Basic Ethernet Network Questions

[Bathrone]

Hi everyone Sorry for asking some basic stuff, but to be sure Ive got the understanding right:

1. The theoretical fast ethernet speed on my calculations for 100mbit works out to be 12.2 megabytes per second?

2. Is that 12.2megabytes per second inclusive of full duplex, or is the actual maximum bandwidth both ways actually 24.2 megabytes per second? Or is it limited to 6.1 megabytes one way?

3. I also calculate gigabit ethernet theoretically gives 122 megabytes per second?

4. In practice, if we assume all the networking gear complies to the standard, its all on switches and not hubs and all devices can send/receive greater than the network bandwidth, is the practical bandwidth limit less than the theoretical of fast ethernet of 12.2 megabytes per second?

e.g. Do you actually get 11.9megabytes per second because of ethernet frame collisions or some other reason?

5. Is an on motherboard gigabit NIC not as good for performance as say a PCIExpress gigabit nic add on card? If so, how much is the practical difference in bandwidth for the add on card?

Thanks

 

[nightowl]

1) Correct
2) the maximum throughput is 12.2MB/s, however once you add in overhead you will see about 10MB/s max
3) Correct, however it is rarely seen with desktops/laptops due to other limitations
4) You are correct that 12.2MB/s is not seen this is not due to switches but due to reasons I stated above. They all operate at speeds much faster than devices. Also, collisions are a thing of the past with switched networks now. They can happen but are very rare and usually due to a configuration issue.
5) It will depend on what the back end connection is from the controller.


Edit: 12.5MB is correct but for rounding purposes 12.2 is close enough.

 

[Madwand1]

1. I don't know how you got 12.2. My calculator gives 12.5 when I divide by 8.

2. Full duplex is twice that, but it harder to achieve than saturating a single direction.

4. Yes, the theoretical limit isn't achieved in practice, and there's protocol overhead to consider. Actual transfers will always come in somewhat less.

5. Issue (4) is much more pronounced when you hit gigabit levels. While it's common to hit say 90% saturation of 100 Mb/s, this is rare with gigabit. The first obvious issue is that typical single hard drives cannot hit this limit. But even when you replace them with fast RAID arrays on all sides, you find that it's rare to approach saturating gigabit during Windows file transfers. This can be due to hardware performance issues at various points, but is also related to inherent limitations and inefficiencies and some tuning issues with Windows itself and its native file transfer protocol.

Around 30 MB/s is typically achieved. With some tuning and luck, around 60 MB/s can be achieved. This can go still higher under a limited number of conditions. Using ftp for example can get around some Windows OS / native file transfer protocol (SMB) issues.

For the most part, HD, OS and file transfer protocol issues make higher-end network performance irrelevant. E.g. if your HD is limited to 50 MB/s (400 Mb/s) it doesn't matter much whether your NICs hit 600 Mb/s or 900 Mb/s. Even more so when your OS limits the performance to around 30 MB/s.

Some on-board NICs perform very well. These tend to be either native to the chipset, or based on PCIe internally. PCI NICs tend to be older designs; not perform as well, and potentially encounter issues with overhead and load on the PCI bus. However, the OS and file transfer protocol issues still apply, so it's often not worth replacing the NIC and worrying about network hardware beyond the initial move to gigabit.

Look around, and you'll see many threads going into these issues with example problems and performance results.

 

[JackMDS]

Q - 5. If it is used in peer-to-peer network runing client OS it would not make a difference.

Since new motherboards come with onboard NIC you try as is.

No Good, they would be very happy to sell you ad on NIC any time.

 

[Bathrone]

Thanks all

 

[Bathrone]

Thanks all