Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1998-08-19
2001-04-10
Ton, Dang (Department: 2732)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S419000, C370S465000
Reexamination Certificate
active
06215797
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to computer networks and, more particularly, to network apparatus and associated methods that allows real-time traffic such as telephone and video to share a computer network with non-real-time traffic. The methods and apparatus of the present invention provide quality-of-service latency and bandwidth guarantees for time-sensitive signals sharing, for example, an Ethernet network with non-time sensitive signals.
BACKGROUND OF THE INVENTION
Computer telephony, that is, the delivery of telephone calls over computer networks, has recently become a focus of attention due to the potential cost savings of sharing these modern high-bandwidth facilities for multiple uses. Because computer networks packetize signals and then mix such packetized signals (or more simply, packets) from many sources over a single link, networks can make more efficient use of communications resources than conventional circuit-switched telephone systems. Furthermore, computer networks leverage the mass-production cost savings and technological advances of commodity products. This sharing of computer communications for non-computer signals therefore has the potential to greatly lower the cost of communications when used with telephone signals.
Computer network traffic from telephone, video, and other time-sensitive sources are generally referred to as real-time traffic because such traffic must arrive at a destination within a specified deadline. Real-time traffic generated from audio or video sources are usually generated in equally spaced time intervals. This type of periodic real-time traffic is referred to as isochronous traffic.
When isochronous traffic is digitized and combined with the sophisticated computer-processing compression techniques, the result is a significant reduction in bandwidth requirements. This use of computer technology to send telephone and video signals thereby results in even further cost savings.
However, conventional computer networks are not designed to handle real-time traffic. Collisions and congestion can induce delays and retransmissions, and can cause real-time traffic, such as video, audio, telemetry and control signals, to arrive late at a destination, thereby missing a deadline. Furthermore, such collision-induced delays are stochastic by nature and therefore unpredictable. Isochronous traffic sources become bursty after traveling through such networks. As a result, the quality of telephone calls placed over the Internet and computer networks in general is very poor at present.
Ethernet computer networks, in particular, use a form of media access control known as Carrier Sense Multiple Access with Collision Detect (CSMA/CD), also sometimes known as Aloha. This protocol is described in detail by the IEEE Standard 802.3. It provides a very simple and effective mechanism for allowing multiple packet sources to share a single broadcast computer network medium. To transmit a new packet, a transmitter need only sense that no packet is currently being transmitted by listening to the network. As a transmitted packet is broadcast to all receivers on the local network, listening to the network for activity is trivial. If a transmitter wishing to send a packet senses that a packet is currently being transmitted, then the transmitter defers transmission until it senses that the network is inactive. Collisions naturally arise as part of this mechanism. The most common scenario leading to a collision is where two or more stations, which are deferring their own respective transmissions during the transmission of another packet, sense a lack of activity at nearly the same time. The protocol detects collisions, and then aborts and reschedules transmission of all packets for a random time later. This protocol, while simple and effective for computer traffic, introduces collisions and delays as part of its natural operation. In fact, overloading such a network causes the entire network to become unusable, resulting in a significant reduction in throughput.
Although Ethernet is now ubiquitous throughout the Internet within local-area computer networks, or intranets, the use of variable packet sizes and Carrier Sense Multiple Access with Collision Detect for link access and control creates an even less predictable and less controllable environment for guaranteeing quality of service for wide-area real-time traffic that must traverse a plurality of Ethernet networks in order to reach a final destination.
DESCRIPTION OF RELEVANT PRIOR ART
A conventional Ethernet network
1
is shown in
FIG. 1
a
. Conventional Ethernet devices
100
, such as personal computers and printers, generate non-real-time traffic and are referred to herein as Non-Real-Time Devices (NRTDs). The NRTDs
100
have a standard Ethernet interface and attach to the conventional Ethernet network
1
through Network Interface Points
2
. The Network Interface Points
2
could represent a 10BaseT port, a 100BaseT port, a 10Base
2
(ThinLAN) port, for example. The Network Interface Points
2
may be interconnected by Repeaters or Ethernet Hubs
3
.
In conventional Ethernet networks, the attached devices
100
are called stations. When a station transmits a packet on the network, the signal is broadcast throughout the network. For a transmission to be successfully received by another station, there must be no other simultaneous transmissions. Thus, an arbitration mechanism to share the network is required. Ethernet networks use an arbitration mechanism known Carrier Sense Multiple Access with Collision Detect (CSMA/CD).
FIG. 1
b
provides an example that illustrates how the CSMA/CD protocol works. A time line of events is illustrated, representing the actions of five stations, labeled Station A, Station B, Station C, Station D, and Station E. These five stations could represent the five NRTDs in
FIG. 1
a
, for example. In this example, Station A transmits a packet
10
on the network after sensing that the network is idle. During the transmission of this packet
10
, Station B generates a packet
12
to transmit on the network, but defers the transmission (indicated by numeral
11
) because Station B senses activity on the network, due to the transmission
10
from Station A. As soon as Station B senses that the network is idle, Station B waits an additional amount of time, known as the Inter-Packet Gap (IPG)
19
, prior to transmitting a packet onto the network. In 10Mbit/sec Ethernet networks, for example, IPG is defined to be 9.6 microseconds, or 96 times. This constraint results in a minimum time spacing between packets. After Station B waits for an additional IPG seconds, it transmits the queued packet
12
. Accordingly, by sensing the network for activity, collisions can be avoided. Collisions, which occur when two or more stations transmit simultaneously on the network, are still possible, however, due to non-zero latency of detecting the state of the network and non-zero propagation delay of signals between the stations.
As shown in
FIG. 1
b
, for example, after Station B finishes transmitting a packet
12
, the network becomes idle. Sometime later, Station C transmits a packet
13
on the network after sensing that the network is idle. During this transmission from Station C, both Stations D and E each happen to generate a packet for transmission onto the network. As activity is detected on the network, due to the transmission
13
from Station C, Stations D and E defer their respective transmissions (indicated by numerals
14
and
15
) until the network is sensed idle. Stations D and E will sense that the network is idle at nearly the same time and will each wait an additional IPG
19
before transmitting their respective packets. Station D and Station E will then start transmitting packets on the network at nearly the same time, and a collision
16
then occurs between Station D and station E. The second station to start transmitting during the collision, say Station E, may or may not be able to detect the beginning of the transmission from the first station tha
Cruz Rene L.
Fellman Ronald D.
Fish & Richardson PC
Path 1 Technologies, Inc.
Sam Phirin
Ton Dang
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