New-generation Protocols 97
frame traffic on the MAC address. This solution, said to be MIM
(MAC-in-MAC), encapsulates the client’s MAC address in an
operator MAC. This means that the core operator only needs to know
its own MAC addresses. In the PBB network, the matching of the user
MAC addresses and network MAC is known only by the edge nodes,
thus preventing the combinatorial explosion of the number of MAC
addresses.
The third solution, called PBT (Provider Backbone Transport), is
fairly similar to the MPLS technique, but provides the properties
necessary for Carrier Grade, such as unavailability of less than 50 ms.
In a manner of speaking, this is a secured MPLS tunnel. The PBT
tunnel is created like an MPLS tunnel, with the references
corresponding to the endpoints of the network. The client and server
VLAN numbers are encapsulated in the MPLS tunnel, which may,
itself, have differentiation into operator VLANs. Thus, the real
reference is 24 + 48 bits, so 72 bits.
The last solution is that of the service PS (PseudoWire) offered by
MPLS. In this case, the user and operator VLANs are encapsulated in
an MPLS service tunnel, which may, itself, be encapsulated in an
MPLS transport tunnel. This solution stems from the encapsulation of
tunnels in MPLS.
Carrier-Grade Ethernet technology is of interest to numerous
operators. Only time will tell which solution ultimately wins out.
However, even at this stage, it can be conclusively stated that VLANwithin-VLAN encapsulation will be present in all such solutions.
4.6. TRILL (Transparent Interconnection of a Lot of Links)
TRILL (Transparent Interconnection of Lots of Links) is an IETF
standard implemented by nodes called RBridges (routing bridges) or
TRILL switches. TRILL combines the strong points of bridges and
routers. Indeed, TRILL determines a level-2 routing using the state of
the links. RBridges are compatible with level-2 bridges defined in the
IEEE 802.1 standard, and could gradually come to replace them.
RBridges are also compatible with IPv4 and IPv6 routers, and
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frame traffic on the MAC address. This solution, said to be MIM
(MAC-in-MAC), encapsulates the client’s MAC address in an
operator MAC. This means that the core operator only needs to know
its own MAC addresses. In the PBB network, the matching of the user
MAC addresses and network MAC is known only by the edge nodes,
thus preventing the combinatorial explosion of the number of MAC
addresses.
The third solution, called PBT (Provider Backbone Transport), is
fairly similar to the MPLS technique, but provides the properties
necessary for Carrier Grade, such as unavailability of less than 50 ms.
In a manner of speaking, this is a secured MPLS tunnel. The PBT
tunnel is created like an MPLS tunnel, with the references
corresponding to the endpoints of the network. The client and server
VLAN numbers are encapsulated in the MPLS tunnel, which may,
itself, have differentiation into operator VLANs. Thus, the real
reference is 24 + 48 bits, so 72 bits.
The last solution is that of the service PS (PseudoWire) offered by
MPLS. In this case, the user and operator VLANs are encapsulated in
an MPLS service tunnel, which may, itself, be encapsulated in an
MPLS transport tunnel. This solution stems from the encapsulation of
tunnels in MPLS.
Carrier-Grade Ethernet technology is of interest to numerous
operators. Only time will tell which solution ultimately wins out.
However, even at this stage, it can be conclusively stated that VLANwithin-VLAN encapsulation will be present in all such solutions.
4.6. TRILL (Transparent Interconnection of a Lot of Links)
TRILL (Transparent Interconnection of Lots of Links) is an IETF
standard implemented by nodes called RBridges (routing bridges) or
TRILL switches. TRILL combines the strong points of bridges and
routers. Indeed, TRILL determines a level-2 routing using the state of
the links. RBridges are compatible with level-2 bridges defined in the
IEEE 802.1 standard, and could gradually come to replace them.
RBridges are also compatible with IPv4 and IPv6 routers, and
www.it-ebooks.info