CPSC 360 - Network Programming More on LANs Michele Weigle Department of Computer Science Clemson University mweigle@cs.clemson.edu February 28, 2005 http://www.cs.clemson.edu/~mweigle/courses/cpsc360 Roadmap! Hardware Addressing "9.1-9.3, 9.8-9.10, 9.12!LAN Wiring "10.1-10.4, 10.8, 10.12! Extending LANs "11.1-11.2, 11.4-11.5, 11.13-11.14! Local Loop Digital Technologies "12.6-12.13, 12.15-12.17
Hardware Addressing LANs! Provide communication across short distances! Example: Ethernet "bus topology "everyone hears all signals!how can a pair of computers communicate efficiently? Hardware Addressing!Each NIC is assigned a physical address "hardware address, or MAC address "assigned by manufacturers "guaranteed to be unique! Each frame contains source address and destination address
Hardware Addressing Network Interface Cards! Captures frames "determine if it is the destination! Checks length of frame! Checks CRC "frame discarded if there are errors! Has its own CPU, ROM, RAM for processing frames! If frame accepted, sends an interrupt to the CPU Hardware Addressing Ethernet Frame Format! Usually header followed by data! Header always same length! Data usually variable
Hardware Addressing Network Analyzers!Can be configured to monitor traffic on a LAN "statistics about frame counts "debug problems!nic put in promiscuous mode "accepts all frames Roadmap! Hardware Addressing!LAN Wiring "10.1-10.4, 10.8, 10.12! Extending LANs "11.1-11.2, 11.4-11.5, 11.13-11.14! Local Loop Digital Technologies "12.6-12.13, 12.15-12.17
LAN Wiring NICs! Built for a specific network technology! Handles details of transmission and reception! Transmission "CPU formats packet in memory "CPU tells NIC to transmit "NIC sends interrupt when done! Reception "CPU reserves buffer in memory "CPU tells NIC to receive "NIC puts frame in buffer "NIC sends interrupt LAN Wiring Twisted Pair Ethernet! Types of wiring "10 Mbps Ethernet - 10BaseT "Fast Ethernet - 100BaseT "Gigabit Ethernet - 1000BaseT! Connects two devices! Hub emulates a physical cable
LAN Wiring Autonegotiation! 100BaseT is backward compatible! Ends perform autonegotiation "link speed is the slowest of the two! 10/100 Ethernet! 10/100/1000 Ethernet Roadmap! Hardware Addressing!LAN Wiring! Extending LANs "11.1-11.2, 11.4-11.5, 11.13-11.14! Local Loop Digital Technologies "12.6-12.13, 12.15-12.17
Extending LANs!How to build a LAN farther apart than our physical layer limitations?!repeaters!bridges!switches Extending LANs Repeaters! Hardware device that connects two cable segments! Amplifies and repeats all signals! Example: Ethernet hub
Extending LANs Bridges! Handles frames rather than just signals! Does not forward collisions or interference! Does not forward frames unless necessary Extending LANs Switches! Simulates a bridged LAN with one computer per segment! In practice, computers connected to hubs, hubs connected to switches
Extending LANs Hubs vs. Switches Hub! Simulates a single segment! At most two computers can communicate at a time! Max throughput of hub is R Switch! Each computer has a simulated LAN segment! Up to 1/2 of computers can send data at same time! Max throughput is RN/2 Roadmap! Hardware Addressing!LAN Wiring! Extending LANs! Local Loop Digital Technologies "12.6-12.13, 12.15-12.17
Local Loop Digital Technologies! Telephone Standards! Digital Subscriber Line Technology! Cable Modem Technology Local Loop Digital Technologies Digital Circuits
Local Loop Digital Technologies Local Subscriber Loop! Connection between the phone company CO and the user! Analog signals "designed for voice "POTS! Bandwidth limited by voice bandwidth and SNR Local Loop Digital Technologies ADSL! Share phone lines "allows higher frequencies than actually used for voice! Asymmetric DSL "more bandwidth downstream than upstream - why? "max downstream - 6.4 Mbps "max upstream - 640 Kbps! Adaptively select frequency and modulation technique! Cannot guarantee rate
Local Loop Digital Technologies Cable Modem! CATV uses coax higher data rates! Need pair of cable modems "one at CATV center "one at user s end! Data encoded in carrier, broadcast across cable! One frequency assigned to set of users! Each users assigned address! Much like shared LAN! Max data rate 36 Mbps "may be shared among other users