Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1998-12-30
2003-07-22
Kizou, Hassan (Department: 2662)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S395100, C370S430000
Reexamination Certificate
active
06597689
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to telecommunications networking technology. More particularly, the present invention relates to a scalable network device, such as a switch or a multiplexer (e.g., DSLAM, ATM switch).
2. Description of Related Art
At its most fundamental level, a telecommunications system should provide service between at least two end users with a minimum level of quality that is acceptable for the kind of traffic that is being transmitted between these end users. End users have different needs from the telecommunications system because of the types and volume of traffic between them. One end user could telephone another user for voice communication. Another end user could use a computer and a modem to send an email to another user for data communication. Additionally, another end user could use a computer and a modem to access any number of Web pages on the Internet. Depending on the type of data (e.g., text, graphics, audio, video) that is being accessed, bandwidth requirements will vary. Thus, one end user may have very basic needs with minimal bandwidth and lots of delays, while another end user may have stringent requirements for lots of bandwidth with minimal delays. How can a telecommunications system, and its components, be designed to accommodate the various uses and needs?
Currently, the telecommunications infrastructure comprises network nodes (e.g., ATM switches, routers, other central office switches) that are coupled together. At the edge of this infrastructure are edge nodes (e.g., DSLAMs) for providing telecommunications service to subscribers (e.g., home users, business users, ISPs) via some local loop technology (e.g., ISDN, DSL). As known to those skilled in the art, local loop (or loop) refers to the interface (typically wires) between the subscriber and the telephone company's central office. Some of these network and edge nodes can be combined to create corporate networks and Intranets. These pieces of node equipment are usually installed and located in central offices as well as corporate offices. Communication between or among subscribers is possible through these network and edge nodes which run various communication protocols.
Although the bandwidth on the telecommunications backbone (e.g., DS3, OC3, STS3, or OC12) may be sufficient for all of the various types of traffic generated by subscribers, the bandwidth on the loop side is limited for today's traffic needs. Historically, analog dial-up with analog signaling was more than sufficient for most traffic. Even the digitization of voice, which requires approximately 4,000 Hz bandwidth, posed no problem since the telephone companies provided 64 Kbits/sec of bandwidth per channel. However, with the rise of the Internet and the increased interest in digital video and audio services, earlier modems were sorely lacking as speeds were as low as 1,200 bits/sec (V.22) to 33.6 Kbits/sec (V.34+) to today's 56 Kbits/sec (U.S. Robotics/3COM and Lucent/Rockwell). Even at 56 Kbits/sec, these modems are still too slow to fully capture digital audio and video services to the end user's satisfaction. Even if modems could use all of the available 64 Kbits/sec bandwidth provided by the telephone company, users would still be dissatisfied for the latest audio and video digital services. To give the appearance that more traffic was being passed through the lines than was actually being transmitted, several companies developed and implemented compression techniques.
For some time, even before the onset of the Internet, several loop technologies were slowly developed for this markef. One such loop technology is ISDN (at 128 Kbits/sec), which failed to deliver on its promise of better digital service because of the high cost of ISDN equipment and the higher cost of upgrading central office hardware and software. Furthermore, ISDN equipment was difficult to set up and make compatible with existing equipment because of poor diagnostics. The rates set by the public utilities commissions of various states are also very high. As of this writing, however, ISDN still has not disappeared and some service providers are offering ISDN service.
The traditional forms of leased line technologies, including T1 (at 24 channels of 64 Kbits/sec each for a total bandwidth of 1.544 Mbits/sec), fractional T1 (where users can get as many T1 channels as desired), and T3 (at 44.736 Mbits/sec or 28 T1 circuits), were also, of course, available. However, their prohibitively high expense makes these line technologies less attractive to the average subscriber. Recently, the pace of loop technology development has picked up due to the rise and proliferation of Digital Subscriber Line (DSL). Other competing technologies include Cable (CATV) Data Networks and Modems (or cable modems) and fiber optics.
At this point, however, DSL appears to be the front runner for the broadest application across the telephone companies' residential and small business subscriber base. However, DSL may not eliminate other technologies (e.g., T1, T3, ISDN, and cable modem) as the various telephone companies will make these technologies available to those who want them and can afford them. Various DSL technologies are available and they differ in technical operation rather than application. However, ADSL is receiving the most attention for loop technology in general and Internet access in particular. The entire XDSL family is provided below in TABLE A:
TABLE A
xDSL Family
Name
Data Rate
Mode
Physical
HDSL
1.544 Mbps
Symmetric
Two wire pairs
HDSL2
2.048 Mbps
Symmetric
One wire pair
SDSL
768 Kbps
Symmetric
One wire pair
ADSL
1.5 to 8 Mbps
Down
One wire pair but 18 Kft max
16 to 640 Kbps
Up
RADSL
1.5 to 8 Mbps
Down
One wire pair but can adapt
16 to 640 Kbps
Up
rates to line condition changes
CDSL
Up to 1 Mbps
Down
One wire pair and require no
16 to 128 Kbps
Up
hardware at CPE premises
ISDL
ISDN BRI
Symmetric
One wire pair
VDSL
13 to 52 Mbps
Down
1 to 4.5 Kft max and needs
1.5 to 6 Mbps
Up
fiber feeder and ATM
The first column, “Name,” identifies the type of xDSL technology. Refer to the GLOSSARY to obtain the full name from the acronym. The second column, “Data Rate,” is the typical maximum rate at which data transfers are accomplished for the various modes (see third column, “Mode”) for each xDSL type. While ADSL, RADSL, CDSL, and VDSL are non-symmetric (the downlink CO-to-subscriber rate is usually faster than the uplink subscriber-to-CO rate), HDSL, HDSL2, SDSL, and ISDL are syrnmetric. The fourth column, “Physical,” provides a brief description of the distinctive physical layer requirements or properties for each of the xDSL types.
To make DSL work at a central office, a DSL access multiplexer (DSLAM) is needed. However, current DSLAMs are limited. Although the various types of DSL technologies will be implemented, most existing DSLAMs cannot support multiple DSL technologies; that is, a given DSLAM can only support one DSL technology. This limits what the telecommunications providers are willing to do to expand DSL throughout their respective network. Given the shortage of space in central offices today, telecommunications service providers may be unwilling to purchase multiple DSLAMs for all the different types of DSLs that are available. In other cases, these telecommunications service providers may only deploy certain DSL types to be supported by the limited DSLAMs.
Compounding the problem of existing DSLAMs being tied to a particular DSL type is the fact that some existing DSLAMs are also tied to a particular modem modulation technique, either CAP or DMT. A DSLAM that is compatible with both modulation techniques would be desirable.
Another problem with existing DSLAMs is the nature of the virtual connections supported. In order for any two subscribers to communicate, a virtual connection must be set up between them. The end users and the network nodes predefine and maintain a virtual circuit and virtual path through the packet-switched mesh-type network t
Buckley Clifford James
Chiu Manfred F.
Eich Steven A.
Grimes Michael E.
Hill Gregory C.
Gorecki John C.
Kizou Hassan
Nortel Networks Limited
Pezzlo John
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