Transmitter and transmitting method, receiver and receiving...

Details Transmitter and transmitting method, receiver and receiving... Transmitter and transmitting method, receiver and receiving...

1998-04-28

2002-06-11

Yao, Kwang Bin (Department: 2664)

Multiplex communications

Data flow congestion prevention or control

Flow control of data transmission through a network

C370S410000

Reexamination Certificate

active

06404739

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to transmitters and transmitting methods, receivers and receiving methods, and transceivers and transmitting/receiving methods, and in particular, for example, to a transmitter and transmitting method, a receiver and receiving method, and a transceiver and transmitting/receiving method which enable the efficient and highly reliable distribution of data to a plurality of users.
2. Description of the Related Art
Methods for efficiently distributing data to a plurality of users include, for example, teletext for transmitting data such as characters, together with images and sound, by using so-called “broadcasting transmission media”, such as terrestrial signals, a satellite link, and a CATV network.
In addition, techniques have been recently proposed in which data are efficiently distributed to a plurality of users by using, for example, the Internet etc. which uses a computer network and not a broadcasting transmission medium.
For example, techniques for efficiently distributing data to a plurality of users in the Internet include one called “Internet protocol (IP) multicast” for multiple broadcasting of data.
FIG. 8
shows the structure of one example of a data distribution system for distributing data by IP multicast, where the system means a logical group of a plurality of apparatuses, and each component apparatus does not need to be in an identical casing.
According to IP multicast, multicast addresses for performing simultaneous multicast (special IP addresses, generally called “class D”, having values from 224.0.0.0 to 239.255.255.255) are assigned to a receiver group as the collection of the receivers as the IP addresses of receivers to which data are distributed. A transmitter
101
, as a server or the like for multicasting data, designates one particular multicast address before transmitting the data, and receivers
103
to
107
, such as computers which receive the multicast data, are designated by the multicast address. In this case, when a router, which performs communication based on a TCP/IP protocol, adapted for multicast on a communication link
102
, receives an IP packet having the designated multicast address, it finds channels in which there are the receivers having the designated multicast address, and transmits duplicates of the packet.
Accordingly, the transmitter
101
can distribute data to a plurality of receivers (receivers
103
to
107
in
FIG. 8
) for receiving the data by simply designating one address (multicast address) without paying attention to the plurality of receivers.
For example, in the communication link
102
, such as the Internet, in order to reduce its traffic, data transfer channel control adapted for the IP multicast, such as omitting the transfer of redundant data and transferring data only to necessary addresses, may be performed.
According to the IP multicast, data transfer is performed in accordance with a user datagram protocol (UDP) as one of several connectionless protocols in which communication is performed without recognizing the reception of data at others (the receivers
103
to
107
in FIG.
8
). Although the communication based on the UDP can reduce transmitting and receiving loads and can increase the processing speed, the reliability of data deteriorates because, at the level (the protocol level), signal ACK (acknowledgment) (hereinafter referred to as “acknowledgement signal ACK” if necessary) representing that data has been successfully received, and signal NAK (negative acknowledgment) (hereinafter referred to as “retransmission request signal NAK” if necessary) for requesting the retransmission of data when the data has not been successfully received, are not transmitted as responses from the receiving end to the transmitting end.
Accordingly, in order to improve the reliability of data, communication protocols such as a reliable multicast transport protocol (RMTP) have been proposed.
According to communication based on the RMTP, at first, the IP multicast is used to multicast data from the transmitter
101
to the receivers
103
to
107
via the communication link
102
, based on the UDP, as shown in FIG.
9
A. As shown in
FIG. 9B
, among the receivers
103
to
107
, those which have successfully received the data transmit acknowledgement signals ACK, and the others which have not successfully received the data transmit retransmission request signals NAK to the transmitter
101
via the communication link
102
, based on the UDP.
As shown in
FIG. 9B
, the receivers
104
and
106
have successfully received the data, and accordingly transmit the acknowledgement signals ACK to the transmitter
101
, while the receivers
103
,
105
and
107
have not successfully received the data, and accordingly transmit the retransmission request signals NAK to the transmitter
101
.
When the transmitter
101
receives the retransmission request signals NAK, it transmits (retransmits) the requested data again, based on the UDP, as shown in
FIG. 9A
, and it repeatedly transmits the data until no retransmission request signals NAK are transmitted, or until a predetermined time while the retransmission request signals NAK are being transmitted.
According to communication based on the RMTP, either the acknowledgement signal ACK or the retransmission request signal NAK is always sent back. Thus, while the efficiency of distributing data to a plurality of users by using the IP multicast is maintained, the reliability of the data can be improved.
When data are distributed using a transmission medium such as terrestrial signals, a satellite link, and a CATV network, the data can simultaneously be multicast in a broad area. At present, protocols based on Internet protocols (IPs) such as the UDP and a transmission control protocol (TCP), which are successfully employed in a computer network, are not supported. Accordingly, when a loss which cannot be restored, or another error is generated while the data are being transmitted, nothing can be done to cope with the error. Therefore, the reliability of the data deteriorates.
In addition, in the case that the IP multicast is performed using, for example, the Internet as a computer network, employing the above-described RMTP can improve the reliability of data. However, in the present Internet, performing the IP multicast causes the repeated transmission of identical data in a wide range, which wastes the limited resources.
Accordingly, techniques for reducing the network traffic include one which implements data transfer channel control adapted for the IP multicast, such as omitting the repeated transferring of data, and transferring data only to necessary receivers, as described above. In this case, a router for performing the control must be provided in the network. However, when it is assumed that, for example, the worldwide Internet is used as the network, replacing every router in the Internet with such a special router is not practical at present.
Many enterprises connected to the Internet often provide a firewall in order to prevent third parties from intruding into their networks. Packets based on the IP multicast are blocked by the firewall. Thus, the network surrounded by the firewall cannot receive packets based on the IP multicast.
In addition, according to the RMTP, it is required that either acknowledgement signal ACK or retransmission request signal NAK should always be sent as a response in order to strengthen the reliability of data, as described in FIG.
9
B.
Accordingly, a network that enables bidirectional communication is needed for combining a transmitter and receivers. In order to accept data distribution service based on the RMTP, the receivers must transmit acknowledgement signals ACK and retransmission request signals NAK to the transmitter.
In addition, for example, in the case that data are distributed to a large number of nationwide or worldwide users, causing every user (user's receiver) to always transmit either acknowledgement signal ACK or retransmission request

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