A method for fast and economic handling of overhead bytes of an incoming high order data stream to form a corresponding outgoing high order data stream, the method comprising a) presenting the incoming high order data stream as a plurality of N component data streams transmitted in parallel, b) providing a common overhead processing unit (COHPU) capable of handling overhead bytes of a single one of the component data streams, c) forwarding overhead bytes of the component data streams to the COHPU in a circular order, while keeping docketing (ID) information for each particular overhead byte; d) processing each of the overhead bytes in the COHPU, and e) modifying the N component data streams to obtain an outgoing high order data stream based on results of the processing and the ID information with respect to each of the processed overhead bytes.

The present invention involves the passing of clock information from a point where a tributary payload is mapped into a carrier to a point where a tributary payload is de-mapped from the carrier. A synchronization signal is generated at the mapping end. Rather than sending clock phase information implicitly by means of the data, as is normally the case, a value of the synchronization signal at a given time, is sent explicitly, independent from the payload data.

An on-chip RAM FIFO (first-in-first-out) buffer for storing SPE overhead bytes wherein each entry of the RAM FIFO stores (1) a byte of the SPE overhead; (2) an indication of which byte of the SPE overhead is currently stored in that entry; and (3) an indication of which STS signal that byte was taken from.

A semi-transparent time division multiplexer/demultiplexer that transmits low rate tributaries from one location to another using a high rate aggregate connection, while preserving substantially all of the TOH and payload for each tributary signal. Transparency of the tributary TOH is accomplished by interleaving both the TOH and the Payload of each tributary into the high rate aggregate signal. Some TOH bytes may be tunneled or re-mapped into unused/undefined TOH locations in the aggregate signal to allow transparency of the TOH without corrupting the aggregate. Errors may be handled by tunneling BIP bytes into unused/undefined aggregate locations and updating the tunneled bytes with error masks calculated at each network elements. Alternatively errors may be forwarded by using an error mask generated from the tributary BIP locations and inserting the mask into the associated aggregate BIP locations. The mask in the aggregate BIP is updated with error masks calculated at each network elements. Re-timing of TOH to a synchronized clock in the tributary framer circuits can be accomplished using controlled slips of overhead frames, whereby an entire frame is dropped or added depending on the relationship of the received clock and the synchronized clock. DCC bytes may be re-timed by adding or deleting flag bytes occurring between respective DCC packets. Re-timing of the aggregate TOH to a transmit clock may be accomplished in a similar manner.

A synchronous optical network (SONET) framer includes a frame dimension unit and a programming interface. The frame dimension unit can be programmed with a frame dimension through the programming interface. The SONET framer converts a data stream to and/or from a frame format based on the frame dimension programmed into the frame dimension unit. For instance, in various embodiments, a SONET framer can be programmed to support a variety of SONET frame sizes and to provide a number of testing and design advantages.