APPENDIX 7
EXPLANATORY NOTES ON BANDWIDTH, NETWORKS AND SERVICE QUALITY
The following information has been provided to define and illustrate
the current and future modes of operation of Australia's telecommunications
networks. Data has been drawn from a cross-section of submissions, evidence
and other technical material provided to the Committee. [1]
Section 1
Bandwidth
Analogue systems transmit continuous signal which vary in amplitude (e.g.
AM radio) or frequency (e.g. FM).
Table 1:Analogue Systems
| |
Bandwidth* |
Comments |
| Voice |
4 kHz |
Single telephone channel |
| Music |
10 kHz |
AM Radio |
| Music |
200 kHz |
FM Radio |
| TV |
6 MHZ |
TV Broadcasting Station |
| *Hz = 1 Hertz = 1 cycle per second |
| Khz = kiloHertz = 1,000 Hertz |
| MHZ = megahertz = 1,000,000 Hertz |
A digital signal is a means of transmitting information in bits, and
is obtained by sampling the amplitude of an AM analogue signal, and coding
the signal into bits (binary digits - 0 and 1). Digital signals are used
in all interexchange networks based on a pulse of light representing a
bit.
Table 2: Digital Systems
| |
Bandwidth* |
Comments |
| Voice |
64kbps |
corresponds to 4 kHz analogue |
| Data |
10 Mbps |
Ethernet for computer networks |
| Video - TV |
96 Mbps |
corresponds to 6 MHZ analogue |
| TV |
approx 6 Mbps |
compression factor = 96/6 = 16 |
*bps = bit per second
kbps = kilobit per second = 1,024 bits per second
Mbps = Megabit per second = 1,048,576 bits per second
Gbps = Gigabit per second = 1,024 Megabits per second
** compression factor involves a trade-off with sensitivity to
noise.
|
In a digital network, services can be aggregated together. Thus the interexchange
network operating at 2.4 Gbps can carry about 20,000 simultaneous telephone
calls per fibre.
A Full Services Network is a (digital) network which can deliver voice,
data and video services. ISDN (Integrated Services Digital Network) is
the extension of the digital interexchange network to the customer access
network (CAN) using 64 kpbs channels on twisted copper pairs. Some services
such as videoconferencing can be supplied by aggregating channels (e.g.
3 ISDN lines gives 182 kbps which can provide poor quality video).
Capacity
The capacity of a communications link is determined by the total available
bandwidth.
Optical Fibre
Coaxial cable
Symmetry
An optical fibre can be used to send signals in both directions.
A coaxial cable is subject to electromagnetic interference, and signals
travelling in opposite directions must be in different `channels' to remove
this by filtering.
In practice, optical fibre can provide high bandwidth capacity in both
directions, whereas coaxial cable can only provide high bandwidth in one
direction.
Cost of Broadband Infrastructure
The Communications Futures Project of the Bureau of Transport and Communications
Economics (BTCE), 1994, considered the relative costings of different
infrastructures and the broadband services they could each support.
The most extensive study was that for hybrid fibre coaxial (HFC) networks,
which indicated that the cost of coaxial TV plus telephony would be $1,600
per home in urban areas. Many broadband services could be delivered on
the HFC network, but not two-way communicative broadband services.
The BTCE, on the basis of an estimate of $10,000 per home for a Fibre-to-the-Home
(FTTH also known as FTTD Fibre-to-the-Door) from Japan, did not consider
such a network as being feasible.
1n 1995, AT&T announced that the cost of FTTC networks would be comparable
to HFC. The BTCE did not study the Fibre-to-the-Curb (FTTC) network.
A Note on Future Rural Services
The cost of providing fibre to rural communities is often stated as a
hindrance to provision of broadband services to these communities. The
BTCE report considers these costs using a demographic model.
However, it is noted that optical fibre cable is becoming more reliable
than copper cable, and is likely to need less maintenance. Optical fibre
units serving 32 customers are presently used by Telstra for providing
telephony to rural and remote communities in areas prone to electrical
storms. The low attenuation of fibre is a technical advantage for fibre
connections in rural and remote areas. Since the cost of installing fibre
or copper is similar, it can be anticipated that optical fibre will begin
to be deployed in rural areas where the lower power consumption of such
optical units is an additional advantage.
The demand for such systems from rural customers may increase as they
link their computer technology to the network because of the potential
for destruction arising from electromagnetic pick-up on copper networks.
Once optical fibre is installed, the upgrade from telephony to broadband
could be small.
Thus the BTCE analysis which stated that the cost of providing broadband
services to rural and remote areas of $24 billion for (HFC) could be significantly
overestimated. The principle reason for a delay for rural communities
in receiving broadband services in the high cost of replacing the existing
copper rural telephony network. Such a replacement may occur as a result
of other technology drivers not related to provision of broadband services.
Section 2
Bandwidth, network types and service
The existing telecommunications network is predominantly a copper network,
and is able to deliver all currently available technologies to some of
the people some of the time. This is accomplished via a combination of
existing cable upgrades to Hybrid Fibre Cable (HFC) in some areas, and
enhancement technologies such as Integrated Services Digital Network (ISDN)
and Asymmetric Digital Subscriber Line (ADSL).
The current copper network does not supply either a standard or a high
grade of non-voice services to a significant portion of the community.
This is particularly true in rural Australia. An estimated 800 000
[2] access links do not have the capacity
for standard fax or data transmission facilities (including the Internet)
to the home.
Telstra began upgrading the existing Copper network to a Hybrid Fibre/Coaxial
(HFC) network in 1992 and if this program continues, the next Australian
telecommunications network will be an HFC network. Full fibre optic links
are currently, with a few exceptions, used solely for major inter capital
and submarine links. There are no current plans for the installation of
a Fibre-to-the-Curb (FTTC) or full Fibre-To-The-Door (FTTD) network.
Bandwidth may be achieved in a variety of ways (refer Table 3).
These methods differ greatly in cost, in long term effectiveness, and
in quality of service provision. Essentially, while it is true to say
that it is possible for the majority of Australians to access the Internet
from home, the current network often provides a slow and erratic service
[3] unless the user has ISDN access.
This is prohibitively expensive for the average household [4].
Yet the same network is able to provide good quality facsimile service
which operates at a substantially higher effective bandwidth. These problems
would be eliminated if the same service were provided via either an HFC
or FTTD network.
Copper and HFC cable are of approximately equivalent material cost and
equivalent installation cost. Upgrading of the current Australian telecommunications
network to HFC has been estimated at a cost of between $24 billion and
$30 billion [5].This estimate represents
total capital investment in cable, buildings, switching upgrades and all
other associated costs.
Table 3: Service quality and speed available through
network types
| Network Type |
Quality/Speed of Common Telecommunications Services |
| Services ==> |
POTS |
Fax |
Data/Internet |
Pay TV |
NVOD |
| Copper |
high |
medium |
low |
NA |
NA |
| HFC |
high |
high |
high |
medium |
medium |
| FTTC
FTTD
|
high
high
|
high
very high
|
high
very high
|
high
very high
|
high
very high
|
Glossary: POTS - Plain Old Telephone Service; ISDN - Integrated
Services Digital Network; ADSL - Asymmetric Digital Subscriber
Line; HFC - Hybrid Fibre/Coaxial; FTTC - Fibre To The Curb;
FTTD - Fibre To The Door.
Upgrading to HFC commenced in 1992 and, if it continues, could be completed
by the year 2004. This represents an approximate annual capital investment
of $2.5 billion. Telstra's capital investment for the 1994-95 financial
year was $3.2 billion. [6]
Current charging zones are predicated on a copper based network requiring
repeaters every 30km. An HFC network requires such repeaters only every
100km. A FTTC network requires further technology from curb to door. An
FTTD network requires few, if any, repeaters. Thus, upgrading should reduce
the overall number of exchanges and associated expenses.
Table 4: Network descriptions and approximate costs
| Network Medium |
Available Enhancements |
Bandwidth Provided (kbps)* |
Service Cost (Capital) |
| Copper |
|
2.4** |
Capital: Exchange Line - $750 Exchange Portion
- $300 |
| |
ISDN |
128 |
As above*** |
| |
ADSL |
64+ |
Capital: As above |
| Hybrid Fibre/Coax (HFC) |
|
64+ |
Capital: $3000 - $4000 |
| Fibre Optic
FTTC/FTTD
|
|
**** |
None available |
Glossary: ISDN - Integrated Services Digital Network; ADSL
- Asymmetric Digital Subscriber Line; HFC - Hybrid Fibre/Coaxial;
FTTC - Fibre-To-The-Curb; FTTD - Fibre To The Door.
* Bandwidth is estimated for data transfer. Other uses/technologies yield
differing bandwidths.
** This service varies in its bandwidth. Telstra `guarantees' 2.4 kbps
to residential clients. Actual bandwidth is commonly much lower (<1
kbps) for home use but, in some major cities, may be as high as 9.6 kbps.
*** ISDN relies on the current Telstra Network (predominantly Copper)
plus additional CAN installed at the clients expense.
**** potential exceeds demands of all current services by high orders
of magnitude
Table 4 sets out the base qualities of the current
carrier technology within Australia's telecommunications networks. Copper,
in several forms, is the most common cable type currently in operation.
Hybrid Fibre/Coaxial (HFC) cabling represents only a small fraction of
the Network. Fibre Optic cabling represents a negligible percentage of
the network. This percentage is utilised in key load bearing capacities
(e.g. the main Sydney-Melbourne cable links).
Footnotes
[1] The Committee gratefully acknowledges the
assistance of Australian Photonics Cooperative Research Centre whose information
is contained in Section 1 of this Appendix.
[2] Dr Roger G. Buckridge, Submission No. 141
Vol.5, p.860.
[3] 2.4kbps data transfer represents the AUSTEL
standard for data transfer. The average home modem operates at 28.8kbps,
with significantly older models operating at 14.4 or 9.6kbps.
[4] $400 connection fee, $960 annual rental
charge, $0.20 flagfall for local data calls ($0.14 for voice) plus a timed
local-call incremental charge. (Actual provision of ISDN service involves
little expense to Telstra.)
[5] Television New Zealand executive Gerry Moriarty
to the Senate Select Committee on Subscription Television Broadcasting
Services (1992), and Australian Telecommunications Users Group Limited
(ATUG).
[6] Telstra 1994-95 Annual Report 1995,
p. 19.