Contention ratios

beyers · Nov 30, 2003

Can someone tell us more about contention ratios? How does it work. If the ratio is 50:1, does it mean all of us share the same 512K, for example. Then I will never get the full 512K in theory....?

What are good ratios on an international standard?

ProAsm · Nov 30, 2003

Contention Ratio.
Lets use a 512k ADSL system for instance.

Basically the ideal Contention Ratio for any connection would be 1:1 or expressed as 512:1
This means that the Service Provider can guarentee you a 512k connection 24/7/365 but it would cost you a fortune, probably in the region of R27000 pm.

So ISP's utilize varing Contention Ratios with the average being 50:1 or expressed as 512:50 which is still excellent.
This means in ADSL terms, the DSLAM you are connected to at the exchange you will share with 50 other users.
Now if all 50 users are all downloading at the same time your download speed theoretically will drop to 512/50 = 10.24 kbits (1.28 KB/sec)

Now because the way data is transmitted on the Internet this is highly unlikely to happen.
For instance, Telkoms ADSL has a Contention Ratio of 512:40 (stand to correction here) which means the DSLAM you are connected to at the exchange holds 40 connections.
Now how many people in high density areas have ever had their ADSL drop to 1KB/sec as 40 connections there is easy to achieve.
Now although a 512:40 looks good and is according to world standards, they go and destroy that by adding a Cap - so at the end of the day you would have been better off with a 512:200 system for instance.
ISDN is in the region of 128:200 - has anyone ever complained there ?
This is where software monitors who are hoggers and who is not and spread things around a bit to even the playing field so to speak.

Basically at the end of the day, the higher the Contention Ration the cheaper the ISP can offer the system.

Why everyone is suddenly worring about Contention Ratio I dont know because at the end of the day all you want is a good and reliable connection, with good pings and decent downloads.
ISP's spend 1000's of Rands on Software to take care of this.

Some information I found and links to follow:

<blockquote id="quote">quote:<hr height="1" noshade id="quote">If the server has a 100kb connection to the net, and there is a connection of 1:1000 - and ALL 1000 sites have a page of 1kb on them, and 1000 different people from 1000 different ISP's all access a site at the exact same time, then 100% of the server bandwidth will be used.
If, however, 2000 people from 2000 different ISP's all access a site at the exact same time, then 200% of the bandwidth is used (which cant happen), so half the people are "given" the file, and then the other half are "given" the file.<hr height="1" noshade id="quote"></blockquote id="quote">
<blockquote id="quote">quote:<hr height="1" noshade id="quote">This describes the maximum number of users sharing the bandwidth on the connection between your local exchange and the Internet Service Provider.. A customer with a contention ratio of 20:1 never has to share this bandwidth with more than 19 other users<hr height="1" noshade id="quote"></blockquote id="quote">
<blockquote id="quote">quote:<hr height="1" noshade id="quote">Contention ratio is the term used to describe the situation whereby customers share capacity on a line or within a network. For example if everyone in Cork phoned someone in Dublin at the same time, not all calls would get through because there is only a limited number of circuits between Cork and Dublin. But the chances of this happening is extremely remote so the contention ratio used has little effect on the service to the customer. However if the number of circuits was further reduced people would begin to notice a reduction in the quality of service (i.e. more busy tones when they try to ring Dublin) so the balance is whats important here.
For IP traffic a contention ratio is even less of an issue (provided the ratio is not extemely high) because, unlike voice telephony, Internet traffic is 'bursty' in nature: when a customer is connected to the Internet they do not use 512kbps at all times. Browsing the web may only use a part of this bandwidth for a number of seconds then none at all until the customer loads the next page.
The 'contention ratio' is the ratio of bandwidth sold to bandwidth provided on the backbone: in eircom's case the contention ratio is 24:1 (48:1 on "starter"), meaning that for every 24 1Mbps connections sold, 1Mbps in total is provided on the backbone for them to share. 48 customers would share 2Mbps and so on. This is about the usual contention ratio for business-class DSL services worldwide .
We do not give any guarantees to customers on contended links, however the chances of them experiencing poor service on our services are low. Remember i-stream is a best effort service and should be sold as such. Remember also that this service connects them to the internet!!!. If congestion is experienced on i-stream the chances are that they have hit a slow connection some where on the internet.<hr height="1" noshade id="quote"></blockquote id="quote">
<blockquote id="quote">quote:<hr height="1" noshade id="quote">In real terms, If you are connected to a 1 MB connection with a 20:1 contention ration, this means that 1MB is provided for a group of 20 users. However, the contention ratio does not apply to one single group of users in the same area. So for 1000 users, 100MB would be available, shared between all 1000 users. Therefore the contention ratio will only affect your connection if all 1000 users on your exchange are online and saturating their downstream link. This is incredibly unlikely due to the sporadic nature of Internet traffic.
Normal Dial up connections are `negotiated' rather than contended. This means that once the maximum number of users are connected at one time, no other users can connect. This is when you would hear an engaged tone. A Contended service means that this never happens, the bandwidth simply redistributes itself depending on how many users are connected.<hr height="1" noshade id="quote"></blockquote id="quote">
http://www.idnet.net.uk/broadband/contentionratio.html
http://www.getonlinebroadband.com/faqs/faq02.html
http://www.getonlinebroadband.com/faqs/faq29.html

chopsky · Nov 30, 2003

Earlier in the forum, Karnaugh suggested that perhaps ProAsm shouldnt have told all of us about the Contention Ratio Sentech will be offering as then we wouldnt be worrying. I think now that ProAsm has provided us with all the necessary info(as shown above), we can all be quite satisfied that Sentech are going to offer us all a great service and that there is indeed nothing to worry about.

Big up to ProAsm!
First month, Im signing on.

beyers · Dec 1, 2003

Thanks ProAsm for the information. It is appreciated.[

]

jus · Dec 3, 2003

At the end of the day contention ratio is the only viable business model for broadband (and even any kind of Internet connectivity) sales from an economic standpoint. It is completely in line with international norms, and 50:1, 20:1 ratio's for residential and business respectively are standard overseas in countries such as the UK. Every ISP operates with contended bandwidth, otherwise they won't succeed as a business. Dial-up style connections are typically contended in the hundreds to one, and Diginet connections even with CIR's are in the region of 15:1 - 20:1. Obviously this differs from ISP to ISP, but in general you pay for what you get, and better ratio's or CIR's cost more.

The reality is as ProAsm said, networks and bandwidth can be carefully managed to ensure a good level of service all round, otherwise no one would buy the access.

Also, with the MyWireless system, it works the other way round to the consumers advantage at some times as well: While if the cell is heavily loaded you will not see such high bandwidth, while the cell is not being used you will probably burst to even higher speeds than you are paying for.

This is because the contention is at a cellular level (35mbit:1000 users) rather than a per-connection level.

I stand to be corrected on some of the details, though...

-jus

chopsky · Dec 3, 2003

<blockquote id="quote">quote:<hr height="1" noshade id="quote">For instance, Telkoms ADSL has a Contention Ratio of 512:40 (stand to correction here) which means the DSLAM you are connected to at the exchange holds 40 connections.
Now how many people in high density areas have ever had their ADSL drop to 1KB/sec as 40 connections there is easy to achieve.
Now although a 512:40 looks good and is according to world standards, they go and destroy that by adding a Cap - so at the end of the day you would have been better off with a 512:200 system for instance.<hr height="1" noshade id="quote"></blockquote id="quote">

Would you rather have 512k:40 or 35mbit:1000?
Let's take a look

35mbit(35840k) / 512k = 70
70 * 40(users per 512) = 2800

Thus Telkom's ADSL in comparison = 35mbit : 2800

Now is Sentech's 35mbit:1000 really THAT bad? I think not... [^]

Zeliard · Dec 3, 2003

35mbit:1000 is great[^], provided that the same or better "contention" ratios are maintained throughout your communication path (i.e. local/intl links). In any event, the narrow-most point will become the bottleneck.

Karnaugh · Dec 3, 2003

The international standard for ADSL is 50:1 in general as ProASM said.

Sentech's 35Mbps:1000 works out to 70 512K connections to 1000 people, a contention ratio of 14:1.

Some other points to note...

Contention ration does not give an acurate idea of the service that you can expect at all. For instance, it may be 40:1 on ADSL, but there are only 2 peering points into the IPNet from there - Thus each half of the ADSL users are routed via Bellville and Rosebank into a ~100Mb connection. For 1:1 (IE, everyone downloading at 512Kbps similtaneosly over the same route) that would allow for 400 ADSL users. International contention gets even worse.

<hr noshade size="1">iActive internet services
http://www.iactive.co.za

jus · Dec 5, 2003

And let me add that a 14:1 contention ratio is exceptionally good. It is way better than ADSL, ISDN, even most Diginets.

-jus

mithrandi · Dec 5, 2003

Exactly. I might add that on my 128K ISDN connection via SAIX (which is what, 100:1 contention?), I have absolutely no problems maxing the connection almost 99% of the time I am online; and that's on international traffic. So, really, there's nothing to complain about as far as Sentech contention ratios are concerned.

mithrandi

Doomy · Dec 12, 2003

Hi Guys,

1st time poster. Lets just say, its more in the region of 20-30:1 ratio. Currently we are trying to get it down to 20 or below, but for know count on 20-30

Doomy out.

PierreLeRiche · Dec 12, 2003

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by mithrandi
 Exactly. I might add that on my 128K ISDN connection via SAIX (which is what, 100:1 contention?), I have absolutely no problems maxing the connection almost 99% of the time I am online; and that's on international traffic. So, really, there's nothing to complain about as far as Sentech contention ratios are concerned.

mithrandi
<hr height="1" noshade id="quote"></blockquote id="quote">

Your logic is flawed. With ISDN you pay for the time that you are online. The usage patterns are therefore completely different. DSL users are always online (as will MyWireless users), and if there's no cap they will leech like crazy. Most ISDN users are only online for a short period during the day to get their e-mail and to do light web browsing - anything more and it becomes too expensive. I have reason to believe that the percentage of people taking advantage of ISDN + R7Call to leech all night and all weekend is quite low.

Karnaugh · Dec 12, 2003

Err no, *your* logic is flawed.

*some* DSL users use it for downloading crap loads of porn etc. Alot of them are companies that use it during the day for just pulling mail ever 15 mins or so.

Thing is for the connection to saturate, *every* person would have to be using their full line at that exact nanosecond, an unlikely event.

Also see multiplexing... [|)]

<hr noshade size="1">
"Since light travels faster than sound, people appear bright until you hear them speak."

NetLink Research

PierreLeRiche · Dec 13, 2003

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Karnaugh
 Err no, *your* logic is flawed.
<hr height="1" noshade id="quote"></blockquote id="quote">

*sigh* let me explain it again:

DSL users don't download because they can't (cap and port shaping). MyWireless won't have restrictions on download so you can expect the usage of a typical user to be greater than a typical DSL user and way way greater than dial-up users (who aren't even connected for 95% of the day).

The "safe" contention ratio is determined by the typical usage pattern of the users. If usage is typically very light (dial-up) then you can stack the contention ratio, but if users will use it more often (uncapped, always-on services) you have to have a lower contention ratio to have a reasonable service level (i.e. percentage throughput of the maximum).

Come on, it's not that hard to understand...

Whether the 35mbit/1000 will be enough only time will tell. Just because ISDN works well with a 200:1 contention does not guarantee anything for MyWireless.

Karnaugh · Dec 14, 2003

Um, no, you are still wrong.

A good percentage of the users do not download because they dont need to.

<hr noshade size="1">
"Since light travels faster than sound, people appear bright until you hear them speak."

NetLink Research

PierreLeRiche · Dec 14, 2003

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Karnaugh
 Um, no, you are still wrong.

A good percentage of the users do not download because they dont need to.

<hr noshade size="1">
<hr height="1" noshade id="quote"></blockquote id="quote">

What's your point? Did you even read my posts, or are you just trolling?

My original post was in response to Mithrandi who claimed that because a 200:1 contention ratio works well for ISDN it would automatically mean that the MyWireless contention will be equally great (i.e. you almost always get the maximum advertised speed).

I have now explained twice why you cannot make that assumption. Are you trying to tell me that Analog dial-up, ISDN dial-up, DSL and MyWireless users all have the same usage patterns? That's rubbish...

microfast · Dec 14, 2003

<blockquote id="quote">quote:<hr height="1" noshade id="quote">
Originally posted by Karnaugh
Um, no, you are still wrong.<hr height="1" noshade id="quote"></blockquote id="quote">
<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by PierreLeRicheWhat's your point? Did you even read my posts, or are you just trolling? <hr height="1" noshade id="quote"></blockquote id="quote">

Hi PierreLeRiche,

ignore him, he had a bad day a while back, seems like it's lasting the whole month.

There's no light at the end of this fellas tunnel [

]

jus · Dec 14, 2003

I think the point is to compare apples with apples, and not another fruit. 35mbit:1000 still represents a better contention ratio than found with many DSL connections in first world countries.

-jus

ProAsm · Dec 15, 2003

A point that everyone seems to misunderstand about Contention Ratios regarding Wireless networking.

Not like ADSL or ISDN which operates on a fixed line, Wireless cannot be determined on a single or a number of connections, simply because you radiate signals in many directions and it is possible to enter several cells at the same time.
So calculating 35mbit / 512 etc, or refering to 20:1 or 50:1 is not really correct.
It is therefore that Wireless Contention Ratios are calculated at the network output of the cell.

mithrandi · Jan 3, 2004

<blockquote id="quote">quote:<hr height="1" noshade id="quote">MyWireless won't have restrictions on download so you can expect the usage of a typical user to be greater than a typical DSL user and way way greater than dial-up users (who aren't even connected for 95% of the day).<hr height="1" noshade id="quote"></blockquote id="quote">

I don't follow; I don't see why the usage profile of MyWireless users would be so incredibly different from dial-up. It probably won't be exactly the same, but I'd expect it to be reasonably similar; ie. that power users will be a fairly small minority. In fact, if the majority of users are power users, then I would expect Sentech to go bankrupt from what would then be a flawed business model.

mithrandi

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