What is the difference between PTM and ATM?

+2 votes
asked Mar 9, 2015 in ADSL by Braydon

1 Answer

+1 vote
Afternoon Braydon!

When you look at ATM and PTM, it is important to realize that ATM and PTM is used in different instances on typical ADSL connection.

ATM, or Asychronous Transfer Mode, was a protocol designed in the 1980's to allow traditional high-throughput data traffic - such as file transfers - as well as real-time, low latency content such as voice and video. ATM has fallen out of favour over the past decade as Internet-Protocol based offerings allow greater speeds and versatility.

PTM, or Pulse-Time Modulation (also known as Pulse-Width Modulation) is used to encode a message into a pulsing signal, within the context of ADSL it is the method used to encode the ADSL signal and transfer it via the telephone copper to the ADSL Exchage.
answered Mar 9, 2015 by AfriGenie (2,280 points)
ATM is Asynchronous Transfer Mode using 53 byte cells in a frame. PTM is Packet Transfer Mode using variable length 1500 byte packets. ATM is an older tech used to carry voice and data in wide area networks by the phone companies, often times in SONET. The small cell size was a tradeoff to allow voice and data to be sent with minimal latency in voice transmission. With better IP QoS these days PTM can be used. ATM had overhead issues sometimes because 53 bytes had to be sent, whether used or not.
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