EECS 122 Spring 2004 University of California Berkeley What are the basic differences between Circuit and Packet Switching Understand Packet Switch network hierarchy LAN MAN WAN What is the motivation behind layering What are the different layers and the corresponding key protocols What are the main performance metrics Howa re they defined and what are the relationships among them 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 What does Shannon s theorem for the channel capacity state How do the basic data encoding schemes NRZ NRZI 4B 5B etc work How do the basic error detection schemes parity CRC etc work What s the motivation behind shared media protocols Ethernet Why is Ethernet an improvement over Aloha How does Ethernet MAC work What s the relationship between the maximum propagation time and the minimum frame size How do hubs bridges and switches operate What are the key differences among them Why is the Spanning Tree algorithm required How does it work 802 11 Wi Fi What are the basic physical layer protocols used by 802 11 How doe the 802 11 MAC work What s the efficiency of 802 11 MAC What are the differences between Ethernet and 802 11 MAC protocols Why are they necessary Understand the key 802 11 MAC ideas RTS CTS NAV different IFS etc Ethernet 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 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 Virtual Carrier Sensing using Network Allocation Vector NAV Understand the addressing scheme What s the motivation behind CIDR How does ARP work How do NAT and DHCP work Understand the operation of the key routing protocols RIP OSPF BGP What are the pros cons of each algorithm 230 13 3 03 0 0 0 0 3 03 032 1 2 3245 7 3 03 06 01 Addressing reflects internet hierarchy 32 bits divided into 2 parts Class A Class B Class C 0 8 0 network 0 10 16 network 0 110 host host 24 network host 2 million nets 256 hosts Problem Class B is facing address space exhaustion If multiple Class C addresses are given out routing table size needed can be too large Solution Assign consecutive Class C addresses and in essence allow network address length to be flexible Example A corporation needs 16 Class C addresses CIDR scheme could assign network addresses 192 4 16 to 192 4 31 i e in the range 11000000 00000100 00010000 00000000 11000000 00000100 00011111 00110001 They share the first 20 bits of 192 4 16 0 Routing tables store the 20 bit prefix Convention 192 4 16 0 20 prefix Intradomain Formulate the routing problem as a Shortest Path Problem Link State v s Distance Vector 44 6 6B BGP 5 2 2 4 3 3 RIP 7 Interdomain 6 13 13 2 1 BGP Path Vector Policies 8 11 10 3 IGRP 13 C OSPF 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 identifiers describe the path to a CIDR prefix Why is a scheduling scheme like WFQ needed Understand the properties of WFQ Bandwidth sharing Work conservative scheduling etc What s the relationship between GPS and PGPS same as WFQ Understand at a high level the algorithm for the WFQ practical implementation based on the GPS finish times 2 34 Solid line shows the evolution under GPS In this example no packets under WFQ finish later than under GPS In general maximum lateness under WFQ is Lmax C where Lmax is the maximum packet size Where do RTP and RTCP fit in the protocol layers What are the services provided by RTP and the companion RTCP What s the rationale behind VoIP being an attractive service over IP networks Understand the basics of the alternative protocol suites for VoIP H 323 and SIP
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