what is the basis for atm?

Question

my chem teacher(hes an idiot) told me that the reason theres less air pressure when you go higher is because the gasses dont have buildings to bounce off of. I thought it was because of the weight of gasses coming down onto you.

Answer 1

Your explanation is closer to the truth.

The gravitational potential gradient induces a pressure gradient. That's just a slightly fancier way of saying that the air above compacts the air below.

Answer 2

ATM is the culmination of all the developments in switching and transmission in the last twenty years. This includes the advent of packet-switching and the change from coaxial to optical.

Switching:
Circuit switching:
This was the first type of data transfer mehanism used. A dedicated line on the network path is allocated to the parties involved in the transfer over the network. Channel capacity has to be available and reserved between each pair of nodes on the path, and each node has to have a switching capability. For different applications, utilization of the line can vary enormously. However there is little delay and effective transparency for the user. It is very efficient for Constant Bit Rate (CBR).

Packet Switching:
Data to be sent is broken down into chunks or packets. Each packet contains data and header information for control e.g. routing. At each node the packet is recsived, stored briefly and passed on. At each node the packets may be put on a queue for further movement into the network. There are two approaches to transport -

1. Datagram, where each packet can take any path through the network as long as they all reach the destination.

2. Virtual Circuit, where all the packets are routed through the same path without having the path dedicated.

Datagram allows for dynamic handling of congestion and no call setup is necessary. Virtual channels allow for sequencing, error and flow control.

Multirate Circuit Switching:
This is an enhancement of the synchronous Time-Division Multiplexing (TDM) approach used initially in circuit switching. In circuit switching a station must operate at a fixed data rate which must be used regardless of application. In multirate switching, multiplexing is introduced. A station attaches to the network by means of a single physical link which carries multiple fixed data-rate channels (B-channel @ 64kbps). Traffic on each channel can be switched independently through the network to various destinations. This is used for simple ISDN. So the user has a number of data rate choices but they are fixed so Variable Bit Rate (VBR) is difficult to accommodate efficiently.

Frame Relay:
Frame relay is essentially identical to packet switching. Frame relay saw its development as a result of high data rates and low error rates in modern high speed communications systems. In old packet switching, there was considerable overhead involved in error recovery, redundancy enhancement and routing information. With Frame relay the packets are now of variable length and not fixed length, meaning that they were designed to operate at up to 2Mbps. This was very good for VBR.

Cell Relay:
This is an evolution from frame relay and multirate circuit switching. Cell relay uses fixed sized packets called cells.

by

http://www.dhaarvi.blogspot.com

Answer 3

there is less pressure at higher altitudes because there is a thinner layer of air, and that means there are less collisions of air particles with each other.

Answer 4

gravitational force pulls everything closer to the center of the earth.. The further you are from the center, the lower the gravitational force

F = G*m1*m2 / d^2

Answer 5

Here is an easy-to-understand page about atmospheric pressure.
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/prs/def.rxml