Figure 1 . The CO supply consumer1 with approx. as much as twice the data rate
consumer2 receives by bonding 2 ADSL2 lines up to consumer1's premises
Bonded ADSL2
In January 2005 the ITU approved the G.998.1 (G.Bond-ATM) standard, which allows to electronically "bond" several ADSL2/2+ links (or any other physical infrastructure of the same kind for that matter) using cooper phone lines, in order to increase bandwidth and achieve ultra high data rates. This is extremely useful for applications demanding high data rates such as HDTV (which without compression needs data rate at 15Mbps). For example, 2 or more lines of ADSL2+ can be bonded to double the data rate on short distances (<1.5km) up to 44Mbps, or on long distances (<3.6km) up to 8Mbps. If bigger data rate is needed - no problem, just bond some more lines together!
Figure 1 . The CO supply consumer1 with approx. as much as twice the data
rate
consumer2 receives by bonding 2 ADSL2 lines up to
consumer1's premises
Main features
Apart from greatly
increasing the data rate, the Bonded functionality offers some important
features:
How it is done
Bonded
ADSL2/2+ combines several pairs of twisted cooper wire to transport a single ATM
cell stream between provider and DSL subscriber. The process is detailed
in the following figure:
Figure 2 . Transmittion
of a single cell stream over bonded ADSL2+
First, the ATM layer delivers a single stream of cells to a layer
called the "ATM bonding layer". This layer then splits the
cells into several substreams while integrating special sequence IDs (SID) into
the cells for reassembling at the receiver side. Finally, each substream is
mapped to a seperate ADSL connection and transmitted to the receiver.
On the
receiving side, the receiver's ATM bonding layer reassemble all of the cells in
the correct order, according to their SID numbers,
to recreate
the original cell stream, which passed to the ATM layer and
on to the higher layers.
The implementation of Bonded ADSL/2/2+ doesn't
require great amount of design changes in current equipment, mostly due to the
fact that ADSL and ADSL2/2+ chipset already support an ATM interface.
The only physical supplements needed are some multiplexing parts on both ends to
divide the data of the single ATM cell stream on send, and reassemble them
back on receive. Note that while both sides needs the right equipment to
benefit the Bonded functionality, a station with Bonded ADSL2/2+ equipment
installed can still communicate (in the regular non-bonded way) with a station
who has the standard ADSL2/2+ equipment.
Other changes required are
in the software which are relatively easy to implement. The basic
protocol stack also needs a face lift adding the bonding
mechanism.
Figure 3 . Protocol stack with the binding layer,
located between the ATM transport protocol and the ATM-TC layer.
for more ATM layer information see the
rad
university
site.
Results
Bonded ADSL delivers great data
rates over greater distance
than the basic ADSL2/2+. As said before, it can reach 8Mbps over
lines in length up to 3.6km. As so it poses a very attractive option
for video applications such as VOD or HDTV.
In addition, Bonded ADSL2/2+ is
very flexible, allows to dynamically bond lines regarding
directly to the consumer's demand for high speed data rates, especially
those who live for then the CO. Furthermore, all of those benefits come
without the need for serious changes in current DSL
infrastructure or equipment, and those with the original ADSL2/2+ equipment are
still compatible
with those who acquired the
Bonded specific equipment.
There is also an economical
advantage to carriers using Bonded ADSL2/2+ as a mean for checking demand for
video services (therefore require high data rates) among a certain population in
a certain area. As Bonded ADSL2/2+ is a lot cheaper and easier to
integrate then setting up fibers to each and every consumer's home, yet still
provides means for delivering high definition video to a satisfied consumer, it
can be used as a temporary (or permanent) mean to supply video applications,
until the level of demand for those services in the area gets clear. If
the area has little demand, we might want to leave the Bonded option instead of
setting fiber-to-the-neighnorhood. If demand rises over time (we use the
term "penetration rate" to scale how quickly demand for a service rises)
then we could invest in a more suitable and expansive infrastructure.
