With demands for faster and better communication, the volume of traffic on corporate and public networks is increasing rapidly. To cope with the demand, networking engineers are seeking to create a new type of network, one that can distinguish between voice and data signals and transmit them efficiently over existing systems of leased lines, ISDN lines, and public networks. A new system should also run on any future system. This was the challenge that motivated engineers at NEC Shizuoka, a design center of NEC Corporation, to design the Simple Node.
An Integrated Node with Hybrid Multiplexing
The Simple Node is an integrated node that uses hybrid multiplexing to combine the functions of a time-division multiplexer (TDM) with a private branch exchange (PBX). Hybrid multiplexing optimizes both the bandwidth and band-pass use of circuits so that voice and data signals with differing speeds and time delays are both transmitted efficiently, reducing communication costs.
The Simple Node processes low-speed, short-time-delay voice data signals, as well as low-speed, longer-time-delay host-terminal data signals and high-speed, burst inter-LAN data signals. It assigns optimum bandwidth and band-pass to these different types of signals, and outputs the data to the transmission line. With the Simple Node, circuit switching and time-division multiplexing is accomplished in one compact system.
The NEC designers used Altera® FLEX® 8000 and MAX® 7000 devices for the Simple Node boards. Their decision to use Altera devices was based on their desire to satisfy customer needs and to bring the product to market quickly. "The key issues were understanding customer needs and reflecting them in the product, and time-to-market," said Yusuke Nishimura, assistant manager of the transmission engineering department of NEC Shizuoka. The flexibility of Altera PLDs and the ease of use of the MAX+PLUS® II software allowed them to set the specifications and design the boards simultaneously, adding new features and modifying the designs as necessary. "One of the reasons we selected Altera devices is the quality of the design tool. The MAX+PLUS II software is very easy to use," said Yusuke Nishimura.
Figure 1 shows the Simple Node block diagram. The Dynamic Band Assign Module (DBM) is the product's innovative feature, where the hybrid multiplexing takes place. Figure 2 shows the DBM block diagram. The DBM controls bandwidth and assigns both fixed and variable band-pass. The DBM boards are shown in Figure 3.
Figure 1. Simple Node Block Diagram
Figure 2. Dynamic Band Assign Module Block Diagram
Figure 3. Three PCBs Comprising the DBM
The Simple Node contains the following Altera devices:
The Simple Node
The Simple Node functions by the fixed channel interface and demand channel interface connecting to the DBM through the main signal bus. Low-speed, short-time-delay data are passed from the fixed channel interface to the DBM, which multiplexes the data as a fixed bandwidth (see Figure 4) and outputs it on the transmission line through the Line Interface (LIF).
Connection calls carrying voice data are passed from the demand channel interface to the DBM. The DBM confirms the changes needed in bandwidth assignment, changes to the required bandwidth in the demand band-pass (see Figures 4 and 5), and then outputs the data to the transmission line through the line interface using high-quality voice compression that complies with ITU-T G.728/G729.
Figure 4. Transmission Band for Dynamic Variable Bandwidth
Figure 5. Band-Pass Assignment
Low-speed, longer-time-delay data signals and high-speed, burst data signals are passed from the Frame Forward/Frame Relay port to the Frame Assembly/Disassembly (FRAD), which performs logic multiplexing on them.
The data from the FRAD is output to the time-division multiplexer (TDM), which multiplexes the data as a frame relay bandwidth (see Figures 4 and 5) and outputs it through the line interface to the transmission line. In networks based on traditional TDMs, the bandwidth is fixed and therefore is occupied even when it is not being used. The bandwidth sharing for the frame relay band-pass and the demand band-pass provided by the FRAD allows bandwidth flexibility and improves circuit efficiency.
Conclusion
With Altera devices and the MAX+PLUS II software, NEC transmission engineers were in full control of the design schedule for the Simple Node integrated node. They were able to incorporate changes into the specifications, integrate new features into the design, and still bring this innovative product to market on time.
