CS 2200

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CS 2200

• Presentation 21
• Networking

2
Questions?
3
Our Road Map
Processor
Memory Hierarchy
I/O Subsystem
Parallel Systems
Networking
4
Overview

• Network Hardware
• Network Protocols
• Distributed Systems
• Remote Procedure Calls (RPC)

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Telephony to Telecom to Networks

• Voice communication was initially analog.
• Digital technology not that big in 1876
• Voice telephony switches to digital in the early
  60s
• Legal ruling (Carterphone) in 68/69 allowed
  devices which were beneficial and not harmful to
  the network to be connected to the Public
  Switched Telephone Network (PSTN).

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Telephony to Telecom to Networks

• Paved the way for computers to communicate using
  the telephone switching infrastructure.
• AT T Introduced Dataphone (first commercial
  modem in 1960.)

• Modulator/Demodulator
• Convert digital signals into analog
• Essentially same technology used today!

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Telephony to Telecom to Networks

• 1965 DoD Advanced Research Projects Association
  begins work on ARPANET
• 1969 ARPANET connects 4 computers
• Stanford Research Institute, UCLA, UC Santa
  Barbara, and the University of Utah
• 1971 The ARPANET grows to 23 hosts connecting
  universities and government research centers
  around the country.
• 1973 The ARPANET goes international

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Telephony to Telecom to Networks

• 1975 Internet operations transferred to the
  Defense Communications Agency
• 1981 ARPANET has 213 hosts. A new host is added
  approximately once every 20 days.
• 1982 The term 'Internet' is used for the first
  time.
• 1983 TCP/IP becomes the universal language of the
  Internet

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Computer/DataComm Evolution

• 1942-Present Mainframes
• Initially batch oriented environment
• Next step Timesharing
• Data terminals connected to mainframes
• 1971 Intel introduces the first microprocessor -
  the Intel 4004.
• 1971 The Kenbak-1, the first microcomputer, is
  introduced in Scientific American, selling a
  total of 40 units in 2 years.
• 1972 Intel launches the 8-bit 8008 - the first
  microprocessor which could handle both upper and
  lowercase characters.

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Computer/DataComm Evolution

• 1972 Xerox develops the Xerox Alto - the first
  computer to use a Graphic User Interface.
• 1973 Robert Metcalfe invents the Ethernet
  networking system at the Xerox Palo Alto Research
  Center.
• 1974 Intel introduces the 8080 microprocessor - 5
  times faster than the 8008. (And the heart of the
  future Altair 8800.)
• 1975 MITS markets the Altair 8800 - the first
  mass-market microcomputer, launching the Personal
  Computer Revolution.

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Computer/DataComm Evolution

• 1975 Bill Gates and Paul Allen form the Microsoft
  company to create software for the new Altair
  8800.
• 1976 Apple Computer is formed by Steve Jobs,
  Steve Wozniak, and Ron Wayne, and launches the
  Apple Computer.
• 1977 Tandy Radio Shack ships its first personal
  computer - the TRS-80. It sells over 10,000
  units, tripling expectations.
• 1977 Apple Computer launches the Apple II, which
  sets new standards for sophisticated personal
  computer systems.

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Computer/DataComm Evolution

• 1978 The C programming language is completed at
  ATT Bell Laboratories, offering a new level of
  programming.
• 1978 Apple and Tandy ship PCs with 5.25" floppy
  disks, replacing cassette tape as the standard
  storage medium for PCs.
• 1978 Hayes Microcomputer Products releases the
  first mass-market modem, transmitting at 300 bps
  (0.3K).
• 1978 Intel ships the Intel 8086 microprocessor,
  with 29,000 transistors, and running at 4.77
  megahertz.

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Computer/DataComm Evolution

• 1979 Personal Software creates VisiCalc for the
  Apple II, the first electronic spreadsheet
  program, selling over 100,000 copies.
• 1979 Intel develops the 8088 microprocessor,
  which would later become the heart of the IBM PC.
• 1979 Motorola develops the Motorola 68000
  microprocessor, offering a new level of
  processing power.
• 1980 Seagate Technology introduces the first
  microcomputer hard disk, capable of holding 5
  megabytes of data.

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Computer/DataComm Evolution

• 1980 Philips introduces the first optical laser
  disk, with many times the storage capacity of
  floppy or hard disks.
• 1980 Xerox creates Smalltalk - the first
  object-oriented programming language.
• 1980 John Shoch at Xerox creates the first worm
  program, with the capacity to travel through
  networks.
• 1981 Ungermann-Bass ships the first commercial
  Ethernet network interface card.

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Computer/DataComm Evolution

• 1981 Xerox introduces the Xerox Star 8010, the
  first commercial Graphic User Interface computer,
  for 16,000-17,000.
• 1981 Microsoft supplies IBM with PC-DOS (which it
  would also sell as MS-DOS), the OS that would
  power the IBM PC.
• 1981 IBM brings to market the IBM PC, immediately
  establishing a new standard for the world of
  personal computers.

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Questions?
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Types of Interconnections

• Massively Parallel Processors (MPP)
• Thousands of nodes
• Short distances
• Local Area Networks (LAN)
• Hundreds of computers
• Several kilometers
• Traffic many to one (clients to servers)
• Wide Area Network (WAN)
• Thousands of computers
• Thousands of kilometers

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Basic Concepts
Each machine has the ability to send a message to
the other a.) Please send me the contents of
address x b.) Here is the contents of address
x Thus, messages must contain an extra bit.
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Basic Concepts
Payload (32 bits)
Header (1 bit)
0
Address
0-Request 1-Reply
1
Data

• Messages are divided into parts
• Payload or actual data to be transferred
• Header (or trailer) data used to control the
  message passing scheme
• System must be designed to work well with
  operating system.
• Multiple Processes
• Error Handling

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Software Steps to Send

• Application copies data into O.S. buffer
• Operating System
• Calculates checksum
• Includes checksum in header and/or trailer
• Starts timer
• Sends data to network interface hardware and
  tells it to send message
• Wait...

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Reception

• Copy data from network hardware into operating
  system buffer
• Calculate checksum from data
• If calculated checksum matches included checksum
• Send acknowledgement
• Copy data into application space
• Else
• Discard message
• Wait for resend

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Sender...

• If acknowledgement arrives
• Discard copy of message in buffer
• If timer times out first
• Resend data
• Restart timer

Header (2 bits) 00Request 01Reply 10Acknowledge
Request 11Acknowledge Reply
Payload Data (32 bits)
Checksum (4 bits)
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Protocols

• Sequence of steps performed by software to send
  and receive messages.
• Issues
• Endianess
• Duplicate messages
• Queue full
• etc.
• More next...

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Vocabulary Fun

• Bandwidth
• Time of Flight
• Transmission Time
• Transport Latency
• Sender Overhead
• Receiver Overhead

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Diagramatically
Sender Overhead
Transmission Time
Sender
Time of Flight
Transmission Time
Receiver Overhead
Receiver
Transport Latency
Total Latency
TIME
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Questions?
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Questions?

• Where do you connect the network to the computer?
• Which media are available to connect computers
  together?
• What issues arise when connecting more than two
  computers
• Additional practical issues?

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Connecting the Computer

• Connection Point
• Memory Bus
• I/O Bus
• Control
• Polling
• Interrupts
• Operating System Involvement

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Connecting the Computer

• Connection Point
• Memory Bus MPP
• I/O Bus LAN/WAN
• Control
• Polling Hybrid
• Interrupts Approaches
• Operating System Involvement
• Avoid invoking O.S. in common case

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There is an old network saying Bandwidth
problems can be cured with money. Latency
problems are harder because the speed of light is
fixed--you cant bribe God.

• David Clark, MIT

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Hierarchy of Media

• Twisted Pair
• Coaxial Cable
• Fiber Optics

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Media

• Twisted Pair
• 1 Mb/Sec 2 km 0.23/m 15
• 20 Mb/sec 0.1 km 0.23/m
• Coaxial Cable
• 10 Mb/sec 1 km 1.64 460
• Multimode Fiber
• 600 Mb/sec 2 km 1.03 2000
• Single-Mode Fiber
• 2000 Mb/sec 100 km 1.64 2000

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Questions?

• So far how many computers have we connected?

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Connecting gt 2

• Shared Media
• Bus
• Ethernet (Vampire Taps)
• Coordination Mechanism
• Carrier Sensing and Collision Detection
• Broadcast
• Switched Media
• Better utilization of bandwidth
• Point to point

Node
Node
Node
Node
Node
Node
Switch
Node
Node
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More About Rings

• Token Ring
• Nodes pass token from one to another
• When you have token you can send

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Connection vs. Connectionless

• Phone System
• To make call a connection or circuit was
  connected (might be multiplexed).
• Not a bad idea for voice
• Connection exists whether or not anyone is
  talking.
• Limit is number of conversations NOT amount of
  data
• Postal System
• Each piece of information is routed according to
  its address
• Long messages can be broken up into pieces or
  packets (or frames).

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Routing

• Shared Media
• Message goes to all nodes. Each looks at address
  to determine if they are recipient
• Switched Media
• Source-based routing
• Message specifies path to destination
• Virtual circuits
• Temporary or permanent
• Destination-based routing
• Deterministic
• Adaptive
• Random

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Routing Policies

• Store and Forward
• Wormhole
• http//www.johnlockhart.com/research/janet/

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Congestion Control

• Circuit switched
• All circuits are busy
• Packet switched
• Deadlock
• Reducing Congestion
• Packet discarding
• Flow control (Window used by TCP)
• Choke packets

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Questions?
41
The Ethernet
A drawing of the first Ethernet system by Bob
Metcalfe.
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Ethernet Evolution

• X_Base_Y
• X stands for the available media bandwidth
• Base stands for base band signaling on the medium
• Y stands for the maximum distance a station can
  be from the vampire tap (i.e. Length of Attach
  Unit Interface)

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Ethernet Evolution

• 10_base_5 (1979-1985)
• 10 Mbits/Sec with base band signaling with a
  maximum station distance of 500 meters
• Thick shielded copper conductor used as the medium

MAU-Medium Access Unit
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• 10_base_2 (1985-1993)
• Thin net, cheaper net
• Distance to the station shrinks to 200 meters
• No more vampire taps
• BNC connector to connect the stations to the
  Attach Unit Interface (AUI) cables, the AUI
  cables to the medium
• The medium is daisy-chained via the stations
  using the BNC connectors

Bayonet Neil-Concelman, or sometimes British
Naval Connector
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• 10_base_T (1993-1995)
• Attach Unit Interface (AUI) is a twisted pair of
  copper wires
• AUIs from the stations come to a hub which is a
  multiplexor/transceiver
• Did away with the BNC connectors which were a
  source of connector problems
• Use phone jack technology (RJ45 connectors) to
  connect AUI cables to the hub
• Hubs are connected to other hubs using the same
  connectors (RJ45)

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• 10_base_T (1993-1995) continued
• All the hubs together form the entire medium
• All the stations in the same collision domain
• Hub is also usually called a repeater

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Repeater

• A repeater acts on a purely electrical level to
  connect to segments. All it does is amplify and
  reshape (and, depending on the type, possibly
  retime) the analog waveform to extend network
  segment distances. It does not know anything
  about addresses or forwarding, thus it cannot be
  used to reduce traffic as a bridge can.

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Bridges

• A bridge will connect to distinct segments
  (usually referring to a physical length of wire)
  and transmit traffic between them. This allows
  you to extend the maximum size of the network
  while still not breaking the maximum wire length,
  attached device count, or number of repeaters for
  a network segment.

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Bridges

• Advent of switched ethernet (late 1990s)
• Bridges have switches inside (e.g. crossbar) that
  allow connecting in-links to out-links
• Partitions hubs into distinct collision domains
  (1 2 talk in parallel with 3 4)
• Bridge buffers packets that want to go on the
  same out-link

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Virtual LANs

• VLANs may span bridges
• Nodes 1 and 5 same VLAN 2, 6, 7 same VLAN
• All nodes on the same VLAN hear broadcasts from
  any node on that VLAN
• VLAN limits the traffic flow among bridges
• A hierarchical network with only bridges results
  in a switched ethernet with no collisions!

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Network Interface Card

• NIC
• Sits on the host station
• Allows a host to connect to a hub or a bridge
• If connected to a hub, then NIC has to use
  half-duplex mode of communication (i.e. it can
  only send or receive at a time)
• If connected to a bridge, then NIC (if it is
  smart) can use either half/full duplex mode
• Bridges learn Media Access Control (MAC) address
  and the speed of the NIC it is talking to.

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Routers

• Routers work much like bridges, but they pay
  attention to the upper network layer protocols
  (OSI layer 3) rather than physical layer (OSI
  layer 1) protocols. A router will decide whether
  to forward a packet by looking at the protocol
  level addresses (for instance, TCP/IP addresses)
  rather than the MAC address. Because routers work
  at layer 3 of the OSI stack, it is possible for
  them to transfer packets between different media
  types (i.e., leased lines, Ethernet, token ring,
  X.25, Frame Relay and FDDI). Many routers can
  also function as bridges.

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Routers

• Repeaters and Bridges understand only Media
  Access Control (MAC) addresses
• Traffic flow between nodes entirely based on MAC
  addresses
• Packet from a host station ltmac-addr, payloadgt
• Routers understand IP addresses
• Special board that sits inside a bridge
• IP layer on all nodes send packets destined
  outside the LAN to the router
• Router sees a packet as ltip-hdr, payloadgt
• uses the ip-hdr to route the packet on to internet

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How are we connected?

• State of COC connectivity to campus backbone and
  internet (Nov 1999)

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Questions?
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