21CN and Broadband

Find out more about BT's 21CN Network

The present day - IPStream and DataStream

If you're using an "up to 8Mbps" ADSL connection (or slower) in the UK, the chances are that you are in fact using the BT Wholesale IPStream product. IPStream has been with us in one form or another since the ADSL roll-out began in 1999. It's a pretty simple product for the retail ISPs to work with; they just buy the tail circuits (i.e. your actual ADSL connection to the exchange) and "Central Pipes" from BT Wholesale - that's it. Central Pipes carry all of the ISP's users' traffic between the BT network and the ISP network. The downside to this simplicity is the lack of flexibility (i.e. fixed contention ratios, fixed bandwidth charges, no QoS), which in turn leads to retail ISPs offering pretty much identical products (with the exception of traffic caps).

DataStream has run alongside IPStream since launch and offers far more flexibility. An ISP using DataStream will still buy the tail circuits (the raw ADSL connections), but instead of taking a Central Pipe they will rent ports on the DSLAM (where your ADSL connection terminates in the exchange) and buy a VP (Virtual Path) at a certain capacity. This VP carries the data back to a POP (Point of Presence) of their choosing, so they can handle the backhaul to their network. Essentially, this is just the ISPs taking on the management of the backhaul, as opposed to BT handling it. The theory is that ISPs with their own networks could utilise these and realise significant cost savings.

However, DataStream has received an appalling reputation primarily due to certain ISPs' use of it. Whilst BT are quite good at managing capacity at the exchange, some ISPs have historically been shown to manage their VP capacity very poorly. This results in overcrowding of VPs, and ultimately very slow connections for end users. That said, DataStream can be very effective for specific purposes. For example, Cable & Wireless sell a 1:1 contended wholesale product on DataStream (each user has their own VP); a service like this is unobtainable on IPStream.

21CN wholesale broadband products

There are two main flavours of 21CN broadband product, which are summarised below:


21CN product structure
  1. IPStream Connect - A 21CN variant of the existing IPStream product, with all of the same options and pricing.
  2. Wholesale Broadband Connect (WBC) - The new broadband product offers up to 24Mbps ADSL2+, QoS and considerably more flexibility for ISPs. In addition to WBC, there also exists WBMC (Wholesale Broadband Managed Connect) and WBCC (Wholesale Broadband Connect Converge).
IPStream Connect

There isn't much to say about IPStream Connect (the 21CN variant of IPStream). It uses the same backend infrastructure as the WBC products (including the MSIL), and therefore allows ISPs to maintain the newer WBC connections and the older IPStream connections on one product from BT. Aside from this backend change, the same product set will be available as on the existing IPStream lineup. The launch of IPStream Connect has been pushed back to Summer 2008 now, due to problems found in testing.

Wholesale Broadband Connect (WBC)

The vanilla WBC product is the most flexible of the three. Crudely speaking, it is not that dissimilar to DataStream. But rather than having to rent capacity at every exchange from BT, the ISP has to install equipment ("have presence") at BT's WBC Aggregation Points (APs). There are twenty of these dotted around the country, and these are the same as the Core nodes discussed on the 21CN overview. One aggregation point will cover a region of the country, so an ISP would need to have presence at all twenty to cover the entire of the UK.


WBC backhaul

This is a significant improvement over DataStream, as there will be less incentive to micro-manage resources right down to the exchange level. ISPs then need to take backhaul to their own data centres. When purchased from BT Wholesale, transit to Aggregation Points comes in the form of Extension Paths (EPs) and a Multi Service Interconnect Link (MSIL). The Ethernet-based MSILs can be used to carry more than just broadband traffic - they are used throughout the 21CN network for voice traffic in addition to data. MSILs operate at 100Mbps or 1Gbps, although a 10Gbps variant is also being developed.

Using the above model, the ISP would have to pay for the tail circuits (the End User Access - EUA - as BT is now calling it), presence at the APs, EPs, MSILs and then their own backhaul. In addition to the cost of these, there is then the task of managing all of these components - something that the ISPs will not have had to deal with with IPStream (Note that a fully managed product called WBMC is discussed further down the page).

The WBC tail circuits (EUAs), which I suspect is what most readers are interested in, offer what we've all be anticipating (See table). These are as follows:

WBC Max 8Mb/s
(ADSL1 or ADSL2+)
WBC Max 24Mb/s
(ADSL2+ Annex A)
WBC Max M
(ADSL2+ Annex M)
DSL line rate (kbit/s) ATM payload rate (kbit/s) DSL line rate (kbit/s) ATM payload rate (kbit/s) DSL line rate (kbit/s) ATM payload rate (kbit/s)
Downstream Line Speed Adaptive 288-8128 kbit/s Adaptive 256-7320 kbit/s Adaptive 288-24384 kbit/s Adaptive 256-22083 kbit/s Adaptive 288-24384 kbit/s Adaptive 256-22083 kbit/s
Upstream Line Speed 448 Adaptive 64-448 kbit/s Adaptive 57-398 kbit/s Adaptive 64-448 kbit/s Adaptive 57-398 kbit/s N/A N/A
Upstream Line Speed uncapped Adaptive 64 kbit/s - uncapped Adaptive 57 kbit/s - uncapped Adaptive 64 kbit/s - uncapped Adaptive 57 kbit/s - uncapped Adaptive 64 kbit/s - uncapped Adaptive 64 kbit/s - uncapped

WBC product line-up [0]

  • WBC Max 8Mb/s - First up we have WBC Max 8Mb/s which provides essentially the same circuit as ADSL Max. However, as can be seen on all WBC products, there is an option for an uncapped upstream variant of the product. On standard ADSL (ITU G.992.1), this would allow for an upstream of up to 1Mbps. Interestingly, whilst the standard product has an upstream capped at 448kbps, there is no 832kbps capped product - which is what current ADSL Max business products are based upon.
  • WBC Max 24Mb/s - This is BT's first ADSL2+ wholesale product. As before, there is an option for having the upstream capped at 448kbps or having no cap at all. ADSL2+ can achieve up to 1Mbps upstream.
  • WBC Max M - This is an ADSL2+ Annex M product, as employed by Be* Unlimited in the UK already. ADSL2+ Annex M offers up to 2.5Mbps upstream in the UK. The news of this product is sure to please many businesses who could previously only find this level of upstream bandwidth with SDSL. Note that there is no option for a capped upstream with this product.
  • Fixed rate services - Finally, there are also options for three fixed rate lines - 512kbps, 1Mbps and 2Mbps. As with IPStream 500, 1000 and 2000, these have an upstream capped at 288kbps. Note that all of the other WBC products apart from these are strictly rate adaptive (like ADSL Max).

In addition to the above, all WBC products are available with QoS (Quality of Service), described in the article immediately below this.

Wholesale Broadband Managed Connect (WBMC)

In the same way that the vanilla WBC product could be seen as a replacement for DataStream, WBMC can be seen as a replacement for IPStream. This product is an end-to-end product, encompassing the EUA (End User Access), presence at the APs (Aggregation Points), EPs (Extension Paths) and an MSIL (Although the MSIL is purchased separately by the ISP). Ultimately this saves the ISP having to manage and maintain presence at the 20 WBC nodes (APs), which would involve considerable initial outlay and ongoing investment. The backhaul is also managed by BT entirely. On the other side of the coin this means the ISP is locked in to a BT platform - which may not necessarily be the cheapest - and it certainly does not offer all of the flexibility that an ISP using WBC would receive. That said, all of the same products and QoS options are available on WBMC as on WBC.

WBMC will also work with the old IPStream Central Pipes [1]. This could be particularly useful to ISPs who already have a large number of Central Pipes. These will likely have to stay in place for quite some time, as the 21CN roll-out will not be finished until 2012.

The final point to note about WBMC and WBC in general is that ISPs are free to mix and match coverage. So, if an ISP has very few customers in one part of the country they may opt to simply connect these customers via WBMC and not maintain presence at the WBC Aggregation Points. This would result in different costs for different areas of the country, but this is nothing new (there are already rebates given for 1016 IPStream exchanges). At present such cost differences are averaged out to form a single national price by the ISPs (although they do not have to do this).

Wholesale Broadband Connect Converged (WBCC)

There is relatively little public information available about this product. It is known to roll the voice and broadband products in to a package, with BT providing the ISP a single bill for both. Given that this product will again be based on WBC, one can only assume that the same product options and QoS would also be available.

QoS and Digital Line Management on WBC

Digital Line Management (DLM), which first made it's appearance with the launch of ADSL Max last year, will remain in place for all WBC products (except fixed rate products). In addition to the standard "fixed rate" and "fully rate adaptive" configurations, a new DLM configuration now seems to be available called "Banded". A line in a Banded configuration may only operate within the bounds of an upper and lower limit - this could be useful for people finding their lines re-syncing at 150kbps!

The QoS (Quality of Service) options are where the WBC products really stand out against IPStream. QoS allows you to prioritise certain types of internet traffic; so you could prioritise a VoIP phone call (which is sensitive to latency) above a large peer-to-peer download (which is far less sensitive). It is worth noting at this point that both 20CN and 21CN IPStream do have a limited form of QoS available to them (Best Efforts and Advanced Services - See BT SIN450). There are three QoS options for WBC:

  • Best Effort - This is the lowest level of QoS offered. Packets may be marked as "Normal" or "Priority", whereby Priority traffic receives preferential weighting of traffic. BT expect that ISPs will make these configurable by the end users as and when they launch applications that require it. How this might work remains to be seen, but BT's STIN refers to the use of DPI (Deep Packet Inspection) as a possibility. Further to this, a broadband line (EUA) will come preset with one of two levels of QoS:
    1. Standard QoS - Targets a minimum throughput of 2Mbps for 90% of the time over the busiest three hour period
    2. Elevated QoS - Targets a minimum throughput of 3Mbps for 90% of the time over the busiest three hour period
    With 24Mbps connections soon to become a reality, some might say that only being assured 2Mbps for 90% of the time is perhaps setting the targets a bit low. For the time being though, this would be sufficient for most video streaming services. It would certainly not be sufficient for HD (High Definition) content streaming though.
  • Assured Rate - Unlike the other two levels, Assured Rate QoS is session based. BT will initiate an Assured Rate session of the desired bitrate and duration at the ISPs request (providing their is sufficient capacity on the network) . So, for example, you may request to watch a movie online, and upon seeing this your ISP would set-up an assured rate session for ~2 hours.
  • Real Time - This is the highest level of QoS, guaranteeing the lowest possible latency (important in VoIP, online gaming and video conferencing). Unlike Assured Rate, Real Time QoS only operates at fixed speeds of 0, 220, 350 and 700kbps.

It is worth noting that QoS policies can be combined together in some instances. Note also that the QoS policies will only apply to downstream traffic - not upstream traffic [3]. Historically upstream bandwidth has been used far less than downstream bandwidth, but with the advent of peer-to-peer applications in recent years this tide is beginning to turn. The WBC Handbook does allow for ISPs to handle upstream QoS themselves, but this would only take effect from their network; so there would be no upstream QoS on the BT network at all, where contention could quite feasibly occur.

Wholesale Broadband Connect (WBC) pricing

Update (Jan 08): Firm and final WBC prices are expected by the end of January 2008.

It is important to stress that there is no firm pricing information available for the WBC product range at this time. However, BT Wholesale have released "indicative trial pricing" at the end of July 2007 [4]. This has changed significantly since January this year, so it is quite feasible that the final pricing could change once again before final indicative prices are revealed this November. Finally, remember that these are prices that these are wholesale prices - not retail prices.

Prices are split into three required components: the EUA (End User Access), rental of APs (Aggregation Points), and MSILs. There is also QoS pricing to consider.

End User Access rental

As with the present IPStream product, BT will offer ISPs cheaper EUA rental on 1016 "Band 1" exchanges. The "Standard" and "Elevated" service levels depicted in the table below refer to the Best-Efforts QoS setting installed on the line (See the QoS item for more).

Price band Standard service EUA rental Elevated service EUA rental
Band 1 (~1016 exchanges) £6.28 £7.98
Band 2 (~4500 exchanges) £8.04 £11.44

The price differences between the Band 1 and Band 2 exchanges are far more pronounced than on the existing IPStream products (Existing IPStream pricing, updated this May, can be found here). Whilst I know of no IPStream based ISP that does not average out the existing Band 1 savings across the entire country, the larger difference in cost between the bands could drive ISPs to rethink this policy. Charging different prices based upon a users region is commonplace with LLU operators already (e.g. AOL, TalkTalk, Tiscali).

The final thing worth adding is that there will be no charges for bulk migration during the WBC trials.

Aggregation Point rental

A provider desiring complete WBC coverage of the entire UK would require a minimum of 20 APs - one for each of the 20 WBC nodes dotted around the country. Similarly, an Extention Path and MSIL would also be required for each AP. The trial pricing table for APs and EPs is presented below.

Product Price
Aggregation Point rental £48,000.00 per annum
Extention Path rental £6,000.00 per annum
Charge for each contracted Mbit bandwidth £67.90 per month
Charge for each Mbit bandwidth over contracted amount £150.00 per month

One nice thing here is that providers have the option of bursting above their contracted bandwidth (Providing there is capacity on the EP and MSIL). This may help in situations where usage is extremely high, but it is undoubtedly something the ISPs would like to avoid given the price per Mbit of bandwidth.

MSIL pricing

At least one MSIL is required by all ISPs using WBC/WBMC. It is this product that delivers the broadband traffic from BT's network to the ISP's network (much in the same way that BT Centrals do in IPStream). For the purposes of the MSIL trial (commencing Autumn 2007), only a 1Gbps product will be available. At launch a 100Mbps product will also be available, and there is already discussion of a 10Gbps product in the making.

MSILs can be delivered to ISPs in one of three ways [5]:

  1. Customer Sited Handover (CSH): BT Wholesale and Openreach provide a point to point link back to the ISPs datacentre, typically via a WES
  2. In Span Handover (ISH): The ISP receives a fibre handover from BT immediately outside (within 100m) of a BT node
  3. In Building Handover (IBH): The ISP already has equipment in the BT node (typically an exchange) and receives a fibre handover internally

Trial pricing for the 1Gbps MSIL is as follows [6]:

  Connection Rental
In Building Handover £16,331 £12,024
In Span Handover £17,561 £12,024
Customer Sited Handover £27,267 £31,660 (+ £690 per Km main link)
QoS Assured and Real Time pricing

As with the EUAs, QoS pricing is again split by the exchange bands, with the differences being very large. The trial pricing for the two products is shown below [7]

QoS Product End User Charge (per month) Session Charges AP Bandwidth Charges
Assured sessions Band 1: £0.40
Band 2: £3.40
1.5p per session + 0.006p per 100Kb/minute £20/month per Mbit contracted
£50/month per Mbit over contract
Real Time Band 1: £2.20 for 220kbps
Band 1: £3.20 for 350kbps
Band 1: £6.20 for 700kbps
Band 2: £6.00 for 220kbps
Band 2: £9.00 for 350kbps
Band 2: £18.00 for 700kbps
Not applicable £70.00/month per Mbit
(in addition to the £67.90 p.m for each contracted Mbit)

Consult21 presents a nice example of how Assured Rate sessions might be used in the pricing of online movie distribution [8]. Naturally this depends on a whole host of variables, but as a rough guide BT's price estimates vary between £1.00 and £0.65 per movie (based upon a length of 110 minutes, streamed at 1600kbps).

Wholesale Broadband Managed Connect (WBMC) pricing

WBMC, the little brother of WBC, has also had its trial prices released. All information in this article is based upon prices publicly available in [9].

Remember that WBMC still requires ISPs to purchase EUA tail circuits, which will be priced the same as WBC EUAs (See previous article). WBMC takes away the cost and trouble of dealing with Aggregation Points and Extension Paths. Instead, ISPs are given a fixed monthly cost per Mbit/s and then just have to take a link back to their own POP where the traffic will enter their network.

Trial pricing for the shared aggregation service is shown below.

Connection Rental
WBMC contracted bandwidth charge £0.00 £107.00/Month per Mbit/s
WBMC fixed charge per end user £0.00 £0.35/Month

Comparing WBC and WBMC prices side by side, it is easy to see how larger ISPs might be tempted by WBC. Whilst £48,000 and £8,000 for each AP and EP is far from pocket change, the £67.90 per Mbps per Month charge in WBC is a massive saving over the whopping £107.00 per Mbps per Month charge in WBMC. If the ISPs have the cash and the number of customers to make it worthwhile, WBC is the clear winner here. Of course, as highlighted previously, ISPs can choose to use WBC in parts of the country where they have lots of customers, and WBMC in others.

Pricing for the host link (back to the ISP's POP) is shown below.

Link speed Connection Base annual rental Annual rental (Host link)
100Mbps £2750.00 £3025.00 £0.54 per metre
1000Mbps £5200.00 £8250.00 £0.54 per metre

This is presumably a WES based circuit, given the similarity in pricing to BT Openreach WES pricing.

Since this item was originally written in August 2007, BT Wholesale have announced the addition of a "dedicated" WBMC service. Unlike the shared service, the dedicated service uses dedicated links (either 1Gbps or 10Gbps) between the WBC aggregation points and back to the ISPs infrastructure. As one might expect, there is a hefty charge for this option!

Migrations to/from the new WBC family

Migrations will be supported between the WBC family of products and IPStream, DataStream and LLU. When migrating between IPStream and WBC (and vice versa), no re-jumpering at the exchange will be required and under 35 minutes downtime is expected (i.e. a similar level of service as is received when migrating between IPStream providers at present).

When migrating between WBC and LLU or DataStream, re-jumpering would be required. This would of course have to be handled by BT Openreach, so the standard downtime applies.

How the migration process will operate is unclear at present, but one can only assume that BT will continue to use MAC codes. One related thing that is changing in is that CBUK codes will not be used in WBC. These will be replaced by a BBEU code.

Finally, it is important to stress once more that 21CN will not affect LLU at all. LLU will continue to use the same copper pair to the end user as it does now.