The present invention generally relates to packet switching systems, and more particularly to a packet switching system with a rationalized data transfer capability.
With the recent spread of packet communication, a data quantity which can be transferred by a packet exchange in one packet is increasing from 1024 octets to 4096 octets, for example. In this case, from the point of view of reducing a transfer time of the packets, it is desirable to minimize transfers of packets having a large data quantity within the packet exchange.
FIG. 1 shows an example of a conventional packet exchange. In FIG. 1, the packet exchange has a plurality of frame level control devices 2.sub.1 through 2.sub.n, a plurality of packet level control devices 3.sub.1 through 3.sub.n which are respectively connected to the frame level control devices 2.sub.1 through 2.sub.n, a system operation management device 4, and a bus 5 which connects the packet level control devices 3.sub.1 through 3.sub.n. A frame level control device 2.sub.i is connected to communication lines 1.sub.i1 through 1.sub.im, where i=1, 2, . . . , n.
For example, an information frame I(CR) including a call out request packet CR for making a call set up is received via the communication line 1.sub.11 which is connected to the frame level control device 2.sub.1. In this case, the frame level control device 2.sub.1 stores the received information frame I(CR) into a memory 2.sub.1b and carries out a known frame level control. Then, the frame level control device 2.sub.1 disassembles the information frame I(CR) to extract the call out request packet CR, and a direct memory access (DMA) controller 2.sub.1a transfers the call out request packet CR to a memory 3.sub.1b of the corresponding packet level control device 3.sub.1.
The packet level control device 3.sub.1 carries out a known packet level control with respect to the call out request packet CR which is transferred to the memory 3.sub.1b and makes a call set up. A DMA controller 3.sub.1a transfers the call out request packet CR via the bus 5 to a memory 3.sub.2b of the packet level control device 3.sub.2 which is connected to a destination communication line 1.sub.21 in this case.
The packet level control device 3.sub.2 carries out a known packet level control with respect to the call out request packet CR which is transferred to the memory 3.sub.2b and makes a call set up. A DMA controller 3.sub.2a transfers the call out request packet CR to a memory 2.sub.2b of the frame level control device 2.sub.2 which is connected to the communication line 1.sub.21.
The frame level control device 2.sub.2 assembles the information frame I(CR) including the call out request packet CR stored in the memory 2.sub.2b and transmits the information frame I(CR) on the destination communication line 2.sub.21.
By the above described process, a call set up is made between the frame level control device 2.sub.1 which is connected to the communication line 1.sub.11 and the frame level control device 2.sub.2 which is connected to the communication line 1.sub.21, via the packet level control devices 3.sub.1 and 3.sub.2.
Thereafter, when an information frame I(DT) including a data packet DT is received at the communication line 1.sub.11, the data packet DT is transferred from the frame level control device 2.sub.1 to the frame level control device 2.sub.2 via the packet level control devices 3.sub.1 and 3.sub.2 in accordance with the set call. The frame level control device 2.sub.2 assembles the information frame I(DT) including the data packet DT and transmits the information frame I(DT) on the communication line 2.sub.21.
According to the conventional packet exchange, the call out request packet CR and the data packet DT received at the communication line 1.sub.11 are transferred from the frame level control device 2.sub.1 to the packet level control device 3.sub.1, then from the packet level control device 3.sub.1 to the packet level control device 3.sub.2 via the bus 5, and further from the packet level control device 3.sub.2 to the frame level control device 2.sub.2. Finally, the call out request packet CR and the data packet DT are transferred from the frame level control device 2.sub.2 to the communication line 2.sub.11. Therefore, when transferring the call out request packet CR and the data packet DT from the frame level control device 2.sub.1 to the frame level control device 2.sub.2, three transfers must be made within the packet exchange. As a result, there is a problem in that it takes a long time to complete the transfer especially when the data packet DT includes a large data quantity. In addition, there is a problem in that the time required to complete the transfer within the packet exchange may exceed a tolerable packet transfer delay time within the packet exchange.