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Unformatted text preview: Sheet1 Page 1 Read chapter 13,14,15,17 bridges vs repeaters repeaters: -packets in transit on both segments at same time-limit on number of repeaters-no error checking bridgeS:-packets are stored in its entirety on bridge and then forwarded-no limit on number of bridges-checks validity of every packet at every hop, and can throw away bad packets without propagating them disadvantages of dumb bridges--forwards packets onto segments that don't need it-increases congestion on segments that don't need data-all packets are seen by all machines (privacy/security issue)-accidental cycles are deadly learning bridges--forward packets only where they need to go PAN- SAN- LAN- MAN- WAN- Final requirement-Routing scalibility 1)routing table size 2)size of routing messages-Forwarding scalibility need to forward packets fast recall that atm cell is 53 octets long with 5 octet header and 48 octet payload-NSAP address is 20 octets long-ATM cells are addressed by using cnonection oriented protocol 1) set up connection - leave routing table info latency takes a packet to propagate from one machine to another types of latency- cannot go faster than speed of light, and speed of light depends on media speed of light is: vacuum -> 3 x 10^8 m/s fiber -> 2 x 10^8 m/s copper -> 2.3 x 10^8-speed of light can vary for same type of media transmission latency- time it takes to send packet out of machine--first bit till the last bit chpt 17 Sheet1 Page 2 Universal service- connectivity between any two nodes on the network and some services are available to all nodes Heterogeneity- connect nodes of dissimilar type (ATM to Ethernet to Wireless to ...) an internet - a logical network that connects dissimilar technologies an internetwork - another name for internet a physical network - underlying technologies connected by an internet packet switching between heterogenous networks is hard because:-packet sizes differ, QoS support vs Best effort, connection vs connectionless, format of frames differ, address format, transm-translation form say ethernet to fddi only works to certain extent. Ethernet to atm doesn't work. Translation is extremely difficu-scalng to wan connecting to many hosts--many hosts is millions to billions-ip makes following assumptions about the physical network technology: send and rec packets between any two machines on physical network implied assumptions: packets can be variable size and unreliable delivery and connectionless delivery-if the network doesn't provide this: the network provides less functionality than the above--needto add some functionality to g...
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- Spring '08