The DS31256 Envoy is a 256-channel HDLC controller capable of handling up to 60 T1 or 64 E1 data streams or two T3 data streams. Each of the 16 physical ports can handle one, two, or four T1 or E1 data streams. The Envoy is composed of the following blocks: Layer 1, HDLC processing, FIFO, DMA, PCI bus, and local bus.