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Unformatted text preview: vices. Shrinking traditional telephony revenues and profitability will force
carriers to do the following:
• reduce the number of overlay network platforms; currently, most
carriers operate separate circuit-switched (voice and private line),
frame relay or asynchronous transfer mode (ATM), and Internet
protocol (IP) networks • cap investment in traditional circuit switches and migrate to a
converged switching infrastructure • provide more profitable, enhanced services from hardware and
software platforms designed to deliver integrated telephony-grade
voice, video, and data services The challenges presented by the shift from voice to data dominance will affect the
profitability and long-term viability of carriers of all stripes, from incumbents to
recent market entrants. Determining and implementing a sound migration
strategy from today’s overlay networks to an integrated circuit- and packetswitched architecture is, therefore, critical to the future of all telecommunications
carriers. 2. Voice and Data—The History
Today’s time-division multiplex (TDM) PSTN was designed to accommodate a
single application: uncompressed voice. The network was built to deliver 99.9994
percent up time, low-latency and jitter, highly scalable call routing through the
SS7 infrastructure, and value-added voice services such as voice messaging and
The PSTN provides voice access services in 64−kbps increments known as DS–0s.
The DS–0s are aggregated by digital access cross-connect systems (DACSs) for
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The International Engineering Consortium 2/14 presentation via DS–1 (1.5–Mbps) or DS–3 (45–Mbps) interfaces to Class 5
switches. The Class 5 switches communicate with access and toll tandem switches
to route calls across the telephone network to destination Class 5 switches. The
DS–0 voice calls are then split back out by DACSs to their original 64–kbps state.
The multiplexing and demultiplexing of voice traffic works well in a...
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- Spring '09