(C) All rights reserved by Professor Wen-Tsuen Chen1 Asychronous Transfer Mode (ATM) ä ATM is originally the transfer mode for implementing Broadband ISDN

(C) All rights reserved by Professor (C) All rights reserved by Professor Wen-Tsuen ChenWen-Tsuen Chen

11

Asychronous Transfer Mode (ATM)Asychronous Transfer Mode (ATM)

ATM is originally the transfer mode for implementing ATM is originally the transfer mode for implementing Broadband ISDN (B-ISDN).Broadband ISDN (B-ISDN).

In 1988, CCITT (from ITU) issued the first two In 1988, CCITT (from ITU) issued the first two recommendations relating to B-ISDN:recommendations relating to B-ISDN: I.113 Vocabulary of Terms for Broadband Aspects of ISDNI.113 Vocabulary of Terms for Broadband Aspects of ISDN I.121 Broadband Aspects of ISDNI.121 Broadband Aspects of ISDN

In 1911, the ATM Forum was created with the goal of In 1911, the ATM Forum was created with the goal of accelerating the development of ATM standards.accelerating the development of ATM standards.


22

Broadband ServicesBroadband Services


33


44


55


66


77


88


99


1010

Information CharacteristicsInformation Characteristics

Voice:Voice: 8Kbps ~ 64Kbps, round trip delay 8Kbps ~ 64Kbps, round trip delay 8ms ,loss 8ms ,loss 10 10-6-6

Data:Data: 1Kbps ~ 10 Mbps, loss 1Kbps ~ 10 Mbps, loss 10 10-9 -9 , Bursty or Stream, Bursty or Stream

HDTV:HDTV: 140Mbps, loss 140Mbps, loss 10 10-6-6, Variable Bit Rate, delay , Variable Bit Rate, delay 5ms, Distributiv 5ms, Distributiv

ee

Graphics / Image:Graphics / Image: 10Mbps (10Mb/picture, 1 sec), Bursty, Delay 10Mbps (10Mb/picture, 1 sec), Bursty, Delay 5s (interactive) 5s (interactive)


1111

ATM CharacteristicsATM Characteristics

No error protection or flow control on a link-by-No error protection or flow control on a link-by-link basis.link basis.

ATM operates in a connection-oriented mode.ATM operates in a connection-oriented mode. The header functionality is reduced.The header functionality is reduced. The information field length is relatively small The information field length is relatively small

and fixed.and fixed.


1212


1313


1414

Physical Layer Interface SpecificationPhysical Layer Interface Specification

SONET STS-3CSONET STS-3C SONET STS-12SONET STS-12 DS3DS3 STP for ATM LANSTP for ATM LAN etc.etc.


1515

Physical Layer Functions for SONET STS-3CPhysical Layer Functions for SONET STS-3C


1616

Physical Layer Functions for DS3Physical Layer Functions for DS3


1717

DLL in ATMDLL in ATM

Transmission convergence sublayer of the ATM physical lTransmission convergence sublayer of the ATM physical layer.ayer.

Header error control: correcting single-bit error of a cell heHeader error control: correcting single-bit error of a cell header.ader.

Cell delineation: cell framing.Cell delineation: cell framing.


1818

Header Error ControlHeader Error Control

HEC checksum: Remainder of the 32 header bits divided bHEC checksum: Remainder of the 32 header bits divided by the polynomial x**8+x**2+x+1, added with 01010101 ty the polynomial x**8+x**2+x+1, added with 01010101 to provide robustness in face of headers containing mostly o provide robustness in face of headers containing mostly 0 bits.0 bits.

Correcting all single-bit errors and detecting many multi-biCorrecting all single-bit errors and detecting many multi-bit errors.t errors.

Suitable for optical fiber: 99.64% of all errors are single-biSuitable for optical fiber: 99.64% of all errors are single-bit errors.t errors.


1919

Cell DelineationCell Delineation

Using the HEC to delineate a cell.Using the HEC to delineate a cell. Cell delineation heuristic: see Fig. 3-30.Cell delineation heuristic: see Fig. 3-30. To protect against malicious users, payload bits arTo protect against malicious users, payload bits ar

e scrambled on transmission and descrambled on re scrambled on transmission and descrambled on reception.eception.


2020


2121

ATM Layer in ATM networksATM Layer in ATM networks

Connection-oriented.Connection-oriented. No acknowledgements.No acknowledgements. Cells arriving destinations in order.Cells arriving destinations in order. Tow-level connection hierarchy.Tow-level connection hierarchy.


2222

Advantages for the Use of Virtual PathsAdvantages for the Use of Virtual Paths

Simplified network architecture.Simplified network architecture. Increased network performance and reliability.Increased network performance and reliability. Reduced processing and short connection setup Reduced processing and short connection setup

time.time. Enhanced network services.Enhanced network services.


2323

ATM Layer ServicesATM Layer Services

The ATM layer provides for the transparent transfer of The ATM layer provides for the transparent transfer of cells between communicating upper layer entities.cells between communicating upper layer entities.

This transfer occurs on a pre-established ATM connection This transfer occurs on a pre-established ATM connection according to a traffic contract.according to a traffic contract.

A traffic contracts is comprised of a QoS class, a vector of A traffic contracts is comprised of a QoS class, a vector of traffic parameters, a conformance definition etc.traffic parameters, a conformance definition etc.

Each ATM end-point is expected to generate traffic which Each ATM end-point is expected to generate traffic which conforms to these parameters.conforms to these parameters.

Two service primitives: ATM-DATA.Request and ATM-Two service primitives: ATM-DATA.Request and ATM-DATA.Indicate.DATA.Indicate.


2424

ATM Cell FormatATM Cell Format


2525

ATM Cell HeaderATM Cell Header


2626

Payload TypePayload Type


2727

Connection Setup/ReleaseConnection Setup/Release


2828


2929

ATM RoutingATM Routing

To route on the VPI field except at the final hop.To route on the VPI field except at the final hop.


3030


3131


3232

ATM Network-Network InterfaceATM Network-Network Interface

Private Network-Network Interface (PNNI) Private Network-Network Interface (PNNI) Specification version 1.0, defined in March 1996Specification version 1.0, defined in March 1996 Function of PNNI routing protocolFunction of PNNI routing protocol

Discovery of neighbors and link statusDiscovery of neighbors and link status Synchronization of topology databasesSynchronization of topology databases Flooding of topology state elementsFlooding of topology state elements Summarization of topology state informationSummarization of topology state information Construction of the routing hierarchyConstruction of the routing hierarchy


3333

ATM Traffic ManagementATM Traffic Management

Defined in Traffic Management Specification Version 4.0, ApriDefined in Traffic Management Specification Version 4.0, April 1996l 1996

Five services categories:Five services categories: CBR, rt-VBR, nrt-VBR, UBR, ABRCBR, rt-VBR, nrt-VBR, UBR, ABR

Generic functions:Generic functions: Connection Admission ControlConnection Admission Control Feedback ControlsFeedback Controls Usage Parameter ControlUsage Parameter Control Cell Loss Priority ControlCell Loss Priority Control Traffic ShapingTraffic Shaping Network Resource ManagementNetwork Resource Management Frame DiscardFrame Discard ABR Flow ControlABR Flow Control


3434

Quality of Service CategoriesQuality of Service Categories


3535


3636

QoS Parameters: CLR, CTD, CDVQoS Parameters: CLR, CTD, CDV CBR: CDV, CTD, CLRCBR: CDV, CTD, CLR rt-VBR: CDV, CTD, CLRrt-VBR: CDV, CTD, CLR nrt-VBR: CLRnrt-VBR: CLR

Traffic Parameters:Traffic Parameters: CBR: PCR, CDVTCBR: PCR, CDVT rt-VBR: PCR, CDVT, SCR, MBSrt-VBR: PCR, CDVT, SCR, MBS nrt-VBR: PCR, CDVT, SCR, MBSnrt-VBR: PCR, CDVT, SCR, MBS

UBR: PCR, CDVTUBR: PCR, CDVT ABR: PCR, CDVT, MCRABR: PCR, CDVT, MCR

where MBS is the maximum burst size.where MBS is the maximum burst size.


3737

Quality of Service ParametersQuality of Service Parameters

The following QoS parameters are negotiated The following QoS parameters are negotiated between the end-systems and the networkbetween the end-systems and the network Peak-to-Peak Cell Delay Variation(peak-to-peak CDV)Peak-to-Peak Cell Delay Variation(peak-to-peak CDV) Maximum Cell Transfer Delay(maxCTD)Maximum Cell Transfer Delay(maxCTD) Cell Lose Ratio(CLR)Cell Lose Ratio(CLR)

The following QoS parameters are not negotiatedThe following QoS parameters are not negotiated Cell Error Ratio(CER)Cell Error Ratio(CER) Severely Errored Cell Block Ratio(SECBR)Severely Errored Cell Block Ratio(SECBR) Cell Misinsertion Rate(CMR)Cell Misinsertion Rate(CMR)


3838


3939

Traffic parametersTraffic parameters

A traffic parameter describes an inherent characteristic A traffic parameter describes an inherent characteristic of a traffic sourceof a traffic source

Traffic parameters includeTraffic parameters include Peak Cell Rate(PCR)Peak Cell Rate(PCR) Sustainable Cell Rate(SCR)Sustainable Cell Rate(SCR) Maximum Burst Size(MBS)Maximum Burst Size(MBS) Minimum Cell Rate(MCR)Minimum Cell Rate(MCR)


4040

Traffic ContractTraffic Contract

A traffic contract specifies the negotiated characteristics of A traffic contract specifies the negotiated characteristics of a connection.a connection.

Traffic contract specification consists ofTraffic contract specification consists of A connection traffic descriptor.A connection traffic descriptor. A set of QoS parameters for each direction of the connection.A set of QoS parameters for each direction of the connection. The definition of a compliant connectionThe definition of a compliant connection..

Connection traffic descriptor includesConnection traffic descriptor includes A set of traffic parameter of the ATM source.A set of traffic parameter of the ATM source. The CDVT.The CDVT. The conformance definition that specifies the conforming cells of The conformance definition that specifies the conforming cells of

the connection.the connection.


4141

The Generic Cell Rate Algorithm(GCRA)

The Generic Cell Rate Algorithm(GCRA)

GCRA (I, L)GCRA (I, L) Where I: IncrementWhere I: Increment L: LimitL: Limit


4242

Traffic Contract Conformance DefinitionTraffic Contract Conformance Definition

Traffic Management specification,Version 4.0Traffic Management specification,Version 4.0 CBR Service:CBR Service:

GCRA (1/PCR, CDVT)GCRA (1/PCR, CDVT)

VBR ServicesVBR Services GCRA (1/PCR, CDVT)GCRA (1/PCR, CDVT) GCRA (1/SCR, BT+CDVT), where BT = GCRA (1/SCR, BT+CDVT), where BT =

(MBS-1)(1/SCR-1/PCR)(MBS-1)(1/SCR-1/PCR)

UBR ServicesUBR Services PCRPCR

ABRABR DGCRADGCRA

321111 ,,,,, ICRPCRMCR

The ATM Forum, April 1996The ATM Forum, April 1996


4343

Usage Parameter ControlUsage Parameter Control

Usage Parameter Control(UPC) is defined as the set of actions tUsage Parameter Control(UPC) is defined as the set of actions taken by the network to monitor and control trafficaken by the network to monitor and control traffic

The monitoring task for UPC is performed for VCCs and VPCs The monitoring task for UPC is performed for VCCs and VPCs respectively by the following two actions:respectively by the following two actions: Checking the validity of VPI and VCI and monitoring the traffic enterinChecking the validity of VPI and VCI and monitoring the traffic enterin

g the network in order to ensure that parameters agreed upon are not violg the network in order to ensure that parameters agreed upon are not violated.ated.

Checking the validity of VPI and monitoring the traffic entering the netChecking the validity of VPI and monitoring the traffic entering the network in order to ensure that parameters agreed upon are not violated.work in order to ensure that parameters agreed upon are not violated.


4444

Congestion ControlCongestion Control

Admission Control with resource reservation.Admission Control with resource reservation. Rate-based Congestion Control for ABR traffic.Rate-based Congestion Control for ABR traffic.

The sender has a current cell rate ACR (Allowed Cell Rate), The sender has a current cell rate ACR (Allowed Cell Rate), MCRMCRACRACRPCR. PCR.

ACR is reduced, if congestion occurs.ACR is reduced, if congestion occurs. For each RM-cell, ER (Explicit Rate) is set by the source to a requested rate For each RM-cell, ER (Explicit Rate) is set by the source to a requested rate

(such as PCR) and may be subsequently reduced by any network element in (such as PCR) and may be subsequently reduced by any network element in the path to a value that the element can sustain. ER is then used to limit the the path to a value that the element can sustain. ER is then used to limit the source ACR to a specific value.source ACR to a specific value.


4545

ABR Flow ControlABR Flow Control

In ABR service, the source adapts its rate to changing In ABR service, the source adapts its rate to changing network conditions.network conditions.

Information about the state of the network like bandwidth Information about the state of the network like bandwidth availability, state of congestion, and impending congestion, is availability, state of congestion, and impending congestion, is conveyed to the source through special control cells called conveyed to the source through special control cells called Resource Management Cells (RM-cells).Resource Management Cells (RM-cells).


4646

ABR Service ParametersABR Service Parameters


4747

ABR Service Parameters(cont.)ABR Service Parameters(cont.)


4848

RM Cell StructureRM Cell Structure


4949

Message Type FieldMessage Type Field


5050

In-rate and Out-of-rate Cell TypesIn-rate and Out-of-rate Cell Types

For ABR,CLP=0 cells are called “in-rate” cells.For ABR,CLP=0 cells are called “in-rate” cells. For ABR ,CLP=1 cells are called “out-of-rate” cells.For ABR ,CLP=1 cells are called “out-of-rate” cells. One use of out-of-rate RM-cells is to enable a rate increase One use of out-of-rate RM-cells is to enable a rate increase

for a connection that has an ACR of zero.for a connection that has an ACR of zero. The source would use the out-of-rate cells as probes to The source would use the out-of-rate cells as probes to

learn when it may increase its rate.learn when it may increase its rate.


5151

Source BehaviorSource Behavior

The following items define the source behavior for The following items define the source behavior for CLP=0 and CLP=1 cell streams of a connection. CLP=0 and CLP=1 cell streams of a connection.

By convention, the CLP=0 stream is referred to as By convention, the CLP=0 stream is referred to as in-rate, and the CLP=1 stream is referred to as out-in-rate, and the CLP=1 stream is referred to as out-of-rate.Data cells shall not be sent with CLP=1.of-rate.Data cells shall not be sent with CLP=1.

1 .The value of ACR shall never exceed PCR, nor 1 .The value of ACR shall never exceed PCR, nor shall it ever be less than MCR. The source shall shall it ever be less than MCR. The source shall never send in-rate cells at a rate exceeding ACR. never send in-rate cells at a rate exceeding ACR. The source may always send in-rate cells at a rate The source may always send in-rate cells at a rate less than or equal to ACR.less than or equal to ACR.


5252

Source Behavior(cont.)Source Behavior(cont.)

2. Before a source sends the first cell after connection setup,2. Before a source sends the first cell after connection setup, it shall set ACR to at most ICR. The firstin-rate cell sent sh it shall set ACR to at most ICR. The firstin-rate cell sent shall be a forward RM-cell.all be a forward RM-cell.

3. After the first in-rate forward RM-cell, in-rate cells shall be 3. After the first in-rate forward RM-cell, in-rate cells shall be sent in the following order:sent in the following order:a) The next in-rate cell shall be a forward RM-cell if and only if, since a) The next in-rate cell shall be a forward RM-cell if and only if, since

the last in-rate forward RM-cell was sent, either:the last in-rate forward RM-cell was sent, either:i) at least Mrm in-rate cells have been sent and at least Trm time i) at least Mrm in-rate cells have been sent and at least Trm time

has elapsed,has elapsed,oror

ii) Nrm-1 in-rate cells have been sent.ii) Nrm-1 in-rate cells have been sent.


5353


b) The next in-rate cell shall be a backward RM-cell if conditib) The next in-rate cell shall be a backward RM-cell if condition (a) above is not met, if a backward RM-cell is waiting foon (a) above is not met, if a backward RM-cell is waiting for transmission, and if either:r transmission, and if either:

i) no in-rate backward RM-cell has been sent since the lai) no in-rate backward RM-cell has been sent since the last in-rate forward RM-cell,st in-rate forward RM-cell,

ororii) no data cell is waiting for transmission.ii) no data cell is waiting for transmission.

c) The next in-rate cell sent shall be a data cell if neither conc) The next in-rate cell sent shall be a data cell if neither condition (a) nor condition (b) above ismet, and if a data cell idition (a) nor condition (b) above ismet, and if a data cell is waiting for transmission.s waiting for transmission.


5454


4. Cells sent in accordance with source behaviors #1, #2, and #3 s4. Cells sent in accordance with source behaviors #1, #2, and #3 shall have CLP=0.hall have CLP=0.

5. Before sending a forward in-rate RM-cell, if ACR > ICR and the ti5. Before sending a forward in-rate RM-cell, if ACR > ICR and the time T that has elapsed since the last in-rate forward RM-cell wame T that has elapsed since the last in-rate forward RM-cell was sent is greater than ADTF, then ACR shall be reduced to ICR.s sent is greater than ADTF, then ACR shall be reduced to ICR.

6. Before sending an in-rate forward RM-cell, and after following 6. Before sending an in-rate forward RM-cell, and after following behavior #5 above, if at least CRMin-rate forward RM-cells havbehavior #5 above, if at least CRMin-rate forward RM-cells have been sent since the last backward RM-cell with BN=0 was rece been sent since the last backward RM-cell with BN=0 was received, then ACR shall be reduced by at least ACR*CDF, unless teived, then ACR shall be reduced by at least ACR*CDF, unless that reduction would result in a rate below MCR, in which case hat reduction would result in a rate below MCR, in which case ACR shall be set to MCR.ACR shall be set to MCR.


5555


7. After following behaviors #5 and #6 above, the ACR value sh7. After following behaviors #5 and #6 above, the ACR value shall be placed in the CCR field of the outgoing forward RM-ceall be placed in the CCR field of the outgoing forward RM-cell, but only in-rate cells sent after the outgoing forward RM-ll, but only in-rate cells sent after the outgoing forward RM-cell need to follow the new rate.cell need to follow the new rate.

8. When a backward RM-cell (in-rate or out-of-rate) is received 8. When a backward RM-cell (in-rate or out-of-rate) is received with CI=1, then ACR shall be reduced by at least ACR*RDF, uwith CI=1, then ACR shall be reduced by at least ACR*RDF, unless that reduction would result in a rate below MCR, in wnless that reduction would result in a rate below MCR, in which case ACR shall be set to MCR. If the backward RM-cell hhich case ACR shall be set to MCR. If the backward RM-cell has both CI=0 and NI=0, then the ACR may be increased by nas both CI=0 and NI=0, then the ACR may be increased by no more than RIF*PCR, to a rate not greater than PCR. If the o more than RIF*PCR, to a rate not greater than PCR. If the backward RM-cell has NI=1, the ACR shall not be increased.backward RM-cell has NI=1, the ACR shall not be increased.


5656


9. When a backward RM-cell (in-rate or out-of-rate) is re9. When a backward RM-cell (in-rate or out-of-rate) is received, and after ACR is adjusted according to source ceived, and after ACR is adjusted according to source behavior #8, ACR is set to at most the minimum of ACbehavior #8, ACR is set to at most the minimum of ACR as computed in source behavior #8,and the ER field, R as computed in source behavior #8,and the ER field, but no lower than MCR.but no lower than MCR.

10. When generating a forward RM-cell, the source shall 10. When generating a forward RM-cell, the source shall assign values to the various RM-cell fields as specified assign values to the various RM-cell fields as specified for source-generated cells in Table 5-4.for source-generated cells in Table 5-4.

11. Forward RM-cells may be sent out-of-rate (i.e., not c11. Forward RM-cells may be sent out-of-rate (i.e., not conforming to the current ACR). Out-of-rate forward Ronforming to the current ACR). Out-of-rate forward RM-cells shall not be sent at a rate greater than TCR.M-cells shall not be sent at a rate greater than TCR.


5757


12. A source shall reset EFCI on every data cell it send12. A source shall reset EFCI on every data cell it sends.s.

13. The source may implement a use-it-or-lose it poli13. The source may implement a use-it-or-lose it policy to reduce its ACR to a value which approximates cy to reduce its ACR to a value which approximates the actual cell transmission rate. Use-it-or-lose-it pthe actual cell transmission rate. Use-it-or-lose-it policies are discussed in Appendix I.8.olicies are discussed in Appendix I.8.


5858

Destination BehaviorDestination Behavior

The following items define the destination behavior for The following items define the destination behavior for CLP=0 and CLP=1 cell streams of a connection.By CLP=0 and CLP=1 cell streams of a connection.By convention, the CLP=0 stream is referred to as in-rate, convention, the CLP=0 stream is referred to as in-rate, and the CLP=1 stream is referred to as out-of-rate.and the CLP=1 stream is referred to as out-of-rate.

1. When a data cell is received, its EFCI indicator is 1. When a data cell is received, its EFCI indicator is saved as the EFCI state of the connection.saved as the EFCI state of the connection.

2. On receiving a forward RM-cell, the destination shall 2. On receiving a forward RM-cell, the destination shall turn around the cell to return to the source. The DIR bit turn around the cell to return to the source. The DIR bit in the RM-cell shall be changed from “forward” to in the RM-cell shall be changed from “forward” to ”backward”, BN shall be set to zero, and CCR, MCR, ER, ”backward”, BN shall be set to zero, and CCR, MCR, ER, CI, and NI fields in the RM-cell shall be unchanged CI, and NI fields in the RM-cell shall be unchanged except:except:


5959

Destination Behavior(cont.)Destination Behavior(cont.)

a) If the saved EFCI state is set, then the destination shall set CI=1 in tha) If the saved EFCI state is set, then the destination shall set CI=1 in the RM-cell, and the saved EFCI state shall be reset. It is preferred that e RM-cell, and the saved EFCI state shall be reset. It is preferred that this step is performed as close to the transmission time as possible;this step is performed as close to the transmission time as possible;

b) The destination (having internal congestion) may reduce ER to whab) The destination (having internal congestion) may reduce ER to whatever rate it can support and/or set CI=1 or NI=1. A destination shall tever rate it can support and/or set CI=1 or NI=1. A destination shall either set the QL and SN fields to zero, preserve these fields, or set teither set the QL and SN fields to zero, preserve these fields, or set them in accordance with ITU-T Recommendation I.371-draft.hem in accordance with ITU-T Recommendation I.371-draft.

The octets defined in Table 5-4 as reserved may be set to 6A (hexadeciThe octets defined in Table 5-4 as reserved may be set to 6A (hexadecimal) or left unchanged.The bits defined as reserved in Table 5-4 for mal) or left unchanged.The bits defined as reserved in Table 5-4 for octet 7 may be set to zero or left unchanged. There maining fields soctet 7 may be set to zero or left unchanged. There maining fields shall be set in accordance with Section 5.10.3.1 (Note that this does hall be set in accordance with Section 5.10.3.1 (Note that this does not preclude looping fields back from the received RM-cell).not preclude looping fields back from the received RM-cell).


6060


3. If a forward RM-cell is received by the destination while anot3. If a forward RM-cell is received by the destination while another turned-around RM-cell (on the same connection) is scheher turned-around RM-cell (on the same connection) is scheduled for in-rate transmission:duled for in-rate transmission:a) It is recommended that the contents of the old cell are overwritten ba) It is recommended that the contents of the old cell are overwritten b

y the contents of the new cell;y the contents of the new cell;b) It is recommended that the old cell (after possibly having been over-b) It is recommended that the old cell (after possibly having been over-

written) shall be sent out-of-rate; alternatively the old cell may be diswritten) shall be sent out-of-rate; alternatively the old cell may be discarded or remain scheduled for in-rate transmission;carded or remain scheduled for in-rate transmission;

c) It is required that the new cell be scheduled for in-rate transmission.c) It is required that the new cell be scheduled for in-rate transmission.4. Regardless of the alternatives chosen in destination behavio4. Regardless of the alternatives chosen in destination behavio

r #3 above, the contents of an older cell shall not be transmitr #3 above, the contents of an older cell shall not be transmitted after the contents of a newer cell have been transmitted.ted after the contents of a newer cell have been transmitted.


6161


5. A destination may generate a backward RM-cell without h5. A destination may generate a backward RM-cell without having received a forward RM-cell. The rate of these backwaving received a forward RM-cell. The rate of these backward RM-cells (including both in-rate and out-of-rate) shall ard RM-cells (including both in-rate and out-of-rate) shall be limited to 10 cells/second, per connection. When a desbe limited to 10 cells/second, per connection. When a destination generates an RM-cell it shall set either CI=1 or NI=tination generates an RM-cell it shall set either CI=1 or NI=1, shall set BN=1, and shall set the direction to backward. 1, shall set BN=1, and shall set the direction to backward. The destination shall assign values to the various RM-cell The destination shall assign values to the various RM-cell fields as specified for destination generated cells in Table fields as specified for destination generated cells in Table 5-4.5-4.

6. When a forward RM-cell with CLP=1 is turned around it m6. When a forward RM-cell with CLP=1 is turned around it may be sent in-rate (with CLP=0) or out-of-rate (with CLP=1).ay be sent in-rate (with CLP=0) or out-of-rate (with CLP=1).


6262

Switch BehaviorSwitch Behavior

The following items define the switch behavior for The following items define the switch behavior for CLP=0 and CLP=1 cell streams of a connection. By CLP=0 and CLP=1 cell streams of a connection. By convention, the CLP=0 stream is referred to as in-convention, the CLP=0 stream is referred to as in-rate, and the CLP=1 stream is referred to as out-of-rate, and the CLP=1 stream is referred to as out-of-rate.Data cells shall not be sent with CLP=1.rate.Data cells shall not be sent with CLP=1.

1. A switch shall implement at least one of the 1. A switch shall implement at least one of the following methods to control congestion at queuing following methods to control congestion at queuing points:points:a) a) EFCI markingEFCI marking: The switch may set the EFCI state in the data : The switch may set the EFCI state in the data

cell headers;cell headers;

b) b) Relative Rate Marking: Relative Rate Marking: The switch may set CI=1 or NI=1 in The switch may set CI=1 or NI=1 in forward and/or backward RM-cells;forward and/or backward RM-cells;


6363

Switch Behavior(cont.)Switch Behavior(cont.)

c) c) Explicit Rate Marking: Explicit Rate Marking: The switch may reduce the ER field of The switch may reduce the ER field of forward and/or backward RM-cells (Explicit Rate Marking) ;forward and/or backward RM-cells (Explicit Rate Marking) ;

d) d) VS/VD ControlVS/VD Control: The switch may segment the ABR control : The switch may segment the ABR control loop using a virtual source and destination.loop using a virtual source and destination.

2. A switch may generate a backward RM-cell. The rate 2. A switch may generate a backward RM-cell. The rate of these backward RM-cells (including both in-rate of these backward RM-cells (including both in-rate and out-of-rate) shall be limited to 10 cells/second, and out-of-rate) shall be limited to 10 cells/second, per connection. When a switch generates an RM-cell per connection. When a switch generates an RM-cell it shall set either CI=1 or NI=1, shall set BN=1, and it shall set either CI=1 or NI=1, shall set BN=1, and shall set the direction to backward. The switch shall shall set the direction to backward. The switch shall assign values to the various RM-cell fields as specified assign values to the various RM-cell fields as specified for switch-generated cells in Table 5-4.for switch-generated cells in Table 5-4.


6464


3. RM-cells may be transmitted out of sequence 3. RM-cells may be transmitted out of sequence with respect to data cells. Sequence integrity with respect to data cells. Sequence integrity within the RM-cell stream must be maintained.within the RM-cell stream must be maintained.

4. For RM-cells that transit a switch (i.e., are 4. For RM-cells that transit a switch (i.e., are received and then forwarded), the values of the received and then forwarded), the values of the various fields before the CRC-10 shall be various fields before the CRC-10 shall be unchanged except:unchanged except:a) CI, NI, and ER may be modified as noted in #1 abovea) CI, NI, and ER may be modified as noted in #1 above

b) RA, QL, and SN may be set in accordance with ITU-T b) RA, QL, and SN may be set in accordance with ITU-T Recommendation I.371-draftRecommendation I.371-draft

c) MCR may be corrected to the connection MCR if the c) MCR may be corrected to the connection MCR if the incoming MCR value is incorrect.incoming MCR value is incorrect.


6565


5. The switch may implement a use-it-or-lose-it policy to 5. The switch may implement a use-it-or-lose-it policy to reduce an ACR to a value which approximates the actual cell reduce an ACR to a value which approximates the actual cell transmission rate from the source. Use-it-or-lose-it policies transmission rate from the source. Use-it-or-lose-it policies are discussed in Appendix I.8.are discussed in Appendix I.8.

Notes:Notes:

1. A switch queuing point is a point of resource contention 1. A switch queuing point is a point of resource contention where cells may be potentially delayed or lost. A switch may where cells may be potentially delayed or lost. A switch may contain multiple queuing points.contain multiple queuing points.

2. Some example switch mechanisms are presented in 2. Some example switch mechanisms are presented in Appendix I.5.Appendix I.5.

3. The implications of combinations of the above methods is 3. The implications of combinations of the above methods is beyond the scope of this specification.beyond the scope of this specification.


6666

Virtual Source and Virtual Destination BehaviorVirtual Source and Virtual Destination Behavior


6767

VS/VD BehaviorVS/VD Behavior

1. Each ABR control segment, except the first, is sourced b1. Each ABR control segment, except the first, is sourced by a virtual source. A virtual source assumes the behavioy a virtual source. A virtual source assumes the behavior of an ABR source end point. Backward RM-cells receivr of an ABR source end point. Backward RM-cells received by a virtual source are removed from the connection.ed by a virtual source are removed from the connection.

2. Each ABR control segment, except the last, is terminate2. Each ABR control segment, except the last, is terminated by a virtual destination. A virtual destination assumes d by a virtual destination. A virtual destination assumes the behavior of an ABR destination end point. Forward the behavior of an ABR destination end point. Forward RM-cells received by a virtual destination shall be turneRM-cells received by a virtual destination shall be turned around as defined in destination behavior #2, and shad around as defined in destination behavior #2, and shall not be forwarded to the next segment of the connectill not be forwarded to the next segment of the connection.on.


6868

VS/VD Behavior(cont.)VS/VD Behavior(cont.)

3. The coupling between two adjacent ABR control se3. The coupling between two adjacent ABR control segments associated with an ABR connection is implgments associated with an ABR connection is implementation specific.ementation specific.

4. MCR shall be conveyed across VS/VD boundaries.4. MCR shall be conveyed across VS/VD boundaries.5. Setting of other parameters at VS/VD is network sp5. Setting of other parameters at VS/VD is network sp

ecific.ecific.


6969

ATM Adaptation LayerATM Adaptation Layer


7070

AAL1,2,3,4 for class A, B,C, and D respectively.AAL1,2,3,4 for class A, B,C, and D respectively. AAL3 and AAL4 are combined as AAL3/4.AAL3 and AAL4 are combined as AAL3/4. AAL5, originally called SEAL (Simple Efficient Adaptation Layer), is AAL5, originally called SEAL (Simple Efficient Adaptation Layer), is

adopted by the ATM Forum to replace AAL3/4.adopted by the ATM Forum to replace AAL3/4.


7171


7272


7373


7474


7575


7676

The message is transmitted by passing it to the SAR sublayer, which does not The message is transmitted by passing it to the SAR sublayer, which does not add any headers or trailer. It breaks the message into 48-byte units and passes tadd any headers or trailer. It breaks the message into 48-byte units and passes to the ATM layer for transmission.o the ATM layer for transmission.

The Internet is expected to transport IP packets over ATM networks with the The Internet is expected to transport IP packets over ATM networks with the AAL5 payload field. RFC 1483 and 1577.AAL5 payload field. RFC 1483 and 1577.


7777

ATM in LANATM in LAN

Support multiple,guaranteed classes of service.Support multiple,guaranteed classes of service. Provide scalable throughput.Provide scalable throughput. Facilitate the interworking between LAN and WAN Facilitate the interworking between LAN and WAN

technology.technology.

ATM LAN emulation by ATM ForumATM LAN emulation by ATM Forum LAN Emulation over ATM Specification,Version 1.0 1995LAN Emulation over ATM Specification,Version 1.0 1995


7878


7979


8080


8181

ATM in InternetATM in Internet

Multiple Protocol Over ATM,Version 1,July 1997Multiple Protocol Over ATM,Version 1,July 1997 For efficient transfer of inter-subnet unicast data in a LAN emulatFor efficient transfer of inter-subnet unicast data in a LAN emulat

ion LANE environment.ion LANE environment. MPOA integrates LANE and NHRP(Next Hop Resolution ProtocMPOA integrates LANE and NHRP(Next Hop Resolution Protoc

ol)to allow inter-subnet,internetwork layer protocol communicatiol)to allow inter-subnet,internetwork layer protocol communication over ATM VCCs without requiring routers in the data path.on over ATM VCCs without requiring routers in the data path.

NHRP is currently an Internet-Draft to determine the internetworNHRP is currently an Internet-Draft to determine the internetworking layer address and Non-Broadcast,MnHi-Access (NBMA)subking layer address and Non-Broadcast,MnHi-Access (NBMA)subnetwork addresses of the “NBMA next hop” towards a destinationetwork addresses of the “NBMA next hop” towards a destination stationn station

Documents

(C) All rights reserved by Professor Wen-Tsuen Chen1 Asychronous Transfer Mode (ATM) ä ATM is originally the transfer mode for implementing Broadband ISDN