EECS 122 University of California Berkeley Network Architecture Network hierarchy Layering Performance Link Layer Ethernet Wi Fi Network Layer Addressing Routing Application Application Data Transport Transport TH Data Asynchronous routed path Network Data Link Control Physical Interface PH Data Asynchronous reliable bit pipe FH Data Synchronous unreliable bit pipe End Node Physical Link Asynchronous routed path Network Data Link Control Physical Interface Router PH Network Data Asynchronous reliable bit pipe FH Data Synchronous unreliable bit pipe Physical Link Data Link Control Physical Interface End Node Link System Throughput Delay Jitter Connection Send W bits window size Wait for ACKs Repeat Assume that the round trip time is RTT seconds Throughput W RTT bps Numerical Example W 64KBytes 512 kbits 512x1 024 524 288 bits RTT 200ms Throughput W T 2 6Mbps 1 1 3 3 01 2 4 3 3 Random Multiple Access Switching Bridged Ethernet 802 11 0 How to share a channel Multiple Access Multiplexing ALOHA First random multiple access system Efficient for many users each with low utilization Try If collide wait random time then repeat CD Analysis Slotted Aloha efficiency 1 e 36 0 Ethernet First version CSMA CD Wait until channel is idle try if collide stop wait repeat Idea CS should improve efficiency if fast enough Wait random multiple of 512 bit times exponential back off Analysis Efficiency 1 1 5a a PROP TRANS Ethernet Later versions Switched Larger aggregate throughput VLANs partition in disjoint logical LANs Link Aggregation Each port is in its own collision domain as opposed to a hub where all ports are in the same collision domain Fast GE 10GE Improved modulation schemes 1 Flat Addressing Learning Watch source addresses Avoiding Loops Spanning Tree Protocol ID presumed root ID distance to presumed root ID Note Not very efficient Not very fast 7 2 9 5 9 6 6 9 6 56 9 58 8 57 5 9 6 5 9 8 9 6 Service Operations Addresses MAC Hub Switch Learning Spanning Tree MAC Why not Aloha Why Switch Why Loops 3 a 5GHz up to 54Mbps b 2 5GHz up to 11Mbps g 2 5GHz up to 54Mbps MAC CSMA CA with or without RTS CTS Distributed DCF CSMA CA using different Interframe Gaps maintain network allocation vector Centralized PCF access point polls nodes 3 0 If medium is idle for DIFS interval after a correctly received frame and backoff time has expired transmission can begin immediately If previous frame contained errors medium must be free for EIFS If medium is busy access is deferred until medium is idle for DIFS and exponential backoff Backoff counter is decremented by one if a time slot is determined to be idle Unicast data must be acknowledged as part of an atomic exchange 3 4 Virtual Carrier Sensing using Network Allocation Vector NAV 3 Why not CSMA CD Objectives of new MAC Why RTS CTS How does NAV work Why different IFS Why more than 2 addresses Why different PHYs Why multiple channels 5 65 Internetworking Addressing Class Based Classless CIDR Routing 5 7 7 1 6 6 6 7 5 5 7 6 7 6 6 6 6 1 6 7 6 6 1 6 1 6 8 0 Addressing reflects internet hierarchy 32 bits divided into 2 parts Class A Class B Class C 0 0 network 0 10 16 network 0 110 host host 24 network host 2 million nets 256 hosts 5 7 Suppose fifty computers in a network are assigned IP addresses 128 23 9 0 128 23 9 49 Range is 01111111 00001111 00001001 00000000 01111111 00001111 00001001 00110001 to They share the first 26 bits of 128 23 9 0 Convention 128 23 9 0 26 prefix There are 32 26 6 bits for the 50 computers 26 64 addresses 5 Intradomain Formulate the routing problem as a Shortest Path Problem Link State v s Distance Vector Both work reasonably well in a well engineered network 44 6 6B BGP 5 22 4 3 3 RIP 7 8 6 13 13 2 1 11 10 3 IGRP Interdomain 13 C BGP OSPF Path Vector Policies 12 Dijkstra Link State Use a flooding protocol to discover the entire topology Find the shortest paths in order of increasing path length from node i Bellman Ford Distance Vector D i d minj N i c i j D j d BGP Path Vector Policy routing Receive and advertise entire routes AS numbers describe the path to a CIDR address 5 Service Operations Addresses Routing Glue L2 L3 ARP Addressing Why CIDR How Why DHCP NAT Routing Why Domains Why different algorithms Pros Cons of each algorithm Network hierarchy Layering Performance Timing Metrics Layer 2 Ethernet MAC Wi Fi MAC Repeaters hubs bridges switches routers Internet addressing Routing
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