During and after this time, he worked as a professional musician, mostly performing on the flute, and also playing folk and art music from the Balkans and the Middle East.

Starting in 1993, he led an organization at TRW that developed one-of-a-kind automation systems for the US military and (to a lesser extent) commercial companies.

In 1995, his team won the contract to develop the US Army's first "digital battlefield" system, called Force-XXI Battle Command Brigade and Below (generally known by the acronym FBCB2).

Also in 1995, his team delivered the US Army's first automated command post, which has been followed by a long series of related capabilities to the present time.

His personal science and engineering contributions included many of the most-important techniques for transitioning the internet from wired to wireless operation.

These include techniques for adapting the internet to operate over the slower and less reliable communications links entailed in wireless operation, such as a patent for performing routing in a constantly-changing network (ultra-low bandwidth intra-network routing[5]) and achieving acceptable dynamics through what he calls "force-structure-aware" networks.

He has also been active in the field of structuring large-scale software developments so as to match the skill distribution encountered in real-world teams.

He is the documented earliest creator of a complete, operating adaptation of the internet to fully-routed wireless operation, and many important / related technologies that are widely used today in such wireless devices, including: Siegel is an experienced musician who plays the flute, târ,[25] ney,[26] and kaval[27] who has more than 1,500 concerts to his credit worldwide.

[29] He is on the board of several non-profit organizations, including the Providence Trinity Health Care Hospice Foundation, the Electric Infrastructure Security Council, and The Institute of Persian Performing Arts.