01- ATM Basic Overview

1 © NOKIA ATM Basic V 4.0 / Kittipong Thamapa

ATM BasicsATM Basics

ByBy

Kittipong ThamapaKittipong Thamapa


Network Transfer ModesNetwork Transfer Modes

•Synchronous Transfer Mode

•Packet Transfer Mode

•Asynchronous Transfer Mode


Synchronous Transfer ModeSynchronous Transfer Mode

• Derived from TDM technology

• Divides the physical bandwidth into logical timeslots

• Circuit switched networks (voice and leased lines)


Synchronous Transfer ModeSynchronous Transfer Mode

• Benefits:+ Fixed and guaranteed bandwidth+ Low and fixed delay+ Less delay variation (jitter)

• Drawbacks:– Waste of physical bandwidth in data networks– No over-subscription in the service provider network– Inflexible bandwidth, not ideal for bursty traffic

• Maximum number of connection equals maximum number of timeslots

• Ideal for uncompressed voice networks


Packet Transfer ModePacket Transfer Mode

• X.25 or Frame Relay technology• A DLCI identifies each virtual connection

( DLCI : Destination Link Control ID)


Packet Transfer ModePacket Transfer Mode

• Benefits:+ Less waste of physical bandwidth in data networks+ Over-subscription in the service provider network is possible+ Guaranteed bandwidth is possible (CIR) Committed Information Rate.

• Drawbacks:– No guarantees for delay and jitter

• Ideal for data networks with less demand of the quality of service

• Variable length and delivery of packets

• Flexible bandwidth


Asynchronous Transfer ModeAsynchronous Transfer Mode

• A compromise for voice, data, and video • QoS defined/negotiated when the initial connection is

made• Asynchronous on layer 2 of the OSI reference model• Compromise of STM and PTM

Voice Video Data

ATM cells

48-octet Payload

ATM 53-octet cells areswitched in hardware


Asynchronous Transfer ModeAsynchronous Transfer Mode

• Benefits:+ Over-subscription in the service provider network possible+ Guaranteed bandwidth, delay and jitter are possible+ Proven technology

• Drawbacks:– Most applications are based on IP instead of ATM– A lot of overhead for IP over ATM– Complicated protocol architecture

• Implemented in voice and data networks

• Transport layer in 3G networks


New world packet networks New world packet networks • Layer 1 to layer 3 in the OSI reference model• Layer 1:

– PDH or (Plesiochronous Digital Hierarch)– SDH/SONET (Synchronous Digital Hierarchy)

(Synchronous Optical Network, SONET)– DWDM optical (Dense Wave Division Multiplexing)

• Layer 2:– ATM – Frame Relay– PPP (Point to Point Protocol)– Ethernet

• Layer 3:– IP (Internet Protocol)


What is ATM?What is ATM?• ATM = Asynchronous Transfer Mode

• Fast packet switching and multiplexing technology (cell-based )

• Support the universe of services • voice, video and data traffic

• Provides quality of service guarantee and reliability

• Offers "bandwidth on demand"

• Connection-oriented, no error correction for user traffic• error correction for user traffic is handled by the end user• the advantages are increased speed of switching and elimination of associated delay

• Utilises statistical multiplexing• less bandwidth can be reserved than if bandwidth reservation would be based on the

peak rate of the connections.• transmission cost saving is achieved


Why ATM is a transport network in 3G?Why ATM is a transport network in 3G?

• ATM provides efficient support for transmission of voice, data, and video

• ATM provides QoS guarantee and reliability

• ATM utilises statistical multiplexing, so• less bandwidth can be reserved• transmission cost saving are considerable

• ATM supports the soft handover functionality


• For a group of bursty connections, less bandwidth can be reserved than if bandwidth reservation would be based on the peak rate of the connections

• Most of the traffic sources send bursty traffic and with a high probability all the sources do not simultaneously transmit at their peak rate

• One of the proposed advantages of ATM is that statistical multiplexing gain can be utilized

Statistical multiplexing gain

Statistical multiplexing Deterministic multiplexing

Requiredbandwidth Peak cell rate of

traffic type 1

Peak cell rate oftraffic type 2

Peak cell rate oftraffic type 3

Statistical Multiplexing GainStatistical Multiplexing Gain


ATM interfaces in 3G networkATM interfaces in 3G network

UNI User Network InterfaceNNI Network Node Interface

PSTNMGW MSCBSUE

A BIu-CSIubUu

UNI NNI

IP networkGGSN

Iu-PS

NNI

RNC

SGSN

RNCBS

BS

Iur

NNI

UNI

UNI

ATM is employed

Gn Gi


ATM Essential for 3GATM Essential for 3G• ATM Cell

• ATM Virtual Path (VP) and Virtual Channel (VC)

• ATM Adaptation Layer (AAL) (AAL2 and AAL5)

• ATM Layer Service Class (CBR,UBR)

• ATM Cross Connect

• Inverse Multiplexing for ATM (IMA)

• ATM over PDH and SDH

• Fractional E1 and Circuit Emulation Service (CES)


ATM cellATM cell

• Header contains routing and error control information

• Payload carries the actual user information, either voice, data or video

Header5 bytes

Payload48 bytes

53 bytes


ATM cellATM cell

GFC Generic Flow ControlVPI Virtual Path IdentifierVCI Virtual Channel Identifier

PT Payload TypeCLP Cell Loss PriorityHEC Header Error Control

User Network Interface (UNI) Network Node Interface (NNI)

VCI

GFC VPI

VPI

VCI

VCI PT CLP

HEC

123457 68

VCI

VPI

VPI

VCI

VCI PT CLP

HEC

123457 68

Payload Payload

Header(5 bytes)

Payload(48 bytes)

Provides local functions, such as identifying multiple stations that share a single ATM interface

The 1st bit - indicates whether the cell contains user data or control dataThe 2nd bit - indicates congestion

Indicates two levels of priority for ATM cells, CLP=1 should be discarded in preference to cells with the CLP=0


ATM cell headerATM cell header

• GFC provides local functions.

• VPI indicates the virtual path over which the cell should be routed.

• VCI identifies a virtual channel over which the cell is to travel.

• PT discriminates between a cell carrying management information or one, which is carrying user information.

• CLP indicates two levels of priority for ATM cells.

• HEC checks for an error and corrects the contents of the header by using a CRC algorithm.


Access ProfileAccess Profile

• VPI Length

• VCI Length

• total Bandwidth

How many VP and VC bit should be set ?

Note: VC = 0 not used and VC = 1- 31 are reserved for internal used


ATM in VP and VCATM in VP and VC

48 bytes

5 bytes

HEADER PAYLOAD

ATM cell (53 bytes)

Transmission path

Virtual Path (VP)

Virtual Channel (VC)ATM Cell

ATM Layer

HEADER

PAYLOAD


Advantages of Virtual Path ConnectionsAdvantages of Virtual Path Connections• Simplified network architecture

• Increased network performance and reliability• The network deals with fewer, aggregated entities

• Segregation of traffic• A form of priority control can be implemented by segregating traffic types

requiring different quality of service (QoS)

• Reduced processing and short connection setup time• New VCCs can be established by executing simple control functions at the

end points of the VPC; no call processing is required at transit nodes

– it can decrease the connection setup delay

• Enhanced network services• The user may define closed user groups or closed networks of VC bundles.


ATM Adaptation LayerATM Adaptation Layer

TypicalUse

FixedConnection

Video&

Audio

FrameRelay

IPServices

AAL AAL1 AAL2 AAL3/4 AAL5

Connection Oriented Connection oriented orconnectionless

Synchronised Not Synchronised

Constant VariableBit Rate

Source & Dest.

Connection

ATM LayerPhysical Layer

A B C DATM Service Classes

PBX

Video Voice Data

AAL


ATM layer functionsATM layer functions

Convergence Sublayer (CS)

PayloadPayload HeaderHeader

48 bytes5 bytes

User data

AAL

Segmentation and Reassembly Sublayer (SAR)

ATM Layer

Transmission Convergence (TC)

48 bytes

Physical Medium Dependent(PMD)

SD

H O

/H

PayloadHeader

Scramble frame and adapts the signals to the optical or electrical transmission medium

STM-1 Frame

Physical Layer


AAL2 (ATM Adaptation Layer 2)AAL2 (ATM Adaptation Layer 2)

String of AAL2 Packet Data Units String of AAL2 Packet Data Units

1 2 3 4 5 6

AAL2header

AAL2 is suitable for delay critical applications

ATM CELLHEADER

ATM CELLHEADER

HEADER = 5 BYTES

PAYLOAD = 48 BYTES

1 2 3 4 4 5 6

ATM cell

OFFSET FIELD, 1 byte (indicates where the next AAL2 PDU starts)

AAL2 PACKET, fixed header, variable length payload (max. 48 bytes)

ATM CELL, 5-byte header + 48-byte payload

PADDING


AAL5 (ATM Adaptation Layer 5)AAL5 (ATM Adaptation Layer 5)

PADDING FIELD, variable length to fill the 48-byte ATM cell

AAL5 PACKET, fixed trailer, variable length payload (max. 64 Kbytes)

ATM CELL, 5-byte header + 48-byte payload

AAL5 Packet Data Unit

USER DATA - Variable length 1 - 65 535 bytes

PAYLOAD = N x 48 BYTES

AAL5trailer

ATM cell 1 ATM cell 2………... ………..ATM cell n

AAL5 is suitable fo

r packet data

AAL5 Packet Data Unit

USER DATA - Variable length 1 - 65 535 bytes


ATM Layer Service ClassesATM Layer Service Classes

• CBR (Constant Bit Rate)

• VBR (Variable Bit Rate)

• ABR (Available Bit Rate)

• UBR (Unspecified Bit Rate)

Time

Bandwidth

Time

Bandwidth


ATM ATM SettingsSettings -- Traffic Descriptor (TRDE)Traffic Descriptor (TRDE)

In AXCLCI:11,VC:2,100; //INTERROGATE TERMINATION POINT

SEGMENT TRAFFIC SHAPINGI/F ID VPI VCI USAGE END POINT VP LEVEL----- ----- ----- ------ --------- --------

11 2 100 FREE NO NO

IN IN EG EGCDVT_PCR CDVT_SCR CDVT_PCR CDVT_SCR----------- ----------- ----------- -----------

334 USEC 334 USEC

IN SERV IN CONFOR IN IN IN QOSCATEGORY DEF EPD PPD CLASS-------- --------- --------- --------- ------CBR CBR1 DISABLED DISABLED C1

EG SERV EG CONFOR EG EG EG QOSCATEGORY DEF EPD PPD CLASS-------- --------- --------- --------- -----CBR CBR1 DISABLED DISABLED C1

IN IN IN IN IN INPCR_01 PCR_0 SCR_01 SCR_0 BURST_01 BURST_0----------- ----------- ----------- ----------- ----------- -----------

3000 CPS 1272 KBPS

EG EG EG EG EG EGPCR_01 PCR_0 SCR_01 SCR_0 BURST_01 BURST_0----------- ----------- ----------- ----------- ----------- -----------

3000 CPS 1272 KBPS

ADMIN EFF ADMIN EFF OPERSTATE STATE STATE-------- --------- --------UNLOCKED LOCKED

In RNC & MGW


VPI 1

VPI 2

VPI 3

VPI 4

VPI 5

VPI 6

VCI 1VCI 2

VCI 1VCI 2

VCI 3VCI 4

VCI 3VCI 4

VCI 5VCI 6

VCI 5VCI 6

Virtual Path SwitchingVirtual Path Switching

VPI 1

VPI 2

VCI 1VCI 2

VCI 1VCI 2

VPI 1

VPI 4

VCI 4

VCI 5VCI 6

VCI 3

VPI 5Port 1

Port 2

Port 3

Virtual Channel SwitchingVirtual Channel Switching

ATM Cross ConnectATM Cross Connect


ATM crossATM cross--connect (AXC)connect (AXC)

VC2 / VP2

VC1 / VP1

RNC

ATMswitch

VC1 / VP1

BTS 1

AXC

VC3 / VP3VC3, VC4 / VP4

VC3, VC4, VC5, VC6 / VP7VC5 / VP5

VC6 / VP6

VC1/VP1 THROUGH-CONNECTED IN AXC2

VC/VP CROSS-CONNECTION TABLEVC3/VP4 <-> VC3/VP 7VC4/VP4 <-> VC4/VP 7VC5/VP5 <-> VC5/VP 7VC6/VP6 <-> VC6/VP 7

AXC / ATM switch

BTS 2

AXC

BTS 3

AXC

BTS 4

AXC

BTS 5

AXC

BTS 6

AXC

StandaloneAXC


Iub NBAP SignallingIub NBAP Signalling• Common NBAP:

– Procedures to create new user equipment contexts

– Setup of first radio link of one UE– Selection of the traffic termination point– Cell configuration– Handling of RACH/FACH and PCH channels– Initialisation and reporting of cell or

NodeB measurement– Fault management

• Dedicated NBAP:– Addition, release and reconfiguration of

radio links for one UE context– Handling of dedicated and shared

channels– Handling of softer combining– Initialisation and reporting of radio link

specific measurements– Radio link fault management

RNCBS

Physical Layer Physical Layer

ATM ATM

AAL5

NBAP NBAP

Convergence Protocol(s) Convergence Protocol(s)

AAL5

Iub


ATM resource management IubATM resource management Iub

Phy

TTPATM

logical interface

VPLtpVPLtp

VCLtp

ATM logical interface

VPLtpVPLtp,

O&M traffic (UBR)

Signalling and user traffic (CBR)

VCLtp

VCLtp

VCLtp

VCLtp

VCLtp

VCLtp

VCLtp

VCLtp

VCLtp

Common NBAP link (C-NBAP)

Dedicated NBAP link (D-NBAP)

Dedicated NBAP link (D-NBAP)

AAL2 signalling link (AAL2SL)

AAL2 signalling link (AAL2SL)

AAL2 user plane link (AAL2UD)



VCLtp

VPLtp


VCLtp

VCLtp

VCLtp

VCLtp

VCLtp

VCLtp

VCLtp

VCLtp

VCLtp

RNC

WAM

WAM

Phy

TTP

O&M / Usage IPOAM


ATM connection TableHW VPI VCI

x x x

VCI

x

VPI

x

HW

x

CIF1CIF1CIF1CIF1

Term-1Term-1Term-1

0000

36333435

120567240

1111

IFUAIFUAIFUAIFUA

Term-2Term-2Term-2

VCI 36

VCI 30

AXU

Private IP addresses

LMP

IFUA

PDH, IMA or SDH

CIF 1 VCI 56 CNBAP

VPI 1(CBR)

VPI 0 (UBR)VCI 32 O&M

Transmission Convergence Adaptor

VPI 4

VPI 0

BTS_ID =1

C-NBAP

O&M

D-NBAP

AAL2 UP

AAL2 sig

WAM 2

O&M Master WAM

VCI 33

VCI 34

VCI 35

VCI 120 AAL2UP

VCI 72 DNBAP

VCI 40 AAL2SIG

IP router

C-NBAP only forTelecom Master WAM

Iub ATM Transport Layer (Example)Iub ATM Transport Layer (Example)


Iub cIub crossross connections in connections in AXCAXC

AXUIFUCslot 2if 1

STM-1CIF 1

VCI 120

VPI 1

VCI 56

BTS

WAM 2

VCI 72

VCI 40

AXC

VCI 36

VPI 0

CNBAP

AAL2UP

VCI 33

VCI 34

VCI 35

Name VPI VP PCR [cells/s]

VCI VC PCR [cells/s]

VPI VP PCR [cells/s]

VCI VC PCR [cells/s]

Service Category

CNBAP 0 58726 33 300 1 4528 56 300 CBRDNBAP 0 58726 34 150 1 4528 72 150 CBR

AAL2SIG 0 58726 35 150 1 4528 40 150 CBRAAL2UP 0 58726 36 3618 1 4528 120 3618 CBR

DNBAP

AAL2SIG


Views inside AXCViews inside AXC--ManagerManager


Creating Creating Cross Cross ConnectionsConnections


• Problem ?: More bandwidth than 2 Mbit/s is needed, but only T1/E1 services are offered by the carrier

PBX PBX

ATM E1 based

Inverse Multiplexing for ATM (IMA)Inverse Multiplexing for ATM (IMA)

PBX PBX

ATM

E1 based

Multiple T1/E1s are bundled for more bandwidth

Solution IMASolution IMA


Tx direction: cells distributed across links in round robin sequence

Rx direction: cells recombined into single ATM stream

Physical Link #0

Single ATM Cell Streamfrom ATM Layer

IMA Virtual Link

IMA Group

PHY

PHY

PHYPhysical Link #1

Physical Link #2

IMA Group

PHY

PHY

PHY

Original ATM CellStream to ATM Layer

Concept of IMAConcept of IMA• Low bit rate transmission lines can be combined into a group that seen

as a single virtual link by ATM• IMA sublayer is part of the physical layer.• It is located between the traditional Transmission Convergence sublayer and the ATM

layer.


Inverse multiplexing for ATMInverse multiplexing for ATM

ATM Layer

Physical Medium Sublayer

Transmission Convergence Sublayer (TC)Physical Layer TC

IMA

• Iub IMA max 8 E1• Iur IMA max 16 E1• All E1 in IMA have to belong to same NIP or IFU• Only one ATM interface/ IMA group• Only one ATM interface per exchange terminal• NIP1 can have up to 16 ATM Interfaces


ATM over SDHATM over SDH

VC-4

OVERHEAD

STM-1 (155,52 Mbps) can fit 44.15 cells per frame -> 353 207 cells per second.

VP1

VP2

VP3

.

.

.


ATM cell mapping into PDH 2048 kbps

• PDH frame structure for 2048 kbps is describedin ITU-T Recommendation G.704

• ATM cell is mapped into bits 9 to 128 and bits 137 to 256(i.e. time slots 1 to 15 and time slots 17 to 31)

• Time slots 0 and 16 are not used for ATM cell

•Nokia AXC supports however only contiguousmapping starting from time slot 1!

<- Bits 1 to 8 ->

<-Tim

e slots (TSs) 0 to 31 ->

Bit 1 Bit 8Bit 9 Bit 16

Bit 121 Bit 128Bit 129 Bit 136Bit 137 Bit 144

Bit 249 Bit 256

Available for ATM cell


TS 1TS 0

TS 30TS 31

ATM over PDH


ATM over E1ATM over E1

Header Payload

0 1 2 16 1817 3115

TS0TS1-15

TS16TS17-31

. . . . . . 0 1 2 16 1817 3115

TS0TS1-15

TS16TS17-31

. . . . . .

E1 frameE1 frame


ATM cell mapping into PDH 2048 kbps

Example Bit 1 Bit 8Bit 9 Bit 16


Bit 249 Bit 256


Bit 249 Bit 256


•• 3G 3G ATM ATM Traffic SharingTraffic Sharing GSM 2M GSM 2M FrameFrame

MetroHubMetroHub

GSMBTS

GSMBTS

WCDMABS

WCDMABS RNCRNC

BSCBSCTDM

Fractional E1

Fractional E1


Fractional and non fractional E1's Fractional and non fractional E1's

RNC

BSC

ET

COMMONTRANSPORTON MICROWAVE

E1's for 3G BTS

WSP WSP WSP

3G BTS AXC

...

WAM

WSP WSP WSP...

WAM

IFU E

ATMSWITCH

•••

•••

• One or several, fractional or non fractional E1's

Non fractional E1Fractional E1 shared with 2G BTS

MetroHub

FXCRRI

FXCE1/T1 NIU

FB1

2G BTSTRX

TRX

TRX

TRX

TRX

TRX

TRUA

RRIC

D-bus

FB2

LIF2

LIF3

FB1

RAN1Phase 1.5


Fractional E1Fractional E1

- Fractional E1 means that some timeslots are not used for ATM traffic (configurable by management), TS0 and TS16 are not allowed by default

- using only three timeslots provides a 192 kbit/s transmission path for ATM traffic- long transmission delays for ATM traffic!

TS0 TS0

fractional E1termination point

fractional E1termination point

3 octets of the ATM cell 3 octets of the ATM cell

53 octets per ATM cell

RAN1Phase 1.5


TDM links with Fractional E1/JT1TDM links with Fractional E1/JT1• Physical link can be Fibre, Microwave, leased service, ...• BTS site:

•WCDMA BTS connected to GSM Abis•WCDMA BTS supports ATM over Fractional E1

• BSC/RNC site:•TDM traffic (GSM + WCDMA) separated by TDM cross-connect Hub•Possible, not earlier groomed, Fractional E1 traffic is terminated with a standalone AXC

GSM BTS

WCDMA BTS

TDM link (PDH/SDH)HUB BSC

RNC

Combined Abis and Iub

TDM crossconnect function (n x 64 kbits/s)

Fractional E1 (partly filled) (n x 64 kbits/s)

Fractional E1

Fractional E1

Full E1 Full E1


ATM cell mapping into FRACTIONAL PDH 2048 kbps

• PDH frame structure for 2048 kbps is describedin ITU-T Recommendation G.704

• ATM cell is mapped into bits 9 to 128 and bits 137 to 256 (i.e. time slots 1 to 15 and time slots 17 to 31)IF they are not reserved for 2G traffic

• Time slots 0 and 16 are not used for ATM cell

• In general any mapping for fractionality is allowed i.e. any mapping of "allowed" time slots, both contiguous or non-contiguous

• Nokia AXC supports however only contiguousmapping starting from time slot 1!

<- Bits 1 to 8 ->

<-Tim

e slots (TSs) 0 to 31 ->

Bit 1 Bit 8Bit 9 Bit 16


Bit 249 Bit 256



TS 1TS 0

TS 30TS 31

Reserved for 2G traffic


GSM GSM Traffic Over Traffic Over ATM ATM

SAXC orWCDMABTS-AXC

SAXC orWCDMABTS-AXC

GSMBTS

GSMBTS

WCDMABS

WCDMABS RNCRNC

BSCBSC

ATM

CES

Circuit Emulation Service (CES)


Circuit EmulationCircuit Emulation

RNC

BSC

ET

E1 from 2G BTS

ATMSWITCH

Non fractional E1

AXCIFU A

NIU

2G BTSTRX

TRX

TRX

TRX

TRX

TRX

TRUAD-bus

LIF1

WSP WSP

3G BTS AXC

...

WSP WSP...

IFU A

IFU EWAM

WAM

•••

•••

CESIWF

Flexbus connection

••

E1

VCC

VCC

VCC

VPC

AXU

CESIWF

VCC

VCC

VCC

VPC

IFU E


Unstructured Circuit Emulation Service Unstructured Circuit Emulation Service

- Transmitting CES interworking function takes the E1 signal and segments that stream into ATM cells

- ATM cells are transported via a CBR VCC to the receiving CESinterworking function

- receiving CES interworking function recovers E1 signal from the ATMcell stream

- Note: CES works bidirectional

CESInterworking Function (IWF)


TS0 TS0 TS0 TS0

G.703 frames

RAN1.5


Structured Circuit Emulation ServiceStructured Circuit Emulation Service

- Transmitting CES interworking function takes only some timeslotsfrom the E1 signal puts these into ATM cells

- ATM cells are transported via a CBR VCC with lower bandwidth compared tounstructured CES to the receiving CES interworking function

- receiving CES interworking function recovers TS from the ATM cell stream- Note: CES works bidirectional- Management configures which timeslots are transmitted

CESInterworking

Function (IWF)


TS0 TS0 TS0 TS0

TS1-TS3

RAN2

01- ATM Basic Overview

Documents

Transcript of 01- ATM Basic Overview