ptn vs dual fabric pots for sdh migration 1212

8/11/2019 PTN vs Dual Fabric POTS for SDH Migration 1212

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www.orcki t.com

Pushing technology to the edge

2011 Orckit-Corrigent

Over the past several years, telecommunication service providers have been experiencing a dramatic

shift from legacy TDM circuits to next generation Ethernet traffic. This shift has been driven by

both residential triple-play services and business Ethernet services, and it has also been marked

by the introduction of Ethernet-based 3G Node B and 4G/LTE mobile networks.

Nevertheless, the demand for SDH circuits is expected to remain solid. While small offices and

home offices (SOHO) have already made the shift towards Ethernet services (mostly based

on broadband xDSL and CATV services), two significant market segments present an ongoingdemand for legacy TDM services.

The first is medium and large enterprise customers. Although such companies are moving to

Ethernet based services, many of them maintain their legacy systems. Carriers, therefore,

will continue to provide them with TDM services. The other segment that demands legacy

services is the mobile market. In order to prevent major forklift upgrades, mobile operators

will continue to support 2G and 3G infrastructure. These technologies contribute to the

SDH demand in metro networks.

Therefore, it is clear that for the foreseen future, TDM and Ethernet will have to coexist

in the metro. Yet, initial deployments of carrier Ethernet solutions have not offered any

support for SDH. Standards bodies such as the MEF decided to focus on the transport of

PDH rates with circuit emulation services but did not define a circuit emulation techniqueor demand for real, high-rate SDH services.

As a result, most of the carriers today use two separate transport systems in their metro

area networks: The first is a legacy SDH network (or MSPP based Next Generation

SDH). At the same time, they have also deployed a packet network composed of

Layer2 aggregation (in some cases, Carrier Ethernet-based aggregation) and a Layer3

IP-MPLS core.

Packet Transport Networks (PTN) equipment and Packet Optical Transport

Systems (POTS) are innovative solutions that address the challenge of an integrated,

single-layer approach for a next generation metro network. Both solutions include

advanced technologies to address Ethernet and SDH in their native forms.

For the foreseen future,

TDM and Ethernet will

have to coexist


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SDH

Processor

Dual Matrix

Packet Function

ProcessorProcessor

PacketData

Processor

UNI

Eth

ProcessorProcessor

SDH/TDMSDH TDM

NNI

Processor

Data

ProcessorEthPacket

Processor

TDM

SDH/TDM

ROADMDWDMCWDM

HO TDM Function

LOXC

Data

EoS

SDH

EoS

TDM

POTS products provide an integrated solution for several

technologies in a single box using a multipurpose centralized

switching fabric or dual matrix fabric architecture. Universalfabric is typically based on cell switching technology and is

capable of performing native packet switching and native SDH

switching simultaneously. The more popular implementationis the dual matrix architecture.

In some cases, interconnection between the TDM fabric and

the packet fabric by means of Generic Framing Procedure

(GFP) encapsulation enables Ethernet over SDH. In other

cases, interconnection between the TDM fabric and thepacket fabric impossible, leading to different fibers for Ethernet

and TDM services. POTS products can be designed so

that the packet switching technology of choice is PB/PBB/

PBB-TE/MPLS/MPLS-TP. For TDM switching, POTS can

be configured with High Order (HO) or Low Order (LO)

switching granularity for SDH. TDM tributaries may includelow rate services such as E1 and up to high rate STM-64

10G interfaces.

The separation of the two switching entities suggests that the

POTS platform is composed of two separate systems: packet

switch and TDM switch. Simply put, the POTS solution is

a combination of a Carrier Ethernet Switch and MSPP in

a single box.

Todays carriers environment generates a large amount of

SDH traffic and packet traffic that needs to be transportedbetween sites in the metro. The deployment of POTS would

require two fiber pairs for every link. One pair would beused to interconnect the SDH part of the network and the

other pair would be used to carry the Packet traffic. The

complete separation between the two technologies implies

that with POTS, the operator actually builds and maintains

two networks on the same physical node.

This significant waste of CAPEX (or OPEX, in the case of

leased fibers) is overcome in one of two ways: Ethernet

over SDH (EoS) or WDM/ROADM technologies withOTN capabilities.

With EoS, POTS implements Virtual Concatenation (VCAT),

Generic Framing Procedure (GFP) and Link Capacity

Adjustment Scheme (LCAS) on dedicated hardware to map

As illustrated in Figure no. 1, POTS that is based on dualmatrix fabric architecture implements both packet switch and

TDM switch. Dedicated hardware, interfaces, capacity, andpower consumption per switch, results in a costly and non

scalable design for high Ethernet capacity. In addition, this

architecture has inefficient fiber usage: blocking operation thatdoes not allow a single fiber to support any mixture of TDM

and Ethernet traffic on any distribution of line cards.

In systems where interconnection is not possible, the double

cost of the fiber infrastructure (or, alternatively, the additional

cost of enabling double the number of wavelengths in the

DWDM network) is prohibitive. With this approach, eachTDM service consumes both the working bandwidth and

the protection bandwidth, while it is desired that when

there is no network failure, protection bandwidth can be

reclaimed and used for excess data traffic. Eventually, two

networks are needed - TDM and packets. For example,in a case where 7Gbps of packet traffic and 2.5Gbps of

TDM traffic should be carried inter-city, it would requiretwo wavelengths to carry that traffic instead of one.

Ethernet into a standard SDH payload. This approach is very

inefficient for high capacities of packet traffic and services.

By using integrated WDM/ROADM with OTN capabilities

in POTS platforms, POTS can carry both SDH and Ethernetover a single fiber pair over 2 separate wavelengths or

2 sub-wavelengths. Although WDM/OTN technologies

significantly increase bandwidth, they also add a significant

amount of complexity and require special care by trained

professionals. Moreover, as operators often already use aWDM network in the metro, the integrated WDM and

ROADM capabilities of POTS adds little value. In this case,

deployment of POTS will require two wavelengths on an

existing WDM infrastructure.

The POTS solution

POTS Services and network architecture

Figure 1:

Typical POTS Architecture

Simply put, the

POTS solution is acombination of aCarrier Ethernetswitch and MSPP ina single box


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SDH technology uses an advanced OAM suite. With

a multilayer OAM approach, SDH offers the ability to

continuously monitor every single circuit, path, multiplexer

section and regenerator section, and initiate consequentactions (such as switch to protection) upon failures in these

layers. It also includes advanced Alarm Indication Signals

(AIS) and Remote Defect Indications (RDI), loopbacks

and alarm correlation tools.

Carrier-grade packet switching technologies are enhanced

to provide a similar level of OAM by providing standard

tools for OAM at different levels. At the Ethernet level,

IEEE 802.1ag - Connectivity Fault Management (CFM)

offers Continuity Check, Loopback and Link trace (trace

route) while ITU-T Y.1731 extends this standard and offers

service-level OAM enhancements such as AIS for alarm

indication and suppression and SLA verification delay,delay variation and frame loss rate.

Carrier Ethernet (CE) technology is ideally designed to

cater to Ethernet services in carrier network environments.

With Carrier Ethernet, carriers benefit from a complete

OAM solution as well as high availability and manageability

features. The underlying transport technology varies

from system to system and can be based on Ethernet

technologies, such as Provider Bridge or PBB/PBB-TE, or

on MPLS technologies, such as IP-MPLS (VPLS/VPWS)or the newly defined MPLS-TP.

A PTN solution was specially designed by Orckit-Corrigent

and integrated into its CM-4000 family of products offering

an enhanced Carrier Ethernet solution with unique

transport capabilities of SDH services. As an example, while

regular CE platforms implement SAToP and CESoPSN

circuit emulation technologies, they are limited to E1

circuits over packet and are far from providing a real

replacement for legacy TDM.

Although these standards are sufficient for Ethernet-based

packet forwarding (PB and PBB), additional OAM tools are

required for MPLS-based networks. This includes IETF

RFCs such as LSP Ping (RFC 4379) for data and controlplane connectivity check, performance monitoring (delay,

jitter and packet loss) and LSP Trace for fault isolation.

The use of POTS in a metro network requires full suite

SDH OAM and Packet OAM. As a result, operators should

actually manage two separate networks that happen to

share the same boxes. The operational complexity is high

and lack of any interworking functionality between the

Packet and TDM layers prevents the operational simplicity

promised by the POTS technology.

PTN solution is capable of providing circuit emulation

for any SDH payload. It also provides HO and LO cross

connection and grooming capabilities, fueling true network

convergence over a single platform and significantly

reducing OPEX.

Figure 2 below depicts the architecture of a typical PTN

platform. The system is built around a packet switch,

which handles all traffic flowing through the product. Asecond switch can be added and configured in standby

mode for 1:1 protection of the switching fabric.

In order to keep costs low, the switching fabric shares a

blade with Ethernet UNI and NNI ports. High port fan-

out is achieved by enabling the ports next to the standby

switch to be fully functional regardless of the status of

their collocated switch. With an extremely low entry

cost, additional services and interfaces are provided by

inserting extension modules. With a pure packet-based

switching fabric, the packet extension modules are also

very cost-efficient.

POTS Operation Administration andMaintenance (OAM)

The PTN approach

Figure 2:

Typical PTN System

Architecture


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A PTN is a pure packet network. With Layer 2 MPLS as

the underlying packet technology, PTN provides network-

wide Traffic Engineering, advanced QoS and Connection

Admission Control (CAC) for SLA assurance.

Circuit emulation packets are assigned with the highest

possible priority and strict priority queues. Synchronization

is also applied on the packet interfaces using Synchronous

Ethernet or IEEE 1588v2. QoS and network synchronization

provide SDH-like quality across the network and are used

to meet the required jitter, delay and wander performance

levels of TDM circuits.

PTN solution can provide a full set of SDH services over

packet networks using Circuit Emulation over Packets

(CEP) encapsulation. These services are transported

with the same delay, jitter and wander tolerances as in

traditional SDH systems and are compliant with ITU-T

and Telcordia specifications. The CEP implementation is

based on IETF standards and provides service protection

in under 50msec for fiber cut or node failure.

This effectively enables circuit switching of STM-1,

STM-4 and STM-16 signals together with HO/LO cross-

connections and grooming of multiple channelized STM-n

signals.

With the integration of Synchronous Ethernet and IEEE

1588v2 Technology, the PTN circuit emulation solution

is based on a synchronized packet network enabling it to

provide the same quality as traditional SDH networks.

The circuit switching (HO and LO cross connection) and

circuit emulation (converting TDM payload into packets)

is performed on the TDM interface cards. This maintains

a low cost for the packet services and adds the TDM cost

burden to the TDM interfaces alone.

The PTN OAM approach is significantly simple, compared

to the POTS OAM. With a single transport technology

for both packet and TDM, the only OAM tools that are

used are the Ethernet and MPLS OAMs. SDH OAM is

terminated by the TDM line cards, thereby significantly

simplifying the OAM processes.

PTN Services andnetwork architecture

PTN is Enabling TDMand Synchronization

PTN OperationAdministration and

Maintenance

Figure 3: Typical POTS and PTN cost breakdown

Case Study Cost comparison

POTS and PTN are optimized for converged solutions that offer a mixture of SDH and Ethernet services. A typical

node configuration would include the following characteristics:

Fully redundant node configuration for switching fabric, control and power

33% of the bandwidth allocated for NNI interfaces and 66% of the bandwidth allocated for UNI interfaces

Traffic mixture of 60% packet and 40% TDM

Figure 3 compares the cost breakdown of typical POTS versus a PTN platform. The PTN solution provides about

40% lower cost, mainly due to the very low cost of the NNI solution. In fact, almost 30% of the POTS cost is

associated with NNI interfaces. The PTN solution, with its on-board UNI/NNI interfaces and the use of one type

of NNI interface (namely Ethernet NNI), maintains a much more competitive price point.

Eth NNISDH Commons

POTS CAPEX PTN CAPEX

100%

80%

60%

40%

20%

0%

The PTN solutionprovides about 40%

lower cost, mainly dueto the very low cost

of the NNI solution


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Conclusions

The migration from legacy SDH to packet-based systems in the metro calls for a hybrid solution that can cost-effectivelyaddress this challenge with a single platform. The two leading candidates for this purpose are POTS with its multipurpose

switching capabilities and PTN which integrate advanced circuit emulation technology into a state-of-the-art carrier

Ethernet platform. The following table compares the key characteristics of the two technologies.

Characteristic PTN POTS

Architecture

Unified switching entity for packet and TDM- PTNpacket switching architecture forwardspackets and TDMin the same way, forming aunified switching architecture.

Two logically separated switching entities(packet plus TDM) - the multipurpose switchingfabric forms two separate switching entities ina single box.

NetworkingA unified packet network, capable oftransporting any mix of packet and TDMtrafficover 1GEand 10GEinterfaces.

Two separate networks, one for TDMand theother for Packets. Both can use the same fiberpairs by addingWDMcomponents at extracost, instead of service cards.

OAMCarrier Ethernet OAMtools including EthernetOAM (IEEE-802.1ag CFMandITU-T Y.1731).TDM OAMat TDMtermination points only.

Separate OAMapproach for Packet traffic andTDMtraffic. Carriers need to master bothtechnologies to manage their network.

NetworkManagement

PTNuses MPLS-based dynamic control planewith full routing and signaling capabilities. Thissignificantly simplifies the establishment andmanagement of all services. Use of NMSisoptional and is mostly used for GUI-basedservice management with full FCAPSsupport.

NMSin POTSis compulsory. All provisioningis static and is based on centralized pathcomputation for SDHservices and on PathComputation Element for packet services.Management of services is complex and differssignificantly from TDMto Packet.

Cost

The PTNarchitecture enables low costsolutions. With a lower entry cost, PTN

technology is extremely cost effective. This costadvantage grows as the node capacity scales.

The POTSarchitecture with its multipurposeswitching fabric imposes high system cost dueto high cost of networking interfaces.

POTS is the technology of choice for multiservice national backbones which require integration between high capacityROADM technology, packet transport and TDM transport in a single box. When attempting to use the same technology

for metro applications, however, its major disadvantages become clear. The multiservice switching technology forcesthe POTS devices to act as two separate products in one cage with TDM traffic handled completely separate from

the packet transport. Converging the two technologies by means of Ethernet over SDH simply turns the POTS intoa regular MSPP.

Furthermore, the POTS technology is very expensive both in terms of CAPEX and OPEX. POTS high entry cost ismostly driven by the need for expensive NNI interfaces. The cost of expansion cards is also high due to the complexswitching architecture and the need to convert any traffic to cells. In terms of OPEX, operators are actually runningtwo networks in one box. This means that network operators are running a TDM network in parallel with a packetnetwork and, in some cases, even with a WDM layer for fiber relief.

PTN solution, on the other hand, is designed and optimized for metro applications. Its unified packet switching keepsthe system cost at a very low price point and the OPEX is kept low with a single transport approach. The selection of

MPLS and MPLS-TP as the underlying transport technologies, introduces state-ofthe-art control plane into the packettransport t world, providing simple operation with assured SLA.

Therefore, it is clear that the optimal solution for next generation transport networks, which are capable of convergingTDM with packet technologies, is PTN.

The optimal solution for nextgeneration transport networks,which are capable of converging

TDM with packet technologies is PTN


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Orckit facilitates telecommunication providers delivery of highcapacity broadband residential, business and mobile servicesover wireline or wireless networks with its Orckit-Corrigentfamily of products. With 20 years of field experience with Tier-1customers located around the world and sound leadership,

Orckit has a firm foothold in the ever-developing world oftelecommunication.

Orckit-Corrigents product portfolio includes Packet TransportNetwork (PTN) switches - an MPLS and MPLS-TP dual stackbased portfolio enabling advanced packet as well as legacyservices over packet networks with a wide set of transportfeatures.

Orckit-Corrigent markets its products directly and indirectlythrough strategic alliances, as well as distribution and resellerpartners worldwide.

Orckit was founded in 1990 and went public in 1996. Thecompany is active in APAC, Western and Eastern Europe,and America.

For more information please visit www.orckit.com.

Pushing technology to the edge

www.orck it. com

2011 Orckit-Corrigent

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ptn vs dual fabric pots for sdh migration 1212

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