What are two methods to achieve differentiated QoS in MPLS? (Choose two)
A.
By creating a separate Label Switch Path for each class.
B.
By using the experimental bits to identify the different classes.
C.
By using the DiffServ Codepoints to identify the different classes.
D.
By using the TOS bits in the Layer 3 header to identify the different classes.
Explanation:
Two general approaches are used to mark MPLS traffic for QoS handling within an MPLS network in the first method, the DiffServ "coloring" information is carried in the experimental (EXP) field of the MPLS shim header. This field allows for eight different QoS markings. Label Switched Paths (LSPs) using this approach are called E-LSPs, signifying that QoS information is inferred from the EXP field. Alternatively, IETF specifications allow for a second method of carrying the DiffServ information. Here, the label associated with each MPLS packet carries the portion of the DiffServ marking that specifies how a packet should be queued. The dropping precedence portion of the DiffServ marking is carried either in the EXP field, if an MPLS shim header is being used, or on fields available for this purpose on underlying technologies (for example, CLP bit for ATM and DE bit for Frame Relay). Switching paths within the MPLS network using this approach are called L-LSPs, signifying that QoS information is inferred, in part, from the MPLS label.
LSPs supporting DiffServ may be established with bandwidth reservation. That is, bandwidth requirements for a label switched path could be signaled at LSP establishment time. Bandwidth reservation could be used to perform admission control on the DiffServ resources that have been provisioned. Though admission control can be performed on an LSP basis, the QoS design within the MPLS network is DiffServ-based, taking advantage of the scalability benefits implicit in that QoSarchitecture.
Reference:
http://www.cisco.com/en/US/tech/ CK4 36/ CK4 28/technologies_white_paper09186a00800a4455.shtml