Cisco SDH Presentation

Network ArchitectureNetwork Architecture

Chapter 1Chapter 1

© 2001, Cisco Systems, Inc.

© 2001, Cisco Systems, Inc. Network Architecture-2

ObjectivesObjectives

Upon completion of this chapter, you will be able to perform the following tasks: • Identify the main terms used to describe

network components

• Describe the link structure and network elements

• Describe the interface options and interface layers


AgendaAgenda

1.1 - Link Structure and Line Interfaces

1.2 - Network Elements

Summary, Information Resources

Link Structure and Line Interfaces

Link Structure and Line Interfaces

Section 1.1Section 1.1




Upon completion of this section, you will be able to perform the following tasks:• Describe the functionality and interaction of the

interface layers

• Define the three overhead layers

• Describe the topology concepts related to the overhead layers

• Describe the main features of electrical and optical interfaces


Overhead Layer ConceptsOverhead Layer Concepts

path

path termination

pathtermination

service (E1, E4..)mapping demapping

service (E1, E4..)mapping demapping

PTE PTE

multiplex section multiplex section

multipl. section termination

ADMor

DCS

regeneratorsection

regen. section termination

regen. sectiontermination

REG REG

PTE = path terminating elementMUX = terminal multiplexerREG = regeneratorADM = add/drop multiplexerDCS = digital cross-connect system

regen.section

regen.section

regeneratorsection


Regenerator SectionRegenerator Section

• Regeneration section layer is the lowest level of link components in a SDH network

• Deals with the transport of an STM-N frame across the physical medium

• Point-to-point connection between two regeneration section termination points with direct optical or electrical domain connectivity

• Terminated by Regenerator Section Terminating Equipment (RSTE)

• The Regeneration section is mainly designed to overcome physical limitations of the transport technology


Multiplex SectionMultiplex Section

• One or more consecutive regenerator sections might compose a multiplex section

– Main element to build different topologies (e.g. ring)

• Deals with the transport of path layer payloads across the physical medium

• Multiplex section is a point-to-point logical link that connects to ADM, MUX, or DCS devices

– These devices might not include a path termination

• Overhead is interpreted and modified by Multiplex Section Terminating Equipment (MSTE)

– Multiplex section (MS) overhead is accessed only after the section overhead has been first terminated


PathPath

• One or more connected multiplex sections may provide a transport service for a path

– Multiplex section may carry multiple paths by multiplexing

• Deals with the transport of various payloads between SDH terminal multiplexing equipment

• Path layer maps payloads into the format required by the MS Layer

• Communicates end-to-end via the Path Overhead (POH)

• POH is terminated and modified by Path Terminating Equipment (PTE)

– Regenerator and multiplex section overhead must be terminated to access the overhead


HO and LO PathsHO and LO Paths

• In SDH the PDH payload multiplexing is done at 2 different layers

• High-order (HO) path carries E3/E4 or similar payloads

– Organized into administrative units (AU) including higher order tributaries

• Low-order (LO) path carries E1/E2 or similar payloads

– Organized into tributary units (TU) including lower order tributaries


Topology ConceptsTopology Concepts

• SDH topologies are designed for providing a flexible and reliable transport for required paths

• Main issues:

– Capacity planning, bandwidth provisioning

– Redundancy, automatic fail-over

– Delay and jitter control

• Typical topology concepts:

– Point-to-point links (with protection) and DCS/MUX

• Arbitrary complex topology may be built

– Interconnected protected rings with ADM/DCS

• Minimum resource usage (physical media) for avoiding single point of failures


Physical Layer - I.Physical Layer - I.

Photonic

Path

Multiplex Section

Regen. Section

STM-N

Signal

Light

Pulse

VC and MS Overhead

Payload and Path Overhead

TerminalRegenerator

Optical Conversion

Terminal

Map internal signal and RS OH

into STM-N signal

Map Payload and Path OH into VC

Map VC and MS OH into internal

signal

Services (E1, E2, E3, E4, Video, etc.)

Regen. Section

Physical

Layers


Physical Layer - II.Physical Layer - II.

• Line coding applied:

– CMI for electrical interfaces

• Guarantees transmit-receive clock synchronization

– Binary NRZ for optical interfaces

• May change for very high speeds (STM-256 or higher) into RZ solitons

• Does not guarantee enough 1-0 or 0-1 changes, and thus clock transmit-receive synchronization

– Depends on the frame content

– Scrambling is needed for a guarantee


Electrical InterfacesElectrical Interfaces

• Defined to be as compatible as possible with existing PDH physical interfaces

–Same hardware should be used

• For intra-office applications only

–Maximum 150 m 75 Ohm coax for STM-1

• 155.520 Mbit/s, CMI line coding


Optical InterfacesOptical Interfaces

• Intra-office (application code: I-<n>)

– LED or MLM laser at 1310 nm or 1550 nm

– Up to 2 km, max. loss 7-12 dB

• Inter-office, short-haul (application code: S-<n.w>)

– Low power SLM or MLM laser at 1310 nm or 1550 nm

– Up to 15 km, max. loss 12 dB

• Inter-office, long-haul (application code: L-<n.w>)

– High power SLM or MLM laser at 1310 nm or 1550 nm (zero-dispersion or dispersion-shifted fiber)

– Up to 40-60 km, loss: 10-28 dB up to STM-1, 10-24 dB up to STM-16


SummarySummary

• Describe the functionality and interaction of the interface layers

• Define the three overhead layers

• Describe the topology concepts related to the overhead layers

• Describe the main features of electrical and optical interfaces


Review QuestionsReview Questions

• How many layers are used to build up a SDH network?

• What is the purpose of the Multiplex Section layer?

• What is the purpose of the HO Path overhead and the LO Path overhead ?

• Why do electrical and optical interfaces have different line coding?

• Is there a Regenerator Section termination in a Terminal Multiplexer?

• Is a usual add-drop multiplexer also a Path terminating equipment?

Network ElementsNetwork Elements





Upon completion of this section, you will be able to perform the following tasks:• Identify main network concepts

• Describe the functions of typical network elements


Network ConceptsNetwork Concepts

• Networks should be designed by decomposition

–Service needs into layers

–Logical connectivity needs into subnetworks

• Devices might be categorized by functionality and role in the network layers and topology

• Multiple set of functionality may be integrated into a single device if it is economically feasible


Terminal MultiplexerTerminal Multiplexer

• Terminal multiplexer is at the edge of the SDH network

–Provides connectivity to the PDH network devices and certain end-user equipment

• It includes a regenerator section, multiplex section, and path termination in one link


RegeneratorRegenerator

• A regenerator simply extends the possible distance and quality of a line by decomposing it into multiple sections

–Replaces regenerator section overhead

–Multiplex section and path overhead is not altered


Add-drop Multiplexer - I.Add-drop Multiplexer - I.

• Add/drop multiplexer (ADM)

– Main element for configuring paths on top of line topologies (point-to-point or ring)

– Multiplexed channels may be dropped and added

– Special drop and repeat mode for broadcast and survivability

– An ADM has at least 3 logical ports: 2 core and 1 or more add-drop

• Ports have different roles

• No switching between the core ports

• Switching only between the add-drop and the core ports


Add-drop Multiplexer - II.Add-drop Multiplexer - II.

• ADM always includes regenerator and multiplex section termination. However paths might not be terminated, but only switched from one multiplex section’s channel to another multiplex section’s channel

• ADM may be integrated with terminal multiplexer functionality for direct interfacing to non-SDH network elements

• ADM always processes and replaces the multiplex section overhead

– ADM may not change the path overhead (POH)

• POH is changed only if terminal multiplexer function is included


SDH Cross-connectSDH Cross-connect

• ADM concept is extended to have many similar capacity ports with any-to-any channel connectivity: the resulting device is called a Digital Cross-connect (DCS)

– SDH DCS may have only 2 logical ports

• Pure SDH DCS may connect only STM-1 or higher channels with each other

– Cross-connects are named after historical patch panels interconnecting regenerator or multiplex section termination devices

• Pure SDH DCS may not include path termination, switching of channels is typically done at the multiplex section layer


Wideband Digital Cross-connect

Wideband Digital Cross-connect

• SDH wideband digital cross-connect (WDCS) is designed for interconnecting a large number of channels at the LO path (e.g. E1 basic PDH) level

• SDH WDCS has only SDH ports carrying a large number of LO path payloads

• Interconnection of LO paths may be done virtually, without a physical LO path termination

–Provides an economical alternative to legacy physical E1 cross-connects


Broadband Digital Cross-connect

Broadband Digital Cross-connect

• Broadband digital cross-connect (BDCS) uses a transparent switch matrix for HO path speeds to interconnect a large number of channels

• HO path BDCS has a similar architecture to a WDCS in an integrated device

• Many SDH ports carrying HO path payloads

– Interconnect without physical HO path termination


Subscriber Loop Access System

Subscriber Loop Access System

• Subscriber loop access system (SLAS) is a concentrator of low speed services

– Provides an efficient feed of subscribers into the central office by using multiplexing to create a higher speed trunk line

• By using SLASs at the edge of the network, the cross-connects and ADMs can be optimized by having ports with concentrated end-user services

• SLAS does not provide a local switching function between the input channels, only aggregation


SummarySummary

• Identify main network concepts

• Describe the functions of typical network elements



• What is the purpose of a regenerator equipment?

• What is a Subscriber Loop Access System (SLAS)?

SummarySummary

Information ResourcesInformation Resources



QuestionsQuestions

?



• Books

–Mike Sexton, Andy Reid: “Broadband Networking: ATM, SDH, and SONET”

• Artech House, 1997. ISBN 0-89006-578-0

• Web

– ITU-T standards

• http://www.itu.int

–ETSI standards

• http://www.etsi.org

http://www.itu.int/

http://www.etsi.org/


SummarySummary

After completing this chapter, you should be able to perform the following tasks:• Identify the main terms used to describe

network components

• Describe the link structure and network elements

• Describe the interface options and interface layers

Frame StructureFrame Structure

Chapter 2Chapter 2



Upon completion of this chapter, you will be able to perform the following tasks: • Identify the main frame concepts

• Describe the basic structure of frames at various hierarchy levels

• Make basic computations for bit rates at various hierarchy levels

• Describe the internal details of payloads and overheads


AgendaAgenda

2.1 - Frame Concept

2.2 - STM-1 Frames

2.3 - STM-n Frames

2.4 - Frames and Rates

2.5 - Payload Internals

2.6 - Overhead Internals


Frame ConceptFrame Concept




Upon completion of this section, you will be able to perform the following tasks:• Describe the notation for electrical and optical

signals

• Describe the two-dimensional frame model

• Describe the main components of the frame


Electrical and Optical SignalsElectrical and Optical Signals

• STM-<N> is electrical, STM-<N>O is optical

• STM-<N>c means concatenated

–Not multiplexed signal

–Originates at that speed

–Administrative overhead optimized compared to real multiplexed signal

• Frame format is independent from electrical or optical signals

–For simplicity we will always refer to STM-<N> only


Two-dimensional Frame ModelTwo-dimensional Frame Model

• Fixed 125 microseconds frame time length

–To support 8 KHz sampled voice applications

• Bytes organized into rows and columns

–Administrative channels are rate decoupled for easier processing

• STM-1 frame is organized into 270 (3 x 90) columns by 9 rows

–Frame size is 2430 bytes

–9 x 270 bytes/frame x 8 bits/byte x 8000 frame/s = 155.52 Mbit/s


SONET CompatibilitySONET Compatibility

• STM-0 frame is defined to be compatible with STS-1 of SONET

– Originally it was only a virtual tool to show SONET compatibility (not part of ITU-T specifications in 1993)

– Recently it has become a valid real-life frame format for microwave links (proposed by ETSI, included into new merged ITU-T G.707 standard in 1996)

• STM-1 has a compatibly structure with STS-3 of SONET

• Although STM-0 is already defined, for historical reasons most SDH discussions are based on STM-1

– In many places specifications use a multiplication by the hierarchy level, so 0 cannot be used


Path Terminator Path TerminatorREG REGADM

or DCS

M-Section M-Section

Path

R-Section R-Section R-Section R-Section

OverheadsOverheads

• 3x3=9 columns section overhead (SOH) for STM-1

– Includes a complex set of OAM information

– 3 rows (27 bytes) for regenerator section (RS) overhead (RSOH)

– 1 row (9 bytes) for administrative unit (AU) pointer

– 5 rows (45 bytes) for multiplex section (MS) overhead (MSOH)

• Path overhead (POH)

– Provides framing for payload, not part of SOH


Payloads - I.Payloads - I.

• Two main types of payloads:

– Multiplexed voice channels originated in PDH based devices

– Transparent bit stream services

• May be used for data packet transport or ATM

• Payloads are organized into paths over the network

– Different path types based on the content

• STM path, HO or LO path etc.

• Payloads are managed by using the multiplex section overhead (MSOH) and the path overhead (POH)


Payloads - II.Payloads - II.

• Payloads are put into a so called payload or VC (virtual container) capacity

– Frames provide a higher bit rate than the payload

• Required to be able to compensate for frequency differences

– Similar concept to PDH stuffing

• Payloads may arrive with very different phases

– Varying line delays cannot be avoided in a WAN with long distances

• Light needs some time to reach from the transmitter to the receiver that is much bigger than the bit timing interval or the frame cycle time


PointersPointers

• Pointers were included into SDH design to provide tools to compensate for incoming payload phase differences

–Without extensive buffering

• So not too much delay and jitter

• Advantage over PDH network where this problem was solved by asynchronous multiplexing and a lot of bad consequences

• Pointers make it possible to create ring topologies (efficient fail-over redundancy) for SDH


SummarySummary

• Describe the notation for electrical and optical signals

• Describe the two-dimensional frame model

• Describe the main components of the frame



• Why are SDH frames repeated every 125 micro-seconds?

• Why are overhead channels distributed evenly in the bit stream?

• Why are pointers needed to implement ring topologies?

STM-1 FramesSTM-1 Frames




Upon completion of this section, you will be able to perform the following tasks:• Describe the overall structure of the frame

• Describe the payload pointer solution for timing differences


General StructureGeneral Structure

9 columns 261 columns

270 columns

VC Capacity(for AUG)

Sectionoverhead(SOH)

1st

2nd

Order of transmission


Synchronous Payload Envelope - I.

Synchronous Payload Envelope - I.

• SPE = Synchronous Payload Envelope is the common sense name (also used for SONET)

• AUG = Administrative Unit Group is the official ITU-T name for the SPE + 4. row of SOH (AU pointer)

– 261 columns x 9 rows

– POH is 1 column

– Fixed stuffing depends on internal structure of AUG

– 260 columns = 2340 bytes for AUG-4 payload capacity

• AUG may be composed by different type of administrative units (AU)

– 1 x AU-4 (specific to carry PDH E4, not compatible with SONET frame structure)

– Or 3 x AU-3 (compatible with SONET frame structure)


Synchronous Payload Envelope - II.

Synchronous Payload Envelope - II.

• Administrative unit is composed of a pointer and a virtual container (VC)

– Pointer for VC-4 inside an AU-4 is the full 4. row of SOH

– Pointer for VC-3 inside an AU-3 is determined by a 1:3 demultiplexing of the 4. row of SOH

• VC inside AU may begin anywhere in STM-1 VC capacity

• AU (payload) pointer in SOH designates the first byte of VC inside AU (SPE)


STM-1 VC-3 Capacity Structure


1 column

87 columns

30. column

Payload Capacity

59. column

Path overhead(POH)

Path overhead(POH)

Path overhead(POH)

Path overhead(POH)Fixed stuffFixed stuff




1 column

261 columns

Payload Capacity

Path overhead(POH)

Path overhead(POH)


Payload PointerPayload Pointer

Section Overhead

90 (VC-3) or 270 (VC-4) Columns

9 Rows

STM-1 Frame #1

9 Rows

STM-1 VC-3 or VC-4

125 μsec

250 μsec

STM-1 Frame #2

H1 H2 H3...

Payload Pointer marksstart of STM-1 VC-3 or

VC-4

Payload Pointer marksstart of STM-1 VC-3 or

VC-4

STM-1 VC-3 or VC-4POH column

STM-1 VC-3 or VC-4POH column


SummarySummary

• Describe the overall structure of the frame

• Describe the payload pointer solution for timing differences



• What is the size of a basic STM-1 frame?

• Which type of frame has been defined to show compatibility with SONET ?

• What are the overheads carried by a STM-1 frame?

• What is the purpose of pointers in a SDH frame?

STM-n FramesSTM-n Frames




Upon completion of this section, you will be able to perform the following tasks:• Describe the overall structure of multiplexing

frames

• Describe the main steps of the multiplexing process

• Identify the concept of concatenated payloads

• Determine the details of frame structures for a common hierarchy level


General StructureGeneral Structure

• STM-N structure

– Byte-interleaving STM-1 modules

• No extra overhead introduced

• Overhead of multiplexed signals taken over, but section overhead (SOH) should be replaced with new information for the STS-N multiplex section

• Overhead is growing in absolute number of bits, but relative size is the same

• New overhead is bigger than necessary for regenerator and multiplex section overheads, so some bytes are unused

– Section overhead (SOH) is frame aligned

– SPE (multiplexed VC-3 or VC-4 channels) is not frame aligned


125 μsec

9 Rows

Section Overhead

270 x N Columns

9xN Columns

STM-N VC capacity

STM-N frameSTM-N frame


Multiplexing ProcessesMultiplexing Processes

• Multiplexing is composed of various processes:

– Mapping

• Tributaries adapted into Virtual Containers (VC) by adding stuffing and POH

– Aligning

• Pointer is added to locate the VC inside an AU or TU

– Multiplexing

• Interleaving the bytes of multiple paths

– Stuffing

• Adding up the fixed stuff bits to compensate for frequency variances


Concatenated FramesConcatenated Frames

FixedStuff(9X-9bytes)

9 Rows

STMPOH

9 bytesSTS-Xc Payload Capacity

(AU-4-Xc)

X x 261 Columns

125 μsec

STM-4c = 599.040 Mbit/sSTM-16c = 2396.160 Mbit/s

X x 260 Columns

SDH terminology is using X instead of N (X = N)

X-1 ColumnsX-1 Columns


Frame Structures for Each Common Hierarchy Level

Frame Structures for Each Common Hierarchy Level

270 Columns

9 Rows

9 Rows

9 Rows

1,080 Columns

4,320 Columns

STM-1

155.52 Mbit/s

STM-4

STM-16

622.08 Mbit/s

2488.32 Mbit/s

STM-64 9 rows x 17280 columns, 9953.28 Mbit/s


SummarySummary

• Describe the overall structure of multiplexing frames

• Describe the main steps of the multiplexing process

• Identify the concept of concatenated payloads

• Determine the details of frame structures for a common hierarchy level



• What is the big advantage of the SDH multiplexing concept over PDH in terms of overhead?

• Why is it important to have more fixed stuffing at higher line rates?

• What is the concept behind allocating the amount of fixed stuffing?

Frames and RatesFrames and Rates




Upon completion of this section, you will be able to perform the following tasks:• Identify the various bit rates used to

characterize TDM networks

• Describe how the multiplexing process affects the bit rates

• Make the computation to summarize the rate hierarchy


Line, SPE and Payload RatesLine, SPE and Payload Rates

• Line rate = SOH + SPE

• SPE rate = POH + payload capacity + fixed stuffing

• VC payload capacity rate = line rate - SOH - POH - fixed stuffing

• Transparent bit-stream capacity rate = line rate - SOH - POH

• Example for STM-1 frame line rate:

–270 columns x 9 rows = 2430 bytes

–8000 fps x 19440 bits = 155.52 Mbit/s


Multiplexing Effect on RatesMultiplexing Effect on Rates

• Because of synchronous TDM byte-multiplexing the line rate is simply multiplied

• Example for STM-4 frame line rate:

– 4 x STM-1 byte-multiplexing

– 4 x 155.52 Mbit/s = 622.08 Mbit/s

• With higher level concatenated frames the transparent bit-stream capacity rate increases slightly as a relative value

– Since the POH is a fixed absolute value in this case

– However, fixed stuff may use up this extra capacity


Rate HierarchyRate Hierarchy

SDH Level

Line Rate (Mbit/s)

SPE Rate (Mbit/s)

Optical Level

Electrical Level

STM-1 OC-3 STS-3 STM-4 OC-12 STS-12STM-16 OC-48 STS-48STM-64

155.52622.08

2488.329953.28 OC-192 STS-192

STM-256 39813.12

150.336601.344

9621.50438486.016 OC-768 STS-768

SONET

2405.376


SummarySummary

• Identify the various bit rates used to characterize TDM networks

• Describe how the multiplexing process affects the bit rates

• Make the computation to summarize the rate hierarchy



• Is the SPE rate a good measure of the capacity available to a data transport client?

• What is the VC payload capacity rate of a concatenated 40 Gbit/s SDH signal? Demonstrate the computation steps!

• How much frequency variation is allowed by the fixed stuffing in a 10 Gbit/s SDH signal? Demonstrate the computation steps!

Payload InternalsPayload Internals




Upon completion of this section, you will be able to perform the following tasks:• Identify the need for special structures to

support a mixture of payloads

• Describe the grouping options of various payloads

• Describe the pointer processing associated with the individual payloads


Administrative and Tributary Units

Administrative and Tributary Units

• Multiplexing of PDH signals inside SDH is organized using administrative and tributary units

– One more multiplexing level than SONET

• Administrative unit (AU) is a special construct for SDH, which allows two alternative ways of multiplexing and thus supporting PDH E4 mapping and SONET compatibility at the same time

• Tributary unit is a construct which accommodates various PDH signals at the lower level

• AU and TU are both called units, because both are composed from a virtual container and a pointer

• Byte-multiplexed AUs and TUs are called an AU group (AUG) and a TU Group (TUG) respectively


Virtual Containers - I.Virtual Containers - I.

• Virtual containers (VC-x) encapsulate a PDH payload with a special framing and a POH

• In SDH terminology, the original PDH payload with special framing is called a container (C-x)

• Various container sizes with some space for stuffing are defined

– C-11 for DS1 (25 bytes = 1.600 Mbit/s)

– C-12 for E1 (34 bytes = 2.176 Mbit/s)

– C-2 for DS2 (106 bytes = 6.784 Mbit/s)

– C-3 for DS3 or E3 (84 columns = 48.384 Mbit/s)

– C-4 for E4 (260 columns = 149.760 Mbit/s)


Virtual Containers - II.Virtual Containers - II.

• Various VC sizes defined:

– With 1 byte allocated for POH

• VC-11 for DS1 (26 bytes = 1.664 Mbit/s)

• VC-12 for E1 (35 bytes = 2.240 Mbit/s)

• VC-2 for DS2 (107 bytes = 6.848 Mbit/s)

– With 1 column allocated for POH

• VC-3 for DS3 or E3 (85 columns = 48.960 Mbit/s)

• VC-4 for E4 (261 columns = 150.336 Mbit/s)


Tributary Unit StructureTributary Unit Structure

• TUs are defined to fit into a number of columns

– This requirement determines the size of virtual containers and containers

– TU-3 adds up 3-byte pointer plus stuffing to VC-3

– Lower TUs add up 1 byte for pointer storage

• Organized into 4 frames (500 μs multi-frame)

• This provides V1, V2, V3, V4 TU pointer bytes

• Lower TUs also organize POH along the multi-frame

– This provides V5, J2, N2, K4 POH bytes


AUAUAU

DS1 E1 DS1C DS2TUDS1 E1 DS1C DS2TUDS1 E1 DS1C DS2TU

Mapping Hierarchy - I.Mapping Hierarchy - I.

STM-N

STS-1 Frame

STS-1 Frame

STS-1 Frame

STM-1 Frame

AU

DS1 E1 DS2 DS3/E3 E4

SPE-Nc

IP/ATM/Video

DS1 E1 DS1C DS2TU

DS3/E3

DS1 E1 DS1C DS2TU


Mapping Hierarchy - II.Mapping Hierarchy - II.

C-4

C-3

C-2

C-12

C-11

VC-4

VC-3

VC-2

VC-12

VC-11

TU-3

TU-2

TU-12

TU-11

VC-3

STM-N AUG AU-4139 Mbit/sATM

AU-3

TUG-3

44 Mbit/s34 Mbit/s

TUG-26.3 Mbit/s

2 Mbit/s

1.5 Mbit/s

xN

x3

x1

x7

x7

x4

x3

x1

x3

STM-0

x1

VT-1.5VT-1.5

VT group

VT group

STS-1SPE

STS-1SPESTS-1STS-1

STS-3NSTS-3N

DS3 BULKDS3 BULK

STS-3c BULKSTS-3c BULK

AUG

Aligning

Mapping

xNMultiplexing

x1


Pointer Processing - I.Pointer Processing - I.

• Pointer processing compensates for phase differences and small frequency variations (lasting for a number of frames)

• 10-bit pointer offset is stored in the H1, H2 overhead bytes (normal range is 0-782)

– Specifies the byte position after the last H3 byte in the VC capacity

– For AU-4 the byte position is 3 x (pointer offset) + 1

• TU pointer processing has a similar concept but different implementation details

– TU-3 uses H1, H2, H3 bytes inside the TU payload capacity

– Lower TUs use V1, V2, V3, V4 bytes in 500 μs multi-frame


Pointer Processing - II.Pointer Processing - II.

• AU-4 positive frequency justification

– If the tributary has a lower speed than its nominal rate, then 3 stuffed bytes are inserted just after the last H3 overhead byte

– Indicated by an inversion of the I-bits in the H1, H2 overhead bytes

• AU-4 negative frequency justification

– If the tributary has a higher speed than its nominal rate, then H3 overhead bytes are used to carry extra payload bytes

– Indicated by an inversion of the D-bits in the H1, H2 overhead bytes


Low- and High-order PathsLow- and High-order Paths

• 2 mapping levels may be clearly identified in SDH:

– AU for high-order (HO) paths

• Direct termination of DS3, E3, E4, ATM

• May carry multiple LO paths by multiplexing

– TU for low-order (LO) paths

• Termination of DS1, DS2, DS3, E1, E3

• 2 special layered networks on top of STM-1 SDH network

– HO and LO networks

– Managed by HO-POH and LO-POH information

• DS3/E3 may be part of both the HO or the LO network


SummarySummary

• Identify the need for special structures to support a mixture of payloads

• Describe the grouping options of various payloads

• Describe the pointer processing associated with the individual payloads



• What are the two pointer options used by an AUG?

• Does an E3 client signal belong to a High-order Path or to a Low-order Path?

• What is the main difference between positive and negative frequency justification?

Overhead InternalsOverhead Internals




Upon completion of this section, you will be able to perform the following tasks:• Describe the multiplexing process of overhead

bytes

• Describe the meaning of overhead bytes at various hierarchy levels


STM-1 OverheadsSTM-1 Overheads

• STM-1 overheads were designed to be compatible with SONET overheads

–Thus STM-1 overhead looks very similar to STS-3 overhead

• Easiest to understand by drawing STM-0 section overhead first

• Then creating STM-1 section overhead by multiplexing STM-0 3 times, and leaving out unnecessary bytes

• POH is not changed by multiplexing


STM-0 OverheadsSTM-0 Overheads

Data ComD8

Data ComD4

Data ComD7

Data ComD10

Data ComD5

Data ComD11

Data ComD6

Data ComD9

Data ComD12

APSK2

APSK1

Data ComD1

Data ComD3

Data ComD2

Section Overhead

Path TraceJ1

BIP-8B3

Signal LabelC2

Path StatusG1

User ChannelF2

Multiframe Indicator

H4

User ChannelF3

APSK3

TandemN1

FramingA1

BIP-8B1

PointerH1

BIP-8B2

SyncS1

OrderwireE1

PointerH2

RS TraceJ0

User ChannelF1

(REI)(M1)

PointerH3

OrderwireE2

HO PathOverhead

R-SectionOverhead

M-SectionOverhead

FramingA2

AU pointer


STM-1 Section OverheadSTM-1 Section Overhead

A1 A1 A1 A2 A2 A2 J0

B1 E1 F1

D1 D2 D3

H1 H1* H2 H2* H3 H3 H3

B2 K1 K2

S1 M1 E2

B2 B2

D4

D7

D10

D5

D8

D11

D6

D9

D12

H1* = 10010011

H2* = 11111111

H2*H1*

R-SectionOverhead

M-SectionOverhead

AU pointer

Δ

Δ

Δ

Δ

Δ

Δ

Δ - media dependent

national use


STM-N Section OverheadSTM-N Section Overhead

• Created by multiplexing STM-1 section overheads

• Only a few bytes are extended into each position

–A1/A2, B2, national use

• Most bytes are not multiplied by multiplexing, only the first appearance is used in the higher level (bigger) frames


Regenerator Section Overhead Bytes

Regenerator Section Overhead Bytes

• Framing bytes (A1, A2)

– Identify the start of each STM-0 frame

• R-Section Trace (J0)

– Used to trace the origin of the STM-1 frame

• BIP-8 = Bit Interleaved Parity (B1)

– Checks even-parity on previous STM-N frame after scrambling

• Orderwire (E1)

– 64 Kbit/s voice path used for communication

• User (F1)

– Optional, vendor specific

• DCC = Data Communications Channel (D1-D3) D1 D3D2

A1

B1 E1

J0

F1

A2

R-Section OH


1 2 3 4 5 6 7 8 268 269 270

271 273

2430

H1 c c H2 c cSTM-1 SDHFrame

Section Overhead (SOH) Path

Overhead (POH)

SPE

D1 D2 D3

R-Section

M-SectionK1 K2

Data Communication Channel (DCC)


• Formed by the D1, D2 and D3 bites in the Section Overhead

• Creates a 192 Kbit/s link

• Used for monitoring, alarms, provisioning, and software download

• Protocol is point-to-point between ADMs

• Today protocol is proprietary

• Moving to IS-IS, CLNS and ES-IS

109


AU Pointers AU Pointers

• Pointer (H1, H2)

– Two bytes used to indicate the offset between the pointer bytes and the first byte of the SPE

– Also indicates concatenation

• Pointer Action (H3)

– Used to compensate for the SPE timing variations

• Positive/negative stuff bytes

– Pointer bytes tell when H3 is being usedK2K1

H1

B2

D7

D10

S1

H2

D8

D11

M1

H3

D9

D12

E2

D6D5D4

M-Section OH


10 268 269 2701 2 3 4 5 6 7 8 9

271 273

2430

H1 H1 H1 H2 H2 H2

87 89 90

810

1 2 3

H1 H2

Section Overhead (SOH)

SPE

STM-1

3 x AU-3's

Pointer Bytes (H1, H2) for AU-3 Based Frames

Pointer Bytes (H1, H2) for AU-3 Based Frames

• STM-1 pointer bytes usage:

– 3 x AU-3 bit streams should be located

Path Overhead (POH)


Multiplex Section Overhead Bytes - I.

Multiplex Section Overhead Bytes - I.

• BIP-24 (B2) interleaved parity

– Used for STM-N multiplex section error monitoring

• Parity check on MSOH and previous STM-N frame before scrambling

• Provided for each STM-1 inside STM-N

• APS = Automatic Protection Switching (K1, K2)

– APS commands and error conditions between line termination equipment

K2K1

H1

B2

D7

D10

S1

H2

D8

D11

M1

H3

D9

D12

E2

D6D5D4

M-Section OH


Multiplex Section Overhead Bytes - II.

Multiplex Section Overhead Bytes - II.

• DCC (D4-D12)

– Uses same protocols and procedures as the RS-DCC

– For OAM&P messages between OSS and SDH multiplex-section-level equipment

• Synchronization Status (S1)

– Allows the SDH equipment to choose the best clocking source from many candidates

• STM-N REI-L (M1)

– Multiplex Section Level Remote Error Indicator

• Orderwire (E2)

– 64 Kbit/s voice channel

• Defined only in the first STS-N signal

K2K1

H1

B2

D7

D10

S1

H2

D8

D11

M1

H3

D9

D12

E2

D6D5D4

M-Section OH


Path Overhead Bytes - I.Path Overhead Bytes - I.

• STS Path Trace (J1)

– Fixed length Access Point ID enabling the path terminator to verify connection

• 15-byte E.164 address plus 1 byte CRC-7

• A 64-byte version permitted for SONET compatibility

• Path BIP-8 (B3)

– Parity check of previous VC before scrambling

Path TraceJ1

BIP-8B3

Signal LabelC2

Path StatusG1

User ChannelF2

IndicatorH4

User ChannelF3

APSK3

TandemN1

Path OH


Path Overhead Bytes - II.Path Overhead Bytes - II.

• Path Signal Label (C2)

– VC content type (mapping)

• Path Status (G1)

– Allows the entire path to be monitored end to end

– Used to notify the originating end of the path

• Performance and status of the entire duplex path

• Carries the Remote Error Indicator (REI) and the path Remote Defect Indicator (RDI)

Path TraceJ1

BIP-8B3

Signal LabelC2

Path StatusG1

User ChannelF2

IndicatorH4

User ChannelF3

APSK3

TandemN1

Path OH


Path Overhead Bytes - III.Path Overhead Bytes - III.

• Path User Channel (F2)

– Used by the network provider for internal network communications

• Position and Sequence Indicator (H4)

– Used when the frame is organized into various mappings like Virtual Tributaries or ATM cells

• User Channel (F3)

• APS (K3)

• Network Operator Byte (N1)

Path TraceJ1

BIP-8B3

Signal LabelC2

Path StatusG1

User ChannelF2

IndicatorH4

User ChannelF3

APSK3

TandemN1

Path OH


SummarySummary

• Describe the multiplexing process of overhead bytes

• Describe the meaning of overhead bytes at various hierarchy levels



• What are the H1 and H2 bytes in the Multplex Section overhead used for?

• What are the A1 and A2 bytes in the Regenerator Section overhead used for?

• Why is the parity computed before scrambling?

• Is there a difference between SDH frames in various countries?

SummarySummary



QuestionsQuestions

?



• Books

–Stamatios V. Kartalopoulos: “Understanding SONET/SDH and ATM”

• IEEE, 1999; ISBN 0780347455


SummarySummary

After completing this chapter, you should be able to perform the following tasks:• Identify the main frame concepts

• Describe the basic structure of frames at various hierarchy levels

• Make the basic computation for bit rates at various hierarchy levels

• Describe the internal details of payloads and overheads

Topology and Protection

Topology and Protection

Chapter 3Chapter 3



Upon completion of this chapter, you will be able to perform the following tasks: • Identify the main issues in topology design

• Define the main topologies

• Identify the main protection switching concepts

• Describe the operations of typical topology configurations


AgendaAgenda

3.1 - Topology Basics

3.2 - Protection Switching

3.3 - USHR Topology

3.4 - BSHR Topology


Topology BasicsTopology Basics




Upon completion of this section, you will be able to perform the following tasks:• Identify main topology alternatives

• Describe routing and provisioning concepts


• Point-to-point

– Used for SDH island trunks in old asynchronous networks, or data services as POS or ATM links

• Linear point-to-multipoint

– Adds up ADM in the middle

– Max. 16 nodes

• Hub network

– A DCS interconnects ADMs

• Ring

– ADMs are put into a ring

– Redundant, multiple connected rings

• Automatic protection switching (APS)USHR

Topology AlternativesTopology Alternatives


Uni- and Bi-directional Routing

Uni- and Bi-directional Routing

• Only working traffic is shown

• Subnetwork (path) or multiplex section switching for protection

A

CE

BF

D

Uni-directional Ring(1 fiber)

C-A

A-CA

CE

BF

D

Bi-directional Ring(2 fibers)

C-A

A-C


Add-drop ProvisioningAdd-drop Provisioning

• Transport connections over a SDH infrastructure are created by add-drop provisioning

–A path is built up by specifying hop-by-hop which channels should be added to a ring and which channels should be dropped from the ring

• Add-drop provisioning is typically done by the network management system

–There is no signaling protocol


ADM2

ADM3

ADM1

ADM4

OC-12

Drop

Add 1-3

Add 3-4

Drop

Add 4-2

Drop

Add and Drop ExampleAdd and Drop Example

• STM-4 Ring

• 4 x STM-1 channels

• Uni-directional routing

• Provisioning:

– add 1-3 (drop 3-1)

– add 3-4 (drop 4-3)

– add 4-2 (drop 2-4)

• 2 channels occupied


Drop and Continue ExampleDrop and Continue Example

• STM-4 Ring

• 4 x STM-1 channels

• Uni-directional routing

• Provisioning:

– add 1-2,3

– add 2-4,1

• 2 channels occupied

ADM2

ADM3

ADM1

ADM4

OC-12

Add 1-2,3

Add 2-4,1

Drop

Drop

Drop & Continue

Drop & Continue


Uni- and Bi-directional Example

Uni- and Bi-directional Example

Provisioning:• add 1-3

• add 3-1

ADM2

ADM3

ADM1

ADM4

ADM2

ADM3

ADM1

ADM4

Uni-directional routing Bi-directional routing


SummarySummary

• Identify main topology alternatives

• Describe routing and provisioning concepts



• Which types of topologies does the SDH network support?

• Is there a signaling protocol that allows the addressing of different SDH nodes within a network?

Protection SwitchingProtection Switching




Upon completion of this section, you will be able to perform the following tasks:• Identify the main alternatives in creating

protection switching solutions

• Describe the main features of various configuration options

• Describe the operational steps in the activation of protection switching


Multiplex Section Protection Switching

Multiplex Section Protection Switching

• Conditions resulting in a protection switch:

– Loss of signal, loss of frame

– Line AIS (all 1’s)

– Signal degrade

• Excessive BIP-24 errors in MS overhead

LOS AIS

OCNREIupstream

downstream

Payload

R-SectionOverhead

M-SectionOverhead

information controllingprotectionswitching


Path Protection SwitchingPath Protection Switching

• Conditions resulting in a protection switch:

– Loss of pointer, STM or VC AIS

– Excessive BIP errors for STM path, BIP errors for VC path

R-SectionOverhead

M-SectionOverhead

Info controllingprotectionswitching

Payload

STMPath

Overhead

VCPath

Overhead

VCPayload


STM -N Mux

K1K2Read/Sel

K1K2Write

WorkingSTM-N

ProtectSTM-N

STM-N Mux

K1K2Write

K1K2Read/Sel

TributaryChannels

TributaryChannels

MSTE

MSTE

Automatic Protection Switching - I.

Automatic Protection Switching - I.

• APS = Automatic Protection Switching

– Allows network to react to failed lines, interfaces, or poor signal quality

• Performed over the entire STM-N payload

• Uses K1 and K2 bytes of MS Overhead


Automatic Protection Switching - II.

Automatic Protection Switching - II.

• K1 byte:

– Type of request (bits 1-4)

– Channel requested (bits 5-8)

• K2 byte:

– Channel selected (bits 1-4)

– Architecture (bit 5)

– Mode of operation (bits 6-8)

• e.g. Alarm Indication Signal (AIS), Remote Defect Indicator (RDI)

STM -N Mux

K1K2Read/Sel

K1K2Write

WorkingSTM-N

ProtectSTM-N

STM-N Mux

K1K2Write

K1K2Read/Sel

TributaryChannels

TributaryChannels

MSTE

MSTE


Uni- and Bi-directional APSUni- and Bi-directional APS

• Uni-directional APS

–Only traffic on the affected fiber is switched to the protect line

• Bi-directional APS

–TX and RX are both switched when channel is affected


Revertive and Non-revertive APS

Revertive and Non-revertive APS

• Revertive switching

–Will restore to the working channel when WTR timer expires

• Non-revertive switching

–Will not move to working channel after failure unless requested


Working facility

Protection facility

ADM/Router ADM/Router

1+1 Protection1+1 Protection

• Bi- or unidirectional

• Non-revertive

• Transmits traffic on both channels


Protection facility

Working facility


1:n Protection - I.1:n Protection - I.

• 1:1 protection (special case of 1:n)

– Bi- or unidirectional

– Revertive

– Typically dedicated protection

– May transmit traffic on both channels, or use protect for low priority traffic


Protection facility

Working facility


1:n Protection - II.1:n Protection - II.

• 1:n protection

– Bi- or unidirectional

– Revertive

– Shared protection facility


APS OperationsAPS Operations

• 1:n Bi-directional switching:

– Switch when transmitted bits K1:5-8 equals received bits K2:1-4

• 1:n Unidirectional switching

– Same as 1:n

• 1+1 Switching

– Bi-directional - as above

– Unidirectional - each end operates independently

• Switch occurs immediately without capability to reset


SummarySummary

• Identify the main alternatives in creating protection switching solutions

• Describe the main features of various configuration options

• Describe the operational steps in the activation of protection switching



• What is APS used for?

• What is the difference between a two-fiber uni- and bi-directional link?

• What is the difference between revertive and non-revertive protection switching?

• Which two bytes of the Multiplex Section overhead are used to initiate an APS?

USHR TopologyUSHR Topology




Upon completion of this section, you will be able to perform the following tasks:• Identify the main concepts in constructing

protected ring topologies

• Describe the main features and application areas

• Describe the typical operational scenarios

• Describe the standardization efforts for interoperability


USHR ConceptsUSHR Concepts

• USHR/P = Unidirectional Self-Healing Ring / Path Switched

• 2-fiber ring topology

– Head-end bridge, tail-end switch logical topology

• 1+1 protection with uni-directional routing on each fiber

• Traffic is sent in both directions on the ring on separate fibers

• The better signal is selected by the receiver


Application AreasApplication Areas

• Used in the access network or MAN

–All traffic homing into a central node

• e.g. CO

• Typical for STM-1, STM-4 rings


FeaturesFeatures

• Simplicity at the expense of capacity

–Bandwidth used, cannot be reused

• VC-1/2 and/or STM visibility

• Quick local fail-over independent from the rest of the network

–No signaling protocol needed


A

CE

BF

D

workingtraffic

protectiontraffic

Operations – Traffic FlowOperations – Traffic Flow

• One direction of duplex traffic between any two nodes goes through each ring link for both working and protection traffic

• Reverse direction of transmission is dedicated to protection

• Therefore, the maximum capacity of this ring equals the line rate, i.e. STM-4, STM-16 etc.


Operations – Fiber Cut - I.Operations – Fiber Cut - I.

• Protection dedicated - head end bridge

• Failure interrupts A-C working traffic

• Receiver at C detects failure

A

CE

BF

D

WorkingTraffic

ProtectionTraffic

Workingtraffic selected


A

CE

BF

D

WorkingTraffic

ProtectionTraffic

Protectiontraffic selected

Operations – Fiber Cut - II.Operations – Fiber Cut - II.

• Fiber cut recovery steps:

– Tail end (receiver) switches to protection traffic

– Only the receiving node knows about the protection switch

• No traffic lost


Operations – Node Failure - I.Operations – Node Failure - I.

• Protection bandwidth dedicated - head end bridge

• Failure interrupts A-C working traffic

• Receiver at C detects failure

A

CE

BF

D

WorkingTraffic

ProtectionTraffic

Workingtraffic selected

Node Failure


A

CE

BF

D

WorkingTraffic

ProtectionTraffic

Protectiontraffic selected

Node Failure

Operations – Node Failure - II.Operations – Node Failure - II.

• Node recovery steps:

– Tail end (receiver) switches to protection traffic

– Only receiving node knows about the protection switch

• Traffic to/from failed node is lost


StandardizationStandardization

• Basic APS operations are defined in ITU-T G.783

• USHR/P is originally not fully defined by ITU-T

• Later defined in ITU-T G.841 as general VC trail protection switching independent of the underlying topology

–USHR/P is called 1+1 unidirectional VC trail switching (ring topology is only a special case) with dedicated protection

• USHR/MS and other variants are more a theoretical possibility than real products


SummarySummary

• Identify the main concepts in constructing protected ring topologies






• Why is the USHR/P based APS very fast?

• Why is it natural to use only uni-directional APS in a USHR/P configuration?

• Why USHR/MS is not a practical idea?

BSHR TopologyBSHR Topology




Upon completion of this section, you will be able to perform the following tasks:• Identify the main concepts in constructing

protected ring topologies





BSHR Concepts - I.BSHR Concepts - I.

• BSHR/MS = Bi-directional Self-Healing Ring / Multiplex Section Switched

• 1:1, or 1:N redundancy options

• 2 fibers with shared protection configuration

– Half the bandwidth in each direction in a link is reserved for the shared protection of all traffic in that reverse direction of the link

• An even number of STM-1s are required

• 4 fibers for dedicated protection configuration

– Bi-directional routing on 2 fibers (working line)

– Each direction has a working and a protect fiber


BSHR Concepts - II.BSHR Concepts - II.

• Multiple fail-over options for 4-fiber BSHR/MS

– In normal operation traffic is sent only in the required direction

– During fiber interruption, the traffic is routed around the break in opposite direction (long path)

• Ring switching

– Optionally if the other 2 fibers are still available, then traffic might be routed onto the parallel 2 fibers (short path)

• Span switching


Traffic to/from an NETraffic to/from an NE

NetworkElement

STM-1 #1-12 all pathsworking traffic

STM-1 #1-12 all paths dedicated protection traffic

STM-1 #1-12 all pathsworking traffic

STM-1 #1-12 all pathsdedicated protection traffic

NetworkElement

STM-1 #1-6 working trafficSTM-1 #7-12 shared protection traffic




Both rings have an add/drop capability of up to 12 STM-1s at any node

shared protection

dedicated protection


Application AreasApplication Areas

• Used in the WAN backbone

–Neighboring traffic pattern is the best fit

• BSHR/MS rings are interconnected in a hierarchy

–Number of hops should be minimized

–Capacity of rings increasing as moving up in the ring hierarchy

• Rings might be classified into aggregation and core


FeaturesFeatures

• More complexity, but more flexible capacity

–Bandwidth used can be reused

–Requires signaling between ADMs

• STM visibility

• Might restore service in less than 50 milliseconds on a 1200 km or less ring


A

CE

BF

Donly workingtraffic shown

Operations – Traffic FlowOperations – Traffic Flow

• Duplex traffic between two nodes goes through a subset of ring links

• Minimum capacity equals line rate (same as USHR/P maximum)

• Line rate must be an even integer of STM-1 for 2-fiber configurations

– Automatically fulfilled with newer standards


A

CE

BF

D

Onlyworkingtrafficshown

B-C

A-B

C-DD-E

E-F

F-A

C-B

B-A

D-CE-D

F-E

A-F

Maximum Bandwidth CapacityMaximum Bandwidth Capacity

• Each link represents half of the line rate of STM-1s (i.e. 8 STM-1s for an STM-16)

• All traffic from a node goes to adjacent nodes

• Max. capacity = 0.5 (line rate) x number of nodes


A

CE

BF

D

Extra Trafficin Protectionbandwidth

WorkingTraffic

Extra TrafficExtra Traffic

• Extra traffic utilizes shared protection bandwidth

• Extra traffic is not protected when a failure occurs

• Extra traffic could be lost when a failure of working traffic occurs

• Extra traffic is ONLY available on a BSHR/MS



• Failure interrupts A-C and C-A traffic

• A and B detect failureA

CE

BF

D

Fiber cut

WorkingTraffic

STM-1#4

STM-1#4



• No dedicated protection bandwidth - only used when protection required

• Only nodes next to the failure know about the protection switch

• No traffic lost

A

CE

BF

DProtectionTraffic

Loops

Fiber cut

WorkingTraffic

STM-1#10 into STM-1#4





Operations – Node Failure - I.Operations – Node Failure - I.

• Failure interrupts D-F and F-D traffic

• A and C detect failure A

CE

BF

D

Node Failure

WorkingTraffic

STM-1#4

STM-1#4


Operations – Node Failure - II.Operations – Node Failure - II.

• No dedicated protection bandwidth - only used when protection required

• Only nodes next to the failure know about the protection switch

• Traffic to/from failed node lost

A

CE

BF

DProtectionTraffic

Loops

Node Failure

LoopsWorkingTraffic






A

CE

BF

D

WorkingTraffic

Node Failure

STM-1#1STM-1#1

STM-1#1

STM-1#1

Squelching ProblemSquelching Problem

• Traffic terminating on nodes cut off by failures could be misconnected to other nodes on the ring in case ofusing a localfail-over decision


Squelching MisconnectionsSquelching Misconnections

• Node F now talking to Node E instead of Node B

• Misconnection would occur

STM-1#1

STM-1#7 STS-1#1

A

CE

BF

D

ProtectionTraffic

Node Failure

WorkingTraffic


Squelching - Path AIS Insertion

Squelching - Path AIS Insertion

• STM Path AIS is inserted instead of the looped STM-1#7

• No mis-connections

STM-1#1

STM-1#7 STS-1#1

A

CE

BF

D

ProtectionTraffic

Node Failure

WorkingTraffic

STM-1#1 Path AIS inserted by Node C

STM-1#1 PathAIS insertedby Node A


Squelching - SummarySquelching - Summary

• Squelching is required to assure that misconnections are not made

– Only required for bidirectional line switched rings since it is the only ring to provide a reuse capability of STM-1s around the ring

– Only required when nodes are cut off from the ring

– Only required for traffic terminating on the cut off nodes

• A ring map that includes all STM and VC Paths on the ring is available at every node on the ring

• Squelching is also required for extra traffic since the extra traffic may be dropped when a protection switch is required


StandardizationStandardization

• Basic APS operations are defined in ITU-T G.783

• BSHR/MS is first defined in ITU-T G.803 (1993), but exact details are referred to as for further study

• Later ITU-T G.841 (1995) defines BSHR/MS, but only for shared protection

– Dedicated protection is referred to as for further study (1998)

• Conflict with common sense terminology

• 4-fiber BSHR is called shared (!) protection since extra traffic might use the protection fibers

• BSHR/P and other variants are more a theoretical possibility than real products


SummarySummary

• Identify the main concepts in constructing protected ring topologies






• Why is signaling required to ensure proper fail-over in a BSHR/MS protection switching?

• What is the difference between shared protection in a 2-fiber and a 4-fiber ring?

• Is 1:n protection available in a 4-fiber ring?

• Why is there a potential misconnection problem at node failures?

SummarySummary



Remember...Remember...

• Unidirectional ring: all working traffic travels around the ring in the same direction for both A to B and B to A traffic; i.e. clockwise or counterclockwise

• Bidirectional ring: all working traffic between two nodes travels the two directions on the same set of fiber links between the two nodes; i.e. A to B clockwise and B to A counterclockwise

• MS switching: APS is based on received MS signal status and MS layer performance parameters

• Path switching: APS is based on received path layer signal status and path layer performance parameters



• Ring switching: alternative path used is in the other direction on the ring

• Span switching: alternative path used is in parallel with the failed path

• Squelching: insertion of AIS for looped signals during protection switching to avoid misconnections

• Extra traffic: the utilization of the the protection bandwidth in a MS switched ring for traffic that can and may be disrupted when a protection switch is established



• + BSHR/MS provides higher bandwidth capacity when internodal traffic exists between ring nodes

• ø BSHR/MS provides the same bandwidth capacity as USHR/P when all traffic homes on a single node, as in some access configurations

• + BSHR/MS evolves to support new service types like ATM easily, path switched rings require new paths to be defined for new services that don’t fit into STSs or VTs

• - USHR/P is perceived to be simpler since it can be thought of as diverse routing

• - BSHR/MS is perceived to be complex because of protection loops and squelching

• ø Both BSHR/MS and USHR/P require synchronization protection switching which in a line switched protection scheme is not needed


QuestionsQuestions

?



• Articles

–Dave Johnson, et al.: “The Evolution of a Reliable Transport Network”

• IEEE Communications Magazine, August 1999, pp.52-57.


SummarySummary

After completing this chapter, you should be able to perform the following tasks:• Identify the main issues in topology design

• Define the main topologies

• Identify the main protection switching concepts

• Describe the operations of typical topology configurations

Time SynchronizationTime Synchronization

Chapter 4Chapter 4



Upon completion of this chapter, you will be able to perform the following tasks: • Identify the main requirements for time

synchronization

• Describe the main synchronization modes

• Describe the principles of network synchronization

• Describe the concept and operation of time synchronization protection


AgendaAgenda

4.1 - Time Synchronization Basics

4.2 - Synchronization Networks

4.3 - Synchronization Protection


Time Synchronization Basics

Time Synchronization Basics




Upon completion of this section, you will be able to perform the following tasks:• Describe the historical evolution of time

synchronization

• List main synchronization requirements

• Describe the network element synchronization modes


History - I.History - I.

• Time synchronization might be needed for all digital voice communication networks

–On point-to-point links transmit and receive frequencies should be the same

– In synchronous multiplexing transmit and receive frequencies should be synchronized everywhere in the network, otherwise information might be lost

– In asynchronous multiplexing the multiplexers are independent from the timing of the multiplexed signals (PDH concept)


History - II.History - II.

• SDH is quite different from PDH, since it uses synchronous multiplexing

• Beginning of 1990s, SDH is used mainly as point-to-point island, no synchronization with E1, direct replacement for asynchronous transport

• Middle of 1990s, SDH becomes time synchronized, using complex topologies, making pointer adjustments


Network Clock(Stratum 1)

• Synchronous DS0/E1 switching network (Stratum 1)• Asynchronous transport network

DS0Switch

CB

E1

M14 M14LT CBLT LT

E4 prop. E4 E1E1 E4 prop. E4 E1

M14 M14

0.000001 ppm

LT

Switching Network

Transport Network

VF

Transport Network

Synchronization in Classical Voice Networks - I.

Synchronization in Classical Voice Networks - I.


Synchronization in Classical Voice Networks - II.

Synchronization in Classical Voice Networks - II.


• Asynchronous transport network uses pulse stuffing and is transparent to E1 timing

DS0Switch

CB

E1

M14 M14LT CBLT LT


M14 M14

0.000001 ppm

LT

f120ppm

f220ppm

f320ppm

f420ppm

f520ppm

f620ppm


• Timing distribution is done using embedded E1 facility• Asynchronous transport network is transparent to E1 timing

Synchronization DistributionSynchronization Distribution


DS0Switch

CB

E1

M14 M14

20ppm

LT CBLT LT


M14 M13

0.000001 ppm

20ppm

LT

Dedicated TimingE1


• SDH used in point-point configuration• Direct replacement for async transport• SDH terminals free-run at 20ppm. Not network synchronized. No pointer adjustments so no issues with E1/E4 mapping jitter !

f120ppm

f220ppm

f320ppm

f420ppm

f520ppm

f620ppm


DS0Switch

CB

E1

M14 M14 CBLT LT

E4 STM-16 E4 E1E1 E4 prop. E4 E1

M14 M14

0.000001 ppm

SDHNE

SDHNE

Initial SDH DeploymentsInitial SDH Deployments


Current SDH Deployments - I.Current SDH Deployments - I.

Questions:• How do I time the SDH network ?• Can I still just free run all my SDH NEs at 20ppm ?• What is the impact of pointer adjustments ?• How do I distribute timing to the CBs and DS0 switches ?


DS0Switch

CB

E1

CBSTM-1

E4 E1E1 E1

0.000001 ppm

STM-16

STM-1 STM-1 STM-1

STM-4

???


• All STM-N interfaces traceable to PRS to avoid excessive pointers• Excessive pointers cause jitter/wander in embedded E1/E4 payloads• Timing distributed to CB and DS0 switches directly via STM-N lines

Current SDH Deployments - II.Current SDH Deployments - II.


DS0Switch

CB CB

BITS

E1E1 E1

0.000001 ppm

STM-16

STM-1STM-1 STM-1

STM-4

STM-1


Synchronization Requirements

Synchronization Requirements

• Frequency variation of bits transmitted should be inside the limits determined by the next hop’s ability to transmit these bits further

– Stuffing allows for some limited tolerance

• Frequencies should be synchronized all over the network to guarantee a low level of BER

• Synchronization is done by recovering the embedded clock signal from the input signal

• Synchronization source should have a very precise clock (reference clock)

• Reference clock might be reached only by multiple hops

– Number of hops should be minimized


• Timing loops can be caused by either careless planning or fault conditions • Timing loops cause unpredictable sync performance• Elimination of timing loops was the driver for sync status messaging (SSM)

Synchronization and Timing Loops

Synchronization and Timing Loops


DS0Switch

CB CB

BITS

E1E1 E1

0.000001 ppm

STM-16

STM-1STM-1 STM-1

STM-4

STM-1

Timing Loop

Fiber Cut


Synchronization Modes for Network Elements

Synchronization Modes for Network Elements

• Each network element has to be configured for time synchronization

• Time reference distribution should minimize delay

• Various timing alternatives:

–External

–Line

–Loop

–Through


WEST

EAST

Network Element

BITS

External TimingExternal Timing

• All signals transmitted from a node are synchronized to an external source received by that node; i.e. BITS timing source


Line TimingLine Timing

• All transmitted signals from a node are synchronized to one received signal

WEST

EAST

Network Element


Loop TimingLoop Timing

• The transmit signal in a optical link, east or west, is synchronized to the received signal from the same optical link

WEST

EAST

Network Element


Through TimingThrough Timing

• The transmit signal in one direction of transmission around the ring is synchronized to the received signal from that same direction of transmission

WEST

EAST

Network Element


SummarySummary

• Describe the historical evolution of time synchronization

• List main synchronization requirements

• Describe the network element synchronization modes



• In general, why is synchronization needed?

• How is synchronization achieved in PDH networks?

• How is synchronization achieved in SDH networks?

Synchronization Networks

Synchronization Networks




Upon completion of this section, you will be able to perform the following tasks:• Identify the reference clock concept

• Describe clock distribution methods

• Describe the concept of using alternative clock sources

• Provide the basic design considerations for synchronization network design


Reference Clocks - I.Reference Clocks - I.

• Precision of internal clock is classified into so called “Stratum” levels

– Accuracy is defined as the ratio of bit slip happening (causing a bit error)

• Stratum 1 => 1 x 10-11 (synchronization to atomic clock)

• Stratum 2 => 1.6 x 10-9

• Stratum 3E => 1 x 10-6

• Stratum 3 => 4.6 x 10-6

• Stratum 4 => 32 x 10-6 (typical for IP routers)

• Accuracy level might decrease at each hop in clock distribution


Reference Clocks - II.Reference Clocks - II.

• Originally providing Stratum 1 clocks for each network element was far from being economical, even providing this service at multiple locations was too much demanding

– So clock distribution methods were developed to minimize the number of high accuracy clocks needed in the network

• Global Positioning System (GPS) includes Stratum 1 atomic clocks on the satellites

• Recently cheap GPS receivers make it possible to have a Stratum 1 time source at almost any place

– Less need for time synchronization network (might even go away in the future…)


Clock Distribution Methods - I.Clock Distribution Methods - I.

• External clock input might be used in case when all equipment is at the same location

– BITS = Building Integrated Timing Signal

• Uses an empty T1 or E1 framing to embed clock signal

• Root of the clock distribution tree

• Might be provided as a dedicated bus reaching into each rack in a CO environment

– BITS should be generated from a Stratum 1 clock

• Typically with a hot spare alternative source for fail-over


Clock Distribution Methods - II.

Clock Distribution Methods - II.

• Network elements not close to a BITS source should recover clock from the line

• Clock distribution should not have loops, so a tree distribution topology should be configured

• Typical carrier network element has Stratum 3 accuracy when running free

– By synchronization to the reference clock, this clock is running at the same rate as the reference clock (that is Stratum 1)

• Minimum requirement for any network element is 20 ppm (that is between Stratum 3 and Stratum 4)


Alternative Clock Sources - I.Alternative Clock Sources - I.

• If the trail to the reference clock source is lost, the network element still continues normal operation

– However, alarm might be generated

• After some time the clock might drift away so much, that bit errors would occur

• Some time is left for switching over to an alternative clock source

– The network element gets into a holdover state

– Requirement is to have less than 255 errors in 24 hours


Alternative Clock Sources - II.Alternative Clock Sources - II.

• A hierarchy of potential clock sources should be configured at each network element to achieve a high-availability operation

– Typically a maximum 3 alternative time reference sources might be configured

– Meaningful only if there are different paths to the alternative time reference sources

• If only one natural path exists to a single time reference source, then the path must be protected by automatic protection switching

– Requires some extra signaling to do it properly

– Called SPS = Synchronization Protection Switching


SummarySummary

• Identify the reference clock concept

• Describe clock distribution methods

• Describe the concept of using alternative clock sources

• Provide the basic design considerations for synchronization network design



• What is the maximum allowed shift in frequency in a SDH network?

• What are the different methods of providing the master clock?

• What is the alternative to embedded clock distribution?

Synchronization Protection

Synchronization Protection




Upon completion of this section, you will be able to perform the following tasks:• Identify the basic concepts of synchronization

protection

• Describe the operational steps in synchronization protection


A

CE

BF

D

BITS

Synchronization Protection Basics

Synchronization Protection Basics

• Normal synchronization around a ring:

– Nodes B-F are line timed

– Node A is timed to an external reference

• In case of failure a new time source should be selected in a reasonable amount of time

• BER is increasing through time if synchronization is not restored


SPS Timing LoopsSPS Timing Loops

• SPS = Synchronization Protection Switching

• During a ring failure, simple reference switching would result in timing loops

A

CE

BF

D

BITS

Fiber Cut

Timing Loop


Operations – Normal FlowOperations – Normal Flow

• Synchronization messaging in normal operation

– S1 = Stratum 1 Traceable

– DU = Don’t Use

– HO = Holdover

A

CE

BF

D

BITS

S1

Synch Msg = S1

S1

S1S1

S1

S1

DU

DUDU

DU

DU



• Node C goes into short term holdover

A

CE

BF

D

BITS

Fiber Cut

Node C inHoldover

HO

S1

S1

HO

HO

S1

DU

DUDU

HO

DUHO



• Node F switches to timing from Node A

A

CE

BF

D

BITS

Fiber Cut

Node C inHoldover

HO

S1

S1

HO

HO

S1DU

DUDU

HO

DU

S1


Operations – Fiber Cut - III.Operations – Fiber Cut - III.

• Ring is reconfigured and all nodes are again synchronized to BITS

A

CE

BF

D

BITS

Fiber Cut

Node Ccomes outof Holdover

DU

S1

S1

DU

DU

S1DU

S1S1

S1

DU

S1


SummarySummary

• Identify the basic concepts of synchronization protection

• Describe the operational steps in synchronization protection



• What kind of signaling is used to prevent timing loops?

• Does SPS work properly in a complex meshed network?

• How long is the Hold-over period in SPS?

SummarySummary





• External timing: all signals transmitted from a node are synchronized to an external source received by that node; i.e. BITS timing source

• Line timing: all signals transmitted from a node are synchronized to one receive signal

• Loop timing: the transmit signal in a optical link, east or west, is synchronized to the received signal from the same optical link

• Through timing: the transmit signal in one direction of transmission around the ring is synchronized to the received signal from that same direction of transmission



• All network elements should be able to trace back clock synchronization to a single reference clock

• Synchronization messaging: messaging procedure that avoids timing loops when protection switching the synchronization source on a ring

• Messaging is based on bits in the S1 byte in the MS Overhead



• Synchronization protection switching is controlled by synchronization messages in bits 5-8 of the S1 byte in the SDH MS overhead, and is considered a MS switching function

• Synchronization protection switching is required for both BSHR/MS rings and USHR/P rings

• Short term holdover is defined as holdover during synchronization reconfiguration on the ring


QuestionsQuestions

?


SummarySummary

After completing this chapter, you should be able to perform the following tasks:• Identify the main requirements for time

synchronization

• Describe the main synchronization modes

• Describe the principles of network synchronization

• Describe the concept and operation of time synchronization protection

SONET versus SDHSONET versus SDH

Chapter 5Chapter 5



Upon completion of this section, you will be able to perform the following tasks: • Relate SONET and SDH concepts to each other

• Translate between SONET and SDH terminology

• Compare SONET and SDH terminology

• Describe the internetworking principles between SONET and SDH


Standardization - I.Standardization - I.

• First: many proprietary solutions

• In 1984 ECSA (Exchange Carriers Standards Association) started on SONET

• SONET became an ANSI standard

–Tuned to carry US PDH payloads

• Later CCITT created SDH as a superset

–Tuned to carry European and international PDH payloads including E4 (140 Mbit/s)


1984 1985 1986 1987 1988

SONET/SDHStandardsApproved

ANSI ApprovesSYNTRAN

Divestiture

Exchange CarriersStandards Associate (ECSA)T1 Committee Formed

ANSI T1X1Approves

Project

Bellcore ProposedSONET PrinciplesTo ANSI T1X1

CCITT ExpressesInterest in SONET

British and JapaneseParticipation in T1X1

CCITT XVIIIBegins StudyGroup

CEPT ProposesMerged ANSI/CCITT

Standard

US T1X1 AcceptsModifications

SONET Concept Developed by Bellcore

Standardization - II.Standardization - II.

• More than 400 technical proposals

• Rate discussions AT&T vs. Bellcore

• International changes for byte/bit interleaving, frames, data rates

• Phase I, II, III, separate APS etc.


Abbrev.Bit Rate Signal Signal speed(Mbit/s) DS1 DS3 E1 E4 (Gbit/s)51.84 STS-1 28 1 STM-0 21 0

155.52 STS-3 84 3 STM-1 63 1622.08 STS-12 336 12 STM-4 252 4

2488.32 STS-48 1344 48 STM-16 1008 16 2.59953.28 STS-192 5376 192 STM-64 4032 64 1039813.1 STS-768 21504 768 STM-256 16128 256 40

ChannelsSONET SDH

Channels

Synchronous TDM HierarchySynchronous TDM Hierarchy

• SONET Synchronous Transport Signal

– STS-<n> electrical, OC-<n> optical

• SDH Synchronous Transport Module

– STM-<n>E electrical, STM-<n>O optical


Comparison of TechnologyComparison of Technology

• Both SONET and SDH use the same technology components

• All the differences might be implemented in software

• Still US based companies tend to be late in SDH implementations

–Mostly because of other customer environment related standards

• Privately SONET or SDH might be used

• Interfacing to public networks requires configuring the proper selection


Comparison of Hierarchy Comparison of Hierarchy

• Hierarchies aligned at 155 Mbit/s

ETSI PDH

2 8 34 140 Mbit/s

US PDH

1.5 6 45

T3

Mbit/s

SONET

VT1.5 VT6 OC-1 OC-12 OC-48 OC-192

52 155 622 2488 9953Mbit/s

OC-3

SDH

TU-12 TUG-2 AU-3 AU-4

STM-1 STM-4 STM-16 STM-64


Comparison of FramingComparison of Framing

• Same framing concept of using 9 rows

• STM-1 frame can be subdivided into 3 virtual STM-0 frames

–STM-0 frame compatible with STS-1 frame

• Multiplexing of STM and STS is the same

• Overhead byte interpretation is slightly different

–Based on different needs for PDH multiplexing and protection


Comparison of PayloadsComparison of Payloads

• Similar concepts, but significant differences in details of payload multiplexing

VT 1.5 VT 6 STS-1

(4)

7(1)

28 DS1s

3 STS-3

84 DS1s

OC-3

DS1

1.5 Mb/s

SONET SONET

(3)

VC-37VC-12 (1)

21 E1s

TUG 3 AUG

63 E1sE1

STM-1

2 Mb/s

SDHSDH


Comparison of Network Architectures

Comparison of Network Architectures

• Similar layered architecture

• Slightly different terminology

–Regenerator section (SDH) = section (SONET)

–Multiplex section (SDH) = line (SONET)

• SDH defines high- and low-order paths, too


Comparison of ProtectionComparison of Protection

• SONET APS schemes are almost the same as SDH MPS and SNCP schemes

• Operations are practically the same

–APS protocol is equivalent

• Terminology is different

–UPSR (SONET) = USHR/P (SDH)

–BLSR (SONET) = BSHR/L (SDH)


InternetworkingInternetworking

• Voice internetworking still requires conversion between μ-law and a-law

• Voice trunks can be accessed with a single step of demultiplexing

• SONET and SDH might carry each others PDH load, so the voice conversion point might be located flexibly anywhere inside the SONET or the SDH network

• Repacking PDH between SONET and SDH might be done in a single step by a single device

• Data internetworking is easy at STM-1 (STS-3) or higher since the payloads are the same size and structure


SummarySummary

• Relate SONET and SDH concepts to each other

• Translate between SONET and SDH terminology

• Compare SONET and SDH terminology

• Describe the internetworking principles between SONET and SDH



• What is the major difference between SONET and SDH?

• Why does SONET start at a signaling rate of 51,84 Mbit/sec?

• Why does SDH start at a signaling rate of 155,52 Mbit/sec?

• What is the purpose of an STM-0 frame?


QuestionsQuestions

?

Network ManagementNetwork Management

Chapter 6Chapter 6



Upon completion of this chapter, you will be able to perform the following tasks: • Describe the basic network management

functions needed in TDM networks

• Describe the architecture and main components of implementing network management solutions


AgendaAgenda

5.1 - Network Management Basics

5.2 - Network Management Internals


Network Management Basics

Network Management Basics




Upon completion of this section, you will be able to perform the following tasks:• Identify the main operational tasks

• Describe OAM functions and layers

• Describe the in-band network management channels


Operational Tasks - I.Operational Tasks - I.

• Basic operational tasks:

– Protection

• Circuit recovery in milliseconds (so failure should not be detected by voice customers)

– Restoration

• Circuit recovery in seconds or minutes (done by manual configuration)

– Provisioning

• Allocation of capacity to preferred routes (according to certain time schedules)

• Configuration time is separated from activation time


Operational Tasks - II.Operational Tasks - II.

– Consolidation

• Moving traffic from unfilled bearers onto fewer bearers to reduce waste trunk capacity

– Grooming

• Sorting of different traffic types from mixed payloads into separate destinations for each type of traffic


OAM Functions and LayersOAM Functions and Layers

• Level 3 - Path

–Assembly and disassembly, cell delineation control

• Level 2 - Multiplex Section

–Loss of frame synchronization, degraded error performance

• Level 1 - Regenerator Section

–Loss of synchronization, signal quality degradation




• DCC is a 192 kb/s in-band channel to facilitate communication between all Network Elements (NE) in a network

– Remote login, alarms reporting, software download, provisioning

DCN

SDHDCC

ManagementServer

OSS

Network Operations Center

ADM

ADM

ADM

GNEGNEGNEGNE

ADM

GNEGNEGNEGNEGNEGNEGNEGNE

ManagementClients

SDHDCC

SDHDCC

ManagementClient

Alarm and Event

Forwarding

TDM

TDM

TDM

TDM

TDM


SummarySummary

• Identify the main operational tasks

• Describe OAM functions and layers

• Describe the in-band network management channels



• What are the operational tasks of a Network Management System?

• What are the OAM functions needed for?

• What is the DCC channel used for?

Network Management Internals

Network Management Internals




Upon completion of this section, you will be able to perform the following tasks:• Identify main requirements for network

element management support

• Describe the typical management interfaces used to access network elements

• List management functions and features typically supported by network elements


Network Element Requirements

Network Element Requirements

• All network elements should support various management interfaces

– Local (craft terminal using TL1)

– Remote (TMN DCN model)

• All network elements should support certain management function areas

– FCAPS (fault, configuration, accounting, performance, security)

• Since original payload is voice, a separate management network is needed for remote management operations

– Data Communications Network (DCN)


Management Interfaces - I.Management Interfaces - I.

OS

DCN

WS

TMN

NE QA

F

XQ3/X/F

Q3 Q3

TMN Model as of M.3010

Reference pointReference point


Management Interfaces - II.Management Interfaces - II.

• CMIP over OSI

– TMN Manager/Agent communication standard

Agent

Mgr.

Agent

Element ManagerLayer

Network Element Layer

CMIP/OSI


Configuration Management Support

Configuration Management Support

• Installation

–Setting up basic parameters (identification, management access and authorization, etc.)

–Activating and testing hardware

• Provisioning

– Implementing add-drop commands

• Status and control

–APS switching messages for manual control


Performance Monitoring Support

Performance Monitoring Support

• Separate handling of section, line, path termination

• Performance data collection

– Error counts: B1, B2, B3

– Historical data presentations

• Threshold settings

• Threshold crossing alerts (TCA)

– For B1, B2, B3

• Performance data reporting

• Accuracy and resolution should be considered

– Typically 15-minute interval is the basis

• Monitoring should be done even in trouble conditions


Fault Management SupportFault Management Support

• Alarms surveillance

– Reactive mechanisms

– Autonomous and requested alarms

• Testing

• Alarm configuration

Alarm Hierarchy

LOS |

LOF |

LAIS => LRDI | |

PAIS => PRDI |

LOP


Accounting SupportAccounting Support

• In voice networks accounting support is implemented in toll switches

• In data networks accounting is supported by data link layer or network layer traffic data collection

• In general, neither voice networks, nor data networks transport on top of SDH require accounting support

• Transport network billing is not based on traffic, since bandwidth is allocated in fixed amounts

– Billing records might be generated by the OSS controlling the provisioning of paths

• Typically no requirement for accounting support in SDH network elements


SummarySummary

• Identify main requirements for network element management support

• Describe the typical management interfaces used to access network elements

• List management functions and features typically supported by network elements



• What network management protocol is mainly used in telecommunication?

• What three functions does Fault Management support?

SummarySummary



QuestionsQuestions

?


SummarySummary

After completing this chapter, you should be able to perform the following tasks:• Describe the basic network management

functions needed in TDM networks

• Describe the architecture and main components of implementing network management solutions

© 2001, Cisco Systems, Inc. Network Management-266

Documents

Cisco SDH Presentation