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ATM
ATM (Asynchronous Transfer Mode) clearly will be the network technology of choice. As the basis for B-ISDN, ATM will support the transmission of asynchronous, synchronous, and isochronous data. Voice, data, video, and image applications are all supported. There remain issues of ATM support for voice and video, but those issues are being addressed and likely will be resolved in the near future.
Server Technology
Server technology is well developed, but experiencing difficulty in the provisioning of video applications, particularly Video-on-Demand. VOD is extremely memory-intensive, requiring very substantial and expensive servers. Hewlett-Packard claims that its Media Server video jukebox will support Video-on-Demand (VOD) to 10,000 simultaneous users. Time Warners Full Service Network (FSN) trial in Orlando, Florida employs servers from Silicon Graphics (CA), currently supporting about 80 movie titles with 40 more planned to be added. The FSN server will allow 25% of the 4,000 subscribers to access the server simultaneously [15-9]. In addition to Hewlett-Packard, and Silicon Graphics, Oracle, IBM and others manufacture such servers.
The Information Superhighway is not free. As it is anticipated that well over $100 billion will be required to construct the I-Way in the United States, alone. That investment by no means ensures that every business and residence in the United States will have high-speed access; rather, deployment will be driven by market potential. The result likely will be much like that of the U.S. system of roads, with urban areas having access to high-speed freeways, loops and the like (hopefully without the congestion). High-speed interstate highways will interconnect the major urban centers. Smaller towns and cities will have lesser access, and rural areas will be relegated to access via even more modest farm-to-market roads. Voice-grade gravel paths will connect to the farms and ranches. The potential providers of the toll roads include the current providers of telecommunications, data communications, CATV, electric power and wireless services. Table 15.1 provides a comparison of telecommunications, data communications and CATV networks along a number of key dimensions.
Voice | Data | CATV | Wireless | Internet | |
---|---|---|---|---|---|
Presence | Ubiquitous | Widely Available | Ubiquitous | Varies | Ubiquitous |
Transmission Mode | Analog/Digital | Digital | Analog | Analog[rarr]Digital | Analog/ Digital |
Bandwidth | 4 KHz to 45 Mbps | 56 Kbps-45 Mbps | 500 MHz+ | Voice Grade | 4 KHz to 45 Mbps |
Call Direction | Two-Way | Two-Way | One-Way | Two-Way | Two-Way |
Switching Technology | Circuit | Circuit, Packet, Frame, Cell | N/A | Circuit/Packet | Circuit/ Packet |
Transmission Medium | UTP Loop, Fiber Backbone | UTP Loop, Fiber Backbone | Coax | Radio Fiber | UTP Loop, Backbone |
Interconnectivity | Absolutely | Varies | Rare | Cellular, Yes; Data, No. | Absolutely |
Network Management | Strong | Strong | Rare | Moderate | Poor |
Market Perception | Excellent | Excellent | Poor | Low Reliability | High Reliability, Low Quality |
Cost | Highly Affordable | Varies | Reasonable | Moderate to High | Free to Reasonable |
Telecommunications networks were developed expressly to support voice communications. They are virtually ubiquitous in developed nations, supporting bidirectional communications on a circuit-switched basis. The national networks are fully interconnected, to provide complete international calling capabilities. Voice networks do not require significant bandwidth at the local-loop level, with the exception of T1 and T3 facilities in support of relatively large PBX systems and data centers, while very large end user environments sometimes are connected via digital, dedicated leased lines (e.g., T1, T3, or ISDN PRI). The networks traditionally have been analog in nature, and still are for most residential and small business applications, although ISDN finally is making an impact. The local loop terminates in a local central office exchange, or Class 5 exchangethese exchanges rapidly are being upgraded to digital switches with ISDN capabilities.
The backbone telecommunications networks largely have been upgraded to fully digital switches and digital fiber optic facilities, which are being upgraded to SDH/SONET. Such upgraded backbone networks certainly provide additional bandwidth, performance, and economies of scale for voice carriers through high-capacity, multichannel facilities. Additionally, they provide the side benefit of supporting certain data communications applications through the same switch/transmission infrastructure.
Voice network providers certainly are eyeing ATM to B-ISDN as the network technology for the next century. However, ATM is not yet entirely appropriate for voice communications for reasons which include its relatively high overhead. Additionally, there is no compelling reason to invest in replacing the embedded circuit-switched network with an expensive ATM network, at least not outside the backbone.
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