ITEC 3210 Lecture Notes - Lecture 4: Ethernet Frame, Lightning, Frame Check Sequence

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mraliice

21 Oct 2021

School

York University

Department

Information Technology

Course

ITEC 3210

Professor

Younes Benslimane

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Document Summary

Rules to decide which computer transmit and when. If multi point circuit is used which is shared circuit, simultaneous transmission cannot be done at the same time, the wait in multi-point increases the response time. If switches are used at the access layer, distribution layer and routers at core level. Point-to-point: any computer on network can send and receive at the same time, this is ideal approach because of performance particularly response time. Hubs or access point: can send and receive at the same time. Contention access: while computer is transmitting, no other computer can transmit because the collisions might happen. Two computers can start transmitting at the same time, which is not acceptable. The receiver node replies with a packet called cts. After the transmitter node receives the cts packet, it transmits the data packets. Encoded within the rts/cts packets is a duration field. In both case, there is centralized controller such as access point.

Related Questions

For many of us, smartphones have become indispensable, but they have also come under fire
for their impact on the way we think and behave, especially among children. Two of the largest
investors in Apple Inc. are urging the iPhone maker to take action against smartphone addiction
among children over growing concerns about the negative effects of technology. An open letter
to Apple on January 6, 2018 from New York-based JANA Partners and the California State
Teachers’ Retirement System (CalSTRS) stated that the firm must do more to help children
fight smartphone addiction. These two shareholders together control about $2 billion in Apple
stock. The investors’ letter urged Apple to offer tools to prevent smartphone addiction and to
provide more parental options for monitoring children’s smartphone usage. The iOS operating
system for Apple smartphones and tablets already has limited parental controls for restricting
Examiners: Dr. Emmanuel Awuni and Dr. Acheampong Owusu Page 2 of 4
apps, features such as location sharing, and access to certain types of content. The investors
felt Apple needs to do more—for example, enable parents to specify the age of the user of the
phone during setup, establish limits on screen time, select hours of the day the phone can be
used, and block social media services.
The average American teenager who uses a smartphone receives his or her first phone at age
10 and spends over 4.5 hours a day on it (excluding texting and talking). Seventy-eight percent
of teens check their phones at least hourly and 50 percent report feeling “addicted” to their
phones. The investors’ letter cited a number of studies on the negative effects of heavy
smartphone and social media use on the mental and physical health of children whose brains
are still developing. These range from distractions in the classroom to a higher risk of suicide
and depression. A recent survey of over 2,300 teachers by them Center on Media and Child
Health and the University of Alberta found that 67 percent of the teachers reported that the
number of students who are negatively distracted by digital technologies in the classroom is
growing. Seventy-five percent of these teachers think students’ ability to focus on educational
tasks has decreased. Research by psychology professor Jean Twenge of San Diego State
University found that U.S. teenagers who spend 3 hours a day or more on electronic devices
are 35 percent more likely, and those who spend 5 hours, or more are 71 percent more likely,
to have a risk factor for suicide than those who spend less than 1 hour. This research also
showed that eighth-graders who are heavy users of social media have a 27 percent higher risk
of depression. Those who spend more than the average time playing sports, hanging out with
friends in person, or doing homework have a significantly lower risk. Additionally, teens who
spend 5 or more hours a day on electronic devices are 51 percent more likely to get less than 7
hours of sleep per night (versus the recommended 9).
Nicholas Carr, who has studied the impact of technology on business and culture, shares these
concerns. He has been highly critical of the Internet’s effect on cognition, and these cognitive
effects extend to smartphone use. Carr worries that excessive use of mobile devices diminishes
the capacity for concentration and contemplation. Carr recognizes that smartphones provide
many useful functions in a very handy form. However, this extraordinary usefulness gives them
too much influence on our attention, thinking, and behaviour. Smartphones shape our thoughts
in deep and complicated ways, and their effects persist even when we aren’t using the devices.
Research suggests that the intellect weakens as the brain grows dependent on the technology.
Carr points to the work of Adrian Ward, a cognitive psychologist and marketing professor at
the University of Texas at Austin, who for a decade has been studying how smartphones and
the Internet affect people’s thoughts and judgment. Ward has observed that using a smartphone,
or even hearing one ring or vibrate, produces distractions that make it harder to concentrate on
a difficult problem or job. Divided attention impedes reasoning and performance.
A study published in Applied Cognitive Psychology in April 2017 examined how smartphones
affected learning in a lecture class with 160 students at the University of Arkansas at
Monticello. It found that students who didn’t bring their phones to the classroom scored a full
letter-grade higher on a test of the material presented than those who brought their phones. It
didn’t matter whether students who brought their phones used them or not. A study of 91 U.K.
secondary schools, published in 2016 in the journal Labour Economics, found that when
schools ban smartphones, students’ examination scores go up substantially, and the weakest
students benefit the most. Carr also observes that using smartphones extensively can be
detrimental to social skills and relationships. Connecting with “friends” electronically via
smartphones is not a substitute for genuine person-to-person relationships and face-to-face
conversations.

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ITEC 3210 Lecture Notes - Lecture 4: Ethernet Frame, Lightning, Frame Check Sequence

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