On Monday 13 November 2006 22:41, Richard Hosking wrote: > http is a "handshaking" synchronous protocol with 5 steps back and forth > between the client and the server to complete a transaction. > > client queries server > server acknowledges > client acknowledges > data sent > client/server acknowledges no of bytes - resend if error You are describing TCP which is common to both SMTP and HTTP.
> No store and forward mechanism is required. In this day of broadband
> most surgeries can be online continually so it isnt an issue
Few surgeries have static IP, so running a reliable server is still hard,
(your server briefly goes down every time your IP changes, haywood.bpa.nu
experiences this about one a week) and violates the user agreement of many
ISPs. The need for store-and-forward is not going anyway for a little while
longer.
> By contrast e mail is asynchronous - the packet of data is simply fired
> off into space in the hope it will reach it's destination.
No, SMTP is a direct connection to the server and clients get an
acknowledgement just they do with HTTP.
SMTP would have about the same level of overhead or less as an equivalent HTTP
service.
The problem is, that SMTP allows store-and-forward, but it doesn't *require*
it, and most people use this feature rather than running their own server.
Using a direct HTTP ("web-service") or a direct SMTP connection both solve
this problem and neither has a particular advantage from an end-users
perspective.
Most importantly, if you implemented store-and-forward with HTTP, which you
could, and probably would have to, you would get all the disadvantages of
SMTP, having done a lot of extra work.
The electrons don't magically become faster or more reliable with HTTP.
However, SMTP has several practical advantages for a developer
- it's an existing, proven standard, for web-services we would need a new
standard.
- standard extensions for encryption and acknowledgement, again, this all
needs to be defined from scratch for web-services.
- the biggie: it's linked to the MX feature of DNS, this allows you to attach
several servers, potentially in different locations, to a given address, if
one fails the clients trying to connect will automatically switch to another,
providing guaranteed uptime. [telstra's mailserver does not use this feature]
- there are existing free libraries 'off-the-shelf' for all this stuff
- yes you can use the ebXML standard over HTTP to do this. Prepare to spend a
lot of money. Oh, and did someone mention overhead ;-)
Ian
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