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Next Generation SDH

Muhammad Zeeshan

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What We Will Cover

Connectionless data transport over SDH

Limitations of SDH

Next Generation SDHGeneric Framing Protocol (GFP)

Virtual Concatenation (VCAT)

Link Capacity Adjusting Scheme (LCAS)

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NG-SDH – The Background

Today’s telecommunications services are based on a diverse combination of technologies such as Ethernet, PDH, IP, SAN, etc

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Ethernet

Ethernet is the prevailing technology for LAN

LOCAL AREA NETWORK

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Ethernet in Metro Networks

Now it is also being considered as a good technology for access and metro networks

Metro

E

THERNET ETHERNET

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Why Worry About Ethernet?

Ethernet, the standard technology for local area networks (LANs), is:

Cheap

Easy to use

Always evolving toward higher rates

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Ethernet in Metro Networks

SDH

SDH

SDHSDH

SDH

SDH

SDH

SDH

METRO NETWORK

SDH

Ring-1

SDH

Ring-2

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NG-SDH – The Background

Carriers are looking at SDH for routing high volumes of Ethernet traffic to get long haul transport

Metro Metro

Metro

A N

Long Haul

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Connectionless Data Transport – A Real Challenge

A number of architectures have been developed for connectionless data transport (PoS, ATM, etc)

These are limited by cost, complexity or poor efficiency

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Connectionless Data Transport

Connectionless data transport requires long-hauls networks:

To encapsulate data packets

The need to use bandwidth accurately

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Why SDH In Long-Haul Networks?

SDH/SONET networks offer features for long-haul transport, that include:

Reliability

Scalability

Built-in protection

Management

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Trouble with SDH

The traffic type is changing

Challenge… How to use bandwidth efficiently for both voice and data traffic

Lack of fine granularity to accommodate all potential clients’ stream rates

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Trouble with SDH

The data packet transport (Ethernet, IP, DVB) is a challenge for SDH

This is because they are connectionless, use statistical multiplexing, and can be best-effort technologies

This is the opposite of SDH which is predictable and based on time division multiplexing (TDM)

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NG SDH – Drivers

The drive to SDH Next Generation development was:

The desire to find one simple encapsulation method that was capable of accommodating any data packet protocolsSecondly, the need to use bandwidth accurately

Solution … A new adaptation protocol layer is required and a new mapping mechanism for controlling bandwidth use

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Next Generation SDH

Next-generation SDH is the evolution and enhancement of existing SDH networks

It improves network efficiency and broadband service potential

SDH Next Generation enables transporting data efficiently, without needing to replace the installed equipment base

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The only change needed to update the network is to replace the edge nodesThe network is then ready to transport Ethernet, PPP, DVB or SAN frames

Next Generation SDH

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Next Generation SDH

How NG SDH resolve the problem

Components of NG SDH:Generic Framing Protocol (GFP)

Virtual Concatenation (VCAT)

Link Capacity Adjustment Scheme (LCAS)

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Next Generation SDH

These functions are implemented on the new MSSP nodes which are located at the edges of the network

They interact with the client data packets that are aggregated over the SDH/SONET backplane that continues unchanged

This means that the MSSPs represent the SDH Next Generation embedded in the legacy SDH network

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Next Generation SDH

The architectures are increasingly demanding long haul transport that today can only be provided by SDH/DWDM having a massive installed base, developed over recent decades

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NG-SDH Features

NG SDH enables operators to provide more data transport services while increasing the efficiency of installed SDH baseThe technology is implemented in the edge nodes only, no need to install an overlap network or migrating all the nodesThis reduces the cost per bit delivered, and will attract new customers while keeping legacy services

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NG SDH Nodes

Multiservice Provisioning Platform (MSPP)Includes SDH multiplexing, sometimes with add-drop, plus Ethernet ports, sometimes packet multiplexing and switching, sometimes WDM

Multiservice Switching Platform (MSSP)MSPP with a large capacity for TDM switching

Optical Edge Device (OED)An MSSP with no WDM functions

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NG SDH Nodes

Multiservice Transport Node (MSTN)An MSPP with feature-rich packet switching

Multiservice Access Node (MSAN)An MSPP designed for customer access, largely via copper pairs carrying Digital-Subscriber Line (DSL) services

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Generic Framing Protocol (GFP)

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GENERIC FRAMING PROTOCOL

Defined in ITU-T G.7041Its a mechanism for mapping constant and variable bit rate data over a transport network like synchronous SDH framesGFP support many types of protocols including those used in local area network (LAN) and storage area network (SAN)

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GENERIC FRAMING PROTOCOL

GFP adds a very low overhead to increase the efficiency of the optical layerThe client signals can be protocol data unit (PDU) oriented (like IP/PPP or Ethernet Media Access Control) or can be block-code oriented (like fiber channel)

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GFP-F Modes

Currently, two modes of client signal adaptation are defined for GFP:Frame-Mapped GFP (GFP-F)

Its a layer 2 encapsulation adaptation modeGFP-F entirely maps one complete client frame into a single GFP frameIdle packets are not transmitted resulting in more efficient transport To perform the encapsulation process it is necessary to receive the complete client packet, but this procedure increases the latencySpecific mechanisms are required to transport each type of protocol

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GFP-F Client Data Mapping

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GFP-T

Transparent GFP (GFP-T)Its a layer 1 encapsulation modeTransparent GFP (GFP-T) is a protocol-independent encapsulation method in which all client code words are decoded and mapped into GFP framesThe frames are transmitted immediately without waiting for the entire client data packet to be received It is used to adapt block-oriented client data (Gigabit Ethernet, Fiber Channel and Digital Video Broadcast (DVB)) GFP-T can adapt multiple protocols as long as they are based on 8B/10B line coding

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Encapsulation mechanism and the transport of the GFP frames into VC containers

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GFP Frame Formats And Protocols

Core Header

Payload Header

Extension Header (optional)

Payload

Checksum (optional

P L I

cHEC (CRC-16)

E X I

eHEC (CRC-16)

PTI PFI EXI Type

U P I

tHEC (CRC-16)

Payload

pFCS (CRC-32)

PLI: PDU Length Indicator

cHEC: core HEC protection

PTI: Payload Type Identifier

PFI: Payload FCS IndicatorEXI Type: Extension Header Identifier

UPI: User Payload Identifier tHEC: Type HEC protection

EXI: Extension Header Identifier

eHEC: Extension HEC protection

Payload: Space for framed PDU

pFCS: Payload FCS

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GFP-F and GFP-T Comparison

Byte GFP-F GFP-T

Protocol Transparency Low High

Efficiency High Low

Delay-sensitive protocols No Yes

Encapsulation Protocol Level Layer 2 Layer 1

Optimized for Ethernet SAN, DVB

Statistical multiplexing of several client signals

Yes No

SAN transport No Yes

Ethernet transport Optimum Possible

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Virtual Concatenation (VCAT)

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Concatenation

Concatenation is the process of summing the bandwidth of “X” containers into a larger container

It is well indicated for the transport of big payloads requiring a container greater than VC-4,

But it is also possible to concatenate low-capacity containers, such as VC-11 or VC-12

There are two concatenation methodsContiguous concatenation

Virtual concatenation

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Contiguous Concatenation

It creates big containers that cannot split into smaller pieces during transmission

For this, each NE must have a concatenation functionality

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ContiguousConcatenation

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Virtual concatenation

It transports the individual VCs and aggregates them at the end point of the transmission path

For this, concatenation functionality is only needed at the path termination equipment

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VirtualConcatenation

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Virtual ConcatenationVirtual ConcatenationNo Concatenation

VCAT

2.5 Gbps OC-48/STM-16

packed at nearly 88% efficiency

Gig Ethernet(1.0/1.2 Gbps)

STS-3c-7v/VC-4-7v(1050 Mbps)

DataData

ESCON(160/200 Mbps)

STS-1-4v/VC-3-4v(196 Mbps)

SANSAN

STS-3/STM-1(150 Mbps)

TDMTDMOC-3/STM-1(155 Mbps)

2.5 Gbps OC-48/STM-16 low

efficiencyGig Ethernet

(1.0/1.2 Gbps)

1050 Mbps

DataData

150 Mbps

TDMTDMOC-3/STM-1(155 Mbps)

155 Mbps STM-1 high efficiency

ESCON(160/200 Mbps)

196 Mbps

SANSAN

622 Mbps OC -23/STM-4 low

efficiency

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Contiguous and Virtual Concatenation Comparison

Contiguous concatenation is less bandwidth-efficient than virtual concatenation

Virtual concatenation (VCAT) is a solution that allows granular increments of bandwidth in single VC-n units

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Contiguous and Virtual Concatenation Comparison

Service Bit Rate Contiguous Concatenation

Virtual Concatenation

Ethernet 10 Mbps VC-3 (20%) VC-11-7v (89%)

Fast Ethernet 100 Mbps VC-4 (67%) VC-3-2v (99%)

Gigabit Ethernet 1000 Mbps VC-4-16c(42%) VC-4-7v (95%)

Fiber Channel 1700 Mbps VC-4-16c(42%) VC-4-12v (90%)

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Link Capacity Adjustment Scheme (LCAS)

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LCAS

Virtual concatenation utilizes predefined bandwidth allocation, which does not match the variable bit rate patterns and the burst nature of most data networks

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Link Capacity Adjustment Scheme

It is standardized by the ITU-T as G.7042

LCAS is a signaling protocol for sizing virtually concatenated paths

With LCAS, VCG can be resized at any time without disturbing network traffic

LCAS can add and remove members of a VCG to match the variable bit rate patterns and the burst nature of most data networks

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Link Capacity Adjustment Scheme

LCAS signaling messages are exchanged to change the number of VCs between the source and the destination of the path

The number of VC can be increased or decreased without any frame loss therefore increasing or decreasing the capacity of the VCG link

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LCAS Protocol

Between the source and the sink LCAS is executed to monitor member status, to indicate changes on the VCAT bandwidth use, and acknowledge the changes.

LCAS is a protocol transported in H4 byte, if HO-VCAT is being used, or in K4, if LO-VCAT is being used

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GLOSSARY

PDUInformation that is delivered as a unit among peer entities of a network and that may contain control information, address information, or data.

PDUs are relevant in relation to one of the first 4 layers of the OSI model as follows:

The Layer 1 PDU is the bit

The Layer 2 PDU is the frame

The Layer 3 PDU is the packet

The Layer 4 PDU is the segment (e.g. TCP segment)

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GLOSSARY

tHECHEC is Header Error Control/Check

tHEC contains error control code to protect the contents of the type field

FCSFrame Check Sequence

pFCS is a CRC to protect the contents of GFP Payload

PoSPacket Over SDH; a protocol for transporting packetized data in the form of point-to-point (PPP) over SDH

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GLOSSARY

ESCONEnterprise Systems Connections; a data connection for mainframe to peripheral communication

DVBDigital Video Broadcasting a suite of standards for digital television

SANStorage Area Networks; an architecture to attach remote computer storage devices (Disk arrays, tape libraries) to servers

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GLOSSARY

STSSynchronous Transport Signal; SONET data rate (STS-1, STS-3 etc)

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THANK YOU