pcb_struct rx_pcb; /* PCB for foreground receiving */
pcb_struct itx_pcb; /* PCB for background sending */
pcb_struct irx_pcb; /* PCB for background receiving */
pcb_struct rx_pcb; /* PCB for foreground receiving */
pcb_struct itx_pcb; /* PCB for background sending */
pcb_struct irx_pcb; /* PCB for background receiving */