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if i have two network devices A and B, and there is a bandwidth link of 1000 Mbps and i would like to send two packages simultaneously each with the size 500 Mb from device A to device B. how it works in real life. option (A) the link only transmits one package at a time until it reaches to its destination then sending the next package. for example, if i sent the two packages at 10:00 pm for the first package it will take (500/1000)(transmission delay) = 0.5 second to reach to device B at 10:05 pm then the next package will reach at 10:10 pm. option (B) the two packages will be sent at the same time and all reach to its destination (device B ) at 10:05 pm as the bandwidth can stand the two packages 500 + 500 = 1000 Mbps. if the second option is the correct answer, then if i want to send three packages each with the size 500 Mb, does that mean the third package will be lost due to inefficient bandwidth ?? please help

i am using a simulator, and in that simulator only one package is transmitted at a time until reaching its destination and then the second package is sent. is that how sending packages work in real life??

Zain
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2 Answers2

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Why would you want to send two packages simultaneously? That's not a rhetorical question. It could make sense to send audio and video simultaneously, so the sound track matches up with the events on screen.

From a programming perspective, you hand off your data to the OS. This function call might not return immediately, if the amount of data is large and the OS has not enough RAM available to buffer it.

Note: you seem to mix up size and bandwidth, when you talk about 500 Mb + 500 Mb = 1000 Mbps. The units make it clear that this does not add up like that. Sending a 500 Mb package over a 1000 Mbps link indeed takes half a second (500 ms), sending 3 such packages takes 1500 ms. There's no magic at the 1000 millisecond barrier that would cause the first two packages to be sent, but the third package to be lost. In fact, it's quite possible to download a 700 MB file (~1 CD, 5800 MBit) over a 10 Mbit line. That just takes 580+ seconds.

MSalters
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  • in my case, there are two servers that sharing workloads. if server A is overloaded, then it will send the overloaded tasks to server B, and server A can send multiple tasks simultaneously to server B. in the network simulator i m using, it sends the first task while putting the rest tasks in a queue, if the first task reaches its destination (server B) then the next task is taken from the queue and sent from server A to server B and so on, until the queue is empty. is this the correct way of sending tasks between servers? – Zain Oct 26 '20 at 22:43
  • @Zain: It appears entirely reasonable. By sending task 1 first, the full bandwidth is available for just that task, and server B can start work earlier. Then, after B has started working on task 1, it can receive task 2 in parallel with the execution of task 1. This sort of overlap (gather data for task N+1 while executing task N) is a common performance optimization when tasks are (approximately) independent. – MSalters Oct 29 '20 at 10:42
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Real world networking is a little more complicated. Firstly the data you send is not just send as a big block of data, but instead split up into Segments, Packets, Frames and bits by the different networking layers. If you want to know more read up on the OSI-model.

If the data is send over a normal networking cable (like CAT6) the Ethernet protocol is used, which depending on the version uses different encoding protocols: Although not used anymore Manchester Code is probably the easiest to get a rough understanding of what those do. Through that only one bit for every time-slot can be received. If you are using an optic carrier it is possible to transmit multiple signals at the same time (compare multiplexing). Since this requires much more complex hardware it is not used between two (normal) computers, but between Providers and cities.

In your specific case the data send by some application is processed first by the operating system and then the network card until it is split up into Ethernet frames of 1518 bytes (compare MTU) which are then send over the network encoded by the specific method determined by the transmission technology. On Host B the same process is reversed. The different parts of your two data-packets can be send after each other, alternating or in some other form, which will be determined by the different layers and depending on their exact configurations.

hippodev
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