1. Multi-Protocol Label Switching University of Southern Queensland

2. MPLS  Packets have an additional field  A stack of labels  Labels lie between IP and link layer  Routers use the labels instead of the IP destn field  Routing is faster because labels are local to each router.

3. Label Switching Table of next label/hop for each label Label Switching Table of next label/hop for each label Label Switching Table of next label/hop for each label  Label table per incoming port.  label -> (new label, next link), OR  label -> pop

4. Label Switched Path (LSP)  A label switched path is like a tunnel.  At the end of an LSP, the label is popped.  If there is another label, use this.  If there is no label, use the router's RT, as usual.

5. Advantages of MPLS  Much smaller tables  forwarding rather than routing  LSP's can have special treatment.  LSP's might use a special technology, eg ATM, WDM.  LSP's keep traffic classes separate.

6. Disadvantages of MPLS  Additional complexity  LSP's must be set up and managed.

7. Example – Campus Router/Switch  When a tcp connection is set up, create an entry in a forwarding table in the switch, one table for each incoming port.  In this way, packets can be forwarded by the switch without the need for routing.  No need for a label in this case.  To generalise this idea, use labels.

8. History  ATM was perceived to have an efficiency advantage due to the use of forwarding rather than routing.  E.g. major Telco's have used ATM transport network, running IP over the top, for cost reasons.  MPLS can achieve similar efficiency to ATM.

9. Present  MPLS is currently proposed as a means to provide network wide VLAN's and/or VPN.  MPLS provides virtual isolation of traffic without real segregation.  (Segregation of traffic is very inefficient).

10. MPLS and WDM  Wavelengths can also be treated as tunnels across the Internet.  In this instance, the wavelength is operating like the label.  Similarly, SDH paths can be regarded as LSP's.

11. Optimization / Efficiency  Using an end-to-end LSP is very efficient as regards routing.  But, if an LSP carries very little traffic, utilization of the path could be very low.  If bandwidth must be reserved for the LSP, this will be inefficient.

12. How to Optimize  Manage bandwidth reserved for each LSP  If LSP bandwidth falls below a certain level, close it down.  If a path through a higher layer network carries more than a certain threshold level of traffic, set up an LSP, or wavelength, or SDH path, to carry it.

13. Example  Suppose I start a download of a large video from across the Internet.  The mechanisms of dynamic GMPLS (Generalised MPLS, ie MPLS including WDM and SDH) will respond to this by setting up a wavelength, end-to-end.  The efficiency of this way of handling this traffic is fantastic.  In addition, if an LSP is set up, peformance will be better (less buffering, less congestion).

14. Why a label stack?  In many cases, the stack will have just one entry.  In some cases, the label will be implied rather than explicit.  However, it can happen that one link in an LSP is really another LSP. In this case, we need the stack.  The top label is the only one referenced, till that LSP ends. Then the label is popped off and the LSP underneath is followed.

15. Performance Differentiation  It is conceivable that LSP's can also be given special, or different treatment, from each other.  E.g. a wavelength will have no buffering and minimal delay. The same is true of an SDH path.  An LSP through the Internet might not really have protection, however. This should not be assumed.