EECS122 Midterm Review

1. EECS122Midterm Review Department of Electrical Engineering and Computer Sciences University of California Berkeley

2. TOC: Midterm Review • Network • Web Browsing • Layers & Protocols • Inside a Router • Check List

3. Review: Network WAN MAN

4. Review: Network WAN LAN MAN

5. Review: Network WAN LAN

6. Review: Web Browsing • Example • Locating Resource: DNS • Connection • End-to-end • Packets • Bits • Points to remember

7. Web: Example • Click Link or URL •  get content from localor remote computer • URL: http://www.google.com/string Specifies • Protocol: http • Computer:www.google.com • String Computer (server) selects contents based on string

8. Web: Locating Resource • www.google.com is the name of a computer • Network uses IP addresses • To find the IP address, the application uses a hierarchical directory service called theDomain Name System

9. Web: Connection • The protocol (http) sets up a connection between the host and cnn.com to transfer the page • The connection transfers the page as a byte stream, without errors: pacing + error control

10. Web: End-to-end • The byte stream flows from end to end across many links and switches: routing (+ addressing) • That stream is regulated and controlled by both ends: retransmission of erroneous or missing bytes; flow control

11. Web: Packets • The network transports bytes grouped into packets • The packets are “self-contained” and routers handle them one by one • The end hosts worry about errors and flow control: • Destination checks packet for errors (using error detection code CKS) and sends ACKs with sequence number # • Source retransmits packets that were not ACKed and adjusts rate of transmissions

12. Web: Bits • Equipment in each node sends the packets as a string of bits • That equipment is not aware of the meaning of the bits

13. Application Application HTTP, FTP, … Data UDP - TCP Transport Transport TH Data Asynchronous routed path Asynchronous routed path Network Network Network PH Data PH Data IP Asynchronous reliable bit pipe Asynchronous reliable bit pipe Data Link Control Data Link Control Data Link Control FH Data FH Data Synchronous unreliable bit pipe Synchronous unreliable bit pipe PhysicalInterface PhysicalInterface PhysicalInterface Physical Link Physical Link End Node Router End Node Review: Layers & Protocols

14. Mapping Layers to Network Devices • Two broad classes of devices • Hosts • Routers • Both sets of devices run applications • Hosts mainly run “user applications” • Routers run “infrastructure applications” • E.g. Topology discovery, Network Management Protocols, BGP etc. • Don’t be confused by thinking that routers don’t run application protocols because they are layer 3 devices

15. ports p1 p2 p1 p2 p3 p1 p2 A B C Layers: Transport Services HTTP RA DNS Application Transport IP [A | B | p1 | p2 | …] UDP: Not reliable TCP: Ordered, reliable, well-paced

16. Layers - TCP: MPX, Error,Flow and Congestion Control window = min{RAW - OUT, W} 65KB W 3DA 3DA TO X0.5 X0.5 X0.5 X0.5 3 3 TO 1 CA SS SS CA

17. C x A B y D E Limit rates: x = y TCP Algorithm: AIMD

18. [ACK | RAW | …] Flow Control • Objective: Avoid saturating destination • Algorithm: Receiver avertizes window RAW window = min{RAW– OUT, W} whereOUT = Oustanding = Last sent – last ACKedW = Cong. Window from AIMD + refinements RAW

19. Layers: IP – Internet Protocol • Addressing • Class-Based Fixed Prefix – M-tree • Classless: CIDR LPM-Patricia Trie • Routing

20. 0 0 network host 8 0 16 network 1 0 host 0 24 ~2 million nets 256 hosts network 1 1 0 host Class-base Addressing • Addressing reflects internet hierarchy • 32 bits divided into 2 parts: • Class A • Class B • Class C

21. Classless Internet Domain Routing Suppose fifty computers in a network are assigned IP addresses 128.23.9.0 - 128.23.9.49 • Range is 01111111 00001111 00001001 00000000 to 01111111 00001111 00001001 00110001 • They share the first 26 bits of 128.23.9.0: • Convention: 128.23.9.0/26 = prefix • There are 32-27=6 bits for the 50 computers • 26 = 64 addresses

22. IP: Routing • 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 4 4 6 BGP B 6 5 7 IntraDomain 2 2 4 8 RIP 6 3 13 3 13 11 2 10 IntraDomain IntraDomain 3 1 13 12 • Interdomain • BGP • Path Vector, Policies C IGRP OSPF

23. Route Computation • 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) = minjεN(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 Choose best route accept, deny, set preferences forward, not forward set MEDs Routes received from neighbors Routes sent to neighbors Import Policy Engine Export Policy Engine Routes used by router Decision process IP Routing table BGP table

24. input interface output interface Inter- connect Review: Inside Router • Input and output interfaces are connected through an interconnect • A interconnect can be implemented by • Shared memory • low capacity routers (e.g., PC-based routers) • Shared bus • Medium capacity routers • Point-to-point (switched) bus • High capacity routers Scheduling GPS WFQ

25. Router: GPS/WFQ • Why service disciplines? • Understand GPS and WFQ well • GPS properties • WFQ tracking result • No later than one packet transmission

26. Review: Check List • Big Picture • Layers • Network Structure (L2, L3) • Where protocols are implemented • Switching Techniques • Applications • DNS • HTTP • Transport • TCP: Service; Go Back N; Flow Control; Congestion Control; AIMD; SS; 3DA; Phases • UDP: Service • Network • Class-Based; Classless Addressing • Dijkstra; Bellman-Ford • Hierarchical routing • Inside Router • Architecture: Input, Output • Scheduling: Fairness, GPS, WFQ