Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-12-01
2001-07-17
Nguyen, Chau (Department: 2663)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S468000, C370S537000
Reexamination Certificate
active
06262990
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a fixed length packet multiplexer of universal data having a burst characteristic along with image coded data or audio coded data at a low speed (1.2 to 19.2 kbps).
DESCRIPTION OF THE PRIOR ART
In a fixed length packet multiplex transmitting of universal data along with image coded data or audio coded data at a low speed, for example, in a case of a MPEG-2 (ISO/IEC 13818-1) system, in general, data (band: 1.5 to 15 Mbps) of a MPEG-2 video (ISO/IEC 13818-2) system as image coded data are employed, or data (band: 64 to 384 kbps) of a MPEG-1 audio (ISO/IEC 11172-3) system as audio coded data are used. The image coded data or the audio coded data are transmitted at a relatively high speed, and packeting does not cause much delay even when a packet length is relatively large. Hence, the packet length is set to a relatively large value such as 188 bytes=4 bytes of a header+184 bytes of a payload.
When data are transmitted in a fixed length packet in a conventional system, the data are input to a multiplex buffer, and, when a predetermined length of payload data of the aforementioned relatively large value are stored, the data are packeted and then transmitted.
FIG. 1
illustrates a conventional fixed length packet multiplexer of universal data along with image coded data or audio coded data. In
FIG. 1
, image coded data, audio coded data and low speed universal data are input to respective exclusive multiplex buffers
1
,
2
and
3
. A buffer monitor
4
monitors whether or not each multiplex buffer
1
,
2
or
3
stores the predetermined length of payload data. The time when each multiplex buffer
1
,
2
or
3
stores the predetermined length of payload data is determined as a packet formable time (called “a release timing” later). The buffer monitor
4
allows a selector
5
to select the multiplex buffers
1
,
2
and
3
in order of the attainment to their release timing. A packet processor
6
adds a header to the predetermined length of payload data to output the formed packet, as shown in FIG.
2
. When the release timing of any multiplex buffers
1
,
2
and
3
are equal, their packet processings are carried out in order of the lower input speed of the data supplied to the multiplex buffers
1
,
2
and
3
.
FIG. 3
shows a timing chart of input burst data, a release timing and a fixed length packet formation. The time when the burst data of the predetermined length of payload are stored in the multiplex buffer becomes the release timing, and the packet is formed at this release timing.
When a packet multiplex transmission is performed in a fixed length packet with the universal data along with the image coded data or the audio coded data at a low speed, the image and the audio are regarded as important, and the image coded data or the audio coded data are transmitted at a high speed. The packet length is set to the relatively large value.
In the conventional fixed length packet multiplexer, when the universal data are transmitted in a fixed length packet at a low speed, the low speed universal data are input to the multiplex buffer, and, when the predetermined length of payload data of the relatively large value is stored in the multiplex buffer, the packet is formed at the release timing and is output. In this system, two problems occur in the packet multiplexing. First, the universal data are transmitted at a low speed, and no packet is formed and transmitted before the predetermined length of payload data are stored in the multiplex buffer. As a result, a multiplex delay turns out large. Second, as shown in
FIG. 3
, when the burst universal data of low speed are input, the rearmost part of the burst data is packeted along with the head part of the following input burst data unless the length of the burst data is a multiple of an integral number of the predetermined length of payload data. Hence, a delay can be caused by a period with no data input between the two burst data.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a fixed length packet multiplexer in view of the aforementioned problems of the prior art, which is capable of reducing a transmission delay of low speed universal data having a burst characteristic in a fixed length packet multiplex transmission of different data with different speeds and large speed differences.
In accordance with one aspect of the present invention, there is provided a fixed length packet multiplexer of low speed universal data having a burst characteristic, comprising means for detecting a momentary velocity (i,e. the instantaneous transmission speed) of burst data of the low speed universal data having the burst characteristic; means for periodically generating a release timing inversely proportional to the momentary velocity; means for producing a fixed length packet carrying the burst data on a payload at the release timing; and multiplex buffer means for storing the burst data of a predetermined length of payload of the packet.
In accordance with another aspect of the present invention, there is provided a fixed length packet multiplexer of low speed universal data having a burst characteristic, comprising means for detecting a rearmost part of burst data of the low speed universal data having the burst characteristic; means for detecting a momentary velocity of the burst data; means for periodically generating a release timing inversely proportional to the momentary velocity; means for producing a fixed length packet carrying the burst data on a payload at either the release timing or a timing when the rearmost part of the burst data is detected; and multiplex buffer means for storing the burst data of a predetermined length of payload of the packet.
In a fixed length packet multiplexer of the present invention, a transmission velocity of the low speed universal data is in a range of 1.2 to 19.2 kbps.
Preferably, the momentary velocity detecting means includes a first counter for counting up burst clocks which are input with the burst data and correspond thereto; a cycle pulse generator for generating a pulse on an enough long cycle so as to measure the momentary velocity of the burst data; a delay for delaying the pulse generated by the cycle pulse generator to output the delayed pulse to a clear terminal of the first counter; and a first latch for latching a counted value of the cleared first counter as a time cycle control signal to output the time cycle control signal in synchronism with the pulse generated by the cycle pulse generator.
Further, preferably, the rearmost part detecting means includes a second counter for counting up burst clocks which are input with the burst data and correspond thereto; a latch pulse generator for generating a pulse on an enough short cycle than a void interval between the two burst data so as to latch a counted value of the second counter by the pulse generated by the latch pulse generator; a comparator for comparing a present counted value latched with a previous counted value latched to output either a low level signal or a high level signal when the present counted value is either equal or not equal to the previous counted value; and a trailing edge detector to output a pulse as a burst data end signal when the signal is changed from the high level to the low level, that is, the rearmost part of the burst data is detected.
In a fixed length packet multiplexer of the present invention, the release timing generating means can include a release timing generating section which inputs a periodic pulse inversely proportional to a velocity as a time cycle control signal and outputs a pulse on either a quick cycle or a slow cycle when the velocity is either low or high, resulting in permitting a multiplex delay to be constant independent to the velocity of the burst data and outputting the burst data end signal and the periodic pulse.
According to the present invention, in a packet processor, a packet formable time (release timing) is not determined to the time when a predeter
Hyun Soon-Dong
NEC Corporation
Nguyen Chau
Ostrolenk Faber Gerb & Soffen, LLP
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