SDLC - Synchronous Data Link Control
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IBM mid-1970s; link layer protocol
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synchronous, bit-oriented developed for SNA architecture
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2 types of nodes:
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primary : control operation of secondaries
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secondary : can transmit data when primary grants permission
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supports variety of link types and topologies
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point-to-point (one primary, one secondary)
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multipoint (one primary, many secondaries)
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loop (one primary, many secondaries)
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hub go-ahead
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can be used with full-duplex and half-duplex; circuit switched and packet switched
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