[Linux] adsl explanation try

[Charles Higgins]

Maybe this will help some folks. If anyone can improve on my ascii art
or technical details please do so. I thought I'd take a stab at this 
so don't think that I consider myself some kind of expert. Also this
is just an example network and any simularities are coincidental. :)


adsl ascii art alert!
-----------------------------------------------------------------------

yahoo.com  * isp access server * dslam     *     modem   *   host

http  <----------------------------------------------------->http
tcp   <----------------------------------------------------->tcp
ip    <--------->ip<---------------------------------------->ip
atm   <---atm---->|<------------>atm<----atm-----> | <------>eth
sonet <--sonet--->|<---sonet----> | <----dmt-----> |
fiber <--fiber--->|<---fiber----> | <-local loop-> | <------>cat5



key:

>ip<     ip router-  packets are examined, modified, and routed

>atm<    atm switch- cells are examined, modified, and switched

>|<      protocol data units( example: ether frames, atm cells, etc)
             don't pass at this layer. they are de-encapsulated
             and pass to the layer above.
             
dmt      one of two adsl technologies
         
             
higher layers like tcp, http are not touched and pass though 
  intermediary devices like access server, atm switches and
  dslams although there might be a proxy-cache at isp.
  
*dslams may include ip routing functions*
---------------------------------------------------------------------- 
             
detail of the ip network:

yahoo.com  *  gblx1   *  gblx2   *  alter1 *   alter2  * isp access server

   <--------->ip<------->ip<-------->ip<-------->ip<-------->ip
               |          | <-atm---> |           | <-atm--->
   <--gigeth-->|<-sonet-> | <-sonet-> | <-sonet-> | <-sonet->
   <--fiber--->|<-fiber-> | <-fiber-> | <-fiber-> | <-fiber->


hmm... I left out mpoa

good references:

William Stallings
Andy Tanenbaum
Uyless Black
the late great W Richard Stevens
Radia Perlman
Douglas Comer