CS472 Computer Networks

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CS472Computer Networks

• Professor Mike Kain
• Class 1 Slides
• Fall 2008-2009

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Tonights Topics

• Overview of class
• Review Syllabus
• Major topics
• Protocols (definitions, characteristics of a good
  protocol)
• Common pieces of all protocols
• TCP/IP all of the protocols
• Security

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Goals of class

• To learn computer networks
• But to understand the nature of the beast
  understand all networks because we understand how
  they have to work.
• Not necessarily to learn all protocols
  (BitTorrent, LimeWire, FTP, SSH, TCP, IP, TLS,
  DCCP, EVDO, and the list goes on), but to
  understand what a protocols job is and how it
  does it.

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What is a computer network?
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A network

• 2 or more computers sharing information.
• Well look at this top-down (from the
  application to the wire)
• Start with what you know (applications like WWW,
  BitTorrent, LimeWire, IM, etc.)
• And work towards the guts (TCP, IP, LAN, wires).

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Network terminology

• Two types of hosts
• Server provide services (WWW, etc.)
• Client use services
• Three types of applications
• Server
• Client
• Peer (both server and client at the same time)

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Network Connections

• Connection-oriented
• Two parties have a handshake before data
• All data is in order
• Like a telephone call
• Connection-less
• No Handshake
• No order
• Like the postal system

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Protocol

• The heart of the network is the PROTOCOL
• Similar to many things that you already use
• telephone conversation
• Ordering food
• What time is it?
• Definition
• Defines the messages sent and received and the
  actions that are performed when messages and
  network events are received

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Network Protocols

• Deterministic only one possible action for each
  message in each state
• Deterministic Finite Automata (DFA)
• Time (some concept) no response in a period of
  time is also an action
• Well defined messages (what makes them up) how
  you know that they are done (OVER)
• State (possibly) different states of the
  conversation
• Trust
• Examples (What time is it?, etc)
• Push vs Pull protocols

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What is a DFA?

• Deterministic Finite Automata (also known as a
  Finite State Machine)
• Graphical representation of a protocol where
• The nodes are the states of the protocol
• The directed edges are messages sent or received,
  or events which happen in the protocol

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The Network

• Review Applications (client, server, peer)
  communicate via the network
• Connection-oriented
• Connection-less
• Connection-less UDP (RFC 768 and others)
• User Datagram Protocol
• Just send
• What is an RFC?

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The reliable network

• Connection-oriented TCP (RFC 793)
• Transmission Control Protocol
• Not really connected just a handshake
• Other features of TCP
• Reliable Data Transfer
• Flow Control
• Congestion Control
• There are other types (SCTP, DCCP, etc.)
• Why?

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Network Core

• How we get between systems (either computers or
  devices)?
• US Mail-like system
• No connection, each envelope has full address, no
  reliability
• Telephone-like system
• Connection each envelope goes along the same
  path (circuit) reliably.
• So, what is the Internet?

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The Internet

• All information is broken up into PACKETS
• The best route is found from source to
  destination
• which links (connections) are the best to use
• Think of driving to the shore which roads are
  best?
• This routing is the same for both US-Mail and
  Telephone based routing (just at different times)

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Network Types

• US-Mail Datagram network
• Telephone-based Virtual Circuit
• Which is better?

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The links

• The direct connection between computers or
  devices
• Two Categories
• Point-to-point
• Shared (e.g. Air, some cables)
• Also two types
• Wired (guided)
• Wireless (unguided)

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TCP/IP Reference Model

• Application Layer (HTTP, FTP, SMTP, POP3, etc.)
• Transport Layer (TCP, UDP, SCTP, DCCP)
• Internetworking Layer (IPv4, IPv6)
• Link Layer (Ethernet)
• Physical Layer (these two are sometimes together
  as Host to Network Layer or NIC Layer)
• Transport Layer Security sublayer added later

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Layering

• Why layers?
• Concentrates similar functions together
• Presents a building block approach to networks
• Allows Mix Match of boxes.
• Sublayers -- Layers can be broken down into
  sublayers if functions can be grouped.
• Service Access Points (SAP)
• Protocol Data Unit (PDU)

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Layering concepts

• Service
• Interface
• Protocol

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Common themes

• Common functions which occur at multiple layers
• Addressing
• Connection Control
• Ordered Delivery
• Segmentation Reassembly
• PDU definition
• Error Detection / Correction
• Flow Control
• Multiplexing (more than one lower or upper
  service)

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The big themes

• Security!
• Data Integrity
• Confidentiality
• Access Control
• Availability
• Authentication
• Non-Repudiation
• Quality of Service (QoS)
• What you get out of a network

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Other models

• The 3 major models
• OSI Basic Reference Model
• TCP/IP
• Asynchronous Transfer Mode (ATM)
• Others BNA, SNA, DecNet, AppleTalk, etc........

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Protocol stacks

• How do we link the stack together?
• Usually a reference in the PDU header which is
  set on the way down the stack for use on the way
  up the stack on the other side.
• Wireshark example

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The Big Picture

• Technology doesnt really drive network design,
  new protocols, etc.
• Influences and is influenced by
• Social / Society (changes the way we communicate
  persona)
• Facebook / MySpace / 20 of interviews
• BFF/BRB IM world
• Googling
• SecondLife / Online gaming

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The Big Picture, part 2

• Business (information distribution)
• RIAA / DRM
• No information hiding
• Trust in information, though? (wikipedia)
• Legal / Criminal (tracking the bad guys!)
• Hacking (Jurisidiction)
• RentaCoder, etc.
• Internet Law, precedences, and case studies
• ChaCha answers questions via IM
• And these overlap. How about online school
  opens up issues?
• At least one article a day!

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For next week

• Homework 1 posted (due next week)
• Read textbook