2001 Copyright SCUT DT&P Labs 1 Principle of ATM （ 2 ）

2001 Copyright 2001 Copyright SCUT DT&P LabsSCUT DT&P Labs 1

Principle of ATMPrinciple of ATM（（ 22 ））


5. ATM Adaptation Layer5. ATM Adaptation Layer


1. 1. QoS Service CatagoriesQoS Service Catagories

CBR Constant Bit Rate

VBR-RT Variable Bit Rate - Real Time

VBR-NRT Variable Bit Rate - Non-Real Time

ABR Available Bit Rate

UBR Unspecified Bit Rate

GFR Guaranteed Frame Rate (later)



1. QoS Service Catagories (cont.)CBRCBR has been defined to support constant bit rate connection-

oriented traffic where end-to-end synchronisation is required. This is otherwise known as ITU-T Class AClass A performance requirements.

VBR-RTVBR-RT has been defined to support variable bit rate connection-oriented traffic where end-to-end synchronisation is required. This is otherwise knownas Class BClass B performance requirements.

VBR-NRTVBR-NRT is for types of traffic which are predictable, yet do not require a timing relationship to be maintained end-to-end.

ABRABR service is designed for economical support of applications with vague requirements for throughputs and delays.



1. QoS Service Catagories (cont.)

UBRUBR operates on a 'best effort' basis, with no reservation of bandwidth.

Signalling used to set up and clear down calls is normally transmitted as UBR,as is Local Area Network Emulation (LANE) traffic.

GFRGFR is a new service category which is still being defined. It is intended to provide a mechanism that will deliver frames (as cells).

If one cell is lost they are all lost. What is guaranteed is a frame rate rather than a cell rate.



Classes as defined by ITU-T rec. I 362

Class A Class B Class C Class D

Timing betweensource and destination Required Not required

Bit rate Constant Variable

Connection mode Connection-oriented Connectionless

AAL 1 AAL 2 AAL 3 AAL 4

AAL 5

RelevantAdaptation Layer



2. General Principles of Adaptation2. General Principles of Adaptation

Adaptation Layer

SAR

CS

Higher layer data

H H

The use of a CS is not required byall AALs Etc.

H T H T H T



3. Usage of Adaptation Layer3. Usage of Adaptation Layer

AAL is used to adapt a source application to ATM ATM switching takes place in the ATM Layer.



4. 4. AAL1AAL1

• A function of the AAL associated with Class A data, AAL1, is to ensure that there is timing integrity between the sending and the receiving end.

• Another function is to carry out clock recovery at the destination.

• The AAL also provides a mechanism to detect lost cells, and inserts a dummy into the cell stream to ensure that the timing information is not lost.



4. AAL 1 (cont.)4. AAL 1 (cont.)To format Class A data into cells, the data stream at the defined operating speed is simply chopped up into 47-byte chunks. Each 47-byte SDU is preceded by a one-byteheader, resulting in a 48-byte payload.



4. AAL 1 (cont.)4. AAL 1 (cont.)The SN field is then split into two parts: the Convergence Sublayer Indication bit (CSI) which is normally set to 0, and three bits for the Sequence Number.This cycles through from 0 to 7 and back to 0 again, and is suitable for identifying missing or misinserted cells.

To ensure the integrity of the SN field, it is protected by the SNP (Sequence Number Protection) field, which is a three-bit CRC check with an additional even-parity bit.



5. 5. AAL2AAL2

• AAL2 defines the transport of VBR traffic that is timing-sensitive, such as VBR audio and video.

• A feature of AAL2 is the ability to accept several streams of traffic and multiplex them together.



5. AAL 2 (cont.)5. AAL 2 (cont.)5. ATM Adaptation Layer5. ATM Adaptation Layer


5. 5. AAL2 (cont.)AAL2 (cont.)

Initial AAL 2 headerInitial AAL 2 header• CID FieldCID Field The channel identifier field identifies the individual

user channels within the AAL2, and allows up to 248 individual users within each AAL2 structure.

• LI FieldLI Field The length identifier identifies the length of the packet payload associated with each individual user, and assures conveyance of the variable payload.

• UUI FieldUUI Field One current use for the User-to-user field is to negotiate a larger Maximum Transfer Unit (MTU) size for IP.




Secondary AAL 2 headerSecondary AAL 2 headerThe Offset FieldOffset Field identifies the location of the start of the next

packet within the flow. For robustness the Start Field is protected from errors by the

Parity bitParity bit (P) and data integrity is protected by the Sequence NumberSequence Number (SN).



6. 6. AAL3/4AAL3/4• The two workgroups, AAL3 and AAL4,discovered that they

had produced near-identical processes. The two work groups subsequently joined forces to produce the single adaptation known as AAL 3/4.

• AAL 3/4 has a relatively high overheadhigh overhead. In this case, 4 octets are consumed by the header and trailer fields. After subtracting this overhead, the payload has been reduced to 44 octets.

• Although originally designed to carry all manner of traditional data traffic, AAL 3/4 was seen as overly complex to implement and also as inefficient due to its high overheads. Consequently, most data traffic is carried in AAL 5.



6. AAL 3/4 (cont.)6. AAL 3/4 (cont.)



6.1 AAL3/4 CS• Type Indicates the units used by the BA and Length fields.• BTag/Etag: These two 'tags' are a numerical value (the

same value), which help to ensure that it is a single CS unit that has been received and not a damaged CS unit created by joining together parts of two CS units.

• BA Size Length of the user information subfield of the CS payload.

• Pad Padding added to ensure that the total length of the CS is divisible by 4 (32 bits).This is an engineering consideration to simplify processing by 32-bit processors.

• Length of the user information subfield. Other fields and subfields are reserved for future definition.



6.2 AAL 3/4 SAR• Segment Type Indicates whether a cell is the first (at the

beginning) of a message (BOM), a continuation of a message (COM), or the last (at the end) in a message (EOM).

• Sequence Indicates the position in a convergence PDU of a SAR PDU.

• MID: This is multiplexing ID field. This can be used to allow the multiplexing of several traffic streams into a single connection.

• Len: This is the length of the actual data in the last cell of a message.

• CRC: A 10-bit Cyclic Redundancy Check computed over the SAR PDU.



7. 7. AAL5AAL5

• AAL5 has significantly lower overheads than AAL 3/4 and is, therefore, very widely adopted.

• In practice, since AAL 2 is not yet widely used and AAL 3/4 is seen as overly complex and cumbersome, only AAL1 and AAL5 are widely used.

• AAL1 is used for CBR traffic and AAL5 for all others: VBR,

UBR and ABR.



7. AAL5 (cont.)7. AAL5 (cont.)5. ATM Adaptation Layer5. ATM Adaptation Layer



AAL5 Frame Format• AAL5 simply takes the network layer packet and adds a

single trailer.• The PAD field is there to pad out the complete PDU so that

it can be divided into an integer number of 48-byte segments for loading into the cells.

AAL5 TrailerThe AAL5 8-byte trailer consists of:• Two 1-byte fields which are unused • A 2-byte length field which indicates the length of the data,

not including the trailer and pad • A 4-byte CRC



7. 7. AAL5 (cont.)AAL5 (cont.)AAL5 Trailer




AAL5 TransmissionAAL5 Transmission

• The PTI field in the header is used. Bit 1 is set to 1Bit 1 is set to 1 when the last celllast cell representing the PDU is assembled, and all other cells have the bit set to 0.

• When the receiver sees the PTI field with bit 1 set to 1, it assumes that the next cellnext cell with the same VPI/VCI number will be the first cell of a newnew PDU.



7. 7. AAL5 (cont.)AAL5 (cont.)AAL5 TransmissionAAL5 Transmission

AAL5 makes use of the PTI field in ATM cell headerBit 1 = 1 indicates this cell carries the AAL5 trailer

48-byte data field

VPI

VPI VCI

VCI

VCI CLP

HEC

GFC

PTI



6. Signalling6. Signalling


1. 1. Signalling FunctionsSignalling Functions• If connections are to be set up on demand, a form of

signalling is essential. Connections set up in this way are referred to as switched virtual circuitsswitched virtual circuits (SVCs).

• it is necessary to adopt a signalling system which is internationally accepted together with an addressing scheme which operates on a global basis.

• The ITU-T standard for signalling in ATM public networks is known as Q.2931Q.2931.

• The ATM Forum derived two separate standards from this for private networks, known as V3.0 and V3.1.

• UNI 4.0UNI 4.0 has also been released. This brings the ATMF signalling subset closer to Q.2931.



1. 1. Signalling Functions (cont.)Signalling Functions (cont.)

• All signalling within ATM is carried over a standard reserved channel: VPI=0, VCI=5.

• Signalling is separately defined for use across the UNIUNI (Q.2931, UNI 3.0, UNI3.1, UNI 4.0) and for use at the NNINNI for setting up the calls (PNNIPNNI).



2. 2. Signalling ControlSignalling Control FunctionsFunctions

Establishing a virtual circuitStatus report for a virtual circuit Maintaining a virtual circuitClearing a virtual circuit



33. . Address FormatsAddress Formats

• Work is still proceeding on defining the most effective addressing structures for use in ATM. Below are listed three formats that are used in private networks.

• The carriers have already declared their intent to use E.164E.164 addresses..



3. Address Formats (cont.)

AFI DCC E.S.I. Sel.

AFI ICD E.S.I. Sel.

AFI E.S.I. Sel.

48-bit ‘MAC’ address

E.164 ISDN Number

I.C.D. Format

D.C.C. Format

E.164 Format

IDPIDI DSP

IDPIDI DSP

IDPIDI DSP

High order DSP

High order DSP

High order DSP



• DCC ATM Address FormatDCC ATM Address FormatAuthority Format Indicator (AFI) = 39 39Data Country Code (DCC)..

• ICD ATM AddressICD ATM AddressAuthority Format Indicator (AFI) = 4747International Code Designator (ICD)

• NSAP Encapsulated E. 164 Address FormatNSAP Encapsulated E. 164 Address FormatAuthority Format Indicator (AFI) = 4545E.164 - An E.164 format (telephone) number(NSAP: Network System Access Point)

GeneralGeneral Domain Specific Part (DSP)End System (or Station) Identifier (ESI)Sel Selector



44. Call Set-up. Call Set-up• A call set-up message is sent by the calling party into the

network to initiate a connection.

• It is also passed from the network to the called party to initiate the connection.

• Assuming successful call establishment, the called party will respond with a connect message.

• With ATM we need to specify a list of characteristics that the network must support, for example, the quality of service (QoS).



4. Call Set-up (cont.)

Internal Set-up(PNNI?)Set-up

Release

OR Call Proceeding

Connect

ConnectConnect

Connect ACK

Connect ACK

Connect ACK

Release

OR Call Proceeding

Set-up

Release

OR Call Proceeding

Calling Party Called PartyUNI UNI



44. Call Release. Call Release

• The release message can be sent by either party to clear down the connection.

• If one party clears, then the network will send a clear message to the other party.

• The network may also initiate the clear-down if, for example,

a network failure occurs, or in the absence of traffic for a pre-determined time period.



4. Call Release (cont.)

release

Release complete

release

Release complete

Calling Party Called PartyUNI UNI

Release complete

release



55. . Point-to-Multipoint ConnectionsPoint-to-Multipoint Connections• Multipoint connections are a feature of ATM networks. They

are used in all LAN techniques.

• They will be a most important feature of broadcast networks such as those providing video on demand.

• The process of setting up a point-to-multipoint connection involves first of all setting up a point-to-point connection. It must be specified that this connection is to be multipoint (This must be done as multipoints are uni-directionaluni-directional.单向的 )



55. . Point-to-Multipoint ConnectionsPoint-to-Multipoint Connections

• Once the initial point-to-point is set up additional destinations (leaves) can be added. There are two alternative mechanisms that can be used here:

(1) Send a request to the root (the originator of the original point-to-point);

(2) With signalling version 4.0 issue a Leaf Initiated Join (LIJ) request to the network.



5. Point-to-Multipoint Connections (cont.)

Internal Set-up(PNNI?)

Set-up

ConnectRelease

OR Call Proceeding

Add-Party

Add-Party Ack

OR Call Proceeding

ROOT Party NEW LeafUNI UNI

Point-to-Point Connection

Release)Drop Party

Release)

Release CompleteRelease CompleteRelease Complete

Point-to-Multipoint Connection



66. . The Traffic ContractThe Traffic Contract• The traffic contract is the sum total of all the parametersall the parameters

required to define the characteristics of a connection.

• The contract includes an indication of how the network is to verify that the user does not use more resources than were requested at set-up time.

• The contract consists of a series of requirements that are encoded for transmission to the network at the ingress ingress switchswitch to the network (this includes a value of required bandwidth and delay).



66. . The Traffic Contract (cont.)The Traffic Contract (cont.)• The set-up message carries the destination 20-byte ATM

addresses, plus the basic bandwidth parameters forward and reverse, and the QoS class.

• The set-up message may also carry the source ATM address.

• The traffic contract between user and network establishes:– Virtual bandwidth reserved in each of the forward and

backward directions;– QoS class for cells in each of the forward and reverse

directions.



66. . The Traffic Contract (cont.)The Traffic Contract (cont.)• The Connection Admission Control (CAC) algorithm of

the switch will then assess the network in the light of the request, before allowing the connection to proceed to set-up.

• The ingress switch will retain a copy of the pertinent parameters (such as PCR,SCR and MBS) and will use this information to check that the connection stays within its contracted bounds (a policing function).



6. User-Network Interface 6. User-Network Interface (UNI) Signalling(UNI) Signalling


11. . The User-Network InterfaceThe User-Network Interface• The user-network Interfaceuser-network Interface (UNI) is that point between the

end-point ATM equipment and the first ATM switch.

• There have been several versions of the UNI specification, defined by the ATM forum: UNI 2.0, UNI 3.0, UNI 3.1 and UNI 4.0 (also known as Sig 4.0).

• Of these specifications UNI 2.0 supports only PVCs, while

the latter three versions also support SVCs.

• The ATMF signalling (from UNI 3.1 onwards) was aligned with the ITU-T Q.2931 signalling standard.

6. UNI Signalling6. UNI Signalling


11. . The User-Network Interface (cont.)The User-Network Interface (cont.) The set-up message will carry the source and

destination ATM addresses, plus the bandwidth and the QoS parameters

The call set-up message is chopped up using AAL5 and sent on reserved channel (VPI= 0, VCI=5).



22. Q.2931 Signalling Format. Q.2931 Signalling Format

• Signalling under ATM consists of joining together a variety of basic building blocks containing the necessary information.

• These building blocks are known as Information Elements (IEs) and each element has a standard 4-byte header followed by the IE content.

• IEs are built as required by the message type and service type.




Message Types:Call Establishment:

CALL PROCEEDINGCONNECTCONNECT ACKNOWLEDGESETUP

Call Clearing: RELEASERELEASE COMPLETERESTARTRESTART ACKNOWLEDGE




Message Types:Miscellaneous:

STATUSSTATUS ENQUIRY

Point-to-Multipoint:ADD PARTY

ADD PARTY ACKNOWLEDGE

ADD PARTY REJECTDROP PARTYDROP PARTY

ACKNOWLEDGE



7. Private Network-to-Network 7. Private Network-to-Network Interface (PNNI)Interface (PNNI)


11. PNNI Overview. PNNI Overview• Although the PNNI specification has been issued for use in

private networks, PNNI proves to be sufficiently scalable and robust to be used in public networks.

• It is likely that the official NNI signalling standard, when it is eventually released, will be strongly based on PNNI.

7. PNNI7. PNNI


1. PNNI Overview (cont.)1. PNNI Overview (cont.)

Signalling protocol to set up connections based on routing information

Routing protocol to distribute reachability, capacity and QoS information

7. PNNI7. PNNI


2. PNNI Targets2. PNNI Targets

To distribute among all participating switches the topology of the ATM network

To operate at the network-network interface To allow for scalability by the creation of groups of switches To allow switches to build routing tables from the topological

information To allow for ‘crank back’ to last the confirmed point and a

search for an alternate route On end-to-end route confirmation, interface with Connection

Admission Control to accept ATM call set-up

7. PNNI7. PNNI


2. PNNI Targets (cont.)2. PNNI Targets (cont.)

PNNI StandardsPNNI Standards• PNNI is an interface specification that uses a Link State

process for the distribution of routing information.

• The ATM Forum standard is P-NNI version 1.0 af-pnni-0055.000 March 1996.

• Error corrections issued as af-pnni-0081.000 July 1997.

• PNNI supersedes an earlier version from December 1994 called Interim Inter Switch Protocol (IISP). This is sometimes referred to as PNNI phase 0.

7. PNNI7. PNNI


3. PNNI Base Level3. PNNI Base Level

• All ATM switch ports have an ATM address of 20 bytes (1) The first 13 bytes are normally fixed for each switch (2) The final 7 bytes are the physical address of the attached device (6 bytes, referred to as the MAC address) plus the selector field which is one byte.

• In the example used here, we have only shown the last few hex digits of an ATM address.

7. PNNI7. PNNI


3. PNNI Base Level (cont.)

7. PNNI7. PNNI


3. PNNI Base Level (cont.)3. PNNI Base Level (cont.)Forming Groups• On start-up, PNNI nodes send 'hellohello' packets on all

interfaces to discover neighbours.

• As part of this process, neighbouring nodes exchange their ID numbers. In this example, a 13-digit match is required.

• All nodes with matching numbers form a logical peer group using the matching digits as a group identifiergroup identifier, for example, group number 202.

• Nodes with at least one link terminating at a switch in a 'foreign' group are considered 'Border NodesBorder Nodes'.

7. PNNI7. PNNI


3. PNNI Base Level (cont.)3. PNNI Base Level (cont.)

Information Exchange• Nodes within a group exchange and relay information about

link status including virtual bandwidth, availability and next hop.

• A reliable transport mechanism is used to ensure that all nodes ultimately share the same database.

7. PNNI7. PNNI


3. PNNI Base Level (cont.)3. PNNI Base Level (cont.)PNNI Groups

7. PNNI7. PNNI


4. Peer Group Leader4. Peer Group Leader• As part of this process the nodes within a group select a

group leader based on a configured priority number, or by selecting the node with the lowest address.

• Group leaders establish logical connectionslogical connections with each other and exchange a summary of information about their groups.

7. PNNI7. PNNI


4. PNNI Peer Group Leaders (cont.)7. PNNI7. PNNI


4. PNNI Logical Network4. PNNI Logical Network• The network, viewed from the perspective of a group leader,

will appear to have the topology as shown in the next diagram.

• Locally, a group leader will retain the detailed view of its own group including border nodesborder nodes and therefore 'real' links to neighbouring groups.

• Group leaders passpass this logical network map to the members of their own group. Each PNNI node, therefore, has a detailed description of its own group and a logical map on how to get to any other group.

7. PNNI7. PNNI


PNNI Logical Network

7. PNNI7. PNNI


5. PNNI Operation5. PNNI Operation• When a UNI signalling request comes in from the end-

station on reserved channel 0,5 its contents will be analysed within the switch.

• The switch first performs a Connection Admission Control (CAC) algorithm which determines whether or not the switch has the resources necessary to handle the incoming call.

• A Generic Connection Admission Control (GCAC) is then performed.

7. PNNI7. PNNI


5. PNNI Operation5. PNNI Operation• This GCAC algorithm determines whether or not the

switches between the source and destination can handle the call.

• Following the GCAC algorithm, the switch prepares a Designated Transit List (DTL) which is an entire route through the network for the signalling request.

• This DTL is added onto the call set-up message and sent to the next node along the intended signalling route.

7. PNNI7. PNNI


Global topology as seen by node 101267. PNNI7. PNNI


PNNI Designated Transit List7. PNNI7. PNNI


6. PNNI Packets6. PNNI PacketsStandard Header

There are many types of packet used for the PNNI protocol. However, they all start with a standard layout header.

PNNI SignallingThe format of PNNI signalling packets is based on UNI 4.0 (Q.2931) with additions to cater for the transit lists and crankback.

7. PNNI7. PNNI


6. PNNI Packets (cont.)

All PNNI packets have a common header:

Packet Type Length Version Supported

0 2 Bytes 4 Bytes 5 Bytes 6 Bytes

Packet Type:1 = Hello2 = PTSP (PNNI Topology State Packet)3 = PTSP Acknowledge4 = Database Summary5 = PTSE Request

Packet Type:1 = Hello2 = PTSP (PNNI Topology State Packet)3 = PTSP Acknowledge4 = Database Summary5 = PTSE Request

Most recently supported protocol version, used toalign protocol versionsbetween different nodes

Most recently supported protocol version, used toalign protocol versionsbetween different nodes

7. PNNI7. PNNI


8. Network Management8. Network Management


1.1. General Management ModelGeneral Management Model

The management protocols used are typically the Simple Network Management Protocol (SNMP) and, in more recent devices, the Hypertext Transfer Protocol (HTTP).

Local ManagementWith local management, the management terminal is plugged directly into the ATM switch, typically into an Ethernet port or a serial port.

Initially an ATM switch may be configured in this manner.



1. General Management Model (cont.)1. General Management Model (cont.)In band Management• In managing an ATM network, management traffic is sent in

band that is over the ATM network itself on an ATM connection.

• An SVC, or more typically a PVC, may be used for this purpose.

ILMI • The Interim Local Management Interface Protocol (ILMI)

is a standard ATM management protocol. • ILMI works only across the UNI interface, that is between

the end ATM station and the first ATM switch.



General Management Model8. Network Management8. Network Management


2.2. Interim Local Management Interface (ILMI)Interim Local Management Interface (ILMI)• The ILMI standards produced by the ATM Forum enable a

number of network management functions to be performed across the UNI.

• ILMI is a model based on the use of SNMP for the interchange of data, which is adapted via AAL5 and transmitted over a predefined VPI/VCI=0/16.

• The important difference between SNMP, as discussed in the previous section, and ILMI is that ILMI is SNMP over AAL5 directly, that is, without using IP.

• ILMI is positioned at the public and private UNIs. ILMI also runs between the public and private network.

• If one wishes to access this information remotely then one must run a management agent locally to access the local MIB.



SNMP and ILMI8. Network Management8. Network Management


3. ILMI Functions3. ILMI Functions

• ILMI was intended originally to handle only the address registration and de-registration process for each end station in an ATM network.

• Now its functions have grown and now include many other housekeeping operations, including control information, switch configuration details, statistics relating to the ATM connections, and the physical and ATM layer data.



ILMI Basic RequirementsSingle MIB for each ATM device

A Management Information BaseManagement Information Base (MIB), which contains data relating to the status of each end station or intermediate switch, is set up for the ATM system.

ILMI providesILMI provides:

Status information

Configuration information

Control information

ILMI handlesILMI handles:

Address registration

Address de-registration

Switch configuration



4. ILMI Agents4. ILMI Agents

• The ILMI requires a management entity at each end of the interface.

• The UNI Management Entity (IME) acts as the server to the network.

• management station client, and performs all necessary communications tasks via AAL5 and ATM cells.

• The IME also controls access to the MIB.



4. ILMI Agents (cont.) The Interface Management Entity (IME) in each ATM

device does the following:Handles the communicationProvides access to the MIBCo-ordinates between ATM and physical layer

information

There are two types of Interface Managed Entity (IME):uIME - User IME (ATM end device)nIME - Network IME (ATM switch)

nIMEuIME

PrivateUNI

ILMI(SNMP over AAL5)

Privateswitch



5. ILMI ATM UNI MIB Tree5. ILMI ATM UNI MIB Tree

ATM Layer

Virtual Path

Connection

Virtual Channel

Connection

ATM Layer

Statistics

ATM UNI ILMI MIB

Physical Layer

Common Specific

Interface Index

Interface Index

Interface Index +

VPI

Interface Index +

VPI + VCI

Interface Index

Network Prefix

Address

Interface Index + Address

Interface Index + Prefix



66. Address Registration. Address Registration• All ATM addresses consist of 20 bytes of data, made up of

two distinct parts:

The end-station address, which is 6 bytes of MAC data plus a selector byte; The network prefix, which is 13 bytes of data.

• The registration of end-station devices is carried out by ILMI using a cold start trap from either the end-station or the ATM switch.



66. Address Registration (cont.). Address Registration (cont.)

Operation • When the ATM interface in the end station is enabled, a cold

start trap is transmitted out along VCI 16.

• The ATM switch receives this start trap and replies with the prefix associated with that ATM switch.

• The end station then adds its own MAC address and selector field to the prefix to form a full ATM address.

• This address is sent to the switch where it is registered.



6. Address Registration (cont.)

ILMI SNMP set message Network Prefix

ILMI SNMP set message Host Address

Cold start trap

ILMI SNMP Response ACK / NACK

ILMI SNMP Response ACK / NACK

nIME

uIME

SNMP in AAL5 on VCI 16SNMP in AAL5 on VCI 16

(Prefix + MAC + Selector )



7. Device Check7. Device Check

• uIMEs are declared ‘down’ if they do not respond after four consecutive polls.

• A uIME is de-registered after the nIME declares that the uIME is down.

• The uIME is de-registered by removing its address entry from the nIME address table.



7. Device Check (cont.)

ILMI SNMP get message connectivity poll

ILMI SNMP response message connectivity ACK

uIME nIME



9. 9. ATM Traffic DescriptorsATM Traffic Descriptors


1. Traffic Management1. Traffic Management

Traffic Management is essential for the proper operation of ATM.

The aim is to ensure that all the different classes of traffic receive the appropriate handling.

Main features of traffic management:Traffic ContractConnection Admission ControlTraffic ShapingTraffic Policing



2. Traffic Descriptor Parameters2. Traffic Descriptor Parameters

These are the parameters requested at connection set-up time:

Peak Cell Rate (PCR)

Sustainable Cell Rate (SCR)

Maximum Burst Size (MBS)

Minimum Cell Rate (MCR)

Cell Delay Variation Tolerance (CDVT)



3. Required Parameters for each Service 3. Required Parameters for each Service CategoryCategory

ServiceCategory PCR SCR MCR CDVT

CBR

VBR-RT

VBR-NRT

ABR

UBR

GFR



4. Peak Cell Rate4. Peak Cell Rate

Peak Cell Rate (PCR) is the absolute maximum rate at which the network guarantees cell delivery A user may send cells at this rate for a short period of

time Rate is reduced to maintain an average (SCR)

PCR is used by CBR, VBR and ABR service categories



5. Sustainable Cell rate5. Sustainable Cell rate

Sustainable Cell Rate (SCR) is the averageaverage rate that a network guarantees cell delivery

Users may burst above the SCR to the PCR (up to a maximum of BT) as long as they reduce their rate of flow to maintain this rate

SCR is only used by the VBR QoS category



6. Burst Tolerance6. Burst Tolerance

Burst Tolerance (BT) is the maximum time that the network will accept cell rates of PCR

BT is only used by the VBR QoS category



7. Minimum Cell Rate7. Minimum Cell Rate

Minimum Cell Rate (MCR) is the highest rate at which the network guarantees delivery of cells

A user may attempt to send at higher rates at the risk of losing cells

This parameter is used to support an ABR service



8. Cell Delay Variation and Tolerance8. Cell Delay Variation and Tolerance

Variation in Cell Delay is a fact of life

Delays are caused by : Multiplexing Queuing OAM cell insertion Physical Layer overhead

An application may need a guaranteed limit on the degree of variation, a specified tolerance


9. 9. Quality of Service ParametersQuality of Service Parameters


1. Quality of Service Parameters1. Quality of Service Parameters

Negotiable QoS Parameters

Cell Loss Ratio (CLR)

Maximum Cell Transfer Delay (Max CTD)

Peak to peak Cell Delay Variation (peak-to-peak CDV) Non-negotiable QoS Parameters

Cell Error Ratio (CER)

Severely Errored Cell Block Ratio (SECBR)

Cell Misinsertion Rate (CMR)



2. Cell Loss Ratio2. Cell Loss Ratio

Ratio of cells successfully delivered to cells presented per VPI/VCI

Cells inCells out

cells dtransmitte Total

cells LostCLR



3. Maximum Cell Transfer Delay3. Maximum Cell Transfer Delay Cell Transfer Delay (CTD) is the time a cell takes to traverse

the network

CTD is made up of Propagation Delay Transmission Delay Switching Delay Queuing Delay

The Maximum Cell Transfer Delay (maxCTD) is the maximum allowable CTD

CDT = time



4. Peak-to-Peak Cell Delay Variation4. Peak-to-Peak Cell Delay Variation

Cell Delay Variation (CDV)

CDV is a measure of the difference between actual time of delivery of a cell and expected time

CDV highlights bursts of cells

typical of LAN-generated traffic

Cells in

Real

Without delay variation

CDV



5. MaxCTD, Peak-to-Peak CDV and CLR5. MaxCTD, Peak-to-Peak CDV and CLR

peak-to-peakCDV

Fixed TransitDelay

maxCTD

Cells delivered lateCells delivered late

Cell Arrival Distribution

The CLR requested at connection setup time actually places a limit on the value of the percentage of the cell arrival probability distribution lying outside the maxCTD arrival times.

The CLR requested at connection setup time actually places a limit on the value of the percentage of the cell arrival probability distribution lying outside the maxCTD arrival times.



6. Accumulation of QoS Parameters6. Accumulation of QoS Parameters

CDVs + maxCTDs

CDV + CDVs1 + CDVs2 + CDVs3 = P2P-CDV

The maxCTD and CDV parameters passed with signalling SETUP calls are accumulated as the call progresses through the network.

The maxCTD and CDV parameters passed with signalling SETUP calls are accumulated as the call progresses through the network.

maxCTD + maxCTD + maxCTD + maxCTD = Total maxCTD



7. One Point CDV7. One Point CDV

Cell Delay Variation = Reference arrival time - Actual arrival time = RCn - ACn

Negative values = gaps in cell streamPositive values = cell “clumping”

Cell Delay Variation = Reference arrival time - Actual arrival time = RCn - ACn

Negative values = gaps in cell streamPositive values = cell “clumping”

ReferenceCell Stream

ActualCell Stream

RC0 RC1 RC2 RC3 RC4 RC5

AC0 AC1 AC2 AC3 AC4 AC5

CDV



8. Non-negotiable QoS Parameters8. Non-negotiable QoS Parameters

Cell Error Ratio, where :

Severely Errored Cell Block Ratio, where :

Cell Misinsertion Rate, where :

cells Errored cells eredly transfSuccessful

cells Errored CER

blocks cell tted transmiTotal

blocks cell errored Severely SECBR

interval Time

cells dMisinserteCMR



9. Factors affecting QoS Parameters9. Factors affecting QoS Parameters

Propagation Delay

Media Errors

Switch Design

Buffer Capacity

Traffic Load

Number of Nodes

Network Failures

CDV CTD CLR CER CMR SECBR



10. Required Traffic Descriptors and QoS 10. Required Traffic Descriptors and QoS ParametersParameters



10. Traffic Control10. Traffic Control


1. Connection Admission Control1. Connection Admission Control

Included in the process of establishing a virtual connection (VPI/VCI):

Traffic descriptors are included either in UNI signalling (SVC) or management setup (PVC)

Network switches check the traffic requirements against handling ability

Admission of the connection is rejected if the network cannot guarantee that it will meet the requirements


1. Connection Admission Control – CAC (cont.)1. Connection Admission Control – CAC (cont.)

UNI signallingI wish to connect to Bwith these QoS parameters

B

NNI signallingAttempt to find a path to BAble to currently support this requestInform CAC of result

UNI signallingCall proceeding

CAC


2. Virtual Bandwidth2. Virtual Bandwidth

Traffic descriptors such as CDV, PCR may be summarised as a connection with a specific virtual bandwidth (Vbw) requirement

Switches along the intended path of the connection check for Vbw

If a switch does not have sufficient Vbw: A new route is selected The request is denied


2. Virtual Bandwidth (cont.)2. Virtual Bandwidth (cont.)

A separate Virtual Bandwidth algorithm is used for each Quality of Service Category.

Service Category Bandwidth Allocated

CBR PCR <= Vbw <= Link rateVBR-NRT SCR <= Vbw <= PCRVBR-RT SCR <= Vbw <= PCRABR Vbw = MCRUBR Under ReviewGFR Vbw = MCR


3. Traffic Shaping3. Traffic Shaping

Traffic shaping is the name given to any technique at the user site to ensure that outgoing cells conform to the traffic contract

This makes the customer premises equipmentcustomer premises equipment (CPE) a well-behaved user

Throttling back to agreed rates can increase throughput as the need to retransmit network discarded cells is removed


4. Traffic Policing4. Traffic Policing

A traffic contract exists across the UNI when a call’s descriptors are accepted

Not all user devices will be well-behaved Traffic policing is necessary to ensure that badly-

behaved devices do not interfere with other users

Cells outside the limits of the contract will: Be discarded Have CLP set for discard at busy switches


5. Generic Cell Rate Algorithm5. Generic Cell Rate Algorithm

Policing traffic is performed by applying the Generic Cell Rate Algorithm (GCRA) GCRA is a continuous state ‘leaky bucket’ algorithm

It checks that cell streams conform to PCR, CDVT, SCR and BT PCR & SCR require separate instances of the leaky

bucket, hence switches employ a ‘dual state leaky bucket’


6. Leaky Bucket Algorithm6. Leaky Bucket Algorithm

Peak Cell RateBucket

cells

Cells which overflow will be droppedor have their CLP set to 1

Tolerance factor to account for jitter - caller the Cell Delay VariationTolerance (CDVT), measured in ms


The End of Part 2The End of Part 2

2001 Copyright SCUT DT&P Labs 1 Principle of ATM （ 2 ）

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Transcript of 2001 Copyright SCUT DT&P Labs 1 Principle of ATM （ 2 ）