The MPLS WG Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] TE
Mike: Please review the following document http://www.seas.upenn.edu/~guerin/publications/qos_ospf_rfc.txt Alex Mondrus http://www.ipoptical.com -----Original Message----- From: owner-mpls@UU.NET [mailto:owner-mpls@UU.NET]On Behalf Of Shahram Davari Sent: Friday, June 23, 2000 11:31 AM To: 'Mike Badil'; mpls@UU.NET Subject: RE: TE Hi Mike, In theory it is possible to do some sort of limited constraint-based routing without Explicit-Routing (with or without MPLS). In order to do that you need to define a new routing protocol (let's call it QoS-OSPF), which can be run on all routers and which can compute the best path according to some predefined constraint. Drawbacks are: 1) All nodes need to do CR computation. 2) You can only support one set of CR rules. Cheers, -Shahram >-----Original Message----- >From: Mike Badil [mailto:hasko10@hotmail.com] >Sent: Wednesday, June 21, 2000 8:49 PM >To: mpls@UU.NET >Subject: Re: TE > > > >Hi > >>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: > >Yes, you are right, explicit routing is clear. I agree with what you >said,but My question was about Constraint Based Routing. How to choose >explicit path(best path according to TE)?, that explicit path is not >shortest path which calculated by OSPF. > > > > >Thanks > > >> >> > 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) >> >> >> > >_______________________________________________________________ >_________ >Get Your Private, Free E-mail from MSN Hotmail at >http://www.hotmail.com >
|
|