BT's Wholesale Broadband Connect (WBC) : QoS at last? - June 08

The rollout of BT’s 21CN will probably impact the VoIP market place most immediately through the imminent arrival of a new range of wholesale broadband products, solutions which offer the promise of a range of QoS options. The impact for business ISPs and LLU operators will be significant, particularly as uncapped uplink speeds become available with SDSL no longer a limited option for peer to peer applications.

The new 21CN products fall into two groups, IPstream Connect (a like for like replacement for the current IPstream) and the much more interesting Wholesale Broadband Connect (WBC) service aimed at replacing BT current Datastream product.

For Service Providers, the new 21CN network topology means that instead of renting ports on DSLAMs at the BT exchange and then Virtual Paths back to their own network, the WBC model now requires them to install aggregation equipment at up to 20 of BT’s interconnect nodes (for full UK coverage). They then need to rent backhaul to their own data centre via Extension Paths and Multi Service Interconnect Links (MSIL) at 100M or 1G capacity; which again will result in a sizable investment.

In essence, WBC moves the point at which Service Providers can extract their customer traffic from BT from the edges of the network (i.e. DSLAMs) to points within the core itself.

The new 21CN products fall into two groups, IPstream Connect (a like for like replacement for the current IPstream) and the much more interesting Wholesale Broadband Connect (WBC) service aimed at replacing BT current Datastream product.

For Service Providers, the new 21CN network topology means that instead of renting ports on DSLAMs at the BT exchange and then Virtual Paths back to their own network, the WBC model now requires them to install aggregation equipment at up to 20 of BT’s interconnect nodes (for full UK coverage). They then need to rent backhaul to their own data centre via Extension Paths and Multi Service Interconnect Links (MSIL) at 100M or 1G capacity; which again will result in a sizable investment.

In essence, WBC moves the point at which Service Providers can extract their customer traffic from BT from the edges of the network (i.e. DSLAMs) to points within the core itself.
Whilst this still leaves a lot for the Service Provider to manage, they no longer will have to ‘manage’ the virtual paths (VPs) through BT network; something that some did better than others.

In addition to the standard WBC structure BT will also be launching Wholesale Broadband Managed Connect (WBMC) and Wholesale Broadband Connect Converged (WBCC).
The WBMC offers a managed option to have BT provide everything but the MSIL itself. This makes sense if the customer density at one of BT’s 20 interconnect nodes doesn’t warrant the capital and operation expense of the Service Provider doing it themselves. There is very little know about the WBCC product as yet, other than the fact that it is intended to provide voice and broadband within a single package.

The important changes to BT broadband service are what’s going to happen in the tail circuits or End User Access (EUA) as BT calls them. In essence this is the connectivity that the customer will see and what can make the economics for quality enabled VoIP more attractive.
The options are; WBC Max 8Mb/s (using ADSL1 or ADSSL2+), WBC Max 24Mb/s (using ADSL2+ Annex A) and WBM Max M (Using ADSL2+ Annex M).

The following table details their explicit speeds

	WBC Max 8Mb/s	WBC Max 24Mb/s	WBC Max M (Annex M)**
Downstream Line Speed	Up to 8Mb/s RA 8128kbit/s	Up to 24Mb/s RA 24384kbit/s	Up to 22Mb/s RA
Upstream Line Speed Option 1	Up to 448 kb/s RA	Up to 448 Kb/s RA	Uncapped RA Default
Upstream Line Speed Option 2	Uncapped RA	Uncapped RA	N/A
Best Efforts Planned Throughput Standard	2Mb/s	2Mb/s	2Mb/s
Best Efforts Planned Throughput Elevated	3Mb/s	3Mb/s	3Mb/s
QoS Options	Real Time/ Assured	Real Time/ Assured	Real Time/ Assured

**Please note this will not be available for the WBC Product Launch.
Ref: Wholesale Broadband Connect Operational Handbook Draft 1
RA – Rate Adaptive
Note the upstream uncapped limit for WCB 8 and 24 is actually 1 Mbit/s and for WBC it’s 2.5Mbit/s

Annex-M

We also note that whilst BT has yet to launch their Annex-M variant, LLU operators such as O2’s BE have had such a service for over 12 months.

Quality of Service

The introduction of QoS is seen as an important feature by BT, intending to allow Service Provider to sell access to their customers in a more ‘application aware’ way. This obviously translates into a more sympathetic network for VoIP and other time sensitive applications such as video streaming.

It should also be noted that QoS is only enabled for the downstream link and that BT have no current plans to introduce a full duplex QoS mechanism. The customer CPE may set uplink priority but they will be ignored by the BT transit element even if the Service Provider’s own network acknowledges it

Three classes of service are offered: Best Effort, Assured Rate and Real time.

The following is an extract from BT Draft Wholesale Broadband Connect Operational Handbook and describes the QoS variant explicitly.

Note
CP – Communication Providers
EUA – End User Access (local loop)
CVLAN - Customer Virtual LAN
EU - End User
SVLAN - Shared Virtual Local Area Network
CAC - Call Admission Control
BRAS - Broadband Remote Access Server

Best Effort

Best Effort (BE) is the basic level of QoS offered by WBC and is suitable for many interactive real-time applications. Best Effort offers:

A high assurance of achieving specified throughput, supported by Capacity Planning to maintain bandwidth utilisation within specified levels.

CPs can choose to pre-configure lines on order as either Standard or Elevated, which are given preferential weighting. We are currently planning target throughputs of above 2Mbit/s for 90% of the time over the busiest 3-hour period for Standard; and above 3Mbit/s for 90% of the time over the busiest 3-hour period for Elevated. This is measured on a network basis.

Both Standard and Elevated options permit two types of End User packet marking - Normal and Priority – and these are expected to give preferential weighting within an EUA’s traffic. This is one of WBC’s features and enables CPs to sell extra flexibility to end users. A Normal or Priority marking has no influence on the bandwidth a particular EUA can obtain at times of SVLAN contention. EUA’s downstream traffic and allows CPs and End Users to prioritise certain applications, at the expense of others, within the available bandwidth. It is anticipated that End Users will have the opportunity to prioritise within their own traffic e.g. video content or traffic for certain applications for an individual. CPs will be expected to mark traffic using Deep Packet Inspection (DPI) within their domain to match the requirement. For the End Users, the CP must provide a utility that specifies applications and users to update the marking within the CP domain accordingly. Normal/Priority markings are outside the scope of BTW’s management of WBC and are the responsibility of the CP.

Assured Rate

The Assured level of QoS offered by WBC is suitable for entertainment and corporate applications. Assured is configured on a EUA when required. Key features include the following:

Call access control is used to provide assured bandwidth for sessions to the EU via an Application-Driven Quality of service (ADQ) platform.

The key performance metric is the Call Admission Control (CAC) blocking rate which measures the number of successful session set-up attempts.

Per-Customer Virtual LAN (CVLAN) policing prevents CPs sending more than the contracted bandwidth; this will include burst-size policing.

Real Time

Real Time offers the highest level of QoS and is principally suitable for stringent VoIP, videoconferencing, gaming and time-sensitive data applications. Real Time QoS is designed to provide a service with minimal packet loss, delay and jitter.

The values currently planned for a EUA are 0, 220, 350 and 700Kbit/s to offer a reasonable fit with the likely combinations of applications and codec’s. These values represent IP rates, based on the assumption of 1500 byte packet sizes. The associated ATM rates in the Digital subscriber Line DSL link are 0, 248, 395 and 791Kbit/s.

Combination

A QoS enabled End User can be provided with any of the following traffic class combinations at any one time:

Best Effort’ + ‘Priority-Best Effort’
Best Effort’ + ‘Priority-Best Effort’ + ‘Assured’
Best Effort’ + ‘Priority-Best Effort’ + ‘Real Time’
Best Effort’ + ‘Priority-Best Effort’ + ‘Assured’ + ‘Real Time’
For CPs that do not require a QoS service, all EUAs are ordered as ‘’Best Effort Normal’’.

The conclusion to be drawn is that whilst LLU operators have had the opportunity to create innovative products for specific markets, i.e "Voice Ready" Premium Broadband product from suppliers such as Tiscali, BT’s range of QoS enabled WBC products with its (eventual) comprehensive national coverage will offer more opportunities to more Service provider than ever before – if the price is right.