KR20180050983A - Method and apparatus for transmitting rtp packet - Google Patents

Abstract

An apparatus for transmitting a real time protocol (RTP) packet sets that an extension header is included after an RTP fixing header in the extension field of the RTP fixing header, represents the sampling time information of the first byte of the RTP packet with time information up to nanoseconds, and then transmits the RTP packet including the RTP fixing header and the extension header. Accordingly, the present invention can provide precise sampling time information for real-time communication.

Description

METHOD AND APPARATUS FOR TRANSMITTING RTP PACKET [0002]

The present invention relates to an RTP packet transmission method and apparatus, and more particularly, to an RTP packet transmission method and apparatus capable of providing accurate sampling time information.

A time stamp indicating a time in a conventional RTP (Real Time Protocol) has a length of 32 bits, has a unit of 1 / 65535sec as a minimum unit, and can be configured with an interval of 15.2us. These RTPs can not be used in environments that require accuracy in time units of 15.2us or less. Also, these timestamps are calculated relatively based on NTP (Network Time Protocol). Due to the network delay between the NTP server and the client and the time error of the NTP server itself, the time stamp calculated based on the NTP may have a significant error of ± 5 to 100 ms.

An object of the present invention is to provide an RTP packet transmission method and apparatus capable of providing accurate sampling time information for real-time communication.

According to an embodiment of the present invention, a method of transmitting an RTP packet in a RTP (Real Time Protocol) packet transmission apparatus is provided. The RTP packet transmission method includes configuring that an extension header is included in an extension field of an RTP header, after the RTP header is included in the extension header, and storing the sampling time information of the first byte of the RTP packet in nanoseconds And transmitting the RTP packet including the RTP header and the extension header.

The extension header may include a plurality of bits for indicating the sampling time information as Year, Month, Day, Hour, milliseconds, microseconds, and nanoseconds. Lt; / RTI > field.

The extension header may further include a buffer field indicating a type of the time synchronization method.

The time synchronization method may include a GPS (Global Positioning System) or a method using wireless standard radio waves.

According to another embodiment of the present invention, an RTP packet transmission apparatus is provided. The RTP packet transmission apparatus includes a processor and a transceiver. The processor sets an extension header in the extension field of the RTP header and sets up sampling time information of the first byte of the RTP packet in nanoseconds in the extension header to generate an RTP packet. The transceiver transmits the RTP packet.

The processor can set the sampling time information in the extension header up to the year, month, day, hour, milliseconds, microseconds, and nanoseconds have.

The processor sets a type of time synchronization method in the extension header, and a method using GPS or wireless standard radio may be used as the time synchronization method.

The transceiver includes a GPS receiver or a standard radio receiver, and the processor can set the sampling time information using time information acquired through the GPS receiver or the standard radio receiver.

According to the embodiment of the present invention, since it is possible to set a very precise time, it can be easily utilized in a need for a very strict real time communication such as telemedicine, military, and the like. In addition, accurate time setting enables real-time network latency measurement and quality measurement performed by expensive network measurement equipment to be performed inexpensively and easily, and only GPS receiver or standard radio receiver can be installed. Do.

1 to 3 are views for explaining time synchronization to which the present invention is applied.
4 is a diagram illustrating a structure of an existing RTP packet header.
5 is a diagram illustrating a structure of an RTP header according to an embodiment of the present invention.
6 is a flowchart illustrating an RTP packet transmission method according to an embodiment of the present invention.
7 is a diagram illustrating an RTP packet transmission apparatus according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification and claims, when a section is referred to as "including " an element, it is understood that it does not exclude other elements, but may include other elements, unless specifically stated otherwise.

Now, an RTP packet transmission method and apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

1 to 3 are views for explaining time synchronization to which the present invention is applied.

Referring to FIG. 1, NTP (Network Time Protocol) is a time synchronization method over a network. The client 120 receives time information from the registered NTP server 110 and applies the time information to the local clock to perform time synchronization. Here, the client 120 corresponds to a user terminal. The client 120 may request time information from the NTP server 110 and time information from the NTP server 110. [ Alternatively, the NTP server 110 may broadcast the time information to the network at regular intervals, and the client 120 may receive the time information broadcast from the NTP server 110. However, in the time synchronization method using NTP, a time error corresponding to the network delay time occurs.

Alternatively, as shown in FIG. 2, there is a time synchronization method using a GPS (Global Positioning System). The client 220 can receive the time information transmitted from the satellite 210 and apply it to the internal clock. As described above, the time synchronization method using the GPS requires very little time error, but the GPS receiver 222 for receiving the satellite signals must be installed outdoors.

Referring to FIG. 3, there is a time synchronization method using a standard radio wave. The client 320 can receive the standard time information of the radio wave from the standard wave transmission device 310 and apply it to the internal clock. The client 320 may include a standard radio receiver 322 to receive a standard radio wave from the standard radio frequency transmission device 310. [ The time synchronization method using the standard radio wave is the most precise and error-free among the time synchronization methods described up to now. However, it can only be used in countries providing standard radio.

Table 1 shows the time errors that can occur in time synchronization using NTP, GPS, and standard radio waves.

[Table 1]

As shown in Table 1, in the case of standard radio waves, the error is about ± 2 × 10 ^-8 ns and the error is extremely low. On the other hand, the error of GPS is ± 1ns, and the error of NTP is about ± 5 ~ 100ms. Therefore, the time synchronization method using NTP can not be used in a real time sensitive environment.

In the embodiment of the present invention, it is assumed that both the server and the client providing the RTP service set the time using standard radio waves or GPS which have almost no error.

4 is a diagram illustrating a structure of an existing RTP packet header.

Referring to FIG. 4, RTP is a protocol for real-time transmission, and the RTP packet header is composed of a fixed header 1 and an extended header 2.

The fixed header 1 includes a version field 10, a padding field 11, an extension field 12, a contributing source count (CSRC) count, A CC field 13, a marker M field 14, a payload type (PT) field 15, a sequence number field 16, a timestamp field 17, a synchronization source (SSRC) field 18, and a CSRC field 19.

The V field 10 is composed of two bits, indicating a protocol version, and the current version is 2.0.

The P field 11 is composed of 1 bit, and is used to form an RTP packet payload in units of 32 bits. The P field 11 indicates whether there is a padding byte. If the value of the P field 11 is set to 1, it indicates that a padding byte is included at the end of the payload of the RTP packet .

The X field 12 is composed of 1 bit and indicates whether there is an extension header 2 between the fixed header 1 and the payload. When the value of the X field 12 is 1, one extension header 2 indicates that the extension header 2 is next to the fixed header 1.

The CC field 13 is composed of 4 bits, and indicates the number of CSRC identifiers appearing after the fixed header (1). The CC field 13 indicates the number of the media when they are synthesized by the RTP mixer. In other words, the RTP packets are transmitted through the network, and the intermediate system receives the RTP packets from various sources and combines them appropriately to create a new type of RTP packet and transmit it to the next system. The intermediate system that performs this function is called an RTP mixer do.

The M field 14 is composed of 1 bit, and is defined by a profile, so the usage method is determined according to the payload type. The M field 14 is used to indicate the frame boundary in the RTP packet stream. For example, the video packet stream may represent the end of a frame, and the audio packet stream may represent the end of talk spurt.

The PT field 15 is composed of 7 bits and indicates the type of the payload in the RTP packet. The RFC 1890 profile corresponds to payload type code in payload format. That is, if the value of the PT field 15 is 0, it indicates the audio information of the encoding system and has a 800 Hz clock rate and one audio channel.

The sequence number field 16 is composed of 16 bits and indicates the sequence number of the RTP packet. The value of the sequence number field 16 increases by one each time an RTP packet is transmitted and the receiver can detect a packet loss through this field and restore the packet order. The initial value of the sequence number field 16 may be set to be random.

The timestamp field 17 consists of 32 bits and represents the sampling instant of the first byte (octet) of the RTP packet in the RTP packet stream. The sampling time is generated from a constantly increasing clock, and the receiver uses this field 17 for synchronization and jitter calculation of received RTP packets.

The SSRC field 18 is composed of 32 bits and identifies the source of the RTP packet. Within one RTP session, each RTP packet has a different SSRC identifier. SSRC is a 32-bit unique value randomly assigned by the source when a new stream starts instead of the sender's IP address. This unique value is irregularly generated and may represent the source identifier of the RTP packet, such as, for example, a camera or a microphone.

The CSRC field 19 is used to identify the contributing sources of the payload contained in the RTP packet. The number of CSRC identifiers is displayed in the CC field 13 and a maximum of 15 CSRC identifiers can be displayed in the CSRC field 19. [ That is, when a plurality of RTP packets are combined through the RTP mixer in the CSRC field 19, the CSRC identifiers of the original sources combined except for the SSRC are listed. If there is only one packet source, the value of the CC field 13 is 1, the SSRC identifier has a value, and the CSRC field 19 is empty.

The extension header 2 is for additional information to be transmitted via the RTP header and may include a profile field 20, a length field 21 and an extended header content field 22. In the embodiment of the present invention, time information included in the time stamp field 17 is more accurately provided using the extension header 2.

5 is a diagram illustrating a structure of an RTP header according to an embodiment of the present invention.

5, the timestamp field 17 of the RTP fixed header is applied in the same manner as before, and the value of the X field 12 indicates that the extended header 2 exists in order to indicate the precise sampling time information. 1 " And the extension header 2 contains precise sampling timing information.

The profile field 20 of the extension header 2 is composed of 16 bits and can be defined by a profile. According to an embodiment of the present invention, the value of the profile field 20 is set to 2048, where the upper four bits of the 16 bits are set to 1.

The length field 21 of the extension header 2 is composed of 16 bits and indicates the length of the extension header 2. According to an embodiment of the present invention, the length field 21 may be set to 32 bits.

The plurality of extension header content fields 22a, 22a of the extension header 2 are each composed of 32 bits. The first six bits of the first extended header content field 22a indicate the year and can be expressed up to 63 years. The next four bits represent the month, which can represent from 1 to 12. The next five bits represent day (1 to 31). The next five bits represent the hour and can represent from 0 to 24 hours. The next six bits represent the minutes and represent 0 to 60 minutes. The next six bits represent seconds and represent 0 to 60 seconds.

 The first two bits of the second extended header content field 22b are composed of a buffer and indicate a time synchronization method. For example, if the value of the first two bits is 01, the time synchronization using GPS is indicated. If the value is 10, the time synchronization method using wireless standard radio waves is shown. The next 10 bits represent milliseconds (milliseconds, ms) and represent 0 to 999. The next 10 bits represent microseconds (us) and represent 0 to 999. The next 10 bits represent nanoseconds (ns) and can represent 0 to 999.

As described above, according to the embodiment of the present invention, since the time information can be expressed in units of nanoseconds by using the extension header 2, a more accurate time can be indicated and it can be used in an environment requiring more accurate time have.

6 is a flowchart illustrating an RTP packet transmission method according to an embodiment of the present invention. In FIG. 6, it is assumed that the RTP client 1 610 desires strict real time (tough real time) and waits in the RTP client 2 620. At this time, it is assumed that the RTP client 1 610 and the RTP client 2 620 have a GPS receiver or a standard radio receiver capable of setting strict real time.

6, when the RTP client 1 610 receives accurate time information through the GPS receiver or the standard radio receiver (S610), it generates an RTP packet as shown in FIG. 5 using time information (S620 , And transmits the RTP packet to the RTP client 2 620 (S630).

The RTP client 2 (620) receiving the RTP packet receives accurate time information through the GPS receiver or the standard radio receiver (S640). The RTP client 2 620 generates an RTP packet as shown in FIG. 5 using time information (S650), and transmits the RTP packet to the RTP client 2 620 (S660).

As described above, the RTP client 1 610 and the RTP client 2 620 can perform strict real-time communication by transmitting and receiving RTP packets including accurate time information.

If either the RTP client 1 610 or the RTP client 2 620 does not have a GPS receiver or a standard radio receiver and can not receive accurate time information via a GPS receiver or a standard radio receiver, And transmits the packet.

7 is a diagram illustrating an RTP packet transmission apparatus according to an embodiment of the present invention.

Referring to FIG. 7, the RTP packet transmission apparatus 700 includes a processor 710, a transceiver 720, and a memory 730.

The processor 710 generates an RTP packet as shown in FIG. Particularly, the processor 710 can set up an extension header in the extension field of the RTP header, and set the time synchronization method and the precise time information in the extension header, thereby generating an RTP packet for strict real-time communication.

The transceiver 720 is coupled to the processor 710 to transmit and receive wireless signals.

The memory 730 stores a command to be executed by the processor 710 or temporarily stores the command by loading the command from a storage device (not shown). The processor 710 may execute instructions that are stored or loaded into the memory 730. The memory 730 may also store information related to the operation of the processor 710.

The processor 710 and the memory 730 are connected to each other via a bus (not shown), and an input / output interface (not shown) may be connected to the bus. At this time, a transceiver 720 is connected to the input / output interface, and peripheral devices such as an input device, a display, a speaker, and a storage device may be connected.

The embodiments of the present invention are not limited to the above-described apparatuses and / or methods, but may be implemented through a program for realizing functions corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded, Such an embodiment can be readily implemented by those skilled in the art from the description of the embodiments described above.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

Claims (8)

A method for transmitting an RTP packet in an RTP (Real Time Protocol) packet transmission apparatus,
Setting an extension field of the RTP fixed header to include an extension header after the RTP fixed header,
Indicating the sampling time information of the first byte of the RTP packet as time information up to the nanoseconds unit in the extension header,
Transmitting an RTP packet including the RTP fixed header and the extension header
Gt; RTP < / RTI > The method of claim 1,
The extension header may include a plurality of bits for indicating the sampling time information as Year, Month, Day, Hour, milliseconds, microseconds and nanoseconds. Gt; RTP < / RTI > The method of claim 1,
Wherein the extension header further comprises a buffer field indicating a type of a time synchronization method. 4. The method of claim 3,
Wherein the time synchronization method includes a Global Positioning System (GPS) or a method using a wireless standard radio wave. An RTP (Real Time Protocol) packet transmission apparatus,
A processor for setting up an extension header in an extension field of an RTP header, setting up sampling time information of a first byte of the RTP packet in units of nanoseconds in the extension header, and generating an RTP packet;
The transceiver that transmits the RTP packet
And an RTP packet transmission unit. The method of claim 5,
The processor sets the sampling time information in the extension header up to the year, month, day, hour, milliseconds, microseconds, and nanoseconds RTP packet transmission device. The method of claim 5,
The processor sets a type of time synchronization method in the extension header,
The time synchronization method uses a Global Positioning System (GPS) or a wireless standard radio wave. The method of claim 5,
The transceiver includes a GPS receiver or a standard radio receiver,
Wherein the processor sets the sampling time information using time information acquired through the GPS receiver or the standard radio wave receiver.

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