A carrier can use four methods to transport your Ethernet frames between MAN sites:
802.1Q tunneling (802.1Q-in-Q [or Q-in-Q, for short])
Ethernet over MPLS (EoMPLS) using Layer 3 tunneling
Access links and 802.1Q were discussed previously. The access link method is equivalent to TLS and is typically implemented using SONET. One problem with access link connections is that they don't scale: The service provider is limited to 4,096 801.1Q VLANs on his trunk, which limits the number of customers it can support. Another problem with access links is that it becomes more difficult for a service provider to manage as you continually add MAN connections. The more connections you have, the more impact they will have on ...