RPR

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RPR

(Resilient Packet Ring) A packet-based protocol that provides fault tolerance and statistical multiplexing for the metropolitan and national SONET and Ethernet networks of the carriers. The RPR architecture is often added to SONET networks to enable them to carry packets. RPR is a data link layer protocol (layer 2) that uses dual counter-rotating rings for fault tolerance.

RPR nodes, which contain the RPR interface cards, are typically routers and switches in a packet environment (Ethernet) or add/drop multiplexers (ADMs) in a TDM environment (SONET). The IEEE has standardized RPR with its 802.17 specification.

Counter-Rotating Rings
RPR nodes are connected in a ring topology by two fibers, each transmitting in the opposite direction. Both inner and outer ringlets are active at the same time. If a failure occurs, traffic capacity is decreased.

Packets move through every node in the ring up to the destination node, where they are stripped off. In an RPR, traffic from multiple nodes travels on the ring concurrently.

RPR includes a "fairness" algorithm. Since packets pass through all intermediate nodes, a node can notify the others to slow the transmission if it cannot get its fair share of bandwidth on the ring to transmit. This traffic adjustment enhances the statistical multiplexing and ensures fair access during congestion. Since SONET interleaves fixed channels, "RPR over SONET" turns SONET into a more dynamic network. See TDM network, SONET and statistical multiplexor.


Normal Operation
Under normal operation, data flows in both ringlet 0 and ringlet 1. In case of failure, overall bandwidth is reduced.







Wrapping the Packets
If a line breaks, the ring is reconfigured using ringlet 0 and 1 together. RPR "wrapping" causes the two nodes at either side of the break to become return nodes and provides the fastest recovery.







Steering the Packets
RPR "steering" can restore a damaged network and also shorten the number of hops packets take compared to wrapping. However, steering takes a little bit longer to complete as all nodes in the network have to be reconfigured. Sometimes, wrapping is performed immediately, and steering is performed afterwards.
References in periodicals archive ?
Before the event got under way, Congressman Paul conducted a brief press conference in which he declared that the Rally for the Republic was being staged to celebrate the freedom movement and to satisfy the enthusiasm for its message.
He narrated a video presentation expanding on what Ron Paul said during his press conference and on the ad that appeared in the Rally for the Republic magazine.
Chirac founded the Rally for the Republic during his tenure as Paris mayor.
The Rally for the Republic made plain that Ron Paul Republicans will have no truck with McCain or Obama.
5 per cent of the vote, almost equalling the 13 per cent score for President Chirac's Rally for the Republic party.
It's obvious that the president will be a candidate to renew his mandate," Philippe Seguin, president of Chirac's Rally for the Republic, said.
PARIS: The head of France's conservative Rally for the Republic party has taken temporary command of a new alliance created to salvage the Right, crippled in two sets of elections that brought defeat and disgrace.
Mr Philippe Seguin was informally named president of the Alliance for France which will bring together the Rally for the Republic (RPR) - the party of President Chirac - and the Union for French Democracy (UDF), a federation of centre-right parties that all but collapsed in the wake of the regional voting.
In last month's regional elections, national leaders of the two main right-wing parties, the Rally for the Republic and the Union for French Democracy , ruled out power deals with the National Front, which was denounced as "racist and xenophobic" byPres ident Chirac.
The mainstream right as it is now organised, with President Jacques Chirac's Rally for the Republic (RPR) and its centrist Union for French Democracy (UDF) allies, could be split.
National leaders of the UDF and its conservative partner the Gaullist Rally for the Republic predicted the deals sealed by local rightists would condemn the mainstream Right to a long period of bitter division and drive away many voters.
Jean-Francois Mancel was thrown out of the Rally for the Republic hours after he released an article which called for the need to forge links with the hardline, anti-immigrant National Front.