lesson-02.html 8.64 KB
  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276  Computer Networks (2)
Please wait, while our marmots are preparing the hot chocolate…
# @chunk: chunks/title.md# @chunk: chunks/objectives.md## Today // higher level/latency/throughput + projects + maybe some tools?- End of intro: latency, bandwidth, throughput- About the projects {itproj}- Some tools {ittools}## Part 1: General Introduction {#plan overview}- Goal - have a tour of the main concepts - that will be seen in details later- Overview - what is internet {it1} - what is a protocol {it2} - the network edge {it3} - layers and encapsulation {it6} - security {it7} - some history {it8} - the network core {it4} - performance: latency, bandwidth, throughput, etc. {it5}# @copy:#plan# @copy:#plan: %+class:inred: .it5## Buffering/Queuing and Packet Loss@SVG: media/part1/link-capacity-3.svg 800px 200px {svg}- Cause - input bitrates are greater than the capacity of the output link - a temporary situation - but long enough to fill the buffer ⇒ need to drop packets- Effects - delay due to the queuing - necessity to handle (at higher levels) the loss // ignore, resend, compensate (interpolate), ...## Four Sources of Delay@SVG: media/part1/link-delays.svg 800px 200px {svg}- Sources of delay/latency - $d_{proc}{}$ : < 1ms {a1} - $d_{queue}{}$: depending on router congestion {a2} - $d_{trans} = \frac{L}{R} = \frac{\text{size}}{\text{capacity}}$ {a3} - $d_{prop} = \frac{d}{s} = \frac{\text{distance}}{\text{speed}}$ {a4}- @anim: #analyze + .a1 | #file + .a2 | #transmission + .a3 | #propagation + .a4## Exercise- Total delay $d\_{total}{}$ includes $d\_{proc} + d\_{queue} + d\_{trans} + d\_{prop}{}$- How much time does it take to transfer - a single 125 kB packet - over a 100 Mbps link - supposing there is no congestion 1. To a computer in the classroom next-door? 1. To a computer in San Francisco? (~ 9000 km)## Capacity, Bitrate, Throughput, Bandwidth- Precise terminology // but still fuzzy in the usage - for a link:     bandwidth == capacity == rate - from a device to another - transfer rate == throughput - the actual throughput is upper bounded by the link capacity - instantaneous throughput, average throughput- Data transfer rates in a network{slide} - analogy with fluids in some pipes- @anim: .svg | #pipeview | #classical + #server | #clients | #rest@SVG: media/part1/link-capacities.svg 800px 200px {svg}# @copy:#plan: %+class:inred:.itproj# Projects {overview no-print}## Projects {libyli}- Subject - peer to peer file sharing, kind of bittorent- Phase 1 - github registration: done? - group and team creation, sending an email - name and github username (of each member) - chosen programming language for the project - deadline: **Tuesday, January 17th, 22h** // then I invite- Phase 2 - distribution of the subject and meta-groups - understanding of the subject - creation of a protocol documentation (version 1) - a clear specification document - the protocol will mix text and binary - deliverable: protocol document## Projects- Subject - peer to peer file sharing, kind of bittorent- Phase 1 - group creation- Phase 2 - understanding of the subject - creation of a protocol documentation (version 1)- Phase 3 {libyli} - implementation - test - documentation of possible evolutions## Projects: evaluation and comments {libyli}- Evaluation - correct usage of git - project that works - proper understanding of the P2P architecture - ability to exchange a file using P2P - interoperability - ability to exchange a file within meta-groups - clean code, robust code, automated tests, … - retrospective, …- Advice - *start today* - specify also you file format for ".torrent" files - communicate in your meta-group if you protocol changes are needed - in the end - tell what works - explain if/how the protocol had to evolve - explain how you tested the robustness - compare the implementations - …# @copy:#plan: %+class:inred:.ittools# Tools {overview no-print}## Telnet: interactive connection- Opens a TCP connection on a host+port- Displays what is received- Sends what is typed (on new line)- Useful for quick testing of a simple text protocol## Ping- Measure the round-trip time to a host- Allows to choose the size of the packets- …## Traceroute (or mtr)- Measures the round-trip time to a host- Measures it for each router between the computer and the destination- Uses packets with a limited TTL- Available online // or mira- Possibility to see an approximate locate of routers on a map- mtr - continuous traceroute## Nslookup: querying DNS servers- Sends requests to name servers - NB: DNS uses a binary protocol- Ex: - nslookup gmail.com - nslookup -querytype=NS gmail.com - nslookup gmail.com ns1.google.com. - nslookup -querytype=MX gmail.com- Possible interactive mode- …- Dig - other tool to query DNS servers## Whois: query the whois database- Gets information associated to a domain name registration- Also available online## Wireshark: intercepts packets- Traces all communications on a network interface- Shows a graphical interface- Allows to filter data for visualization- Very useful to see encapsulated data- …

/ will be replaced by the authorwill be replaced by the title