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contended service

Danish translation: konkurrende service


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English term or phrase:contented service
Danish translation:konkurrende service
Entered by: Kate Persson
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13:03 Oct 23, 2002
English to Danish translations [PRO]
Tech/Engineering / IT manual
English term or phrase: contended service
There must be a spelling error, I think contended is correct
Kate Persson
Local time: 10:44
konkurrerende service
Service er brugt i IT. Contended kan oversættes til stridende eller lignende.
Selected response from:

Suzanne Blangsted
Local time: 01:44
Grading comment
Det er helt sikkert det mest korrekte, når jeg ser sammenhængen. Tak og goodnight.

4 KudoZ points were awarded for this answer


Summary of answers provided
4konkurrerende serviceSuzanne Blangsted
4delt båndbredde
Sven Petersson



39 mins   confidence: Answerer confidence 4/5Answerer confidence 4/5
delt båndbredde

A wee oversimplification but ....

From reference:

You will see the term contention used throughout the description of the ADSL service, and other services such as BTnetstart, etc. Contention is a complicated issue to explain properly. The simplest explanation is that a contended service is a shared service - however this in itself is far too simplistic.
A key point to remember is that the internet is a shared service at all levels. No one server or web site has sufficient capacity to allow every single user of the internet to transfer every page from that server as fast as their link can go. Everything is shared.
Contention ratios
Firstly, what is the contention ratio. You will see 20:1 quoted as the contention of the BT office/ethernet ADSL service. This means that at a specific point (in this case the local BT exchange) there will be 20 times as much capacity to the end users as to the next point in the link. e.g. 100 x 2Mbps ADSL customers in to a 10Mbps pipe. 100x2=200 which is 20x10, i.e. 20:1
The internet is made up of links between computers and networks. The traditional dialup internet connection consists of one or more computers at your end, and a link via a modem or ISDN line to an internet provider. That provider has lots of customers. The ISP has a number of ports or modems for dialup. The ISP then has on-going links to other ISPs (the internet). Just this example has several points of contention or sharing. Lets assume a small network on a ISDN router.
More than one machine may be connected to your internet link, typically using a 10Mbps or 100Mbps network. This is then fed via a 64Kbps link to your ISP. This means contention of several computers at high speed all trying to use the same small 64Kbps link. In this case it is easy to see that if two users on the network try to transfer data at full speed then they will typically get 32Kbps each. This is a packet by packet contention - you get a reduced speed as some of your packets don't make it and some do so transfers slow down automatically to fit.
The 64K link to the ISP is not shared as such - but the ISP will not have a port for each and every possibly user. If every one of the ISPs users were to dial up at exactly the same time you would get a busy tone some of the time. This is a circuit connected contention - you get a link or you don't and there is probability.
The ISP will have a number of ports and then links to other ISPs. The links to the other ISPs will add up to less than the total of the 64Kbps links to customers. This is a packet level contention where if every ISP connected customer tried to transfer 64Kbps at the same time then they would slow down.
The various links in the internet are also contended/shared with increasing numbers of people and ultimately some web server will have a link to their ISP which will only be a specific size, so that everyone (in the whole world) who might want to get to that site has to share with everyone else.
As you can see - a lot of sharing. What you have not seen generally is the contention levels being published. ISPs will ensure they have enough ports so that at peak times there are a few spare so that nobody gets busy tones - there is no point in them having any more. Once upon a time ISPs would work on 20:1 user:modem rations or worse - i.e. a modem for each 20 users. These days they tend to work on lower (better) contention figures, especially as ISPs usually get revenue from calls that come in. As for capacity to the internet the ISP will also work on having enough, i.e. some headroom at busy times, and again there is no point in having any more. They probably don't even know the contention ratio unless they work it out.
As long as any link has some spare capacity and can cope with the peak demand, the fact that it is a shared service does not matter. This is simply because you just don't get everyone trying to transfer data all at the same time.
Full links
Until a link gets full the contention is irrelevant - no packets are lost so it is the same as an uncontended link. As soon as things start getting full then you notice. There are two effects.
High latency - the routers will hold on to some packets for a while waiting for previous packets to go through the link. This allows very short bursts of traffic to manage without dropping packets but means that packets are delayed - adding latency. This means things are less responsible, and it is very important for on-line interactive games to have low latency.
Dropped packets - if the routers buffers get too full then packets are dropped. This causes the transfer of data to slow down to accommodate the speed that is possible. Dropping packets is the way the internet protocols manage overloaded links and does not mean you get gaps in you web pages, just that they are slower. You could also see odd pauses.
A good analogy is a funnel with water going through it. Put a bit cup of water in the funnel and it will fill up while the water goes through the hole as fast as it can - you can see some of the water took some time to go through. Put several big cups in and eventually the funnel overflows at the top (dropped packets).
Pipe size
This point of having spare capacity at busy times is what is important. To do this you have to have the advantage of large numbers of customers on your side. A 2:1 contention where you literally have 2 PCs on one internet link results in one person clearly and noticeably slowing down the other when they access the internet.
A 20:1 contention by having 20 x 2Mbps customers in to one 2Mbps link to the internet is not good. One customer alone can fill the pipe. If there are two, then they both notice a big slow down. However a 20:1 contention by having 100 x 2Mbps customers in to a 10Mbps pipe and you have a different story. In that case it would take 5 customers using the service at full speed before a 6th would cause any slow down. This is far less likely that 2 users filling their pipe at the same time, and the effect of that extra user is less.
So, the bigger the pipe, the better - simply because it is more likely that everyone's normal usage of their links will fit in the big pipe's capacity and less likely for lots of people to want the transfer lots of data at exactly the same time. We look at usage and our planning rules ensure 100% extra capacity to ensure we are not the bottleneck even at peak times.
Leased lines vs ADSL
A leased line internet connection is an uncontended service. This means if you pay for 2Mbs then you get 2Mbs - all the way to your ISP, and the usage of other customers cannot affect that.
The way such ISPs work is that they have a number of leased line customers, and feeds to other ISPs (the Internet) - but still they do not have the links to the Internet totalling the full capacity of their leased line customers. There is contention. The ISP will allow enough capacity to have some headroom even at peak times, but that may well be a 20:1 contention. BT looked at the contention in use before deciding on the 20:1 and 50:1 contention ratios they use for ADSL. From our own experience, letting people use as much as they want, people do use around the 5% of what they could, on average - i.e. 20:1 contention.
Until the links get full, the fact that there is contention is not relevant at all. So, if the natural level of usage of an ISP happens to be 20:1 or worse, then using ADSL links to connect to their customers is not any different than using uncontended leased lines. The overall usage will be low enough to ensure pipes do not get full.
The ADSL service is also uncontended, but only to the local BT exchange.
Some actual numbers
Within BT there are two services for ADSL connection and two places for bottlenecks. At each local exchange there are virtual paths to which users from all ISPs are connected. What we have been told is that these are 10Mbps for Office services at 20:1 contention, and 12.5Mbps for Home 500 are 50:1 contention. It may be that these are bigger. There is then a possible bottleneck where all of our customers connect to us - at the fat pipe end of the service. Here we aim to allow 100% extra capacity over normal usage levels to allow for bursts and peaks in traffic.
So how fast will it go?
We cannot guarantee anything - you are connected to the internet. We are not saying your line will go at most at 1/20th of your speed. In fact most of the time, when you want it, your link to us will be the full speed you have ordered. What happens then is down to the internet. The only way you can be sure it to try it yourself.
We have tested 2Mbps ADSL links, transferring data from the UK academic mirrors site at peak times during the day and got a sustained near 2Mbps transfer rate (i.e. over 245KBps). Obviously if all our customers did this at the same time, then we would not see this. They don't, and that's the whole point.
Playing fair
What is fair? We have no objection to people downloading the occasional 650MB ISO CD image. If people are, overall, on average, using the amount 20:1 suggests then everything will work. It's not a hourly limit or even a daily one - its a question of overall usage across all of our customers being fair.

As we are allowing ample "head room" on our links to BT and the internet, for our office products we use a bench mark based on 10:1 contention - i.e. 1/10th of the maximum you could transfer in an hour.

For Home 500 the average per user rate works out at about 10MB/hour. For office 500 this is about 20MB/hour. For Office 1000 this is about 40MB per hour and for Office 2000 this is about 80MB per hour. However but these are not hard limits . In practice some customers use less and some use more. What is not playing fair is to use a 500Kb/s link to load 5GB a day every single day. Lower levels of usage are a grey area, and there has been lengthly debate in newsgroups on what is a fair usage without a clear concensus. We will consider usage reasonable as long as the total usage for all customers is within the sharing level we sell the service. If its not, then it will be the highest users (relative to the service they have) who we will talk to.

We do have some all you can eat high usage packages available for those that expect to use a lot of internet traffic, or simply do not want to worry about usage. Whilst they use the same connection via BT, we have priced these to cover the possibly 100% constant usage of the service, so our other customers are not subsidising such high usage.
Its important to realise that the rest of the services are not an all the bandwidth you can eat, and just because you can download 5GB a day on a 500Kb/s link, every day does not mean that it is acceptable. We provide a lot of headroom to ensure a good service, but the costs are worked out on the 20:1 (home ) and 10:1 (office) sharing. Our planning rules actually provide an additional 100% bandwidth for peaks in traffic, and we often have many times this. If anyone uses the service in a way that would affect the service we offer to other customers, which includes simply making the service non viable financially, we may take action to limit bandwidth. We hope never to have to do this, and it is very rare that we have to contact a customer regarding their usage.
Generally, the fair play policy has worked well, and we are pleased to say that have never kicked anyone off the service.
So, play fair and share sensibly. Use the service for what you need and don't waste bandwidth. We do provide on-line bandwidth usage logs for your benefit, and this can be helpful when managing a large office. We even had one customer found that an unused PC was on, playing an internet audio stream with the sound muted for weeks and this was slowing their internet service down. If you do want to do very long on-going data transfers every day then it would be fairer and you would have more bandwidth available to do this at off peak times (peak times are generally 9-6 Mon-Fri). Help us maintain one of the best quality services by making responsible usage of the service.
Have fun.

    Reference: http://aa.nu/adsl/info/contention.html
Sven Petersson
Local time: 10:44
Native speaker of: Native in SwedishSwedish, Native in EnglishEnglish
PRO pts in pair: 672
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2 hrs   confidence: Answerer confidence 4/5Answerer confidence 4/5
konkurrerende service

Service er brugt i IT. Contended kan oversættes til stridende eller lignende.

Suzanne Blangsted
Local time: 01:44
Native speaker of: Native in DanishDanish, Native in EnglishEnglish
PRO pts in pair: 2808
Grading comment
Det er helt sikkert det mest korrekte, når jeg ser sammenhængen. Tak og goodnight.

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