ATM vs X.25

[copyright_1978]

Can someone please explain in simple terms what ATM and X.25 is? what are the comparissons of both protocols? what technology or app uses them?

[mbossman2]

X.25 technology was implemented (in 1970's) (and still is) with the assumption that the physical data line is unreliable and prone to a higher level of errors. X.25 had incorporated in the standard a high level of error checking to ensure that data that got from point A to point B was actually correct and usable. The reasons that it is not used much anymore are: 1) data lines have become much more reliable, & 2) Frame relay networks have a much lower overhead and lower latency (due to the lowered need for error checking). The lower level of latency in a frame relay helps in the transmission of time sensitive data (like video and voice) where a high level of latency will discrupt the usefulness of the data.

ATM - Asynchronous Transfer Mode. The technology is different than others (like X.25) in the way that ATM chops up data into discrete 53 byte cells (i think that 53 is the right number) and ships them down the line. The advantages of this is that it allows for lower latency, higher bandwidths (up to 622+mbps), improved quality of service (especially in the voice and video areas). So in nutshell, ATM by using a standardized packet size, allows for much faster and more efficient transfer of data at much higher speeds. The disadvantage of this technology is that the equipment is more expensive than other competing technologies (like frame relay and X.25).


Where would I use these different protocols?
X.25 when you are moving large blocks of data, but not in a transactional WAN (a lot of back and forth data transfer)

ATM when you are doing a converged network (voice, video and data) where you will be scaling to extremely high speeds.

hope this answers your questions

[copyright_1978]

Thanks for the reply, do you know of any hardware or software that uses the above protocols? Thanks again. :)

[mbossman2]

On the hardware side:

Almost any commerical grade router can support X.25. I know that Cisco supports this on all current router platforms with the IP only feature pack (which means it is supported on all other feature packs as well).

ATM: This protocol has higher levels of processing power required and there is specialized hardware required to support this protocol (ie AIM-ATM card or other ATM line cards that are model dependant from Cisco) as well as specific IOS feature packs depending on the type of traffic (video, voice etc).

On the software side?

Seeing these are both networking protocols (layer 3/4 or lower on the OSI model), application software (OSI layers 5-7) really do not come into play. When to use these 2 protocols comes into play when analyzing traffic flow on the LAN/WAN. Again, X.25 works well in areas/needs where large blocks of data are moved around (ie remote site data backups to a central site, copying large data blocks from one site to another) but not where there is a lot of back and forth of data (like an order entry system) where latency can be wreak havoc on the transfer. ATM is used when you are 1) looking at a converged network (voice/video and data) where the potential need to move at high speeds may be necessary (ATM is supported up to 600+mpbs, where as IP traffic needs to be converted over to a protocol called SONET at those speeds, but that is changing).