Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1999-12-21
2002-10-01
Kizou, Hassan (Department: 2631)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S463000, C370S465000, C370S466000
Reexamination Certificate
active
06459708
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to the field of telecommunications, and more particularly to an apparatus and method for providing T1/T1 telecommunications links over a high bandwidth data network.
2. Description of the Related Art
Along with the widespread proliferation of the telephone in the early 1900's came the attendant development of the supporting infrastructure required to interconnect millions of these communication devices. A complex network of wires, cables, and switching equipment was developed to support the switching of calls from their source to their destination. To a significant degree, this infrastructure is still in place today.
The backbone of the public switched telephone network (PSTN) consists of a network of local exchanges, or local switches. A local switch is the point at which all of the telephones within a its local area connect into the PSTN. A switch is also referred to as a central office switch or a telecommunications switch. Each of the telephones in a local area are connected to a pair of telephone wires and all of the telephone wires in the local area originate at the central office switch. When a user picks up the receiver of his/her telephone, equipment within the local switch generates the dial tone that he/she hears in the receiver. When the user dials a destination number, the equipment in the local exchange decodes the number and routes the call to its destination. If the destination telephone is also connected to the local switch, or central office switch, then the equipment connects the calling telephone pair to the destination telephone pair for the duration of the call. During the conversation, voice signals are transmitted as over the connected pairs of wires. When the user hangs up the telephone receiver, then the switching equipment terminates the connection between the two pair of wires.
The above scenario applies, however, only to the interconnection of telephones within a local exchange. There are, in fact, hundreds of thousands of local exchanges all over the world. And to support the switching of calls from telephones in a source exchange to a destination exchange, there also exists a network of cables and supporting equipment. A cable or other medium that interconnects telephone exchanges, or telecommunications switches, is referred to as a trunk. A trunk typically is specified to support an average number of calls between its source telecommunications switch and destination telecommunications switch. Hence, when a call is placed from a source telephone interfaced to the source switch to a destination telephone interfaced to the destination switch, the switching equipment in both the source exchange and the destination exchange interact to effect the call. The source telecommunications switch decodes the called number and switches, or routes, the call over one of the trunks connected to the destination exchange. The destination telecommunications switch receives the call over the trunk from the source exchange, and further decodes the called number so that the call is routed to the destination telephone. In any metropolitan area today, there is network of local telephone exchanges along with their associated inter-exchange trunks to handle the switching of calls made within that area.
Similarly, these larger, metropolitan networks of exchanges are interconnected together in the same manner: A series of trunks interconnect all of the metropolitan areas within the United States and likewise, trunks interconnect most of the countries of the world. A trunk is the primary interconnection media for the PSTN.
In earlier years, as noted above, trunks essentially consisted of some number of wires between two central office switches. But in addition to the wires, trunks also consisted of a number of in-line signal amplifiers to prevent degradation of the analog voice signals that were routed over the interconnecting trunks.
In the 1960's, a major development within the telecommunications industry enabled service providers to improve the quality of trunk interconnections, while at the same time drastically reducing the number of wires which were theretofore required to provide trunk interconnections between central office switches. This development, the T1 carrier protocol, prescribes a series of time-division multiplexed formats for the transmission of digitized telephone conversation data, each of which allow up to 24 separate conversations to be carried between switches on the same pair of telephone wires. A basic T1 signal is a pulse coded modulation carrying 24 8-bit data elements, each of the 8-bit data elements containing a digitized and encoded sample of one of the 24 conversations. Samples are taken from each of the 24 conversations, or channels, at a rate of 8,000 samples per second and these samples are continuously transmitted at a 1.544 Mbps carrier frequency over a single pair of wires. A 125-microsecond portion of the transmission that contains encoded samples from channels
1
through
24
is known as a T1 frame. In actual practice, out-of-band signaling bits and other information are also contained in a T1 frame, however, the basic structure of a T1 frame is as described above.
The T1 carrier protocol is the basis protocol that is used to transmit trunk data within the United States. Today, it is more common to find high speed inter-exchange trunk links such as T3 links or OC-48 links. These links are, however, aggregates of T1 links that are generated by combining T1 link signals through devices commonly referred to as add drop multiplexers (ADMs). In Europe, the basis protocol used for trunks is E1. The E1 protocol varies from the U.S. standard in terms of the encoding of the signals, in terms of the number of channels that are sampled and transmitted at the 8,000 sample/second rate, and in the absence of signaling bit information. In E1, there are 32 channels per frame rather than 24. To achieve the 8,000 sample/second rate, the E1 carrier is transmitted at 2.048 Mbps. In Europe, ADMs are also used to aggregate E1 links into higher speed trunks such as E3 trunks.
The benefits provided by the T1(E1) protocol caused a significant expansion in the services provided over the. PSTN. As a result, telephone service providers have invested substantially in switching equipment that provides trunk signals compatible with the T1(E1) protocol. It is virtually impossible today to find a telecommunications switch which does not employ some form of the T1 protocol for the provision of inter-switch trunks. And service providers have continued to increase their investment in T1 switching technologies for nearly forty years. As alluded to above, a typical present day trunk consists of a number of aggregated T1 links, the most common form adhering to OC-48 protocol. OC-48 prescribes a 2.5 Gbps transmission rate.
Two developments during the 1980's, however, began to push the telecommunications industry to provide expanded and more varied services, i.e., services other than the transmission of voice signals. Advances in microcircuit design and fabrication techniques have enabled a significant percentage of the civilized world to have a computer in the home or office. In conjunction, advances in computer networking techniques and protocols have enabled all of those computers to communicate over the Internet. The Internet is a global network of interconnected computers that utilize a packet-switched communications protocol known as Internet Protocol (IP). And since the cables and trunks within the PSTN already provided the initial skeletal structure for integrating local, metropolitan, and global networks of computers, telephone service providers began to provide, and continue to provide, routing and distribution services for computer data that is transmitted via the Internet.
Five years ago, approximately 95 percent of the traffic passed over the PSTN was voice traffic. Today, voice traffic accounts for only 50 percent; computer data accounts for the remaining 50 p
Cox James
Gerlach Jack
Mott James
Pearson Robert
Huffman James W.
Huffman Richard K.
Kizou Hassan
Toledo Communications, Inc.
Tsegaye Saba
LandOfFree
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