Lecture-02-overview tcp-ip stack-part 2

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Design of ARPANET •  History –  –  –  –  –  Created by Department of Defense (DoD) during Cold War World’s first operational packet switching network Predecessor of the Internet Four IMPs – first generation of routers (UCLA, Stanford, UCSB, U. of Utah) First message sent over ARPANET 1969 (by UCLA student Charley Kline, supervised by Professor Leonard Kleinrock) •  First routing algorithm: –  1969 –  Distance Vector (Bellman-Ford) •  Next: –  1979 –  D-SPF (Link State): •  Averaged delay measurement as link cost •  Over a 10s period WNC 2011 1 Design of ARPANET (cont.) •  Revised Metrics: –  Link cost in term of hops –  Good paths vs. best path •  Congestion Avoidance: –  Congestion Collapses: 1986, 32Kbpsà40bps WNC 2011 2 Original Goals of DARPA Internet Protocol •  Top level goal: –  Effectively Inter-connect different existing networks •  Second level goal (in order of importance): –  Survivability (routing, state/stateless) –  Multiple type services –  Variety of networks –  Dist. management of its resources –  Cost effective (small/large packet with header overhead) –  Host attachment –  Accountable •  Why in this order? WNC 2011 3 Link State Routing •  Dijkstra’s algorithm •  Assumed each node knows its directly attached neighbors and the corresponding distance to each neighbor –  Each router tells the world about its neighbors •  Each node broadcasts these distance to the whole network •  Each node eventually has an identical and complete view of the network –  Track the status and connection type of each links –  Produces a calculated metric based on these and other factors •  Each node runs the Dijkstra’s algorithm to compute the least cost paths –  May take a path which has more hops, but that uses a faster medium over a path using a slower medium with fewer hops WNC 2011 4 Distance Vector Algorithm •  Each node sends information to its directly neighbors. •  No global view •  Each node only knows the information about the directly neighbor WNC 2011 5 Which One is Better? •  Link State Routing –  Global –  Flood (number of messages exchanged, new update must be sent to all) –  Scale (complete map) –  No count to infinitive problem –  Require more processing power and memory •  Distance Vector Routing –  Distributed –  Less flood (messages are sent at each iteration only if link cost of neighbors are changed) –  Convergence time –  Count to infinitive problem –  Simpler à require simpler hardware WNC 2011 6 Hierarchical Routing •  Millions, billions of computer •  How to route? –  Scale: Number of messages exchanged, time converge –  Administrative autonomy: hiding, preference routing, which routing algorithm to use? •  Aggregating routers into AS (Autonomous Systems) –  Router within the same AS all run the same routing algorithm (intra-AS routing) –  Routing between AS using inter-AS routing protocol WNC 2011 7 Intra-AS routing •  RIP (Routing Information Protocol) –  Distance Vector Algorithm •  OSPF (Open Shortest Path First): –  Link State Algorithm WNC 2011 8 Inter-AS Routing •  BGP (Border Gateway Protocol) •  Path Vector Protocol •  Propagate path information (sequence of ASes on a route to a destination AS) •  Policy based, no cost information included WNC 2011 9 Transport Layer •  Reliability? –  Did the data reach the destination? –  Did the data arrive in the correct order? •  Congestion? –  Am I overloading the network? –  How do I know? How do I fix it? •  Flow control? •  2 types: –  TCP (Transmission Control Protocol) –  UDP (User Datagram WNC Protocol) 2011 10 TCP •  Connection Oriented: Handshake (how many ways?) •  Reliable: –  Complete –  Undamaged (which mechanism protect this?) –  In order •  Congestion Avoidance •  Suitable for transfer important data: –  Files –  Email WNC 2011 11 Quiz •  Intermediate node maintain state? –  Which layer the packet will have to go through in intermediate node? •  One sender to many receiver using TCP? –  Point-to-point WNC 2011 12 UDP •  Connectionless •  Best effort/Unreliable: no verification if data arrived •  No congestion control •  Suitable for real-time streaming (audio, video) where on-time arrival more important than reliability •  Suitable for simple query/response application like DNS WNC 2011 13 DNS •  Domain Name Service •  Store hostname and domain name in a kind of distributed database •  Provide IP address for each hostname •  Ex: www.yahoo.com into WNC 2011 14 DNS (iterative queries) •  Host A needs to know IP of www.yahoo.com •  Host A check its cache •  If not found, A check one of the root server •  Root server reply server B know *.com domain •  A ask B for www.yahoo.com •  B reply server C know *.yahoo.com •  A ask C, and C reply WNC 2011 15 DNS (recursive queries) •  The intermediate server forwards the DNS query on behalf of the host A •  Mostly are recursive queries, except for root server WNC 2011 16 Time to Live •  Each DNS response include a TTL •  The client store the DNS response in the cache until TTL expires •  Ex: –  The TTL is set to 6 hour and the response is sent to client at 1:00PM –  If the root server change the IP at 1:01PM, the client won’t receive the update until 7PM. •  Not necessary all machines have the same map of DNS at a given time WNC 2011 17 Quiz •  What should the TTL field be for “www.yahoo.com”? Short or long? WNC 2011 18 Quiz •  Does DNS use Centralized or Distributed model? •  Since the root server will delegate to other server, so there is no centralized server to store a complete DNS database. Why? WNC 2011 19 Application Layer •  Applications make use of TCP/UDP are associated with a well-known port number: –  FTP: 21 –  SSH: 22 –  Telnet: 23 –  HTTP: 80 –  DNS: 53 •  Which one uses TCP, which one uses UDP? WNC 2011 20
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