A Simple Network Analogy

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A Simple Network Analogy
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Components of our Imaginary Mail Network

• Assistant
• Warehouses of documents stored in folders
• Warehouse address operators
• Packets (envelopes) of information
• Local Mail Room
• Gateway mail routing center
• Regional/national mail routing centers

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Purpose of our Mail Network

• Your assistant is to request documents (by mail)
  and interpret them for you.

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Limitations and obstacles

• We cant remember addresses, only names.
• We can only mail to addresses.
• We use small envelopes.
• We have an envelope/hr. limit.

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Limitations and obstacles (contd)

• Warehouse worker is fast, but not very bright.
• We must specify the document location within the
  warehouse.
• Warehouses can be reorganized, shut down, or
  renamed overnight.
• While the document language is supposedly
  standardized, some document authors use slang
  terms.

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The Perfect Process

• Give assistant warehouse name, document name and
  location.
• Assistant contacts warehouse address operator for
  address.
• Assistant mails warehouse requesting the
  document.
• Warehouse mails assistant the document in pieces.
• Assistant assembles the document.
• If pieces are missing, assistant mails warehouse
  to re-send.
• Assistant interprets document and presents to you.

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Structure
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Packet - Named
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Structure
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Structure
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Packet - Addressed
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Structure
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Analogies

• Mailing method Transfer Protocol (e.g., http)
• Warehouse Name Domain Name (e.g.,
  www.education.umd.edu)
• Document location Pathname
• Document name Document name (often includes type
  or language)
• Document language Hypertext Markup Language
• MailingMethod//WarehouseName/DocLoc/DocName
  Uniform Resource Locator (URL)

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Analogies

• Warehouse Address Operator Domain Name Server
  (DNS)
• Missing pieces re-send Transfer Control Protocol
  (TCP)
• Mail Room Routing Rules Internet Protocol (IP)
• Numerical Address IP address
• Local Mail Room Local/Wide Area Network
  (LAN/WAN)
• Packet Data Packet

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Analogies

• Warehouse Web Server
• Mail Routing Centers Routers
• Assistant Browser

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Structure
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Structure - Internet
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Packet - Unresolved Request
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Packet - Request to DNS
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Structure - Internet
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Structure - Internet (DNS Request)
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Packet - Response from DNS
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Packet - Unresolved Request
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Packet - Addressed Request
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Structure - Internet (Request with IP)
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Structure - Internet (Routing Protocol)
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Structure - Internet (Request recd)
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Structure - Internet (Doc handled)
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Structure - Internet (Req. honored)
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Structure - Internet (Packet sending)
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Structure - Internet (Packet sending)
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Structure - Internet (Packet sending)
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Structure - Internet (Packet sending)
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Structure - Internet (Packet sending)
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Structure - Internet (Packets sent)
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Structure - Internet
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Structure - Internet
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The Perfect Process - Internet

• Type in your browser a transfer protocol, domain,
  pathname and document (some missing can be
  assumed).
• Browser contacts DNS for Domain ltgt IP Address
  resolution.
• Browser uses IP address to mail server your
  request.
• Server mails result to your browser in packets of
  data.
• Browser assembles the data.
• If pieces are missing, TCP allows for resending
  of packets.
• Browser interprets document and displays result.

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Summary

• The fact that the resulting received file can
  contain links puts the hyper in the hypertext.
• Document size matters to transmission speed and
  error reduction.
• Work computers (at CoE) are still on a relatively
  high speed connection modem links will be
  considerably slower.
• The internet is a relatively simple idea, but a
  complex set of connections.
• Graphics and other multimedia are
  disproportionately large compared to their text
  counterparts.