EFM - Speed Vs Bandwidth

satanicguardian

satanicguardian

satanicguardian

Associate
Joined
20 Aug 2007
Posts
1,333
Location
Solihull
Hi guys, I'm trying to get to grips with this concept - it has perplexed me for quite a while now. I think it's a fairly common misconception that bandwidth relates to your download speed on things like speedtest.net

I believe I've come to a very vague understanding using dodgy diagrams in pen and some crap analogies.

53100597-0864-46b3-9ce7-11b62367c2af.jpg


The left diagram labelled A (I forgot to label the right one!) shows an example of a standard broadband connection. I've just used the numbers there as examples too.

Sooo..if we imagine it's a standard ADSL connection with a download SPEED of 8Mbps, an upload SPEED of 1Mbps and a BANDWIDTH of 0.5mb..this allows 500kb packets of data to travel downloads at speeds up to 8mbps and the same packet to upload at speeds of 1mbps..

I think this is correct, please say if not!

In the second example I am using the same SPEEDS but have quadrupled the bandwidth just for example purposes, so now it's a 2mb bandwidth.. here's where I'm going out on a limb..

This second example SHOULD allow 4 x 500kb packets of data to travel in any direction SIMULTANEOUSLY at the max up/down speed, if you're following?

OK BREAK TIME, NEED TO COLLECT THOUGHTS

And continuing..

The way I've made this into an analogy is using roads/motorways; if we imagine that the download speed is the road speed limit for this example, and the bandwidth is the amount of lanes on said road.

So a speed limit of "70mph" or 8mbps is on a single lane, it means a single car/packet of data can travel at that speed consistently providing there is no other traffic in the way, if more cars/packets are introduced everything slows down.

If we had a 4 lane motor way (or 4x as much bandwidth) instead of just 1 with a 70mph/8mbps speed limit, this hypothetically means that 4 cars/packets can travel at 70mph without being constricted.. yes? I think?

Sooooooo, all in all.. this should mean that a dedicated EFM line with a wider bandwidth than previous broadband, it should be much more efficient and heavy usage from multiple users will affect internet speed less..

As I said, this is a minefield of a topic and I believe this is how it's supposed to work in basic terms, can anyone comment/fill in? It's never a concept I've ever really needed to understand or visualise.

Thanks guys!

Jamie
 
?????

The upload/download speed is the 'bandwidth' (Mbps).

The fact that an EFM connection uses multiple lines is totally transparent to the end user. It's just a connection with an upload/download speed exactly the same as any other connection.
 
Last edited:
I'm not entirely sure what point you're trying to get across here?

Is this information or are you asking a question?
 
Your motorway lanes analogy is more appropriate to aggregating multiple links of the same type. So if you had 2 x 1Gbps Ethernet links, then theoretically you could get 2Gbps out of them (in practice link aggregation has lots of limitations).

However, the speed of your Internet connection is determined by the underlying technology that is transmitting and receiving the data at the physical layer, and depends on many things. For example, BT Infinity, called "fiber", is a technology called VDSL that is transmitting and receiving over the exact same copper wires that have been buried in the ground for decades. BT installed some VDSL equipment in the cabinet, gave you a VDSL modem, and hey-presto, you can now get up to 80 Mbps. 5 years ago you could only get ADSL on those exact same copper wires, giving you maybe 15 Mbps. So researchers have come up with ways to transmit (and reliably receive, just as important) far higher speeds on existing media. The same applies to fiber connections, nowadays 40 Gbps fibre is available, and increasing. Under-sea fibres upgrade the equipment at each end, and double/triple/quadruple their capacity, without ever sending out a submarine.

What I'm saying is that it isn't just more lanes. The cars now have jet engines, there are more people inside the cars, the cars are painted with a special paint that makes them less wind-resistant, the people in the cars have all been put on diets to lose weight so more can fit inside, etc. etc. etc. There are countless aspects to improving the speed of a link, and many millions of £ of research goes into this area. Each technology uses combinations of technologies and techniques to improve the speed.
 
:confused: as well! I'm not sure what the question is.

EFM is symmetric, so the 8Mbps down / 1Mbps up only adds to the confusion.
 
You've made up a term, 'speed' is a very loose definition. Packets are made up from electrons, they all travel at the speed of light (yes this is a simplification), any further delays are due to the processing time required at each hop.

The greater your bandwidth the more packets you can push or receive simultaneously, leading to increased throughput.

There's no such thing as a 'slow' wire.
 
Sorry for slow reply! It was a question but with myself trying to talk it through, although it seems I have been mislead by the people I have asked about this thus far!

Could someone please explain why a 2mb converged, uncontended EFM circuit will be far superior to ASDL for hosting a small business's voip and internet access?

I think I have an idea of it now but I'd like some clarification if someone would be willing to assist? :)

Cheers!
 
satanicguardian said:
Sorry for slow reply! It was a question but with myself trying to talk it through, although it seems I have been mislead by the people I have asked about this thus far!

Could someone please explain why a 2mb converged, uncontended EFM circuit will be far superior to ASDL for hosting a small business's voip and internet access?

I think I have an idea of it now but I'd like some clarification if someone would be willing to assist? :)

Cheers!
Click to expand...

I think you are very confused.

A 2Mb converged 1:1 contention EFM Circuit will be better for VOIP/Internet over ADSL for the SHEER fact it's synchronous Download/Upload and has 1:1 contention - No other reason.

Bigger Upload > Smaller Upload.
1:1 contention > 40:1 contention

That's it. Stop complicating it.

Converged/Aggregated links actually have some downsides over single link connectivity options. Especially WAN based ones for internet connectivity.

PERSONALLY I would take a 2Mbit single link connection over an aggregated link.

To really simplify things for you consider this:

A 10Mbit single link internet connection is NO different in terms of download speed potential to a link made up of 5 x 2Mbit links.
 
Last edited:
Sin_Chase said:
I think you are very confused.

A 2Mb converged 1:1 contention EFM Circuit will be better for VOIP/Internet over ADSL for the SHEER fact it's synchronous Download/Upload and has 1:1 contention - No other reason.

Bigger Upload > Smaller Upload.
1:1 contention > 40:1 contention

That's it. Stop complicating it.

Converged/Aggregated links actually have some downsides over single link connectivity options. Especially WAN based ones for internet connectivity.

PERSONALLY I would take a 2Mbit single link connection over an aggregated link.

To really simplify things for you consider this:

A 10Mbit single link internet connection is NO different in terms of download speed potential to a link made up of 5 x 2Mbit links.
Click to expand...

I am very confused correct, perhaps even more so now but I'll try and follow! :)

EFM uses multiple connections that kinda combine to create the total yeah? So hypothetically you could have either:

1 x single link EFM with 1:1 contention @ 2mbits
4 x aggregated(?) EFM with 1:1 @ 0.5mbits each

Does that work or am I even more confused now? D:

This confusion is purely down to being told different things by different people in various partner companies, I wish I could wipe my mind clean and go from scratch
 
IMO the most important factor is the service-level agreement (SLA). If the business is using the connection for VoIP then you need to know that the connection will be there as close to 100% of the time as possible.

You don't need to worry about how an EFM connection works, just accept that it does. They'll be multiple lines used to provide the bandwidth and some level of redundancy. From the end user point-of-view it just gets presented as a single Ethernet port you can connected your equipment to.
 
All the EFM connections I've seen use multiple copper pairs to present a single link

I'd also offer the opinion that a 2Mbps circuit isn't big enough to handle VoIP and Internet Access without stringent QoS. A single download could kill your voice quality.
 
Last edited:
Bremen - I agree, I don't really need to know but it's one of those things where I feel more comfortable dealing with something when I have a full understanding of it. It's tricky to find a website/article that explains EFM without trying to sell the solution to me instead :P

Chris - The EFM connection is going to be hosted by Gamma, it has SLA's and assurance on the line (apparently) - it's supposed to be pretty fail safe, it's just all so confusing cause lots of people say it will support voip and internet fine, and others that say it may not :(
 
I've had a read through the wikipedia, but the people I was speaking to at that point contradicted it - also there are higher speeds available but that's when the cost starts to climb dramatically
 
We do a fair amount of business with Gamma. The primary connection for our office is is with them (though it's 100Mbps fibre). Are you looking at Horizon or IPDC?
 
This is the only EFM circuit, the others are fibre:

Bearer - EFM
Bandwidth - 2Mbit/s
Spare Bandwidth - 0Mbit/s
Internet Bandwidth - 1Mbit/s
No Channels - 7
Codec - G711
Monthly Circuit Rental - £182.00

It's for 6-8 pc users on office 365 and 8 or so phones with about 4-5 concurrent max
 
From the product spec it looks like they are reserving 'channels' (I hate that term with SIP since it's essentially made-up) for voice calls, leaving 1Mbps for internet access.

If internet access is that bad then use good old ISDN for phones and use the full 2Mbit for data. What's your postcode?
 
You must log in or register to reply here.
Back
Top Bottom