the scope and expectations of a senior-level classthe scope and expectations of a senior-level class...
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The scope and expectations of asenior-level class
Although a lot of new material is introduced, the emphasis is on critical thinking, and integration of existing knowledge and skills.Some of the elements to integrate in this class:•Knowledge of computer systems•Programming (we use Python)•Algorithms (COSC 2341 is prerequisite)•Calculus (MATH 2414 is prerequisite)•Elementary probability (MATH 1342 is helpful)
Introduction
Chapter 1
Networks, internetworks,distributed systems
interconnected computers = computers able to exchange information
network = collection of autonomous computers • interconnected by a single technology and• with one owner/administratorinternetwork = internet (not necessarily The Internet!):• multiple technologies and/or
• multiple owners/administrators
internet vs. Internet - AP doesn’t get it ...
https://www.theverge.com/2016/4/2/11352744/ap-style-guide-will-no-longer-capitalize-internet(linked on our webpage)
Interconnected computers Internetworks
Networks
Interconnected computers Internetworks
Networks
Give an example system in each of the four (?) parts of this Venn diagram!
Interconnected computers Internetworks
Networks
Unconnected computers
Tarleton intranet
The network of desktops in this
room
Tianhe-2 supercomputer(33.8 petaflop)
16,000 Intel-based computers
Sunway TaihuLight supercomputer (93 petaflop)
40,960 Sunway-based computers
PC connected wirelessly to
printer
Distributed system = collection of autonomous computers that appears to its users as a single coherent system
• It is a software construct, built on top of a network or internetwork
• The software is called middleware
Example: the WWW.
Networks, internetworks,distributed systems
Represent distributed systems in this Venn diagram!
Interconnected computers Internetworks
Networks
Interconnected computers Internetworks
Networks
Distributedsystems
QUIZ: How would you classify a Remote Desktop
system?
Image source: http://pcuserinfo.com/remote-desktop-services/
QUIZ: How would you classify Dropbox?
Image source: https://cacoo.com/diagrams/r2b7tm121FwMEOgI-3FFE3.png
QUIZ: How would you classify a supercomputer?
Image source: https://en.wikipedia.org/wiki/Supercomputer
1.1 Uses of networksThe client-server model
The client initiates communication by placing a request to the server
Client characteristics• Always initiates requests to servers.• Waits for and receives replies.• Usually connects to a small number of servers at any one time.• Usually interacts directly with end-users using user interface (e.g. GUI).
Server characteristics• The opposite!
1] Several PCs in an office using the same printer2] A bank database handling withdrawals and deposits from
several ATMs3] Microcontroller system monitoring tire pressure in a car.
There is a “smart” sensor in each tire.4] A team of mobile robots sending live video wirelessly to
a home base.5] Music fans exchanging mp3 files by email.
QUIZ: For each application, specify which part should be the client and which the server:
Peer-to-Peer (P2P)
In peer-to-peer system there are no fixed clients and servers.
Wireless vs. mobile computing
This table needs some reworking!
Ubiquitous computing
A.k.a. pervasive computing, cooperating objects, or“every light-bulb should have an IP address”
To do for next time:
Read the entire Section 1.1 and take notes.
1.2 Network HardwareBroadcast, Multicast, Unicast
Types of transmission technology:• Broadcast links
– Broadcast: everyone receives– Multicast: only a sub-group receives
• Point-to-point (a.k.a. unicast) links
For each of the scenarios below, decide if transmission is uni-, multi-, or broadcast:
1. The dean is sending a message to the dept. heads, to be distributed:
(a) only to tenured faculty.(b) to all faculty.
2. Two people whisper to each other in a noisy bar.3. Airhorn tornado alarm.
Decide if transmission is uni-, multi-, or broadcast:
4] The game of “telephone”
QUIZ
And now let us inject some probability
4] The game of “telephone”There are 8 people in the game, and the probability of a
change to occur between any two people is 0.25 (25%), what is the probability for the message to propagate unchanged to the last person?
Hint: How many transmissions are there?
QUIZ
Answer: 0.75^7 = 0.133
Network size Home Area Nw = HAN
Controller AreaNw = CAN
Systems AreaNw = SAN(e.g. computer cluster)
Storage AreaNw = SAN
1,000,000 km Solar system Earth-to-Mars
Wikipedia has even more listed: https://en.wikipedia.org/wiki/Municipal_wireless_network
Local Area Nw = LAN
Two broadcast topologies(a) Bus(b) Ring
Local Area Nw = LAN
QUIZ: Your boss asks you to design a network with a bus topology to connect the company offices in Stephenville, Granbury and Ft. Worth.
What is your answer?
Metropolitan Area Nw = MAN
MAN based on cable TV Wireless MAN (802.16)
https://loiscolton.com/2007/family/don/wireless/
Another type of wireless MAN
Wide Area Nw = WAN
The subnet contains only routers, no hosts.What is a host?
– In 99% of the cases, server, PC, or smart-phone.– Other types of hosts: mainframes, supercomputers, smart
sensors, telerobots etc.
WAN
A stream of packets moving from sender to receiver• Routing vs. forwarding• Store-and-forward vs. cut-through
QUIZ
A packet has 1000 bits, and it has to pass through 3 network nodes: A, C, E, as shown above.
All links have the same speed, 1000 bps. Processing times inside all nodes and speed-of-light propagation delays are negligible.
Find the total transmission time for store-and-forward vs. cut-through forwarding. Compare.
Hint for cut-through: It’s pipelining!
33
n k
# of steps is n+k-1
QUIZ
A packet has 1000 bits, and it has to pass through 3 network nodes: A, C, E. All links have the same speed, 1000 bps. Processing times inside all nodes and
speed-of-light propagation delays are negligible.Find the total transmission time for store-and-forward vs. cut-through forwarding.
Compare.Answers:• Store-and-fwd: 4000 ms = 4 s• Cut-through: n = 1000, k = 4 1003 steps 1003 ms• As expected, cut-through is faster (but remember the downsides!)
EXTRA-CREDIT QUIZ
Wireless NwsCategories of wireless Nws:• System interconn. (PAN, e.g. Bluetooth)• Wireless LANs (802.11)• Wireless MANs (802.16)• Wireless WANs (satellite, cellular)
Almost all wireless Nws eventually connect to a wired Nw (because the content is in wired facilities, a.k.a. server farms).
Wireless Nws
(a) Bluetooth configuration (master-slave)(b) Wireless LAN
To do for next timeRead the entire sections 1.1 and 1.2 and take notes
Redo today’s quizzes
Start a list of acronyms in your notebook, like:• CAPTCHA, LAN, WAN, MAP, PAN, VLAN, ISP
1.3 Network software
… and networks have layers, too!
In CS, this concept takes many forms: abstraction, information hiding, ADTs, encapsulation, etc.
The philosopher-translator-secretary stack.
Layer lingo
Entities, protocols, interfaces, services, peers Peers communicate horizontally using that layer’s protocol
Layer lingo
Layer N-1 is a Virtual Machine for layer NThe peers on layer N are said to have a Virtual Connection
Encapsulation, segmentation
Information flow supporting virtual communication on L5
String of bits String of bits
Voltages, amplitudes, phases0
QUIZ
The peers on L5 want to exchange a file that is 1024 Bytes long.L4 adds 16-Byte header.L3 breaks the packet into chunks that are at most 256 Bytes long
(fragmentation), and adds 8-Byte header.L2 adds a 10-Byte header and a 4-Byte trailer.What is the total overhead of this transmission (%)?
Design Issues for the Layers• Addressing = identifying senders & receivers.• Logical channels (priorities)• Direction of transfer (simplex, half-duplex, duplex)• Error Control• Reordering of messages• Flow Control• QoS (Quality of Service): reliable, unreliable• Disassembly & Reassembly• Multiplexing• Routing
Connection-Oriented vs. Connectionless
Connection-oriented: e.g. the (analog) telephone system.Connectionless: e.g. the postal system.
Trade-off:Connectionless is simple, w/little latency, but unreliable.Connection-oriented is more reliable, but adds latency,
information overhead and hardware/software complexity in the core network.
Connection-Oriented vs. Connectionless Trade-offs:Parameter Connection-oriented ConnectionlessOut of order pkts. No PossibleReliability High (dedicated “ circuit” ) Low (“ best effort” )Negotiation Yes (complexity) NoStateful nodes Yes (complexity) No (stateless)Address overhead Low HighLatency High LowThroughput High Low
QUIZ
Hint: Denote the unknown distance by x and calculate the data rate as a function of x.
Solution
Discussion
Note that Bernie’s instant data rate is not constant, actually, for most of the time it is zero! It’s really the average data rate (a.k.a. throughput) that is 150 Mbps or higher.
Consider the maximum distance found for this problem ≈ 6km. At this distance, Bernie’s average data rate (a.k.a. throughput) is exactly 150 Mbps.What is Bernie’s latency for this distance?
Discussion
Quality of Service (QoS) There are many measures of quality. Here we mention only
reliability:
Unreliable service – data can easily be lost (e.g. regular mail)
Reliable service – data is not lost (e.g. registered mail) Usually implemented through acknowledgements
(ACK) and retransmission in case of failure
Service primitives
Five service primitives for implementing a simple connection-oriented service.
Primitives = operations available to a process (can be system calls, if the protocol stack is part of the OS)
Service primitives in action
Packets sent in a simple client-server interaction on a connection-oriented network.
Service primitives in action
Many things could go wrong in the interaction above, e.g. errors, congestion etc.
A good protocol should be able to deal with such conditions.
To do for next time
Read entire section 1.3 and take notes
1.4 Reference Models(= examples of protocol architecture)
Mantra: “Keep the core dumb (and fast) and the edge smart (but slower)”
ISO-OSI reference model
Short description of functions performed on each of the 7 ISO-OSI layers (pp. 41-45 → Read and take notes!)
• PHYSICAL: voltages, durations, duplexing, cables, pins
• LINK: frames, error detection/correction, flow ctrl., medium access
• NETWORK: addressing, routing, congestion, QoS
• TRANSPORT: fragmenting/reassembly, end-to-end
• SESSION: tokens, synchronization (continuing a long transmission after a crash, e.g. SmartFTP)
• PRESENTATION: semantics (conversion between different file formats), compression, encryption
• APPLICATION: programs the user interacts with, e.g. FTP, HTTP, SMTP
The TCP/IP reference model(cca 1974 - ARPANET, Internet)
Protocols and networks in the TCP/IP model
Source: http://www.serviceassurancedaily.com/2011/10/the_state_of_the_network_take_1.html
Comparing OSI and TCP/IP ModelsThe short story:OSI has better structure, clearly distinguishing among
Services, Interfaces and Protocols. This makes it more modular, so it’s easy to replace protocols when technology changes.
But OSI designers did not have much experience in practical networking → did not optimally assign functionalities to layers (e.g. MAC)
TCP/IP has great implementations, written by the people with the most experience (e.g. Berkeley sockets!)
Comparing OSI and TCP/IP ModelsBut TCP/IP is not very modular, e.g. the Link “layer” not
really a layer, but an interface between host and network.
This makes it hard to change TCP/IP when technology changes. There are minor TCP/IP protocols deeply entrenched, that are hard to replace, e.g. Telnet knows nothing of mice or graphical interfaces.
For the long story, read pp. 49-54 of our text.
Bad Timing
The apocalypse of the two elephants: ISO-OSI got “ crushed” (and TCP/IP was too early)!
Too early for standards!
Too late for standards!
The story behind the “elephants”
From David Clark himself:https://groups.csail.mit.edu/ana/People/DDC/Apocalypse.html
Hybrid Model (used in our text)
For next time
Read Section 1.4 and take notes.
Internet Usage• 1990 = the year when the government got out of the Internet: the non-
profit ANS corporation takes over NSFNET and upgrades its long-distance links from T1 (1.5 Mbps) to T3 (45 Mbps) →ANSNET
• 1995 ANSNET is sold to AOL, but by then many other ISPs exist
What is means “to be on the Internet”:• Run TCP/IP protocol stack• Have IP address• Be able to send IP pkts to any other machine that’s on the Internet
Traditional applications (1970 – 1990) • E-mail (as opposed to snail-mail)• News (electronic billboards)• Remote login (telnet, rlogin etc.)• File transfer (FTP)
Internet Usage - WWW
Early history of the WWW:• 1989: Physicist Tim Berners-Lee (CERN) makes the initial
proposal for a web of linked documents.See what the man is up to these days: The Semantic web
• 1990: First operational text-based web (prototype).A taste of Lynx – initially developed by students at U Kansas in 1992 for Unix and VMS!
• 1993: Computer scientist Mark Andreessen (U.Illinois) releases Mosaic – the first graphical browser.
• 1994: Andreessen founds Netscape Communications Corp.
Architecture of the Internet
Fig 1-29. Overview of the Internet.
Where to find a Texas ISP
The Cooperative Association for Internet Data Analysis - CAIDA
2002
2007
The n-squared problem in the earlydays of the telephone (Boston, MA, USA)
The “Telephone Tower” in Stockholm, Sweden (1890)
Computer Nws vs.Telecommunications Nws
Source: https://en.wikipedia.org/wiki/Telecommunications_network
1.6 Network StandardizationRead this section and write in your notebook what the following
acronyms stand for:• ISO• ANSI• NIST• ITU
ITU-RITU-TCCITT
• IEEE• IAB (the current meaning)
IETFRFC
IRTF
IEEE 802 Standards
The 802 working groups. The important ones are marked with *. The ones marked with are hibernating. The one marked with † gave up.
More about pioneers and the early days
http://www.ibiblio.org/pioneers/index.html
See more links on our webpage!
1.7 Metric unitsStorage applications (e.g. HDD, RAM, file size): kilo =
1024 = 210
• A 3 MB file has 3*1024*1024 BytesTransmission applications (e.g. modem, satellite,
DSL): kilo = 1000• A 54 Mbps link means that 54*1000*1000 bits are
transferred every second
How long does it take to send a 3 MB file over a 54 Mbps link (ignoring overheads?)
Homework for Ch.1: End of chapter 5, 6, 7, 8, 16, 18, 19, 23