
146 ◾ IP Communications and Services for NGN
1. e 20-bit label field is used to identify the packet to a particular LSP
2. e experimental bits (EXP), 3 bits, identify the class of service, which is used
for priority queuing through the network. At each hop along the path, the
EXP value determines which packets receive preferential treatment within
the tunnel.
3. e Stacking (S) bit shows that this MPLS packet has more than a label asso-
ciated with it.
4. TTL (8 bits), or the time-to-live value, gives the number of hops that this
MPLS packet is permitted to travel in the network. At each LSR, the TTL is
decremented by 1 until the TTL = ...