Digital Data Services (DDS)
What is DDS?
A Telecom NZ service :-(
Telecom's Digital Data Service is the standard DDS service for providing
point to point connections between locations in New Zealand.
A lower cost version of this DDS is the Metropolitan DDS (MDDS), available
only in several major cities.
There are 2.4Kbit, 4.8Kbit, 9.6Kbit, 19k2bit 48Kbit, 64Kbit and 128Kbit DDS
DDS services may not be available from all locations and exchanges in NZ.
A call to the nearest Telecom Business Centre will provide the most up to
date DDS coverage.
DDS is a dependable digital service and is ideally suited for full time
connections to the Internet in New Zealand.
What does it cost?
Installation is $410 per end of the DDS link - $820 total
It is the same installation cost for all speeds of DDS.
DDS monthly rental consists of an access charge per end of the link,
a tail circuit charge per end and a transmission charge.
There are no ongoing time related charges, no per minute rental charges
or link distance charges. Thbe DDS can be fully utilised or just move
minimum data volumes and the cost is the same.
DDS prices for the faster 64K and 128K speeds are rumoured to be reducing
in Mid 1996 so exact pricing should be obtained from Telecom.
Ordering a DDS link
Telecom supply standard application forms for DDS services.
These can be obtained from the nearest Telecom Business Centre or Sales
office and they will post original copies to you or fax them directly.
The application consists of four pages.
Page 1. General Company information and billing addresses
Pages 2 and 3. The site drop information, address, contact people, location
in building where DDS is to be terminated. There is one page for each end
of the DDS link. You will have to contact your Internet Service Provider
to get the exact details to complete for their end of your MDDS link.
Some service providers prefer to complete the whole document as it makes
sure there are no delays due to incorrect or missing answers.
Page 4. DDS interface type and control signal options. The options here
for interface type depend on the DDS speed. For 9K6 and below an asynchronous
v24 interface or an X21bis synchronous interface is available.
48K and above are available only as synchronous serial with either X21 or v35
After the completed application is returned to Telecom it can take
anything from one day to 15 days for the DDS to be installed. In a very few
metropolitan areas there could be longer delays if some upgrading is required
of the local exchange. Even longer delays are probable if new cables need to
Normal installation time is about 5 to 7 days. In any case Telecom will
provide a latest date for commissioning the new link.
Equipment shortages seem to be a recurring problem that cause delays with
DDS installation. At different times there can be shortages of the NTU 2
needed for 48Kbit DDS,
then when these are in plentiful supply there are no control cards available
to install in the exchange. Sometimes a delay may occur because a card
frame needs to be installed at the exchange.
The situation with the higher speed DDS equipment has been much worse.
The Open Technology NTUs used for 64Kbit and 128Kbit have just not been
available for as long as two months and often Telecom have offered to
connect a 48K DDS until equipment becomes available.
There was a period where there was no 48Kbit NTUs and Telecom were
installing 64K DDS in their place and charging the customer for just
a 48K DDS link. This did not last too long before Telecom were asking for
the monthly rental to be paid for a 64Kbit DDS.
Just about all DDS installations are now carried out by Installation
companies that contract to Telecom. The good news is that the actual
people who do the installations are usually ex-Telecom staff and they
tend to know what they are doing. The same person will often install
both ends of an DDS and will phone the contact people (as included in
the application site forms) to arrange a mutually suitable time to call
and do the site installation.
With the higher speed 64K and 128K DDS these still tend to be installed
by real Telecom staff although this too may soon cease.
DDS requires a single copper line pair. It cannot be installed on a line
used for 1+1 or other multiplexing schemes for providing more than one
analogue (phone) service over a copper pair.
The installation cost will include stringing an overhead cable from a
Telecom street pole to the building and hence to the required NTU location.
It will NOT include installing new trunking or excavating for an underground
cable on the customer's property or building.
An DDS link is terminated at each end in a modem-like box known as an
Network Terminator Unit or NTU.
For DDS up to 48Kbit the NTU can either be an older type made
by Telettra, usually with a brown plastic case and black front panel, or the
newer NTU2 in a grey plastic case.
64K and 128K DDS use a fairly large cased NTU made by Open Technology.
All NTUs require a 240v AC mains power outlet. Power consumption for the
older Telettra NTUs is about 40 Watts, the newer NTU2 is about 10 Watts
and the Open Technology NTUs need about 20 Watts.
The lower power NTU2 can be stacked. Telettra NTUs will overheat if stacked.
Both types are able to have two beside each other on a standard 19inch
rack frame shelf.
The larger Open Technology type NTU cannot be stacked due to its wedge
shape, nor will it fit beside other NTUs in a rack frame. It requires
its own rack frame shelf and is a general pain to deal with. Telecom
have no plans to provide a more rack-frame, shelf-space or desktop
friendly 64k/128k DDS NTU.
Internet connection using DDS
DDS is probably the only option for many Internet connections where the
link has to be made between cities or locations that are outside of
the coverage possibilities of a radio based system.
The price of DDS is a major annoyance factor with many ISPs as the
New Zealand pricing is one of the most expensive on this planet.
For Internet connections the 48Kbit 64Kbit and 128Kbit DDS are the most
Data Compression can significantly increase the throughput over a DDS
although this will require router hardware at each end of the DDS with
sufficient cpu grunt and memory.
Connecting DDS to an Internet network.
The exact type of connection will depend on the interface provided (or
requested) on the NTU. The slower 9k6/19K2 NTU with its async interface can
be directly connected to an async port on a PC or workstation. This workstation
will probably need to be running routing software, most Unix OS will
include routing, and other OS such as OS/2, MacOS, Windows NT etc usually
have routing capability either built in or by installing additional
Synchronous DDS links will require a router or computer interface that
supports synchronous serial connections.
Usually an external ethernet (or token ring) router box is used to manage
a synchronous DDS link. This often turns out to be the single most expensive
hardware required to connect an DDS.
See Routers from KCCS.
These routers will totally manage an Internet connection providing the
required sync serial port interface (usually X21). They also include full
routing capability, provide internet routing management and may often
include limited firewall capability.
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Last modified: 1 October 1996.