4c. Communication Network - SDHpdf

7/28/2019 4c. Communication Network - SDHpdf

1/105

SYNCHRONOUSDIGITAL HIERARCHY

OVERVIEW


2/105

Outline

Background (analog telephony, TDM, PDH)

SONET/SDH history and motivation

Architecture (path, line, section)

Rates and frame structure

Payloads and mappings

Protection and rings

VCAT and LCAS

Handling packet data


3/105

Background


4/105

The Present PSTN

subscriber line

Analog voltages and copper wire used only in last mile,

Time Division Multiplexing of digital signals in the

network

Extensive use of fiber optic and wireless physical links T1/E1,PDH and SONET/SDH synchronous protocols

Signaling can be channel/trunk associated or via separate network

(SS7)

PSTN Network

class 5 switchclass 5 switch

tandem switch

last mile


5/105

TDM Timing

Time Domain Multiplexing relies on all channels

(timeslots) having precisely the same timing

(frequency and phase)

In order to enforce this, the TDM device itselffrequently performs the digitization

analog

signals

digital

signals


6/105

If The Inputs Are Already Digital

If the TDM switch does not digitize the analog signals

then there can be a problem

the clocks used to digitize do not have identicalfrequencies

we get byte slips! (well, actually, we can get bit slips first )exaggerated pictorial example

Numerical example:

clock derived from 8000 Hz. quartz crystal

typical crystal accuracy = 50 ppmSo 2 crystals can differ by 100 ppmi.e. 0.8 samples / second

So difference is 1 sample after 1 seconds

1

1

1

1

1

1

2

2

2

2

2

2

3

3

3

3

3

3

4

4

4

4

4

4

5

5

5

6

6

6

5

5

5

7

7

7

6

6

6

8

8

8

9

9

9

7

7

7

9

8

8

component

signals

TDM


7/105

The Fix

We must ensure that all the clocks have the same frequency

Every telephony network has an accurate clock called a

stratum 1, or Primary Reference Clock

All other clocks are directly or indirectly locked to it (master

slave) A TDM receiving device can lock onto the source clock based

on the incoming data (FLL, PLL)

For this to work, we must ensure that the data has enough

transitions

(special line coding, scrambling bits, etc.)

1

0

transitions no transitions


8/105

Comparing Clocks

A clock is said to be isochronous (isos=equal, chronos=time)

if its ticks are equally spaced in time

2 clocks are said to be synchronous (syn=same chronos=time)

if they tick in time, i.e. have precisely the same frequency

2 clocks are said to be plesiochronous (plesio=near chronos=time)

if they are nominally if the same frequency

but are not locked


9/105

PDH principle

If we want yet higher rates, we can mux together TDM

signals (tributaries)

We coulddemux the TDM timeslots and directly remux

them but that is too complex

The TDM inputs are already digital, so we must

insist that the mux provide clock to all tributaries

(not always possible, may already be locked to a network)

somehow transport tributary with its own clock across a higher

speed network with a different clock (without spoiling remote clock

recovery)


10/105

PDH Hierarchies

64 kbps

2.048 Mbps 1.544 Mbps 1.544 Mbps

6.312 Mbps 6.312 Mbps8.448 Mbps

34.368 Mbps

139.264 Mbps

44.736 Mbps 32.064 Mbps

97.728 Mbps274.176 Mbps

CEPT N.A. Japan

4

3

2

1

0level

* 30* 24

* 24

* 4

* 4

* 4

* 4

* 7

* 6

* 4

* 5

* 3

E1

E2

E3

E4

T1

T2

T3

T4

J1

J2

J3

J4


11/105

Framing and Overhead In addition to locking on to bit-rate, we need to recognize

the frame structure

We identify frames by adding Frame Alignment Signal

The FAS is part of the frame overhead (which also includes

"C-bits", OAM, etc.)

Each layer in PDH hierarchy adds its own overhead

For example

E1 2 overhead bytes per 32 bytes overhead 6.25 % E2 4 E1s = 8.192 Mbps out of 8.448Mbps

so there is an additional0.256 Mbps = 3 %

altogether 4*30*64 kbps = 7.680 Mbps out of 8.448 Mbps or 9.09% overhead


12/105

PDH overhead

Overhead always increases with data rate !

digital

signal

data rate

(Mbps)

voice

channels

overhead

percentage

T1 1.544 24 0.52 %

T2 6.312 96 2.66 %

T3 44.736 672 3.86 %

T4 274.176 4032 5.88 %

E1 2.048 30 6.25 %

E2 8.448 120 9.09 %

E3 34.368 480 10.61 %

E4 139.264 1920 11.76 %


13/105

OAM

Analog channels and 64 kbps digital channels Do not have mechanisms to check signal validity and quality

major faults could go undetected for long periods of time

hard to characterize and localize faults when reported

minor defects might be unnoticed indefinitely

Solution is to add mechanisms based on overhead

As PDH networks evolved, more and more overheadwas dedicated to

Operations, Administration and Maintenance (OAM)functions

including: monitoring for valid signal

defect reporting

alarm indication/inhibition (AIS)


14/105

PDH Justification

In addition to FAS, PDH overhead includesjustification control (C-bits) and justification opportunity stuffing (R-bits)

Assume the tributary bitrate is B TPositive justification

payload is expected at highest bitrate B+Tif the tributary rate is actually at the maximum bitrate

then all payload and R bits are filled

if the tributary rate is lower than the maximumthen sometimes there are not enough incoming bitsso the R-bits are not filled and C-bits indicate this

Negative justificationpayload is expected at lowest bitrate B-Tif the tributary rate is actually the minimum bitrate

then payload space suffices

if the tributary rate is higher than the minimumthen sometimes there are not enough positions to accommodateso R-bits in the overhead are used and the C-bits indicate this

Positive/Negative justificationpayload is expected at nominal bitrate Bpositive or negative justification is applied as required


15/105

SONET/SDH Motivation and

History

15


16/105

First step

With the disvestiture of the US Bell system a new need arose

MCI and NYNEX couldnt directly interconnect optical trunks

Interexchange CarrierCompatibility Forum requested T1 to solve problem

Needed multivendor/ multioperator fiber-optic communications standard

Three main tasks: Optical interfaces (wavelengths, power levels, etc)

proposal submitted to T1X1 (Aug 1984)T1.106 standard on single mode optical interfaces (1988)

Operations (OAM) systemproposal submitted to T1M1T1.119 standard

Rates, formats, definition of network elementsBellcore (Yau-Chau Ching and Rodney Boehm) proposal (Feb 1985)proposed to T1X1term SONET was coinedT1.105 standard (1988)


17/105

PDH limitations

Rate limitations

Copper interfaces defined

Need to mux/demux hierarchy of levels (hard to pull out a single

timeslot)

Overhead percentage increases with rate

At least three different systems (Europe, NA, Japan)

E 2.048, 8.448, 34.348, 139.264

T 1.544, 3.152, 6.312, 44.736, 91.053, 274.176

J 1.544, 3.152, 6.312, 32.064, 97.728, 397.2

So a completely new mechanism was needed


18/105

Idea Behind SONET

Synchronous Optical NETwork

Designed foropticaltransport (high bitrate)

Direct mapping of lower levels into higher ones

Carry all PDH types in one universal hierarchy ITU version = Synchronous Digital Hierarchy

different terminology but interoperable

Overhead doesnt increase with rate

OAM designed-in from beginning


19/105

Standardization ! The original Bellcore proposal:

hierarchy of signals, all multiple of basic rate (50.688)

basic rate about 50 Mbps to carry DS3 payload

bit-oriented mux

mechanisms to carry DS1, DS2, DS3

Many other proposals were merged into 1987 draft document (rate

49.920) In summer of 1986 CCITT express interest in cooperation

needed a rate of about 150 Mbps to carry E4

wanted byte oriented mux

Initial compromise attempt byte mux

US wanted 13 rows * 180 columns CEPT wanted 9 rows * 270 columns

Compromise! US would use basic rate of 51.84 Mbps, 9 rows * 90 columns

CEPT would use three times that rate - 155.52 Mbps, 9 rows * 270 columns


20/105

SONET/SDH Architecture

20


21/105

Layers

SONET was designed with definite layering concepts Physical layer optical fiber (linear or ring)

when exceed fiber reach regenerators regenerators are not mere amplifiers, regenerators use their own overhead fiber between regenerators called section (regenerator section)

Line layer link between SONET muxes (Add/DropMultiplexers) input and output at this level are Virtual Tributaries (VCs) actually 2 layers

lower order VC (for low bitrate payloads) higher order VC (for high bitrate payloads)

Path layer end-to-end path of client data (tributaries) client data (payload) may be

PDH ATM packet data


22/105

SONET architecture

SONET (SDH) has at 3 layers:

path end-to-end data connection, muxes tributary signals path section

there are STS paths + Virtual Tributary (VT) paths

line protected multiplexed SONET payload multiplex section

section physical link between adjacent elements regenerator section

Each layer has its own overhead to support needed functionality

SDH terminology

Path

Termination

Path

Termination

Line

Termination

Line

Termination

Section

Termination

path

line line line

ADM ADMregenerator

section section sectionsection


23/105

STS, OC, etc.

A SONET signal is called a Synchronous Transport Signal

The basic STS is STS-1, all others are multiples of it - STS-N

The (optical) physical layer signal corresponding to an STS-N is an OC-N

SONET Optical rate

STS-1 OC-1 51.84M

STS-3 OC-3 155.52M

STS-12 OC-12 622.080MSTS-48 OC-48 2488.32M

STS-192 OC-192 9953.28M

* 3

* 4* 4

* 4


24/105

Rates and Frame Structure

24


25/105

SONET / SDH Frames

Synchronous TransferSignals are bit-signals (OC are optical)

Like all TDM signals, there are framing bits at the beginning of the frame

However, it is convenient to draw SONET/SDH signals as rectangles

Framing


26/105

SONET STS-1 frame

Each STS-1 frame is 90 columns * 9 rows = 810 bytes

There are 8000 STS-1 frames per second

so each byte represents 64 kbps (each column is 576 kbps)

Thus the basic STS-1 rate is 51.840 Mbps

90 columns

9rows

Framing


27/105

SDH STM-1 frame

Synchronous Transport Modules are the bit-signals for SDH

Each STM-1 frame is 270 columns * 9 rows = 2430 bytesThere are 8000 STM-1 frames per second

Thus the basic STM-1 rate is 155.520 Mbps

3 times the STS-1 rate!

270 columns

9

rows


28/105

SONET/SDH Rates

STS-N has 90N columns STM-M corresponds to STS-N with N = 3M

SDH rates increase by factors of 4 each timeSTS/STM signals can carry PDH tributaries, for example:

STS-1 can carry 1 T3 or 28 T1s or 1 E3 or 21 E1s

STM-1 can carry 3 E3s or 63 E1s or 3 T3s or 84 T1s

SONET SDH columns rate

STS-1 90 51.84M

STS-3 STM-1 270 155.52M

STS-12 STM-4 1080 622.080M

STS-48 STM-16 4320 2488.32M

STS-192 STM-64 17280 9953.28M


29/105

SONET/SDH tributaries

E3 and T3 are carried as Higher Order Paths HOPs)

E1 and T1 are carried as Lower Order Paths (LOPs)(the numbers are fordirect mapping)

SONET SDH T1 T3 E1 E3 E4

STS-1 28 1 21 1

STS-3 STM-1 84 3 63 3 1

STS-12 STM-4 336 12 252 12 4

STS-48 STM-16 1344 48 1008 48 16

STS-192 STM-64 5376 192 4032 192 64


30/105

Synchronous Payload Envelope

STS-1 frame structure

9rows

Transport

Overhead

TOH

6ro

ws

3rows

Section overhead is 3 rows * 3 columns = 9 bytes = 576 kbps

framing, performance monitoring, management

Line overhead is 6 rows * 3 columns = 18 bytes = 1152 kbps

protection switching, line maintenance, mux/concat, SPE pointer

SPE is 9 rows * 87 columns = 783 bytes = 50.112 Mbps

Similarly, STM-1 has 9 (different) columns of section+line overhead !

90 columns

9rows


31/105

STM-1 frame structure

Section

Overhead

SOHSTM-1 has 9 (different) columns of transport overhead !

RS overhead is 3 rows * 9 columns

Pointer overhead is 1 row * 9 columns

MS overhead is 5 rows * 9 columns

SPE is 9 rows * 261 columns

270 columns

RSOH

MSOH


32/105

Even Higher Rates

3 STS-1s can form an STS-3

4 STM-1s (STS-3s) can form an STM-4 (STS-12)4 STM-4s (STS-12s) can form an STM-16 (STS-48)

etc. for STM-N (STS-3N)

The procedure is byte-interleaving

9 rows

9*Ncolumns

270*N columns


33/105

Byte-interleaving

. . .


34/105

Scrambling

SONET/SDH receivers recover clock based on incoming signal

Insufficient number of 0-1 transitions causes degradation of clock

performance

In order to guarantee sufficient transitions, SONET/SDH employ a scrambler

All data except first row of section overhead is scrambled

Scrambler is 7 bit self-synchronizing X7 + X6 + 1

Scrambler is initialized with ones

A short scrambler is sufficient for voice data

but NOT for data which may contain long stretches of zeros


35/105

Scrambling

When sending data an additionalpayloadscrambler is used

modern standards use 43 bit X43 + 1

run continuously on ATM payload bytes (suspended for 5 bytes of

cell tax) run continuously on HDLC payloads

Z-43

Xn Yn = Xn + Yn-43


36/105

STS-1 Overhead

The STS-1 overhead consists of

3 rows of section overhead

frame sync (A1, A2) section trace (J0) error control (B1)

section orderwire (E1) Embedded Operations Channel (Di)

6 rows of line overhead pointer and pointer action (Hi) error control (B2) Automatic Protection Switching signaling (Ki)

Data Channel (Di) Synchronization Status Message (S1) FarEnd Block Error(M0) line orderwire (E2)

A1 A2 J0

B1 E1 F1

D1 D2 D3

H1 H2 H3

B2 K1 K2

D4 D5 D6

D7 D8 D9

D10 D11 D12

S1 M0 E2

section

overhead

line

overhead


37/105

STM-1 Overhead

A1 A1 A1 A2 A2 A2 J0 res res

B1 m m E1 m F1 res res

D1 m m D2 m D3

B2 B2 B2 K1 K2

D4 D5 D6

D7 D8 D9

D10 D11 D12

S1 M1 E2

RSOH

MSOH

SOH

m media

dependent(defined forSONET radio)

res reserved for

national use

AU pointers


38/105

A1, A2, J0 (Section Overhead)

A1, A2 - framing bytes

A1 = 11110110

A2 = 00101000

SONET/SDH framing always uses equal numbers of A1 and A2 bytes

J0 - regenerator section trace (in early SONET - a counter called C1)

enables receiver to be sure that the section connection is still OK

enables identifying individual STS/STMs after muxing

J0 goes through a 16 byte sequence

MSBs are J0 framing (100000)

Cs are CRC-7 of previous frame

S are 15 7-bit characters

section access point identifierSSSSSSS0

SSSSSSS0

C7C6C5C4C3C2C11


39/105

B1, E1, F1, D1-3 (Section Overhead)

B1 Byte Interleaved Parity-8 byte

even parity of bits of bytes of previous frame after scrambling

only 1 BIT-8 for multiplexed STS/STM

E1 section orderwire

64 kbps voice link for technicians

from regenerator to regenerator

F1 64 kbps link for user purposes

D1 + D2 + D3 192 kbps messaging channel

used by section termination as Embedded Operations Channel (SONET)

orData Communications Channel (SDH)


40/105

Pointers (Line Overhead)

In SONET, pointers are considered part of line overhead

For STS-1, H1+H2 is the pointer, H3 is the pointer action

H1+H2 indicates the offset (in bytes) from H3 to the SPE

(i.e. if 0 then J1 POH byte is immediately after H3 in the row)

4 MSBs are New Data Flag, 10 LSBs are actual offset value (0 782)

When offset=522 the STS-1 SPE is in a single STS-1 frame

In all other cases the SPE straddles two frames

When offset is a multiple of 87, the SPE is rectangular

To compensate for clock differences

we havepointer justification

When negativejustificationH3 carries the extra data

Whenpositivejustificationbyte after H3 is stuffing byte


41/105

SONET Justification

If tributary rate is above nominal, negative justification is needed

When less than 8 more bits than expected in buffer

NDF is 0110

offset unchanged

When 8 extra bits accumulate

NDF is set to 1001

extra byte placed into H3 offset is decremented by 1 (byte)

If tributary rate is below nominal, positive justification is needed

When less than 8 fewer than expected bits in buffer

NDF is 0110

offset unchangedWhen 8 missing bits

NDF is set to 1001

byte after H3 is stuffing

offset is incremented by 1 (byte)

H1 H2 extra

H1 H2 H3 stuff


42/105

B2, K1, K2, D4-D12 (Line Overhead)

B2 BIP-8 of line overhead + previous envelope (w/o

scrambling) N B2s for muxed STM-N

K1 and K2 are used for Automatic Protection Switching (see

later) D4 D12 are a 576 Kbps Data Communications Channel

Between multiplexers

Usually manufacturer specific OAM functions


43/105

S1, M0, E2 (Line Overhead)

S1 Synchronization Status Message

indicates stratum level (unknown, stratum 1, , do not use)

M0 FarEnd Block Error

indicates number of BIP violations detected

E2 line orderwire

64 kbps voice link for technicians

from line mux to line mux


44/105

Payloads and Mappings

44


45/105

STS-1 HOP SPE Structure

We saw that the pointer the line overhead points to the STS path overhead POH(after re-arranging) POH is one column of 9 rows (9 bytes = 576 kbps)


46/105

STS-1 HOP

1 column of SPE is POH

2 more (fixed stuffing) columns are reserved

We are left with

84 columns = 756 bytes = 48.384 Mbps for payload

This is enough for a E3 (34.368M) or a T3 (44.736M)

1 875930


47/105

STS-1 Path overhead

1 column of overhead for path (576 Kbps)

POH is responsible for

path type identification path performance monitoring status (including of mapped payloads) virtual concatenation path protection trace

J1

B3

C2

G1

F2

H4

F3

K3

N1

POH


48/105

J1, B3, C2 (Path Overhead)

J1 path trace

enables receiver to be sure

that the path connection is still OK

B3 BIP-8 even bit parity of bytes

(without scrambling)

of previous payload

C2 path signal label

identifies the payload type

(examples in table)

C2(hex)

Payload type

00 unequipped

01 nonspecific

02 LOP (TUG)

04 E3/T3

12 E4

13 ATM

16 PoS RFC 1662

18 LAPS X.85

1A 10G Ethernet

1B GFP

CF PoS - RFC1619


49/105

G1, F2, H4, F3, K3, N1 (Path Overhead)

G1 path status

conveys status and performance back to originator

4 MSBs are path FEBE, 1 bit RDI, 3 unused

F2 and F3 user specific communications

H4 used for LOP multiframe sync and VCAT (see later)

K3 (4 MSBs) path APS

N1 Tandem Connection Monitoring

Messaging channel for tandem connections


50/105

LOP

To carry lower rate payloads, divide the 84 available columns into 7 * 12

interleaved columns, i.e. 7 Virtual Tributary (VT) Groups

VT group is 12 columns of 9 rows, i.e. 108 bytes or 6.912 Mbps

VT group is composed of VT(s) there are different types of VT in order to carry different types of payload

all VTs in VT group must be of the same type (no mixing)

but different VT groups in same SPE can have different VT types

A VT can have 3, 4, 6 or 12 columns

1 875930 1 2 3 4 5 6 77 VTGs

SO /S / C


51/105

SONET/SDH : VT/VC types

VT/STS VC column

rate

payload

VT 1.5 VC-11 3 1.728 DS1 (1.544)

VT 2 VC-12 4 2.304 E1 (2.048)

VT 3 6 3.456 DS1C (3.152)

VT 6 VC-2 12 6.912 DS2 (6.312)

STS-1 VC-3 48.384 E3 (34.368)

STS-1 VC-3 48.384 DS3 (44.736)

STS-3c VC-4 149.760 E4 (139.264)

LOP

HOP

standard PDH rates map efficiently into SONET/SDH !

4 per group

3 per group

2 per group

1 per group

LO Path Overhead


52/105

LO Path Overhead

LOP OH is responsible for timing, PM, REI,

LO Path APS signaling is 4 MSBs of byte K4

V5

J2

N2

K4

V1pointer

V2pointer

V3pointer

V4pointer

VC11 25B

VC12 34B

125 msec

500 msec

H4=XXXXXX00

H4=XXXXXX01

H4=XXXXXX10

H4=XXXXXX11

VC11 27B

VC12 36B


53/105

Payload Capacity

VT1.5/VC-11 has 3 columns = 27 bytes = 1.728 Mbps

but 2 bytes are used for overhead (V1/V2/V3/V4 and V5/J2/N2/K4)

so actually only 25 bytes = 1.6 Mbps are available

Similarly

VT2/VC-12 has 4 columns = 36 bytes = 2.304 Mbps

but 2 bytes are used for overhead

So actually only 34 bytes = 2.176 Mbps are available


54/105

LOP Overhead

V5 consists of BIP (2b)

REI (1b)

RFI (1b)

Signal label (3b) (uneq, async, bit-sync, byte-sync, test, AIS)

RDI (1b)

J2 is path trace

N2 is the network operator byte may be used for LOP tandem connection monitoring (LO-TCM)

K4 is for LO VCAT and LO APS


55/105

SDH Containers

Tributary payloads are not placed directly into SDH

Payloads are placed (adapted) into containers

The containers are made into virtual containers (by addingPOH)

Next, the pointer is used the pointer + VC is a TU or AUTributary Unit adapts a lower order VC to high order VC

Administrative Unit adapts higher order VC to SDH

TUs and AUs are grouped together until they are big

enough

We finally get an Administrative Unit Group

To the AUG we add SOH to make the STM frame


56/105

Formally

C-n n = 11, 12, 2, 3, 4

VC-n = POH + C-n

TU-n = pointer + VC-n (n=11, 12, 2, 3)

AU-n = pointer + VC-n (n=3,4)TUG = N * TU-n

AUG = N * AU-n

STM-N = SOH + AUG


57/105

Multiplexing

An AUG may contain a VC-4 with an E4 or it may contain 3 AU-3s each with a VC-3s with an E3

In the latter case, the AU pointer points to the AUG and inside the AUG are 3 pointers to the AU-3s

J1

B3

C2

G1

F2

H4

F3

K3

N1

H1 H1H1 H2 H2H2 H3 H3H3


58/105

More Multiplexing

Similarly, we can hierarchically build complex

structures

Lower rate STMs can be combined into higher rate

STMs

AUGs can be combined into STMs

AUs can be combined into AUGs

TUGs can be combined into high order VCs

Lower rate TUs can be combined into TUGs

etc. But only certain combinations are allowed by

standards

All SDH Mappings


59/105

pp g

STM-N

AU-3 VC-3 C3

VC-3TU-3TUG-3

C-4VC-4AU-4AUG

AUG

AUG

C2

C12

C11

TUG-2 VC-2TU-2

VC-12TU-12

VC-11TU-11

STM-0

ATM 2.144 M

E4 139.264 M

ATM 1.6 M

ATM 149.760M

ATM 48.384 M

ATM 6.874M

E3 34.368 M

T3 44.736 M

T2 6.312 M

E1 2.048 M

T1 1.544 M

* 3

*7

* 3

*7

* 4

* 3

All SONET M i


60/105

All SONET Mappings

STS-N STS-3 SPESTS-3c

STS-1

VT6 SPE

VT2 SPE

VT1.5 SPE

VT6

VT-2

VT1.5

ATM 2.144 M

E4 139.264 M

ATM 1.6 M

ATM 149.760M

ATM 48.384 M

ATM 6.874M

E3 34.368 M

T3 44.736 M

T2 6.312 M

E1 2.048 M

T1 1.544 M

*NSTS-1 SPE

VTG

*7

pointer processing

* 3

* 4


61/105

Tributary Mapping Types

When mapping tributaries into VCs, PDH-like bit-stuffingis used

For E1 and T1 there are several options

Asynchronous mapping (framing-agnostic)

Bit synchronous mapping

Byte synchronous mapping (time-slot aligned)

E4 into VC-4, E3/T3 into VC-3 are always asynchronous

T1 into VC-11 may be any of the 3(in byte synchronous the framing bit is placed in the VC overhead)

E1 into VC-12 may be asynchronous or byte

synchronous

WAN PHY (10 GbE i STM 64)


62/105

WAN-PHY (10 GbE in STM-64)

There is a special case where the bit-rates work out relatively well

GbE 10GBASE-R (64B/66B coding) can be directly mapped

into a STM-64 (with contiguous concatenation - see later) without need for GFP

MAC creates "stretched InterPacket Gap" to compensate for rate being < 10G

This is the fastest connection commonly used for Internet traffic

Complication: SDH clock accuracy is 4.6 ppm, GbE accuracy is 20 ppm64*(270-9) = 16704 columns

J1

63 columns of fixed stuff

10GBASE-W 802.3-2005 Clause 50


63/105

Protection and Rings

63

Wh t i t ti ?


64/105

What is protection ?

SONET/SDH need to be highly reliable (five nines)Down-time should be minimal (less than 50 msec)

So systems must repair themselves (no time for manual intervention)

Upon detection of a failure (dLOS, dLOF, high BER)

the network must reroute traffic (protection switching)from working channel to protection channel

The Network Element that detects the failure (tail-end NE)initiates the protection switching

The head-end NE must change forwarding or to send duplicate traffic

Protection switching is unidirectionalProtection switching may be revertive (automatically revert to working channel)

head-end NE tail-end NE

working channel

protection channel


65/105

How Does It Work?

Head-end and tail-end NEs have bridges (muxes)

Head-end and tail-end NEs maintain bidirectional signaling channel

Signaling is contained in K1 and K2 bytes ofprotection channel

K1 tail-end status and requests K2 head-end status

head-end bridge tail-end bridge

working channel

protection channel signaling channel

Linear 1+1 protection


66/105

Linear 1+1 protection

Simplest form of protectionCan be at OC-n level (different physical fibers)

or at STM/VC level (called SubNetwork Connection Protection)

or end-to-end path (called trail protection)

Head-end bridge always sends data on both channels

Tail-end chooses channel to use based on BER, dLOS, etc.No need for signaling

If non-revertive

there is no distinction between working and protection channels

BW utilization is 50%channel A

channel B

Linear 1:1 protection


67/105

Linear 1:1 protection

Head-end bridge usually sends data on working channel

When tail-end detects failure it signals (using K1) to head-end

Head-end then starts sending data over protection channel

When not in use

protection channel can be used for (discounted) extra traffic

(pre-emptible unprotected traffic)

May be at any layer (only OC-n level protects against fiber cuts)

working channel

protection channel

extra traffic

Li 1 N t ti


68/105

Linear 1:N protection

In order to save BW

we allocate 1 protection channel for every N working channels

N limited to 14

4 bits in K1 byte from tail-end to head-end 0 protection channel 1-14 working channels 15 extra traffic channel

working channels

protection channel

Two Fiber vs Four-Fiber Rings


69/105

Two Fiber vs. Four-Fiber RingsRing based protection is popular in North America (100K+ rings)

Full protection against physical fiber cutsSimpler and less expensive than mesh topologies

Protection at line (multiplexed section) or path layer

Four-fiber ringsfully redundant at OC levelcan support bidirectional routing at line layer

Two-fiber ringssupport unidirectional routing at line layer

2 fibers in opposite directions

Unidirectional vs bidirectional


70/105

Unidirectional vs. bidirectional

Unidirectional routingworking channel B-A same direction (e.g. clockwise) as A-Bmanagement simplicity: A-B and B-A can occupy same timeslotsInefficient: waste in ring BW and excessive delay in one direction

Bidirectional routingA-B and B-1 are opposite in directionboth using shortest routespatial reuse: timeslots can be reused in other sections

A

BA-B

B-A

A

B

B-A

A-B

C

B-C

C-B

UPSR vs BLSR (MS-SPRing)


71/105

UPSR vs. BLSR (MS-SPRing)

Of all the possible combinations, only a few are in use

Unidirectional Path Switched Ringsprotects tributariesextension of 1+1 to ring topology

Bidirectional Line Switched Rings (two-fiber and four-fiber versions)called Multiplex Section Shared Protection Ring in SDH

simultaneously protects all tributaries in STMextension of 1:1 to ring topology

Path switching

Line switching

Two-fiber

Four-fiber

Unidirectional

Bidirectional

UPSR

BLSR

UPSR


72/105

UPSR

Working channel is in one directionprotection channel in the opposite direction

All traffic is added in both directionsdecision as to which to use at drop point (no signaling)

Normally non-revertive, so effective two diversitypaths

Good match for access networks

1 access resilient ringless expensive than fiber pair per customer

Inefficient for core networksno spatial reuse

every signal in every spanin both directions

node needs to continuously monitorevery tributary to be dropped

BLSR


73/105

BLSR

Switch at line level less monitoringWhen failure detected tail-end NE signals head-end NE

Works for unidirectional/bidirectional fiber cuts, and NE failures

Two-fiber version

half of OC-N capacity devoted to protection

only half capacity available for traffic

Four-fiber version

full redundant OC-N devoted to protectiontwice as many NEs as compared to two-fiber

Example

recovery from unidirectional fiber cut

VCAT and LCAS


74/105

VCAT and LCAS

74

Concatenation


75/105

Concatenation

Payloads that dont fit into standard VT/VC sizes can be accommodated

by concatenatingof several VTs / VCs

For example, 10 Mbps doesnt fit into any VT or VC

so w/o concatenation we need to put it into an STS-1 (48.384 Mbps)

the remaining 38.384 Mbps can not be used

We would like to be able to divide the 10 Mbps among

7 VT1.5/VC-11 s = 7 * 1.600 = 11.20 Mbps or

5 VT2/VC-12 s = 5 * 2.176 = 10.88 Mbps

Concatenation (cont.)


76/105

( )

There are 2 ways to concatenate X VTs or VCs:

Contiguous Concatenation (G.707 11.1)

HOP STS-Nc (SONET) or VC-4-Nc (SDH)

orLOP 1-7 VC-2-Nc into a VC-3

since has to fit into SONET/SDH payload

only STS-Nc : N=3 * 4n or VC-4-Nc : N=4n

components transported together and in-phase

requires support at intermediate network elements

Virtual Concatenation (VCAT G.707 11.2)

HOP STS-1-Xv or STS-Nc-Xv (SONET) or VC-3/4-Xv (SDH)

orLOP VT-1.5/2/3/6-Xv (SONET) or VC-11/12/2-Xv (SDH)

HOP: X 256 LOP: X 64 (limitation due to bits in header)

payload split over multiple STSs / STMs fragments may follow different routes

requires support only at path terminations

requires buffering and differential delay alignment

Contiguous Concatenation:

STS-3c


77/105

270 columns

9rows

9 columns of

section and

line overhead

3 columns of

path overhead

258 columns of SPE

STS-3

270 columns

9rows

9 columns of

section and

line overhead

1 column of

path overhead

260 columns of SPESTS-3c

258 columns * 0.576 = 148.608 Mbps

260 columns * 0.576 = 149.760 Mbps

STS-N vs. STS-Nc


78/105

STS N vs. STS Nc

Although both have raw rates of 155.520 Mbps

STS-3c has 2 more columns (1.152Mbps) available

More generally, For STS-Nc gains (N-1) columns

e.g. STS-12c gains 11 columns = 6.336Mbps vis a vis STS-12STS-48c gains 47 columns = 27.072 Mbps

STS-192c gains 191 columns = 110.016 Mbps !

However, an STS-Nc signal is not as easily separable

when we want to add/drop component signals

Virtual Concatenation


79/105

VCAT is an inverse multiplexing mechanism (round-robin)VCAT members may travel along different routes in SONET/SDH network

Intermediate network elements dont need to know about VCAT

(unlike contiguous concatenation that is handled by all intermediate nodes)

H4

SDH virtually concatenated

VCs


80/105

VCs

So we have many permissible rates1.600, 2.176, 3.200, 4.352, 4.800, 6.400, 6.528, 6.784, 8.000,

VC Capacity (Mbps) if all members in one VC

VC-11-Xv 1.600, 3.200, 1.600X in VC-3 X 28 C 44.800

in VC-4 X 64 C 102.400

VC-12-Xv 2.176, 4.352, 2.176X in VC-3 X 21 C 45.696

in VC-4 X 63 C 137.088

VC-2-Xv 6.784, 13.568, , 6.784X in VC-3 X 7 C 47.448

in VC-4 X 21 C 142.464

SONET virtually concatenated

VTs


81/105

VT Capacity (Mbps) If all members in one STS

VT1.5-Xv 1.600, 3.200, 1.600X in STS-1 X 28 C 44.800

in STS-3c X 64 C 102.400

VT2-Xv 2.176, 4.352, 2.176X in STS-1 X 21 C 45.696

in STS-3c X 63 C 137.088

VT3-Xv 3.328, 6.656, 3.328X in STS-1 X 14 C 46.592

in STS-3c X 42 C 139.776

VT6-Xv 6.784, 13.568, 6.784X in STS-1 X 7 C 47.448

in STS-3c X 21 C 142.464

So we have many permissible rates

1.600, 2.176, 3.200, 3.328, 4.352, 4.800, 6.400, 6.528, 6.656, 6.784,

Efficiency Comparison


82/105

y p

Using VCAT increases efficiency to close to 100% !

rate w/o VCAT efficiency with VCAT efficiency

10 STS-1 21% VT2-5v

VC-12-5v

92%

100 STS-3c

VC-4

67% STS-1-2v

VC-3-2v

100%

1000 STS-48c

VC-4-16c

42% STS-3c-7v

VC-4-7v

95%

PDH VCATVCAT


83/105

Recently ITU-T G.7043 expanded VCAT to E1,T1,E3,T3

Enables bonding of up to 16 PDH signals to support higher rates

Only bonding oflike PDH signals allowed (e.g. cant mix E1s and T1s)

Multiframe is always per G.704/G.832 (e.g. T1 ESF 24 frames, E1 16 frames)

1 byte per multiframe is VCAT overhead (SQ, MFI, MST, CRC)

Supports LCAS (to be discussed next)

TS0

1st

frameof4 E1s

VCAToverhead

octet

timeeach E1

PDH VCAT Overhead Octet


84/105

There is one VCAT overhead octet per multiframe, so net rate is

T1: (24*24-1=) 575 data bytes per 3 ms. multiframe = 191.666 kB/s

E1: (16*30-1=) 495 data bytes per 2 ms multiframe = 247.5 kB/s

T3 and E3 can also be used

We will show the overhead octet format later

(when using LCAS, the overhead octet is called VLI)

TS0

frames

of an

E1

VCAT

overheadoctet

Delay Compensation


85/105

802.1ad Ethernet link aggregation cheats each identifiable flow is restricted to one link

doesnt work if single high-BW flow

VCAT is completely general works even with a single flow

VCG members may travel over completely separate pathsso the VCAT mechanism must compensate fordifferential delay

Requirement for over second compensation

Must compensate to the bit level

but since frames have FrameAlignment Signal

the VCAT mechanism only needs to identify individual frames

VCAT Buffering


86/105

Since VCAT components may take different paths

At egress the membersare no longer in the proper temporal relationship

VCAT path termination function buffers members

and outputs in proper order (relying on POH sequencing)

(up to 512 ms of differential delay can be tolerated)

VCAT defines a multiframe to enable delay compensation

length of multiframe determines delay that can be accommodatedH4 byte in members POH contains : sequence indicator (identifies component) (number of bits limits X) MFI multiframe indicator(multiframe sequencing to find differential delay)

Multiframes and Superframes


87/105

Here is how we compensate for 512 ms of differential delay512 ms corresponds to a superframe is 4096 TDM frames (4096*0.125m=512m)

For HOP SDH VCAT and PDH VCAT (H4 byte or PDH VCAT overhead)

The basic multiframe is 16 frames

So we need 256 multiframes in a superframe (256*16=4096)

The MultiFrame Indicator is divided into two parts:

MFI1 (4 bits) appears once per frame

and counts from 0 to 15 to sequence the multiframe

MFI2 (8bits) appears once per multiframe

and counts from 0 to 255

For LOP SDH (bit 2 of K4 byte)

a 32 bit frame is built and a 5-bit MFI is dedicated

32 multiframes of 16 ms give the needed 512 ms

Link Capacity Adjustment Scheme


88/105

LCAS is defined in G.7042 (also numbered Y.1305)LCAS extends VCAT by allowing dynamic BW changes

LCAS is a protocol for dynamic adding/removing of VCAT members

hitless BW modification

similar to LinkAggregation Control Protocol for Ethernet links

LCAS is not a control plane or management protocol it doesnt allocate the members

still need control protocols to perform actual allocation

LCAS is a handshake protocol

it enables the path ends to negotiate the additional / deletion

it guarantees that there will be no loss of data during change it can determine that a proposed member is ill suited

it allows automatic removal of faulty member

LCAS how does it work?


89/105

LCAS is unidirectional (for symmetric BW need to perform twice)LCAS functions can be initiated by source or sink

LCAS assumes that all VCG members are error-free

LCAS messages are CRC protected

LCAS messages are sent in advance

sink processes messages after differential compensation

message describes link state at time of next message receiver can switch to new configuration in time

LCAS messages are in the upper nibble of

H4 byte for HOS SONET/SDH

K4 byte for LOS SONET/SDH

VCAT overhead octet for PDH VCAT and LCAS Information

LCAS messages employ redundancy

messages from source to sink are member specific

messages from sink to source are replicated

J1

B3

C2

G1F2

H4

F3

K3

N1

POH

LCAS control messages


90/105

LCAS adds fields to the basic VCAT ones

Fields in messages from source to sink:

MFI MultiFrame Indicator

SQ SeQuence indicator(member ID inside VCAT group)

CTRL ConTRoL (IDLE, being ADDed, NORMal, End of Sequence, Do Not Use)

GID Group Identification (identifies VCAT group)

Fields in messages from sink to source (identical in all members): MST Member Status (1 bit for each VCG member)

RS-Ack ReSequence Acknowledgement

Fields in both directions

CRC Cyclic Redundancy Code

The precise format depends on the VCAT type (H4, K4, PDH)

Note: for H4 format SQ is 8 bits, so up to 256 VCG members

for PDH SQ is only 4 bits, so up to 16 VCG members

H4 formatMFI1


91/105

MFI2 bits 1-4 0 0 0 0

MFI2 bits 5-8 0 0 0 1CTRL 0 0 1 0

0 0 0 GID 0 0 1 1

0 0 0 0 0 1 0 0

0 0 0 0 0 1 0 1

CRC-8 bits 1-4 0 1 1 0

CRC-8 bits 5-8 0 1 1 1MST bits 1 0 0 0

more MST bits 1 0 0 1

0 0 0 RS-ACK 1 0 1 0

0 0 0 0 1 0 1 1

0 0 0 0 1 1 0 0

0 0 0 0 1 1 0 1

SQ bits 1-4 1 1 1 0

SQ bits 5-8 1 1 1 1

16fram

emultiframe

reservedfields

reservedfields

H4 Format


92/105

CRC-8 (when using K4 it is CRC-3)

covers the previous 14 frames (not synced on multiframe)

polynomial x8 + x2 + x + 1

MST

each VCG member carries the status of all members

so we need 256 bits of member status

this is done by muxing MST bits there are MST bits per multiframe

and 32 multiframes in an MST multiframe

no special sequencing, just MFI2 multiframe mod 32

GID

single bit indentifier all members of VCG share the same bit cycles through 215-1 LFSR sequence different VCGs use different phase offsets of sequence

LCAS Adding a Member (1)


93/105

When more/less BW is needed, we need to add/remove VCAT membersAdding/removing VCAT members first requires provisioning (management)

LCAS handles member sequence numbers assignment

LCAS ensures service is not disrupted

Example: to add a 4th member to group 1

Initial state:

Step 1: NMS provisions new member

source sends CTRL=IDLE for new member

sink sends MST=FAIL for new member

GID=g SQ=1 CTRL=NORM


GID=g SQ=3 CTRL=EOS



GID=g SQ=3 CTRL=EOS

GID=g SQ=FF CTRL=IDLE

LCAS Adding a Member (2)


94/105

Step 2: source sends CTRL=ADD and SQsink sends MST=OK for new member

if it has been provisioned if receiving new member OK if it is able to compensate for delay

otherwise it will send MST=FAIL

and source reports this to NMS

Step 3: source sends CTRL=EOS for new member

new member starts to carry traffic

sink sends RS-ACK

Note 1: several new members may be added at onceNote 2: removing a member is similar

Source puts CTRL=IDLE for member to be removed and stops using it

All member sequence numbers must be adjusted



GID=g SQ=3 CTRL=EOS

GID=g SQ=4 CTRL=ADD




GID=g SQ=4 CTRL=EOS

LCAS Service Preservation


95/105

To preserve service integrity if sink detects a failure of a VCAT member

LCAS can temporarily remove member(if service can tolerate BW reduction)

Example: Initial state

Step 1: sink sends MST=FAIL for member 2

source sends CTRL=DNU (special treatment if EoS)

and ceases to use member 2

Note: if EoS fails, renumber to ensure EoS is active

Step 2: sink sends MST=OK indicating defect is clearedsource returns CTRL to NORM

and starts using the member againNote: if NMS decides to permanently remove the member, proceed as in previous slide




GID=g SQ=4 CTRL=EOS


GID=g SQ=2 CTRL=DNU


GID=g SQ=4 CTRL=EOS

Handling Packet Data


96/105

96

Packet over SONET


97/105

Currently defined in RFC2615 (PPP over SONET)

obsoletes RFC1619

SONET/SDH can provide a point-to-point byte-orientedfull-duplex synchronous link

PPP is ideal for data transport over such a link

PoS uses PPP in HDLC framing to provide a byte-oriented

interface to the SONET/SDH infrastructure

POH signal label (C2)

indicates PoS as C2=16 (C2=CF if no scrambler)

PoS Architecture


98/105

PoS is based on PPP in HDLC framing

Since SONET/SDH is byte oriented, byte stuffing is employed

A special scrambler is used to protect SONET/SDH timing

PoS operates on IP packets

If IP is delivered over Ethernet

the Ethernet is terminated (frame removed) Ethernet must be reconstituted at the far end

require routers at edges of SONET/SDH network

IP

PPP

HDLC

SONET/SDH

PoS Details


99/105

IP packet is encapsulated in PPP default MTU is 1500 bytes

up to 64,000 bytes allowed if negotiated by PPP

FCS is generated and appended

PPP in HDLC framing with byte stuffing43 bit scrambler is run over the SPE

byte stream is placed octet-aligned in SPE

(e.g. 149.760 Mbps of STM-1)

HDLC frames may cross SPE boundaries

POS Problems


100/105

PoS is BW efficientbut POS has its disadvantages

BW must be predetermined

HDLC BW expansion and nondeterminacy

BW allocation is tightly constrained by SONET/SDHcapacities

e.g. GBE requires a full OC-48 pipe

POS requires removing the Ethernet headers

so lose RPR, VLAN, 802.1p, multicasting, etc

POS requires IP routers

LAPS


101/105

In 2001 ITU-T introduced protocols for transportingpackets over SDH

X.85 IP over SDH using LAPS

X.86 Ethernet over LAPS

Built on series of ITU LAPx HDLC-based protocols Use ISO HDLC format

Implement connectionless byte-oriented protocols

over SDH

X.85 is very close to (but not quite) IETF PoS

GFP Architecture

A h t b d HDLC


102/105

A new approach, not based on HDLC

Defined in ITU-T G.7041 (also numbered Y.1303)originally developed in T1X1 to fix ATM limitations(like ATM) uses HEC protected frames instead of HDLC

Client may be PDU-oriented (Ethernet MAC, IP)

or block-oriented (GBE, fiber channel)

GFP frames

are octet aligned contain at most 65,535 bytes

consist of a header + payload area

Any idle time between GFP frames is filled with GFP idle frames

Ethernet IP other

GFP client specific part

GFP common partSDH OTN other

HDLC

GFP Frame Structure

E GFP f h 4 b t h d


103/105

Every GFP frame has a 4-byte core header

2 byte Payload Length Indicator

PLI = 01,2,3 are for control frames

2 byte core Header Error Control

X16 + X12 + X5 + 1

entire core header is XORed with B6AB31E0

Idle GFP frames have PLI=0

have no payload area

Non-idle GFP frames

have 4 bytes in payload area

the payload has its own header 2 payload modes : GFP-F and GFP-T

optionally protect payload with CRC-32

PLI (2B)

cHEC (2B)

payload header

(4-64B)

payload

optional payloadFCS (4B)

core

header

payloadarea

GFP Payload Header


104/105

GFP payload header has

type (2B)

type HEC (CRC-16)

extension header (0-60B)eithernullorlinear extension (payload type muxing)

extension HEC (CRC-16)

type consists of Payload Type Identifier (3b)

PTI=000 for client data PTI=100 for client management (OAM dLOS, dLOF)

Payload FCS Indicator (1b) PFI=1 means there is a payload FCS

Extension Header ID (3b) User Payload Identifier (8b)

values for Ethernet, IP, PPP, FC, RPR, MPLS, etc.

type (2B)

tHEC (2B)

extension header

(0-60B)

eHEC (2B)

UPI (8b)

PTI (3b) EXI (3b)PFI

GFP Modes


105/105

GFP-F - frame mapped GFP

Good for PDU-based protocols (Ethernet, IP, MPLS)or HDLC-based ones (PPP)

Client PDU is placed in GFP payload field

GFP-T transparent GFP

Good for protocols that exploit physical layer capabilities

In particular

8B/10B line code

used in fiber channel, GbE, FICON, ESCON, DVB, etc

Were we to use GFP-F would lose control info, GFP-T is transparentto these codes

Also, GFP-T neednt wait for entire PDU to be received (adding delay!)

Documents

4c. Communication Network - SDHpdf