SONET Technology Primer

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SONET Technology Primer

by

Martin Schulman



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2

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


Topics To Be Covered


Motivation & History


Termination
Equipment And
Frame Formats


Electrical And
Optical Encoding


Topologies And
Redundancy


PPP Over SONET


Relationship To
Other Standards



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COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


<1984 NA Digital Telephony

Key System Aspects:



M13 Building Blocks



Asynchronous Operation



Electrical DS3 Signals



Proprietary Fiber Systems



Brute Force Cross Connect



AT&T Network/Western
Electric Equipment

Central

Office

Central

Office

Central

Office

Fiber

Fiber Optic

Transmission

Systems



Switches



Leased Line

M13

M13

DS3

DS1

DS3

DS1 Cross

Connect

M13

DS1

DS1

No Guaranteed

Timing

Synchronization



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COMPANY CONFIDENTIAL

NANOG, May 23
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25

Copyright © 1999, Juniper Networks, Inc.


Post
-
Divestiture Dilemmas

Faster Fiber Coming:



Need “Mid
-
Span Meet”



Support New Services



Allow Other Topologies



Standardize Redundancy



Common OAM&P



Scalable Cross Connect

Different

Carriers,

Vendors



Switches



Leased Line



LAN Services



Data Services

M13

Support

Other

Topologies,

Protect Fibers

DS1

Internal

DS3 Cross

Connect



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COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


The Standards Process

1984

1985

1986

1987

1988

SONET/SDH

Standards

Approved

ANSI Approves

SYNTRAN

Divestiture

Exchange Carriers

Standards Associate (ECSA)

T1 Committee Formed

ANSI T1X1

Approves

Project

Bellcore Proposed

SONET Principles

To ANSI T1X1

CCITT Expresses

Internet in SONET

British and Japanese

Participation in T1X1

CCITT XVIII

Begins Study

Group

CEPT Proposes

Merged ANSI/CCITT

Standard

US T1X1 Accepts

Modifications

Standard That Almost Wasn’t



>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.

SONET Concept Developed By Bellcore



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COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


SONET Defined


Synchronous Optical Network


Set of Layer 1 Standards For
Communication over Fiber Optic (and
Electrical) Links In Order To Facilitate:


Fiber Optic Link Speed Increases


Variety Of Topologies and Grooming
Functions


Operations, Administration, Maintenance,
and Provisioning (OAM&P)


When Used As Telephony Carrier
Equipment And CPE Interconnect



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7

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


Equipment Types

PTE

All Perform Electro
-
Optical

Conversion



Section Termination (STE)



Line Termination (LTE)



Path Termination (PTE)

Data Between PTE May
Traverse Multiple LTE, STE

Line

SONET End

Device
-

I.e.

Telephony

Switch, Router

Path

Sections

Repeaters

PTE



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8

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


STS
-
1 Frame Format

90 Bytes

Or “Columns”

9

Rows

Each Small Rectangle

Represents One Byte


Transmitted MSB First

Frame Transmission



Top Row First, Sent Left To Right



125
m
猯䙲慭a



810 Bytes/Frame



51.84 Mbps Rate



Frame Contains One Payload



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COMPANY CONFIDENTIAL

NANOG, May 23
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Copyright © 1999, Juniper Networks, Inc.


Section Overhead (SOH)

A1

=0xF6

A2

=0x28

J0/Z0

STS
-
ID

B1

BIP
-
8

E1

Orderwire

F1

User

D1

Data Com

D2

Data Com

D3

Data Com

Section Overhead



9 Bytes Total



Originated And Terminated By All
Section Devices (Regenerators,
Multiplexers, CPE)



Other Fields Pass Unaffected

Rcv

SOH



A1,A2
-

Framing Bytes



J0/Z0
-

Section ID,
Reserved



BIP
-
8
-

Bit Interleaved
Parity



E1 Orderwire
-

Craft Voice
Interface Between Sections



F1 User
-

Proprietary
Management



D1
-
D3
-

192 Kbps OSI/CMIP
Channel

Xmt

SOH



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COMPANY CONFIDENTIAL

NANOG, May 23
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25

Copyright © 1999, Juniper Networks, Inc.


Line Overhead (LOH)

H1

Pointer

H2

Pointer

H3

Pointer Act

B2

BIP
-
8

K1

APS

K2

APS

D4

Data Com

D5

Data Com

D6

Data Com

Line Overhead



18 Bytes Total



Originated And Terminated By All
Section Devices (Regenerators,
Multiplexers, CPE)



LOH+SOH=TOH (Transport OH)



H1
-
3
-

Payload Pointers



BIP
-
9 Bit Parity



K1, K2
-

Automatic Protection
Switching



D4
-
D12
-

576 kbps OSI/CMIP



S1
-

Time Sync Indicator



M0
-

Return Error Indicator



E1 Orderwire
-

Craft Voice
Interface Between Sections

D7

Data Com

D8

Data Com

D9

Data Com

D10

Data Com

D11

Data Com

D12

Data Com

S1

Sync

M0

REI

E1

Orderwire

Rcv

SOH

Xmt

SOH

Xmt

SOH

Xmt

LOH

Rcv

SOH

Rcv

LOH



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11

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


Path Overhead (POH)

J1

Trace

B3

BIP
-
8

C2

Sig Label

Path Overhead



H1,H2 Point To Beginning
-

Beginning Floats Within Frame



9 Bytes (1 Column) Spans Frames



Originated And Terminated By All
Path Devices (I.e. CPE, Switches)



STE Can Relocate Payload



J1
-

Repeated
ID String



BIP
-
8
-

Parity



C2
-

Payload
Type Indicator



G1
-

End End
Path Status



F2
-

User



H4
-

Use
Depends On
Payload



Z3
-
5
-

Future
Growth

G1

Path Stat

F2

User

H4

Indicator

PTE

Z3

Growth

Z4

Growth

Z5

Tandem

PTE

STE

Frame N

Frame N+1

Frame N

Frame N+1



Slide
12

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


SPE

Synchronous Payload Envelope



Contains POH + Data



First Byte Follows First Byte Of POH



Wraps In Subsequent Columns



May Span Frames



Up To Single 49.536 Data Signal
-

Enough for DS3

Defined Payloads



Virtual Tributaries
(For DS1, DS2)



DS3



SMDS



ATM



PPP



More...



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13

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


Accommodating Jitter

Positive Stuff

Negative Stuff

Byte After H3 Ignored, Or H3 Holds Extra Byte To Shorten/Lengthen Frame

H1, H2 Values Indicate Changes
-

Maximum Every 4 Frames

Requires Close (Not Exact) Clock Synchronization Among Elements



Slide
14

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


Clock Synchronization

Building Integrated Timing System



Hierarchical Clocking Distribution



Normally All Synch’d To Stratum 1
(Can Be Cesium/Rubidium Clock)



Dedicated Link Or Recovered



Fallback To Higher Stratum In Failure
(Temperature Controlled Crystal)

PTE

PTE

BITS

BITS

BITS

Primary

Reference

Backup

Reference


Level 1: 10
-
11


Level 2: 1.6x10
-
8


Level 3: 4.6x10
-
6


Level 4: 32x10
-
6



Slide
15

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


STS
-
N Frame Format

Composite Frames



Byte Interleave STS
-
1’s



Clock Rate = Nx51.84 Mbps

90xN Bytes

Or “Columns”

N Individual STS
-
1 Frames


Examples

STS
-
1

51.84 Mbps

STS
-
3

155.520 Mbps

STS
-
12

622.080 Mbps

STS
-
48

2.48832 Gbps

STS
-
191

9.95323 Gbps



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16

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


STS
-
Nc Frame Format

Composite Frames



Same TOH Structure And Data
Rates As STS
-
N



Not All TOH Bytes Used



First H1, H2 Point To POH



Single Payload In Rest Of SPE



Accommodates FDDI, E4, etc.

90xN Bytes

Or “Columns”


Examples

Only 1 BIP
-
8 for section layer (B1)

Only One DCC (D1
-
D3)

Only Two E1, E2 Orderwires

Only One User (F1)

Only One APS (K1 and K2)

Only One DCC (D4
-
D12)

Transport

Overhead



Slide
17

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


Transmission Encoding

OC
-
N Is Optical Carrier STS
-
N

Long Reach: 40 km


1310 or 1550 nm SM

Intermediate Reach: 15 km


1310 or 1550 nm SM

Short Reach:Long Reach 2 km


1310 nm MM

E O

Electrical Transmission Standard



STS
-
1: B3ZS (BPV), 450’



STS
-
3: Coded Mark Inversion, 225’



Useful Intra
-
Office Connection

1+x
6
+x
7

Scrambling



Ensures Ones Density



Does Not Include A1, A2, C1 Bytes



Output Is NRZ Encoded



Slide
18

COMPANY CONFIDENTIAL

NANOG, May 23
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25

Copyright © 1999, Juniper Networks, Inc.


Network Elements

Nonstandard, Functional Names

TM: Terminal Mux

ADM: Add
-
Drop Mux

DCC: Digital Cross Connect


(Wideband and Broadband)

MN: Matched Node

D+R: Drop and Repeat

ADM

TM

DS1s

DS1s

MN

MN

MN

DCC

D+R

D+R

D+R

MN



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19

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


Topology Building Blocks

DCC

ADM

ADM

ADM

DCC

ADM

ADM

ADM

2 Fiber Ring

Each Line Is

Full Duplex

DCC

ADM

ADM

ADM

4 Fiber Ring

Each Line Is

Full Duplex

DCC

ADM

ADM

ADM

Uni
-

vs. Bi
-

Directional

All Traffic Runs Clockwise,
vs Either Way



Slide
20

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


OAM&P

Manageability Is Required

Well Defined Protocols, Alarms:


Loss of Signal: All 0’s


Loss Of Frame: Cannot Find A1,A2


Alarm Indication Signal
-

Line:
Remote Side Sees LOS or LOF


Remote Defect Indication
-

Line:
Remote Seeing Above Alarms


Alarm Indication Signal
-

Path:
Indication To Downstream Devices
Of A Problem


Remote Defect Indication
-

Path:
Indication To Upstream Devices Of A
Problem





SONET Processing Hardware

OSI Node

Hardware

Error Detection

Hardware

Error Signaling

DCC Links



Slide
21

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


APS

ADM

Line Protection Switching

Uses TOH

Trunk Application

Backup Capacity Is Idle

Supports 1:n, N=1
-
14

Automatic Protection Switching



Line Or Path Based



Revertive vs. Non
-
Revertive



Mechanism For Intentional Cutover



Restoration Times ~ 50 ms



K1, K2 Bytes Signal Change



Common Uses: 2 Fiber UPSR or ULSR,
4 Fiber BPSR

ADM

ADM

ADM

Path Protection Switching

Uses POH

Access Line Applications

Duplicate Traffic Sent On Protect

1+1

ADM

ADM



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22

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


Packet Over SONET (POS)

PPP

Byte

Stuff

FCS

Scrambling

SONET

Framing

Standard PPP Encapsulation



Magic Number Recommended



No Addres and Control Compression



No Protocol Field Compression

Standard CRC Computation



OC3 May Use CRC
-
16



Other Speeds Use CRC
-
32

Special Data Scrambler



1+ x43 Polynomial



Protects Against Transmitted Frames
Containing Synch Bytes Or Insufficient
Ones Density

SONET Framing



OC3, OC12, OC48, OC192 Defined



C2 Byte = 0x16 With Scrambling



C2 Byte = oxCF Without (OC
-
3)



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23

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


Technology Relationships


Synchronous Digital Hierarchy (SDH)


International Diffs
-

Terms, OH Fields


Rates: STS
-
N
-
> STM
-
N/3 For N>=3


SDL Proposal


Fix HDLC For High Speed Use


Pt
-
Pt Links Without SONET Overhead


WDM/DWDM:


More Capacity
-

Optical Routing For
Redundancy


No Access To Lower
-
Level (I.e. DS1
Signals)



Slide
24

COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


Acronyms


ADM: Add
-
Drop Multiplex


APS: Automatic Protection Switching


BIP: Bit Interleaved Parity


BITS: Building Integrated Timing Supply


OC: Optical Carrier


POH: Path Overhead


POS: Packet Over SONET


PTE: Path Terminating Entity


SDH: Synchronous Digital Hierarchy


SONET: Synchronous Optical Network


SPE: Synchronous Payload Envelope


STE: Section Terminating Entity


STM: Synchronous Transport Module


STS: Synchronous Transport Signal


TOH: Transport Overhead


VT: Virtual Tributary



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COMPANY CONFIDENTIAL

NANOG, May 23
-
25

Copyright © 1999, Juniper Networks, Inc.


References


Telcordia (Bellcore) GR
-
253
-
CORE


ANSI T1.105 and T1.106


ITU
-
T G.707 and G.783


SONET
, Walter J. Goralski, McGraw
-
Hill
Series on Computer Communications


RFC
-
1619 and Successor


http://search.ietf.org/internet
-
drafts/draft
-
ietf
-
pppext
-
pppoversonet
-
update
-
04.txt

http://www.juniper.net