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Recently, I've decided to connect my laptop at home to my modem/router through Ethernet cables built into my apartment. As these built-in Ethernet cables are usable via plugs built into the walls (called powerline adapters), I use some additional cabling (STP CAT6 cables) from my laptop/router to the plugs. In addition, I don't know any technical details about these built-in cables (as they're not visible), only the maximal bandwidth (1 GBit => Cat6?) that they're supporting. The built-in cables are Cat. 5e Ethernet cables.

The problem is now that when I set up the connection, I cannot use the full bandwidth that my internet connection is actually offering (100 Mbit/s), only about 85 Mbit/s between 85 - 88 Mbit/s, despite the fact that all cables involved should support the maximal bandwidth. In addition, my network card only reports a connection speed of 100 Mbit/s. I know from other tests with one of the Ethernet cables in use that I can use almost 99 Mbit/s when I connect my laptop directly to the router/modem using only this one cable. In this test, my network card also reports a connection speed of 1 Gbit/s. In addition, it is very unlikely that the length of the resulting cable connection from my laptop to my router involving the built-in cables exceeds 100 m.

So, what possible reasons for this loss of bandwidth exist? And how I can fix this issue?

I hope this might help resolve the issue: The built-in cables appear to be Cat. 5e Ethernet cables. So, is there any problem when I connect Cat6 Ethernet cables directly to Cat5e Ethernet cables via the plugs?

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What model are the powerline adapters? –  Pier-Luc Gendreau Dec 17 '12 at 15:51
They're not powerline adapters. I've just checked some documents that that I got when I moved in here, and I found out that the built-in cables are Cat. 5e Ethernet cables. –  Caspar Dec 17 '12 at 16:56
You can do gigabit over Cat5e so that's not your issue here. Is your laptop reporting the connection speed to be 100 Mbps or 1 Gbps? If it's 100 Mbps, then that explains your 80-ish Mbps speeds. –  Pier-Luc Gendreau Dec 17 '12 at 17:26
Interesting. When I connect my laptop through the built-in cables, it reports a connection speed of only 100 MBit/s. When I connect it to the modem/router directly (as discribed above, not through the built-in cables), it reports a connection speed of 1 Gbit/s ... What's causing this? Can I fix it? –  Caspar Dec 17 '12 at 17:38
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2 Answers

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Since the it's the house's built-in cabling limiting the speed to 100 Mbps and not your own cabling, router or modem, there's nothing you can do short of rewiring the house.

It's also probably not Cat5e since gigabit Ethernet will happily run over such cables.

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Each powerline adpater has a fixed MPS. The smallest I think is 85MBPS up to 500 MBPS.

I would guess you have the 85MBPS.

Plus, even the good quality powerline adapters typically suggest to not go above 20 meters.

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