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Broadband Symmetric Q&A
1. What is SHDSL technology?
SHDSL is the acronym for Symmetric High bit rate Digital Subscriber Line.
SHDSL is one of a number of services that utilise digital subscriber line (DSL)
technology. It is a technology which allows high speed digital transmission
over copper telephone lines. Maximising the frequency capacities of copper,
SHDSL can tap into what can be massive amounts of unused capacity, to
carry high-speed data traffic at the same rate in two directions. This identical
'Up-stream' and 'Down-stream' data transfer speed means that information
can be simultaneously received at the same speed that it is sent back.
2. What services are you are offering?
Our SHDSL products are referred to as Broadband Symmetric and we offer
two variants as follows:
BT IPstream Symmetric
is a one-to-many broadband service that enables
customers to develop their own digital packages and deliver them to an
unlimited number of End Users via an IP based data network.
The BT IPstream Symmetric service enables symmetric IP connectivity
between customers and their End Users providing a SHDSL interface. End
Users are connected to the Customers BT Central link over BT's High Speed
Data Network. The contention level over BT's Network is managed by BT.
The service is aimed at End-Users who require business class connectivity to
their Service Provider with higher upstream data rates than those offered over
the ADSL variants. The service is ideal for applications such as fast file
transfer and web hosting.
BT Datastream Symmetric
is aimed at Service Provider’s and Network
Operators to sell on to the Small to Medium Enterprise (SME) and Corporate
The service enables Customers to offer LAN interconnect, file transfer, video
conferencing, VPNs, derived voice and other data transport applications
requiring a symmetric traffic flow capability to their End Users.
The service will offer multiple Virtual Circuits (VC) to your End User and a
range of ATM service categories to enable different applications to be
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3. What is the difference between ADSL and Broadband Symmetric?
Asymmetric DSL products such as BT IPstream allow information to be
transmitted at greater speed, in one direction than another. So for instance an
ADSL product may be able to receive information at speeds of up to 1Mbps
and be able to transmit at up to 256kbps. Broadband Symmetric products are
able to send and receive information at identical rates.
4. Is Broadband Symmetric better than ADSL? Will it supersede ADSL?
Broadband Symmetric and ADSL provide complementary solutions suited to
supporting different applications. For example ADSL is ideally suited to end
users who generally want to download material from the web, whereas
Broadband Symmetric is more suited to applications where there is a more
equal flow of data such as the e-mail and net meeting applications suited to
the SME environment. Broadband Symmetric is priced higher than ADSL
which is more suitable for consumer use where symmetric bandwidth is less
of a requirement.
5. Why such a big difference between ADSL and Broadband Symmetric
The Broadband Symmetric prices are set with three drivers in mind;
1. The need to recover the costs associated with a start up business over a
reasonable time period
2. The need to recover product development costs over a reasonable time
3. Consideration of the market price for the product
these costs, together with the volumes associated with a business' market
offering, have led to the price design.
6. Does Broadband Symmetric go further than ADSL?
Indicative reach figures for our Broadband Symmetric products are shown
below. These vary depending on noise and copper dimensions.
256Kbit/s – 3.9km
512Kbit/s – 3.4km
1Mbit/s – 2.5km
2Mbit/s – 1.6km
7. What speeds will it operate at?
Typically speeds up to 256Kbit/s, 512Kbit/s, 1024Kbit/s and 2048Kbit/s
including ATM overheads.
8. Who will Broadband Symmetric benefit, business customers or
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BT Wholesale aims to offer this service to service providers and OLOs who
we anticipate will be targeting the business market.
It provides a versatile solution that has high push / pull bandwidth available
and all the associated benefits of broadband. Customers can send and
receive the same quantities of information both ways simultaneously – this is
particularly useful for e-mail, netmeeting, conferencing, web hosting, and
business to business applications.
9. How does Broadband Symmetric fit with traditional leased line
The Broadband Symmetric market is expected to be a new, growing market
rather than substitution for leased lines. We do expect a small amount of
migration from leased line products to broadband products but we expect the
leased line market to continue to grow. The shared nature of the broadband
infrastructure means Broadband Symmetric products would not be
appropriate to all applications used over a dedicated leased line.
10. When will you be offering 2.3 Mbit/s?
Currently there are no plans to launch a 2.3Mbit/s service however BT
Wholesale is continually developing it’s product offerings to meet the
requirements of it’s customers. BT Wholesale is not convinced with the
demand for this product due to reach limitations.
11. When will you be offering dual pair operation?
There are no plans for BT to offer dual pair operation.
12. What are the contention ratios on these Broadband Symmetric
services compared to ADSL?
Reflecting the type of market these products are being aimed at, the
contention ratio is up to 10:1 as opposed to up to 50:1 for mass market ADSL
13. When do I order my BT Datastream Symmetric service package?
All orders for the BT Datastream Symmetric service packages need to be
placed at the same time as the order for the corresponding VPs.
14. Can I use BT Datastream VPs for ADSL and Broadband Symmetric?
No, Broadband Symmetric Virtual Paths (VPs) are designed in multiples of
256kbps. The VP sizing has been designed so that it exactly matches the
ATM rate in the end user access. This allows one Virtual Circuit (VC) to
match one VP enabling service providers to offer a fully un-contended
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service. If the VPs were designed to offer multiple VCs then it becomes
impossible to offer an un-contended service for end users.
15. Can I mix ATM service categories on VPs?
No, by only allowing one ATM service category on a single VP BT are
optimising the performance of the network and allowing traffic prioritisation for
end users. BT associate ATM service categories with virtual paths (VPs)
rather than virtual circuits (VCs). Within a CBR VP there would be high priority
traffic which is delay sensitive, therefore needs to be routed across the
network with minimal delay and no loss to ensure the end user experience is
meet. If UBR traffic was mixed with CBR traffic then low priority traffic would
get mixed with high priority traffic and would be treated in the same way
which, could have detrimental affects for end users.
16. Do I need to order a new copper pair to get Broadband Symmetric?
The copper pair is integrated as part of the Broadband Symmetric service.
The Broadband Symmetric service assumes that is can be provided on an
existing spare copper pair. A spare pair is an unused pair which exists from
the BT exchange to the distribution point which serves an end users
premises. If a spare pair does not exist new copper can be installed at an
additional cost depending on the work required.
17. Does the connection charge for Broadband Symmetric include the
Yes, if there is a spare pair ( where copper exists from the exchange to the
DP that serves the site). If new copper needs to be run from the exchange
then there will be an additional installation charged dependant on the work
involved. This will be treated in a similar manner as LLU charges.
18. Can I use ADSL modems for the Broadband Symmetric products?
The Broadband Symmetric Products require modems that support SHDSL
technology. Modems that support other technologies such as ADSL can not
19. Will there be any Customer Premises Equipment (CPE) included?
BT will not provide CPE as part of this service, other parts of BT Wholesale
may be able to offer CPE as part of a managed service. Customers or end
users using Broadband Symmetric must provide, install and maintain their
own CPE. BT provides a CPE test lab at Adastral Park where CPE vendors
may evaluate their equipment against a reference model of the BT Wholesale
20. What diagnostics are being used for Broadband Symmetric?
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BT IPstream Symmetric uses the WOOSH suite of diagnostic tools. BT
Datastream Symmetric requires the Service Providers and OLOs to support
ATM OAM functionality according to ITU T I6.10 at their main site and on the
end users CPE. For full details please refer to SIN 404
21. What service level is included?
BT Wholesale provides a standard care service level for its Broadband
Symmetric products in tariff. This provides a 40 hr clock clear for all reported
22. What are your service availability figures for your products?
BT will not be offering service availability figures for its Broadband Symmetric
products. However, Service Level Agreements for provision and repair will be
available from launch.
23. When will you be offering through-put guarantees?
BT has no plans to offer through-put guarantees for its Broadband Symmetric
24. What SLA's/SLG's are available ?
Broadband Symmetric is available with SLAs on end user provisioning and
repair similar to those being offered by the ADSL products. SLGs will be
considered once the product is established.
25. Is there an enhanced service package available for Broadband
Symmetric products as with ADSL?
Yes, BT offers an enhanced service package for both BT IPstream Symmetric and BT
Datastream Symmetric which provides a 20hr clock clear and is charged at a monthly
26. What is wetting current and why do you use it when other SHDSL
suppliers do not?
BT has undertaken research that suggests a continuous low dc current,
(known as wetting current ) when applied to Metallic Paths such as those
used for Broadband Symmetric can reduce fault rates. Most BT services such
as PSTN already have a low current present so additional precautions are
unnecessary. With Broadband this currently does not normally exist but has
been applied by BT to improve service reliability.
27. What new equipment would be needed at the exchanges?
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Broadband Symmetric can be provided on the Fujitsu second generation
DSLAMs, where these do not exist then new equipment needs to be
28. Do BT utilise the same DSLAM for ADSL & Broadband Symmetric
Within the Fujitsu second generation DSLAMs different line cards are used for
the ADSL and Broadband Symmetric services.
29. Would users be able to get voice telephony over the same line while
it is being used for Broadband Symmetric service?
Unlike ADSL end users would not be able to use the line simultaneously for
30. Will eCo be used for placing orders for Broadband Symmetric ?
No. A system called "Symmetric Order System" (SOS) is used. This is a web
based system accessed via the btwholesale.com site. Customers will need to
register on the btwholesale site (username and password required) and
request access to SOS. Checks will be done to ensure the appropriate
contracts have been signed before access to the SOS is given.
31. How do I find out if my customer is served by a Broadband
Symmetric enabled Exchange?
Availability for the Broadband Symmetric products can be found using the
availability checker on the following website www.btwholesale.com/broadband
32. What are the prices for my customers?
Pricing is available with-in the Service Provider price list
. Potential customers
should also discuss this with their BT Account Managers. The Service
Provider will determine the retail price.
33. What is the minimum term for Broadband Symmetric?
The minimum term is 12 months.
34. How do I sign up?
Anyone interested in ordering Broadband Symmetric Products should refer to
the Terms and Conditions and other associated documentation, including
35. Is there a list of SHDSL providers on the www.bt.com
Yes, there is a list of Service Providers who offer BT SHDSL services to End
Users available at www.bt.com/broadband
. If you are a BT SHDSL provider
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and wish to appear in this list please send your company details to
36. What bandwidths speeds are available on the Symmetric VPs?
The Broadband Symmetric VPs start at 1meg and increase in increments of
1mbit/s to a maximum of 10mbit/s.
37. Can I migrate from ADSL to Broadband Symmetric?
Yes, BT offers the facility to migrate customers from ADSL to Broadband
Symmetric within the product sets.
38. Can my upstream and downstream traffic run concurrently?
Yes, Broadband Symmetric supports concurrent throughput.