protection switching scheme for ng-sdh based switching system

Protection Switching Scheme for NG-SDH based Switching System

Kiwon Kim, Byungho Yae OAM Technology Team, BcN Core Technology Group, BcN Division

Electronics and Telecommunications Research Institute 161 Gajeong-dong Yuseong-Gu Daejeon

KOREA. [email protected], [email protected]

Abstract: - As Next Generation – Synchronous Digital Hierarchy (NG-SDH) based switching system, which integrates and provides the connection of synchronous digital (SONET/SDH) signals, and Ethernet signals, mutually exchanges the synchronous digital signals and the Ethernet signals, and performs synchronous timeslot switching and packet switching in one system. This system needs the integrated monitoring and control functions for equipments deal with synchronous digital signals and Ethernet signals, and when it occurs faults, has to provide the protection switching functions for the survivability of networks. This paper presents the integrated multi-layered Operation Administration Maintenance (OAM) architecture and the scheme of multi-layered protection switching for synchronous digital signals and Ethernet signals. Key Words: - OAM, NG-SDH, Ethernet, EOS, Multi-layered, Protection Switching, LCAS. 1 Introduction

Recently, the increased multi-service nature of a converged transport network infrastructure requires efficient handling of narrowband, wideband, and broadband traffic sources whether from voice, Web pages, electronic data exchanges, packetized digital audio, or video. Furthermore, service providers demand an enduring public transport network infrastructure that provides a flexible and affordable service evolution path despite unpredictable traffic patterns, service models, and technology evolution. Such an integrated NG-SDH based TDM/data transport approach is attractive to established carriers as they can deploy new packet-switching technology to implement data transport services [1][2]. Generally, a synchronous optical network (SONET), a synchronous digital hierarchy (SDH) network use paths and bandwidths exclusively, thereby providing highly reliable and safe communications service. However, the exclusive use of the bandwidths decreases the usage efficiency of the bandwidths and the service usage price expensive. On the other hand, an Ethernet network that transfer Internet Protocols (IP) in frames does not use paths and bandwidths exclusively, and sharing of bandwidths is possible by using a statistical multiplexing function. Thus, the usage efficiency of the bandwidths is high and the

service usage price is moderate. However, the communications reliability and safety is inferior to the SONET/SDH network because data loss through burst or runway occurs. Therefore, in order for a network service provider to provide a service with high reliability and safety at a moderate price in various bandwidths, both SONET/SDH network and Ethernet are needed. However, to operate and manage both networks requires high initial investments and system maintenance costs. As way to solve this problem, integrated systems and methods that can accept both SONET/SDH and Ethernet signals in a single system, and switch and transfer the SONET/SDH and Ethernet signals are frequently used [3].

The NG-SDH based Switching System which we are developing, is an integrated switching system that can accept SONET/SDH and Ethernet signals. This switching system can support forming a switch fabric with only a packet switch, forming a switching fabric with only timeslot switch, and forming a switching fabric with a packet switch, a timeslot switch, and a signal conversion block between the packet switch and the timeslot switch. Therefore, our developing system provides various and reliable communications service at a moderate price to users and provides decreased investment cost and maintenance cost to carrier service providers. In this

Proceedings of the 4th WSEAS Int. Conf. on Information Security, Communications and Computers, Tenerife, Spain, December 16-18, 2005 (pp526-530)

paper, we will explain for this system, describe the integrated multi-layered OAM hardware and software architecture, and present the multi-layered protection switching for this switching system. 2 OAM Hardware Configuration

NG-SDH based switching system has interfaces for transferring of SONET/SDH and Ethernet signals, packet switch for integrated switching this signals and control unit for monitoring and controlling of the units.

Centralcontrol

processorunit

PacketswitchPacket

switch

Ethernetsignal

connectioninterface

Packetswitching

unit

SONET/SDHsignal

connectioninterface

Ethernetframe

forwarding

Ethernetframe

forwarding

EOS

.

.

.

.

.

.

control link

10/100Ethernet

GbEXGbE

WorkingOC-M,STM-N

ProtectionOC-M,STM-N

Macprocessor

EMS

EOS unit

Ethernet unit

Fig.1 OAM Hardware Configuration

Fig. 1 shows NG-SDH based OAM hardware configuration of NG-SDH based switching system. Interface units in the system are divided into Ethernet over SONET/SDH (EOS) and Ethernet unit. According to definition of EOS techniques in ITU-T G.707,G.7041, and G.7042 [4], EOS unit includes a SONET/SDH connection interface that maps optical carrier level (OC)-M/synchronous transport module level (STM)-N signals into a virtual container level (VC) 3 or 4 signal, a timeslot switch that switches a timeslot of VC3/4, and generates and distributes a system synchronizing signal by receiving a network synchronizing signal, and a packet/timeslot switch that transforms the Ethernet signal extracted from the timeslot switched VC3/4 into packets with a predetermined length, and mapping the Ethernet signal generated by reassembling the packets switched to the VC3/4 and carrying out an EOS.

Ethernet unit transforms the Ethernet signal into packets with predetermined length as a basis outputting the packets. The system includes a packet switching unit that switches the packets and a Central Control Processor Unit (CCPU), i.e. main OAM processor unit) that generates and manages the provisioning information which includes switching, bridging, and framing information of the input/output signals, controls a flow, and carries out a SONET/SDH protection switching. There is local craft terminal (LCT) and equipment management system (EMS) that perform all OAM functions by operator for this system. The OAM function surveils each processor in the units and CCPU, supervises system and provides network connections with remote sites and with the system graphic user interface (GUI) of EMS or LCT. EMS, LCT and CCPU are connected with each other by Ethernet with TCP/IP. OAM software, running in EMS, LCT and CCPU, communicates through common object request broker architecture (CORBA) each other and, which is provided by the real time operating system. 3 OAM Software Configuration

The OAM software in CCPU are composed of alarm surveillance, performance monitoring and control module (Table.1). The target signals to monitor are conventional SONET/SDH, EOS and Ethernet OAM signals. Fig.2 illustrates OAM software configuration.

OAMSubsystem

OAMSubsystem

Embedded Linux with Realtime featuresEmbedded Linux with Realtime features

EMSSubsystem

EMSSubsystem

ConnectionControl

Subsystem

ConnectionControl

Subsystem

SNMP API module/CORBA API Module

Device API module

LCTSubsystem

LCTSubsystem

CORBA API

Module

CORBA API Module

Fig. 2 OAM Software Configuration

OAM Subsystem, which is running on real time operation system (RTOS), is transferred the alarm and performance data from lower OAM function in a unit, convert this information into appropriate message format, and report the message to LCT


Subsystem or EMS Subsystem. Connection Control Subsystem, which is running on CCPU, performs connection control function and communicates with OAM subsystem through CORBA. Operator can be provided the status of services, the connection control, the provisioning and the protection switching of the system by OAM software Table. 1 Fault, Performance and Control Monitoring

Traffic Input bytes

Traffic Output bytes

Traffic Input packets

Traffic Output packets

Traffic Drop packets

Mac statistics

Link Speed

MTU, Link-level type

Aggregated ethernet options

Physical link-layer encapsulation

Gigabit ethernet options

Hold time for link up and link down

disable SNMP notifications on state changes

Policy Based Routing to be applied to the interface

Limit overall port rate using QoS

PPP Options

Logical interface

Support VLAN tagged packets

VCG port configuration

LCAS configuration

Bit Interleaved Parity-B1&B2&B3

Remote Error Indication-B2&B3

Ber-sd-limit

Ber-sf-limit

j0-value

Loopback option

Pathtrace

Protection Switch (APS) configuration

Performance

&

configuration

Ethernet port internal test failed

Aggregate Ethernet interface bandwidth is below its thereshold

Error correction code

Resource management checksum error


Parity error

An error in communication

lost frame sync

core Hec error

Frame Check sum error

Group id error

MFI unlock

sequence number Mismatch

not aligned before reading

not aligned before writing

message CRC error]

LCAS state machine fail

LCAS Rx_MST

Alarm Indication Signal on line&path,

Bit Error Ratio in excess of the provisioned Signal Degrade limit,

Loss of Frame

Loss of pointer

Loss of Signal

Path Label Mismatch

Remote Defect Indication

Unequipped Path signal

Optical Module Not Present

Optical Module Tx Fault

Loss of Synchronization

Loss of external timing reference source

Fault

&

Alarm

Ethernet

signal

connection

interface

EOS

(Ethernet Over SONET)

SONET/SDH

signal

connection

interface

Traffic Input bytes

Traffic Output bytes

Traffic Input packets

Traffic Output packets

Traffic Drop packets

Mac statistics

Link Speed

MTU, Link-level type

Aggregated ethernet options

Physical link-layer encapsulation

Gigabit ethernet options

Hold time for link up and link down

disable SNMP notifications on state changes

Policy Based Routing to be applied to the interface

Limit overall port rate using QoS

PPP Options

Logical interface

Support VLAN tagged packets

VCG port configuration

LCAS configuration

Bit Interleaved Parity-B1&B2&B3

Remote Error Indication-B2&B3

Ber-sd-limit

Ber-sf-limit

j0-value

Loopback option

Pathtrace

Protection Switch (APS) configuration

Performance

&

configuration

Ethernet port internal test failed

Aggregate Ethernet interface bandwidth is below its thereshold

Error correction code



Parity error

An error in communication

lost frame sync

core Hec error

Frame Check sum error

Group id error

MFI unlock

sequence number Mismatch

not aligned before reading

not aligned before writing

message CRC error]

LCAS state machine fail

LCAS Rx_MST

Alarm Indication Signal on line&path,

Bit Error Ratio in excess of the provisioned Signal Degrade limit,

Loss of Frame

Loss of pointer

Loss of Signal

Path Label Mismatch

Remote Defect Indication

Unequipped Path signal

Optical Module Not Present

Optical Module Tx Fault

Loss of Synchronization

Loss of external timing reference source

Fault

&

Alarm

Ethernet

signal

connection

interface

EOS

(Ethernet Over SONET)

SONET/SDH

signal

connection

interface

4 Multi-Layered OAM Architecture

Because the NG-SDH based switching system mutually change the SONET/SDH signals and Ethernet signals, this system shouldn’t be dealt with independent OAM functions between conventional SONET/SDH transmission system and Ethernet. At the adjustment of two signals, the mutual mapping of SONET/SDH OAM signal and Ethernet OAM signal is necessary in order to guarantee the continuity of signal. Therefore, it is very important to build an OAM functions for service reliability of the system. Fig. 3 illustrates signal propagation between layers and mutual changing SONET/SDH signals and Ethernet signals in the system. The system provides

framing information of the input OC-M/STM-N signals, transforming of the Ethernet signals into packets with predetermined length by EOS techniques, and then transports the packets to destination through the packet switch unit by way of Ethernet framing forwarding. In case of opposition, input Ethernet signals are transformed and transported SONET/SDH through the reverse processing on the contrary. There is multi-layered OAM architecture that includes SONET/SDH layer of physical signal, EOS layer of mutual adaptation with SONET/SDH and Ethernet signals, and multiprotocol label switching (MPLS) layer which is specified framework that provides for the designation, routing, forwarding and switching of traffic flows through the network.

SONET/SDHsignal

connectioninterface

Ethernetframe

forwarding

EOS...

Ethernetsignal

connectioninterface

Physical interface

Regenerator Section

Multiplex Section

VC-n,m

Path

GFP

VCA

T Group, LC

AS

Ethernet Packet Forw

arding

Eth

ern

et P

acket F

orw

ard

ing

SONET/SDHLayer

EOSLayer

EthernetLayer

MutualChange

Upstream & Downstream Alarm Propagation

EOS unit Ethernet unit

Fig.3 Multi-Layered Signal Propagation

5 Protection Switching

This NG-SDH based switching system has completely duplicated trail-switching function and provides the link capacity adjustment scheme (LCAS) fault tolerance of a dynamic restoration method. The system provides protection switching for trail in case it received only one tributary signal as input. However when layer accepts tributary signals with 1+1 protection structure - that is the case of tributary system has sub-network connection protection (SNCP). The LCAS performs automatic removal and restoration of a failure path that occurs


in a virtual concatenation, and the function to increase or decrease the capacity of link without an error. The LCAS uses a control packet according to the ITU-T G.7042 standard [5]. The LCAS function performs the automatic removal and restoration of the failure path in this switching system. To be more specific, when service of a member of a virtual concatenation (VCAT) group (VCG) in a SONET/SDH Network is provided due to network failure, the LCAS function automatically reduces the capacity of link by repairing the member or automatically returns the capacity of link by restoring the network failure so as to restore multi-layers using the LCAS.

When an input signal is connected without SNCP, switching system supplies 1+1 trail protection. 1+1 trail protection concept is that the switching system provides two network connections with one independent tributary signal. This architecture shows that transmission port uses permanent bridge to transport signals and receiving port surveils two signals and selects appropriate traffic. Above scheme follows 1+1 unidirectional path switching with non-revertive protection. The system does not need automatic protection protocols because receiving port select signal with own information. Fig.4 gives you an idea of 1+1 protection architecture in the linear type network and Fig.5 illustrates protection architecture in the ring type network. Fig.6 illustrates the general software control architecture of protection switching for SONET/SDH network [6].

10/100Ethernet

GbEXGbE

Working LinksOC-M,STM-N

ProtectionLinks OC-M,STM-N

EOS

EOSX X

EOS

EOS

EOS

EOS

EOS

EOS

MAC

MAC

MAC

MAC

Bridging & Selecting

10/100Ethernet

GbEXGbE

OC-M,STM-N

OC-M,STM-N

1+1 ProtectionSwitching



LCAS Fault Tolerance



QSS120-A Node QSS120-B Node

Fig.4 1+1 Linear Protection

Working Ring Protection

Ring

EOS

EOS

X

EOS

EOS

MAC

MAC

10/100Ethernet

GbEXGbE

OC-M,STM-N

10/100Ethernet

GbEXGbE

X

EOS

EOS

EOS

EOS

MAC

MAC

OC-M,STM-N





EOS EOSX

EOS EOS MAC MAC

10

/10

0E

the

rne

t

Gb

EX

Gb

E

OC

-M

,S

TM

-N1+1 Protection

Switching


NG-SDH UPSR

Network

QSS120-A Node

QSS120-B Node QSS120-C Node

Fig. 5 1+1 UPSR Protection

APS controllerAPS controllerDetected Failures

(Both sides)Detected Failures

(Both sides)

Local equipmentfailures

Local equipmentfailures

Externally initiatedcommands

Externally initiatedcommands

Incoming K-byte signalling

(both sides)

Incoming K-byte signalling

(both sides)

both SF/SD

aps-modeswitch-state by external commandcurrent operation-state

Failure of Protocol

Request of K1, k2 byte

Fig. 6 Software Control Architecture

for SONET/SDH Protection Protection switching in this switching system

has four kinds of switching types, which are automatic switching, manual switching, forced switching and lockout. System operator can command manual switching as long as both working and protection signal is normal status. But switching is impossible when one of the signals has fault or higher priority switching, such as automatic switching, forced switching or lockout, is applied. When fault of working signal occurs, automatic switching is executed unless force switching or lockout state. Forced switching can change current


state if there is no lockout command. When lockout is applied, none of switching can be activated.

START

DetectingSONET/SDH

Defects

Is Protection Switching function ?

Process LCAS

Fault Tolerance

Process ProtectionSwitching

END

Yes

No

No

Is SONET/SDH

Defects ?

Is Protection Switching Success ?

Yes

No

Yes

DetectingLCAS

Defects

Is LCAS Defects ?

Is Protection Switching function ?

Yes

Process LCAS

Fault Tolerance

No

No

Yes

Is SONET/SDH

Defects ?

No

Yes

Yes

Fig. 7 Flow of Multi-layered Protection Switching

This NG-SDH based switching system has conventional SONET/SDH protection switching scheme and LCAS fault tolerance scheme for high reliability of system service. Fig. 7 illustrates proposed algorithm of multi-layered protection switching software that both schemes are linked with each other. SONET/SDH protection switching performs if a network failure is detected so that the service is restored. LCAS fault tolerance performs if SONET/SDH protection switching does not repair the network failure. 6 Conclusion

This paper introduces the architecture of OAM hardware and software for the NG-SDH based switching system. This paper also presents the multi-layered protection switching architecture for the survivability in NG-SDH based switching system. This result will be helpful to design the OAM functions and protection switching in the NG-SDH

based switching systems. For further study, the scheme we present is going to be applied to commercial system. And we have the plan to estimate the aspects of the performance and reliability for the system. References: [1] Enrique Hernandez-Valencia, Hybrid Transport

Solutions for TDM/Data Networking Services, IEEE Communications Magazine, May 2002.

[2] Kurenai Murakami, Su-Hun Yun, Osamu Matsuda, Motoo Nishihara, New Transport Services for Next-Generation SONET/SDH Systems, IEEE Communications Magazine, May 2002.

[3] ITU-T G.784, SDH Management, June 1999. [4] ITU-T G.806, Characteristics of Transport

Equipment – Description Methodology and Generic Functionality, Feb. 2004.

[5] ITU-T G.7042/Y.1305, Link Capacity Adjustment Scheme (LCAS) for Virtual Concatenated Signals. Feb. 2004.

[6] ITU-T G.841, Types and Characteristics of SDH Network Protection Architectures, Feb. 1998.


protection switching scheme for ng-sdh based switching system

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