resilient packet rings

Resilient Packet RingsThe way forward

Pranav KoushikSurbhi Sinha

WHITE PAPER - December 2001

Wipro TechnologiesInnovat ive Solut ions, Qual i ty Leadership.

© Wipro Technologies Page :

White Paper

Table of Content

Introduction .....................................................................................................01

Limitations of current technologies ............................................................... ... 01

Packet Ring Technology .................................................................................. 02

Advantages of Packet Ring Technology.............................................................. 03

Packet Ring Applications.................................................................................. 03

Packet Ring standards .................................................................................... 04

Pre standard development ................................................................................04

Wipro�s expertise ............................................................................................ 05

Conclusion.......................................................................................................05

About the Authors.............................................................................................06

About Wipro ....................................................................................................08

Wipro in Telecommunication Technologies .........................................................08

Resilient Packet Rings

Page: Table of Content


White Paper Resilient Packet Rings

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Introduction

Packet based networks are moving from the LAN to MAN. This increase in the data traffic

in the MAN has posed considerable challenges as the MAN was traditionally designed for

circuit switched voice services. Inefficiencies of carrying increasing amounts of data traffic

over voice�optimized circuits make it difficult for service providers to provision new

services. Packet based transport technology, which is a natural fit for the IP protocol, is

considered by many as an alternative for scaling today�s metro networks.

Gigabit Metro Ethernet is the first step in optimizing the MAN for packet-based transport.

Most of the Internet Protocol traffic today begins and ends its trip on the Internet as

Ethernet frames. Hence, carrying data in consistent format from start to finish reduces

complexity and costs.

This paper gives an overview of the emerging technology, information on the

standardization effort and gives a case study of work being done at Wipro. Engineers and

Managers involved in developing Network elements based on the Packet Ring technology

may use this paper.

1. Limitations of current technologies

SONET transport

Some of the disadvantages of SONET based transport are listed below.

Fixed Circuit based transportPoint-to-point circuits are provisioned for nodes on a SONET ring. Each circuit gets

a fixed amount of bandwidth. This fixed allocation of bandwidth limits the maximum

burst traffic data between nodes. Also, when the circuit is not being used that

bandwidth is wasted. N new point-to-point connections need to be created for each

added node.

Bandwidth utilisationIf a mesh topology network is to be designed, the ring bandwidth needs to be

divided by the number of provisioned circuits. Apart from this inefficient use of ring

bandwidth, provisioning these circuits is also difficult. Another reason for inefficient

utilisation of bandwidth in SONET rings is the bandwidth dedicated for protection

switching mechanism.

Multicast TrafficMulticast traffic requires each node on a SONET ring to send a separate copy of the

packet to each destination. This results in multiple packets travelling around the

ring, wasting the bandwidth.

Expensive TDM interfaces on IP devicesTo enable IP routers to sit on SONET rings, these devices have to be provided with

expensive SONET / SDH/POS interfaces.


White Paper Resilient Packet Rings

Ethernet transport

Some of the disadvantages of Ethernet are listed below.

ResiliencyEthernet does not make good use of Ring topology for protection mechanisms.

Using link aggregation (802.1ad) link level protection can be provided. But this is

comparatively slow. (~500ms).

Bandwidth SharingBandwidth sharing on a ring is not effective by using Ethernet. Ethernet switches

are equipped to provide link level fairness but this does not translate into a global

fairness policy.

2. Packet Ring Technology

With the disadvantages listed above in mind, we will examine the Packet Ring

technology and some of its advantages. As shown in Figure 1 below, the packet ring

technology is focussed on creating only a new Media Access Control (MAC)

addressing scheme for ring-based networks. The advantage of this approach is that

Physical Layer is left open. This makes Packet ring technology compatible with

SONET, Ethernet, DWDM and any new physical layer standards. Thus, Packet Rings

can operate over existing SONET rings, optimising them for better data services

without the need to abandon SONET equipment or voice traffic. In case where dark

fiber is available, a packet ring can operate without the need to purchase expensive

layer 1 equipment.

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Figure 1: Layers of Packet Ring Technology.................................................................................................................

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The packet ring technology standard is bound in scope to the MAC layer. The functions

that will be addressed by this technology are

n MAC addressing

n Packet forwarding

n Topology discovery

n Protection mechanism

n Global bandwidth fairness algorithm

3. Advantages of Packet Ring Technology

Bandwidth efficient for packets

The bandwidth efficiency of the ring is increased by statistical multiplexing techniques.

Dynamic bandwidth sharing

Due to the dynamic nature of bandwidth allocation, no bandwidth is wasted because

of pre-allocation as it happens on SONET rings. Spatial reuse of bandwidth between

nodes is possible.

Simple topology discovery mechanism

There is a need to create N new point-to-point circuits for each new node added in

today�s SONET network. Providing a topology discovery mechanism that each node

goes through on startup eliminates this drawback.

Ring protection

One of the key objectives of the new Packet Ring technology is to provide SONET

comparable protection switching mechanism. This mechanism can co-exist with the

SONET Automatic Protection Switching (APS) mechanism.

Broadcast and Multicast Support

The nodes on a packet ring simply forward the multicast/broadcast packet until it is

stripped out of the ring by the source. Thus on a packet ring multicast and broadcast is

supported by transmitting only one copy of the packet.

4. Packet Ring Applications

Packet ring technology can meet the needs of many service providers. It is helpful

anywhere data transport over a ring is needed and resiliency and bandwidth sharing

are also essential. One example is a metro service provider who wants to provide data

transport services without the SONET overhead. Packet rings can fit ideally in such


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cases. Here a Packet ring can serve multiple buildings in a given geography. With such

a solution in place the Metro service provider can sell protected bandwidth with < 50 ms

failover to the customers. The fairness algorithm ensures that all nodes on the rig get a

fair share of the bandwidth preventing a single node from hogging all the available

bandwidth.

5. Packet Ring standards

The IEEE 802.17 RPR working group is developing a standard that will define a Resilient

Packet Ring Access protocol. The working group has been approved and a plenary

meeting was held in March 2001. Some of the goals of this working group are

n Support for dual counter rotating rings

n Full compatibility with IEEE�s 802 architecture as well as 802.1D, 802.1Q and 802.1f

n Sub 50ms fail-over

n Destination stripping of packets for Spatial Reuse

n Adoption of existing physical layers

A lot of debate in the standards organization is centered on defining the CoS and QoS

support required from RPR. Vendors have a widely divergent view of the extent to which

traffic shaping, differentiation, congestion control and CoS related functionality need to be

supported and standardized by the RPR working group.

Apart from the above, the standards organization is also working towards defining the

Framing and encapsulation, protection and fault recovery mechanisms, performance

management and Fault isolation, topology discovery support required for RPR.

The draft standards are to be ready by November 2002 and the final standards will be

formalized by March 2003. To support and supplement the working group a RPR alliance

has been created. This is a group of interested companies who are co-operating to

promote this standard.

6. Pre standard development

Fiber rings are extremely common in the metro-networking environment. The time is ideal

for a transport technology that exploits benefits of ring topology and is also easy to use with

Ethernet and SONET technologies. Due to the preliminary schedule and such benefits of

RPR technology, it is granted that vendors will start shipping pre standard products.

Many vendors are veering towards pursuing some form or other of the existing SRP

standards (RFC 2892) to provide transparent bridging functionality within the ring. The

RFC 2892 has also won support from chip vendors such as Conexant for pre-standard

implementation.

In-spite of the support from various vendors, the RFC by itself does not address some

crucial aspects required for providing intra-ring and multiple ring transparent LAN bridging.

The RFC 2892 was evolved to support routers in a ring configuration and treats each ring

as a separate subnet with a (virtual) shared media. As such address resolution


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required between the layer 3 IP address and the SRP Mac layer address is similar to the

address resolution required between the layer 3 IP address and the Ethernet MAC layer

and is carried out using the Address Resolution Protocol (ARP).

This address resolution need not extend beyond the subnet (ring). In this routing solution

packets are routed between rings at layer3.

RFC 2892, therefore, does not concern itself with support for multiple interconnected

rings at layer2. It does not define either the encapsulation technique for carrying Ethernet

traffic within RPR frames, or the protocol to be used for resolving Ethernet address to

SRP MAC address. However the RFC 2892 does provide a robust sub-50msec fault

recovery protocol for a packet ring. The RFC 2892 Intelligent Protection Switching is

broadly based on SONET BLSR concepts, such as protection event hierarchy, wait to

restore etc and behaves in a very similar fashion. The RFC also satisfies the plug and

play feature mandated by 802.17 through its support of automatic Topology Discovery on

the ring. And, even though the RFC does not concern itself with support for all aspects of

CoS, QoS and congestion support, it does support global and local fairness on the ring.

The other packet-ring technology already in the field is Nortel�s proprietary interwan

Packet Technology.

In conclusion, we believe that RFC 2892 is an essential starting point for a vendor trying

to provide pre-standard packet-ring solution. It is a proven, robust technology and many of

its features are likely to influence the standard. However, it needs to be modified and

extended to support a versatile Layer 2 Transparent LAN solution.

7. Wipro�s expertise

Wipro has a detailed working knowledge of RFC 2892. We have implemented a modified

version of RFC 2892 (including Topology Discovery, Fairness Algorithm and Intelligent

Protection Switching). Wipro has helped clients in extending & implementing the RFC

2892. The extended RFC 2892 being implemented by Wipro supports a) encapsulation of

Ethernet Frames while on the ring, b) providing either Ring Steering or Ring wrapping

under fault scenarios c) MAC address-SRP address interworking. A Ring-Hardware

simulator was developed to thoroughly test out the protocol code in a Windows NT

environment under various ring conditions. The GUI provides the facilities to trigger

various ring conditions such as Signal Fail, new node creation on the ring etc. The

protocol code � which is OS and Hardware independent, will be later ported on to the

target hardware.

Conclusion

Wipro�s extensive experience in related technologies like SONET BLSR/UPSR, bandwidth

management, fairness and congestion control, routing technologies (OSPF and MPLS

etc), Gigabit Ethernet, RTOS and FPGA/ASIC/Board design effectively complement the

Packet Ring Technology expertise.


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This gives us an in-depth understanding of the issues that need to be addressed for

implementing any RPR solution. In addition Wipro is already working on providing a

solution for Layer 2 Transparent LAN Bridging across Multiple rings. (Please refer to the

companion whitepaper RPR for Cascaded RIngs) This makes us an ideal partner for

vendors planning to offer pre-standard or customized RPR solutions and products.

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About the Authors

Pranav Koushik is a Software specialist at Wipro Technologies. Pranav has over 7 years

of experience in broadband transport technologies and his area of work currently includes

embdedded software for Optical networking products.

Surbhi Sinha is a Consultant at Wipro Technologies and specialises in Optical

Networking solutions. Surbhi has been with Wipro for the past 8 years.

Contact Us

if you need to contact us regarding any clarification of feedback, mail us at

[email protected]

Table 1: Acronyms and Definitions

APS Automatic Protection Switching

CoS Class Of Service

DWDM Dense Wavelength Division Multiplexing

IP Internet Protocol

LAN Local Area Network

MAC Media Access Control

MAN Metro Area Network

MPLS Multi Protocol Label Switching

POS Packet Over SONET

QoS Quality Of Service

RPR Resilient Packet Ring

TDM Time Division Multiplexing

SONET Synchronous Optical Network


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About Wipro

Wipro Technologies is a part of Wipro Limited (NYSE:WIT) and is a leading global provider

of high-end IT solutions. The IT solutions provided include application development

services to corporate enterprises and product engineering services to technology

companies. The company's top clients include Nortel, Cisco, Canon, Fujitsu, Microsoft

and Alcatel, to name a few.

With over 10000 consultants Wipro integrates people processes and technologies to

deliver innovative solutions that enable implementation of product development strategies

efficiently and cost-effectively. Wipro is also the first IT services company in the world to

achieve the highest level of quality certification, the SEI-CMM Level 5. Wipro currently runs

large development facilities for industry leaders and start-ups alike, and has more than

4000 consultants focused on communication hardware and software alone.

Wipro in Telecommunication Technologies

Wipro solutions for the technology sector are in areas of Optical networking, Data

networking, Wireless networking, Voice switching, and Network Management systems.

These solutions span across a vast spectrum of technologies in the hardware (VLSI,

FPGA, Board design, DSP, RF), embedded software (VxWorks, EPOC, pSOS) and Network

Management software (CORBA, UML, SNMP, TL1) and many more. With over 10 years of

experience in the telecom space, Wipro offers engineering services like architecting,

design, development, verification, validation and maintenance.

© Copyright 2001. Wipro Technologies. All rights reserved. No part of this document may bereproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic,mechanical, photocopying, recording, or otherwise, without express written permission from WiproTechnologies. Specifications subject to change without notice. All other trademarks mentioned hereinare the property of their respective owners. Specifications subject to change without notice.

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