GFP Eth Frame

8/8/2019 GFP Eth Frame

1/89

Connection-Oriented Networks - Harry Perros 1

Chapter 2:SONET/SDH and GFP

TOPICS

T1/E1

SONET/SDH - STS 1, STS -3 frames

SONET devices

Self-healingrings

Generic frame protocol, and Data over SONET


2/89


T1/E1

Time division multiplexing allows a link

to be utilized simultaneously by many

users

M

U

X

D

E

M

U

X

N inputlinks N outputlinks

link

1

2

N

1

2

N


3/89


The transmission is organized into frames. Each frame contains a fixed number of time slots.

Each time slot is pre-assigned to a specific inputlink. The duration of a time slot is either a bit or a

byte. If the buffer of an input link has no data, then its

associated time slot is transmitted empty.

A time slot dedicated to an input link repeats

continuously frame after frame, thus forming achannelor a trunk.


4/89


Pulse code modulation

TDM is used in telephony

Voice analog signals are digitized at the

end office using Pulse Code Modulation.

A voice signal is sampled 8000 times/sec,

or every 125 sec.

A 7-bit or 8-bit number is created every

125 sec.


5/89


6/89


T carrier / E carrier The DS signal is carried over a carrier system

known as the T carrier.

T1 carries the DS1 signal,

T2 carries the DS2 signal etc

The ITU-T signal is carried over a carrier systemknown as theE carrier.

The DS and ITU-T hierarchy is known as the

plesiochronous digital hierarchy (PDH). (Plesionmeans nearly the same, and chronos meanstime in Greek).


7/89


Digital signal number Voice channels Data Rate (Mbps)DS0 1 0.064DS1 24 1.544

DS1C 48 3.152DS2 96 6.312DS3 672 44.736

DS3C 1344 91.053DS4 4032 274.176

Table 2.1: The North American Hierarchy

Level number Voice channels Data Rate (Mbps)0 1 0.0641 30 2.0482 120 8.4483 480 34.3684 1920 139.2645 7680 565.148

Table 2.2: The international (ITU-T) hierarchy


8/89


The DS1 signal

24 8-bit time slots/frame Each time slot carries 8 bits/ 125 sec, or the channel

carries a 64 Kbps voice.

Every 6th successive time slot (i.e, 6th, 12th, 18th,24th, etc), the 8 bit is robbed and it is used for

signaling. F bit: Used for synchronization. It transmits the

pattern: 10101010

FTime

slot 1

Time

slot 2

Time

slot 3

Time

slot 24. . .


9/89


T1: Total transmission rate: 24x8+1 = 193 bits per 125

sec, or 1.544 Mbps

E1 30 voice time slots plus 2 time slots for

synchronization and control

Total transmission rate: 32x8 = 256 bits per 125 sec,or 2.048 Mbps


10/89


Fractional T1/E1

Fractional T1 or E1 allows the use of only

a fraction of the T1 or E1 capacity. For example: if N=2, then only two time

slots are used per frame, which corresponds

to a channel with total bandwidth of 128

Kbps.


11/89


12/89


The synchronous optical network(SONET)

Proposed by Bellcore (Telecordia).

It was designed to multiplex DS-n signals andtransmit them optically.

ITU-T adopted the synchronous digitalhierarchy (SDH), as the international

standard. It enables the multiplexing of level 3 signals

(34.368 Mbps)


13/89


STS, STM, OC

The electrical side of the SONET signal is

known as the synchronous transport signal

(STS)

The electrical side of the SDH is known as

the synchronous transport module (STM).

The optical side of a SONET/SDH signal isknown as the optical carrier(OC).


14/89


The SONET/SDH hierarchyOptical

level

SONET

level

(electrical)

SDH

level

(electrical)

Data rate

(Mbps)

Overhead

rate

(Mbps)

Payload

rate

(Mbps)

OC-1 STS-1 - 51.840 1.728 50.112

OC-3 STS-3 STM-1 155.520 5.184 150.336

OC-9 STS-9 STM-3 466.560 15.552 451.008

OC-12 STS-12 STM-4 622.080 20.736 601.344

OC-18 STS-18 STM-6 933.120 31.104 902.016

OC-24 STS-24 STM-8 1244.160 41.472 1202.688

Oc-36 STS-36 STM-12 1866.240 62.208 1804.932

OC-48 STS-48 STM-16 2488.320 82.944 2405.376

OC-96 STS-96 STM-32 4976.640 165.888 4810.752

OC-192 STS-192 STM-64 9953.280 331.776 9621.504

OC-768 STS-768 STM-256 39813.120 1327.104 38486.016

OC-N STS-N STM-N/3 N*51.840 N*1.728 N*50.112


15/89


SONET/SDH is channelized.

STS-3 consists of 3 STS-1 streams, and each STS-1 consists of a number of DS-1 and E1signals.

STS-12 consists of 12 STS-1 streams

Concatenated structures (OC-3c, OC-12c, etc) The frame of the STS-3 payload is filled with

ATM cells or IP packets packed in PPP or HDLC

frames.

Concatenated SONET/SDH links are commonlyused to interconnect ATM switches and IP routers

(Packets over SONET).


16/89


The STS-1 frame structure

1 2 3 4 5 6 90

1 1 2 3 4 5 6 90

2 91 92 93 94 95 96 180

3 181 182 183 184 185 186 270

4 271 272 273 274 275 276 360

5 361 362 363 364 365 366 450

6 451 452 453 454 455 456 560

7 561 562 563 564 565 566 630

8 631 632 636 634 635 636 720

9 721 722 723 724 725 726 810


17/89


Main features

The frame is presented in matrix form and it is

transmitted row by row.

Each cell in the matrix corresponds to a byte

The first three columns contain overheads The remaining 87 columns carry the

synchronous payload envelope (SPE), which

consists of user data, and additional overheads

referred to as thepayload overhead(POH)


18/89


An SPE may straddle between

two successive frames

Frame i

Frame i+1

1 2 3 4 5 6 . . . 90

1

2

3

4

5

6

7

8

9

276

276275

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

1

2

3

4

5

6

7

8

9


19/89


The section, line, and path overheads

Section

Line

STS-1 STS-1

A B

regeneratorregeneratorSTS-1

A1

A12

STS-12

. . .

STS-1

B1

B12

STS-12

. . .

Section Section Section Section

LineLine

Path


20/89


Section: a single link with a SONET deviceor a regenerator on either side of it.

Line: A link between two SONET devices,

which may include regenerators The section overhead in the SONET frame

is associated with the transport of STS-1

frames over a section, and the line

overhead is associated with the transport ofSPEs over a line.


21/89


The SONET stack

Section

Line

Path

Photonic

Section

Line

Path

Photonic

Section

Line

Photonic

Section

Photonic

Section

Photonic

Section

Line

Photonic

Ai

A Regenerator Regenerator Bi

B


22/89


STS-1: Section and line overheads

SOH

LOH

Column

1 2 3

1 A1 A2 J0

2 B1 E1 F1

3 D1 D2 D3

4 H1 H2 H3

5 B2 K1 K2

6 D4 D5 D6

7 D7 D8 D9

8 D10 D11 D12

9 Z1 Z2 E2


23/89


The following are some of the bytes in the

section overhead (SOH) : A1 and A2: These two bytes are called the

framing bytes and they are used for framealignment. They are populated with the value

1111 0110 0010 1000 or 0xF628, whichuniquely identifies the beginning of an STS-frame.

J0: This is called the section trace byte and itis used for to trace the STS-1 frame back to itsoriginating equipment.


24/89


B1: This byte is the bit interleaved parity byteand it is commonly referred to as BIP-8. It isused to perform an even-parity check on theprevious STS-1 frame after the frame has beenscrambled. The parity is inserted in the BIP-8field of the current frame before it is scrambled

E1: This byte provides a 64 Kbps channel canbe used for voice communications by fieldengineers.


25/89


The following are some of the bytes in the line

overhead (LOH) that have been defined:

H1 and H2: These two bytes are known as thepointer

bytes, and they contain a pointer that points to the

beginning of the SPE within the STS-1 frame. The

pointer gives the offset in bytes between the H1 andH2 bytes and the beginning of the SPE.

B2: This is similar to the B1 byte in the section

overhead and it is used to carry the BIP-8 parity check

performed on the line overhead section and the

payload section. That is, it is performed on the entire

STS-1 frame except the section overhead bytes.


26/89


The path overhead bytes

J1

B3

C2

G1

F2

H4

Z3

Z4

Z5

J1

B3C2

G1

F2

H4

Z3

Z4

Z5

Location of the POH The POH bytes


27/89


The following are some of the bytes that have

been defined:

B3: This byte is similar to B1 used in the section

overhead and B2 used in the line overhead. It is used to

carry the BIP-8 parity check performed on the payload

section. That is, it is performed on the entire STS-1frame except the section and line overhead bytes.

C2: This byte is known as the path signal labeland it

indicates the type of user information carried in the

SPE, such as, virtual tributaries (VT), asynchronous

DS-3, ATM cells, HDLC-over-SONET, and PPP over

SONET.


28/89


The STS-1 payload

The payload consists of user data and the

path overhead.

User data: Virtual tributaries: sub-rate synchronous data

streams, such as DS-0, DS-1, E1, and entire

DS-3 frames

ATM cells and IP packets


29/89


Virtual tributaries

The STS-1 payload is divided into seven

virtual tributary groups (VTG).

Each VTG consists of 108 bytes (12 columns)

Each VTG may carry a number ofvirtual

tributaries, i.e., sub-rate streams.


30/89


The following virtual tributaries have beendefined:

VT1.5:This virtual tributary carries one DS-1

signal and it is contained in three columns, that

take up 27 bytes. Four VT1.5s can betransported in a single VTG.

VT2: This virtual tributary carries an E1 signal

of 2.048 Mbps. VT2 is contained in four

columns, that is it takes up 36 bytes. ThreeVT2s can be carried in a single VTG.


31/89


VT3: This virtual tributary transports theunchannelized DS-1 signal. A VT3 iscontained in 6 columns that takes up 54 bytes.This means that a VTG can carry two VT3s.

VT6: This virtual tributary transports a DS-2signal, which carries 96 voice channels. VT6 iscontained in 12 columns, that is it takes up 108bytes. A VTG can carry exactly one VT2.


32/89


ATM cells

Mapped directly onto the SPE. An ATMcells may straddle two SPEs.

10

Cell 1 Cell 2

Cell 2 Cell 3

Cell 14 Cell 15

Cell 15

904

1

9

2

8

3

POH


33/89


IP packet over SONET

IP packets are first encapsulated in HDLC andthe resulting frames are mapped into the SPE

payload row by row as in the case above forATM cels.10 904

1

9

2

8

3

POH

7E 7E 7E

7E7E7E


34/89


IP packets can also be encapsulated in PPPinstead of HDLC.

A frame may straddle over two adjacent SPEs, asin the case of ATM.

The interframe fill 7E is used to maintain acontinuous bit tstream


35/89


The STS-3 frame structure

Overhead section Payload section

1 2 3 4 5 6 7 8 9 10 11 12

270

.

.

.

1st

S TS

-1

1stSTS-1

1stSTS-1

1stSTS-1

1stSTS-1

2ndS

TS-1

2ndS

TS-1

2ndS

TS-1

2ndS

TS-1

2ndS

TS-1

3rd

STS-1

3rd

STS-1

3rdS

TS-1

3rdS

TS-1

3rd

STS-1


36/89


The channelized STS-3 frame is constructed by

multiplexing byte-wise three channelized STS-1frames. As a result:

Byte 1, 4, 7, , 268 of the STS-3 frame contains byte1, 2, 3, , 90 of the first STS-1 frame.

Byte 2, 5, 8, , 269 of the STS-3 frame contains byte

1, 2, 3, , 90 of the second STS-1 frame Byte 3, 6, 9, , 270 of the STS-3 frame contains byte

1, 2, 3, , 90 of the third STS-1 frame.

This byte-wise multiplexing, causes the columnsof the three STS-1 frames to be interleaved in theSTS-3 frame


37/89


The first 9 columns of the STS-3 framecontain the overhead part and the

remaining columns contain the payload

part. Error checking and some overhead bytes

are for the entire STS-3 frame, and they are

only meaningful in the overhead bytes of

the first STS-1 frame.


38/89


SONET/SDH devices

Several different equipment exist: Terminal multiplexer (TM)

Add/drop multiplexer (ADM)

Digital cross connect(DCS)


39/89


It multiplexes a number of DS-n or E1 signalsinto a single OC-N signal

It consists of a controller, low-speed interfaces

for DS-n or E1 signals, an OC-N interface, and atime slot interchanger (TSI)

It works also as a demultiplexer

. . .

DS-n

OC-N

DS-n

TM

The terminal multiplexer (TM):


40/89


It is a more complex version of the TM

It receives an OC-N signal from which it candemultiplex and terminate (i.e., drop) anynumber of DS-n or OC-M signals, where M


41/89


SONET rings

ADM

1

ADM

2

ADM

3

ADM

4

OC3

OC3

OC3

OC3

SONET/SDH ADM devices are typically connected toform a SONET/SDH ring.

SONET/SDH rings are self-healing, that is they canautomatically recover from link failures.


42/89


An example of a connection

A

B

TM

1

TM

2

ADM

1ADM

2

ADM

3

ADM

4

DS1

OC12

DS1

OC12

OC12

OC12

OC3

OC3


43/89


A transmits a DS-1 signal to TM 1

TM 1 transmits an OC-3 signal to ADM 1 ADM 1 adds the OC-3 signal into the STS-

12 payload and transmits it out to the nextADM.

At ADM 3, the DS-1 signal belonging to Ais dropped from the payload andtransmitted with other signals to TM 2.

TM 2 in turn, demultiplexes the signals andtransmits As DS-1 signal to B.


44/89


Connection setup: Using network management procedures the

SONET network is provisioned appropriately.This is an example of apermanent connection.

It remains up for a long time. The connection is dedicated to user A

whether the user transmits or not.


45/89


A digital cross connect (DCS)

Ring 1 Ring 2ADM

ADM

ADM

ADM

ADM

ADM

DCS

It is used to interconnect multiple SONET rings

It is connected to multiple incoming and outgoing OC-N

interfaces. It can drop and add any number of DSn and/or

OC-M signals, and it can switch DSn and/or OC-M

signals from an incoming interface to any outgoing one.


46/89


Self-healing SONET/SDH rings

SONET/SDH rings have been specially

architected so that they are available 99.999% of

the time (6 minutes per year!) Causes for ring failures:

Fiber link failure due to accidental cuts, and

transmitter/receiver failure

SONET/SDH device failure (rare)


47/89


Automatic protection switching (APS)

SONET/SDH rings are self-healing, that is, the

rings services can be automatically restored

following a link failure or degradation in thenetwork signal.

This is done using the automatic protection

switching (APS) protocol. The time to restore the

services has to be less than 50 msec.


48/89


Protection schemes: point-to-point

Schemes for link protection

dedicated 1+1

1:1

Shared 1:N

ADM

Working

Protection

ADM


49/89


Working/protection fibers The working and protection fibers have to

be diversely routed. That is, the two fibers

use separate conduits and different physicalroutes.

Often, for economic reasons, the two fibers

use different conduits, but they use the

same physical path. In this case, we saythat they are structurally diverse.


50/89


Classification of self-healing rings Various ring architectures have been

developed based on the following threefeatures:

Number of fibers

2 or 4 fibers

Direction of transmission:

Unidirectional bidirectional

Line or path switching


51/89


Number of fibers: 2- or 4-fiber rings

Two-fiber ring: fibers 1, 2, 3, and 4 areused to form the workingring (clockwise),

and fibers 5, 6, 7, and 8 are used to formtheprotection ring (counter-clockwise).

1

2

3

4

5

6

7

8

ADM 1 ADM 2

ADM 3ADM 4

ADM 1 ADM 2

ADM 3ADM 4


52/89


In another variation of the two-fiber ring, each set of fibersform a ring which can be both a working and a protectionring. In this case, the capacity of each fiber is divided intotwo equal parts, one for working traffic and the other for

protection traffic. In a four-fiber SONET/SDH ring there are two working

rings and two protection rings, one per working ring.

1

2

3

4

5

6

7

8

ADM 1 ADM 2

ADM 3ADM 4

ADM 1 ADM 2

ADM 3ADM 4


53/89


Direction of transmission

Unidirectional ring:

signals are only transmitted in one

direction of the ring. Bidirectional ring:

signals are transmitted in both directions.


54/89


Line and path switching

Path switching: Restores the traffic on the

paths affected by a link failure (a path is an

end-to-end connection between the pointwhere the SPE originates and the point where

it terminates.)

Line switching: Restores all the traffic that

passes through a failed link.


55/89


Based on these three features, we have thefollowing 2-fiber or 4-fiber possible ringarchitectures:

Unidirectional Line Switched Ring(ULSR) Bidirectional Line Switched Ring(BLSR)

Unidirectional Path Switched Ring(UPSR)

Bidirectional Path Switched Ring(BPSR)


56/89


Of these rings the following three areused:

Two-fiber unidirectional path switched ring(2F-UPSR)

Two-fiber bidirectional line switched ring(2F-BLSR)

Four-fiber bidirectional line switched ring(4F-BLSR)


57/89


Two-fiber unidirectionalpath switched ring (2F-UPSR)

ADM 1 ADM 2

ADM 3ADM 4

5

264 8

3

7

A

Protection ring

Working ring

1

B


58/89


Features:

Working ring consists of fibers 1, 2, 3 and 4,

and the protection ring of fibers 5, 6, 7, and 8.

Unidirectional transmission means that traffic

is transmitted in the same direction. Atransmits to B over fiber 1 of the working ring,

and B transmits over fibers 2, 3, and 4 of the

working ring.

Used as a metro edge ring to interconnectPBXs and access networks to a metro core ring


59/89


Self-healing mechanism:

Path level protection using the 1+1 scheme. Thesignal transmitted by A is split into two. One

copy is transmitted over the working fiber 1, and

the other copy is transmitted over the protection

fibers 8, 7, and 6.

During normal operation, B receives two

identical signals from A, and selects the one

with the best quality. If fiber 1 fails, B will

continue to receive As signal over theprotection path. The same applies if there is a

node failure.


60/89


Two-fiber bidirectional line switchedring (2F-BLSR)

ADM 1 ADM 2 ADM 3

ADM 4

7

396 12

5

11

A B

1

8

4

2

10

ADM 5ADM 6

C


61/89


Features:

Used in metro core rings.

Fibers 1, 2, 3, 4, 5, and 6 form a ring, call it ring 1, onwhich transmission is clockwise. Fibers 7, 8, 9, 10, 11,and 12 form another ring, call it ring 2, on which

transmission is counter-clockwise. Both rings 1 and 2 carry working and protection traffic.

This is done by dividing the capacity of each fiber onring 1 and 2 to two parts. One part is used to carryworking traffic and the other protection traffic.

A transmits to B over the working part of fibers 1 and2 of ring 1, and B transmits to A over the working partof fibers 8 and 7 of ring 2.


62/89


Self-healing mechanism:

The ring provides line switching. If fiber 2 fails

then the traffic that goes over fiber 2 will be

automatically switched to the protection part of

ring 2.

That is, all the traffic will be re-routed to ADM

3 over the protection part of ring 2 using fibers

7, 12, 11, 10, and 9. From there, the traffic for

each connection will continue on following the

original path of the connection.


63/89


Four-fiber bidirectional line switched

ring (4F-BLSR)

Working rings

ADM 1 ADM 2 ADM 3

ADM 4

A B

ADM 5ADM 6

Protection rings


64/89


Features

Two working rings and two protection rings.The two working rings transmit in opposite

directions, and each is protected by a

protection ring which transmits in the same

direction. The advantage of this four-fiber ring is that it

can suffer multiple failures and still function.

In view of this, it is deployed by long-distance

telephone companies in regional and nationalrings.


65/89


Self-healing operation (span switching):

If a working fiber fails, the working traffic willbe transferred over its protection ring. This isknown as span switching.

ADM 1 ADM 2 ADM 3 ADM 1 ADM 2 ADM 3

Normal operation Span switching


66/89


Self-healing operation (ring switching):

Often, the working and protection fibers arepart of the same bundle of fibers. When thebundle is cut the traffic will be switched to theprotection fibers. This is known as ringswitching.

B

ADM 1 ADM 2 ADM 3

ADM 4

A

ADM 5ADM 6

Working

Protection

ADM 1 ADM 2 ADM 3

ADM 4

A

B

ADM 5ADM 6

Working

Protection

B


67/89


Generic Framing Procedure (GFP)

This is a light-weight adaptation scheme

that permits the transmission of differenttypes of traffic over SONET/SDH and in

the future, over G.709.


68/89


GFP permits the transport of

a) frame-oriented traffic, such as Ethernet, andb) block-coded data for delay-sensitive storage

area networks (SAN) transported by networks

such as Fiber Channel, FICON, and ESCON

over SONET/SDH and G.709.

GFP is a result of joint standardizationeffort by ANSI committee T1X1.5 and ITU-T.

It is described in ITU-T recommendationG.7041


69/89


Private

linesEthernet ESCON FICON

Fiber

Channel

Frame Relay POS

ATM

SONET/SDH

WDM/OTN

GFP

Voice Data (IP, MPLS, IPX) SAN

DM

Video

Existing and GFP-based transport options

for end-user applications

HDLC


70/89


The GFP stack

GFP

GFP client-dependent aspects

GFP client-independent aspects

SONET/SDH G.709

Ethernet IP over PPP SAN data


71/89


GFP frame structure

Payload

Core header

Payload length

Payload length

Core HEC

Core HEC

Payload header

Payload

Payload FCS

GFP core header

Payload length indicator

(PLI) - 2 bytes. It gives the

size of the payload.

Core HEC (cHEC) - 2bytes. It protects the PLI

field. Standard CRC-16

enables single bit error

correction and multiple bit

error detection.


72/89


73/89


GFP payload headervariable-length area from 4 to 64 bytes.

Payload type - 2 bytes

Payload type identifier (PTI) - 3 bits.

Identifies the type of frame:

User data frames , Client mgmt frames

Payload FCS indicator (PFI) - 1 bit.

Identifies if there is a payload FCS

Extension header identifier (EXI) - 4 bits.Identifies the type of extension header.

User payload identifier (UPI) - 8 bits.

Identifies the type of payload

Frame-mapped Ethernet

Frame-mapped PPP (IP, MPLS)

Transparent-mapped Fiber Channel

Transparent-mapped FICON

Transparent-mapped ESCON

Transparent-mapped GbE

Type HEC (tHEC) - 2 bytes. It protects the

payload header. Standard CRC-16.

Payload type

Payload type

Type HEC

Type HEC

0-60 bytes

Of

Extension header

PTI

UPI

PFI EXI


74/89


GFP payload trailer

Payload header

Payload

Payload FCS

Payload FCS

Payload FCS

Payload FCS

Payload FCS

Optional 4-byte FCS.

CRC-32

Protects the contents ofthe payload

information field.


75/89


GFP-client independent functions

The client independent sublayer supports

the following functions:

Frame delineation

Client/frame multiplexing

Payload scrambler

Client managment


76/89


Frame delineation

The frame

delineation

mechanism is similarto the one used in

ATM.

The cHEC is used to

assure correct frameboundary

identification

hunt

Presync

Sync

Correct

cHEC2nd

cHEC match

Non-correctable

core header error

No 2ndcHEC


77/89


Operation:

Under normal conditions, the GFP receiver

operates in the Sync state. The receiver

examines the PLI field, validates the cHEC,

and extracts the framed higher-level PD. It

then moves on to the next GFP header.

When an uncorrectable error in the core

header occurs (i.e., cHEC fails and more than

one bit error is detected), the receiver enters

theHuntstate.


78/89


Hunt state:

Using the cHEC it attempts to locate the

beginning of the next GFP PDU, moving one

bit at a time (Same as in ATM - see Perros An

introduction to ATM networks, Wiley 2001.

Once this is achieved it moves to the Pre-Sync

state, where it verifies the beginning of the

boundary of the next N GFP PDUs.

If successful, it moves to the Sync state,otherwise it moves back to the hunt state.


79/89


Frame multiplexing

Client data frames and client management

frames are multiplexed, with client data

frames having priority over clientmanagement frames.

Idle frames are inserted to maintain a

continuous bit flow (rate coupling

)


80/89


GFP client-specific functions

The client data can be carried in GFP

frames using on of the two adaptation

modes: Frame-mapped GFP (GFP-F) applicable to

most packet data types

Transparent-mapped GFP (GFP-T) applicable

to 8B/10B coded signals


81/89


Frame-mapped GFP

Variable length frames such as:

Ethernet MAC frames,

PPP/IP packets HDLC-framed PDUs

can be carried in the GFP payload.

One frame per GFP payload.

Max. size: 65,535 bytes


82/89


Transparent-mapped GFP

Fiber Channel, ESCON, FICON, GigabitEthernet high-speed LANs use 8B/10B

block-coding to transport client data andcontrol information.

Rather than transporting data on a frame-by-frame basis, the GFP transparent-mapped

mode, transports data as a stream ofcharacters.


83/89


Specifically, the individual characters are

de-mapped from their client 8B/10B blockcodes and then mapped into periodic fixed-length GFP frames using 64B/65B blockcoding.

This reduces the 25% overhead introducedby the 8B/10B block-coding.

Also, transparent mapping reduces latency,

which is important for storage relatedapplications


84/89


The first step, is to decode the 8B/10B

codes. The 10 bit code is decoded into itsoriginal data or control codeword value.

The decoded characters are then mappedinto 64B/65B codes. A bit in the 65-bit

code indicates whether the 65-bit blockcontains only data or control characters arealso included

8 consecutive 65-bit blocks are grouped

together into a single superblock. A GFP frame contains N such superblocks.


85/89


Data over SONET/SDH (DoS)

The DoS architecture provides an efficientmechanism to transport data coming from

interfaces such as: Ethernet, Fiber Channel,ESCON/FICON over SONET/SDH.

It relies on a combination of

GFP,

Virtual concatenation, andLink capacity adjustment scheme (LCAS)


86/89


Virtual concatenation

This procedure maps an incoming traffic streaminto a number of individual sub-rate payloads.

The sub-rate payloads are switched through the

SONET/SDH network independently of eachother

At the destination, they are used to reconstruct theoriginal traffic stream.


87/89


Example

Let us consider the case of transporting the

1 GbE signal over SONET/SDH.

According to the specifications, an STS-

48c (2,488 Gbps) has to be used, thusleaving a lot of unused capacity.

Using the virtual concatenation scheme, 7

independent STS-3c (7x155,520 = 1,088)

can be employed to carry the 1 GbE signal

at full rate.


88/89


This works as follows:

At the transmitter the incoming stream isde-multiplexed and distributed in somefashion over 7 different payloads, each anSTS-3c.

Intermediate SONET/SDH nodes only seedifferent payloads and they are not awareof the concatenation

At the destination, the seven flows getmultiplexed into the single original GbEstream.


89/89


Link capacity adjustment scheme

(LCAS)

This scheme permits to dynamically adjust

the number of sub-rate payloads allocated

to a traffic stream, whose transmission ratemay vary over time.

LCAS can be also used when re-routing

traffic due to a failure.

GFP Eth Frame

Documents

Transcript of GFP Eth Frame