Flow control mechanism for block switching nodes

In a communication network including a plurality of block switching nodes interconnected by links (232,244) with a receive buffer (202) being provided for each incoming link and a transmit buffer (208) being provided for each outgoing link in each node, a flow control mechanism in each node characterized by:

• means (396) for maintaining a token indication at each transmit buffer reflecting available buffer capacity in the receive buffer at the receiving end of the respective link,
• means (266, 382, 397, 398) for updating said token indication when a data block is transmitted from said transmit buffer, and also in response to a received token updating signal,
• means (252, 264, 372, 374, 376, 378) for looking ahead across the node when a data block is to be dispatched from a receive buffer, to the transmit buffer of the appropriate outgoing link and means (250, 254, 256, 344, 352, 354, 366, 368, 370) to cause transfer of the data block to said transmit buffer when buffer space is available,
• means (272, 360, 388, 392, 416, 418) for transmitting a token updating signal to the token indication means at the respective link in the previous node when a data block is dispatched from a receive buffer (FIG. 11 . . . FIG. 16).

Block switching node in a communication network, for selectively transferring addressed data blocks from a plurality of incoming links (22, 22';

• 232, 234) to a plurality of outgoing links (26, 26';
• 244, 246), a receive buffer (30;
• 202, 204) being provided for each incoming link, said block switching node comprising a flow control mechanism and being characterized by:
• output circuitry (16, 16';
• 208, 220, 238, 210, 222, 240) for each outgoing link for receiving a data block in transfer from a receive buffer to the associated outgoing link, and including token indication means (42;
• 396) for receiving token signals and reflecting available buffer capacity in the receive buffer at the remote receiving end of the respective outgoing link;
• token sending means (24, 34;
• 272, 360, 386, 388, 392, 416, 418) associated with each receive buffer for transmitting a token signal reflecting available buffer space to token indication means at the remote transmitting end of the respective incoming link;
• control means (44, 46, 48, 56, 58, 64, 70, 72, 74, 76;
• 252, 254, 260, 262, 264, 302, 304, 306, 308, 320, 322, 324, 338, 340, 346, 372, 374, 376) for
• polling receive buffers to preselect a receive buffer containing a data block to be transferred,
• forwarding a data block destination address from the preselected receive buffer,
• preselecting and testing the appropriate output circuitry of the outgoing link associated with said destination address, and
• generating a positive response signal when said preselected output circuitry can accept a data block from the preselected receive buffer;
• and
• transfer circuitry (32, 40, 50, 52, 54, 62, 68;
• 250, 284, 296, 344, 352, 366, 368) responsive to said control means and said positive response signal for transferring a data block from the preselected receive buffer to the preselected output circuitry (FIG. 6;
• FIGS. 11, 12, 13, 14, 16).