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Course Overview and Introduction

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Title: Course Overview and Introduction


1
Course Overview and Introduction
  • CS 4251 Computer Networking IINick
    FeamsterSpring 2008

2
Goals
  • You have presumably already learned the basics,
    so we will focus on
  • Depth
  • More in-depth treatment of various topics
  • Hands-on experience and skills
  • Testbeds Emulab, PlanetLab, VINI
  • Tools Scriptroute, Click, XORP
  • Analysis of real traces

3
Goals
  • Design Experience and Insights
  • Internet was based on design priorities
  • Applications and requirements have changed
  • You will gain experience re-evaluating design
    decisions and changing protocols
  • Many recurring design tricks
  • Tree forming
  • Layering
  • Resource allocation and sharing
  • Naming

4
Logistics
  • Course Web page
  • http//www.gtnoise.net/classes/cs4251/fall_2008/
  • Check this page regularly for updates to the
    syllabus, assignments, readings, etc.
  • Course mailing list
  • Sign up now/today if you are not already on it
  • http//www.gtnoise.net/mailman/listinfo/cs4251

5
Who Am I?
  • Nick Feamster
  • Assistant Professor
  • Networking Operations and Security
  • Office Klaus 3348
  • Email address on web page use subject CS
    4251
  • Office Hours Wednesday, 2-3 p.m., by appt

6
Overview of Lectures
  • Holistic approach
  • Lectures organized by theme
  • Tree forming/path finding
  • Layering
  • Resource allocation and sharing
  • Naming
  • Textbook reading, research papers, current
    events
  • Read the readings before class!
  • Historically, many things covered in class that
    are not in texts

7
Lecture Structure User-Generated
  • One strongly positive review of last years
    course just in time topics
  • This year Formalize this notion
  • Every Friday Post a link to the course wiki
    (link soon) with a paper and one-line topic
    summary
  • Voting over weekend
  • Discuss paper in second half of Wednesday lecture
  • I will do this, too

8
Networking in Current Events
Threats to the Internets naming system
Network Neutrality
9
Other Things Youll Learn
  • How does BitTorrent find your file?
  • How does the Georgia Tech wireless network allow
    you to roam across campus with the same IP
    address?
  • How do ISPs connect to one another?
  • Protocols, Economics,
  • What could you do with two (or more) Internet
    connections at home?

10
Still More Things Youll Learn
  • How many bits can you push over a physical
    channel?
  • How can you use encoding to increase this?
  • Whats inside a router?
  • Function, power issues, trends (e.g.,
    programmability)
  • Performance guarantees (e.g., telephony, video)?
  • Can a networks resources be subdivided?

11
Still More Things Youll Learn
  • Are we running out of IP addresses? Who cares,
    and how can we combat this?
  • How do we reduce power utilization in data
    centers?
  • What are the bad guys doing?
  • Can we stop unwanted traffic?
  • How do we make it easier to run the network?
  • How do we make the network go faster?
  • Why is it so hard to figure out whats wrong?
  • Social networks?

12
Class Components and Grading
  • Problem sets (20)
  • Paper and pencil
  • First assignment September 3
  • Hands-on Assignments (30)
  • Experience with tools and traces
  • 2 Quizzes (25)
  • Quiz March 3
  • Final will set date soon (perhaps last week of
    class)
  • 1 Project (25)
  • TBD. Work in groups. Programming/analysis/etc.
  • Most likely Pict from a list, or propose your
    own
  • Late policy Maximum of 72 hours late throughout
    the term

13
Collaboration Policy
  • See the Georgia Tech Honor Code
  • Working together on assignments is fine, but you
    must turn in your own assignments, and ultimately
    write your own code, analysis, etc.

14
Who are you?
  • Why are you taking this class?
  • What do you hope to learn?
  • (What have you learned already)
  • What do you want out of a class project?
  • Did you take 3251?

15
Overview of Course Content
16
Themes
  • Routing Trees and Paths
  • The Protocol Stack Protocols and Layering
  • Resource Allocation
  • Naming
  • Trust
  • Other themes
  • Hierarchy
  • Caching
  • Randomization

17
The Internet A Network of Networks
Autonomous Systems (ASes)
Abilene
Comcast
ATT
Cogent
  • Interconnected of the Internet Service Providers
    (ISPs) provide data communications services
  • Networks are connected using routers that support
    communication in a hierarchical fashion
  • Often need other special devices at the
    boundaries for security, accounting,
  • Hosts and networks have to follow a common set of
    rules (protocols)

18
Challenges
  • Scale 100,000,000s of hosts
  • Heterogeneity
  • 25,000 administrative domains (competing!)
  • Thousands of applications
  • Lots of users
  • Diversity of network technologies and media
  • Security Adversarial environment

19
Trends and Open Problems
  • Reducing power consumption
  • E.g., in data centers
  • Making networks easier to manage
  • Improving trust/identity in networks
  • Spam, phishing attacks, etc.
  • Policy-related issues (net neutrality)
  • Programmability in routers/switches

20
Tree Forming and Route Finding
21
Computing Routes
  • To deal with large scale, Internet routing
    employs hierarchy
  • Internet Service Providers connect to one another
    with interdomain routing protocols (BGP)
  • ISPs have business relationships with one another
  • ISPs have PoPs that are connected with
    intradomain routing protocols

22
Gateways Routers and Switches
  • Interconnect nodes to nodes
  • And networks to networks
  • No state about ongoing connections
  • Stateless packet switches
  • We can also think of your home router/NAT as
    performing the function of a gateway

68.211.6.12050878
Home Network
Internet
68.211.6.12050879
(more on NATs in lecture 17)
23
Challenge Scale
24
The Protocol Stack
25
Protocols Interconnection
  • The syntax and semantics by which hosts and nodes
    agree on how to talk
  • Must be standardized and agreed upon by all
    parties
  • Standardization process
  • IETF Requests for Comments (RFC)
  • De-facto standards
  • Format of messages
  • Expectations for message delivery

26
Layering
  • Helps manage complexity
  • Each layer
  • Relies on services from layer below
  • Provides services to layer above
  • For example IP (network) layer
  • IP relies on connectivity to next hop, access to
    medium
  • IP provides a datagram service
  • Best effort delivery
  • Packets may be lost, corrupted, reordered, etc.
  • Layers on top of IP (e.g., TCP) may guarantee
    reliable, in-order delivery

27
Layering Mechanism Encapsulation
User A
User B
Application(message)Transport(segment)Networ
k(datagram)Link (frame)
Get index.html
Connection ID
Source/Destination
Link Address
  • This can be more complex
  • Example Network layers can be encapsulated
    within another network layer

28
The Internet Protocol Stack
  • Need to interconnect many existing networks
  • Hide underlying technology from applications
  • Decisions
  • Network provides minimal functionality
  • IP as the Narrow waist

Applications
Technology
29
The Narrow Waist
  • Facilitates interconnection and interoperability
  • IP over anything, anything over IP
  • Has allowed for much innovation both above and
    below the IP layer of the stack
  • Any device with an IP stack can get on the
    Internet
  • Drawback very difficult to make changes to IP

30
Resource Sharing
31
Resource Sharing
  • How? Multiplexing
  • Switched network
  • Party A gets resources sometimes
  • Party B gets them sometimes
  • Interior nodes (Routers or Switches)
    arbitrate access to resources

32
Circuit Switching
  • Resources are reserved
  • Source first establishes a connection (circuit)
    to the destination
  • Source sends the data over the circuit
  • Constant transmission rate
  • Example telephone network
  • Early early versions Human-mediated switches.
  • Early versions End-to-end electrical connection
  • Today Virtual circuits or lambda switching

33
Resource Sharing in Circuit-Switched Networks
  • Frequency-Division Multiplexing (FDM)
  • Link dedicates a frequency to each connection
  • Width of this frequency band is called
    bandwidth
  • We will discuss the capacity in Lecture 10
  • Time-Division Multiplexing
  • Each circuit gets all of the bandwidth on a link
    for brief periods of time

34
Circuit Switching
  • Advantages
  • Fast and simple data transfer, once the circuit
    has been established
  • Predictable performance since the circuit
    provides isolation from other users
  • Guaranteed bandwidth
  • Disadvantages
  • What about bursty traffic?
  • Users with differing needs for bandwidth
  • What if all resources are allocated?

35
Packet Switching
  • Resources are not reserved
  • Packets are self-contained
  • Each has a destination address
  • Source may have to break up single message
  • Each packet travels independently to the
    destination host
  • Routers and switches use the address in the
    packet to determine how to forward the packets

36
Resource Sharing Packet Switching
  • Statistical multiplexing
  • Switches arbitrate between inputs
  • Can send from any input thats ready
  • Links are never idle when traffic to send
  • Efficiency!
  • Requires buffering/queues
  • Implies a service model/discipline (Lecture 21)

37
Delay in Packet Switched Networks
  • Four contributors to hop-by-hop delay
  • Processing Lookup, etc. (Lectures 6 and 7)
  • Queueing Time the packet must wait before being
    transmitted (Lecture 21)
  • Transmission time to push the packet onto the
    link
  • Propagation time for the packet to propagate
    from A to B
  • End-to-end performance metric throughput
  • What (else) affects throughput

38
Forwarding Packet-Switched Networks
  • Each packet contains a destination in the header
  • Much like a postal address on an envelope
  • Each hop (router or switch) inspects the
    destination address to determine the next hop
  • Will a packet always take the same path?
  • How do the hops know how to forward packets?
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