A Simple Network Analogy
Components of our Imaginary Mail
Network
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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
Purpose of our Mail Network
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Your assistant is to request documents (by mail) and
interpret them for you.
Limitations and obstacles
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We can’t remember addresses, only names.
We can only mail to addresses.
We use small envelopes.
We have an envelope/hr. limit.
Limitations and obstacles (cont’d)
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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.
The Perfect Process
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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.
Structure
Packet - Named
Structure
Structure
Packet - Addressed
Structure
Analogies
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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)
Analogies
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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
Analogies
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Warehouse: Web Server
Mail Routing Centers: Routers
Assistant: Browser
Structure
Structure - Internet
Packet - Unresolved Request
Packet - Request to DNS
Structure - Internet
Structure - Internet (DNS Request)
Packet - Response from DNS
Packet - Unresolved Request
Packet - Addressed Request
Structure - Internet (Request with IP)
Structure - Internet (Routing Protocol)
Structure - Internet (Request rec’d)
Structure - Internet (Doc handled)
Structure - Internet (Req. honored)
Structure - Internet (Packet sending)
Structure - Internet (Packet sending)
Structure - Internet (Packet sending)
Structure - Internet (Packet sending)
Structure - Internet (Packet sending)
Structure - Internet (Packets sent)
The Perfect Process - Internet
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Type in your browser a transfer protocol, domain, pathname
and document (some missing can be assumed).
Browser contacts DNS for Domain <> 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.
Summary
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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.