet will simply be lost. In some situations when Packet Loss occurs there can be a significant performance degradation and thus it might be interesting to us to try to minimize the amount of packetloss occuring. This is no biggie for network protocols however since it is all based on "Duh, the network is supposed to be lossy. Wireshark has an option under Analyze -> Expert Information that shows a summary of packet loss Previous segments(s) not captured., retransmission. Even worse, sometimes packets will be reordered by the network, or even duplicated by the network. This is especially true for the RealWorld, and that means that sometimes packets sent by the network will never arrive at the proper destination. Unfortunately not all networks are perfect.