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TCOM 500
Introduction to Networks
and Protocols
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A Few Words About Logistics Meeting times: Mon. & Wed. 12:00pm-1:30pm, Towne 100 (Heilmeier Hall)
Course wiki: http://alliance.seas.upenn.edu/tcom500-wiki
Announcements, documents, Q&A forums, homeworks, exams
Use https instead to access Private Content (Assignments & Solutions, pastexams, etc.) and edit the Discussion Forums to post and view questions
Grades posted on Sakai: https://learning.upenn.edu/xsl-portal
Instructor: R. Guerin ([email protected]) Office Hours: Mon. & Wed. 2:30pm-3:30pm (367 GRW )
TAs/Graders: Answer class related questions on wiki and grade homeworks
Hadi Afrasiabi ([email protected]) Office Hours: Tuesday 2:00pm-4:00pm (Moore 306)
Sangeetha Abdu Jyothi ([email protected])
Office Hours: Thursday 5:30pm-7:30pm (Moore 306)
Recitation: Towne 307, Friday 5pm-6pm
Project presentations: Towne 309, Thursday 5pm-6pm (after 11/03/11)
http://alliance.seas.upenn.edu/tcom500-wikihttps://learning.upenn.edu/xsl-portalmailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]://learning.upenn.edu/xsl-portalhttps://learning.upenn.edu/xsl-portalhttps://learning.upenn.edu/xsl-portalhttp://alliance.seas.upenn.edu/tcom500-wikihttp://alliance.seas.upenn.edu/tcom500-wikihttp://alliance.seas.upenn.edu/tcom500-wiki -
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Course Structure and Material
Course material
Textbook: Peterson & Davie Computers Networks: A System Approach, 5th Ed.
Course slides, handouts, links to lots of useful material on wiki
Course grading
Homeworks (5%)Low weight, but dont do them at your own risk
On average one new homework every week
Due at beginning of class (no late homework unless agreed upon in advance)
Gradually increasing penalty (-0pts, -5pts, -10pts, -10pts, )
OPTIONAL Project - In-class Presentation + Report (20%)
Teams of 1 or 2 students
Short two-page report on selected topic (see wiki for a listSelect by 9/30/11)
15 mins (10+5 mins) presentations in 2ndhalf of semester (Thursdays 5pm)
Exams With/Without Projects: 30%/40% (Midterm); 45%/55% (Final)
Midterm in class on Monday 10/24/11 (after Fall break)
Final exam on Monday 12/19/11 9:00am-11:00am (Room TBA)
Oralmake-up exams only for reasons approved under University policy
Schedule: Full syllabus and tentative class schedule on wiki
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More on Policies
Please review Penns Code of Academic Integrityathttp://www.vpul.upenn.edu/osl/acadint.html
Collaboration
Permitted on homeworks, but what you turn in must be yours
No verbatim copies!
Grade of zero for first homework violation; course grade of F for repeat offense Projects are collaborative in nature
Both students get the samegrade
You MUST explicitly cite/acknowledge any material used in your project
Exams
Obviously, no collaboration is allowed during exams!
They are open-book and brand new every year
Access to soft copies during exams is allowed, but Internet access is prohibited
Violations of the courses collaboration policy will be punished by an
F in the class and immediate referral to the Office of StudentsConduct for further action
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Courses Goals
To give you an understanding of the variouscomponents involved in realizing moderncommunication systems and the trade-offthey embody
Generating and receiving bits, and protectingthem from errors or malicious users
Connecting devices and allowing them to deliver
bits to an increasingly large number of systems Quantifying the performance of different system
and technologies, and the associated trade-offs
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Courses Formal Objectives
Develop your Ability to assess the different components of network protocols
and packet switches in terms of their functionality andperformance and their applicability in different environments
Awareness of key performance metrics for data communication
systems and how to interpret them Ability to identify suitable networking technologies and systems
based on given performance and functionality targets
This being said, this is only an introduction to Networks andProtocols, so we will only be able to scratch the surface
Important: In order to maximize the odds that theseobjectives can be successfully met, please ASK QUESTIONS
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Reading Assignment
Textbook: Chapter 1 Sections 1.1-1.3
Section 1.5
Section 1.4 (optional)
Marsic online book: Section 1.1 (optional) Bonaventure online book: Chapter 2
(optional)
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Our Scope Broadly Speaking
What are the core technologies behind
the Internets content delivery abilities?
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Internet Content DeliveryJane watches a YouTube video
How does her computer find thelocal YouTube server?
How does data get delivered backand forth to ensure smooth video
delivery?
R1
R2
Jane
The Internet
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A Day in the Life of a (basic) Packet
1. Name to IP address (DNS)
2. IP address to IP address (defaultgateway local routing)
3. IP address to MAC address (ARP)
We have just identified three of the
core layers involved in theInternets operation
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R2
Jane
The Internet
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Local Delivery From Jane to R1
MAC layer forwarding(IP packet in MAClayer frame)
R1
R2
Jane
The Internet
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Crossing the Internet(A network of networks)
From R1 to R2
IP routing
(based on CNNs
destination address)
R1
R2
Jane
The Internet
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Local Delivery From R2 to CNN server
MAC layer forwarding(IP packet in MAClayer frame)
R1
R2
Jane
The Internet
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Our Scope
Well look at both the protocols involved inrealizing content delivery, and the factorsthat influence the performance of this
delivery As a preview: Two examples of issues
associated with the latter
Downloading large files Streaming real-time data, e.g., audio/video
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Living in a Packet World
Download
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Download time calculation1st packet: Starts at t=0 and arrives at R3 att1=12,000/10
9+1s+12,000/1010+3ms+12,000/1010+3ms=6.0154ms laterFrom this point onward R3 transmits non-stop until the whole file has beensent (subsequent packets arrive faster than they are transmitted at 5Mbps)Last (85,000th) packet:
- Departs R3 at tL=6.0154ms+85,000x12,000/5x106
1.026sec- Arrives at destination 1s laterNote:- No lost or erroneous packets- Bottleneck link (5Mbps) dominates the delay- Assumes R3 can store most of 1GBfile- No TCP like congestion/flow control (non-stop transmissions by sender)
File 1Gbps10Gbps 10Gbps 5Mbps
1GB 85,000 pkts
1s 3ms 3ms1s
1 pkt
12,000 bits
R1 R2 R3
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Living in a Packet World
Streaming
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100Mbps
10Gbps 10Gbps 5Mbps
8kbps and
120Bytes pkts(100B payload
+20B header)
1s 3ms 3ms 1s
Delay time calculationPacketization delay (time to generate one packet worth of bits)- 800bits/8kbps = 100ms
Transmission delay-t= 960/108+1s+960/1010+3ms+960/1010+3ms+960/5x106+1s6.2ms
Playback delay (data not played immediately when received to avoid gapsin case the next packet is late, e.g., because of network congestion)- (k-1)x100ms, where kis number of packets at received before playbackNote:- Delay dominated by packetization/playback delay- And (possibly) bottleneck link (5Mbps)
R1 R2 R3
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Identifying Internet ComponentsThe Role of Layers
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network
Data Link
Physical
Network
Data Link
Physical
Network
End-System End-System
Why Layers? Avoid duplication of functionality
Facilitate evolution (modular)
Shield upper layers from details
and differences of lower layers
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Our Focus
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network
Data Link
Physical
Network
Data Link
Physical
Network
End-System End-System
Two players and their interactions
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How does a packetgets created in thefirst place?
The role or layers
Jane
R1
R2
The Internet
What happens in there?
Illustrating Layers: The User/Host Side
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Host Interfaces
Host 1 Host 2
Service
interface
Peer-to-peerinterface
High-lev elobject High-lev elobject
Protocol Protocol
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Protocol Machinery
Applications select services based on their needs
Services are invoked through well-defined interfaces
Services provide specific functionality, e.g., reliability, timing, etc.
Services can invoke other services (a nested set of interactions)
Protocols specify the semantics of service invocation and functions
Host 1 Host 2
Fileapplication
Digitallibrary
application
Videoapplication
Fileapplication
Digitallibrary
application
Videoapplication
Internet
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Illustrating Layers: The Network Side
R1
R2
Jane
The Internet
Mapping an application/service to anaddress: Naming service (DNS)
Mapping an (IP) address to a packetforwarding decision: Routing service
Mapping IP routing decisions to local
physical resources: IP address to MACaddress (ARP)
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The Internet View of Layers
Application
Network
IP
TCP UDP
Data Link &Physical
Network
Transport
ApplicationPresentationSession
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Revisiting Course Syllabus (1)
Information Generation & Transmission
Issues: Volume, speed, correctness ofinformation transmission (what is information?)
Accessing transmission resources
Controlling (or not) access to transmissionresources across users
Bits &low-levelpacketissues(PHY)
Primarilylink layer
?
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Revisiting Course Syllabus (2)
Locating and delivering information
Managing end-to-end informationdelivery
??
Where is Nikkei.com? How do I get there?
IP layer issues,i.e., name
resolution, routing
Transport layerissues, i.e.,congestion, QoS,security
What bandwidth sharefor which flow?
What security, where?
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Course Coverage
The local view Dealing with bits (phy. layer)
Generating and receiving bits
Detecting and correcting errors
Framing bits into packets
Arbitrating transmissions (link layer)
Wired and wireless links A detour into modeling
Queueing systems
Markov chains
The small network view
Connecting wires together
Switches
Connecting switches together
Locating where things are
Forwarding packets
The large network view Knowing where things are anddeciding how to get there
Naming services
Routing protocols
Forwarding packets at
increasingly high speeds The end-to-end view
End-user resource management
TCP (the end-to-end principle)
Managind network resources
Service differentiation and
resources allocation
Securing information
Encryption and authentication
Protecting access toinformation (firewalls)