CSC
104 Slog-Week
Eleven (Mar 25th - Mar 31th)
❤Something new learned in the class:
[Network]
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| Network |
※Examples:
①Token ring
※There must be just one sender at a
particular time. ※They pass a signal,
a bit pattern called a token, around the ring. ※A machine that has messages to send retains
the token until it can confirm that its messages have been received, and then
passes it along. ※Machines that have no messages to
send pass along the token as soon as they receive it.
②Star configuration
※Failure of the hub machine breaks the star. ※A disadvantage of the star
configuration is that if the main machine goes down, they will all go down.
③Bus (e.g. Ethernet) configuration
※Able to transmit messages at any
time. ※If a machine detects that another
machine is transmitting at the same time (a collision), it waits for a random
interval of time before re-transmitting. ※The success of the protocol depends on the
random intervals being (on the average) different for different machines. ※Failure of a single machine
doesn't break the network, although other machines may re-transmit many
messages to it.
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| Internet |
❀ The address
space for this network of networks is comprised of four bytes, the dotted quad,
which divides into a portion to identify the network, and a portion to identify
the particular machine (or host) on that network. ※These four bytes are to decide whether the recipient of a message is on
the local network (in which case it sends the message directly to it) or
whether it is on some other network (in which case it forwards the message to
another router, and eventually it reaches the network hierarchy responsible for
that network).
❀There is a
translation between the dotted-quad and symbolic names. The symbolic names
indicate the top-level domains (.org, .com, .net, .edu, and two-character
country codes) that group many networks under them.
❀The
hierarchy of domains and sub-domains in the symbolic name indicate the chain of
responsibility for keeping track of the mapping between symbolic and numeric
addresses, and (for example) which machines handle mail for other machines.
❀Capabilities of
the Internet
※Email
※Execution of programs on a remote machine
※Sharing of resources, such as disk drives and
printers between dispersed machines
※Transfer of files between dispersed machines
※Online shopping
❀Hypertext
Markup Language (HTML)
❀Web-pages
containing files in HTML format are specified/located through a Uniform
Resource Locator (URL).
❀ Programs ran by the browser are
restricted by (a) the size of file that can reasonably be transmitted over the
net, and (b) caution about allowing a program from a remote site to carry out
certain functions --- for example accessing your hard drive.
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| Programs |
[Computers and work]
❀On the one
hand, the amount of textiles and metal goods that could be produced in a day
increased dramatically during the Industrial Revolution, due to both the use of
power (first steam, and later oil, and electricity), and division of labor. On
the other hand, the land and resources used for older forms of production were
taken over (in some cases by military force), first in Europe and then
throughout the world. Increasing production required ever-expanding markets,
and those who produced goods using older forms of production were thrown out of
work. Some of them (for example, traditional weavers in the north of England)
responded by smashing the machinery that deprived them of a livelihood. Those
who did gain employment with the new machinery (often children) were often pushed
to work 12, 14, or even longer shifts each day.
❀Measures of
personal wealth (the number of square feet of housing, cars, or the amount of
food, per capita) have similarly increased. Entirely new categories of jobs
(e.g. webmaster) have been created, as well as new ways of working
(telecommuting).
❀Early in
the era of automation there were both dire and rosy predictions: some predicted
overwhelming unemployment and social dislocation, while others predicted a
utopia with plenty of wealth and leisure time. Neither has come to pass (yet). We
have traded more stuff for less time: the average home has more floor space and
more cars parked in front of it than half a century ago, and the price is that
we have to work more hours, or perhaps a second job. On
the other hand, unemployment rates seem to ebb and flow with the business cycle
(cyclical recessions and recoveries) rather than showing a massi
ve increase as
automation takes jobs from humans.
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| Telecommuting |
❀Telecommuting
※Benefits of
telecommuting include flexible work hours (so work may be combined with other
responsibilities, such as daycare), lower costs for office infrastructure, and
a smaller social impact of commuting (good for the environment.
※Drawbacks
of telecommuting include intrusion into home life (flexible hours are often
longer), reduced impact with co-workers, and less "visibility" to
superiors.
❤ Challenges
I met this week
❀Understanding three types of networking and
their characteristics is kind of difficult. However by looking it up on the
internet and searching examples of photos of them, I got to well understand them.
❤The
test/quiz/assignment
❀We had a test this week so we do not have any
tutorial this week which is a good thing. However, I found some things that I
did not command really well. For example, I made
mistake in (list-ref n) function. I thought it represented the rest of the list
but actually it means the stuff on the nth position of the list.
❤Feedback
to the other’s slogs
❀I read Emily Zhang’s slog ths week. She mentioned the privacy problem in the lecture. And I
left a message: “Indeed the privacy problem
is really annoying :( ".
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| Internet and privacy |
