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<!DOCTYPE html>
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<title>Computer Networks (2)</title>
<meta name="cours-n" content="2">

<meta name="author" content="Rémi Emonet">
<meta name="venue" content="DWA M1 WI/MLDM">
<meta name="date" content="2017">
<meta name="affiliation" content="Université Jean Monnet − Laboratoire Hubert Curien">
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# @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






<!-- bitrate, throughput, latency, etc -->
# @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 &rArr; 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
- $d_{proc}{}$ : &lt; 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}





<!-- PROJECTS -->
# @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
- …




<!-- TOOLS -->
# @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
- …





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