Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1998-05-20
2002-06-18
Yao, Kwang Bin (Department: 2664)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S395200
Reexamination Certificate
active
06407996
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a communications apparatus and a method of operating the same, and to a method of connecting a plurality of computer apparatus for communication with each other.
2. Related Art
It is known to provide a conventional personal computer or computer workstation with a microphone and an audio speaker operated by the processor of the personal computer or work station to allow voice communication between users of two such PCs or workstations. The facility of voice communication through a personal computer is known as an “Internet phone”. Sound pressure waves produced by a person speaking at a first sending computer are converted by the microphone into an electronic audio signal which is digitized by the processor. The digitized signal is divided into shorter packet signals by the processor, which are transmitted over a communications link to the processor of a second receiving personal computer or workstation or the like, which reassembles the packet signals to reconstitute the audio signal. The audio signal is then used to drive an audio speaker of the receiving computer, producing an audible sound. Similarly, a microphone operated by the receiving computer converts a voice sound signal into an audio electrical signal, which is digitized by the processor of the receiving computer, packetized and sent over the communications link to the first computer. The processor of the sending computer reassembles the packetized signals into an audio signal which is used to drive the audio speaker associated with the first sending computer. The communications link may be a local area network, for example an Ethernet, an intranet of networks which are interconnected by a common protocol, or the global Internet evolved from the original ARPANET.
A network architecture for the transmission of data in data packets is detailed in International Patent Publication Number WO 91/05419. This provides for the combination of both audio voice and data to be distributed through the same switch using a common packet structure. It allows for the dynamic allocation of bandwidth but does not facilitate the setting up of audio voice communications in a manner which is familiar to anyone using conventional voice-based equipment.
Referring to
FIG. 1
herein, there is shown schematically by way of example, a communication between a first personal computer
1
of the lap top variety having a microphone and a speaker, and a second, personal computer
2
also having a microphone and a speaker, via a communications link comprising a first modem
3
, a telephone network
4
, a second modem
5
, the second modem
5
linked to the worldwide Internet
6
via an Internet service provider gateway
7
and the second personal computer
2
connected to the Internet
6
by a second service provider gateway
8
.
A user of the first PC
1
is presented with an image of a telephone key pad on a display device
9
of the first PC. Under control of the processor of the first PC
1
, the user can dial up an address of the second PC
2
. The user of the second PC
2
can receive the packetized signals from the first PC, and voice communication between the first PC
1
and the second PC
2
is made, such that the user of the first PC can talk to the user of the second PC
2
. Similarly, a packetized signal is sent from the second computer
2
to the first computer
1
, so that a user of the second computer
2
can talk to the user of the first computer
1
.
Referring to
FIG. 2
herein, another example of use of Internet phones is shown, within a local area network (LAN). A plurality of computers are connected at a site by a local area network consisting of a communications link comprising an ethernet cable eg a co-axial cable or a twisted pair. A user of one PC
10
, connected to the LAN, may use the Internet phone facility to communicate with the user of another PC
11
, connected to the LAN. Computers connected to the local area network may access a wide area network (WAN) or an intranet of connected networks via a gateway computer, for example the computer
12
in FIG.
2
.
In each of the examples described with reference to
FIGS. 1 and 2
herein, a sound pressure wave signal is converted to an electronic data signal by a microphone, which is then digitized and packetized, and transmitted over the physical communications links, for example the ethernet cable and the cables connecting intermit sites, the transmission between computers being made in accordance with one or more protocols.
For communication across an intermit or the global Internet, messages are transferred over a number of communications links between a number of computers. Communication between a sender computer and a receiving computer is made in accordance with a point-to-point protocol (PPP) and each computer may support a range of such protocols. Referring to
FIG. 3
herein an individual voice packet signal
30
containing voice data, and produced by an application program which converts a voice signal to a plurality of signal packets, is provided with a first header signal
31
by a first protocol. The first header signal contains information in the form of bytes of data added to the packet signal
30
. For example where the first header signal is added to the packet signal in accordance with the sequence to packet exchange (SPX) protocol, packet sequencing information may be included in the header signal to ensure that the packet signals arrive in order, and a handshaking protocol is included, to ensure that as packets are received by the receiving computer the receiving computer acknowledges receipt of the packet signals.
Whilst some protocols, such as the SPX protocol are reliable for sending packet signals over an LAN, other protocols are less reliable. For example the Internet packet exchange (IPX) protocol sends packet signals over a network independently of each other. In
FIG. 3
herein the IPX protocol takes the first header signal
31
and the packet signal
30
and treats this as a composite packet signal
32
, to which is added an IPX protocol header signal
33
.
The IPX protocol makes a “best effort” to deliver the packet signal to the address specified in the header signal
33
, but it cannot guarantee delivery because it does not include error detection or correction. The IPX protocol defines a hierarchical address structure that, within reason, is independent of the underlying physical network. This independent structure allows packet signals to be routed between networks and passed over dissimilar physical networks. However, the IPX protocol relies upon the underlying network, or other layers of protocol to provide reliable delivery. Where packet signals are sent over an incompatible network, the packet signals are encapsulated in header signals that are compatible with the network, in accordance with a protocol which is compatible with the particular section of network which is to be traversed. For example an IPX headed packet can be encapsulated in a user datagram protocol (UDP) header and then in an Internet protocol (IP) header in order to tunnel the IPX packet through a transmission control protocol\Internet protocol (TCP\IP) network.
In a TCP\IP network, the Internet protocol defines a datagram ie the basic unit of information signal transmitted over the TCP\IP network, and defines the addressing used by TCP\IP, thereby routing the packet signals. The user datagram protocol (UDP) is the TCP\IP transport protocol used for packet delivery. The UDP does not have the overhead of creating connections and verifying delivery.
Referring to
FIG. 4
herein, as another example of encapsulation of packet signals by protocol headers, the SPX and IPX protocols can be replaced by a single NetWare protocol header signal. A packet signal
40
having a NetWare header signal
41
may be encapsulated by the UDP and IP protocol headers signals
42
,
43
respectively for transmission over the global Internet. By encapsulating packets of signals
British Telecommunications public limited company
Nixon & Vanderhye P.C.
Yao Kwang Bin
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