Data Transferring method

Details Data Transferring method Data Transferring method

1999-06-07

2003-05-13

Vanderpuye, Ken (Department: 2661)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S432000

Reexamination Certificate

active

06563822

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a data transferring method, and in particular to a data transferring method in case of transmitting data to a plurality of terminals over a network.
In recent years, various services have been remarkable utilizing networks such as the Internet or intranet. As an example, are taken services which utilize those networks to distribute images or voice data. In these services, users can freely access to watch the images or listen to the voice data saved in servers.
These services are usually performed by a data transferring method which is called a unicast in which data are transmitted individually, that is one to one. Also, there are services in which data are transmitted simultaneously to users, e.g. by a multicast.
Hereinafter, the operations of the unicast and the multicast will be described referring to
FIGS. 17 and 18
, respectively.
(1) Unicast: see
FIG. 17
The data transmission is performed one to one in the unicast. Namely, as shown in
FIG. 17
, a server S
1
which is on a transmitting side transmits data with a proper address “192.168.100.201” of a terminal C
1
as a destination address. Then the data will be transmitted to the terminal C
1
which is the destination.
(2) Multicast: see
FIG. 18
A multicast address is prepared for each service in the multicast. For example, an address “224.1.1.100” is prepared for sports programs. Users who wish to have this service can receive the data by joining the multicast address “224.1.1.100”.
The server which is on a transmitting side only has to transmit data to the address “224.1.1.100” as in the case of unicast. Then, copies of data are made as required in the process of data transmission, so that the data are finally sent to all of the terminals (C
1
and C
4
) which have requested to receive.
In the multicast, since the data transmission by the server can be performed once no matter how many terminals there are to receive the data, it is characterized that loads of the network and the servers are reduced.
Therefore, the multicast is expected to have a large effect upon transmitting image data, such as relaying sports, events, or lecture images in a broadcast-like service form, which give heavy loads on the network and the servers.
However, there is no mechanism for guaranteeing data arrivals in the multicast. In other words, the server transmits data one-sidedly without taking any measures even if the data get lost on the way.
Also, when there is a difference between the rate in which receiving terminals consume the images or the voice data and the transmission rate of the server, it is possible for buffers in the receiving terminals to undertow or overflow.
From this point of view, a resending control for compensating the lost data (packets) when distributing data over the network and a flow control for controlling buffers in the receiving terminals not to overflow or underflow are required.
2. Description of the Related Art
(1) Prior Art Related to Resending Control
Firstly, a transmitting terminal (e.g., a server) embeds sequential numbers into transmitting packets. Receiving terminals (clients) can detect lost packets by checking the sequential numbers. The receiving terminals which have detected the lost packets request the transmitting terminal to resend the data, which will be compensated by having the transmitting terminal resend the requested data.
(2) Prior Art Related to Flow Control
{circle around (1)} Fixed Rate Control
Since the consumption rate of data is preliminarily determined for the images and the voice data, the transmitting terminal keeps sending the data at the same rate. Taking an example of 6 Mbps images data, the transmitting terminal transmits the data at the rate of 6 Mbps.
{circle around (2)} Window Control
This is a method by which the receiving terminals notify the receipt of data as well as their remaining buffer quantities to the transmitting terminal every time the receiving terminals receive the data.
The transmitting terminal transmits data based on empty buffer quantities of the receiving terminals. If there is an empty buffer of 100 KB in a receiving terminal, the transmitting terminal transmits 100 KB data, which is similarly repeated as shown in
FIG. 19
(a method used in TCP).
{circle around (3)} ACK Base Control
Firstly, the transmitting terminal transmits data at a fixed rate as shown in FIG.
20
. The transmission rate of the transmitting terminal is preset a little higher than the actual consumption rate of the images or the voice data. Then the data will accumulate in the buffer of the receiving terminal. When the receiving terminal detects that the buffer is about to overflow, the receiving terminal transmits a packet (ACK packet) indicating that the buffer is overflowing to the transmitting terminal. The transmitting terminal which has received this packet stops the transmission for a fixed period of time, thereby suppressing the buffer overflow in the receiving terminal.
(1) Problems Related to Resending Control
The above-mentioned prior art of the resending control has no problem as for a unicast data transfer. However, as for the multicast, since the number of the receiving terminals cannot be specified, there is a possibility that a large number of resending request packets are generated (see FIG.
21
). In this case, not only the resending process but also other data transfer processes are disabled, resulting in harmful influences over the entire network.
(2) Problems Related to Flow Control
The problem related to the above-mentioned fixed rate control {circle around (1)} is that even if the transmission rate of the transmitting terminal is fixed, a buffer failure of the receiving terminal may occur in the course of the continuous transmission (see FIG.
22
). This is caused by a little difference between the clock timings of the transmitting terminal and the receiving terminal. For example, the buffer failure occurs when the clock on the transmitting terminal side indicates that one hour has elapsed whereas the clock on the receiving terminal side indicate that only 59 minutes and 59 seconds have elapsed. This kind of difference occurs similarly in case of multicast for each terminal (see FIG.
23
).
As for common problems between the above-mentioned window control {circle around (2)} and ACK base control {circle around (3)}, the following three points are cited:
(i) Utilization for Multicast not Being Considered
Regarding the window control {circle around (2)}, when different quantities of empty buffers are notified from the receiving terminals, it is difficult to determine how much data to transmit. Regarding the ACK base control {circle around (3)}, only the receiving terminal which has the buffer occupied finally with the largest quantity is to be controlled so that the other receiving terminals are not considered.
(ii) Weakness for Network Delay
Regarding the window control {circle around (2)}, unless a packet from the receiving terminal which notifies the empty space of the buffer arrives at the transmitting terminal, the transmitting terminal cannot transmit the next data. Therefore, a throughput performance decreases in a network with a large delay.
Regarding the ACK base control {circle around (3)}, there is a possibility in a network with a large delay that the buffers of the receiving terminals fail before the ACK packets from the receiving terminals reach the transmitting terminal to effect the stop of transmission.
Namely, both control methods {circle around (2)} and {circle around (3)} are unsuitable for the utilization in a large-scaled network.
(iii) Increase of Transmission Packets
Regarding the window control {circle around (2)}, since the flow is to have the receiving terminals notify empty buffers and then to have the transmitting terminal transmit the data, there is a proportional relationship between the numbers of transmitting packets and control packets.
Regarding the ACK base control {circle around (3)}, although it depends on the transmission rates or the st

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