Ethernet -- Topology: Ethernet MAC: Hub Single collision domain Hub Hub Relay Collision! After a collision, stop for a random time wait for a random time, then try again. (Walrand/Varaiya slides) - computers connected to hub in a star topology - The hub copies any incoming packet onto all other lines thus collisions!!, thus need retransmissions!! [need protocol!]
Ethernet -- Addressing: (Walrand fig. 2.1) - Physical (Ethernet) address: assigned by manufacturer, hardwired onto Ethernet card, e.g. 8:0:20:1:C9:7E (48 bits in hex) - Network (IP) address: assigned by system administrator, e.g. 128.200.9.148 - Name: assigned by system administrator, e.g. jordan.ece.uci.edu
Ethernet -- Addressing - Physical (Ethernet) address: assigned by manufacturer, hardwired onto Ethernet card, e.g. 8:0:20:1:C9:7E (48 bits in hex) - Network (IP) address: assigned by system administrator, e.g. 128.200.9.148 - Name: assigned by system administrator, e.g. jordan.ece.uci.edu Ethernet packet contains source and destination Ethernet addresses. Q. IP address -> Ethernet address??
Q. IP address -> Ethernet address?? A. "Address Resolution Protocol" (ARP) Ethernet MAC: Address Resolution Protocol Router IP2, MAC2 IP5, MAC5 IP1, MAC1 IP3, MAC3 IP4, MAC4 Layer 2 Switch (Walrand/Varaiya slides) To send to IP5, any other node must learn MAC5. To learn MAC5, IP2 send broadcast message: [To All, From MAC2, ARP: IP5?] When it sees this message, IP5 replies: [To MAC2, From MAC5, ARP: I am IP5]
ARP: - Each computer keeps a IP to Ethernet address translation table. - If a computer wants to find a new Ethernet address, it broadcasts a message to all other computers on the LAN with the IP address. - The computer corresponding to the IP address replies. Note: This requires each machine to initially know its IP address. Q. What if a computer is diskless?
ARP: - Each computer keeps a IP to Ethernet address translation table. - If a computer wants to find a new Ethernet address, it broadcasts a message to all other computers on the LAN with the IP address. - The computer corresponding to the IP address replies. Note: This requires each machine to initially know its IP address. Q. What if a computer is diskless? A. "Reverse ARP" (RARP) - Computer broadcasts message with its Ethernet address. - At least 1 computer per LAN is a "server", which responds with the IP address.
Ethernet -- Topology: Ethernet: Physical Layer UTP unshielded twisted pair up to 110m Fiber 100Mbps: 2000m Gbps: 220m, 500m, 5000m Wireless 2.4GHz DSSS: 1Mbps, 2Mbps, 5.5Mbps, and 11Mbps 25m - 200m (Walrand/Varaiya slides) - 10base5 & 10base2 are often bus topologies. - 10baseT is a star topology. - Note max cable lengths.
Ethernet -- Physical Layer: One example of modulation -- logical 0 and 1 are encoded as +0.85V -0.85V 0.1microsec and +0.85V -0.85V 0.1microsec (Tanenbaum fig. 4-20) - The transitions allow for synchronization & determination of idle.
Ethernet -- MAC Layer: Use ALOHA, but take advantage of a shorter distance. Add: - Carrier Sensing (CS): start to transmit only if idle. - Collision Detection (CD): stop transmission if collision. protocol name: CSMA-CD (Carrier Sense Multiple Access - Collision Detection) brand name: Ethernet Methods for CS and CD depend on version, e.g. excess current for CD.