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I've cut some bits out of the main article for discussion as we try and get it straight :-) Wikipedians/Alex

To quote:

"The motivation of the small cell size was the reduction of jitter in the multiplexing of cell streams.

At the time ATM was designed, 155 Mbits/s (135 Mbits/s payload) was a fast optical network. At this rate, a 53 byte (424 bit) cell would take 3.1 µs to transmit. Since then, networks have become much faster. Now (2001) a 1500 byte (12000 bit) full-size Ethernet packet will take 1.2 µs to transmit on a 10 Gbits/s optical network, removing the need for small cells
to reduce jitter, and greatly reducing the need for ATM."

and

" (This is much less important today (2001) given the increase in backbone speeds: see note above)."

Yes an no. Its not the only thing that affects latency (and therefore delay on voice calls). When dealing with voice traffic the time taken to fill a cell is also a factor. Standard voice band still runs at a 8Khz sampling rate. If you fill a typical 1500 byte IP packet at that rate you still introduce a lot of delay. Of course you could sub-fill a cell but then you defeat the whole point.

I've also cut out my:

"The larger the payload, the more efficent the transport of packet traffic (like IP) however the larger the latency in transport (which affects Voice telephony)."

Until we have a consensus.

I could be wrong but do I detect a slight bias against ATM?


The VoIP argument: yes, use ATM on the access ADSL link (see my comments there) - but not in the backbone.

Alas, I have extensive ATM experience (up to and including building one of the first international switched virtual circuit ATM networks, and later ripping it all out in favour of Ethernet/IP). Really, I am striving for NPOV. -- The Anome


Ok. I suggest we move the bits about Telco addopation and its intended goals etc, outside the article for now and just concentrate on consolidating the facts on ATM. Once the main article is straight we can tackle the ATM Part, present and future bit (mainting NPOV :-)

For the record I'm probably quite pro-ATM, although I can understand the headaches SVC's have caused you! Alex


SVCs were no problem - but getting telcos to understand them was more or less impossible. As you say, PVCs work (and map nicely onto the telco 'leased line' concept) but so do any of a number of other Layer 2 traffic segregation techniques (Gigabit Ethernet VLANs, MPLS, etc...) used as an under/over layer for IP - and they work just as well in the backbone (which means anywhere >= 1 Gbps nowadays) and they're cheaper. Still, I agree, we need to work together on giving ATM a good article - it's not going to go away for some time yet...

-- The Anome


I have now reedited/rewritten the article, hopefully preserving existing content and retaining NPOV on the matters discussed here (expanded and re-integrated). Let me know what you think.

-- The Anome

Added stuff about GFC, PT and NNI format. Also AALs. -- The Anome


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Last edited December 4, 2001 10:21 pm by The Anome (diff)
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