Subject: difference between LSP and LSP tunnel?

From: d6942004 <[email-masked]>
Date: Fri, 31 Mar 2000 09:54:41 +0800

hi,

Can somebody tell me the differences between LSP and LSP tunnel?

I see the definition in "draft-ietf-mpls-arch-0.6txt".

1.
LSP tunnel example:

3.27.4. Hierarchy: LSP Tunnels within LSPs

   Consider a LSP <R1, R2, R3, R4>. Let us suppose that R1 receives
   unlabeled packet P, and pushes on its label stack the label to cause
   it to follow this path, and that this is in fact the Hop-by-hop path.

   However, let us further suppose that R2 and R3 are not directly
   connected, but are "neighbors" by virtue of being the endpoints of an

   LSP tunnel. So the actual sequence of LSRs traversed by P is <R1, R2,

   R21, R22, R23, R3, R4>.

   When P travels from R1 to R2, it will have a label stack of depth 1.
   R2, switching on the label, determines that P must enter the tunnel.
   R2 first replaces the Incoming label with a label that is meaningful
   to R3.  Then it pushes on a new label. This level 2 label has a value

   which is meaningful to R21. Switching is done on the level 2 label by

   R21, R22, R23. R23, which is the penultimate hop in the R2-R3 tunnel,

   pops the label stack before forwarding the packet to R3. When R3 sees

   packet P, P has only a level 1 label, having now exited the tunnel.
   Since R3 is the penultimate hop in P's level 1 LSP, it pops the label

   stack, and R4 receives P unlabeled.

but from the LSP definition

In other words, we can speak of the level m LSP for Packet P as the
   sequence of routers:

      1. which begins with an LSR (an "LSP Ingress") that pushes on a
         level m label,

      2. all of whose intermediate LSRs make their forwarding decision
         by label Switching on a level m label,

      3. which ends (at an "LSP Egress") when a forwarding decision is
         made by label Switching on a level m-k label, where k>0, or
         when a forwarding decision is made by "ordinary", non-MPLS
         forwarding procedures.

So my questions are

1. Is  <R2, R21, R22, R23, R3, R4>  a  LSP?
2. Is  <R1,R2, R21, R22, R23, R3, R4> a LSP tunnel?
3. Trsffic engineering works on LSP or LSP tunnel?

Sincerely yours

Ling-chih Kao

---

From: Eric Gray <[email-masked]>
Date: Fri, 31 Mar 2000 10:55:29 -0800

Ling-chih,

	See below.

> 1. Is  <R2, R21, R22, R23, R3, R4>  a  LSP?

There is an LSP (let's call it LSP-A) consisting of R1, 
R2, R3 and R4 that includes an LSP (we'll call it LSP-B) 
consisting of R21, R22 and R23 as the logical link 
between R2 and R3.

In the example you cite, LSP-B is used to tunnel labeled
packets from R2 to R3, so it is referred to as an LSP
tunnel.  In fact, LSP-B could easily be an IGP-based LSP
setup using hop-by-hop LDP which would mean it could move
around a lot and would not be an LSP tunnel in the sense
that the term is used in both RSVP-TE and CR-LDP.  For
this reason, I would tend to refer to LSP-B as an LSP
that is being used to tunnel labeled packets rather than
the more easily said "LSP tunnel".

> 2. Is  <R1,R2, R21, R22, R23, R3, R4> a LSP tunnel?

LSP-A (R1, R2, R3 and R4) is an LSP and LSP-B (R21, R22 and
R23) is an LSP. Any LSP may be used as a tunnel - to tunnel
either labeled or unlabeled packets.  In the sense that TE
uses the term tunnel, however, it is not certain that either
of these LSPs is a traffic engineered tunnel.

> 3. Trsffic engineering works on LSP or LSP tunnel?

Yes.

--
Eric Gray