Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1997-11-12
2003-09-23
Jung, Min (Department: 2663)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S474000, C370S476000, C370S535000, C714S748000
Reexamination Certificate
active
06625166
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a communication system for communicating a plurality of time-division multiplexed data, and a control method therefor.
2. Description of the Relates Art
In general, a multimedia communication system uses a method of transmitting real-time data in a PBX (private branch exchange) that combines voice data and the like, and non-real-time data that permit a delay to some extent in a LAN (local area network by, e.g., time-division multiplexing. Recently, a system that transmits data by dynamically assigning time slots using a statistical multiplexing effect has come into existence.
The time-division multiplexing method will be explained below.
FIG. 26
shows the arrangement upon multiplexing telephone data and data communication data using a 4-msec frame as a fundamental frame on a 64-kbps transmission path. The multiplexing includes a method of permanently assigning time slots to the individual media, and a method of dynamically and variably assigning time slots.
These two methods will be explained below with reference to FIG.
26
. Assume that two telephone data and one data communication data are to be multiplexed. In this case, the 4-msec frame in the 64-kbps path corresponds to a 32-byte length. Numerical values in parentheses in
FIG. 26
respectively indicate time slots assigned to the individual communications.
In the permanent assignment method, the individual media data occupy the entire multiplexed datastream. More specifically, for example, if there is no second telephone channel data (not busy), empty data is set in that period to make communications ((
1
) of FIG.
26
).
In contrast to this, in the dynamic time slot assignment method, if there is no second telephone channel data, a message indicating that transmission of a communication frame having no second channel data is supplied in advance to the other end-system or other host, and thereafter, that time slot is assigned to the data communication, thus saving the total length of the multiplexed datastream ((
2
) of FIG.
26
).
In another method, the entire multiplexed line length remains the same, and the time slot of the data communication is increased accordingly ((
3
) of FIG.
26
).
In this case as well, when the contents of the format of the communication frame change, a message indicating the change in contents of the format of the communication frame is supplied in advance to the other end-system, and thereafter, the changed communication frame is transmitted.
However, in the permanent time slot assignment method in TDM used in the conventional multimedia communication system, since each transmission time slot to be used is assured even in an inactive state, the transmission time slot cannot be used by other media even when the time slot is not in use in practice. Also, since data transfer is done by one-to-one communications, data transfer cannot be done by simultaneously connecting multipoints.
In the system that transmits data by dynamically assigning time slots using the statistical multiplexing effect, since the data multiplexing method is the unique one, data transfer is done by one-to-one communications, but cannot be done by simultaneously connecting multipoints, as in the former TDM method. In addition, this system cannot be connected to a public network.
Furthermore, since private networks such as LANs are to be connected using services such as a dedicated channel network, frame relay network, and the like, voice communications cannot be simultaneously made.
In the method of dynamically assigning time slots, when the communication frame format is dynamically changed, a message that indicates the change in format of the communication frame must be supplied to the other end-system before transmission of the communication frame whose format has changed.
After this message is supplied, the communication frame whose format has changed is transmitted.
Communications that include IP packet communications using an Internet protocol as data communications, which are transfer-controlled by a TCP (Transmission Control Protocol) will be examined below. The TCP operation will be explained below.
In the TCP, handshake is attained by the sequence number, acknowledgement number, and control bits, and the transmission interval and volume of transfer data are controlled by the window size and retransmission timeout time.
FIG. 29
shows the format of a TCP header.
In
FIG. 29
, “Source Port” indicates a port number of a source, and “Destination Port” indicates the port number of a destination. “Sequence Number” is a number that indicates the head of data to be transmitted, and “Acknowledgement Number” is the number of data next to the received data. “Data Offset” indicates the head of the data area in the header.
As the control bits, “URG” is a bit indicating the validity of an urgent pointer, and “ACK” is a bit indicating the validity of the acknowledgement number. “PSH” is a bit for instructing transfer of data to the application layer, and “RST” is a bit for forcibly terminating connection. “SYN” is a control bit for sequence number synchronization, and “FIN” is a bit for terminating connection.
“Window” indicates the data volume that can be transmitted without any acknowledgement. “Checksum” is the checksum of the header and data, and “Urgent Pointer” is a pointer indicating the end of data requiring real-time processing.
“Options” indicates the maximum segment length, and “Padding” is data (padding) to be set so that data can start from a 32-bit boundary. “data” is the data to be actually transferred.
A typical procedure for establishing a connection will be described below with reference to
FIGS. 27 and 28
.
For example, when communication terminals A
2701
and B
2702
make communications based on an FTP (File Transfer Protocol), these communication terminals execute the following processing.
(a) An FTP process of communication terminal A
2701
issues a connection establishment request to communication terminal B
2702
to a TCP module.
(b) The TCP module of communication terminal A
2701
handshakes with a TCP module of communication terminal B
2702
to request connection establishment.
(c) The TCP module of communication terminal B
2702
sends back a response to the connection establishment request.
(d) Process A
2707
sets data to be transferred by the TCP in a buffer
2703
.
(e) Subsequently, process A
2707
issues a data transmission request to TCP module A
2705
.
(f) TCP module A
2705
fetches the data in the buffer in units of TCP transmission segments.
(g) Furthermore, TCP module A
2705
adds a header set with control bits and the like to the data, and sends it to the TCP module of communication terminal B
2702
.
(h) The TCP module of the communication terminal B
2702
sends back a response indicating data reception.
(i) At the same time, TCP module B
2706
stores the response in a communication buffer
2704
.
(j) TCP module B
2706
informs process B
2708
of data reception.
(k) Process B
2708
receives that data as FTP data. The operations of the two TCP modules from (b) to (g) will be described in more detail below.
(1) The TCP module of the transmitter is in the inactive state (CLOSED), and the TCP module of the receiver is in a receivable state (LISTEN) of communication data from another terminal.
(2) TCP module A that received the connection establishment request from process A sends a TCP segment set with an appropriate sequence number (100) and SYN of the control bits to TCP module B (b).
(3) TCP module B sends back a response to that segment using appropriate SEQ (sequence number)=300. At this time, ACK (acknowledgement number) is incremented by one from the received number, and SYN and ACK are set as the control bits (c).
(4) TCP module A sends back a response to that ACK with SEQ=101 and ACK=301, which is incremented by one from the received number.
In this manner, synchronization (SYN) of SEQ is established between TCP modules A and B. Thereafter, TCP modules A and B ma
Ohuchi Masatomo
Tsukamoto Takahiro
Canon Kabushiki Kaisha
Jung Min
Morgan & Finnegan , LLP
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