Subject: TE

From: "Mike Badil" <[email-masked]>
Date: Tue, 20 Jun 2000 20:21:38 EDT

Hi all

I just reading MPLS document, I have a question which I am not really clear 
to understand, if someone helps I will be happy.

The Question is:

What makes MPLS to support constraint based routing?
If it just adding contsraint metrics to conventional routing in order to 
support TE.
Why it is not possible without MPLS.

In other word, in conventional IP routing, if we add constraint metrics, can 
conventional IP routing support it also?

Thanks.

________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com

---

From: "Darek Skalecki" <[email-masked]>
Date: Wed, 21 Jun 2000 09:43:39 -0400

> conventional IP routing support it also?

Constraint based routing is not only about metrics but also bandwidth such as
maximum reservable and how much is actually available.

Darek

---

From: David Charlap <[email-masked]>
Date: Wed, 21 Jun 2000 10:16:17 -0400

Mike Badil wrote:
> 
> I just reading MPLS document, I have a question which I am not really
> clear to understand, if someone helps I will be happy.
> 
> The Question is:
> 

The existance of LSPs makes traffic engineering easier to implement.  It
does not make it impossible, however.

> If it just adding contsraint metrics to conventional routing in order
> to support TE.

Sure, it's possible.  Who said it wasn't?

> In other word, in conventional IP routing, if we add constraint
> metrics, can conventional IP routing support it also?

I think you're missing the point of MPLS.

MPLS's purpose is not to create the ability to perform constraint-based
routing and traffic engineering where it was previously impossible.

MPLS's purpose is to create a connection-oriented link layer (COLL). 
Where forwarding decisions are made solely on the basis of a packet's
label, and not on any other content in the packet.

The use of a COLL is not a requirement for traffic engineering.  It
simply makes it easier to implement.  With a COLL, the hard work of
determining the path that data packets must take can be done once, when
the LSP is set up.  Without a COLL, this work must be done by every
switch, for every data packet.

Connection oriented link layers are not new.  ATM and Frame Relay also
use them.  The big thing that makes MPLS special is that it can run over
nearly any transport medium (ATM, FR, POS, Ethernet, etc) instead of
being tied to a specific layer-2 encapsulation.  Also, because it uses
IP for its addressing, it can work with many common routing and
signalling protocols (like OSPF, IS-IS, and RSVP).

-- David

---

From: David Charlap <[email-masked]>
Date: Wed, 21 Jun 2000 10:21:31 -0400

David Charlap wrote:
> 
> The existance of LSPs makes traffic engineering easier to implement.
> It does not make it impossible, however.

Correction:

	The absence of LSPs does not make traffic engineering 	impossible.

-- David

---

From: Jay Wang <[email-masked]>
Date: Wed, 21 Jun 2000 11:31:44 -0400

Mike,

    MPLS is not created to support constraint based routing
    and it doesn't.  It let you set up layer two tunnels using
    label switching.  An IP network can benefit from the
    existence of MPLS with at least the following:

    1. Faster data forwarding at the transient (core) routers -
        This is because there is only label (index) lookup and
        no IP header processing.  This however became much
        weaker an argument lately since lots of work that used
        to be done by software (e.g., header processing,
        classification) now are typically done in ASIC in vendor's
        box.

    2. Traffic Engineering - MPLS allows you to set up tunnels
        with explicit routing so that you can design your routes
        off-line in order to achieve best traffic distribution to
        minimize network hot spots (which often occur in OSPF
        type routing) and improve network capacity efficiency.
        Load balancing (parallel MPLS tunnels running between
        a source-dest pair) and trunk protection also become easy.

    3. QoS/VPN  - MPLS interworking with Diffserv gives you traffic
        isolation (and hence some performance protection). Also,
        MPLS with proper support of resource
        reservation signaling mechanism (e.g., RSVP), you can specify
        thE size of each MPLS 'pipe'.  With a careful traffic trunk
analysis,
        you may set up a set of corresponding pipes (using constraint based
        or explicit routing) such that you can place some application
specific
        (e.g., voice,  video) flows on the trunks while meeting some
        stringent real-time specs (e.g., loss, jitters, latency).

- Jay

--
Jay Wang - http://math.research.bell-labs.com/~wang/wang.htm
Bell Laboratories, Lucent Technologies     Tel: (908) 582-7223
600 Mountain Avenue, Room 2C-308,          [email-masked]
Murray Hill, NJ 07974-2070

---

From: [email-masked] (David Wilder)
Date: Wed, 21 Jun 2000 12:01:56 -0400 (EDT)

Very well put Jay.

- Dave

---

From: "alex.mondrus" <[email-masked]>
Date: Wed, 21 Jun 2000 13:47:44 -0400

In general to do an explicit path set up you do not need to use MPLS.

Alex Mondrus

http://www.ipoptical.com

Traffic Engineering - MPLS allows you to set up tunnels

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of David
Wilder
Sent: Wednesday, June 21, 2000 12:02 PM
To: Jay Wang
Cc: [email-masked]; [email-masked]
Subject: Re: TE

Very well put Jay.

- Dave

---

From: "Arup Das" <[email-masked]>
Date: Wed, 21 Jun 2000 14:01:00 -0400

True - you can do that in IP too.

However, in IP if you want to do explicit routing, you need to include the full
path information in each IP packet header. Now, that will dramatically increase
the IP packet header size and consequently, the processing time will increase.
The explicit path used in MPLS has much less overhead compared to that in IP.

--
Regards,
Arup Das
(763-1863)

---

From: Jay Wang <[email-masked]>
Date: Wed, 21 Jun 2000 16:21:34 -0400

Alex,

    Yes, you can statically set up an explicit route for a set of
    flows without MPLS.  But the focus really is in traffic
    engineering. Static routing will not be a proper solution to deal
    with TE for any sizable ISP.  In addition to the salability
    concern as Arup pointed out, there is also a management issue.
    With MPLS, in ISP's management system pertaining to TE each
    tunnel can be handled as a single unit. The signaling and control
    is all done "in the network".  On the other hand, without MPLS the
    ISP's external management system most likely has to provide a
    wrapping (to create a view of a "logical tunnel") that signals and
    coordinates all the participating routers externally.  This raises the
    issue of complexity (as if managing thousands of MPLS-LSPs is not
    complex enough) and perhaps reliability.

- Jay