Multiplex communications – Channel assignment techniques – Combining or distributing information via time channels...
Reexamination Certificate
1999-01-19
2003-03-25
Olms, Douglas (Department: 2661)
Multiplex communications
Channel assignment techniques
Combining or distributing information via time channels...
C370S400000
Reexamination Certificate
active
06539027
ABSTRACT:
BACKGROUND OF THE INVENTION
In the early part of the 20th century, long-distance telephone companies, primarily AT&T/Bell Telephone, made significant investments to establish an infrastructure of trunk lines running between the major cities. During the past 30 years, telephone companies have sought to upgrade this infrastructure with systems capable of high-speed digital connections.
To accomplish this conversion, trunk circuits and switching systems have been redesigned from analog to digital equipment. In older analog systems, each wire pair in the copper cable comprised a dedicated circuit supporting only one voice or data connection. Because of the high cost of copper cable, special equipment was developed to carry more than one speech conversation on a pair of wires. This technique, known as multiplexing, combines the data from several telecommunications devices onto one communications circuit. At the other end of the circuit, another multiplexer splits the data and routes it appropriately. The two common types of multiplexing are frequency multiplexing and time division multiplexing. Frequency division multiplexing, which involves dividing a trunk line's available bandwidth into discrete frequency bands, was used for transmitting multiple analog circuits via one pair of twisted copper wires. Time division multiplexing (TDM), which allocates discrete, reiterated time slots for each circuit, was developed to accommodate multiple digital transmission services sent over a single circuit.
In conjunction with TDM, the T1 digital carrier system was developed in the 1960's as a short distance transmission system for carrying digital signals over a single twisted pair of copper wires without interference. The bandwidth of a T1 line is 1.54 Mbps, yielding a capacity for 24 64 kbps digital channels and 8 kbps for keeping the ends of the trunk synchronized by imposing a framing process. To make use of the T1 system, voice signals are required to be converted into digital format, generally using a pulse code modulation (PCM) encoding scheme.
Conversion of voice and other analog sources to digital format is carried out by a channel bank, which samples each of the 24 analog circuits at a rate of 8000 times per second to produce a snapshot of the analog signal at precisely synchronized instants. The amplitude of the snapshot is rounded off the nearest of several specific, predetermined levels, in a quantization process. The quantized snapshot level is converted into an 8 bit binary representation of the analog signal. Thus, every channel is represented by an 8 bit PCM byte for analog signals, or one data byte for digital signals.
The term ‘channel bank’ is used because it may contain sufficient processing power to encode to digital format a bank of up to 24 individual channels per T1 port, and to decode these channels as well. Thus one channel bank encoding up to 24 channels may generate the composite digital signal to feed one T1 circuit, and a channel bank is required at either end of the T1 circuit.
Modern T1 circuits are formed by two twisted-pair cables (four wires total), enabling nodes at either end of a T1 line to transmit and receive in both directions simultaneously in full duplex mode. A T1 multiplexer divides a T1 line into 24 separate 64 kbps channels, each channel comprising a digital signal level 0 (DS-0). The multiplexed T1 signal format is termed digital signal level 1 (DS-1). The T1 digital carrier system can carry both data and nondata traffic, such as voice and video, because all these types of transmitted information can be digitally encoded. Therefore, the T1 line can carry “integrated” traffic so that a customer does not need to have separate lines (or trunks) for voice, video, and data.
A multiplexer placed at each end of a T1 line acts like a funnel allowing multiple sources and formats to be mixed at the transmitting end and to be extracted and appropriately routed at the receiving end. A T1 multiplexer typically consists of a T1 interface, a strobe unit, a power source, and control logic. Multiplexer devices also usually contain open slots to accommodate various types of channel cards, such as circuit cards or feature cards. The two most common types of channel cards are designed to support voice or data applications. A voice card provides a connection to an analog circuit, and carries out the digital to analog and analog to digital conversions. A data card provides a connection to a digital circuit, and may reformat or reframe the signal. The T1 multiplexer combines the digital signals from the voice and data channel cards and combines them into a single 1.544 Mbps circuit of 24 DS-0s.
For users who need less than 1.544 Mbps bandwidth, telecommunication companies offer fractional T1 service, allowing users to pay for the portion of the T1 bandwidth they use. This approach makes leased services more affordable for small businesses. For users who require more than the T1 bandwidth, telecommunications companies offer T3 trunks with a capacity of 28 multiplexed T1 lines, equivalent to 672 DS-0s, with a bandwidth of 44.7 Mbps. The T3 line is referred to as a digital signal level 3 (DS-3) channel.
Although the multiplexing and transmission of telecommunications traffic appears straightforward in conceptual terms, the actual task of setting up and managing a telecommunications system is extremely complex. A wide variety of input signals must be accepted, such as analog and digital voice, data, video, fax, modem, LAN/WAN, internet and intranet, and the like. These inputs may have differing protocols, framing, and timing, and must be reliably synchronized, transmitted and decoded. Circuits must be set up and maintained without interruption or fault, and signals must be routed to and from a large number of telecommunications devices. Bandwidth requirements may change on a regular basis, according to workday schedules, or may change abruptly due to unexpected demands. At any node on a transmission system, some channels may be required to be unloaded and replaced with other signals, whereas other channels may be passed through the node without alteration. These factors all contribute to an extremely complex signal processing environment.
SUMMARY OF THE INVENTION
In one aspect, the present invention generally comprises a modular, reconfigurable, intelligent signal multiplexer for telecommunications purposes. The multiplexer is comprised of a rack or shelf adapted to support a plurality of printed circuit cards. The cards may include feature cards, such as line cards, and at least one central controller card. All of the cards includes backplane connectors that are adapted to connect to customer premises equipment and to telecommunications lines and networks. The cards further include midplane connectors that are adapted to interconnect all of the circuit cards for data exchange under program control.
Each feature card also contains an embedded microprocessor with associated embedded operating system, as well as RAM memory and flash RAM. Consequently, all cards are software-independent, thereby reducing or eliminating the need for systemwide software upgrades. This design also facilitates system upgrades and new feature card installation without requiring new common equipment. Software control of the feature cards resides in the cards themselves, instead of residing within the central controller card.
The signal multiplexer processes digital inputs from a wide range of user equipment for transmission over digital facilities, including T1 and T3 lines. The trunk bandwidth is managed with programmable bandwidth allocation, which enables the service provider to allocate bandwidth to specific customers on an as-needed basis, and to alter the bandwidth allocation virtually instantaneously. The system employs a Simple Network Management Protocol (SNMP) to perform network configuration as well as to obtain performance reports, statistics collection and alarm monitoring. SNMP is accessed through a SNMP network manager or web browser that provides an intuitive graphical i
Coastcom
Pizarro Ricardo M.
Zimmerman, Esq. Harris
LandOfFree
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