Are blocking networks an issue with packet-switched networks? I feel like blocking networks are only an issue when the network is circuit switched. A blocking network would prevent some circuits from being made at some times, but in a packet-switched network, the blocked link would quickly become available as the link is only blocked for the duration of a single packet. Is this correct?
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cwswanso
That sounds correct to me. I think the issue is if you wanted to say establish a connection, you'd need control over the wire yourself. But if you're just sending packets, I think you're correct, you wouldn't have it for long.
Although, I think it's still an issue, since if all nodes on the left were sending data at a high frequency, the link with the conflict couldn't keep up, and would therefore decrease the overall throughput. Whereas if there weren't any conflicts, we could just have the maximum throughput of the links/switches.
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jmnash
So the conflict only happens if the two messages want to go along the same connection? Does it matter if they want to go through the same switch? If going through the same switch does matter, then there are a lot of ways to block messages in this network, since pairs of nodes share a switch at the right-hand side.
Also, I'm somewhat confused about the difference between blocking and rearrangeable non-blocking. If going through the same switch doesn't matter, then wouldn't this be rearrangeable non-blocking? Because you can rearrange the connections on the inside of the network to make the 1-to-6 message go to the third node in the second column, then the third node in the third column, and then the last node in the third column.
Am I misunderstanding rearrangeable non-blocking, or is it the fact that they go through the same switch that causes the conflict?
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tomshen
Rearrangeable non-blocking doesn't mean you can rearrange links, which is what I believe you're saying in your example. It means that you can connect any permutation of sources to destinations (3-to-7 and 1-to-6 is one permutation), but in order to switch to another permutation (e.g. also connecting 2-to-4) may require switching how you connected 3-to-7 and 1-to-6. A strictly non-blocking network means that no matter what permutation of sources and destinations you have, or how you switch between permutations, you won't have to rearrange the connections.
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tcz
@tomshen The confusion might be over the term "connection". I understand it to mean a path along the network from a source to a destination, but jmnash may have misunderstood the concept to the edge from one node on the network to anotter.
@jmnash The blocking does not happen at the switches, but at the edges/wires/connections.
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ruoyul
What does the word 'blocking' actually refer to? Does these has anything to do with blocking and non-blocking send? The word blocking comes from the fact that if we want to send from 1->6 and 3->7 at the same time, one of them will block the other, right?
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aew
@rouyul I believe "blocking" refers to one message preventing the other from moving forward, as you said. This occurs because both 1->6 and 3->7 want to go through the same switch and connection. I think this isn't related to blocking and non-blocking send, except that in both scenarios one message/send is preventing another from making progress. Can someone verify this?
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tcz
In general, "event a is blocking" means that there exists some situation where the occurrence of event a prevents some other even from occurring.
Blocking/non-blocking send has to do with program execution. A blocking send will halt other execution until the send completes. A non-blocking send will allow other code to execute.
In this case, @aew is correct. A message from 1->6 blocks the event 3->7 from happening.
However, I'm not sure that switches have anything to do with blocking/non-blocking. I think it all comes down to wires, because wires can only carry one message at a time, whereas switches can handle multiple messages in some way.
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tianyih
Still not sure what rearrangeable non-blocking means. Can anyone clarify this concept?
Are blocking networks an issue with packet-switched networks? I feel like blocking networks are only an issue when the network is circuit switched. A blocking network would prevent some circuits from being made at some times, but in a packet-switched network, the blocked link would quickly become available as the link is only blocked for the duration of a single packet. Is this correct?
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That sounds correct to me. I think the issue is if you wanted to say establish a connection, you'd need control over the wire yourself. But if you're just sending packets, I think you're correct, you wouldn't have it for long.
Although, I think it's still an issue, since if all nodes on the left were sending data at a high frequency, the link with the conflict couldn't keep up, and would therefore decrease the overall throughput. Whereas if there weren't any conflicts, we could just have the maximum throughput of the links/switches.
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So the conflict only happens if the two messages want to go along the same connection? Does it matter if they want to go through the same switch? If going through the same switch does matter, then there are a lot of ways to block messages in this network, since pairs of nodes share a switch at the right-hand side.
Also, I'm somewhat confused about the difference between blocking and rearrangeable non-blocking. If going through the same switch doesn't matter, then wouldn't this be rearrangeable non-blocking? Because you can rearrange the connections on the inside of the network to make the 1-to-6 message go to the third node in the second column, then the third node in the third column, and then the last node in the third column.
Am I misunderstanding rearrangeable non-blocking, or is it the fact that they go through the same switch that causes the conflict?
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Rearrangeable non-blocking doesn't mean you can rearrange links, which is what I believe you're saying in your example. It means that you can connect any permutation of sources to destinations (3-to-7 and 1-to-6 is one permutation), but in order to switch to another permutation (e.g. also connecting 2-to-4) may require switching how you connected 3-to-7 and 1-to-6. A strictly non-blocking network means that no matter what permutation of sources and destinations you have, or how you switch between permutations, you won't have to rearrange the connections.
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@tomshen The confusion might be over the term "connection". I understand it to mean a path along the network from a source to a destination, but jmnash may have misunderstood the concept to the edge from one node on the network to anotter.
@jmnash The blocking does not happen at the switches, but at the edges/wires/connections.
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What does the word 'blocking' actually refer to? Does these has anything to do with blocking and non-blocking send? The word blocking comes from the fact that if we want to send from 1->6 and 3->7 at the same time, one of them will block the other, right?
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@rouyul I believe "blocking" refers to one message preventing the other from moving forward, as you said. This occurs because both 1->6 and 3->7 want to go through the same switch and connection. I think this isn't related to blocking and non-blocking send, except that in both scenarios one message/send is preventing another from making progress. Can someone verify this?
This comment was marked helpful 0 times.
In general, "event a is blocking" means that there exists some situation where the occurrence of event a prevents some other even from occurring.
Blocking/non-blocking send has to do with program execution. A blocking send will halt other execution until the send completes. A non-blocking send will allow other code to execute.
In this case, @aew is correct. A message from 1->6 blocks the event 3->7 from happening.
However, I'm not sure that switches have anything to do with blocking/non-blocking. I think it all comes down to wires, because wires can only carry one message at a time, whereas switches can handle multiple messages in some way.
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Still not sure what rearrangeable non-blocking means. Can anyone clarify this concept?
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