Radia Perlman

Radia Joy Perlman (born 1951) is an American computer programmer and network engineer. She is most famous for her invention of the spanning-tree protocol (STP), which is fundamental to the operation of network bridges, while working for Digital Equipment Corporation. She also made large contributions to many other areas of network design and standardization, such as link-state routing protocols.

More recently she has invented the TRILL protocol to correct some of the shortcomings of spanning-trees. She is currently employed by Dell EMC.

Radia Perlman
Radia Perlman 2009
Born1951 (age 67–68)
Alma materMIT
Known forNetwork and security protocols; computer books
Scientific career
FieldsComputer Science
ThesisNetwork layer protocols with Byzantine robustness (1988)
Doctoral advisorDavid D. Clark

Early life

Perlman grew up near Asbury Park, New Jersey. Both of her parents worked as engineers for the US government. Her father worked on radar and her mother was a mathematician by training who worked as a computer programmer. During her school years Perlman found math and science to be “effortless and fascinating”, but had no problem achieving top grades in other subjects as well. She enjoyed playing the piano and French horn. While her mother helped her with her math homework, they mainly talked about literature and music.[1]

Despite being the best science and math student in her school it was only when Perlman took a programming class in high school that she started to consider a career that involved computers. She was the only woman in the class and later reflected "I was not a hands-on type person. It never occurred to me to take anything apart. I assumed I'd either get electrocuted, or I'd break something".[2]


As an undergraduate at MIT Perlman learned programming for a physics class. She was given her first paid job in 1971 as part-time programmer for the LOGO Lab at the (then) MIT Artificial Intelligence Laboratory, programming system software such as debuggers.[3]

Working under the supervision of Seymour Papert, she developed a child-friendly version of the educational robotics language LOGO, called TORTIS ("Toddler's Own Recursive Turtle Interpreter System"). During research performed in 1974–76, young children—the youngest aged 3½ years, programmed a LOGO educational robot called a Turtle. Perlman has been described as a pioneer of teaching young children computer programming.[4]

As a math grad at MIT she needed to find an adviser for her thesis, and joined the MIT group at BBN Technologies. There she first got involved with designing network protocols.[5] Perlman obtained a B.S. and M.S. in Mathematics and a Ph.D. in Computer Science from MIT in 1988.[6] Her doctoral thesis at MIT addressed the issue of routing in the presence of malicious network failures.[7]

When studying at MIT in the late 60s she was one among the 50 or so women students, in a class of about 1,000 students. To begin with MIT only had one women’s dorm, limiting the number of women students that could study. When the men’s dorms at MIT became coed Perlman moved out of the women’s dorm into a mixed dorm, where she became the "resident female". She later said that she was so used to the gender imbalance, that it became normal. Only when she saw other women students among a crowd of men she noticed that "it kind of looked weird".[8]


She is most famous for her invention of the Spanning Tree Protocol (STP), which is fundamental to the operation of network bridges, while working for Digital Equipment Corporation. Perlman is the author of a textbook on networking and coauthor of another on network security. She holds more than 100 issued patents.[9] She was a Fellow at Sun Microsystems and has taught courses at the University of Washington, Harvard University and MIT, and has been the keynote speaker at events all over the world. Perlman is the recipient of awards such as Lifetime Achievement awards from Usenix and the Association for Computing Machinery’s Special Interest Group on Data Communication (SIGCOMM).[10]

Spanning Tree Protocol

Perlman invented the spanning tree algorithm and the Spanning Tree Protocol (STP). While working as a consulting engineer at the Digital Equipment Corporation (DEC) in 1984 she was tasked with developing a straightforward protocol which enabled network bridges to locate loops in a local area network (LAN). It was required that the protocol should use a constant amount of memory when implemented on the network devices, regardless how large the network was. Building and expanding bridged networks was difficult because loops, where more than one path leads to the same destination, could result in the collapse of the network. Redundant paths in the network meant that a bridge could forward a frame in multiple directions. Therefore loops could cause Ethernet frames to not reach their destination, flooding the network. Perlman utilised the fact that bridges had unique 48 bit MAC addresses, and devised a network protocol so that bridges within the LAN communicated with one another. The algorithm implemented on all bridges in the network allowed the bridges to designate one root bridge in the network. Each bridge then mapped the network and determined the shortest path to the root bridge, deactivating other redundant paths. Despite Perlman's concerns that it took the spanning tree protocol about a minute to react when changes in the network topology occurred, in which time a loop could bring down the network, it was standardised as 802.1d by the Institute of Electrical and Electronics Engineers (IEEE). Perlman said that the benefits of the protocol amount to the fact that "you don't have to worry about topology" when changing the way a LAN is interconnected. Perlman has however criticised that changes were made in the course of the standardisation of the protocol.[11]

From the paper "An Algorithm for Distributed Computation of a Spanning Tree in an Extended LAN":[1]

I think that I shall never see
A graph more lovely than a tree.
A tree whose crucial property
Is loop-free connectivity.
A tree which must be sure to span
So packets can reach every LAN.
First the root must be selected.
By ID it is elected.
Least cost paths from root are traced.
In the tree these paths are placed.
A mesh is made by folks like me
Then bridges find a spanning tree.

Other network protocols

Perlman was the principal designer of the DECnet IV and V protocols, which are part of the DECnet network protocol suite for peer-to-peer network architectures. She also made major contributions to the Connectionless Network Protocol (CLNP). Perlman has collaborated with Yakov Rekhter on developing network routing standards, such as the Open System Interconnection Routing Protocol (IDRP), which allows routers in packet switching networks to communicate with one another across broadcast domains. At DEC she also oversaw the transition from distance vector to link-state routing protocols. Link-state routing protocols had the advantage that they adapted to changes in the network topology faster, and DEC's link-state routing protocol was second only to the link-state routing protocol of the Advanced Research Projects Agency Network (ARPANET). While working on the DECnet project Perlman also helped to improve the intermediate-system to intermediate-system routing protocol, known as IS-IS, so that it could route the Internet Protocol (IP), AppleTalk and the Internetwork Packet Exchange (IPX) protocol.[12] The Open Shortest Path First (OSPF) protocol relied in part on Perlman's research on fault-tolerant broadcasting of routing information.[13]

Perlman subsequently worked as network engineer for Sun Microsystems, now Oracle. She specialised on network and security protocols and while working for Oracle obtained more than 50 patents.[14]



  • Perlman, Radia (1999). Interconnections: Bridges, Routers, Switches, and Internetworking Protocols (2 ed.). Addison-Wesley Professional Computing Series. ISBN 978-0-201-63448-8.
  • Perlman, Radia; Kaufman, Charlie; Speciner, Mike (2002). Network Security: Private Communication in a Public World (2 ed.). PTR Prentice Hall. ISBN 978-0-13-046019-6.


  1. ^ Salim, Nancy (18 October 2010). "Radia Perlman: Don't Call Me the Mother of the Internet". The Atlantic. Retrieved 20 March 2018.
  2. ^ Salim, Nancy (18 October 2010). "Meet the Mother of the Internet". IEEE Women in Engineering Magazine. 4 (2): 10–12. doi:10.1109/MWIE.2010.938214. Retrieved 20 March 2018.
  3. ^ Salim, Nancy (18 October 2010). "Radia Perlman: Don't Call Me the Mother of the Internet". The Atlantic. Retrieved 20 March 2018.
  4. ^ Leonel Morgado; et al. (2006). "Radia Perlman – A pioneer of young children computer programming". Current Developments in Technology-Assisted Education: 1903–1908. CiteSeerX
  5. ^ Salim, Nancy (18 October 2010). "Radia Perlman: Don't Call Me the Mother of the Internet". The Atlantic. Retrieved 20 March 2018.
  6. ^ "Radia Perlman". MIT. Retrieved 14 October 2012.
  7. ^ Radia J. Perlman (1988). "Network Layer Protocols with Byzantine Robustness (Ph.D. thesis)". MIT. Retrieved 5 March 2010.
  8. ^ Salim, Nancy (18 October 2010). "Radia Perlman: Don't Call Me the Mother of the Internet". The Atlantic. Retrieved 20 March 2018.
  9. ^ "Patents by Inventor Radia J. Perlman". Justia Patents. Retrieved 29 August 2013.
  10. ^ "Radia Perlman | Internet Hall of Fame". internethalloffame.org. Retrieved 2017-11-23.
  11. ^ Juneau, Lucie (18 Oct 1992). "Radia Perlman". Network World. 9 (41): 103. ISSN 0887-7661.
  12. ^ Juneau, Lucie (18 Oct 1992). "Radia Perlman". Network World. 9 (41): 103. ISSN 0887-7661.
  13. ^ Cisco.com. "Open Shortest Path First".
  14. ^ Salim, Nancy (18 October 2010). "Meet the Mother of the Internet". IEEE Women in Engineering Magazine. 4 (2): 10–12. doi:10.1109/MWIE.2010.938214. Retrieved 20 March 2018.
  15. ^ "Internet Hall of Fame Pioneer Radia Perlman". Internet Society.
  16. ^ "2010 SIGCOM Lifetime Achievement Award given to Radia Perlman". SIGCOMM.
  17. ^ Fuller, Brian (18 October 2005). "Perlman, Samuelson, Tsao, honored for innovations". EETimes. UBM Electronics. Retrieved 29 June 2011.
  18. ^ "Inventors of The Year", Silicon Valley Intellectual Property Law Association (SVIPLA). Retrieved 2 July 2013.
  19. ^ "ACM Recognizes New Fellows", Communications of the ACM, 60 (3): 23, March 2017, doi:10.1145/3039921.

External links

1951 in science

The year 1951 in science and technology involved some significant events, listed below.

Anita Borg Institute Women of Vision Awards

The Anita Borg Institute Women of Vision Awards honor exceptional technical women. Three awards are presented by the Anita Borg Institute for Women and Technology each year, recognizing women in the categories of Innovation, Leadership, and Social Impact.

Communications receiver

A communications receiver is a type of radio receiver used as a component of a radio communication link. This is in contrast to a broadcast receiver which is used to receive radio broadcasts. A communication receiver receives parts of the radio spectrum not used for broadcasting, that includes amateur, military, aircraft, marine, and other bands. They are often used with a radio transmitter as part of a two way radio link for shortwave radio or amateur radio communication, although they are also used for shortwave listening.

Data center bridging

Data center bridging (DCB) is a set of enhancements to the Ethernet local area network communication protocol for use in data center environments, in particular for use with clustering and storage area networks.

David D. Clark

David Dana "Dave" Clark (born April 7, 1944) is an American computer scientist and Internet pioneer who has been involved with Internet developments since the mid-1970s. He currently works as a Senior Research Scientist at MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL).

Internet Hall of Fame

The Internet Hall of Fame is an honorary lifetime achievement award administered by the Internet Society (ISOC) in recognition of individuals who have made significant contributions to the development and advancement of the Internet.

Link-state routing protocol

Link-state routing protocols are one of the two main classes of routing protocols used in packet switching networks for computer communications, the other being distance-vector routing protocols. Examples of link-state routing protocols include Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS).

The link-state protocol is performed by every switching node in the network (i.e., nodes that are prepared to forward packets; in the Internet, these are called routers). The basic concept of link-state routing is that every node constructs a map of the connectivity to the network, in the form of a graph, showing which nodes are connected to which other nodes. Each node then independently calculates the next best logical path from it to every possible destination in the network. Each collection of best paths will then form each node's routing table.

This contrasts with distance-vector routing protocols, which work by having each node share its routing table with its neighbours, in a link-state protocol the only information passed between nodes is connectivity related. Link-state algorithms are sometimes characterized informally as each router, "telling the world about its neighbours."

List of Internet pioneers

Instead of a single "inventor", the Internet was developed by many people over many years. The following are some Internet pioneers who contributed to its early development. These include early theoretical foundations, specifying original protocols, and expansion beyond a research tool to wide deployment.

List of Sun Microsystems employees

These notable people worked at Sun Microsystems at some point prior to its acquisition by Oracle Corporation.

Network security

Network security consists of the policies and practices adopted to prevent and monitor unauthorized access, misuse, modification, or denial of a computer network and network-accessible resources. Network security involves the authorization of access to data in a network, which is controlled by the network administrator. Users choose or are assigned an ID and password or other authenticating information that allows them access to information and programs within their authority. Network security covers a variety of computer networks, both public and private, that are used in everyday jobs; conducting transactions and communications among businesses, government agencies and individuals. Networks can be private, such as within a company, and others which might be open to public access. Network security is involved in organizations, enterprises, and other types of institutions. It does as its title explains: It secures the network, as well as protecting and overseeing operations being done. The most common and simple way of protecting a network resource is by assigning it a unique name and a corresponding password.


Perlman is an Ashkenazi Jewish surname. Notable people with the surname include:

Alfred E. Perlman, railroad executive

Anita Perlman, see B'nai B'rith Girls

Eliezer Yitzhak Perlman, birth name of Eliezer Ben-Yehuda, a Jewish Litvak lexicographer, the driving spirit behind the revival of the Hebrew language in the modern era.

Elliot Perlman, author and barrister

Fredy Perlman, anarchist author, publisher and activist

Isadore Perlman, American chemist

Itzhak Perlman (born 1945), Israeli-American violinist, conductor, and pedagogue

Nathan David Perlman, lawyer and politician

Philip B. Perlman, United States Solicitor General and Maryland Secretary of State

Radia Perlman, software designer and network engineer

Ralph Perlman, Louisiana state budget director, 1967–1988

Rhea Perlman, actress

Ron Perlman, actor

Selig Perlman, economist and labor historian

Steve Perlman, entrepreneur and inventor

Routing bridge

A routing bridge or RBridge, also known as a TRILL Switch, is a network device that implements the TRILL protocol, as specified by the IETF and should not be confused with BRouters (Bridging Routers). RBridges are compatible with previous IEEE 802.1 customer bridges as well as IPv4 and IPv6 routers and end nodes. They are invisible to current IP routers and, like routers, RBridges terminate the bridge spanning tree protocol.

The RBridges in a campus share connectivity information amongst themselves using the IS-IS link state protocol. A link state protocol is one in which connectivity is broadcast to all the RBridges, so that each RBridge knows about all the other RBridges, and the connectivity between them. This gives RBridges enough information to compute pair-wise optimal paths for unicast, and calculate distribution trees for delivery of frames either to destinations whose location is unknown or to multicast / broadcast groups. IS-IS was chosen as for this purpose because:

it runs directly over Layer 2, so it can be run without configuration (no IP addresses need to be assigned)

it is easy to extend by defining new TLV (type-length-value) data elements and sub-elements for carrying TRILL information.To mitigate temporary loop issues, RBridges forward based on a header with a hop count. RBridges also specify the next hop RBridge as the frame destination when forwarding unicast frames across a shared-media link, which avoids spawning additional copies of frames during a temporary loop. A Reverse Path Forwarding Check and other checks are performed on multi-destination frames to further control potentially looping traffic.


The SIGCOMM Award recognizes lifetime contribution to the field of communication networks.

The award is presented in the annual SIGCOMM Technical Conference.

The awardees have been:

2018 Jennifer Rexford

2017 Raj Jain

2016 Jim Kurose

2015 Albert Greenberg

2014 George Varghese

2013 Larry Peterson

2012 Nick McKeown

2011 Vern Paxson

2010 Radia Perlman

2009 Jon Crowcroft

2008 Don Towsley

2007 Sally Floyd

2006 Domenico Ferrari

2005 Paul Mockapetris

2004 Simon S. Lam

2003 David Cheriton

2002 Scott Shenker

2001 Van Jacobson

2000 Andre Danthine

1999 Peter Kirstein

1998 Larry Roberts

1997 Jon Postel

1997 Louis Pouzin

1996 Vint Cerf

1995 David J. Farber

1994 Paul Green

1993 Robert Kahn

1992 Sandy Fraser

1991 Hubert Zimmerman

1990 David D. Clark

1990 Leonard Kleinrock

1989 Paul Baran

Spanning Tree Protocol

The Spanning Tree Protocol (STP) is a network protocol that builds a loop-free logical topology for Ethernet networks. The basic function of STP is to prevent bridge loops and the broadcast radiation that results from them. Spanning tree also allows a network design to include backup links to provide fault tolerance if an active link fails.

As the name suggests, STP creates a spanning tree within a network of connected layer-2 bridges, and disables those links that are not part of the spanning tree, leaving a single active path between any two network nodes. STP is based on an algorithm that was invented by Radia Perlman while she was working for Digital Equipment Corporation.In 2001, the IEEE introduced Rapid Spanning Tree Protocol (RSTP) as 802.1w. RSTP provides significantly faster recovery in response to network changes or failures, introducing new convergence behaviors and bridge port roles to do this. RSTP was designed to be backwards-compatible with standard STP.

STP was originally standardized as IEEE 802.1D but the functionality of spanning tree (802.1D), rapid spanning tree (802.1w), and multiple spanning tree (802.1s) has since been incorporated into IEEE 802.1Q-2014.

TU (Time Unit)

A time unit (TU) is a unit of time equal to 1024 microseconds. It was originally introduced in the meanwhile obsolete IEEE 802.11-1999 standard but continues to be used also in newer issues of the IEEE 802.11 standard.A whole number of such units are used to describe several intervals in that standard. The use of the term is to avoid using the term "millisecond", which is slightly different. The unit allows for maintaining intervals that are easy to implement in hardware that has a 1 MHz clock (by dividing the clock signal in half ten times, rather than operating a phase-locked loop or digital divider to divide such a clock signal by 1000).

One time unit is equal to one millionth of a kibisecond (1 TU = 10−6 Kis).

Teus Hagen

Teus Hagen (* 6 October 1945 in Wijnjeterp) is a Dutch Internet pioneer.


The USENIX Association is the Advanced Computing Systems Association. It was founded in 1975 under the name "Unix Users Group," focusing primarily on the study and development of Unix and similar systems. In June 1977, a lawyer from AT&T Corporation informed the group that they could not use the word UNIX as it was a trademark of Western Electric (the manufacturing arm of AT&T until 1995), which led to the change of name to USENIX. It has since grown into a respected organization among practitioners, developers, and researchers of computer operating systems more generally. Since its founding, it has published a technical journal entitled ;login:.USENIX was started as a technical organization. As commercial interest grew, a number of separate groups started in parallel, most notably the Software Tools Users Group (STUG), a technical adjunct for Unix-like tools and interface on non-Unix operating systems, and /usr/group, a commercially oriented user group.

It sponsors several conferences and workshops each year, most notably the USENIX Symposium on Operating Systems Design and Implementation (OSDI), the USENIX Symposium on Networked Systems Design and Implementation (NSDI), the USENIX Annual Technical Conference, the USENIX Security Symposium, the USENIX Conference on File and Storage Technologies (FAST), and with LISA (formerly SAGE), the Large Installation System Administration Conference (LISA).

USENIX's founding President was Lou Katz.

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