Radia Joy Perlman (born January 1, 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.
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 computer programmer. At school math and science were “effortless and fascinating” to Perlman. Though she achieved As also in subjects she was less fond of, because she memorised facts, dates and names in advance of tests. She enjoyed playing the piano and French horn. While her mother helped her with her math homework, they mainly talked about literature and music.
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 women 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".
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.
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.
As a math grad at the 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. Perlman obtained a B.S. and M.S. in Mathematics and a Ph.D. in Computer Science from MIT in 1988. Her doctoral thesis at MIT addressed the issue of routing in the presence of malicious network failures.
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 the 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 use 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".
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. She was a Distinguished Engineer 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).
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 devises, 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 to 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. 
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). Perlam 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. 
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