Enhanced Packet Loopback Device
Original Publication Date: 2003-Oct-25
Included in the Prior Art Database: 2003-Oct-25
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The use of loopback modes is relevant, for example, to optical transport networks to check the service availability of the carrier network between the interfaces and the customer devices. For packet switched technologies, the use of simple loopback mechanisms is not possible, since the routing tables become inconsistent. A packet switched device consists of an ingress port, where the packets enter the device, an egress port, where the packets exit the device, and a routing block, which is responsible for routing the ingress traffic to the destination egress port (Fig. 1). The loopback is done by directing the traffic from the egress side of port B back to the ingress side, and then using the routing mechanism to forward the packet back to port A. The packet carries the source and destination address, an ingress and an egress port. The routing mechanism uses the information of the source and destination fields, associated with the ingress and egress ports, to build the routing table. A problem occurs when the loopback is activated, since the routing block will receive packets coming from the ingress port of side B, where it has just sent them to, thus, contradicting its routing table. There are some test devices which allow to implement "smart" loopbacks, but these are usually stand-alone units to be placed at the connection end points in case of maintenance. The use of such devices leads to considerable intrusion into the carrier network, as well as increased costs.