03 LCAS Technology-B

8/10/2019 03 LCAS Technology-B

1/21

Document No. Product Name

Intended Audience Product Version

Compiled by Document Version

LCAS Technology

Prepared by Date

Reviewed by Date

Reviewed by Date

Approved by Date

Huawei Technologies Co., Ltd.

All Rights Reserved


2/21

LCAS TechnologyConfidentiality Level:

Internal Use Only

2009-6-17 Huawei Confidentiality. No Disclosure Without Permission. Page 2 of 21

Revision History

Date Version Author Description

2007-12-21 V1.10 Holisticoptimization

OSN product family


3/21


Internal Use Only


Table of ContentsChapter 1 Background of Emergence of LCAS Technology.........................................................6

Chapter 2 Introduction to LCAS Technology..................................................................................6

2.1 LCAS Characteristics.............................................................................................................7

2.2 LCAS Implemented in Virtual Concatenation ........................................................................7

2.2.1 Application of LCAS in Virtual Concatenation .............................................................7

2.2.2 Overview of Application Mode .....................................................................................7

2.3 Bandwidth Adjustment Handshake ........................................................................................8

1.1.1 Functions of Control Packets and Implementation Method ......................................10 2.3.2 Definition and Description of Fields in Overhead Control Packet.............................12

Chapter 3 Operation of Control Packet When the Bandwidth Changes....................................16

1.1 Adding a New Member When the Traffic Increases ............................................................16

3.2 Deleting a Member Temporarily When the Traffic Decreases .............................................17

3.3 Supplementary Description on Deleting a Member .............................................................17

Chapter 4 Interconnection Between LCAS and Non-LCAS Networks .......................................17

4.1 Interconnection Between LCAS-Enabled Source and LCAS-Disabled Sink.......................18

4.2 Interconnection Between LCAS-Enabled Sink and LCAS-Disabled Source.......................19

4.2.1 Asymmetric Connection of LCAS..............................................................................19 4.2.2 Symmetric Connection of LCAS................................................................................19

Chapter 5 Relationship Between LCAS and Other Technologies ..............................................20

5.1 LCAS and LAPS ..................................................................................................................20

5.2 LCAS and SDH/SONET ......................................................................................................20


4/21


Internal Use Only


List of Tables

Table 2-1 Application indication of control packet of higher order overhead H4 byte ............. 10

Table 2-2 Application indication of bit 2 control packet of lower order overhead K4 byte.......... 12

Table 2-3 Definition of lower order control packet................................................................... 14

Table 4-1 Setting of higher order overhead H4 byte defined by G.707 ................................... 18

Table 4-2 Bit 2 of lower order overhead K4 byte defined by G.707......................................... 18


5/21


Internal Use Only


Keywords

LCAS, virtual concatenation

Abstract

This document introduces the background of emergence of the LCAS

technology and the technical characteristics of LCAS, and analyzes its

application in the optical network system.

Acronyms and Abbreviations

VC: Virtual Concatenation

VC: Virtual Container

LCAS: Link Capacity Adjustment Scheme

SDH: Synchronous Digital Hierarchy

OTN: Optical Transport Network: SONET/SDH

CRC: Cyclic Redundancy Check

CTRL: Control word sent from source to sink

DNU: Do Not Use

EOS: End of Sequence

GID: Group Identification

LOM: Loss of Multiframe

MFI: Multiframe Indicator

MST: Member Status

NORM: Normal Operating Mode

RS-Ack: Re-sequence acknowledge

Sk: Sink

So: Source

SQ: Sequence Indicator

TSD: Trail Signal Degraded

TSF: Trail Signal Fail

VCG: Virtual Concatenation Group

1st multi-frame

2nd multi-frame

References

None


6/21


Internal Use Only


Chapter 1 Background of Emergence of LCAS

Technology

With the development of SDH/SONET for transmitting multiple services, the

access bandwidth requirements are increasing. The existing container

(maximum of VC-4 granularity) is not enough for meeting the requirements,

and thus the concatenation technology emerges. In the concatenation

technology, virtual concatenation is more flexible than contiguous

concatenation, and utilizes the bandwidth more efficiently.

Both virtual concatenation and contiguous concatenation involve the following

problems:

Procedure 1 Failure of any physical channel in the concatenation will makethe whole concatenated channel fail. In other words, the service will be

interrupted completely.

Procedure 2 The bandwidth adjustment of the service affects the serviceseriously. If the service bandwidth is adjusted after the user service is

established, the user service will usually be interrupted for some time.

Procedure 3 It takes a long time to make the service available: The period

from applying for the service to activating the service is too long.

LCAS is a link capacity adjustment scheme, and is a supplement to the virtual

concatenation technology.

(Note: Only virtually concatenated channels can use the LCAS technology.)

The LCAS can solve the following problems:

Procedure 1 The LCAS can dynamically adjust (add, delete or modify) the

service bandwidth without affecting the availability of the existing service.

Procedure 2 If there are failed physical channels in virtual concatenation, the

LCAS will shield these physical channels. Other physical channels in the

virtual concatenation can still transmit services. Therefore, service interruption

will not occur as a result of failure of a single physical channel.

Chapter 2 Introduction to LCAS Technology

LCAS is a technology applied in virtual concatenation for improving the

performance of virtual concatenation. It transmits the control information by

using the reserved overhead bytes of SDH (that is, H4 byte in case of higher

order virtual concatenation, K4 byte in case of lower order virtual


7/21


Internal Use Only


concatenation), and dynamically adjusts the quantity of virtual containers for

mapping the required service to meet different service bandwidth requirements

and improve the bandwidth utilization.

2.1 LCAS Characteristics

Seamless bandwidth adjustment: Bandwidth can be adjusted without

damaging the service.

Complete control packet structure: The control packet is composed of 16

continuous H4 bytes (or 32 K4 bytes).

Asymmetric connection: To be described later.

2.2 LCAS Implemented in Virtual Concatenation

2.2.1 Application of LCAS in Virtual Concatenation

In the virtual concatenation transmission of SONET/SDH, the LCAS

technology can dynamically decrease or recover the quantity of virtual

containers, and thus adjust the total mapping capacity. Moreover, the LCAS in

this application can adjust (decrease) the capacity of virtual containers

automatically after detecting a failed member (for example, a VC-12) on the

network, and increase the capacity automatically after detecting recovery of

this member. This capacity adjustment is feasible to every member.The capacity of virtual containers in the LCAS is adjusted by exchanging

control information between the source and the sink. The control information

indicative of capacity requirements is defined in G.707, G.783 (SDH), G.709

and G.798 (SONET).

Note: "Member" here means a virtual container for mapping other service, for

example, VC-4, or VC-12.

2.2.2 Overview of Application Mode

When the LCAS is applied to the virtual concatenation, the control mechanism

between the source and the sink can adjust the Virtual Concatenation Group

(VCG) capacity according to the traffic of the service to be mapped and the

required bandwidth. Meanwhile, the LCAS will cancel the connection

temporarily when the link of a virtual container with mapped service fails. (The

establishment and cancellation of links of a member are not covered by

LCAS.)

Note: VCG here means a group of virtual container sequences to which a

service is mapped, and a group of members with the same GID. All VC-3 or

VC-12 containers bound onto a VC trunk can be regarded as one VCG.


8/21


Internal Use Only


2.3 Bandwidth Adjustment Handshake

Procedure 1 Increase bandwidth dynamically

I want toadd a

member

Addition isallowed.

I want toadd

Isee

Let me checkwhether it works

Well,It works.

Source Sink

Note: Delimited by red lines. The load will becarried in the new member at the source and thedata will be retrieved from the new member for

assembling frames at the sink only after thehandshake operation is completed.

Procedure 2 Decrease bandwidth dynamically

Source Sink

I want to delete a member

I see!

Note: Unlike increasing bandwidth, the source decides deletion of members,

without acknowledgement of the sink. Afterward, the source will not carry

payload in a deleted member. After receiving the deletion indication, the sink

will not retrieve data in the deleted member.

Procedure 3 Delete a failed member


9/21


Internal Use Only


Source Sink

Oh, why is that?That's a trouble. Ihave to handle it

immediately.

Hey. Themember

failed

Note: Once the sink detects that the memberfails, the sink will notify the source not to putload into the failed member; and will notretrieve data from the failed member.

Procedure 4 Recover a failed member

Source Sink

Well, theload can be

put into itnow.

Themember

hasrecovered

I see.

Note: Once the sink detects that the member isrecovered, it will notify the source immediately. Itwill retrieve data from the recovered member onlyafter receiving an instruction from the source.

The above handshake diagram tells the rough principles. The detailed control

method is described below.


10/21


Internal Use Only


1.1.1 Functions of Control Packets and Implementation Method

The control packet traces the change of traffic between the source and the

sink. Each received control packet describes the state of the link that exists atthe time of receiving the next control packet. That is, the information of link

change is sent by the control packet in advance. Therefore, the receiver can

handle or change the relevant configuration as soon as any change occurs.

Because the LCAS is established on the basis of virtual concatenation, its

control packet is H4 (or K4 for lower order) byte. 16 continuous H4 bytes make

up one control packet.

The CRC check for ensuring certainty of the control frame is specially intended

for the control packet overhead. After a control packet is received, the CRC

check can be carried out immediately to decide whether its contents areavailable.

Definition of control packet (that is, implementation method):

In case of higher order (HO): Every 16 frames make up a multiframe (Note:

8000 frames are transmitted per second).

Composed of overhead byte H4: Composed of 16 continuous frames from

frame 8 of multiframe N (2nd multi-frame) to frame 7 of multiframe N+1 (see

the red line box in Table 2-1).

Table 2-1 Application indication of control packet of higher order overhead H4byte

H4 Byte

Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7 Bit 8

Sequencenumber of

frame in the

multiframe

Sequence

number of

multiframe

Sequence indicator MSB ( bits

14)1 1 1 0 14

Sequence indicator LSB ( bits

58)1 1 1 1 15

N-1

2nd multi-frame indicator MSB

( bits 14)0 0 0 0 0

2nd multi-frame indicator LSB

( bits 58)0 0 0 1 1

N

CTRL 0 0 1 0 2


11/21


Internal Use Only


GID ("000x") 0 0 1 1 3

Reserved ("0000") 0 1 0 0 4

Reserved ("0000") 0 1 0 1 5

CRC-8 0 1 1 0 6

CRC-8 0 1 1 1 7

Member status 1 0 0 0 8


RS-ACK 1 0 1 0 10

Reserved ("0000") 1 0 1 1 11

Reserved ("0000") 1 1 0 0 12

Reserved ("0000"), to extend

Seq. Ind.1 1 0 1 13

Sequence indicator MSB ( bits

14)1 1 1 0 14

Sequence indicator LSB ( bits58)

1 1 1 1 15

N+1

2nd multi-frame indicator MSB

( bits 14)0 0 0 0 0

2nd multi-frame indicator LSB

( bits 58)0 0 0 1 1

CTRL 0 0 1 0 2

GID ("000x") 0 0 1 1 3

Reserved ("0000") 0 1 0 0 4

Reserved ("0000") 0 1 0 1 5

CRC-8 0 1 1 0 6

CRC-8 0 1 1 1 7


N+1


12/21


Internal Use Only


In the above table, bits 5 8 of H4 byte in each frame represent the range of the

frame (015). Bits 1 4 of H4 byte in each frame, however, represent different

contents in different frames. For example, bits 14 of frame 0 and frame 1

make up one byte for storing the sequence number of a multiframe; bits 14 of

frame 8 and frame 9 make up one byte for indicating the member status. For

details, see the red line box in the table. For the detailed interpretation and

functions of each field (for example, CTRL), see the definition and description

of fields in the overhead control packet.

In case of lower order (LO):

Composed of overhead byte K4 bit 2: For bit 2 of K4 byte of 32 continuous

frames, see Table 2-2.

Table 2-2 Application indication of bit 2 control packet of lower order overheadK4 byte

2.3.2 Definition and Description of Fields in Overhead Control Packet

I. Higher order overhead

Multi Frame Indicator field (MFI)

At the source, the MFI is equal among all members of the same VCG, and is 1

greater than the MFI of the previous frame. To put it simply, the MFI is a

sequence number of multiframe.

At the sink, the MFI is used to arrange the payload carried by all received

members. That is, it is used to indicate the delay of different members in the

same VCG.

Sequence Indicator field (SQ)

The sequence indicator indicates the sequence number of the member. It

starts from 0, and indicates the sequence number of the VC in the virtual

concatenation. In a virtual concatenation structure, the bytes are interleaved in

each VC. Therefore, to recover the service, it is necessary to know which VC

comes first and which VC comes next. The sequence indicator is a basis for

sorting. The sequence indicator of LCAS is similar to that specified in G.707

and G.709.


13/21


Internal Use Only


In the initialization, the SQ value of VCG at the source will be initialized into the

possible maximum value.

When more than one member is added at a time, the SQ will be allocated tothose that return MST=OK first.

For example, four VC-4 containers are bound to a VC trunk at the source. An

SQ is allocated to each VC-4 at the source, and the VC-4 containers are

sorted by the SQ at the sink.

Control field (CTRL)

The control field is used to transmit the information of the link from the source

to the sink, and synchronize signals at the sink. The control field must be able

to provide the status information of each member in this group in time. The

definition of the control field is shown in the following figure:

In the initialization, the control field of all members at the source is IDLE=0101.

At the sink, the packet with the control word "EOS" is the member of the

highest sequence number (the last member), and all other members have the

control word "NORM" or "DNU".

Group ID bit (GID)

The GID is used to differentiate between different VCGs. The GID of all

members in one VCG is the same. Therefore, for the sink, the members of the

same GID come from the same source. The contents of the GID are

pseudo-random binary sequences.

For example, if multiple VC trunks bind multiple VC-4 containers, the GID of

members in different VC trunks is different, and the GID of members in the

same VC Trunk is the same.

Note: The GID is invalid when the control field is in the IDLE state.

CRC field


14/21


Internal Use Only


Cyclic Redundancy Check (CRC) of the 8BIT control packet. At the sink, the

contents of the control packet that has passed CRC will take effect

immediately; the contents of the control packet that has failed CRC will be

rejected. The CRC generation multinomial is x8 + x2 + x + 1.

Member status field (MST)

The MST is used to send the status of all members in the same VCG from the

sink to the source: OK or FAIL, OK=0, FAIL=1.

The source will allocate an SQ to a new member in the group only after

receiving the normal MST state from the sink.

In the process of initializing the sink, any MST must be set to FAIL, including

the idle MST value.

Re-Sequence Acknowledge bit (RS-Ack)

When a change of the status of the members in a VCG is detected at the sink,

the value of this bit will be reverse. This bit aims to report to the source that the

change of the sequence number of a VCG member has been acknowledged.

II. Definition of Fields in Lower Order Overhead Control Packet

Multiframe Count

The multiframe counter [0-31] is the count of multiframes, which falls within

[0-31].

Sequence Indicator field (SQ) Sequence indicator is the sequence number of lower order virtual containers,

which falls within [0-63]. In the initialization, all sequence indicators are set to

the maximum value.

Control field (CTRL)

Like the higher order application, the control field is used to transmit the

information of the link from the source to the sink. The control field must be

able to provide the status information of each member in this link in time. The

definition of the control field is shown in Table 2-3.

Table 2-3 Definition of lower order control packet


15/21


Internal Use Only


In the initialization, the control field of all members is IDLE=0101.

At the sink, the packet with the control word "EOS" is the member of the

highest sequence number, and all other members have the control word

"NORM" or "DNU".

Group ID bit (GID)

GID is the ID of a VCG. The GID is used to differentiate between different

VCGs. The GID of all members in one VCG is the same. Therefore, for the

sink, the members of the same GID come from the same source. The contents

of the GID are pseudo-random binary sequences, and the format of generated

GID is 215-1.

Note: The GID is invalid when the control field is in the IDLE state.

Member status field (MST)

The MST is used to send the status of all members in the same VCG from the

sink to the source. OK or FAIL, OK=0, FAIL=1.

All 64 members will be transmitted within 128 ms.

Re-Sequence Acknowledge bit (RS-Ack)

When a change of the state of a member in a VCG is detected at the sink, the

value of this bit will be reverse. This bit aims to report to the source that the

change of the sequence number of a VCG member has been acknowledged.

CRC field

Cyclic Redundancy Check (CRC) of 8BIT control packet. At the sink, the

contents of the control packet that has passed CRC will take effect

immediately. The CRC generation multinomial is x8 + x2 + x + 1.


16/21


Internal Use Only


Chapter 3 Operation of Control Packet When the

Bandwidth Changes

Control packets are main contents of LCAS. A control packet contains various

status information of the source and the sink.

Procedure 1 Forward control packet (from the source to the sink): MFI, SQ,

CTRL, GID, and CRC

Procedure 2 Backward control frame (from the sink to the source): MST,

RS-Ack, and CRC

Note: In the same VCG, the MST and the RS-Ack of all control frames are thesame.

In the forward control packet and backward control frame: CRC and all idle

reserved bits must be set to 0.

1.1 Adding a New Member When the Traffic Increases

When a member is added, the sequence number added is always greater than

the greatest sequence number of the existing members (EOS in the control

field).

When this member whose control field is ADD is executed, the MST of this

new member must be set to OK, and the value of its control field will be set to

EOS. The member whose control field is EOS will be set to NORM.

Note: The member whose control field is ADD will not stop being sent until the

member with MSK=OK in the control field is received at the local end from the

opposite end.

When more than one member is added, if the corresponding MSK=OK is

received at the same time, the sequence number of such members will be set

from the maximum number according to the sequence of receiving the

members. All the sequence numbers are greater than that of the current

member at EOS. The control field of the member with the maximum sequence

number is set to EOS. Likewise, the member whose control field is EOS shall

be changed to NORM.

Moreover, a control packet shall be sent to the new member, and the new

member comes immediately after this control packet.


17/21


Internal Use Only


3.2 Deleting a Member Temporarily When the TrafficDecreases

At the sink, when a member is detected as failure, the sink will send a

MST=FAIL message to the source. After receiving this message, the source

will change NORM (or EOS) of this frame to DNU, and then fill EOS into the

control field of the previous member.

When the detected member is recovered from failure at the sink, the sink will

send a control packet for the member with MST=OK to the source. After

receiving this packet, the source will replace the current DNU with NORM or

EOS, and then fill NORM into the control field of the previous member, and

send it to the sink.

Moreover, for the temporarily deleted member, it is necessary to delete the

payload of the member from the VCG. The control field of the last member

whose payload is deleted must be DNU. In this way, the payload field of the

next virtual container will be all 0s. When the sink receives the member whose

control field is DNU, the sink will not add it to the normal VCG.

When it is necessary to use this member later, the payload of this member

may be filled again. And this member must immediately follow the previous

member, and the control field of this member must be NORM or EOS.

3.3 Supplementary Description on Deleting a Member

If a member is deleted, the sequence number of all other members in the

same VCG will change. If the member with the greatest sequence number is

deleted, the previously second greatest sequence number will become the

currently greatest sequence number, the control field of the deleted member

will change from EOS to IDLE, and the control field of the member with the

currently greatest sequence number will change to EOS. If the deleted

member does not have the greatest sequence number, all sequence numbers

previously greater than this sequence number will decrease by one, and the

control field of the deleted member will change to IDLE.

Chapter 4 Interconnection Between LCAS and

Non-LCAS Networks

The application of interconnection between LCAS network and non-LCAS

virtual concatenation network involves two cases.


18/21


Internal Use Only


4.1 Interconnection Between LCAS-Enabled Source andLCAS-Disabled Sink

In this case, as long as the source that supports LCAS works in the non-LCAS

virtual concatenation mode, the virtual concatenation service sent from the

source to the sink will need no special handling. The higher order overhead H4

byte of the source will be set according to the G.707 protocol (the higher order

byte setting is shown in Table 4-1). The lower order overhead K4 byte will be

set according to G.707 protocol (the lower order byte setting is shown in Table

4-2). At the sink, other bits will be ignored, and the returned MSK is constantly

OK. All LCAS overhead byte contents will be ignored.

Table 4-1 Setting of higher order overhead H4 byte defined by G.707

Table 4-2 Bit 2 of lower order overhead K4 byte defined by G.707

Interpretation of K4 byte:

Bit 2 of K4 byte of lower order VC-n POH is used to transmit the information of

rearranging the virtual concatenation signals from the source to the sink.


19/21


Internal Use Only


Bit 2 is retrieved from K4 of every frame. After 32 frames, a serial-like 32-bit

string (as shown in Table 2-3) is generated for labeling the information. This

string will complete a cycle at frame 128. The lower order framing information

of a virtual concatenation is included in it.

Note: The overhead of the virtual concatenation of VC-12 must use the

extended label (for details of bit 2 of the lower order virtual concatenation

overhead K4 byte, see G.707).

4.2 Interconnection Between LCAS-Enabled Sink andLCAS-Disabled Source

In this case, because the control field and the CRC field sent by the source

that does not support LCAS are all 0s, when the sink that supports LCASreceives the control field and CRC field that are all 0s, the processing is as

follows:

Do not process fields except MFI and SQ.

Process the MFI and SQ in the same way as in standard virtual concatenation.

4.2.1 Asymmetric Connection of LCAS

LCAS supposes that the protocol execution process is direction-independent.

In other words, the traffic flow sent from the source to the sink is independent

of the traffic flow sent from the sink to the source, and needs no special

processing. All contents discussed herein are intended for the asymmetric

connection mode.

4.2.2 Symmetric Connection of LCAS

The specific scheme is still under research.

In this connection mode, each member has a peer member in the reverse

direction (like bidirectional connection). That is, each VCG has a reverse VCG.

The state of the sink is returned only in this peer member to the source. In thisworking mode, it is recommended to configure the NE in other ways.


20/21


Internal Use Only


Chapter 5 Relationship Between LCAS and Other

Technologies

5.1 LCAS and LAPS

With respect to application, the Ethernet signals are bursty and variable in

length, and sharply different from the SONET/SDH frames that require strict

synchronization. Therefore, a proper link layer adaptation protocol is required

for implementing frame mapping from the Ethernet to the SONET/SDH. This is

much similar to the thought of the IP over SONET/SDH (POS) system that

adopts the IP/PPP/HDLC/SDH. Two protocols can be used to map andencapsulate the Ethernet signals: (1) LAPS (Link Access Procedure SDH,

ITU-T X.86), which is put forward by Wuhan Postal & Telecommunication

Bureau on behalf of China to ITU-T; (2) GFP (Generic Framing Procedure,

ANSI T1X1.5), which is put forward by Lucent and Nortel. The former has

become an official international standard; the latter is still an ANSI draft, and is

estimated to be approved at the beginning of next year. Both are

connectionless-oriented data link layer protocols.

For the Ethernet over SDH implemented through the GFP/LAPS/HDLC

protocol, the frame mapping process includes two steps:Encapsulate the MAC frame of the Ethernet into a GFP/LAPS /HDLC protocol

frame.

Map the GFP/LAPS/HDLC protocol frame into an SDH frame.

Encapsulating MAC frames into LAPS protocol frames is an operation on the

upper layer of virtual concatenation, and is unrelated to LCAS. In the operation

of mapping after encapsulation, that is, virtual concatenation operation, it is

appropriate to use LCAS to adjust the mapping capacity dynamically

according to the LAPS/HDLC service capacity, or the NMS configures the

capacity as required. This makes the bandwidth controllable and reasonablyutilized.

5.2 LCAS and SDH/SONET

Currently, LCAS is only applied to the virtual concatenation mapping of

SDH/SONET. For SDH and SONET, the LCAS operation is the same, and the

frame structure of the control packet is also the same. As required by the

virtual concatenation protocol, for the users who need to transmit virtual

concatenation services, the terminals with concatenation services can be

deployed at the source and the sink of the existing SDH device, without


21/21


Internal Use Only


changing the existing transmission network structure. Therefore, the LCAS is

rather adaptive to the existing SDH/SONET network, and can be implemented

by only applying the LCAS-enabled virtual concatenation at the source and the

sink.

Documents

03 LCAS Technology-B