Headquarters Harris Stratex Networks, Inc.

Research Triangle Park

637 Davis Drive

Morrisville,

North Carolina 27560

United States

Tel: 919-767-3230

Fax: 919-767-3233

www.harrisstratex.com

White Paper

Eclipse RWPR: Carrier-Class RSTP

Keynote No. 5 This is White

Paper No. 5 in a

series produced

by Harris Stratex

Networks on

Carrier Ethernet.

This paper introduces RSTP, and the Eclipse RWPR enhancements to RSTP to realize carrier-class switching times.

RWPRTM (Resilient Wireless Packet Ring) enhances industry-standard RSTP with a unique rapid failure detection (RFD) capability to provide carrier-class network reconvergence times on Eclipse GigE ring and mesh networks. Depending on the network topology, reconvergence (service restoration) times are as low as 50 ms.

RWPR delivers reliable and consistent RSTP operation, even in the presence of link fading. It may be used over Eclipse radio and fiber links, and over Eclipse link-aggregated links.

Eclipse RWPR networks satisfy the MEF (Metro Ethernet Forum) Carrier Ethernet guidelines for service availability (redundancy) on RSTP ring and mesh networks.

Only Eclipse GigE incorporates an intelligent layer 2 switch that supports carrier-class RSTP on wireless networks.

RWPR is a Harris Stratex Networks development. A patent is pending.

Background First there was STP, then RSTP, to support Ethernet operation on ring and mesh networks.

Reconvergence

times on Carrier

Ethernet networks

must be sub-

second.

STP (Spanning Tree Protocol) is a link management protocol for media access control bridges (Layer 2 switches). Its purpose is to prevent live network loops and to provide path redundancy in networks where two or more paths exist between network nodes. But STP suffers from long re-convergence times. It can take up to 50 seconds or more for a network to be restored to service after a path failure.

RSTP (Rapid Spanning Tree Protocol) was introduced in 1998 as an evolution of STP. For an RSTP network comprising external switches with radio point-to-point links, reconvergence times are typically in excess of 1 to 2 seconds, though can be longer than 7 seconds where the radios do not incorporate a port shutdown capability on link failure.

For carrier-class Ethernet (Carrier Ethernet) network reconvergence times need to be more than an order of magnitude better. MEF reliability (redundancy) guidelines call for reconvergence times as low as 50ms.

To this end, various proprietary enhancements have been introduced by switch vendors. These typically bypass the normal port-port handshaking needed to confirm that a physical path has failed.

RWPR, as incorporated in Eclipse GigE switches, represents a particularly effective enhanced RSTP protocol. When configured in Eclipse ring and mesh networks, reconvergence times are reduced to as low as 50 mS.

1/25/2008 Carrier Ethernet #5 Eclipse Carrier Class RSTP.doc Page 1 of 2

1/25/2008 Carrier Ethernet #5 Eclipse Carrier Class RSTP.doc Page 2 of 2

Copyright 2008 Harris Stratex Networks, all rights reserved.

White Paper

Introduction to RWPR RSTP action when a link failure occurs involves failure detection and subsequent reconfiguration of the network to bypass the failed link. RWPR virtually

eliminates RSTP

failure detection

time and

accelerates the

convergence

process.

For an RSTP network comprising Ethernet wireless links and external RSTP switches, there are two primary link failure detection mechanisms, the aging out of keep-alive messages between switches either side of the failure, or the shutdown of the Ethernet ports on the failed link.

For a radio link that does not have a port shutdown capability, failure detection using the aging out of keep-alive messages typically takes 6 seconds.

For a radio link that does have a port shutdown capability, sub-second failure detection times are possible.

Subsequently, the RSTP process reconfigures the network, which may take up to 1 second or more.

Overall, reconvergence times are typically in excess of 7 seconds for radios that do not have a port shutdown capability, or 2 seconds where they do.

Eclipse RWPR

delivers carrier-

class network

reconvergence

times.

Eclipse RWPR essentially eliminates failure detection time (less than 1 ms) using a unique rapid-failure-detection (RFD) mechanism, then uses dynamic message timing to accelerate the RSTP convergence process. The result is carrier-class reconvergence times:

On a 5-node 150 Mbit/s or 300 Mbit/s Eclipse ring, reconvergence times are typically 50 ms.

On a 10-node 150 Mbit/s or 300 Mbit/s Eclipse ring, reconvergence times are typically 100 ms.

These times meet MEF (Metro Ethernet Forum) carrier Ethernet guidelines for service availability on RSTP ring and mesh networks.

For more detailed information on RWPR operation, see Paper No. 6 in the Harris Stratex Networks Carrier Ethernet series.

Summary Only Eclipse GigE RWPR wireless links incorporate the intelligence needed to support carrier-class RSTP reconvergence times.

Eclipse RWPR delivers performance that cannot be equaled using external RSTP switches with radio links.

For information on Eclipse GigE Intelligent L2 operation, see Paper No. 2 in the Harris Stratex Networks Carrier Ethernet series.

Eclipse RWPR: Carrier-Class RSTPKeynoteBackgroundIntroduction to RWPRSummary