ATM Network Termination Unit

The Metrodata ATM Network Termination Unit (NTU) provides a media conversion and ATM service demarcation function for STM-1/OC-3 ATM services. A wide variety of copper and fibre interface types are supported which mean that these services can be installed with whatever is the most suitable cabling, and offer the exact interface required by the user thereby minimising installation costs.

The ATM NTU has two different ATM interfaces. Cell traffic received at these interfaces is analysed for errors, idle cells are deleted and valid traffic is then forwarded to the ATM cell buffer. When bandwidth is available traffic is extracted from the ATM cell buffer and transmitted out of the other interface. If the ATM cell buffer becomes full, then cells are discarded until space becomes available. If there is no traffic queued, the DSU transmits idle cells in lieu of traffic.

The ATM NTU has built in diagnostic loops which segment the link and assist in locating device, cabling or network faults. Extensive performance monitoring statistics are also gathered and stored for 24 hours. This provides a substantial database for assessing the performance of the network, which can be used to identify alarms, errors or data loss. Front panel LEDs also give indication of major and minor alarms.

The default configuration is sufficient to get most installations applications operational, making this a truly plug and play device. Configuration can be performed via a menu driven console port, or via an integrated LM1100 SNMP enabler port which offers substantial Telnet and SNMP capability.

The electrical interfaces supported are as follows:

• G.703 BNC offering transmission over coaxial cable
• RJ45 offering transmission over twisted pair cable
  

The main fibre interfaces supported are as follows:

• 1300nm multimode offering transmission distances up to 5km over multimode fibre
• 1300nm singlemode short haul offering transmission distances up to 30km over singlemode fibre
• 1300nm singlemode long haul offering transmission distances up to 70km over singlemode fibre

Using fibre optics these products extend the operating distance for an STM-1/OC-3 interface to 5km using low cost multimode fibre, or to either 30km or 70km using singlemode fibre. Despite these quoted maximum operating distances, specific installations may only operate over lower distances due to the variations in losses of different types of fibre cable, the use of connecting fibre cables, or patch panels. When operating over 50% of the maximum distances it is advisable to calculate all fibre optic connector and cable losses and compare these with the fibre optic loss budget specified for this product.

As standard fibre ports are supplied with SC connectors and operate at a nominal wavelength of 1300nm. Other wavelengths are available on request, e.g. 850nm, 1550nm, 1550/1300 WDM. Other connector options are also available on request, e.g. ST, FC.