Jtdylktuy

A software vendor I work with requires gigabit ethernet connections for a classical client-server software setup. To my surprised question why they would need to transfer such a large amount of data between client and server, the vendor answered that they don't transfer any large, but many small packets. He told me that in their experience, this works a lot faster on gigabit than 10 or 100 megabit connections.

Having understood ethernet as a serial connection and transfer speed being limited mostly by the medium (fibre, copper, etc.), I am puzzled. Is there a theoretical explanation for the phenomenon as explained by the vendor that I may be missing? My background is not exactly in hardware so maybe there are optimization measures in gigabit standards that somehow optimize for this special case.

So assuming I would have to sent 1,000,000 packets of only a few bytes each, is there a reason why this could be faster on gigabit ethernet than 10/100 megabit ethernet?

The packet rate (pps) is a direct result of dividing line speed by packet size. As such, it scales linearly with line speed.

The minimum Ethernet frame size is 84 bytes while the maximum (disregarding Jumbo Frames) is 1,538 bytes. As such, the following frame rates are possible:

• 100 Mbit/s: 8,127 f/s to 148,809 f/s


• 1 GBit/s: 81,274 f/s to 1,488,096 f/s

More bandwidth is always better in terms of throughput. It may be worse in terms of latency and will probably use more power.

if I have a packet that is 5kb, why would it matter if the line is able to transmit 10, 100 oder 1000mbit?

The line isn't measured in "megabits", it's measured in megabits per second. It's a unit of rate that applies equally to any data size – just like "kilometers per hour" applies equally to any distance. (For example, travelling 10 meters at 20 km/h is still ten times faster than doing so at 2 km/h.)

The units can be scaled down if you want – for example, 1 km/h can be converted to ~0.27 m/s. Similarly 1 Gb/s can be converted to 1 kb/µs. That's still the same value, but you can see that transferring 5 kilobits at 1 kb/µs (1 Gb/s) takes 5 microseconds – ten times faster than 50 µs.

[I sure hope I got the math right]

So assuming I would have to sent 1'000'000 packages of only a few bytes each, is there a reason why this could be faster on gigabit ethernet than megabit ethernet?

It's called "Gigabit Ethernet" because its data transfer rate is 1 Gbps (gigabits per second). That's not actually a capacity, but a fixed clock rate. For example, if you send one gigabit, it'll be transferred in one second at 1 Gbps. But if you send 10 megabits, they'll be transferred in 0.01 seconds, still at 1 Gbps, and the link will stay idle for the remaining 0.99 secs.

In other words, it doesn't change gears depending on packet size. Whether you send X Gb consisting of large packets, or X Gb consisting of small packets, they're always sent at the same 1 Gbps rate, which is always 10 times faster than 100 Mbps.

Having understood ethernet as a serial connection and transfer speed for small packets being limited mostly by the medium (fibre, copper, etc.),

Not all serial connections work alike. The bit rate you can achieve over the same medium can vary, depending on the coding and modulation that you use to put these bits on the wire. (Plus quite a few other things that I have no knowledge of.) In addition to that, Gigabit Ethernet (and similarly USB 3.2, PCI-e, SATA, and many other serial links) uses multiple lanes to send several data chunks simultaneously.