802.5 Token-Ring Networks: Topology An alternative to Ethernet LANs Physical Layer Topology: Ring –Stations connected in a loop –Signals go in only one direction, station-to- station –Not bus physical layer topology like Ethernet 802.3

802.5 TRN Physical Layer: Topology Access Unit STP link from Station to Access Unit Stations Station UTP Link from Station to Access Unit Physically, stations connect to access units which are connected in a ring

802.5 TRN Physical Layer: Wiring Access Unit STP link between Access Units STP link from Station to Access Unit Stations Station UTP Link from Station to Access Unit Most connections use shielded twisted pair (STP), which has each pair and the whole cable covered with a metal shield to reduce interference

802.5 TRN: Physical Speed Speeds –Initially, 4 Mbps –Now, mostly 16 Mbps –100 Mbps is standardized but not widely used

802.5 TRN MAC Layer: Token Passing Media Access Control –Not CSMA/CD –Token passing –Special frame called a token circulates –Station can only transmit if it has the token Token Transmits

Token-Ring Networks Token-Ring versus CSMA/CD-Bus –Token-Ring is more reliable –Token-Ring is more efficient –Token-Ring is more expensive –Token-Ring has a small market share –Companies buy something good enough to meet requirements, and standards do this

802.3 Ethernet versus Token-Ring Network LLC MAC Access Control CSMA/CDToken Passing PHY Topology BusRing Both use Standard at the LLC Layer MAC Layer: CSMA/CD versus token- passing PHY Layer Topology: Bus versus Ring