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Technology Stocks : Nortel Networks (NT) -- Ignore unavailable to you. Want to Upgrade?

To: Kenneth E. Phillipps who wrote (9538)	2/3/2001 2:46:31 PM
From: Kenneth E. Phillipps	Read Replies (2) \| Respond to of 14638

An excellent explanation for a layman like myself as to how MPLS works at the optical layer. This explains how a channel is set aside as a control channel for signaling to allow communication with the other network elements. See the part in bold. computertelephony.com " Even in the non-optical IP world, there are downsides to taking a look at each and every packet. This has given rise to the IETF's multi-protocol label switching (MPLS) protocol. As originally conceived, MPLS made it more efficient to send IP traffic across ATM networks. Routers at the edge of the ATM mesh operate at slower throughput rates and can comfortably consider each packet. With a destination and route determined for the packets from a given session, however, the routers affix a highly abbreviated routing label to the front of each packet. Switches in the ATM fabric are able to route those packets into the correct circuit with considerably less overhead, meaning that their higher throughputs aren't compromised. The same idea applies in the context of optical switching, except that there aren't actually tags affixed to the front of whatever packets may be traveling in the data streams (which may or may not be packet oriented). "We're bringing the control plane from the data world to the transmission world," says Lucent's Austin. "The connections are circuit-based as opposed to packet-based - traditionally the circuits have been controlled with operations support systems - so, out of band control. This is the first time we'll bring intelligence to the switch so that the network element is aware of who its neighbors are and can set up connections. The customers basically request a connection between points and the LambdaRouters cooperate to make that happen. "So in terms of the transmissions, it's still a circuit type of connection. But from a control plane perspective, it's more similar to a router than it is to a traditional cross connect. What typically happens is that on a fiber you have a DWDM system that's dividing the fiber up into a large number of wavelengths and one of those wavelengths is used as a control channel for the network elements to communicate." At present, the control channel uses proprietary signaling, but signaling that's generally modeled on MPLS. The signaling arrives at the switch in the form of photons, which are converted via OEO to electronic packets that provide instruction for which inputs are to be aimed at which outputs. There's a lot less signaling than there is data on the non-control channels, so the time required for OEO on the out-of-band signaling channel is unimportant."