TCP/IP Tutorial and Technical Overview - IBM Redbooks

A.2.6 Stream merge
Label distribution methods
There are two methods to initiate communication between MPLS nodes to
exchange label information:
► Downstream-on-demand: An LSR can request a label binding for a particular
FEC. The request is made to the next hop MPLS node for that FEC.
► Unsolicited downstream: An LSR can distribute bindings to LSRs that have
not explicitly requested the information.
Both of these distribution techniques can be used in the same network at the
same time. For a given set of peers, the upstream LSR and the downstream
LSR must agree on the technique to be used.
Stream merge is the aggregation of a large number of data flows into a single
downstream flow. The device performing the merge consolidates the individual
streams so that they are treated as a single stream by subsequent MPLS nodes.
The merged stream is represented by a single label. After the merged packets
are transmitted, any information that the packets arrived with different incoming
labels is lost.
Stream merge is a major component of MPLS scalability.
A.3 Emulating Ethernet over MPLS networks
As MPLS gaining popularity, there is a trend to carry non-IP traffic over MPLS
network directly. One example is the encapsulation method for transport of
Ethernet over MPLS networks.
Instead of using Ethernet cable or switch, we use MPLS as the underlying
transport. The Ethernet service operates on top of the MPLS network layer as
illustrated in Figure A-5 on page 940.
Appendix A. Multiprotocol Label Switching 939