Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
2001-03-01
2001-11-20
Marcelo, Melvin (Department: 2663)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S471000
Reexamination Certificate
active
06320875
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to communication protocols in digital networks. More particularly, the invention relates to methods and apparatus for protocol conversion in order to minimize latency and to improve efficiency and quality of packet transmission in applications including Internet telephony.
BACKGROUND OF THE INVENTION
More and more information is being shared and transmitted over computer networks, and more and more two-way communication is taking place using computer networks. With the growth and ubiquity of the Internet, more and more people are becoming familiar with computer networks and desire to conduct more and more of their daily affairs using computer networks, especially the Internet. With the increasing popularity of the Internet and other networks, there is a growing demand for increased speed and quality of service. The higher the quality of a particular product or service that can be provided over the Internet, the greater will be the demand for that product or service.
Smaller and more uniform computer networks can provide high-quality services without excessive difficulty, since greater control can be maintained over the network servers and clients. In such an environment, strict standards and protocols can be dictated and maintained. The Internet, on the other hand, must serve a tremendous variety of users, all over the world, and must provide means for transferring data over paths which may be extremely circuitous, with components having differing characteristics and bandwidths. One application which is stimulating considerable interest and which is growing rapidly in popularity, but which is still subject to significant obstacles, is Internet telephony or in other words, real-time voice communication over the Internet. This application has the promise of introducing the Internet into the daily lives of large numbers of people in a substantial way. The promise is of providing a low-cost substitute for a long distance telephone service with which people are familiar, and which they use frequently, but which, because of its cost, they are constrained to use much less frequently than they might otherwise choose to if the costs were significantly lowered while still providing comparable service. Internet telephony holds forth the promise of allowing people to communicate with friends and loved ones all over the world for the cost of an making an Internet connection. In the present state of the art, there remain, however, significant obstacles to high-quality Internet telephony. These obstacles arise in part because of the protocols used by the Internet for data transmission. For real time voice traffic, latency must be kept to a minimum or the delays incurred will significantly interfere with the quality of the voice conversation. For limited-bandwidth transmission channels such as modems, transmission control protocol (“TCP”), through the use of Vant Jacobsen compression, can accommodate small packets without the excessive overhead caused by a large header size. Such compression algorithms do not presently exist for user datagram protocol (“UDP”).
If small packets are used for UDP transmission, the available bandwidth provided by today's modems may not be enough to accommodate them, given their large overhead. However, if larger UDP packets are used for telephony, voice quality is degraded because a significant latency results. Such latency may arise because a wait is necessary to allow a large UDP packet to fill with data before it is dispatched.
On the other hand, if TCP is used to provide transmission all the way from the initial sender, over the Internet, and to the remote receiver, latencies may be too great for telephony because of the delays occasioned by detecting and resending lost packets. When measured against the quality of standard telephone service, an acceptable quality of Internet telephony service is not yet available. Thus, there exists a need in the art for methods and apparatus to provide Internet telephony data packet transmission which can accommodate a low-bandwidth connection between a user and a local host, but which can provide high-quality data transmission with low latency.
SUMMARY OF THE INVENTION
The present invention provides methods and apparatus for protocol conversion between transmission control protocol (“TCP”) and user datagram protocol (“UDP”). In one aspect of the present invention, TCP is used between the user and the local host. TCP is suitable for use in a modem link between a local user and an Internet Service Provider (“ISP”), because the modem itself provides a reliable connection, detecting and resending lost-data. Thus, the latencies caused by TCP's detecting and retransmitting lost packets are unlikely to occur. This provides a reliable connection-oriented transmission which can transmit small packets within the bandwidth provided by a typical modem and consistent with local telephone connections such as those provided by twisted wire pairs and standard telephone wires connecting most people to the phone network. The latency caused by TCP's detection and resending of lost packets is tolerable, because very few packets are lost at the connection between the user and the local host.
After each packet arrives at the local host, it is converted to UDP format and transmitted over the Internet. While the UDP packets have a big header and thus a high overhead with respect to the amount of data per packet, the local host is able to transmit such packets using UDP with low latency, because the bandwidth between the local host networks is great enough to tolerate the overhead caused by the large header size of the UDP packets. When the packet arrives at the destination node of the local host network, it is reconverted to TCP, and thence transmitted to the user of the destination node. This conversion allows for the transmission of low latency small packets. By tailoring the protocols used to take advantage of the characteristics of the different connections, significant improvements in efficiency and quality of service may be achieved.
A more complete understanding of the present invention, as well as further features and advantages of the invention, will be apparent from the following Detailed Description and the accompanying drawings.
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Katseff Howard Paul
Robinson Bethany Scott
AT&T Corp.
Marcelo Melvin
LandOfFree
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