CS455 Introduction to Computer Networks

1
CS455 Introduction to Computer Networks
WSU Vancouver

• Dr. Wenzhan Song
• Assistant Professor, Computer Science

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About Me

• Working Experiences
• 1997-1999, Jiangsu Intrasoft Network
• 1999-2001, Alcatel Shanghai Bell
• 2004 Summer, Lucent Technologies
• 2001-2005, Ph.D. research, Illinois Institute of
  Technology
• 2005-present, Assistant Professor, Washington
  State University - Vancouver
• Teaching evaluation
• Average 4.5/5
• Research experiences
• Dozens of articles in top journal and conferences
  
• 2M research funding support from NASA, USGS,
  Boeing and WSU
• Research has been cited by MIT technology review
  and many other top national media

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Course information

• Instructor WenZhan Song
• Office VELS 130A
• Tel [phone]
• Email song_at_vancouver.wsu.edu
• Homepage http//www.vancouver.wsu.edu/fac/song
• Textbooks
• Required Computer Networking - a top-down
  approach featuring the Internet, 3rd Edition, by
  James F. Kurose, Keith W. Ross
• Optional Computer Networks, 4th Edition, by
  Andrew S. Tanenbaum
• Optional Unix Network Programming - Vol. 1, 3rd
  Edition, by W. Richard Stevens, Bill Fenner,
  Andrew M. Rudoff
• Prerequisite courses
• CS360 System Programming

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Grading

• Homework Assignments (30)?
• About five
• Written
• Network Programming (40)?
• Client/Server, UDP, TCP sockets
• Protocol simulation, system design
• TinyOS
• Midterm (15)?
• Final (15)?
• Highly encourage innovation and think out of
  box!!!

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What to expect

• Significant exposure to computer networking
  concepts and fundamental design principles.
• Coverage of Internet protocol stacks.
• running example TCP/IP
• Details of network control algorithms.
• e.g. routing, congestion control, flow control,
  ...
• Able to do UNIX network programming.
• Berkeley Sockets

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What not to expect

• End-user training.
• e.g. How to use FTP, NetWare, WWW or HTML,
• Trade school stuff.
• e.g. How to get Novel NetWare certified, how to
  setup a Cisco router, how to administrate network
  system
• Detailed discussion of non-TCP/IP protocols.
• e.g. OSI, Appletalk, ...
• Massively Parallel Processing
• e.g. large numbers of interconnected, identical
  processors programmed to solve problems in
  parallel
• Telecommunication networks and standards

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Course roadmap

• Introduction
• Application Layer WWW, FTP, email, DNS,
  multimedia
• Transport Layer reliable end-end data transfer
  principles, UDP, TCP
• Network Layer routing, congestion control, QoS
• Data Link Layer framing, error control, flow
  control
• Medium Access Control (MAC) Layer
  multiple-access, channel allocation
• Physical Layer wired, wireless, satellite
• Other Topics network security, social issues,
  hot topics, research directions

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Human Talk vs Computer Communication
Hi
TCP connection req
Hi

• human conversation vs computer network protocol

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Communication is challenging

• The two-army problem

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Introduction Roadmap

• Physical overview of Internet
• Physical architecture
• Network Edge - Internet access technologies
• Network Core Switching technologies
• Software overview of Internet
• Software architecture
• The OSI and TCP/IP Reference Models
• Internet history
• Network standardization body

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Physical overview of Internet

• millions of connected computing devices hosts
  end systems
• running network apps
• communication links
• fiber, copper, radio, satellite
• transmission rate bandwidth
• routers forward packets (chunks of data)?

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Physical overview of Internet

• protocols control sending, receiving of msgs
• e.g., TCP, IP, HTTP, FTP, PPP
• Internet network of networks
• loosely hierarchical
• public Internet versus private intranet
• Internet standards
• Called RFC (Request for comments), developed by
  IETF (Internet Engineering Task Force)?

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Metric Units

• metric prefixes for data rate

Note data rates kbps (103), Mbps(106),
Gbps(109) bits per seconddata sizes KB
(210), MB(220), GB(230), bytesms(msec)
millisecond µs microsecond ns nanosecond
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Introduction Roadmap

• Physical overview of Internet
• Physical architecture
• Network Edge - Internet access technologies
• Residential access
• Company access
• Network Core Switching technologies
• Software overview of Internet
• Software architecture
• The OSI and TCP/IP Reference Models
• Internet history
• Network standardization body

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Residential Internet Access

• Phone Company
• Dialup
• ADSL
• Cable TV Company
• HFC
• Wireless Company
• WiMax

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Residential access Phone Company

• Dialup via modem
• up to 56Kbps direct access to router (often
  less)?
• Cant surf and phone at same time cant be
  always on

• ADSL asymmetric digital subscriber line
• up to 1 Mbps upstream (today typically lt 256
  kbps)?
• up to 8 Mbps downstream (today typically lt 1
  Mbps)?

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Dialup

• Local loops
• Analog twisted pairs going to houses and
  businesses
• Trunks
• Digital fiber optics connecting the switching
  offices
• Toll Office (Switching offices)?
• Where calls are moved from one trunk to another

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ADSL asymmetric digital subscriber line

• Design goal
• (1) Work over exist 3 UTP twisted pair local
  loops.
• (2) Not affect customers existing telephone and
  fax machine
• (3) Much faster than 56kbps
• (4) Always on monthly charge

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ADSL

• A typical ADSL equipment configuration.

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ADSL

• 256 Channel over 1.1MHz
• 0 (POTS), 1-5(unused), 6-255(data channels)?
• ANSI T1.413 and ITU G.992.1 up to 8 Mbps
  downstream and 1 Mbps upstream.
• Standard service 512 kbps downstream and 64 kbps
  upstream
• Premium service 1 Mbps downstream and 256 kbps
  upstream

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Residential access Cable TV Company

• HFC hybrid fiber coax
• asymmetric up to 27Mbps downstream, 9 Mbps
  upstream
• network of cable and fiber attaches homes to ISP
  router
• homes in same community share bandwidth
• deployment available via cable TV companies

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Community Antenna Television

• An early cable television system.

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HFC

• Internet over TV Cable

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Compare to ADSL

• Internet over ADSL

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Cable vs ADSL
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Spectrum Allocation

• Frequency allocation in a typical cable TV system
  used for Internet access

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Signal Splitter
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Cable Modems

• Typical details of the upstream and downstream
  channels in North America.
• Upstream QPSK, slotted Aloha with binary
  exponential backoff
• Downstream QAM64/QAM-256, time division
  multiplexing

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Residential access Wireless Company
400700kbps Up to 2Mbps - according to Verizon

• Wireless Local Loop
• Example IEEE 802.16 WiMax Verizon Wireless

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Other ways for residential access?

• Electricity company
• PLC (Power Line Communication)?
• BPL (Broadband over Power Line)?
• http//en.wikipedia.org/wiki/Power_line_communicat
  ion

• How about other utility companies Gas, Water,
  Sewer ?

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Introduction Roadmap

• Physical overview of Internet
• Physical architecture
• Network Edge - Internet access technologies
• Residential access
• Company access
• Network Core Switching technologies
• Software overview of Internet
• Software architecture
• The OSI and TCP/IP Reference Models
• Internet history
• Network standardization body

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Company access local area networks

• company/univ local area network (LAN) connects
  end system to edge router
• Ethernet
• shared or dedicated link connects end system and
  router
• 10 Mbs, 100Mbps, Gigabit Ethernet

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Wireless access networks

• Shared wireless access network connects end
  system to router
• via base station aka access point
• wireless LANs
• 802.11b (WiFi) 11 Mbps
• 802.11a, 802.11g
• wider-area wireless access
• WiMax talked before
• 3G 384 kbps
• Will it happen??
• WAP/GPRS in Europe
• wireless ad hoc networking
• Talk with each other directly inside
• Through a gateway to visit outside

mobile hosts
router
base station
Ad hoc networking
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Introduction Roadmap

• Physical overview of Internet
• Physical architecture
• Network Edge - Internet access technologies
• Network Core Switching technologies
• circuit switching
• packet switching
• Software overview of Internet
• Software architecture
• The OSI and TCP/IP Reference Models
• Internet history
• Network standardization body

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The Network Core

• mesh of interconnected routers
• the fundamental question how is data transferred
  through net?
• circuit switching dedicated circuit per call
  telephone net
• packet-switching data sent thru net in discrete
  chunks

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Network Core Circuit Switching

• End-end resources reserved for call
• link bandwidth, switch capacity
• dedicated resources no sharing
• circuit-like (guaranteed) performance
• call setup required

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Network Core Circuit Switching

• network resources (e.g., bandwidth) divided into
  pieces
• pieces allocated to calls
• resource piece idle if not used by owning call
  (no sharing)?

• dividing link bandwidth into pieces
• frequency division
• time division

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Circuit Switching FDM and TDM
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Numerical example

• How long does it take to send a file of 640,000
  bits from host A to host B over a
  circuit-switched network?
• All links are 1.536 Mbps
• Each link uses TDM with 24 slots
• 500 msec to establish end-to-end circuit
• Solution
• Each circuit transmission rate 1.536Mbps/24
  64kbps
• Time to transmit file 640,000bits/64kbps 10
  sec
• Total 10.5 sec

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Network Core Packet Switching
10 Mb/s Ethernet
C
A
statistical multiplexing
1.5 Mb/s
B
queue of packets waiting for output link

• Sequence of A B packets does not have fixed
  pattern ? statistical multiplexing.
• In TDM each host gets same slot in revolving TDM
  frame.

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Network Core Packet Switching

• each end-end data stream divided into packets
• user A, B packets share network resources
• each packet uses full link bandwidth
• resources used as needed

• resource contention
• aggregate resource demand can exceed amount
  available
• congestion packets queue, wait for link use
• store and forward packets move one hop at a time
• Node receives complete packet before forwarding

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Packet-switching store-and-forward
L
R
R
R

• Example
• L 7.5 Mbits
• R 1.5 Mbps
• delay 15 sec

• Takes L/R seconds to transmit (push out) packet
  of L bits on to link of R bps
• Entire packet must arrive at router before it
  can be transmitted on next link store and
  forward
• delay 3L/R

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Packet switching versus circuit switching

• Packet switching allows more users to use network!

• 1 Mb/s link
• each user
• 100 kb/s when active
• active 10 of time
• circuit-switching
• 10 users
• packet switching
• with 35 users, probability gt 10 active less than
  .0004

N users
1 Mbps link
probability of exact n of N users active
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Packet switching versus circuit switching

• Is packet switching a slam dunk winner?

• Great for bursty data
• resource sharing
• simpler, no call setup
• Excessive congestion packet delay and loss
• protocols needed for reliable data transfer,
  congestion control
• Q How to provide circuit-like behavior?
• bandwidth guarantees needed for audio/video apps
• still an unsolved problem

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Packet-switched networks forwarding

• Goal move packets through routers from source to
  destination
• well study several path selection (i.e. routing)
  algorithms
• datagram network
• destination address in packet determines next
  hop
• routes may change during session
• analogy driving, asking directions
• virtual circuit network
• each packet carries tag (virtual circuit ID),
  tag determines next hop
• fixed path determined at call setup time, remains
  fixed thru call
• routers maintain per-call state

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Network Taxonomy
Networks
e.g., Internet
e.g., telephone networks
e.g., ATM networks

• Datagram network is not either
  connection-oriented
• or connectionless.
• Internet provides both connection-oriented (TCP)
  and
• connectionless services (UDP) to apps.

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Connection-oriented vs Connectionless

• Key differences
• Connection-oriented packets arrives in the order
  of sending out (e.g., FIFO), and need connection
  setup phase
• Connectionless packets may (or may not) arrive
  in different order of sending out, and does not
  need connection pre-setup
• Example
• Circuit Switch Network connection-oriented
• Packet Switch Network
• Virtual circuit network connection-oriented
• Datagram network depends on layers and protocols
• TCP connection-oriented
• UDP, IP - connectionless

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Introduction Roadmap

• Physical overview of Internet
• Physical architecture
• Network Edge - Internet access technologies
• Residential access dialup, ADSL, cable, WiMax
• Company access LAN, WLAN
• Network Core Switching technologies
• Circuit switching setup path before
  communication, have dedicated resource per call
• Packet switching store and forward, share
  resource and need contend for
• Software overview of Internet
• Software architecture
• The OSI and TCP/IP Reference Models
• Internet history
• Network standardization body

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Protocol Layers

• Networks are complex!
• many pieces
• hosts
• routers
• links of various media
• applications
• protocols
• hardware, software

• Question
• Is there any hope of organizing structure of
  network?
• Or at least our discussion of networks?

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Internet protocol stack

• application supporting network applications
• FTP, SMTP, HTTP, etc
• transport host-host data transfer
• TCP, UDP
• network routing of datagrams from source to
  destination
• IP, routing protocols
• link data transfer between neighboring network
  elements, including encapsulating bits into
  frames
• PPP, Ethernet, etc
• physical bits on the wire

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Analogy scenario
The philosopher-translator-secretary architecture.
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Services to Protocols Relationship

• The relationship between a service and a
  protocol
• each layer implements a service
• via its own internal-layer actions or protocols
• relying on services provided by layer below

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Why layering?

• Dealing with complex systems
• explicit structure allows identification,
  relationship of complex systems pieces
• layered reference model for discussion
• modularization eases maintenance, updating of
  system
• change of implementation of layers service
  transparent to rest of system
• e.g., changing common language of translators
  does not affect the communication between the
  philosopher
• layering considered harmful?

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Typical network flow
source
message
application transport network link physical
segment
datagram
frame
switch
destination
application transport network link physical
router
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General situation of end-end flow

• Example information flow supporting virtual
  communication in layer 5.

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Introduction Roadmap

• Physical overview of Internet
• Physical architecture
• Network Edge - Internet access technologies
• Network Core Switching technologies
• Software overview of Internet
• Software architecture
• The OSI and TCP/IP Reference Models
• Internet history
• Network standardization body

57
The design principles of OSI Reference Models

• A layer should be created when a different
  abstraction is needed
• Each layer should perform a well-defined function
• The function of each layer should be chosen with
  an eye toward defining internationally
  standardized protocols
• The layer boundaries should be chosen to minimize
  the information flow across the interfaces
• The number of layers should be large enough that
  functions need not be thrown together in the same
  layer out of necessity and small enough that the
  architecture does not become unwieldy

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OSI Reference Models
Concern the syntax and semantics of information
transmitted
The OSI reference model.
Allow users on different machines to establish
sessions
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TCP/IP Reference Models

• The TCP/IP reference model.

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TCP/IP Reference Models
123

• Major protocol and application components common
  to most commercial TCP/IP software packages and
  their relationship

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A Critique of the OSI Model and Protocols

• Bad timing
• Bad technology
• Bad implementations
• Bad politics

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A Critique of the TCP/IP Reference Model

• Service, interface, and protocol not
  distinguished
• Not a general model
• Host-to-network layer not really a layer
• No mention of physical and data link layers
• Minor protocols deeply entrenched, hard to replace

63
Hybrid flow in the lecture

• application supporting network applications
• FTP, SMTP, HTTP, DNS
• transport host-host data transfer
• TCP, UDP
• network routing of datagrams from source to
  destination
• IP, routing protocols
• link data transfer between neighboring network
  elements, including encapsulating bits into
  frames
• MAC (Multiple Access Control) sublayer
• physical bits on the wire

64
Introduction Roadmap

• Physical overview of Internet
• Physical architecture
• Network Edge - Internet access technologies
• Network Core Switching technologies
• Software overview of Internet
• Software architecture
• The OSI and TCP/IP Reference Models
• Internet history
• Network standardization body

65
Internet History
1961-1972 Early packet-switching principles

• 1961 Kleinrock - queueing theory shows
  effectiveness of packet-switching
• 1964 Baran - packet-switching in military nets
• 1967 ARPAnet conceived by Advanced Research
  Projects Agency
• 1969 first ARPAnet node operational

(a) Structure of the telephone system. (b)
Barans proposed distributed switching system.
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Internet History
1961-1972 Early packet-switching principles

• 1972
• ARPAnet demonstrated publicly
• NCP (Network Control Protocol) first host-host
  protocol
• first e-mail program
• ARPAnet has 15 nodes

Growth of the ARPANET (a) December 1969. (b)
July 1970. (c) March 1971. (d) April 1972.
(e) September 1972.
67
Internet History
1972-1980 Internetworking, new and proprietary
nets

• 1970 ALOHAnet satellite network in Hawaii
• 1973 Metcalfes PhD thesis proposes Ethernet
• 1974 Cerf and Kahn - architecture for
  interconnecting networks
• late70s proprietary architectures DECnet, SNA,
  XNA
• late 70s switching fixed length packets (ATM
  precursor)?
• 1979 ARPAnet has 200 nodes

• Cerf and Kahns internetworking principles
• minimalism, autonomy - no internal changes
  required to interconnect networks
• best effort service model
• stateless routers
• decentralized control
• define todays Internet architecture

68
Internet History
1990, 2000s commercialization, the Web, new apps

• Early 1990s ARPAnet decommissioned
• 1991 NSF lifts restrictions on commercial use of
  NSFnet (decommissioned, 1995)?
• early 1990s Web
• hypertext Bush 1945, Nelson 1960s
• HTML, HTTP Berners-Lee
• 1994 Mosaic, later Netscape
• late 1990s commercialization of the Web

• Late 1990s 2000s
• more killer apps instant messaging, P2P file
  sharing
• network security to forefront
• est. 50 million host, 100 million users
• backbone links running at Gbps

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Internet Usage

• Traditional applications (1970 1990)
• E-mail
• News
• Remote login
• File transfer
• Today in addition
• WWW news, shopping, gaming, maps, trading, etc
• Multimedia Internet video, audio, radio
• P2P file sharing
• Blogs
• Messenger

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Introduction Roadmap

• Physical overview of Internet
• Physical architecture
• Network Edge - Internet access technologies
• Network Core Switching technologies
• Software overview of Internet
• Software architecture
• The OSI and TCP/IP Reference Models
• Internet history
• Network standardization body

71
Network Standardization

• Telecommunications World
• ITU (International Telecommunication Union),
  called CCITT during 1956-1993
• International Standards World
• ISO (International Standards Organization)?
• U.S ANSI (American National Standards
  Institute)
• Other countries
• IEEE (Institute of Electrical and Electronics
  Engineers)?
• Internet Standards World
• Internet Society
• IAB (Internet Activities Board)?
• IRTF (Internet Research Task Force) long-term
  research
• IETF (Internet Engineering Task Force)
  short-term engineering issues RFC documents

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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.
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Summary

• Covered a ton of material!
• Physical overview of Internet
• Physical architecture
• Network Edge - Internet access technologies
• Network Core Switching technologies
• Software overview of Internet
• Software architecture
• The OSI and TCP/IP Reference Models
• Internet history
• Names and terms in network society

• You now have
• context, overview, feel of networking
• more depth, detail to follow!

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Suggestion

• Read Chapter 1
• Preview Chapter 2 (Application Layer)?