Alcatel-Lucent 7750 SR OS - ATM Virtual Trunk over IP;MPLS Packet-Switched Network; Figure 17: VT Application Example

Virtual Leased Line Services
7750 SR OS Services Guide Page 115
ATM Virtual Trunk Over IP/MPLS Packet-Switched Network
Figure 4: VT Application Example
ATM virtual trunk (VT) implements a transparent trunking of user and control traffic between two
ATM switches over an ATM pseudowire. Figure 17 depicts ATM 2 and ATM 3 switches that
appear as if they are directly connected over an ATM link. Control traffic includes PNNI signaling
and routing traffic.
The virtual trunk (VT) SAP on a 7750 PE is identified by a tuple (port, VPI-range) meaning that
all cells arriving on the specified port within the specified VPI range are fed into a single ATM
pseudowire for transport across the IP/MPLS network. Note that a user can configure the whole
ATM port as a VT and does not need to specify a VPI range. No VPI/VCI translation is performed
on ingress or egress. Cell order is maintained within a VT. Note that, as a special case, the two
ATM ports could be on the same PE node.
By carrying all cells from all VPIs making up the VT in one pseudowire, a solution is provided
that is both robust, for example no black holes on some VPIs but not others, as well as
operationally efficient since the entire VT can be managed as a single entity from the Network
Manager (single point for configuration, status, alarms, statistics, etc.).
ATM virtual trunks use PWE3 N:1 ATM cell mode encapsulation to provide a cell-mode transport,
supporting all AAL types, over the MPLS network. Cell concatenation on a pseudowire packet is
supported. The SDP can be of an MPLS or a GRE type.
The ATM PW is initiated using Targeted LDP (TLDP) signaling (defined in draft-ietf-pwe3-
control-protocol-xx.txt, Pseudowire Setup and Maintenance using LDP). In this application, there
is no ATM signaling on the 7750 gateway nodes since both endpoints of the MPLS network are
configured by the network operator. ATM signaling between the ATM nodes is passed
transparently over the VT (along with user traffic) from one ATM port on a 7750 PE to another
ATM port on a remote (or the same) 7750 SR PE.
PW2
PW1
VT1
VT1
VT2
VT2
PE2PE1
7750 SR
(PE2)
7750 SR
(PE1)
ATM 2
ATM 1
CE1
ATM 3
ATM/PNNI
ATM/PNNI
ATM/FR
UNI
CE2
ATM 4
ATM 5
IP/MPLS
ATM Edge
ATM Edge
OSSG054
Virtual Trunks
On ATM Link
PSN Tunnel N:1 ATM PWs