Subject: French eng. student having questions

From: Carl CREANGE <[email-masked]>
Date: Fri, 11 Aug 2000 11:16:54 +0100

Hi !                                                                            
                                                                                
As a French Engineering student leading my end-of-studies project on MPLS, I    
have read several relevant internet draft, RFCs and some white papers.          
Consequently, I need some explanatory statements to understand MPLS concepts as 
well as possible. If you have some time to answer few questions, I will be very 
grateful to you.                                                                
I am aware that some of theses questions may appear naive to you, however any   
help is very welcome.                                                           
                                                                                
1/ referring to draft-ietf-mpls-arch06.txt.                                     
I have understood the label stacking (3.9) and tunnels (3.27) concepts, but     
maybe you could give me an example of application and illustrate "Sometimes a   
router Ru takes explicit action to cause a particular packet to be delivered to 
another router Rd, even though Ru and Rd are not consecutive routers on the     
Hop-by-hop path for that packet" (3.27)                                         
                                                                                
2/ referring to draft-ietf-mpls-diff-ext05.txt and also to Avici Systems White  
paper : "Traffic Engineering with MPLS" published on 03/16/00                   
Label inferred LSP (L-LSP) can be potentially excessively resource consuming    
since each LSR needs a mapping of each of the 64 possible DCSP values with a    
label.                                                                          
Even Avici WP says: "This method requires than an association of specific       
DiffServ codepoints to LSPs be pre-established prior to traffic flow" :         
Does it mean that, for each ELSR pair (say ELSR A and B ), 64 different LSPs are
pre-established, and consequently at least 64 labels are reserved on each LSR on
the path between A and B?                                                       
                                                                                
3/ I would like to know where to find MPLS CoS definitions.                     
                                                                                
4/ Concerning the Forward Equivalent Class (FEC) concept, that I do not feel    
tangible.                                                                       
Is it right to say that a FEC is mapped on an LSP at an ingress LSR?            
Has a FEC a local or global significance?                                       
                                                                                
Two "more open" questions:                                                      
                                                                                
5/ Despite draft-ietf-mpls-diff-ext05.txt, I have some difficulties to see the  
developments achieved to tackle "QoS management through adjacent networks"      
What could you say about the two following scenari (and others we can easily    
imagine)?                                                                       
                                                                                
 	A/                                                                            
                                                                                
   ------------------        -----------------         ------------------       
  |                   |	|                 |       |                   |         
  |  non MPLS  |	|   MPLS     |       |   non MPLS |                            
  |  network      |-----|   Network  |-------|   network      |                 
  |  Inserv         |	|   DiffServ   |       |   Inteserv      |                
  |                   |	|                 |       |                    |        
   -------------------       -----------------         ------------------       
	B/                                                                             
                                                                                
   ------------                 ------------               ----------------     
  |                   |	   |                 |       |                   |      
  |  non MPLS  |	   |   MPLS     |       |   non MPLS |                         
  |  network      |--------|   Network  |-------|   network      |              
  |  DiffServ      |	   |   Int serv   |       |   Diffserv       |             
  |                   |	   |                |       |                    |      
   -------------------          ----------------         --------------------   
                                                                                
6/ MPLS over satellite.                                                         
Has it be ever considered?                                                      
Briefly, may high bandwidth-delay-factor links hamper MPLS working properly.    
What issues and adaptation do you see when evocating MPLS over satellite?       
                                                                                
I really thank you for your reading and your help.                              
                                                                                
Sincerely,                                                                      
                                                                                
Carl Creange.                                                                   
                                                                                
Institut National des Télécommunications - FRANCE