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Under the situation in a network including a transmitter and a receiver in which a transmitter converts a non-compressed packet to be transmitted as a full-header packet including a full header or a header-compressed packet including a compressed header, and sends the converted packet to the receive

Under the situation in a network including a transmitter and a receiver in which a transmitter converts a non-compressed packet to be transmitted as a full-header packet including a full header or a header-compressed packet including a compressed header, and sends the converted packet to the receiver, the transmitter sends at least an important packet in the non-compressed packet to be transmitted as a full-header packet. The important packet means for example, a packet containing the data serving an important role when the data terminal eventually receiving each packet reproduces the audio and/or image in accordance with the data in each packet.

대표청구항 ▼

What is claimed is: 1. A packet transmitting method for transmitting packets from a sender node to a receiver node through a network, comprising the steps of: determining by a communication apparatus provided at the sender node, whether each non-compressed packet to be transmitted is an important p

What is claimed is: 1. A packet transmitting method for transmitting packets from a sender node to a receiver node through a network, comprising the steps of: determining by a communication apparatus provided at the sender node, whether each non-compressed packet to be transmitted is an important packet, on the basis of a header, a timestamp, or size of each non-compressed packet; converting by the communication apparatus provided at the sender node, each non-compressed packet which is determined to be an important packet into a refresh-header packet, the refresh-header packet including a refresh header, the refresh header including enough information to recover synchronization in the receiver node; and transmitting a packet stream containing the refresh-header packet and a header-compressed packet to the receiver node, the header-compressed packet including a compressed header, the compressed header including less information than the refresh header. 2. The packet transmitting method of claim 1, wherein the refresh header is a full header containing a content of an original header included in the non-compressed packet. 3. The packet transmitting method of claim 1, wherein a format of the refresh header comprises a first format which can be used in a first initialization of a reconstruction process in the communication apparatus at the receiver node beginning to receive the packet stream, and a second format which can be used in a second initialization and following initialization, and the communication apparatus at the sender node converts the important packet in each of second and following packets in the packet stream into the refresh-header packet containing a refresh header whose header is the second format, and the communication apparatus at the sender node transmits to the receiver node the refresh-header packet. 4. The packet transmitting method of claim 1, wherein the refresh header is a header produced with reference to a header which has already been transmitted to the receiver node and acknowledged by the receiver node. 5. The packet transmitting method of claim 1, wherein the communication apparatus at the sender node determines whether each one of the non-compressed packets is an important packet, on the basis of a condition of marker bits of real-time transport protocol headers included in the non-compressed packets. 6. The packet transmitting method of claim 5, wherein a non-compressed packet is determined as the important packet when a non-compressed packet transmitted immediately prior to the non-compressed packet has the marker bit set. 7. The packet transmitting method of claim 5, wherein a non-compressed packet is determined as the important packet when the non-compressed packet has the marker bit set. 8. The packet transmitting method of claim 1, wherein the communication apparatus at the sender node determines whether each one of the non-compressed packets to be transmitted is an important packet, on the basis of packet sizes of the non-compressed packets. 9. The packet transmitting method of claim 8, wherein a non-compressed packet is determined as the important packet when the non-compressed packet has a larger size than a predetermined size. 10. The packet transmitting method of claim 8, wherein a non-compressed packet is determined as the important packet when the non-compressed packet has a larger size than a predetermined size and the next non-compressed header has a smaller size than a predetermined size or when the non-compressed packet has a smaller size than the predetermined size and the next non-compressed header has a larger size than the predetermined size. 11. The packet transmitting method of claim 1, wherein a non-compressed packet is determined to be an important packet when the non-compressed packet contains configuration information which is referred to in order to interpret data in the packet in the receiver node. 12. The packet transmitting method of claim 1, wherein the data in each of the packets comprises at least part of image data representing an image for several frames, and the important packet comprises a packet containing the first information in each of said frames. 13. The packet transmitting method of claim 12, wherein a non-compressed packet is determined as the first packet of the frame when the non-compressed packet contains a timestamp different from a timestamp contained in a preceding non-compressed packet. 14. The packet transmitting method of claim 1, wherein data in each of the packets represents a voice, and a non-compressed packet is determined to be an important packet when the non-compressed packet contains data representing a voice portion. 15. The packet transmitting method of claim 14, wherein the non-compressed packet containing data representing the voice portion is obtained on a basis of a change in packet size of a set of non-compressed packets to be transmitted. 16. The packet transmitting method of claim 1, wherein: data in each of the packets comprises at least a part of coded data representing image for several frames obtained by means of an algorithm containing intra-frame coding process and inter-frames prediction coding process, and a non-compressed packet is determined to be an important packet when the non-compressed packet comprises a packet containing a coded data obtained by the intra-frame coding process. 17. The packet transmitting method of claim 1, wherein: data in each of the packets comprises at least part of a layered coded data consisting of data in a base layer and data in an enhanced layer, and a non-compressed packet is determined to be an important packet when the non-compressed packet comprises a packet containing the data in said base layer. 18. The packet transmitting method of claim 1, wherein the communication apparatus at the sender node converts a non-compressed packet into a full-header packet even if the non-compressed packet is not an important packet, when a prescribed time has passed or a prescribed number of compressed-header packets has been transmitted after transmission of a last full-header packet. 19. The packet transmitting method of claim 1, wherein the communication apparatus at the sender node transmits the refresh-header packet every time when a specific number of packets are transmitted or packets ranging for a specific period of time are transmitted. 20. The packet transmitting method of claim 1, wherein when a synchronization loss occurs in a packet communication, the communication apparatus at the sender node transmits a refresh-header packet while transmission intervals thereof are exponentially increased. 21. The packet transmitting method of claim 1, wherein the communication apparatus at the sender node transmits a non-compressed packet to be transmitted as a refresh-header packet, in response to a request from the receiver node. 22. A program for causing a computer to execute a packet transmitting method for transmitting packets from a sender node to a receiver node through a network, the method comprising the steps of: determining by a communication apparatus provided at the sender node, whether each non-compressed packet to be transmitted is an important packet, on the basis of a header, a timestamp, or size of each of the non-compressed packets; converting by a communication apparatus provided at the sender node, each non-compressed packet which is determined to be an important packet into a refresh-header packet, the refresh-header packet including a refresh header, the refresh header including enough information to recover synchronization in the receiver node; and transmitting a packet stream containing the refresh-header packet and the header-compressed packet to the receiver node, a header-compressed packet including a compressed header, the compressed header including less information than the refresh header. 23. A computer readable storage media for storing a program which makes a computer execute a packet transmitting method for transmitting packets from a sender node to a receiver node through a network, the method comprising the steps of: determining by a communication apparatus provided at the sender node, whether each non-compressed packet to be transmitted is an important packet, on the basis of a header, a timestamp, or size of each of the non-compressed packets; converting by the communication apparatus provided at the sender node, each non-compressed packet which is determined to be an important packet into a refresh-header packet, the refresh-header packet including a refresh header, the refresh header including enough information to recover synchronization in the receiver node; and transmitting a packet stream containing the refresh-header packet and a header-compressed packet to the receiver node, the header-compressed packet including a compressed header, the compressed header including less information than the refresh header. 24. A relay apparatus provided in a network for receiving packets from a sender node of the network and transmitting the packets to a receiver node of the network, the relay apparatus comprising: a determining unit that determines whether each non-compressed packet to be transmitted is an important packet, on the basis of a header, a timestamp or size of each of the non-compressed packet; a compresser that converts each non-compressed packet which is determined to be an important packet into a refresh-header packet, the refresh-header packet including a refresh header, the refresh header including enough information to recover synchronization in the receiver node; and a transmitter that transmits a packet stream containing the refresh-header packet and a header-compressed packet to the receiver node, the header-compressed packet including a compressed header, the compressed header including less information than the refresh header. 25. A data terminal comprising: a determining unit that determines whether a non-compressed packet to be transmitted is an important packet, on the basis of a header, a timestamp or size of the non-compressed packet; a compresser that converts each non-compressed packet which is determined to be an important packet into a refresh-header packet, the refresh-header packet including a refresh header, the refresh header including enough information to recover synchronization in a receiver node; and a transmitter that transmits a packet stream containing the refresh header packet and the header-compressed packet to the receiver node, a header-compressed packet including a compressed header, the compressed header including less information than the refresh header.