broadband internet, downstream, upstream frequency

Answered Question
May 16th, 2010
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Hi  every body.


i was reading about broadband cable internet. My book says  for upstream 2Mbps bandwidth and for downstream 6Mbps bandwidth are allocated.


Let say we have cable internet in  a certain neighborhood. For the sake of simplicity, assume there are only two users in the neighborhood, u1 and u2.


fc1  is carrier for downstream  (  that is cable modem receives on this frequency)

fc2 is carrier for upstream    ( that is cable modem transmit on this frequency)


When u1 has to some data such as e mail to send across internet, it will use  fc2 to  send email to email server on internet. When someone sends some data across internet  to  u1, u1 receives it on fc1.

How about if u1 has to send some data to u2? U1 will use fc2 to transmit but U2 is not receiving on this frequency. So how these two users ,u1 and u2 communicate?





thanks and have a nice weekend.

Correct Answer by Giuseppe Larosa about 6 years 9 months ago

Hello Sarah,


Media Acces control is needed to decide what user can access the shared upstream frequency.


U1 to U2 communication is not direct but it requires cable modem head end in the middle to move the frame in the downstream frequency (bridging between the two upstream and downstream )


see for example

http://www.howstuffworks.com/cable-modem.htm/printable


http://www.althos.com/aw_cablemodem.PDF


cable modem is shared, DSL lines are dedicated


cable modem can be used in parallel with cable modem TV tuner (at different frequencies)


Hope to help

Giuseppe

Correct Answer by Calin Chiorean about 6 years 9 months ago

Hi there!


First, the 2 cable modems are not communicating directly one to the other.

Second, Cable modem communication is based on FDM which assign different frequency to different stations (subscribers if you want).

In your case if the u1 had fc1 downstream and fc2 upstream, than u2 will have fc3 downstream and fc4 upstream by analogy.

Next, when u1 is sending something to u2, fc2 doesn't have to be the same as fc3, this is not Ethernet where you connect 2 device back to back with crossover cable.

The information is send from one subscriber through upstream cable to a multiplexor / demultiplexor device and from there to receiver. You can have 2 modems in the same house, over the same cable, and they will communicate through multiplexor device at the signaling level.


P.S. I'm not a transmission engineer and it's have been a while since I've worked with cable modems, so it may be that this information is not very technical or maybe a little bit erronate.

If somebody else has  a different opinion...


Let me know if you understood.


Calin

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Correct Answer
Calin Chiorean Tue, 06/01/2010 - 03:50
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Hi there!


First, the 2 cable modems are not communicating directly one to the other.

Second, Cable modem communication is based on FDM which assign different frequency to different stations (subscribers if you want).

In your case if the u1 had fc1 downstream and fc2 upstream, than u2 will have fc3 downstream and fc4 upstream by analogy.

Next, when u1 is sending something to u2, fc2 doesn't have to be the same as fc3, this is not Ethernet where you connect 2 device back to back with crossover cable.

The information is send from one subscriber through upstream cable to a multiplexor / demultiplexor device and from there to receiver. You can have 2 modems in the same house, over the same cable, and they will communicate through multiplexor device at the signaling level.


P.S. I'm not a transmission engineer and it's have been a while since I've worked with cable modems, so it may be that this information is not very technical or maybe a little bit erronate.

If somebody else has  a different opinion...


Let me know if you understood.


Calin

Correct Answer
Giuseppe Larosa Tue, 06/01/2010 - 07:17
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Hello Sarah,


Media Acces control is needed to decide what user can access the shared upstream frequency.


U1 to U2 communication is not direct but it requires cable modem head end in the middle to move the frame in the downstream frequency (bridging between the two upstream and downstream )


see for example

http://www.howstuffworks.com/cable-modem.htm/printable


http://www.althos.com/aw_cablemodem.PDF


cable modem is shared, DSL lines are dedicated


cable modem can be used in parallel with cable modem TV tuner (at different frequencies)


Hope to help

Giuseppe

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