At the customer-premises site, a network interface unit (NIU) provides the gateway between the RF component and in-building appliances. NIUs are manageable by the network management system provided in the network control center (see Figure 8). These NIUs are available in scalable and nonscalable forms depending on customer requirements.

Figure 8. NIU Network Implementation

Fully Scalable/Configurable NIU

A scalable NIU is flexible, fully configurable, and chassis-based. It is located at the subscriber site and supports two-way digital wireless voice, data, and video communications for commercial and business uses. The NIU can be configured with 10BaseT, analog voice, structured and unstructured T1/E1, T3/E3, OC–1, OC–3/STS–3 fiber communications, ATM 25.6, and video communications in a single chassis.

As part of the wireless broadband network, the NIU communicates with the base-station equipment through a two-way transceiver forming a part of the point-to-multipoint network solution. This solution allows network operators to deploy their services instantly without the need for building the subscriber wireline infrastructure, thereby, capturing the rapidly growing telecommunications market just in time.

The NIU's basic building blocks consist of the following components:

• a radio-modem module supporting 4, 16, and 64–QAM and featuring either FDMA or TDMA access mode
• a data-processor module (DPM) supporting various services such as T1/E1, 10BaseT, and ATM 25.6 services through an ATM SARing processor
• a chassis-interface module (controller providing processing resources)
• a power supply

Modular design of the NIU allows network operators to meet each subscriber's requirements efficiently. The network operator can configure multiple radio modems to support the total bandwidth required by the configured services. The NIU should work in conjunction with the broadband microwave system to maximize the use of available RF–spectrum resources. The radio-modem and DPM ratios can be optimized with mix and match options from one-to-one mapping to multiplexing the data streams from several DPMs.

NonScalable NIU

A nonscalable NIU is a stand-alone, cost-effective piece of CPE that provides a fixed combination of interfaces. The combination is designed to meet the requirements of small- to medium-sized business market segments. Services may include structured and unstructured T1/E1; T3/E3; 10BaseT; video; POTS; frame relay; ATM 25.6; and integrated services digital network (ISDN) basic-rate interface (BRI), primary-rate interface (PRI). Using this interface unit, subscribers can deploy various one-way or two-way voice, video, Internet and/or computer multimedia applications in a chassis using a single carrier frequency spectrum.

This nonscalable NIU communicates with the base station through a two-way transceiver consisting of the following components:

• a variable-bandwidth radio modem (supporting 4, 16, and 64–QAM, TDMA or FDMA depending on the type of services provided by the NIU)
• an ATM segmentation-and-reassembly (SAR) processing unit (types of ATM SARing depend on the types of services provided by the NIU)
• a subscriber equipment interface

The service mix and the interfaces provided by the NIU are not user-configurable and therefore reduce product cost to the market. This type of nonscalable NIU allows network operators to offer services cost effectively into small office home office (SOHO) environments. Various vendors will have different NIU products and strategies.