Week 2: Fundamental networking concepts - IDATA2304, IELEA2001 Computer communication and network programming - Computer networks course
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Week 2: Fundamental
Check-In: Brosundet
networking concepts
IDATA2304, IELEA2001 Computer communication and
network programming
Girts Strazdins, gist@ntnu.no, NTNU i Ålesund, 2021
Topics for week 2 1. Nuts and bolts description (devices) 2. Service description 3. Protocols 4. Encoding data as packets for transmission 5. Queues, delays and packet loss 6. Internet service providers 7. Core network and access networks
See videos for details…
Let's look at devices first… What useful devices do we have on the network?
End-devices All the devices doing something meaningful for the users
How do we connect the end- devices? If we have n end-devices. How many links to connect any to any? n * (n-1) / 2
Hierarchy of connections
Postal service hierarchy
Universal Postal
Union
Norwegian Swedish
authorities authorities
Nasjonal
Posten kommunikasjons- …
myndighet
Posten Oslo Posten Ålesund
Rema 1000 Amfi
Spar Larsgården
Moa
… …
Computer communication
hierarchy (imaginary, but realistic)
Scandinavia
Norway Sweden
University
NTNU …
of Oslo
NTNU NTNU
Trondheim Gjøvik
NTNU
Ålesund
Brosundet Fytrårnet
Three building blocks of computer networks 1. End devices 2. Wired and wireless links 3. Routers Users of the network Infrastructure for end devices
What are routers?
Home router != router
Routers = routing + forwarding
What router manufacturers do you know?
Manufacturers are not important All routers are alike. Why?
Router interface
implements
Cisco router Mikrotik router … Noname routerHow do we describe Router interface? What is a router? How do we describe tasks for a router?
Protocols For Any device on the network: "device A has a role X in the network" == "device A provides a set of services S(X), implemented according to protocols P(X)"
What is a protocol?
Communication protocols A protocol is an agreement on actions and reactions for a service. A protocol is a common language. Two objects* can communicate if and only if they share a common protocol. * Objects can be anything: humans, animals, computer software, computer hardware, quantum entangled particles, aliens, …. In the context of computer networks, the objects are computer software.
Example human protocols • Buying lunch at the canteen • Sending a mail message to a friend • Sorting and forwarding mail at a post office • Oral exam at a university
Exercise: example protocol Describe a protocol for distribution of information sheets to all students in a class. All students and all sheets are equal (i.e, doesn’t matter which students gets which sheet as long as everyone gets one).
Exercise: Example protocol Describe a protocol for distribution of information flyers to all students in a class. All students and all flyers are equal (it doesn’t matter which students gets which flyer as long as everyone gets one). The remaining flyers should be returned to the teacher. Students are organized (sitting) in rows.
A possible solution
Protocol for the teacher: Protocol for students:
1. Show the flyers to 1. Wait for a pile of
students flyers to arrive
2. Explain that they 2. Take a flyer from the
should take one and pile
pass along 3. If I’m not the last
3. Give a bunch of flyers (rightmost) student in
to the leftmost the row, pass it to the
student in each row right
4. Wait for remaining 4. If I’m the last
flyers, collect them student, return the
when students return remaining flyers to
them the teacherNetwork protocol A network protocol is an agreement on: 1. What and when to send 2. How to react on received data
Computer network protocols at different levels • WhatsApp – how to send messages to and from Facebook servers • SSL – data encryption • TCP protocol – chunking a stream of data into packets, retransmission in case of a lost packet • IP protocol – addressing of devices, packet format, network hierarchy • WiFi – connection to wireless access points, transmitting data to/from the access points
End-users
Delivery
network
infrastructure
(routers)
Custom protocols at each level
You don’t care about the protocols
They don’t read your booksApps and services communicating
MagicConnecting the end devices We have end devices. We can get routers. How to connect each end-device to any other? If two students want to communicate – do they buy routers?
Internet Service Providers (ISPs)
ISPs in Ålesund
…How to connect ISPs?
access access
net net
access
net
access
access net
net
access
access net
net
connecting each ISP to each
access
other directly doesn’t scale: access
net
O(N2) connections. net
access
net
access
net
access
net
access
net
access access
net access net
netMultiple tiers
Can Google be fast in Russia?
Google’s data centers https://www.google.com/about/datacenters/locations/
Core network and access networks
Core network = routers AKA network backbone
Access networks Access network is a network connecting end-users to the first ISP router
Some popular
access network
typesDSL: reusing phone lines
Fiber optics cables
Home network
DSL or Fiber opticsEnterprise network
Wireless LAN and cellular nets For example, ISP network in hotels
Let's talk about routers…
Store-and-forward devices
C
A
D
B
EWhat if the outgoing link is slow?
100Mbps C
A 1Mbps
D
B
queue of packets E
waiting for output linkFour sources of packet delays
transmission
A propagation
B
nodal
processing queueing
drouter = dproc + dqueue + dtrans + dpropWhich delays depend on the
amount of traffic?
transmission
A propagation
B
nodal
processing queueing
drouter = dproc + dqueue + dtrans + dpropWhich delays depend on the
amount of traffic?
transmission
A propagation
B
nodal
processing queueing
drouter = dproc + dqueue + dtrans + dprop
Queueing delay is variable, the rest is constant. Processing varies, but just a little.How about propagation speed?
The light is not that fast! • Speed of light: 200’000’000m/s • Earth radius: 40’000’000m 8’000’000m -> 0.04 seconds!
What if the queue is
full?Packet loss
buffer
(waiting area) packet being transmitted
A
B
packet arriving to
full buffer is lostOK, now to data transmission…
How to transmit data?
MagicLinks can transmit bits
10011010…Ones and zeros • Computers work with bits (1s and 0s): • store bits • transmit bits • How to get from bits to texts and multimedia?
Converting numbers to binary An excellent 3min video on converting numbers to binary: https://www.youtube.com/watch?v=XdZqk8BXPwg In short: divide by two, write 1 under odd numbers, 0 under even numbers
From multimedia to bits (step 1)
Integer
numbers
Bits (1s and 0s)Audio -> numbers?
Audio to numbers (sampling)
Picture -> numbers?
Image to bits • Divide the image into pixels • Each pixel has a color • Number all possible colors • Each pixel becomes a number
Text -> numbers
Each character gets a number
From multimedia to bits
Video
Audio Image
Image
Image Text
Integer
numbers
Bits (1s and 0s)Size limitations • Each packet has a maximum size • How to transmit the gigabytes of cat videos?
Long bit streams to packets 10011010101011101001000111010111 10011010 10101110 10010001 11010111 #1 #2 #3 #4
Have I convinced you? 1. Any data => numbers => bits (binary numbers) 2. Split bit streams into packets, number them
Packet analysis with Wireshark • See video tutorial • We work with that in the Labs
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