On 2009-01-14, at 15:56, Murphy, Jay, DOH wrote:

In your humble opinion, which transmission method is more efficient, packet or cell?

When you say "transmission method" are you just interested in packet/ cell forwarding, or are you also including the effort involved in segmentation and reassembly? And when you say "efficient" are you talking about power consumption, or cost per bit, or payload versus header, or minimising jitter for isochronous applications, or something else? If the question is a pragmatic one (e.g. "which will allow me to get the most sleep, and spend the least money") then perhaps at low speeds, with Nortel's bankruptcy imminent, you could expect to find a lot of cheap ATM gear on the used market that would be the right short- term answer. It'd have to be pretty cheap though. I have met clueful people who have come to this conclusion, astonishing though it seemed to me at the time. At higher speeds, you might find that ATM gear either doesn't exist, or is so ludicrously expensive compared to ethernet switches that it makes you laugh coffee all over your keyboard. Joe

On Wed, Jan 14, 2009 at 12:56 PM, Murphy, Jay, DOH <Jay.Murphy@state.nm.us> wrote:

In your humble opinion, which transmission method is more efficient, packet or cell? ... Trying to make a decision on the transport mode for cost, delay, jitter, ROI, etcetera.

It really depends on what your applications are. I've spent the last decade as the regional ATM specialist (among other things) for an international carrier, and since we can sell you koolaid in ATM, Frame, MPLS, VPLS, IPv4, and IPSEC flavors, I can be fairly neutral about technology recommendations for my customers. The most efficient transmission method is the one for which you know how to set up your router to match the way the carrier's network works, so you'll need to train your people. If that's ATM, you may need to do some ATM-specific things, and they're different for different carriers; if it's Ethernet, you'll need to decide how to handle access line failure detection. And the work you need to do is much different if the ATM/Frame/Ethernet is a Layer 2 end-to-end service or if it's an access line for a routed service such as MPLS. ATM can give you really good control over jitter, but only if you set it up correctly. Dedicated Ethernet access typically has lower jitter than shared switched Ethernet access, but it only comes in a couple of sizes and may cost more if that's bigger than what you need. As far as cost-effectiveness goes, ATM cells have about 10% overhead, but some carriers price their services to charge you for it and some don't, and they have different policies about bursting; what you really care about is what price they're going to charge you for the data circuits you need. Ethernet also has a lot of overhead, if you're carrying lots of small packets; it's very significant if you're carrying VOIP, and trivial on big file transfers. These days circuit costs have decreased enough that router costs can be a significant part of your total cost. ATM cards are traditionally expensive, but if you're buying a VLAN-based switched ethernet access service, ask your router vendor what size router you'll need to handle traffic shaping - even if the Ethernet is built-in, a large teal-colored box costs more than a medium box. My main concerns about ATM, other than whether it matches your applications, are whether it'll scale to the size you need, and how long you'll be able to get good router vendor support. I don't see Frame/ATM interworking going away as a method for handling lots of small endpoints like cash machines reliably, at least until there are good ways to manage thousands of IPSEC sessions, but it's not the technology you're going to want for OC48s. DSL is usually ATM underneath, but that may or may not be how you connect to your DSL carrier. -- ---- Thanks; Bill Note that this isn't my regular email account - It's still experimental so far. And Google probably logs and indexes everything you send it.