The MPLS WG Archive

[Shahram Davari <Shahram_Davari@pmc-sierra.com>]

Hi,

 

Your confusion comes from the fact that RSVP is only used for Intserv and not MPLS. But RSVP-TE can support:

 

1) MPLS signaling (for label distribution)

2) Intserv or Diffserv signaling (for indicating the CoS, BW, ...)

 

When somebody says that Diffserv eliminates RSVP, you should probably interpret it as Diffserv eliminates RSVP use as Intserv signaling.

 

The other point is that Diffserv and RSVP-TE operate on completely different dimensions (not different scale). RSVP-TE is used to setup the LSPs and signal the QoS requirement, while Diffserv is the scheduling mechanism implemented in an LSR.

 

Regards,

-Shahram

-----Original Message-----
From: Robben Paul [mailto:paul.robben@worldonline.be]
Sent: Thursday, September 14, 2000 11:06 AM
To: mpls@UU.NET
Subject: question: DiffServ versus RSVP

Hi,

 

I'm currently making a thesis regarding IP-based VPN's, paying special attention to traffic engineering and QoS.

Something isn't clear to me. I read a couple of articles regarding the use of explicit routes with CR-LDP and the extended RSVP.

Apparently, some companies prefer the former, others the latter, but there doesn't seem to be an official statement yet of which one's the best. But however, RSVP still is a "hot topic".

On the other hand, I also read some articles about DiffServ, mentionning that DiffServ evolved from Intserv, which is based on RSVP, and that, within some time, DiffServ will eliminate the need to use RSVP in WAN area's.

 

I think I must be missing something here...

1. Some time ago, a reader from the MPLS-list described DiffServ as a traffic light with reserved lanes for taxi's and busses. Its job is to help prioritize things once congestion starts, and to penalize some flows to allow others to get less delay or loss. So, I guess DiffServ doesn't operate on the level of 1 LSP, but on a whole bunch of them?

2. On the other hand, the extended RSVP is a way to set up explicit routes. So RSVP is important for each LSP separately?

 

So, I don't really understand how DiffServ could eliminate the use of RSVP??? It seems to me that, although they both serve QoS, they are working on a complete different scale...

 

Can anybody make me see the light in the darkness?

:)

Thanks in advance,

 

Françoise Beckers

(Global One)