25.02.2013 Views

TCP/IP Tutorial and Technical Overview - IBM Redbooks

TCP/IP Tutorial and Technical Overview - IBM Redbooks

TCP/IP Tutorial and Technical Overview - IBM Redbooks

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

fast keepalive mechanism between the nodes. The latter is required if lower-level<br />

mechanisms are not available to detect control channel failures.<br />

If the LMP fast keepalive is used over a control channel, LMP Hello messages<br />

must be exchanged over the control channel. Other LMP messages may be<br />

transmitted over any of the active control channels between a pair of adjacent<br />

nodes. One or more active control channels can be grouped into a logical control<br />

channel for signaling, routing, <strong>and</strong> link property correlation purposes.<br />

Link property correlation<br />

Link property correlation is used to synchronize the Traffic Engineering (TE) link<br />

properties <strong>and</strong> verify the TE link configuration. The link property correlation<br />

function of LMP is designed to aggregate multiple data links (ports or component<br />

links) into a TE link <strong>and</strong> to synchronize the properties of the TE link.<br />

As part of the link property correlation function, a “LinkSummary” message<br />

exchange is defined. The LinkSummary message includes:<br />

► The local <strong>and</strong> remote Link_Ids<br />

► A list of all data links that make up the TE link<br />

► Various link properties<br />

A “LinkSummaryAck” or “LinkSummaryNack” message must be sent in response<br />

to the receipt of a LinkSummary message indicating agreement or disagreement<br />

on the link properties.<br />

Additional LMP procedures are defined for link connectivity verification <strong>and</strong> fault<br />

management. These procedures are particularly useful when the control<br />

channels are physically diverse from the data links.<br />

Link connectivity verification is used for data plane discovery, Interface_Id<br />

exchange (Interface_Ids are used in GMPLS signaling, either as port labels or<br />

component link identifiers, depending on the configuration), <strong>and</strong> physical<br />

connectivity verification. This is done by sending Test messages over the data<br />

links <strong>and</strong> TestStatus messages back over the control channel.<br />

Note: The Test message is the only LMP message that must be transmitted<br />

over the data link. The ChannelStatus message exchange is used between<br />

adjacent nodes for both the suppression of downstream alarms <strong>and</strong> the<br />

localization of faults for protection <strong>and</strong> restoration.<br />

Appendix A. Multiprotocol Label Switching 945

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!