Integrated Services Digital Network (ISDN)

NOTE: To find out what ISDN is there is an excellent ISDN FAQ posted fortnightly to the news.answers newsgroup.

What is ISDN in New Zealand?

Both Basic rate and Primary rate ISDN services are available in NZ. Basic rate (BRI) consists of two 64Kbit B channels and one 16k D channel. The B channels can be used as digital data links for connecting between internet hosts. The D channel is used in NZ for control signalling and for optional Pacnet services.

Primary rate (PRI) ISDN is supplied over a 2megabit Digital Data Service and this DDS needs to be installed before PRI ISDN is enabled. PRI can provide up to 32 64Kbit B channels, number from 0 to 31. Channel 15 is used for control and management of the other B channels, Channel zero is reserved for timing management. This leaves 30 64Kbit channels for use as dial in/dial out lines.

A major feature with ISDN in most countries apart from New Zealand is that Caller Line Identification (CLI) is available. This is often used as a security measure with data circuits sometimes in addition to the more standard forms of user access security. Telecom NZ have said that CLI will become available after certain issues relating to privacy have been worked through. In early 1996 there have been live trials of CLI in certain regions but as yet there is no definite date for it to be generally available either with ISDN or normal phone circuits.

Basic Rate Ordering and Availability

Limited details on Telecom's ISDN offerings can be obtained from your nearest Telecom Business Centre. This should include pricing and an idea of availability and installation time.

ISDN services are definitely NOT available from all exchanges in NZ. Most likely all large cities will have isdn available within their central business district exchange. Outlying exchanges may have ISDN capability but will need some equipment upgrades to enable ISDN.
Telecom may not be prepared to undertake such an upgrade or they may quote some astronomical price to provide the service.
As recently as October 1996 quotes were obtained for over $4000 installation fee to make basic rate isdn available at suburban exchanges in Auckland.

Unofficially the Telecom policy seems to be to upgrade an exchange if there are several definite orders for ISDN. The exact number required has never been disclosed but one or two orders is insufficient. Sufficient complaining and pointing out that other residential exchanges nearby have ISDN capability has spurred Telecom to reconsider and implement the exchange upgrades.
One reason given for this policy was the high cost and limited availability of the exchange isdn equipment.

Also as recently as last quarter 1996 into January 1997 there was an extreme shortage of NT units and other hardware that needs to be installed in customer premises. This has been reported in the computer press for that period.

Telecom seem to order the equipment on a minimal basis. A significant growth in popularity of a service will usually lead to an equipment shortage and subsequent long lead time to install ISDN. A similar situation exists with Digital Data Services.

Basic Rate ISDN costs

This depends on your location. Ask Telecom.
For major cities there is a $400 installation fee and then BRI rental is $150 per month.
In the central business district of Auckland the monthly rental is $120 per month.
The installation may be more if Telecom have difficulty in getting additional copper cables into your property.
They may also charge extra if additional cables need to be laid in the street or other lines used for voice phone need to be doubled up (1+1) to vacate a copper pair for your ISDN connection.
If you do get such a quote then NEVER accept it without a full explanation and insist on getting this in writing.
Always complain about such additions as the base fee of $400 should take such extra provisioning into account.
Very often Telecom will give way and waive extra charges or be prepared to meet some proportion of them especially if the new cable(s) make it easier for them to supply additional services to other Telecom customers.

The $400 installation will cover stringing an extra cable from a pole outside your property where Telecom cables are already from that pole into your or adjacent properties.
It will definitely NOT cover the cost of an excavation if a new underground cable needs to be installed. Fortunately most modern underground installations will involve a trunking (usually a plastic pipe) through which it should be possible to pull an additional cable.
If not then you will be paying for a new trunking to be installed.

Every 64Kbit B channel connection has a per minute charge which is the same as a business telephone charge. The full peak time rate is 4c per minute with an off peak rate of 0.4c per minute starting at 10pm and lasting to 7am. There is no weekend cheap rate (at least not so far) Toll call charges apply as per normal phone calls.

Basic Rate installation

When BRI is installed it uses one copper line pair. A jack point labelled with the ISDN circuit number is installed at the customer location. An rj45 plugged cable goes from this jack to an NT power supply, usually a black power brick. This plugs into the mains supply and via a second rj45 connector on the brick connects to a Network Terminator (NT) device. An output rj45 socket on the NT is for connecting to the customer supplied router or isdn modem. The cable is a standard 8pair straight through with rj45 connectors on each end (such as a twisted pair ethernet patch cable).

This installation is not very neat as there are several cables between the various boxes including AC power and the isdn connection to the router. The NTU usually supplied is an NEC NT which can be wall mounted near to the ISDN wall jack or at a convenient point closer to the router equipment. The external power supply can run warm so needs to be in an open air location.

When there is more than one planned BRI circuit it may be possible for Telecom to supply a single power supply to power up to four NT units. There may also be a rack frame option available that can accomodate up to eight NT cards.

Basic Rate routers and modems

Almost every day there appears to be a new router or modem appearing in NZ for use with Basic Rate ISDN. The trend now is towards ISDN modems for dial up connections to the Internet. The home user and small business market is now looking at ISDN since analogue modems have now just about reached the technology limits with maximum throughput of 33Kbits/sec

For commercial internet applications where routing is necessary (ie the connecting site has its own network that is to be connected to the internet) there have been several ISDN routers, approved for use in NZ, available for over six months.

NOTE: Customer equipment that is directly connected to Telecom's ISDN NT1 must have been approved by Telecom. Usually there will be a green tick approval label on the equipment.

Routers known to work and Telecom approved are:

Network Dynamics, Christchurch
ACE 1830, ACE 1870, ACE 28x0, ACE 38x0

Cisco New Zealand, Auckland
Cisco 1003, Cisco 2503, Cisco 4x00 (4 and 8 port BRI interface modules)

Kaon Technologies, Auckland
Spider ATTO, Spider ATTO+, Spider MEZZA (with BRI card)

Megadyne Communications, Auckland
Motorola model 311 router

The above are all 'external' routers that connect to an ethernet network. Internal router cards for PC type computers are available from Cisco and several other sources.

ISDN capable modems are just starting to appear in NZ. Motorola, 3Com and Zyxel all have ISDN modems that are either going through final testing or are now available.
For up-to-date information on any of these contact the distributors.

Zyxel 2864i ISDN/v34 modem cost about $1400, Meridian, Auckland
contact: Peter Felhofer

Motorola Bitsurfer+, ISDN/v34 modem, $950, Megadyne, Auckland
contact: Peter Armstrong

3com ISDN modem, Com Tech NZ, Auckland

Cisco 200 internal PC isdn modem, Cisco NZ
contact Andrew Murray

Various ISDN modems both internal and external are now appearing at the larger PC distributors in Auckland.

Basic Rate ISDN and the Internet

With analogue modem technology having just about reached its technical limitations in speed, it has been long recognised that the next logical step in dial up connections to the Internet will be ISDN.

Moving from Analogue to Digital technology will in itself lead to more reliable and noise free connections. The jump in connection speed from around 33Kbits to 64Kbits will give significant performance increases.
ISDN is a digital service and therefore does not suffer from the line and switching noise that can degrade and often disconnect an analogue modem connection.
The two B channels in a BRI ISDN can be aggregated to provide a single 128Kbit data pipe. This type of connection has over four times the throughtput and a much more reliable service when compared to current v34 analogue modem technology.

Costwise ISDN is comparable to using analogue modems over the PSTN. Telecom per minute charges for a business phone are the same as for a BRI ISDN B channel. The improved throughput of an ISDN data channel should allow much shorter connection times for data file transfers (including Web surfing) and hence reduce the connection time charges.

The time from dial up to connection is less than one second. This will allow ISDN to appear like a DDS connection since many Internet programs will not time out while waiting for a responce from a remote server (at the end of a dial up ISDN connection).
It is possible to have WWW servers and other server systems that provide Internet services connected to the Internet via ISDN. The call connect time is so short that even with a security dial back system, where two ISDN calls are made before an IP link is established, timeouts will not occur due to slow connection times.

Primary Rate ISDN Ordering and Availability

Primary Rate ISDN (PRI ISDN) services are only available at a limited number of locations in NZ.
In Auckland PRI connections are provided at one of three main exchanges. These are Takapuna (North Shore), Mayoral Drive (Central and West Auckland), and Remuera (East and South Auckland)

PRI may not be immediately available for a number of reasons ranging from equipment shortages to no PRI circuits available at the exchange.
PRI installations have been significantly delayed due to software problems with the NEC NEAX61E PRI switches used at the exchanges. For over 3 months in late 1995 no new PRI ISDN circuits could be installed in Auckland due to software problems with the NEC equipment. From mid 1996 no further PRI were available in Auckland as all resources had been alloctaed or used.
The appearance of Telecom's Xtra ISP saw all avilable PRI in Auckland being reserved for Xtra.

Initial enquiry about PRI should be to the local Telecom Business Centre. If it is available then on ordering it Telecom will confirm a service installation date. This may take several weeks while available resources are checked and made available.
The installation date is the latest date when the service will be completed and available for customer use.
Although Telecom quote a three week period for completing installation from the time of the order this is unlikely to happen. Six to eight weeks is more likely although this should reduce as more exchanges become PRI capable.

Primary Rate ISDN costs

PRI ISDN requires a 2megabit DDS circuit to be installed.
The installation charge for this is $4000 if this is the first 2meg circuit installed at the customer location. If there is already a 2meg circuit installed (for Wide Band DDS, Stacked Wide Band DDS, or PRI ISDN) then the installation charge reduces to $2800.

Monthly rental for PRI ISDN is based on the cost of 2meg DDS circuit plus additional charges for the number of ISDN 64Kbit channels provided with the PRI ISDN.
Each B channel rental is $38 per month
The total rental is made up of:
$500 per month access charge
$280 per month circuit charge
$38 per month multiplied by the number of B channels provided

So, for example a PRI with 10 B channels enabled will cost $500 + $280 + (10 * $38) = $1160 per month.

In addition to this monthly rental there is also a per minute connect charge for each B channel (for outgoing calls only) This is the same charge levied for BRI ISDN.

Primary Rate installation

PRI ISDN uses a 2megabit DDS circuit into the customer premises. This circuit uses three copper wire pairs, one for receive, one for transmit and one for control and circuit monitoring.

Telecom install a wall mounted chassis knowm as a CLTE (Customer line termination equipment) with a microcomputer based terminator unit for the 2meg circuit. Each chassis can accomodate two such terminator units. Power for the TUs is obtained from the Telecom copper pairs and there is no need for the customer to provide a power outlet for the TUs. The chassis is permanently wired to the copper pairs. There are no rj45 wall sockets for the lines as provided for BRI ISDN and normal telephone lines.
Output cables from a CLTE usually terminate in a wall box with two pairs of BNC 75ohm sockets or two 100ohm rj45 sockets. Each pair BNC sockets is a G703 interface and will be marked receive and transmit.

Telecom can supply as part of the installation a 75ohm unbalanced to 100ohm balanced convertor. This is another wall box containing two baluns with short cables that plug into the 75ohm unbalanced sockets and two more output BNC connectors which is the G703 100ohm balanced interface.

This interface will then connect into the customer supplied ISDN router equipment via an appropriate cable supplied with the router.

Primary Rate routers

Primary Rate ISDN requires a channel managed 2Mbit interface controller Although many router manufacturers have such an interface available there seem to be very few of them that will work with NZ Telecom's Primary Rate Switch equipment (currently NEC NEAX61E)

There are two routers available in NZ that are known to work cleanly with NZ Telecom's PRI ISDN.

The first is the PRI interface supplied by Network Dynamics for their ACE range of routers. A single or dual PRI interface is available and is supplied with quite detailed configuration software and full instruction and reference manuals.
The PRI interface is only supplied for use with the 38xx and 48xx series of ACE routers.
The config software has specific options for selecting NZ PRI so is fairly straighforward to set up.

The second is the cE1 interface supplied by Cisco for their 4x00 series of mid range routers and the dual E1 interface for the 7x00 high range routers.
Cisco's IOS software for their routers automatically detects a channelised E1 controller installed in the router and enables the various configuration options for the card.
This same cE1 controller is also used for normal channelised DDS (the stacked wideband service from NZ Telecom) so it has to be configured specifically for PRI ISDN service. This is a very straightforward exercise.
There is full online help with the Cisco configuartion software.

There is no specific configuration command for NZ PRI, however the switch type can be selected as 'primary-net5' and this will work cleanly with the NEAX61E switch.

Primary rate ISDN and the Internet

PRI ISDN is an ideal method for an Internet Services Provider (ISP) to provide many 64Kbit ISDN dial up lines.
If an ISP and its customers use the same manufacturers ISDN routers then very often link compression can be implemented. Unfortunately most compression schemes are proprietry to each router manufacturer so it is not often possible to get compression between different makes and sometimes different models of router from the same manufacturer.
The more powerful mid range routers with plenty of memory can provide compression more readily than the basic router models.

Recently available modem servers using PRI ISDN and providing dual mode digital ISDN/analogue v34 connect capability have been designed for Internet Service Provider market.
Examples of such products are:
Cisco AS5200 modem server, which can connect two E1 ISDN PRI to provide sixty dial in modems lines.
Ascend Max/PRI which can also connect two E1 ISDN PRI to provide up to sixty dial in modem lines. Ascend also have modem servers that connect to multiple ISDN BRI (up to eight in the Ascend model 1800).

Some of the pros and cons of PRI ISDN when compared to multiple Basic rate connections are:


  • PRI requires only three copper pairs into the ISP premises for up to 30 dial in ISDN lines.
  • Only one router is required to handle all 30 lines
    Routers than can manage two PRI and handle up to 60 isdn lines.
  • ISDN line and call management is centralised in one router and multiple B channels can be aggregated to allow individual high bandwidth connections.
  • Initially Telecom will enable as many B channels as required. Later this can be expanded by any number up to 30 in total.
  • there is no further installation charges as more B channels are added.
  • One phone number with auto step-on for all B channels as well as individual numbers for each channel.


  • The initial investment in PRI ISDN is very high, $4000 installation for the 2meg WDDS and PRI capable routers normally cost in excess of $10,000 (although cheaper models are now becoming available). Installation is significantly lower if 2meg circuits are already installed for other Telecom services.
  • Monthly rental for PRI only becomes cost effective with over 24 B channels enabled when compared to renting multiple BRI ISDN connections.
  • PRI is not as widely available as BRI, only select exchanges in NZ can support PRI.

    Euro ISDN Another explanation fo ISDN service

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    Last modified: 20 March 1997.