Hints for Exercises: Chapter 4

  1. Trace the history of telephone modems, from the earliest system until V.92. Explain why modems stop at V.92.

    Links. The world is moving on from modems over voice channels, better technologies are widespread. Also, V.90 and V.92 achieve the fastest rates that can theoretically be achieved through a standard voice channel, so there is not a lot of room for growth!

  2. Show in detail how the message "Hello {world}" would be transmitted in
    1. (a) a SLIP
    2. (b) a PPP (use protocol field 0000)

    (a) "Hello {world}" is the bytestream (hex)

    48 65 6c 6c 6f 20 7b 77 6f 72 6c 94

    Under SLIP this becomes

    c0 48 65 6c 6c 6f 20 7b 77 6f 72 6c 94 c0

    with framing.

    (b) Now we get

    7e ff 03 00 00 48 65 6c 6c 6f 20 7b 77 6f 72 6c 94 20 79 7e

    The checksum algorithm is the same as used in Ethernet.

  3. The T and E hierarchies have (historically) been very important in the expansion of data networks. Read up on their history and development.


  4. Frame Relay, ATM and MPLS are direct competitors in the market. For various scenarios (a multi-site company; an ISP; a telecoms provider, etc.) discuss and compare them as solutions.

    Links. Of course, there is no simple solution to this question: some reflection on the various technologies is expected. MPLS and ATM can actually run side-by-side, so they can be deployed together.

  5. ADSL is just one of several DSL standards. Write notes on as many of the others as you can find.

    Links. There are (at least) ADSL, CDSL, HDSL, IDSL, PDSL, RADSL, SDSL, SHDSL, UDSL, VDSL and their variants (e.g., ADSL2).

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