While talking about UDP I saw/heard congestion come up a few times. What does that mean?
+5
A:
congestion is when you are trying to send too much data over a limited bandwidth, it cannot send the data faster than the incoming amount so additional packets are dropped.
When congestion occurs, you can see these effects:
Delay due to the queue at one end of the connection being too big, so it takes time for your packet to be transmitted.
Packet loss when new packets are simply dropped, forcing connection resets (and often causing more congestion).
Lower quality of service, protocols like TCP will do a cutback on the transmission rate, so your throughput will be lowered.
Blocking, certain networks have protocol priorities, so your UDP packets may be dropped in favor of allowing TCP traffic through.
Its like a traffic jam, imagine right after a sports game where a parking lot full of cars is trying to empty out into a small side street.
yx
2009-04-29 19:46:28
Clearly you've tried to leave during the 4th quarter of a Panthers game!
Adam Robinson
2009-04-29 19:49:57
and... Unlike, say, TCP, the UDP protocol layer does not offer any features for detecting congestion and reducing offered load. So that's up to the UDP-using application. Some applications may be more robust than others at detecting congestion and taking appropriate action. It's easy to write a naive UDP application that will "fill the pipe" (but it's antisocial).
Liudvikas Bukys
2009-04-29 19:50:56
+1
A:
It means that network-connected devices are attempting to send more data across the network than it can handle, e.g. 20 Mbps of data across a 10 Mbps link.
In context of UDP, it's your main source of lost datagrams under ordinary circumstances.
chaos
2009-04-29 19:47:02
A:
Hi,
Most LANs use some sort of a collission detection/avoidance system. A congestion typically means that the amount of data which is being transmiited on the medium is causing enough collissions to deteriorate the quality of service defined for that medium. You may want to read up CSMA/CD at wikipedia. As UDP packets can often be broadcasted, congestion can occur more often.
Kind regards,
SharePoint Newbie
2009-04-29 19:49:51
A:
For instance, Ethernet is a broadband protocol. Once a message is sent, every node receives it but ignores if the packet are not sent to them. What happens when two nodes send a packet at the same time? It will cause a collision and data loss.
So, both of the nodes will have to resend the message. To avoid more collisions, nodes are designed to wait a random number of milliseconds. Otherwise they keep going on sending messages simultaneously and packages will collide forever.
Burcu Dogan
2009-04-29 19:54:41