The Internet

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The Internet

• Making a Connection Packet Switching, Addressing
  and Routing

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Host Computer or Terminal
An Internet
Router
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The Internet

• The Internet, or more correctly,
• a digital packet-switched network using the
  TCP/IP set of protocols,
• is
• A collection of hosts (computers and other
  information devices)
• connected by a variety of digital communications
  networks, consisting of
• digital communication links and
• switches, which are called routers.

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Protocols

• Information is transmitted on the Internet as
  binary information, 1s and 0s, under the
  control of standardized procedures called
  protocols.

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The TCP/IP Suite of Protocols

• Originated with ARPANET and DDN to meet US DoD
  requirements
• Survivability
• no central point of failure security
• Network interoperability
• accommodate heterogeneous networks and equipment
• Ability to handle surge traffic
• Allow priority
• Be always available

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Sending Information on the Internet

• Every entity (computer or router) on the Internet
  has an address.
• The address is a 32-bit binary number
• 10000110010101011111111011100011
• The IP address is usually expressed in dotted
  decimal form
• 134.117.254.227
• Part of the address is the NetID and the
  remainder the HostID

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Packets

• The message to be sent is packaged into packets
• A packet is a like an envelope that holds a block
  of data
• Each packet includes
• The address of the sender
• The address of the destination

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• If the message is short
• it is sent in one packet
• If not
• it is fragmented and
• sent in a secession of packets.

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Routing (Switching)

• Packets are sent independently from router to
  router
• Each router determines the next router to be used
  by consulting a local directory called a routing
  table

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Routing at Host

• If the NetID is the same as that of the
  originating host, the packet is handled locally
• IP address is converted to the physical address
  of the host and the packet delivered
• If not the same, a memory-resident routing table
  is consulted to determine next recipient of the
  packet

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Routing at Router

• The NetID is analyzed to determine if this is
  last hop.
• If not, the IP of the local router (using
  memory-resident tables) selects the best path to
  the destination
• Packet is encapsulated again and sent one hop
  closer to final destination
• And so on

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Routing Information

• Hosts maintain sufficient information to forward
  packets to other hosts or interior routers within
  the same network
• Interior routers maintain sufficient information
  to forward packets to hosts within the same
  system
• Exterior routers maintain sufficient information
  to forward packets to other interior or exterior
  routers

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Routing Tables

• Each router keeps its memory-resident tables with
  an optimum path to every destination in the
  system
• Routing-table update involves exchange of routing
  table information between routers using a
  built-in data communications system called ICMP.
• Every router in the Internet does this call the
  time!!!!

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Internet Control Message Protocol ICMP

• Provides feedback about problems in the
  communications environment
• Error reporting
• Reachability testing
• Congestion Control

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Datagram Delivery
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Error Control

• The network makes no effort to detect or correct
  errors in the transmitted data.
• It is up to the recipient to detect errors and
  ask for retransmission.
• This end-to-end task is handled by TCP, or the
  Transmission Control Protocol

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Transmission Control Protocol (TCP)

• TCP provides traditional connection oriented data
  communications service to programs - the reliable
  stream transport service
• TCP provides a virtual circuit, called a
  connection
• provides flow control, error checking and
  interrupt capability

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TCP Services

• Multiplexing
• Connection Management
• establish
• maintain
• terminate
• Data Transport
• Full-duplex
• Timely
• Ordered
• Labeled
• Flow controlled
• Error checked

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The Domain Name Service - DNS

• DNS is a hierarchical collection of directories
  (databases) that play a vital role in the
  Internet.
• DNS is the directory of IP addresses, that
  contains the names associated with IP addresses.
• Names, like sce.carleton.ca allow people to use
  the Internet.

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Finding an IP Address

• When ask my browser to open a web page at
  www.sce.carleton.ca, a query is sent by my
  computer to the nearest DNS server (at my ISP)
• If it knows the IP address it sends it back to my
  computer, otherwise it sends a query to the next
  level DNS server, maybe .ca
• This continues until an answer is found or not.

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• When a match is found, say 134.117.4.60 or
  whatever, the IP address is sent to my computer,
  which sends a connect message to the web site
  using this IP address.
• Every interaction with the Internet goes through
  the same process.
• How can the Internet sustain and increase - its
  capacity????

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Domain Name Service
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Moving on
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Paths to Evolution

• Fundamental Technologies
• Electronics
• Communications
• Software
• Systems Engineering
• Provide better ways
• to organize and use
• faster processors with
• more memory
• at lower cost