Computer networks -- 2007-2008 -- info.uvt.ro/Course 10

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Important! These pages are somehow outdated and it is recommended to consult the newer version at Computer networks -- 2008-2009 -- info.uvt.ro (by Ciprian Crăciun).

Quick links:


WAN communication[edit]

  • connection types:
    • dedicated -- synchronous serial:
      • usually through leased lines;
      • advantages: speed, 100% online;
      • disadvantages: cost, in case of failure;
    • circuit switched -- asynchronous serial:
      • usually through the telephony system;
      • either normal modems, ISDN or DSL;
      • advantages: cost and simplicity;
      • disadvantages: speed;
    • packet switched -- synchronous serial:
      • usually used to share the bandwidth (and costs) with other companies;

DSL, ADSL, and ISDN[edit]

HDLC[edit]

  • HDLC -- High Level Data Link Control:
  • created by IBM as a simple data link layer protocol;
  • works with synchronous serial links;
  • it works at bit level;
  • it has low overhead;
  • it is an ISO standard;
  • it doesn't support multiple network layer protocols;
  • it doesn't support authentication;
  • frame structure:
    • flag -- 8 bits;
    • address -- 8 or more bits;
    • control -- 8 or 16 bits;
    • data -- 0 or more bits;
    • FCS -- Frame Check Sequence -- 16 or 32 bits -- a CRC;
    • flag -- 8 bits;
  • links:

PPP[edit]

Tunneling and VPN[edit]

Miscellaneous[edit]

  • JSON example:
 {
     "firstName": "John",
     "lastName": "Smith",
     "address": {
         "streetAddress": "21 2nd Street",
         "city": "New York",
         "state": "NY",
         "postalCode": 10021
     },
     "phoneNumbers": [
         "212 555-1234",
         "646 555-4567"
     ]
 }
  • XML example:
 <recipe name="bread" prep_time="5 mins" cook_time="3 hours">
   <title>Basic bread</title>
   <ingredient amount="3" unit="cups">Flour</ingredient>
   <ingredient amount="0.25" unit="ounce">Yeast</ingredient>
   <ingredient amount="1.5" unit="cups" state="warm">Water</ingredient>
   <ingredient amount="1" unit="teaspoon">Salt</ingredient>
   <instructions>
     <step>Mix all ingredients together.</step>
     <step>Knead thoroughly.</step>
     <step>Cover with a cloth, and leave for one hour in warm room.</step>
     <step>Knead again.</step>
     <step>Place in a bread baking tin.</step>
     <step>Cover with a cloth, and leave for one hour in warm room.</step>
     <step>Bake in the oven at 350(degrees)F for 30 minutes.</step>
   </instructions>
 </recipe>
  • ASN1 definition example:
FooProtocol DEFINITIONS ::= BEGIN

    FooQuestion ::= SEQUENCE {
        trackingNumber INTEGER,
        question       IA5String
    }

    FooAnswer ::= SEQUENCE {
        questionNumber INTEGER,
        answer         BOOLEAN
    }

END