The figure below presents a network applying the multi-protocol label switching (MPLS) principle.

The network consists of routers and links. We distinguish two types of routers: Label edge routers (LER) and label switching routers (LSR).

The LSR performs one of the following label operations:

Swapping: replace current label by a new label.

Pushing: move label onto label stack.

Popping: remove label from label stack.

• Who assigns incoming packets to a FEC and based on which criteria?
• Explain briefly the use of the TTL field in the shim header. Which other protocol includes a TTL field?
• How many service classes can MPLS support?
• How many different labels does MPLS support, knowing that labels ranging from 0 to 15 are reserved for special purposes?

LSP2 IP packet LER IF LSP Label = 45 LSR5 IF2 IF LSR2 TF2 LSP 3 IF IF 2 LSR4 LSP 1 Label = 1234 MPLS cloud IP packet LER3 IF: Interface