The MPLS WG Archive

["Arup Das" <arupdas@nortelnetworks.com>]

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.
"alex.mondrus" wrote:

> 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
> >         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.
>
> -----Original Message-----
> From: owner-mpls@UU.NET [mailto:owner-mpls@UU.NET]On Behalf Of David
> Wilder
> Sent: Wednesday, June 21, 2000 12:02 PM
> To: Jay Wang
> Cc: hasko10@hotmail.com; mpls@UU.NET
> Subject: Re: TE
>
> Very well put Jay.
>
> - Dave
>
> > 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
> >
> > David Charlap wrote:
> >
> > > 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:
> > > >
> > > > What makes MPLS to support constraint based routing?
> > >
> > > 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.
> > > > Why it is not possible without MPLS.
> > >
> > > 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
> >
> > --
> > 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,          wang@research.bell-labs.com
> > Murray Hill, NJ 07974-2070
> >
> >
> >

--
Regards,
Arup Das
(763-1863)