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The destination MAC/IP (and/or VLAN) of the duplicated packets can be different as the chip supports more than
one MAC/IP address in the packet classifier.
10.6.17 OAM Signaling
TDMoP bundles require a signaling mechanism to provide feedback regarding problems in the communications
environment. In addition, such signaling can be used to collect statistics related to the performance of the
underlying PSN. The OAM procedures detailed below are ICMP-like.
10.6.17.1 Connectivity Check Messages
In most conventional IP applications, a server sends some finite amount of information over the network after an
explicit request from a client. With TDM-over-Packet, the source sends a continuous stream of packets towards the
destination, without knowing whether the destination device is ready to accept them, leading to flooding of the
PSN. The problem may occur when a TDM-over-Packet gateway fails or is disconnected from the PSN, or the
bundle is broken. After an aging time, the destination gateway disappears from the routing tables, and intermediate
routers may flood the network with the TDM-over-Packet traffic in an attempt to find a new path.
The solution to this problem is to significantly reduce the number of TDM-over-Packet packets transmitted per
second when bundle failure is detected, and to return to full rate only when the bundle is restored. The detection of
failure and restoration is made possible by the periodic exchange of one-way connectivity check messages.
Connectivity is tested by periodically sending OAM messages from the source gateway to the destination gateway,
and having the destination reply to each message.
The connectivity check mechanism can also be useful during setup and configuration. Without OAM signaling, one
must ensure that the destination gateway is ready to receive packets before starting to send them. Since TDM-
over-Packet gateways operate full duplex, both must be set up and properly configured simultaneously to avoid
flooding. By using the connectivity mechanism, a configured gateway waits until it can detect its destination before
transmitting at full rate. In addition, errors in configuration can be readily discovered by using the service-specific
field.
10.6.17.2 Performance Measurements
In addition to one-way connectivity, the OAM signaling mechanism can be used to request and report on various
PSN metrics, such as one-way delay, round trip delay, packet delay variation, etc. It can also be used for remote
diagnostics, and for unsolicited reporting of potential problems (e.g. dying gasp messages).
10.6.17.3 Processing OAM Packets
In the Ethernet-to-CPU direction, the device identifies OAM packets as described in section
10.6.13.3.In the CPU-to-Ethernet direction the chip timestamps packets when the
Stamp field of the buffer descriptor field is
set. The timestamp location in the packet is specified by the
Ts_offset buffer descriptor field. When the CPU
transmits an OAM packet, the buffer descriptor must identify the packet as a non-TDMoP/MPLS packet (i.e. is not
assigned to any bundle), as other packet types are not time-stamped in any case.