Subject: RE: Control and Forwarding functions

From: "David Allan" <[email-masked]>
Date: Tue, 4 Sep 2001 10:24:14 -0400

MPLS is not always connection oriented. An LDP DU infrastructure combined
with liberal label retention leads to a massively overprovisioned network of
connection segments (LSHs). Each LSR uses information from connectionless
routing to implement "this moments" converged forwarding configuration by
connecting the "best" segments together. An explicitly routed LSP is the
MPLS instantiation of "connection oriented". 
 
So what MPLS's "lifestyle preference" is depends on the application and we
should steer clear of blanket statements.
 
cheers
Dave

-----Original Message-----
From: Ding Aijun [mailto:[email-masked]]
Sent: Monday, September 03, 2001 1:20 AM
To: Hongwei; David Escobar
Cc: mpls
Subject: Re: Control and Forwarding functions

Hi,
 
MPLS is a connection-oriented. So, it needs a data plane, a control plane.
ATM network architecture is a good reference. 
 
Forwarding lies in the data plane, while signaling in the control plane.
Signaling, as well as call admission control, helps to set up the virtual
link. And then, data forwarding happens on the pre-established link. This is
a rough procedure. I hope it helps to explain the seperation between the
control and forwarding function.
 
regards,
aijun

----- Original Message ----- 
From: Hongwei <mailto:[email-masked]>  
To: David  <mailto:[email-masked]> Escobar 
Cc: [email-masked] <mailto:[email-masked]>  
Sent: Monday, September 03, 2001 3:59 AM
Subject: RE: Control and Forwarding functions

Hi David,
 
As much as I understand, MPLS technology is connection-oriented, and is
below or at the same level of IP. Like all connection-oriented protocols,
MPLS needs a set-up procedure before traffic begins. PVC or SVC is
established then. So called Control is the setup procedure(label requesting
and label mapping in LDP and CR-LDP). It establishes the forwarding
table,and it is before the traffic begins. So called Forwarding is in the
traffic stage. The outgoing port is easily got from the forwarding table
just because the setup procedure has established an explicit VC. So the
traffic becomes easy. Label swapping is needed because the labels in the
MPLS shim are locally significant, not globally(IP address is globally
important). The locally important label can be dynamically allocated and
released by the router. This adds flexibility. ATM also needs VCI/VPI
swapping. If globally important identifiers such as (source IP, destination
IP) pair are used as label of VC, multiple traffic between different
processes in the source machine and different processes in the destination
machine can't be distinguished.
 
While IP has no setup procedure because it is a connectionless technology.
So I just see its Forwarding function. At every hop, every IP packet has to
find next hop's IP address and its corresponding MAC address by ARP. 
 
It is true that both IP and MPLS need consult the table, so MPLS forwarding
is not necessarily faster than IP if packet's destination IP address can
always match an entry in IP routing table. And now it is more apparent that
MPLS is intended to combine the advantages of ATM and IP. MPLS can help to
realize traffic engineering over IP networks, such as explicit routing can
help allocate traffic evenly, and turn to alternative route quickly in case
of network failure.
 
I am just brave(rash?) enough to make above comments. I will appreciate any
correction of my mistakes. THX in advance:)
 
--Hongwei

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of David Escobar
Sent: 02 September 2001 18:32
To: [email-masked]
Subject: Control and Forwarding functions

Hi:
It is said that MPLS makes a good separation between the Control and the
Forwarding functions. It is also said that MPLS may use extensions of
existing IP protocols to piggyback label distribution (MPLS-BGP,
MPLS-RSVP-TUNNELS).
What is the meaning of good separation between the Control and the
Forwarding functions? MPLS still uses the same Control protocols, just a
little altered to provide label distribution by piggybacking and the
Forwarding function still needs to make table look up to find the next hop.
Even worse, it needs to make label swapping. Conventional IP also makes
table look up but with the advantage of not requiring label swapping. Why
can be inferred that conventional IP does not make a good separation of the
Control and Forwarding function while MPLS does?

---

From: Loa Andersson <[email-masked]>
Date: Tue, 04 Sep 2001 18:35:41 +0200

OK, here we go again....

To its nature MPLS is not "connection oriented"! I also depends quite a
bit on the definition of "connection oriented", but if we e.g. let an
ISDN
phone call be the model of a connection oriented technology, then you 
immediately see that MPLS misses the most important part of what a 
connection oriented technology is all about.
ISDN is separated into two parts "call control" and "connection
handling",
together they form the connection orientation.

So the "call control" handle e-2-2 compatibility and ability to take the 
call. This does not exist in MPLS. The call control also OK's the set
up of the call and is once it is established dependent of the e-2-e 
connectivity, if the connectivity is broken the call is released.
Nothing
of this is present in MPLS.

Sometimes one hear that MPLS is connection oriented because there is 
a mapping from node to node over the network, strictly this is not true,
the only thing that is mapped incoming label to outgoing label and
interface.
The rest is routing in the standard IP connections way.

As for the arguments that "most of the" LSP setup is connection
oriented,
usually meaning end-to-end (which really is edge-to-edge, there is not 
much idea to establish a connection edge-to-edge. But even so

LDP DU independent liberal is not connection oriented
LDP DU independent conservative is not connection oriented
LDP DU ordered liberal is not connection oriented
LDP DU ordered conservative is not connection oriented

LDP DoD independent liberal is not connection oriented
LDP DoD independent conservative is not connection oriented
LDP DoD ordered liberal is not connection oriented
LDP DoD ordered conservative could at best emulate part of a connection
        oriented technology (signaling)

RSV-TE mostly strictly follows IP routing and is not connection oriented
       and if there are explicit routes it falls into the same category
       as LDP DoD ordered conservative

We are left with a technology where it is required to have an
MPLS-external
application that do the call control part of connection orientation. Why
we would like to do that is beyond me, as we loses all the benefits of
the
IP and MPLS combination.

/Loa

-- 
Loa Andersson
Chief Architect,
Utfors Research, Architecture and Future Lab (URAX)
Utfors AB
Råsundavägen 12
Box 525, 169 29 Solna
Office          +46 8 5270 2000
Office direct   +46 8 5270 5038
Mobile          +46 70 848 5038
Email           [email-masked]
WWW             www.utfors.se

---

From: David Escobar <[email-masked]>
Date: Tue, 04 Sep 2001 13:44:08 -0500

Can you provide "guaranteed QoS" in MPLS?
Note: I make a difference between "guaranteed QoS" and "differentiated QoS".
"Guaranteed QoS" means that you can guarantee parameters like Packet Loss
Ratio, Packet transfer Delay, Packet Delay Variation in a given
transmission. "Differentiated QoS" means that you can only define packet
priority. You can only assign a priority to some packets so they are treated
better by routers (i.e. dropped last, forwarded faster, etc) but you still
can not guarantee any QoS.
----- Original Message -----
From: "Loa Andersson" <[email-masked]>
To: "David Allan" <[email-masked]>
Cc: "Ding Aijun" <[email-masked]>; "Hongwei"
<[email-masked]>; "David Escobar" <[email-masked]>;
"mpls" <[email-masked]>
Sent: Tuesday, September 04, 2001 11:35 AM
Subject: Re: Control and Forwarding functions

OK, here we go again....

/Loa

---

From: Loa Andersson <[email-masked]>
Date: Tue, 04 Sep 2001 22:53:57 +0200

David,

yes we do run an MPLS network and yes we deliver the services we
guarantee our 
customers, e.g. we run a E1 over the MPLS network according tp the E1
specification.
This is practice and seems to contradict the staement below of what
can and
can't be done in MPLS networks.

/Loa

-------------------
Loa Andersson
Chief Architect,
R?ndav?n 12

---

From: "Sukanta Ganguly" <[email-masked]>
Date: Tue, 04 Sep 2001 21:47:31 -0700

Not exactly. MPLS does exhibit the connection oriented nature via setting up the LSP's. There are not IPism going on their. Once the LSP is setup then the exact path specified via the LSP is followed. So it is connection oriented. The label distribution protocols take care of the label expiration and resetting up the paths if and when broken at any point of time.

SG

*********** REPLY SEPARATOR  ***********

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From: "Sukanta Ganguly" <[email-masked]>
Date: Tue, 04 Sep 2001 21:53:49 -0700

MPLS does not provide anything intrinsically that provides Guaranteed QOS. Although it provides a method for such type on an implementation to exists by sharing those information within the LSP from end-to-end for the path. Guarantees are proprietory implementation. Nothing that you can get of the standard draft.

SG

---

From: Eric Osborne <[email-masked]>
Date: Wed, 5 Sep 2001 00:47:07 -0400

On Tue, Sep 04, 2001 at 09:47:31PM -0700, Sukanta Ganguly wrote:
> Not exactly. MPLS does exhibit the connection oriented nature via
> setting up the LSP's. There are not IPism going on their. Once the
> LSP is setup then the exact path specified via the LSP is
> followed. So it is connection oriented. The label distribution
> protocols take care of the label expiration and resetting up the
> paths if and when broken at any point of time.

It seems to me there's an awful lot of people who can't tell the
difference between LDP-signalled labels and TE-signalled (RSVP or
CR-LDP) labels.

It's arguable that TE-signalled labels are "connection-oriented",
inasmuch as they define an ingress point and an egress point.  But I
really doubt you'll be able to argue that LDP is connection-oriented,
especially over non-ATM interfaces.  And if you want to go the route
of arguing that LDP (essentially a destination-rooted SPT) is
connection-oriented, then you have to be able to argue that IP is not
connection-oriented.  Because everybody knows IP isn't
connection-oriented, right?

But if MPLS (TE) is CO, so what?  "a rose by any other name..." and
all that jazz.  I suppose if I wanted to, I could come with a
definition of connection-oriented that meant Ethernet ARP was
connection-oriented.  But if I did, does that change how ARP works?
No.  

eric

---

From: "Sukanta Ganguly" <[email-masked]>
Date: Tue, 04 Sep 2001 22:31:30 -0700

Eric,
   I did not the logical bridge of bringing Ethernet ARP to explain connection orientedness, but I guess you have that understanding. Your point of signalling to LDP and TE (RSVP or CR-LDP) implies that their is some connection related matter going on.
  I don't wanna argue to much there. I would let others in the group decide what that means.

SG

---

From: Eric Osborne <[email-masked]>
Date: Wed, 5 Sep 2001 01:34:19 -0400

On Tue, Sep 04, 2001 at 10:31:30PM -0700, Sukanta Ganguly wrote:
> Eric,
>    I did not the logical bridge of bringing Ethernet ARP to explain
>    connection orientedness, but I guess you have that
>    understanding. Your point of signalling to LDP and TE (RSVP or
>    CR-LDP) implies that their is some connection related matter
>    going on.

'signalling' != 'connection oriented'.

If LDP over non-ATM interfaces is connection-oriented because of its
signalling, then is RIP connection-oriented?

I think we're dancing around the question of whether you need more
than just a signalling protocol to be connection-oriented.  Do you
need the transport protocol to do stuff to maintain a "connection", a
la TCP or SONET?  Or do you just need signalling to define a
connection, while having a common encap for CO (TE) and CL (LDP)
services?  Personally, I could care less; data gets from A to B no
matter what you call the connection paradigm.

>   I don't wanna argue to much there. I would let others in the group

Nobody ever wants to argue "too much".  Just enough so that people
admit they're right and then stop arguing. :)

eric

---

From: "Sukanta Ganguly" <[email-masked]>
Date: Tue, 04 Sep 2001 22:54:47 -0700

Eric,
  I see your point.

SG