Krishan Sabnani

Murray Hill, NJ, USA


Krishan was Vice President of Networking Research at Bell Labs from Jan. 2000 to Sept. 2013. In that role, he managed all networking research in Bell Labs, comprising nine departments in seven countries: USA, France, Germany, Ireland, India, Belgium, and South Korea. 

Upon his graduation in 1981, he joined Bell Labs, Murray Hill, New Jersey as a Member of Technical Staff and was promoted to Department Head in 1993.  He was named VP of Networking Research in 2000.  He is also an Adjunct Professor at Columbia University and an honorary professor at IIT Delhi. 

Krishan retired from Bell Labs in Jan 2017. He received an award upon his retirement  - appointment as Ambassador-at-large for Bell Labs. He is the first person to receive this award. 

Krishan has made many seminal contributions to the Internet infrastructure design, protocol design, and wireless networks. Here is their summary.

Internet infrastructure Design:

Krishan (with T. V. Lakshman and T. Woo)  made a breakthrough in Internet re-design.  The main idea behind this work was to separate control functions and complex software from the forwarding portions on Internet routers. This work made it possible for forwarding technologies (e.g., different link layer and switching protocols) to evolve and be deployed independently from control protocols (e.g., routing, security).  This contribution is a precursor to the current Software Defined Networking (SDN) revolution. A patent based on this work was awarded the 2010 Edison Patent Award.

Protocol Design:

Krishan also made many seminal contributions to protocol design and analysis.  His early work focused on formal methods such as efficient algorithms for validation of communication protocols, conformance of implementations to design, and automated methods for constructing protocol converters.  His work started a new testing research area and the widespread use of formal testing throughout the telecommunications industry.  Krishan has designed several breakthrough protocols.  His work has led to one of the most popular reliable multicast transport protocols (RMTP) and a revolutionary high-speed transport protocol (SNR).  

Krishan also developed techniques and tools for conformance testing, protocol verification, protocol conversion, and reverse engineering. Until early 90’s conformance testing typically used ad-hoc techniques. Krishan’s work was the first effort to invent formal methods for this area. It introduced the notion of unique signatures for states: Unique Input Output (UIO) sequences. These techniques resulted in a complete testing capability and a reduction in test time from weeks to a few hours. It was instrumental in the creation of a new research field: formal methods for conformance testing. It generated a number of doctoral thesis and hundreds of follow-up papers. It resulted in a tool used in AT&T for conformance testing of all ISDN and ATM standards. UIO sequences have become a well-accepted term. Follow-up research has resulted in terms such as partial UIOsmultiple UIO, etc.

Prior to Krishan’s pioneering work, large-scale deployment of reliable multicasting was considered to be difficult because of problems associated with maintaining the necessary state for making multicasts reliable. Because of the prevalence of low-bandwidth network links in the mid-1990s, multicasting was essential for many applications such as maintaining consistent billing information. Despite the need for deploying a scalable and reliable multicast infrastructure, the lack of a scalable protocol made commercial deployment impossible. Krishan’s research resulted in the creation of a new protocol, Reliable-Multicast-Transport-Protocol (RMTP) that enabled reliable multicasting of data over the Internet.  He invented a new technique to avoid the problem of too many feedback messages; this makes multicast intrinsically scalable. Krishan’s research has also been very influential in the area of multicast congestion control; he helped develop fundamental ideas on extending TCP like congestion control mechanisms to multicasts.

RMTP has been deployed in AT&T’s billing network, where very high reliability and scalability are imperative. It was used to distribute billing records from AT&T’s core switching machines (such as 4ESS switches) to several billing systems and backup systems. This system must be up continuously; any downtime would lead to enormous losses. This work resulted in the formation of a successful new company -- Globalcast --which was later acquired by Talarian.

Krishan created a revolutionary high-speed transport protocol. The key idea was to create a protocol that is not reactive, but instead periodically exchanges state information to greatly increase throughput. This was a breakthrough in transport protocol design, as the prevailing view of transport protocols at the time was to design them to react to key events, such as data reception or loss. The main concept from this protocol was incorporated in the SSCOP protocol, a standard used in high-speed ATM networks. SSCOP was used in thousands of ATM networks deployed around the world. This work also resulted in the Leonard G. Abraham Prize Paper Award and the best paper at ACM SIGCOMM 1989.

Wireless networking:

In 1995, Krishan initiated a project on wireless messaging long before text messaging had become popular, and before email was delivered to cell phones and mobile web browsing was possible.  This project resulted in outstanding research results that were published in many top conferences and journals, several patents, and finally the first product from Lucent for the Mobile Internet market.  The novelty in this work was designing systems that adapted content so that a rich set of features could be used on simple wireless devices.  This included the introduction of thin clients in mobile phones, novel methods of encoding messages and responses, and the transformation of email and web content to fit cell phone screens.

The modularization of call processing software also eased the ability to perform protocol interworking.  Krishan recognized that as wireless networks continued to mature, and as new wireless networks were introduced, interworking between these systems became of paramount importance.  He combined his expertise in protocol conversion with modular call processing to invent a system which enabled global roaming by connecting disparate wireless networks and allowing them to easily interwork.  This work was not only built upon fundamental research results but led to a product line which now supports over 400 million subscribers.  This also won the Thomas Edison Patent Award in 2009.




Doctorate in electrical engineering, Columbia University, 1981.

Masters Degree in EE (with distinction), Netherlands Universities, 1977.

Bachelor of Technology in EE, Indian Institute of Technology, New Delhi, 1975.

Professional activities

  • Invited to be keynote speaker at  several top networking conferences including ACM   ACM Mobisys 2015, ACM Mobicom 2002, IEEE  High Speed Switching Conf., 2000, SAINT 2003, COMSWARE 2006, TESTCOM 2006, ICDCS 2006, IWQoS 2006, MASS 2006,  Networking 2007, ACM  MobiArch 2007, COMSWARE 2008, WWRF 2009, ISWCS 2009, COMSNETS 2010, and several other conferences.
  • Served as editor for many premier networking Journals: , IEEE/ACM Transactions on Networking, 1992-98; the Wireless Networks Journal, 1995-99; IEEE Transactions on Communications, 1988-92; IEEE Transactions on Computers, 1988-92, Journal of Systems Integration, Journal of High Speed Networks, 1992-94, Computer networks, 2001-present and ACM Journal on Wireless Networks, 1996-present.  Guest Editor, JSAC, September 1989 and Computer Networks and ISDN Systems, April 1990.
  • Played an active role in organizing major networking conferences: Program Committee Member of several premier networking conferences including ACM SIGCOMM, 1989, 1999, 2000, and ACM MOBICOM, 1995-98 Program Chairman of two major networking conferences: ICNP '94 and PSTV ‘88.
  • Served on peer-review panels at NSF, NASA, & Texas High-Education Coordination Committee.
  • Served on the IEEE Fellow Committee, 1995-98.
  • Participated in several NSF workshops on networking.
  • Delivered distinguished lectures at several major universities such as Duke, Washington, Georgia Tech, IIT Delhi.
  • Delivered Bharti Lecture in the Bharti School of Telecommunication Technology & Management, New Delhi.  
  • Served as a UNDP consultant for setting up an educational data network called ERNET in India, 87.

Selected articles and publications

“Multidestination Protocols for Satellite Communications,” K. Sabnani, M. Schwartz, IEEE Transactions on Communications, 33(3), 232 – 240 (1985).

” A Protocol Test Generation Procedure,” K. Sabnani, A. Dahbura, Computer Networks &  ISDN Systems,15(4), 285 – 297 (1988).

An Algorithmic Technique for Protocol Verification,” K Sabnani, P Wolper, A Lapone, IEEE Transactions on Communications, 36(8), 924 – 931 (1988).

“A High Speed Transport Protocol for Datagram/Virtual Circuit Networks,” K Sabnani, AN Netravali - ACM SIGCOMM  (1989).

Probabilistic Verification of Communication Protocols,” NF Maxemchuk, K Sabnani, Distributed Computing (Historical Archive,) 3(3), 118 – 129 (1989).

Design and Implementation of a High-speed Transport Protocol,” A.N. Netravali, W.D. Roome, K. Sabnani, IEEE Transactions on Communications,38(11), 2010 – 2024 (1990).

“AIRMAIL: A Link-Layer Protocol for Wireless Networks,” E. Ayanoglu, S. Paul, T.F. La Porta, K.K. Sabnani, R.D. Gitlin, ACM/Baltzer Wireless Networks Journal. 1(1),47-60 (1995).

Reliable Multicast Transport Protocol (RMTP),” S. Paul, K. Sabnani, J.C.H. Lin, S. Bhattacharyya,  IEEE Journal on Selected Areas in communications, 15(3), 407 – 421 (1997).

“Pigeon - A Wireless Two-Way Messaging System,” T.Y.C. Woo, T.F. La Porta, K. Sabnani, IEEE Journal on Selected Areas in Communications ,15( 8), 1391-1405 (1997).

Fundamental Observations on Multicast Congestion Control in the Internet,” S.J. Golestani, K.K. Sabnani,  IEEE INFOCOM, 1999.

“The Softrouter Architecture,” T. V. Lakshman, N. Nandgopal, R. Ramjee, K. Sabnani, T. Woo, ACM Hotnets, 2004.

“Multi-Protocol Home Location Register and method of use,” US Patent #7,522,632. Winner of the 2009 Edison Patent Award.