User manual

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Cisco 10000 Series Router Software Configuration Guide
OL-2226-23
Chapter 21 Configuring L2VPN Interworking
Ethernet/VLAN to ATM AAL5 Interworking
Figure 21-4 Network Topology for ATM to Ethernet AToM Bridged Interworking
The advantage of this architecture is that the Ethernet PE (connected to the Ethernet segment) operates
similarly to Ethernet like-to-like services.
On the PE with Interworking function, in the direction from the ATM segment to MPLS cloud, the
bridged encapsulation (ATM/SNAP header) is discarded and the Ethernet frame is encapsulated with the
labels required to go through the pseudowire using the VC type 5 (Ethernet) (
Figure 21-5).
In the opposite direction, after the label disposition from the MPLS cloud, Ethernet frames are
encapsulated over AAL5 using bridged encapsulation.
Figure 21-5 shows the protocol stack for ATM to Ethernet AToM Bridged Interworking. The ATM side
has an encapsulation type of aal5snap.
Figure 21-5 Protocol Stack for ATM to Ethernet AToM Bridged Interworking—Without VLAN
Header
ATM AAL5 to Ethernet VLAN 802.1Q AToM—Bridged Interworking
This interworking type provides interoperability between ATM attachment VC and Ethernet VLAN
attachment VC connected to different PE routers. Bridged encapsulation is used, corresponding to the
Bridged (Ethernet) Interworking mechanism.
270312
Ethernet
VPI/VCI
ATM Link Ethernet Link
Tunnel LSP
Pseudowire using EoMPLS
P Router
P Router PE
PE with
interworking
function
ATM CE
MPLS Network
Ethernet
CE
270313
ATM
CE
ATM
PE
Eth
PE
Eth
CE
ATM EthernetMPLS Emulated VC of
ATM Header
MAC Header
DA
SA
MAC Header
Control Word
Tunnel Label
VC Label
DA
SA
Type/Length Type/Length Type/Length Type/Length
Remainder of
MAC Frame
Remainder of
MAC Frame
Remainder of
MAC Frame
Remainder of
MAC Frame
CPCS - UU CPI
Length
CRC
LLC (AA-AA)
LLC(03) OUI (00)
OUI (80-C2)
PID (00-07)
PAD (00-00)
MAC Header
Control Word
Tunnel Label
VC Label
DA
SA
MAC Header
DA
SA
LAN FCS