Suppose you are the CTO of a company which operates in a wide area covering several metro areas and offers core network services mainly to business customers including other ISP. With all the network neutrality discussions aside, you decided to differentiate the customer traffic based on the QoS requirements of the customers. After evaluating a number of networking technologies, you consider MPLS (Multi-Protocol Label Switching) to be the networking technology in your core network for the conceivable future.
Explain how ATM and Metro Ethernet traffic can be mapped to L-LSP and E-LSP connections while preserving the QoS requirements. In MPLS-ATM QoS Inter-working, consider only provisioned connections.
Some background on QoS support of MPLS: MPLS supports traffic engineering through creation of virtual connections (aka Label Switched Paths - LSPs) with specified bandwidth rates. It supports QoS by realizing the Differentiated Services (DiffServ) service classes. The following are the main DiffServ QoS classes supported:
• Expedited Forwarding (EF): This is the highest priority class.
• Assured Forwarding (AF): There are actually four of them as AF1, AF2, AF3 and AF4. These are the next level of priority after EF. Within this family, AF1 is the highest, AF2 is the next and so on.
• Best Effort (BE): This is the lowest priority. Usually no resource is reserved for this class.
There are also others but we will not worry about them.
With MPLS, operators may create two kinds of virtual connections:
• L-LSP: This is an MPLS connection carrying packets of a single QoS class (e.g. EF only).
• E-LSP: This is an MPLS connection carrying packets of up to 8 different QoS classes.
Both L-LSPs and E-LSPs allow creation of MPLS connections with reserved bandwidth rates (e.g. You may create an L-LSP with 620M rate).
ATM has service categories of CBR, VBR (rt and nrt), ABR and UBR. CBR and VBR are of highest priorities. ABR is next and UBR is last. Resources (i.e. bandwidth) is allocated for all service categories except UBR.
Metro Ethernet has 8 levels of priority where level 0 is lowest and level 7 is highest. Resources may or may not be allocated for different priority levels.