1. INTRODUCTION

NETWORK PARADIGMS

ATM LANSGigabit Ethernet ATM

Voice,Image,Video,Data

Fast EthernetFDDI

Ethernet/Token Ring/Token Bus

Frame Relay

X.25

LAN MAN/WAN Distance

Bandwidth(Mbps)

1000

100

10

1

SMDS(DQDB)

NETWORKING EVOLUTION

Traditionally Disjoint Networks

• Voice Telephone networks• Data Computer networks and LAN• Video Teleconference Private corporate networks• TV Broadcast radio or cable networks

* These networks are engineered for a specific application and are ill-suited for other applications, e.g., the traditional telephone network is too noisy and inefficient (capacity limited) for bursty data communication.

* Data networks are not suitable for voice and video traffic because they cannot satisfy the time-sensitivity of these traffic types.

PSTNX.25

Internet

PBX LAN

Voice Data

WIDEAREA

LOCAL

Old Fashioned

Before Integration

WIDEAREA

LOCAL

B-ISDNA SingleUnifying

Technology

Video, Image, Voice and Data

Broadband ISDN

After Integration

1.6-64 kbps => Narrowband1.5-45 Mbps => Wideband> 45 Mbps => Broadband

GOAL INTEGRATION

GOAL INTEGRATION

Source Destination

(One Network Carrying Multimedia Traffic)

BroadbandIntegrated Services Network

(Data, Voice, Video, Still Image)

• WHY INTEGRATION?

Voice Traffic (based on AT&T data, 1993)

125 to 130 Million Calls/day x 5 min/call x 64 kbps = 28.8 Gbps= 1 / 1000th of fiber capacity

GOAL INTEGRATION

Updated statistics for 1998• Average calls per business day = 272.2 million• Average calls per day = 226.2 million• Average length per business call = 2.5 min.• Average length per consumer call = 8.0 min.

Suppose 200 Million x 24 hours/day x 64 kbps = 12.8 TbpsBottomline: Gigantic Capacity of fiber cannot be utilized only by Voice Traffic!!!

FURTHER REASONS:• Convergence of computer and communications technologies• Integration could offer efficiencies (lower cost) and support of new applicatons• Single network management & maintenance• No duplication of cables, plants (since one physical network) => Less costs

INTEGRATION PROBLEMS

Integration is not easy because different applications have different performance requirements.

TelemetryTelecontrolTelealarmVoiceTelefax

Low SpeedData

Hifi Sound MediumSpeed Data

Video Telephony High SpeedData

High Quality VideoVideo LibraryVideo Education

Very HighSpeed Data

INTEGRATION PROBLEMS

•Voice

•Video

•Data

•Still Image

• 64 Kbps (Bandwidth Demand)• 2 min. (End-to-End Delay on the Average) (Request-Transfer Cycle)

• > 140 Mbps (BW Demand)• 60 min. (E2E Delay on the Average)

• Extremely variable (BW Demand)• Extremely variable (E2E Delay on the Average) e.g., long “telnet” sessions; short “finger” requests

• 1-50 Mbps (BW Demand)• 1 Sec. (E2E Delay on the Average)(Cannot be seen as data traffic because it may have real-time nature, e.g. medical image retrieval; geographic databases)

ATM NETWORKS

Asynchronous Transfer Mode (ATM):

A new multiplexing and a new switching

technique to realize the

Broadband Integrated Services Digital Networks (B-ISDN)

Asynchronous: Packet transmission is not synchronized to a global (network) clock!!!

Multiplexing

Defines the means by which multiple streams of information share a common physical transmission medium.

Demux.

Sources

Mux.Physical Link (Channel)

NShares single output between many inputs.

Sinks(Destinations)

Demux has one input which must be distributed among outputs.

Multiplexing Techniques

Multiplexing Techniques

Frequency DivisionMultiplexing

Time DivisionMultiplexing

Synchronous TDM Asynchronous TDM(Statistical Multiplexing)(STM)

(ATM)

STM Circuit Switching used for Telephone Networks (also for N-ISDN) (Time Division Multiplexing) (Classical TDM)

Information is transferred with a certain repetition frequency.e.g., 8 bits every 125sec for 64kbps 1000 bits every 125sec for 8Mbps

From Nyquists Sampling Theorem4kHz voice signal requires 8000 samples/sec 8 bits/sample

One 8 bit sample every 125sec = 64kbps (Golden Rule of Tel. Networks) (DS0 Channel)

Basic unit of repetition frequency is called a TIME SLOT.

STM

Each slot is assigned to a particular call. The call is identified by the position of the slot. When the user is assigned a slot, it owns a circuit. The user uses the same slot within consecutive frames. If a user is not transmitting data in its own slot, that time slot remains reserved (nobody else can transmit there).

Time Slot

Start of each Frame

Periodic Frame (one cycle)

L sec ( bits can be transmitted)

1 12 2. . . . . .n n . . .

STM

ATM — In ATM, the MUX takes a packet (one or more packets) & appends a header (5 Bytes) and transmits based on statistical characteristics of the sources. MUX can take according number of cells from a source & transmit.

Video

Voice

Data

Video

1

2

3

4

5

Header 11 3121 41 42

Physical TrunkMUX

ATM

e.g., from a video source 10 cells can be taken, while from voice source 1 cell because of their bandwidth demands.

Each packet must have a header (control information)!!

No SYNCHRONIZATION!! (No network clock!)

ATM

STM vs. ATMSimple Example:

1 2 3 2 3 4 5 1 3 5ATM

1 2 3 I I I 2 3 4 5 1 I 3 I 5STM

4 5 1 2 41 cycle 1 cycle 1 cycle

1 Bit 1 Bit1

1 Bit 1 Bit2

1 Bit 1 Bit 1 Bit3

1 Bit4

1 Bit 1 Bit5

Sources

STM vs. ATM

STM (Synchronous Transfer Mode)

Channel1

Channel2

ChannelN

Channel1

Channel2

ChannelN

. . . . . .

Time Slot

FRAME (Cycle) FRAME (Cycle)Frame Header

ATM (Asynchronous Transfer Mode)

Channel1

Channel5

Channel1

Channelunused

Channel7

Channel5

Channel2

HeaderData (cell)

. . .

STM vs ATM

ABCD

Users t0 t1 t2 t3 t4

To Network

First Cycle

First Cycle Second Cycle

Second Cycle

A1 B1 B2 C2

Wasted Bandwidth

Extra BandwidthAvailable

Synchronoustime-divisionmultiplexing

Asynchronous Statisticaltime-divisionmultiplexing

Data Address

D2A2D1C1

A1 B1 B2 C2

(STM) (ATM)

MUX (Multiplexer)

STM

Advantages No overhead in

packetization. Constant repetition of frames

low delay jitters. Easy to maintain

synchronization between sender & receiver.

Disadvantages Limited flexibility

i) BW (bandwidth) allocation at 64kbps modularity

ii) Inefficient for VBR (Variable Bit Rate) traffic

Long connection set-up delays.

Complex switching system.

ATM Advantages

Flexible BW-Allocation (sources with widely different bit rates).

i) Accommodate bursty sources (e.g., VBR)ii) Asymmetrical link bandwidths

A wide range multimedia traffic types. High efficiency due to statistical multiplexing. Allows Quality of Service (QoS) guarantees. Simple routing (small buffers). Simple switching.

High BWLow BW

ATM Disadvantages

Overhead for cell header.48 + 5 (bytes) 40Bits overhead 10% overhead

Requests fast switching technology (need new switches).

Complex scheduling algorithms needed. Connection set-up & signaling overhead. Traffic management problem. Difficult to reroute virtual circuits. Jitter problem.

SWITCHING TECHNIQUE

Takes multiple instances of a physical transmission medium containing multiplexed info streams and rearrange the info streams between input & output.

In other words, information from a particular physical link in a specific multiplex position is switched to another output physical link.

SWITCHING TECHNIQUE

… …

1

2

N M

2

1

Switch

Ports Fabric

Inlets = Inputs Outlets = Outputs

Switch Architectures Single Bus Self-Routing (Blocking) Multiple Bus Self-Routing (Non-Blocking Queueing - Internal Queueing

- Input Queueing- Output Queueing

(Shared Buffer Theoretically optimal Achieves maximum throughput!)

Actual ATM switches have combination of input, output, and internal queueing.

The way how these functions are implemented, where in the

switch these functions are located, will distinguish one switching solution from another.

Question :Why could existing switch architectures(circuit-switches for voice, packet-switches for data )NOT be used for ATM ?

Reasons :

1. High speed at which the switch must operate (155-622 Mbps; now on Gigabit levels)2. Statistical behavior of ATM streams passing through the switch3. ATM has small fixed cell size & limited header functionality

SWITCHING

ATM SWITCHING

Combines Space & Time Switching Principles!!

xyz

w x

zwy1

23

N N

321Switch

Inlets Outlets

… …

Space (Rerouting) Switching

Switch

Inlet Outlet

Time Switching

x y z wt y x z tw

ATM Basic Switching Principle

Switch

… …a b b

d c a

data Header

e b c

Cell

p k q

y y p

r y k

I1

I2

Ij

O1

O2

On

t

data

Header / link

translation table

Incoming Headers

Outgoing Headers

Routing Table

Incoming Link

Outgoing Link

HeaderHeader

…

acd

pkq

kyr

cbe

I1

Ij

O1

On

Translation Table

ATM Switching

• All cells which have header a or (c or d …) on incoming I1 are switched to O1 and their header is translated (switched) to value p or (k or q …).

• All cells with a header c (or b or e) on link Ij are also switched to outlet On, but their header gets values k (or y or r).

Remark: On each incoming & outgoing link individually, the values of the header are unique, but identical headers can be found on different links, e.g., c on link I1 and Ij.

Realization:

• Routing info is contained in the header (label), not explicit address.

• Explicit addressing is not possible because of short fixed size cell.

• A physical Inlet/Outlet, characterized by a physical port number.

• A logical channel on the physical port characterized by a VCI and/or VPI.Routing Tables Must be set up in advance (signaling phase)

Either pre-defined or dynamically allocated

SwitchVCIbVPIa

HeaderVCIyVPIx

Header

Input Port P Output Port Q

Routing Info: Input Port VPI VCI Output Port VPI VCI

P a b Q x y

Basic Functions Space Switching (Routing)

Header Switching

Queueing

Why Queueing?Suppose 2 cells from different Inlet (I1 & In) arrive simultaneously at ATM switch and are destined to the same outlet O1.

Thus, they cannot be put on the output or the outlet at the same time buffering, i.e., to store the cells which cannot be served. (No pre-assigned time slots, statistical multiplexing)Remark: The way these 3 functions are implemented, where in the switch these functions are located, will distinguish one switching solution from another.

ATM SWITCHING

ATM NETWORK

Host

ATMSwitch

Host

ATMSwitch

ATMSwitch

ATMSwitch

NNI

NNI

UNI

NNI

UNI

Backbone Network

ATM CELL STRUCTURE

• Octets are sent in increasing order 1,2,3 …• Within an octet the bits are sent in decreasing order 8,7,6,5,4 ...

1

2

3

4

5

:

:

53

8 7 6 5 4 3 2 1

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

User Network Interface (UNI)Cell Structure

Network Network Interface (NNI)Cell Structure

GFC

VCI

VPI VPI

VPIVPI VCI

VCI

VCI

VCI

VCI PT PT PRPR

HEC HEC

PAYLOAD(48 octets)

PAYLOAD(48 octets)

GFC : Generic Flow ControlVPI : Virtual Path IdentifierVCI : Virtual Channel IdentifierPT : Payload TypePR : PriorityHEC : Header Error Control

ATM Interfaces

UNI / NNIHost

ATMSwitch

Host

ATMSwitch

ATMSwitch

ATMSwitch

NNI

NNI

UNI

NNI

UNI

Backbone Network

ATM Network Interfaces (Detailed)

computerPrivate Switch

Public Switch

Public Switch

Public Switch

Public Switch

private

UNI

public

UNI

Public

NNIIntersystem Switching

Interface (ISSI)

Regional Carriers (Intra-LATA)

(Local Access & Transp

Area)

Long Distance Carrier

B-ICI (Broadband Inter-Carrier

Interface)

(Inter LATA ISSI) B-ICI

computer Private Switch

private

UNI

computer Router Digital Service

Unit

Public

UNI

DXI

DXI: Data Exchange Interface, between packet routers & ATM Digital Service Units (DSU)

Private NNI (P-NNI)

Generic Flow Control (GFC) (4 Bits) (only at UNI)It provides flow control information towards the network. It allows a multiplexer to control the rate of an ATM terminal. Currently, no standard. 0’s are used for this field. Routing Field (VPI/VCI)24 Bits (8 Bits for VPI, 16 for VCI) at UNI.28 Bits (12 for VPI, 16 for VCI) at NNI.VPI/VCI have only local significance only; they identify the next destination.

Remark: Each physical UNI to support not more than 28=256 VPs. NNI 212 = 4096 VPs. Each VP can support 216 = 65,636 VC on UNI and NNI. Payload Type Field (PT) (3 Bits)PT indicates whether the cell contains users data, signaling data or maintenance information. Cell Loss Priority (CLP) (1 Bit)CLP indicates the priority of the cell. Lower priority cells are discarded before higher priority cells when congestion occurs.

Remark:If CLP =1 Cell has low priority dropped in heavy load.If CLP =0 Cell has high priority not discarded. Header Error Control (HEC) (8 Bits)HEC detects and corrects errors in the header. (i.e., single Bit Error Correction or Multiple-Bit Error Detection). The info field is passed through the network intact, with no error checking or correction. ATM relies higher protocols for this purpose.

ATM Cell

PAYLOAD TYPE (PT)

First Bit 0 User Information

First Bit 1 Network Management or Maintenance Function

Second Bit Whether CONGESTION has been experienced or not.

Third Bit known as AAU (ATM-User-to-ATM-User) used in AAL5 to convey information between end users.

Contents: [EFCI (Explicit Forward Congestion Indication)]

0 0 0 User Data Cell; Congestion No (EFCI=0); AAU=0

0 0 1 User Data Cell; Congestion No (EFCI=0); AAU=1

0 1 0 User Data Cell; Congestion Yes (EFCI=1); AAU=0

0 1 1 User Data Cell; Congestion Yes (EFCI=1); AAU=1

1 0 0 Segment Operation and Maintenance (OAM) (F5) Cell

1 0 1 End-to-End (OAM) Flow F5 Cell

1 1 0 Resource Management Cell

1 1 1 Reserved for Future Function

ATM CELL

Pre-Assigned (Pre-Defined) (Reserved) Header Values

Cell Types

• Idle Cell: Inserted and extracted by PHY in order to adapt the cell flow rate at the boundary between ATM layer & PHY layer to the available payload capacity of the transmission system.

• Valid Cell: has a header with no error or which has been corrected by the HEC verification process.

• Invalid Cell: has a header that has errors that have not been modified by the HEC verification process (discarded at PHY layer).

• Assigned Cell: provides service to an application using ATM layer service.

• Unassigned Cell: Not an assigned cell. Does not contain any useful information.

Cell Types (Cont.)

AssignedCell

UnassignedCell

SAP

Idle Cell ValidCell Invalid Cell

Network

Idle Cell

AssignedCell

UnassignedCell

Source Destination

ATM Layer ATM Layer

PHY Layer PHY Layer

Upper Layers Upper Layers

Trash

SAP

Difference Idle Cells vs. Unassigned Cells

Unassigned Cells Visible to ATM & PHY layer.Idle Cells Visible only to PHY layer not to ATM layer.

Unassigned Cells are sent whenever there is no information available at the sender. It allows full asynchronous operation of sender/receiver.

Idle Cells are inserted by the PHY layer in order to match the transmission rate to the transmission system or for other PHY layer purposes. Octet 1 Octet 2 Octet 3 Octet 4 Octet 5

0 . . . 0 0 . . . 0 0 . . . 0 0 . . . 0 0 . . . 0

Each octet of Info. field of an “idle cell” is filled with 01101010.

Cell Types (Cont.)

The Size of the ATM Cell(WHY 48 + 5 = 53 BYTES?)

1. Transmission Efficiency2. Delays3. Implementation Complexity

1) Transmission Efficiency

L

L

where L is the information size of the packet in bytes and is the header size of the packet in bytes.

x

L8 16 32 64 128

x5060

70

80

90

100

x

x x

x

xx x

Transmission

Efficiency

The longer the info. field, the higher is the efficiency for the same header size.A header of 4 or 5 Bytes is typical value for ATM cell.(Assumption: All packets are completely filled.)

Packetization Delay (Segmentation)

Transmission Delay (depends on the distance between both endpoints). (Range 4-5sec per km; depends on the transmission medium).

Switching Delay

Queueing (Buffering) Delay

Depacketization Delay (Reassembly)

Queues are necessary to avoid massive loss of cells. Delay varies with the load of the network and is determined by the behavior of queues.

Conclusions:

* The queueing delays increase with the size of information field.

* The end-to-end delay must be below 24 ms to avoid ECHO problems for voice traffic!!!

2. DELAYS

Transmission of 64 kbps voice traffic over ATM.

Voice signal is sampled 8000 times per second, which gives rise to 8000 bytes/sec or 1 byte every 125 usec.

* If the packet size is 16 bytes, then it will take (16*125) usec or 2ms to fill up a packet.

* If the packet size is 64 bytes, then it will take (64*125) usec or 8ms to fill up a packet.

So the smaller the packet size, the less the delay to fill up a packet.

The packetization delay could be kept small if a packet is partially filled; however, this will lead to under-utilization of the network capacity.

EXAMPLE: [Packetization Delay (Segmentation)]

The longer the packet, the more time the switch has to do the header conversion.

Consider an ATM switch with OC-3 capacity, i.e., 155 Mbps.

If the cell size is 53 bytes, then a maximum of about 365 566 cells can arrive per second. This translates to 2.7 usec per cell, i.e., assuming that cells arrive back-to-back, a new cell arrives approximately every 2.7 usec. This means that the switch has 2.7 usec available to carry out the header conversion.

Suppose a cell size of 10 bytes. A maximum of about 1 937 500 cells can arrive per second, i.e., if cells arrive back-to-back, a new cell arrives approximately every 0.5 usec. The switch has then only 0.5 usec for the header conversion.

EXAMPLE: [Time for Header Conversion]

Two parameters play a role in determining the complexity of a system:

• The speed [Transmission (Processing) Time (P) = (Cell Size/Data Rate) ]• The number of required bits (MEMORY: M)) = The number of cells (BUFFER SIZE IN CELLS) multiplied by the (CELL SIZE).

Tradeoff Memory Size and Processing Speed

To guarantee a certain limit on the cell loss ratio, a number of cells must be provided per queue. This number is independent of the cell size. So the larger the cell size, the larger the queue in bits will be (e.g., doubling the cell size will also double the memory requirements).

3) Implementation Complexity

On the other hand, for every cell, the header must be processed. This processing must be performed in one cell time, so the longer the cell size, the larger the available time and the lower the speed requirements of the system.

In Figure we show the speed and memory size in function of the cell size, if the system operates at 150 Mbps and if the queue is dimensioned for 50 cells (the header is 4 Bytes).

32

16

8

4

2

8000

16000

32000

64000

M (memory size in bits)

P (processing time per cell in s)

P

M

16 32 64 128 256 cell size

IMPLEMENTATION COMPLEXITY

Explanation of the FIGURE:Assume 50 Cells; Cell Size: 16 + Header: 4 = 20 Bytes (Low)

Cell Size: 256 + Header: 4 = 260 Bytes (High)

Memory (M) =

= Cell Size * Buffer Size in Cells = 20*50 = 1000 Bytes = 8000 Bits (Low)

= 260*50=13000 Bytes=104000 Bits (High)

Processing Speed (P) =

Transmission Time = {Cell Size}/{Data Rate}=160 Bits/{150*10^6 bps} ~ 1 musec (L)

=2080/{150*10^6 bps} ~ 13.8 musec (H)

1. We see that for a cell of 16 bytes, we need only about 8000 bits for the memory, but the header processing of each cell must be performed in less than 1 sec.

2. For a cell of 256 bytes, we need already more than 64,000 bits for a single queue. But we have about 15 sec for the header processing of a single cell.

3. However, as seen in Figure, the speed is not the most critical issue, since in 1 sec (in case of 16 Bytes) HIGH processing can be achieved; so the limiting factor is the memory space requirement.

FINALLY – THE RESULT:

Contradicting factors are contributing to the choice of the cell size. However, a value between 32 and 64 bytes is preferable.

Europe was in favor of 32 bytes (because of the requirement for echo cancellers for voice) where US and Japan were in favor of 64 bytes because of higher transmission efficiency.

Finally ==> a compromise of 48 Bytes reached at CCITT meeting in June 1989.

Variable vs. Fixed Length Packets

Facts to consider in decision

– Transmission Bandwidth Efficiency

– Achievable Switching Performance

(i.e., the switching speed vs. complexity)

– The Delay

Transmission Bandwidth Efficiency

Fixed Packet Length,

where Number of useful information in bytes Information Size of the Packet in bytes Header size of the packet in bytes represents the smallest integer larger than or equal to

Bytes Overhead ofnumber The

)( Bytesn Informatio ofnumber The

L

L

)( HLLXX

F

F

XLHz z

This efficiency is optimal for all information units which are multiples of the packet information size, i.e.,

Optimal Case (Substitute the above value into the prev. one)

XLL

X

HL

LOPTF

has a sawtooth shape (Opt. L=48;H=5)F

48 96 144 192 240 288 336 X[number of useful

information bytes]

100

90

80

70

60

50

40

30

20

10

% Transmission Efficiency

OPTF

Fixed Length

Variable Length

F

V

The efficiency depends very much on the useful information bytes to be transmitted

If the number of useful information bytes is large, the optimal achievable efficiency is approached

Only if the number of useful information bytes is small, this efficiency is rather low.

So, the distribution of the number of useful information bytes to be transmitted largely determines the efficiency.

Voice: – Since voice is a CBR (Constant Bit Rate) service, we

can take the option at the sending terminal only to transmit a packet when it is completely filled (therefore, introducing a packetization delay).

– So, the efficiency can reach the optimal achievable value, if packets are completely filled which then puts limitation on the packet size in order to limit the packetization delay.

Different Applications

Video: • Where fixed bit rate video coding techniques are

used, this service can be considered as a CBR service, again reaching the optimal efficiency

• Where variable bit rate video coding techniques are used, it may occasionally happen that packets are not completely filled.

• However, a typical video image contains thousands of bytes, so the optimal achievable efficiency will be very closely approached.

Different Applications

Data: • Distinguish low speed and high speed data.• Low speed applications, e.g., keyboard input:

small information units must be considered, so the efficiency is rather small (around 10%)

• High speed applications, e.g., file transfer, image transfer for CAD, etc: the very long information field (e.g., file, image, etc) can be sent into fixed packets giving rise to an efficiency very close to the optimal efficiency,

e.g., for 1000 bytes, the efficiency is 89%, instead of an = 90.5% in the figure)

OPTF

Different Applications

Remark: •Since traffic in a broadband network will largely be composed of video, high speed data, and voice, the overall transmission efficiency approaches the optimal, even if fixed length packets are used.

Here the overhead is determined by the header and the flags to delimit the packets, e.g., 6 bits in HDLC, plus in addition, some stuffing bits to ensure proper flag recognition.

Also, add to the header, a length indicator, determining the length of the packet

where is the specific packet header overhead mentioned above

vv hHX

X

vh

Variable Length Packets

In Figure, we assume 5 bytes and 2 bytes of . We see the transmission efficiency can be very high (close to 100%) for very long packets

Remark: For practical reasons such as buffer dimensioning, delay, the max variable length packets must be limited to a certain threshold.

vh

H

– The transmission efficiency of variable length packets is better than that of fixed length packets

– However, in broadband networks, this gain of transmission efficiency is rather limited since the main traffic constituting broadband services will consist of a combination of voice, video, bulk data transfer.

CONCLUSIONS

SWITCHING SPEED AND COMPLEXITY

Two factors for complexity of ATM switch implementation

• Speed of Operation• Queue Memory Size Requirements

A) Speed of Operation

Header processing

Let us assume that header functions are the same for fixed and variable length case. For fixed length packets, available time to perform all functions is fixed, (e.g., 2.8 sec in the 48 + 5 bytes solution at 150 Mbps.)

For variable length packets, the available time depends on the worst case (i.e., the smallest packet), so the speed requirements are much higher (e.g., to perform same functions for a 5 + 5 byte packet at 150 Mbps only 553 ns are available.).

SWITCHING SPEED AND COMPLEXITY

B) (Queue) Memory Management

Variable Length Packets Memory management system must be able to assign memory stocks in multiples of bytes so that algorithms like “find best fit”, “find first fit”,…, can be used. Memory management is complex.

CONCLUSION: Regarding “speed of operation” and “queue memory size”“Fixed Length Packet Size” is preferred!!!!In 1988, fixed packet size has been accepted for ATM.

Fixed Length Packets Memory management system can assign memory stocks with the same size, namely, the same size of the packets. This operation is simple and management of free memory list is easy.

FACTS on ATM TECHNOLOGY

* Provides a way of linking a wide range of devices (from telephones to computers) using the seamless network

* Also removes the distinctions between LAN, MAN and WAN)

* Combines packet and circuit switching* It can be sent on any physical media (copper, fiber). Wide

range of transmission speed.* Scalable* Allows QoS parameters (voice, video, still image, etc.)* Supports any type of traffic* Allows sources of different bit rates* Uses fixed size packets called “CELLS”.

FACTS on ATM TECHNOLOGY

* No error protection or flow control on hop base* Header functionality is reduced* Information field is very small.* Operates in Connection-Oriented Mode* Supports Connectionless Mode

HISTORY of ATM

1980 Narrowband ISDN adoptedEarly 80’s Research on fast switches1985 B-ISDN Study Group formed 1986 ATM approach chosen for B-ISDN1987 ATM is standardized by ITU-TJune 1989 Cell Size (48+5) chosenOct. 1991 ATM Forum formedJuly 1992 UNI V2 released by ATM ForumOctober 1999 AAL Layers finalized1993 First Gen. ATM SwitchesOctober 1995 Traffic Management Finalized1996 Second Gen. ATM Switches1999 Third Gen. ATM SwitchesCurrently: Heavily used in Backbone Networks (ISP: Internet Service Providers);ADSL (Residential Access Networks)Passive Optical Networks (PONs) deployed in Residential Access Networks

ATM FORUM TECHNICAL COMMITTEES

* Traffic Management* Signaling* Physical Layer* Testing* B-ICI* LAN Emulation* SAA (Service Aspects & Applications) (VTOA)* Network Management* P-NNI* Multiprotocol over ATM (MPOA)* Residential Broadband

ATM NETWORKS

End Destinations

ATM Switch

ATM Switch

ATM Switch

End Sources

(Native ATM )

ATM Switch

ATM Switch

ATM Switch

End Sources

End Destinations

(Non-native ATM )

PSTN

LAN/MAN Internet