Whenever data is moved and we want the data not to follow the routing protocol dedicated path but to redirect to the path which we select for the traffic to follow. When we determined the path for traffic or data to follow so there are some concept on which Multiprotocol Label Switching - Traffic Engineering (MPLS-TE) is based:
When Routing Protocol is configured on a node it results about the interface parameters like Bandwidth information:
1. MPLS-TE also gives us some information like Bandwidth of the link, how much bandwidth is left (remaining) or Bandwidth is available. Basically it gives the link properties (all these are link constraints).
2. Protocol is needed which carry information and these information are carried by Link State Protocol either OSPF or IS-IS.
3. Constraint based SPF or Path Calculation algorithm is needed for the determination of best path to various routes. This CBSPF use many constraints for path selection other than bandwidth.
4. We have to make sure that the connectivity is available on that path which is selected for traffic. Resource Reservation Protocol (RSVP) is used to reserve bandwidth on the path. For example, we need 10 Mbps on a link, so RSVP ensures this much of bandwidth & RSVP also do the label, changing end-to-end changing (information).
Path Message: Which ensure Bandwidth?
Reserve Message: Confirmation of Bandwidth
In TE, the tunnel headed router decided which path the traffic should follow
a: The LSP Path/Tunnel is one way
b: TE Tunnel configuration is done on Head router, that’s why one way
c: We can use RSVP and LDP parallel like some traffic will pass through tunnel which will use Tunnel Label while some traffic will pass out of Tunnel which will use LDP Label.
d: We can have multiple Tunnels so we can have more than one label.
e: In MPLS TE we basically decided: How to allow the traffic in tunnel means How to route the traffic to the tunnel? & How to feed the traffic in Tunnel?
f: In TE we basically engineer, Like we select another path other than the path which is selected by routing protocols. Routing protocols select best path using only metric which TE use many other parameters for it.
I hope this will be informative for you !