slides07

Question 1

contention

Answer 1

You may have noticed at home that your connection is faster during the day than it is in the evening when all the neighbours are at home streaming movies or Skyping their relatives overseas.

With EFM internet there’s no need to worry about contention; the connection is exclusive to your business. That means that it won’t slow down at peak times and your business isn’t going to suffer due to activity elsewhere that’s outside your control.

Question 2

encoding bits?

Answer 2

A simple way would be 0V for 0 and 1V for 1, running at 10MHz

Question 3

Manchester Encoding

Answer 3

• Split the time interval for a bit into two parts
• Low then high voltage is a 0
• High then low voltage is a 1

So the average is 0V
-0.85V for low, +0.85V for high

Question 4

self clocking

Answer 4

It is described as self clocking, as the reading end does not need a clock to determine where the bits are

Question 5

Manchester Encoding in cat 5?

Answer 5

We can’t use even Cat 5 cables with Manchester as it is only specified to 100MHz, and we would need 200Hz

Instead we start by encoding 4 data bits as 5 physical bits in a 4B/5B encoding; e.g., 0000 become 11110

Question 6

4B/5B

Answer 6

The 4B/5B translation ensures that every chunk of 5 symbols has at least two transitions, so average voltage is roughly 0

Question 7

symbol

Answer 7

A physical representation is called a symbol

Question 8

baud rate

Answer 8

The baud rate is the number of symbols per second

1 pysical symbol takes 5 cycles and 4 digital bits
rate is 31.25MHz (100 Mb/s)
4*31,25=125MBaud

Question 9

qam

Answer 9

Quadrature amplitude modulation (QAM) is a modulation scheme that moderates two sinusoidal carriers 90 ° out-of-phase with each other

Question 10

V series

Answer 10

V series is a series of communication standards developed by the International Telecommunication Union (ITU). V series protocols define methodologies for exchanging data over the public telephone system by using telecommunications devices such as modems and multiplexers.

Question 11

Integrated Services Digital Network isdn

Answer 11

a telecommunications network through which sound, images, and data can be transmitted as digitized signals.

Question 12

adsl asymmetry

Answer 12

divides the available bandwidth unequally into (say) 24Mb/s downstream (towards the user) and 2Mb/s upstream (towards the Internet)

Question 13

G.fast

Answer 13

DSL for very short loops: up to 500m

Question 14

exchanges, street cabinets,distribution points,premises

Answer 14

5500 exchanges
10,000s street cabinets 1,000,000s distribution points 30,000,000 premises
ADSL copper 24Mb
VDSL fibre + 80Mb FTTC copper
G.fast fibre + 300Mb FTTdp copper
Ethernet fibre 1GB FTTP