Management Plan

AAL

ATM Layer

Physical Layer

Signaling Protocol

Applications

TCP/IPNative

User Plane Control Plane

B-ISDN Protocol Reference ModelSNMP: Simple

Network ManagementProtocol

CMIP: CommonManagementInformationProtocol

Control Plane Supports Signaling Call Setup, Call Control, Connection Control

User Plane Data Transfer, Flow Control, Error Recovery

Management Plane Operation, Administration, & Maintenance

Management Plane(Provides control of ATM switch)

Layer Management(Layered)

Plane Management(No Layered)

– Use to manage each of the ATM layers with entity corresponding to each ATM layer

– OAM issues

– Concerned with management of all the planes

– All management functions (Fault, Performance, Configuration, Operation, & Security) which relates to the whole system are located in the Plane Management

– Provides coordination between all planes

Broadband Networking with SONET and ATM

USER

USER

USER

USERATM SW ATM SW

VideoImageDataetc…

UNI UNINNI

Higher Layers

ConvergenceSublayers (CS)

SegmentationReassembly

Sublayer (SAR)

ATM Layer

Physical Layer

•Flow Control•Error Handling•Message Segmentation

•Segmentation Type•Message Number•Message ID

•5 Byte Header•48 Byte Payload•Handles cont. and bursty traffic

•SONET

Higher Layers

ConvergenceSublayers (CS)

SegmentationReassembly

Sublayer (SAR)

ATM Layer

Physical Layer

USER USER

AdaptationLayer

ATM Layer

Physical Layer

ATM Layer

Physical Layer

ATM Protocol Reference Model in the User Plane

Upper Layers

1 2 3 4class A class B class C class D

CellInformationFieldAAL

ATM

PL

CS

SAR

•Handling lost / misdelivered cells•Timing recovery•Interleaving

•Split frames / bit stream info cells•Re-assemble frames / bit stream

•Cell routing•Multiplexing / demultiplexing•Generic flow control

TC

PM

•Cell header verification and cell delineation•Rate decoupling (insert idle cells)•Transmission frame adaptation•Bit timing•Physical medium

CellHeader

AAL = ATM Adaptation LayerSAR = Segmentation and ReassemblyCS = Convergence SublayerPL = Physical LayerTC = Transmission ConvergencePM = Physical Medium

Abbreviations

Class

Service Classes for AALType

ABCD

Constant Bit RateVariable Bit RateConnection Oriented DataConnectionless Data

• SEAL = Simple and Efficient Adaptation Layer•Type 5 AAL•Acknowledged info transfer

Remark: See next page

Remarks: PMD Physical Medium Dependent

TC Transmission Convergence

Sublayer

It separates transmission from the physical interface and allows ATM interfaces to be built on a large variety of physical interfaces

Physical Layer Functionsa) Physical Medium (PM)

– PM sublayer provides the bit transmission capability including bit alignment

– Line coding and, if necessary, electrical/optical conversion is performed in this sublayer

– Optical fiber is used for the physical medium. Other media, coax cables are also possible

– Bit rates 155 Mbps or 622.080 Mbps.

Physical Layer Functionsb) Bit Timing

– Generation and reception of waveforms which are suitable for the medium, the insertion, and extraction of bit timing information and the line coding if required

– CMI (Code Mark Inversion) (CCITT G.703) proposed for 155.520 Mbps interface.

– NRZ “Nonreturn to Zero” code proposed for optical interface.

Line CodingElectrical Interface: Coded Mark Inversion (CMI)

– For binary 0 always a positive transition at the midpoint of the binary unit time interval.

– For binary 1 always a constant signal level for the duration of the bit time. This level alternates between high and low for successive binary 1s.

0 0 0 0 0 01 1 1

Level A1

Level A2

1 1

Line Coding (cont.)

Optical Interface: Nonreturn to Zero (NRZ)– For binary 0 Emission of light– For binary 1 No emission of light– Transition: 0 1 or 1 0

Otherwise no transition

0 0 0 0 0 01 1 1

Level A1

Level A2

1 1

• SONET/SDH : 155 Mbps and 622 Mbps over OC-3 (single mode fiber)• Cell Based• PDH Based (ATM cells mapped into PDH signals) (59 columns and 9 rows frame). Frame at 34.368 Mbps.• FDDI based or 100 Mbps (same as in FDDI PMD uses multimode fiber and line coding of 4B/5B). (called TAXI interface). Early private UNI interfaces were based on TAXI interfaces.• DS-3 (45 Mbps) Transfer of ATM cells on T3 (DS-3) public carrier interface. It is cheaper than SONET links. • STS-3 (155 Mbps) over Multimode fiber uses line coding of 8B/10B.• STS-3 (155 Mbps) over Twisted Pair (using Taxi interface) uses line coding of 8B/10B.• D1-T1 carriers (1.5 Mbps)

ATM INTERFACES

•This interface consists of a continuous stream of cells where each cell contains 53 octets.

•Synchronization achieved through HEC basis.•Maximum spacing between successive physical layer cells is 26 ATM layer cells.•After 26 consecutive ATM layer cells, a physical layer cell (idle cells or OAM cells) is enforced to adapt transfer capability to the interface rate.

CELL BASED INTERFACE

26 0 1 26 0 1

Physical layer OAM cell

1) Transmission Frame Adaptation

•Adapts the cell flow according to the used payload structure of the transmission system in the sending direction.

•In the opposite direction, it extracts the cell flow out of the transmission frame.

Transmission Convergence Sublayer (TC)

• After initialization receiver is in the “Correction Mode”• Single bit error detected corrected• Multiple bit error detected cell discarded

• Receiver switches to “Detection Mode”• In “Detection Mode”, each cell with a detected single-bit error is discarded.

• If a correct header is found, receiver switches to “Correction Mode”

2. Header Error Control (HEC)

Correction Mode Detection ModeNoError

Error detectedCell discarded

Multiple-bit errror (Cell discarded)

CorrectionSingle-bit error

No error

Example:

p Probability that a bit is in error

(1-p) Probability that a bit is NOT in error

p40 Probability that 40 bits are in error

(1-p)40 Probability that 40 bits are correct

a) With what probability a cell is rejected when the HEC state machine is in the "Correction Mode"?

Correction Mode

Probability of a cell being rejected

Different Perspective: When is a cell accepted?

* Probability of having no errors in cell headerOR

* Probability of having a single bit error in cell header

b) With what probability a cell is rejected when the HEC state machine is in the "Detection Mode"?

Detection Mode

HEC will only accept ERROR-FREE cells.

Different Perspective:

What is the probability that a cell header is correct?

c) Assume that the HEC state machine is in the “Correction Mode.” What is the probability that n successive cells will be rejected, where n >= 1 ?

Correction Mode

Probability of n successive cells being accepted (n>1)

n=1:Probability that 1 cell is accepted, i.e., the entire header is error-free.What is that probability?

ORThere is at most one bit error in the header.What is that probability?

n=2:

Probability that the cell header (2) is correct ANDPrevious case for cell 1

ORProbability that the cell header (2) has at most 1 bit error ANDProbability that the cell header (1) is correct (error free)

12

n=3:

Probability that the cell header (3) is correct ANDPrevious case for cell n=1

ORProbability that the cell header (3) has at most 1 bit error ANDProbability that the cell header (2) is correct ANDThe case for n=1

123

d) Assume that the HEC state machine is in the “Correction Mode.” What is the probability p(n) that n successive cells will be accepted, where n >= 1 ?

First cell is rejected:

What is the probability that a cell is rejected? Case a)

Different Perspective:

Probability that all header bits of a cell are correct

Probability that one single bit error in a cell header

Remaining n-1 successive cells:

Now, HEC is in Detection Mode

What is the probability that (n-1) successive cells are rejected, i.e., there will be errors in the headers for the remaining (n-1) cells

EFFECT OF ERROR IN CELL HEADERIncoming Cell

Error inHeader?

Valid cell(intended service)

No

Yes

Error detected

No Apparently valid cellWith errored header(unintended service)Yes

Current mode?

DetectionDiscarded Cell

CorrectionError

incorrectable?Yes

NoCorrection

attemptUnsuccessful

Successful

HEC Generation Algorithm (I.432)• Every ATM cell transmitter calculates the HEC value

across the first 4 octets of the cell header and inserts the result in the fifth octet (HEC field) of the cell header.

• The HEC value is defined as “the remainder of the division (modulo 2) by the generator polynomial x8+x2+x+1 of the product x8 multiplied by the content of the header excluding the HEC field to which the fixed pattern 01010101 will be added modulo 2.”

• The receiver must subtract first the coset value of the 8 HEC bits before calculating the syndrome of the header.

• Device always preset to 0s.[Key Word: CRC (Cyclic Redundancy Check Algorithm)]

ATM CELL STRUCTURE

1

2

3

4

5

:

:

53

8 7 6 5 4 3 2 1

8 7 6 5 4 3 2 112345:::

53

PAYLOAD(48 octets)

HEADER(5 octets)

Octet

GFC

VCI

VPI

VPI

VCI

VCI PT PR

HEC

PAYLOAD(48 octets)

HEC Generation Algorithm

• The HEC field contains the 8-bit FCS (Frame Check Sequence) obtained by dividing the first 4 octets (32 bits) of the cell header multiplied by 2^8 by the CRC code (generator polynomial)

(x8+x2+x+1)

HEC Generation Algorithm (I.432)• This HEC code can

1) Correct single bit errors2) Detect multiple bit errors

•Protects the header control information•Helps to find a valid cell (cell delineation and boundaries)

Purpose:

CELL DELINEATION

(This process allows identification of cell boundaries)

HUNT

SYNCH

PRESYNC

Correct HEC

Incorrect HEC

Cell-by-CellBit-by-Bit

consecutiveincorrect HEC

consecutivecorrect HEC

Cell Delineation (cont.)• In Hunt State a cell delineation algorithm is performed

bit-by-bit to determine if the HEC coding law is observed (i.e., match between received HEC and calculated HEC).

• Once a match is achieved, it is assumed that one header has been found and the method enters the PRESYNCH state.

• The HEC algorithm is performed cell-by-cell. If consecutive correct HECs are found, SYNCH state is entered; if not the system goes back to HUNT state.

• SYNCH is only left (to HUNT) state if consecutive incorrect HECs are identified.

Cell Delineation (cont.) and are design parameters that influence the

performance of cell delineation process.(=7 and =6).

• Greater values of result in longer delays in recognizing a misalignment but in a greater robustness against false alignment.

• Greater values of result in longer delays in establishing synchronization but in greater robustness against false delineation.

Cell Delineation (cont.)Remarks:

• A 155.520 Mbps ATM system will be in SYNCH state for more than 5349 years even when the bit error probability is BER=10-4.

• This method may fail if the header HEC occurs in the info field (maliciously or accidentally) Cell Payload Scrambling.

• To overcome the info field contents scrambled using a self-synchronizing scrambler with polynomial X43 + 1. Header itself is not scrambled.

The probability of 7 consecutive incorrect HEC withBER=10-4

A= The probability that 7 consecutive cells are in error.

[1- (1-10-4)40 ]7 = 1.616*10-17 = A

1/A The number of cells sent in order to have a 7

consecutive error cells; (Unit Cells);How often does event A occur in terms

of ATM cells.

{53 * 8} / {155.52 Mbps} = C

(53*8) = # of bits/cell ; Link Speed = # of bits/sec

How long does it take to send one ATM cell through the 155 Mbps link.{[1 / { A}] * C ={6.187*106} * 53 * 8} / {155.52 Mbps} =

1.6868*1011 = 5349 Years

End Result in terms of seconds

End result/(365*24*60*60) approx. 5349 years..

Cell Rate Decoupling(Speed Matching)

• Adapts cell stream into Transmission Bit Rate (Insertion / Discarding idle cells; in particular for SONET Interface). SONET uses synchronous cell time slots!

Note: Cell Based Interface No need for this function.

Cell Rate Decoupling (cont.)(Speed Matching)

Buffer

+

VPI/VCI

VPI/VCI

VPI/VCI

-

Insert Idle or Unassigned cells Remove the Idle or Unassigned cells

ATM Transmitter ATM Receiver

Transmitter multiplexes multiple streams; queueing them if anATM cell is not immediately available. If the queue is empty, when the time arrives to fill the next synchronous cell time slot, then the Transmission Convergence Sublayer inserts an Idle cell (or the ATM layer inserts an Unassigned cell.)

ATM Layer Functions

• Cell Multiplexing/Demultiplexing

• Cell VPI/VCI Translation

• Cell Header Generation/Extraction

• GFC Function

ATM Layer Functions (Cont’d)

• Cell Multiplexing/Demultiplexing In the transmit direction, cells from individual VPs and VCs are multiplexed into one resulting stream.

At the receiving side the cell demultiplexing function splits the arriving cell stream into the individual cell flows appropriate to the VP or VC.

ATM Layer Functions (cont.)

ii) Cell VPI/VCI Translation

- At ATM switching nodes, the VPI and VCI translation must be performed.

- Within VP switch, the value of the VPI field of each incoming cell is translated into a new VPI value for the outgoing cell.

- At a VC switch, the values of the VPI as well as the VCI are translated into new values.

ATM Layer Functions (cont.) iii) Cell Header Generation / Extraction

- This function is applied at the termination points of the ATM layer. - Transmit Side: After receiving the cell information from the AAL, the cell header generation adds the appropriate ATM cell header except for the HEC values. HEC is done at Physical Layer. VPI/VCI values could be obtained by a translation from the SAP identifier. - Receive Side: The cell header extraction function removes the cell header. Only the cell information is passed to the AAL. - This function could also translate a VPI/VCI value into a SAP identifier.

ATM Layer Functions (cont.)

iv) GFC functions

- Supports the control of the ATM traffic flow

in a UNI. It can be used to alleviate short

overload conditions.

- Control of cell flows toward the network

but not flow control from the network.

- No effect within the network.

Virtual Path and Virtual Circuit Concept•ATM cells flow along entities known as VIRTUAL CHANNELS. A VC is identified by its virtual circuit identifier (VCI).

VC set up between 2 end-users (like VC in X.25 => Indiv. Log connection).

VP Bundle of VCs having the same end points (Group logical connection; reserved trunk of connections).

•All cells in a given VC follow the same route across the network and are delivered in the order they were transmitted.

•VCs are transported within Virtual Paths (VPs). A VP is identified by its virtual path identifier (VPI). VPs are used for aggregating VCs together or for providing an unstructured data pipe.

Virtual Path and Virtual Circuit Concept

• Optical links will be capable of transporting hundreds of Mbps where VCs fill kbps. Thus, a large number of simultaneous channels have to be supported in a transmission link. Typically 10K simultaneous channels are considered (thus, VCI field up to 16bits).

• Since ATM is connection oriented, each connection is characterized by a VCI which is assigned at Call-Set-Up.

• When connection is released, VCI values on the involved links will be released or can be reused by other components.

VIRTUAL PATH / VIRTUAL CIRCUIT CONCEPT

VCI =1 (text)

VCI =2 (voice)

VCI =3 (video)

TRANSMISSION PATH

Text

Voice

Video

ATM Network Interface

Virtual Path

VP

VC

VIRTUAL PATH/VIRTUAL CIRCUIT CONCEPT

• Each VP has a different VPI value and each VC within a VP has a different value.

• Two VCs belonging to different VPs at the same interface may have identical VCI values.

• VPI is changed at points where a VP link is terminated.

• VCI is changed at points where a VC link is terminated.

Goal Multimedia Communication Video & Voice Time Sensitive (Delay bounds) Data Loss Sensitive (Loss bounds) Allows the network to add or remove

components during the connection

e.g. Video Telephony Start with voice (only single VC)

Add video later (on another VC)

Add data (on another VC)

Signaling (on another VC)

A B

T1 T2

T3

EXAMPLE

A B

p p2

q q2

r r2

• Three VP connections exist from A to B. They are seen by A as corresponding to the values p, q, r of the VPI field, and by B as corresponding to the values p2, q2, r2. Whenever A wants to send some information to B on the VP connection seen as p, it writes the value p in the VPI field of the cell.

• The VP switches T1, T2 and T3 swap the VPI labels according to the lookup tables. The VCI field is not changed by the VP switches, so it can be used by A to multiplex several VC connections on any one of the three VP connections. Therefore, at the VC level, A has at its disposal three direct links to B.

VP Level VC Level

p

p1

p2

q q2

r r2

SWITCHING OF VCs and VPs•Routing functions for VPs are performed at a VP switch.•This routing involves translation of the VPI values of the incoming VP links to the VPI values of the outgoing VP links. VCI values remain unchanged.

•VC switches terminate both VC links and necessarily VP links.•VPI and VCI translation is performed.

VP Switch/Cross Connect

VPI1

VPI2

VPI3

VPI4

VPI5

VPI6

VCI 21

VCI 22

VCI 23

VCI 24

VCI 25

VCI 24

VCI 23

VCI 24

VCI 25

VCI 24

VCI 21

VCI 22

VP Switching

VCI 23

VCI 24

VPI 2

VCI 25

VCI 21

VPI 4

VPI 5

VCI 23

VCI 24

VCI 25

VCI 21

VC Switch/Cross Connect

VP and VC SWITCHING

MORE ABOUT VCs and VPs

A VP Connection:•Contains multiple VC connections.•VC connections may be built up of multiple VP connections.•Use of VPI simplifies routing table lookup.

Virtual Channel Connection

A BTD1 D2 D3 D4

Virtual Path Connection x Virtual Path Connection y

VCI = a1 VCI = a2

VPI=x1 VPI=x3VPI=x2 VPI=y3VPI=y2VPI=y1

Virtual Channel View

A T B

VCI=a1 VCI=a1 VCI=a2 VCI=a2

Other VCI Other VCI Other VCI Other VCI

VCs and VPs (Cont.)• The inter-networking of the VP and VC switches is illustrated in Figure.

• There exist VP connections (x and y) between A and T; T and B.

• Assume now that A wants to setup a VC connection to B using those two VP connections.

• The network has to provide a VCI value, say a1, for the A to T link, and a VCI value, say a2, for the T to B link.

• The VC connection from A to B is thus made of two VC links only.

• At switching points D1 through D4, only the VPI field is swapped.

• At the switching point T, both VPI and VCI fields are swapped.

• The situation is thus similar to that where A and B would be access nodes in a circuit switched network, T would be a transit node, and D1 through D4 would be cross-connects.

ATMNode 1

ATMNode 2

ATMNode 3

A B

C

VPI=4, VCI=1,2,3

VPI=6VCI=3,4

VPI=2VCI=3,4

VPI=6VCI=1,2,3

VPI=6VCI=1,2,3

VPI=8VCI=3,4

26VPIOUTVPIIN

VPIOUTVPIIN

68

46 64VPIOUTVPIIN

Example for VCIs and VPIs• A VP is established between Subscriber A and Subscriber C

transporting 2 individual connections, each with a separate VCI.• Remark: The VCI values used (1,2,3 and 3,4 in the example) are NOT

translated in the switches, which are only switching on the VPI field.

Namings• VC

Virtual Channel Virtual Circuit

• VC Link A point where a VCI value is assigned to another where that value is translated or terminated.

• VC Identifier A value which identifies a particular VC link for a given VP Connection.

• VCC (Virtual Channel Connection) A concatenation of VC links that extends between 2 points. (cell sequence integrity preserved)

• VP

Bundle of VCs.

• VP Link

A group of VC links, identified by a common value of VPI, between a point where a VPI value is assigned and the point where that value is translated as terminated.

• VP Identifier

Identifies a particular VP Link.

• VPC (Connection)

A concatenation of VP Links.

PVC and SVC• Permanent Virtual Circuits (PVC)

Established by a network operator in which appropriate VPI/VCI values are programmed for a given source and destination (for long time).

VPs 0, …, 256 (manually configured)

PVCs are established by provisioning & usually last a long time (months/years).

• Switched Virtual Circuits (SVC)Established automatically through a signalling protocol (Q.2931B) and lasts for short time (minutes/hours).

VCs 0, …, 65535 (automatically configured)

SOFT PVC (addendum)• Part of the connection is permanent and part of

it is switched. • Hybrid of PVC and SVC!!!

• VCC 0 - 31• 0, 5 Call set up (Signalling)

• 0, 16 Network Management (Integrated Local Management Interface ILMI)

• 32 - 65535 User Data• 0, 17 For LAN Emulation Configuration Server

(LECS)

• 0, 18 For Private NNI (PNNI)• 0, 19 or 0, 20 Reserved for future use.

Advantages of VP/VC Concept• Simplified Network Architecture: Network transport functions

can be separated into those related to an individual logical connection (VC) and those related to a group of logical connections (VP).

• Increased Network Performance and Reliability: The network deals with fewer, aggregated entities.

• Reduced Processing and Short Connection Setup Time: Much of the work is done when the VP is set up. The addition of new VCs to an existing VP involves minimal processing.

• Enhanced Network Services: The VP is used internal to the network but is also visible to the end user. Thus, the user may define closed user groups or closed networks of VC bundles.