QoS in MPLS VPN Networks

BC.

MPLS VPN (RFC 2547bis) networks use Quality of Service (QoS) mechanisms to ensure that different types of traffic are treated according to their relative priorities. Here are the explanations for each answer:

A. MPLS QoS is a scalable and simple solution because it only requires application at the Edge-LSR.

This statement is not entirely accurate. While MPLS VPN QoS is simpler than other QoS solutions, it requires the application of QoS policies at all LSRs (Label Switching Routers) along the LSP (Label Switched Path). However, compared to traditional IP-based QoS mechanisms, MPLS VPN QoS is simpler and more scalable because it uses the MPLS label stack to carry QoS information rather than relying on per-packet processing.

B. MPLS can force packets into specific paths and bandwidths based on Edge-LSR mapping of DSCP to EXP.

This statement is accurate. MPLS VPN QoS uses the EXP (Experimental) field in the MPLS header to carry QoS information. The Edge-LSR maps the DSCP (Differentiated Services Code Point) value of the IP packet to the EXP field of the MPLS header. The EXP field is used by the intermediate LSRs to determine the QoS treatment of the packet, such as which path to take and what bandwidth to allocate.

C. DiffServ information must be made known to the LSR in the MPLS header using the EXP field.

This statement is accurate. MPLS VPN QoS uses the DiffServ (Differentiated Services) model to carry QoS information. The DSCP value in the IP header is used to classify the traffic into different service classes, which are then mapped to the EXP field in the MPLS header. This allows the intermediate LSRs to apply the appropriate QoS treatment based on the service class of the packet.

D. On egress from the Edge-LSR, the EXP field is used for PHB QoS towards the C.

This statement is not entirely accurate. The EXP field is used by all LSRs along the LSP to provide QoS treatment to the packet. On egress from the Edge-LSR, the EXP field is used to provide QoS treatment to the packet based on the service class and the QoS policies configured at the Edge-LSR. The packet is then forwarded to the appropriate CE (Customer Edge) device based on its destination address.