Traditionally ATM has a long and distinguished service record for voice communications. It is also ideally suited to multiplexing environments and can be readily configured to carry VoIP traffic streams.

In fact today we find that most consumer ADSL2+ implementations do offer a choice of PPPoE or PPPoA as their transport protocols (at least here in Perth). PPPoA stands for Point-to-Point Protocol over Asynchronous Transfer Mode.

The importance of this cannot be overlooked as it means that ATM in some form or other will be with us for some time into the future. In fact the Japanese have just recently deployed a communications satellite with an onboard ATM switch. They obviously think there is life in ATM yet.

Introducing Asynchronous Transfer Mode (ATM)

Originally intended to be a unified networking strategy Asynchronous Transfer Mode (ATM) is a connection-oriented, circuit-switched, cell relay “Jack-of-all-trades” transport protocol that uses small uniform fixed-sized cells to redress Quality of Service (QoS) issues so important to voice/video communications and the multitude of streaming applications upon which we are all so dependant.

ATM Origins and Development

During development of the standards for the Asynchronous Transfer Mode (ATM), in the mid 1980s, the goals were to create a unified networking strategy that could act as an all-round transport system for real-time video and audio as well as for image, text and email. ATM is pretty much a “Jack-of-all-trades” transport system. The two groups primarily responsible for the development of the ATM standards were the International Telecommunications Union [ITU 2004] and the ATM Forum [ATM 2004].

Over time we have seen that the majority of implementations and uses that ATM has fulfilled have been primary concerned with telephony and IP networks. Ethernet and the Internet Protocol (IP) are packet-switched network technologies that use packets of variable size referred to as frames.

ATM Protocol Basics

In marked contrast to packet-switched networking technologies; ATM is a connection-oriented, Data Link Layer (OSI Reference Model Layer 2), circuit-switched, cell relay protocol that runs over Synchronous Optical Network (SONET) Physical Layer links (OSI Reference Model Layer 1) using cells of identical and never varying size. Consistent predictability is the underlying ethos here.

Being a connection-oriented channel-based technology means that ATM must always establish a “logical” connection between the two endpoints prior to commencement of data exchange. Significantly, ATM encodes data traffic into small uniform fixed-sized cells. ATM cells are always 53 bytes in size and are comprised of 48 bytes of data and 5 bytes of header information.

ATM Cell Structure

Regardless of the original size of the packets to be transmitted ATM breaks all packets, data, and voice streams into 48-byte chunks and then adds a 5-byte routing header to each one thereby making a total of 53-bytes for each and every cell. The 5-byte header is essential for later reassembly. During development of ATM it was considered that 10% (5 bytes) of each cell (payload) being dedicated to the header for routing information was more than sufficient.

ATM multiplexes these 53-byte cells instead of the larger packets and in so doing reduces the worst-case queuing jitter by a factor of almost 30, thereby removing the need for echo cancellers. I will discuss queuing jitter along with other types of jitter shortly.

ATM Cell Formats

ATM defines two different cell formats the Network-Network Interface (NNI) and the User-Network Interface (UNI). Most ATM links use the UNI cell format.

ATM Adaption Layers (AAL)

ATM Adaptation Layers (AAL) are the rules for segmenting and reassembling packets and streams into cells. It is the AALs that provide the support for the various services delivered by ATM.

Currently, there are five different AALs and the information concerning which one is being used for each cell on a cell-by-cell basis is not contained within the cell or in the cell header. Rather, this information is negotiated by or configured at the endpoints on a per-virtual-connection basis. Here are the five different AALs and their main uses:

1. AAL1

   Constant Bit Rate (CBR) Services, Circuit Emulation

2. AAL2

   Variable Bit Rate (VBR) Services

3. AAL3

   Variable Bit Rate (VBR) Services

4. AAL4

   Variable Bit Rate (VBR) Services

5. AAL5

   Data Transport

ATM Connectivity

Because ATM is a connection-oriented channel-based technology it must establish a “logical” connection between the two endpoints prior to commencement of data exchange. ATM does this by implementing Virtual Circuits, Channels, Paths and Identifiers as follows:

• Virtual Circuits (VC)

  Virtual Circuits (VC) are admirably suited to multiplexing scenarios. Simply by including an 8-bit or 12-bit Virtual Path Identifier (VPI) and a 16-bit Virtual Channel Identifier (VCI) pair in every ATM frame's header each Virtual Circuit (VC) is uniquely identifiable.

• Virtual Channel

  An ATM Virtual Channel represents the basic means of communication between two end-points. Cells are given a unique identifier called the Virtual Channel Identifier (VCI) which is placed into the ATM cells' header. All ATM cells containing identical VCIs are transported in the same Virtual Channel.

• Virtual Path (VP)

  A Virtual Path (VP) denotes the transport of ATM cells belonging to virtual channels which share a common identifier called a Virtual Path Identifier (VPI). The VPI is included in the header of every ATM frame. In other words a Virtual Path (VP) is a bunch of Virtual Channels (VC) connecting the same end-points. These will also have a common traffic allocation.

• Virtual Path Identifier (VPI)

  The Virtual Path Identifier's (VPI) length varies depending on the interface it is sent on (inside the network or on the edge of the network.

ATM Traffic Contracts

When an ATM circuit is set up each ATM switch is informed of the traffic class of the connection. These ATM contracts constitute part of ATM's Quality of Service (QoS) mechanisms. There are four basic types of contracts:

1. Constant Bit Rate (CBR)

   A constant specified Peak Cell Rate (PCR) is set

2. Variable Bit Rate (VBR)

   An average cell rate is specified. This may peak at a certain predefined maximum level for a certain length of time before becoming problematic

3. Available Bit Rate (ABR)

   A minimum guaranteed rate is specified

4. Unspecified Bit Rate (UBR)

   Traffic is allocated all remaining transmission capacity

ATM Traffic Contract Delivery and Monitoring

Traffic Shaping

The intended objective of traffic shaping is to ensure that cell flow will meet its traffic contract and is usually done at the entry point to an ATM network.

Traffic Policing

To maintain network performance it is possible to “police” virtual circuits against their traffic contracts. Basic policing works on a cell by cell basis, but this is sub-optimal for encapsulated packet traffic. If a circuit is exceeding its traffic contract, the network can either drop the cells or mark the Cell Loss Priority (CLP) bit (to identify a cell as being discardable farther down the line).

Benefits of Using Small Fixed Size Cells

The major benefits derived from using small data cells are a reduction in queue delay and jitter; particularly in multiplexing data streams. By using small, fixed-sized cells ATM is able to transport large data files all the while maintaining minimal queuing delays. Minimal queuing delays are essential to the delivery of both voice/video communications.

Queue Delay

Queue delay related issues include problems associated with end-to-end-round-trip delays and delay variance particularly when carrying voice traffic. High traffic volumes and/or congested networks along with the arrival variance associated with variable route routing are among the main causes of queue delay issues.

Jitter

Although jitter results from queuing delay issues deviations or displacement of various aspects of high frequency pulses such as amplitude, phase timing and signal pulse width as a direct result of electromagnetic interference (EMI) and crosstalk (noise) also cause jitter. Think of jitter as being the production of “jerky” results or in video applications flicker. By using small fixed-size cells ATM is able to overcome the effects of queue delay as well as other types/sources of jitter.

Multi Purpose Transport Protocol

Asynchronous Transfer Mode (ATM) carries many different data types and formats (text, audio, video, graphics, photos etc.) from a multitude of sources and of variable sizes. When combined with standard queuing strategies, maximum queuing delays were common. This is totally unacceptable where voice and real-time video traffic is concerned.

Compression/Decompression Algorithms (Codec)

Because of the way in which many Compression/Decompression Algorithmswork special considerations need to be implemented in order to ensure they work properly as intended including:

Time

The nature of time as we humans perceive it is an analogue continuum (that is to say time is a linear progression). Once past, there is no way as yet to recover the loss.

Jitter and Queue Delay

Jitter and queue delay are of great importance because of the nature and manner of operation of the compression/decompression (codec) algorithms used in the conversion of a digitalized data stream back into an analogue audio signal. This conversion process (digital-to-analogue) is very much a “real-time, on-the-fly” process and is more attuned to” just-in-time” transport protocols.

Real-Time Streaming

In order to produce reliable, consistently “acceptable” output the codec needs the data items (the digitized voice data) to be presented to it in a predictable, regulated and evenly spaced in time data stream, hence the term “real-time streaming”.

Late Arrivals

If the data arrives after its allotted position/reception window in the time sequence (relating to that part of the data-stream) the codec will simply drop it. Not surprisingly this is unacceptable for IP telephony. Remember to keep in mind that time is analogue in nature and once a “time window” elapses, the “lost” time becomes unrecoverable.

Codec Packet Handling Options

If the transport protocol is unable to present the data as and when the codec expects it, the codec, has no choice but to assume either silence, make a “best guess” or simply drop the packet. Any way is unacceptable where voice is concerned as the conversation rapidly becomes untenable and the message does not get through.

ATM Deployment Indicators and Scenarios

ATM WAN Core Implementation

ATM production environment implementations have over time proved to be very successful in the Wide Area Network (WAN) scenarios. Numerous telecommunication providers and Internet Service Providers (ISPs) have implemented ATM in their Wide Area Network (WAN) cores.

Slow Links

For slow links less than 2M-bit/s, ATM still makes sense, which is why many ADSL systems use ATM as an intermediate layer between the physical link layer and a Layer 2 protocol like PPP or Ethernet.

Linear Audio and Video Streams

Interest in using native ATM for carrying live video and audio has increased recently. It is in these environments, where ATM can deliver the low latency and very high Quality of Service (QoS) required for handling linear audio and video streams.

Gigabit Ethernet

Today we are finding that for both new WAN implementations and for existing WAN implementation upgrades, high speed, high performance Ethernet (Gigabit Ethernet, 10Gbit Ethernet, and Metro Ethernet etc.) are rapidly replacing ATM as the technology of choice.

Relative Performance

At the time ATM was designed, 155Mbit/s (135Mbit/s payload) over fiber-optic cable was very fast in comparison to the other carrier/transport technologies available at the time. Since then however; these other technologies have evolved and are now considerably faster than they once were.

Jitter

Today; a 1,500 byte (12,000 bit) full-size Ethernet packet takes only 1.2 µs to transmit across a 10Gbit/s optical network. With this sort of speed, jitter is no longer the issue it once was. By overcoming the potential adverse effects of jitter through this ramping up of network transfer speeds we have at the same time removed the need for using small uniform cells to overcome jitter.

Complexity

Unfortunately, due to ATM's complexity it proved to be unsuitable for deployment in many of the scenarios that its creators had originally intended.

Converged Networks

The speed and traffic shaping requirements of many converged networks are also proving to be very challenging for ATM.

The Advantages of Fiber Optical Networking

First of all, we must note that the biggest advantage of using fiber optic networking and hence the use of fiber optic cable as a transmission medium is the high degree of immunity to noise, cross-talk and Electromagnetic Interference (EMI) that this medium provides.

Spanning Large Distances - With the fiber optic technologies currently available today signal degradation and regeneration issues are not what they once were and so the distance factor that so limits copper-based media is of negligible consequence where fiber optic transmission is concerned.

Environmental Damage - Environment factors such as moisture and Radio Frequency Interference (RFI) are also not of the same criticality as they are for copper-based media. The reasons for fiber optic cable as a transmission medium providing a high degree of immunization to noise (EMI) as opposed to other transmission media all stem from the use of light to convey the information (signals) and the construction of the medium (the fiber optic cable).

Security - Due to the degree of difficulty in “tapping” fiber optic transmission lines without being detected, fiber optic transmission media offer a more secure medium than copper-based or wireless technologies.

The result is that fiber optic transmission media are the media of choice when it comes to “long haul” applications such as intercontinental, cross-continental and oceanic (marine) backbone links. It is also the preferred medium for tier one ISP backbone links. This means that new WAN implementations and applications are now predominantly fiber optic cable based. Wireless rollouts being the major exception.

Additional information regarding fiber optic cable construction, signal propagation, signal regeneration, connectors, cable rollout and modes (single-mode and multi-mode fibers) can be found at Fiber Optic Cable.

I will now discuss the major standards and implementations of fiber optic networking starting with the Fiber Distributed Data Interface (FDDI) standard and then the Synchronous Optical Networking (SONET) and the Synchronous Digital Hierarchy (SDH).

Fiber Distributed Data Interface (FDDI)

FDDI which evolved from the IEEE 802.4 token bus timed token protocol is a fault tolerant 100Mbit/sec token passing counter-rotating dual ring LAN standard that permits data transmission between two end-point devices that can be many tens of kilometers apart.

As its name indicates, fiber optic cable is the main form of physical transmission medium used in FDDI. Although a copper-based implementation called, Copper Distributed Data Interface (CDDI) does exist. Although conceived as a LAN standard FDDI has also been used for MAN and WAN implementations.

FDDI Topology - In essence FDDI is a ring network similar to IBM's Token Ring network but with a number of critical differences. The most noticeable of which is that a FDDI uses a dual-attached, counter-rotating token ring topology (see Figure 1: FDDI).

Fault Tolerance - One ring acts as the primary transmission ring and in the original implementations was capable of delivering transmission speeds of up to 100Mbit/sec. The other or secondary ring was originally intended solely to act as a backup.

This meant that the secondary ring was inactive and remained so for as long as the primary ring was functional. In the event of failure of the primary ring the secondary ring would become active. Now all traffic goes to the secondary ring for transmission. It is this built-in redundancy that makes FDDI is a fault tolerant technology.

Higher Effective Sustained Data Throughput - Another factor in FDDI's favor was that it used a much larger frame size than Ethernet which meant that it was capable of much higher effective sustained throughput rates than standard 100Mbit/sec Ethernet. Administrators also had the option of using the secondary ring for data transport rather than having it stand idly by thereby doubling transmission capacity to 200Mbit/sec.

Coverage and Scalability - Not only can FDDI traverse large distances it also scales much better than 100Mbit/sec Ethernet. This means it provides superior support for expanding enterprise networks consisting of hundreds or thousands of users.

Fiber Distributed Data Interface II (FDDI-II) - FDDI-II is a more recent development of FDDI that has added support for circuit-switched services thereby enabling FDDI to carry both voice and video signals as well. For more on FDDI including applicable standards please see About Fiber Distributed Data Interface (FDDI).

Synchronous Optical Networking - SONET

Synchronous Optical Networking (SONET) is an established high-speed WAN alternative for communicating digital information using lasers or Light-Emitting Diodes (LEDs) over optical cable offered by several telecommunications companies.

SONET was originally developed to replace the Plesiochronous Digital Hierarchy (PDH) system for transporting large amounts of telephone and data traffic as well as providing the mechanisms that allow for interoperability between equipment from different vendors. The result is that there are multiple, very closely related standards that describe synchronous optical networking including:

Synchronous Digital Hierarchy (SDH) - The SDH standard was developed by the International Telecommunication Union (ITU) and is documented in standard G.707 and its extension G.708. SDH is used throughout the world but not in North America

Synchronous Optical Networking (SONET) - The SONET standard as defined by GR-253-CORE from Telcordia™. Primarily used exclusively in Canada and the USA where SDH has not been implemented, although it can be found in other countries.

Synchronization is Key - Through the use of atomic clocks synchronous networking data transport rates are very tightly regulated which allows for entire inter-country networks to operate synchronously while greatly reducing the amount of buffering required between elements in the network. This reduction in overhead (buffering) translates into greater effective net data throughput rates.

Encapsulation - Both SONET and SDH can be used to encapsulate earlier digital transmission standards, such as the PDH standard, or used directly to support either ATM or so-called Packet over SONET/SDH (POS) networking.

Generic Transport Containers - SDH and SONET are generic all-purpose transport containers for moving voice and data rather than just communications protocols per sec.

SDH and SONET Frame Structures

Standard packet or frame oriented data transmission frames usually consist of a header and a payload with the header of the frame being transmitted first, followed by the payload and a trailer (e.g. CRC). With synchronous optical networking both the header, which is referred to as the overhead and the payload still exist but the big difference is that the overhead is not all transmitted before the payload, rather the transmission is interleaved.

Interleaved Transmission - With interleaved transmissions the transmission of the conversation goes like this:

First of all, a portion of the overhead (header) is transmitted. This is followed by part of the payload. After which the next part of the overhead is transmitted. This is followed by the next part of the payload and so on until the entire frame has been transmitted. Figure 2: Interleaving above shows this.

SONET Frame Size and Transmission Sequence - SONET frames are 810 octets in size, transmitted as 3 octets of overhead, followed by 87 octets of payload, nine times over until 810 octets have been transmitted. The total frame transmission time is 125 microseconds.

SDH Frame Size and Transmission Sequence - SDH frames are 2430 octets in size transmitted as 9 octets of overhead, followed by 261 octets of payload, also nine times over until 2430 octets have been transmitted. Again the total frame transmission time is also 125 microseconds.

It doesn't take much brain power to see that SDH is capable of an effective data throughput rate three times that which the North American implementation of SONET can achieve.

Ethernet over Fiber Optic Cable

Today we see the Gigabit Ethernet over fiber optic cable and 10G Ethernet over fiber optic cable standards being the most common implementations of optical local area networks (LANs) currently being rolled out. They are also used extensively as the network core layer's transport medium of choice particularly Ethernet networks.

The majority of the big players in the networking hardware arena like Cisco, Juniper, and Redback etc all produce numerous products with fiber optic support including Ethernet over Fiber Optic modules. Note see Network Design: Hierarchiesfor more about network design and the functions and features of a network's core layer.

Asynchronous Transfer Mode (ATM) is a connection-oriented Data Link Layer (OSI Reference Model Layer 2), circuit-switched, cell relay protocol that runs over Synchronous Optical Network (SONET) Physical Layer (OSI Reference Model Layer 1) links. ATM encodes data traffic into small uniform (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells.

Origins of Asynchronous Transfer Mode (ATM)

During development of the standards for the Asynchronous Transfer Mode (ATM), in the mid 1980s, the goals were to create a unified networking strategy that could act as an all-round transport system for real-time video and audio as well as image, text and email. A “Jack-of-all-trades” transport system if you will.

The two groups primarily responsible for the development of the ATM standards were the International Telecommunications Union [ITU 2004] and the ATM Forum [ATM 2004].

Main Implementations of ATM

The majority of implementations and uses that ATM has fulfilled have been primary concerned with telephony and IP networks.

Unlike Ethernet and the Internet Protocol (IP) which are packet-switched based network technologies, that use packets of variable size referred to as frames, ATM is a circuit-switched cell relay protocol that uses cells of identical and never varying size. Consistent predictability is the underlying ethos here.

Benefits of Using Small Fixed Size Cells

The major benefits of using small data cells were to reduce jitter in multiplexing data streams as well as overcoming problems associated with end-to-end-round-trip delays and delay variance particularly when carrying voice traffic.

The reason this is important is inherently due to the nature of operation of the compression/decompression (codec) algorithms used in the conversion of a digitalized data stream back into an analogue audio signal, which is very much a “real-time” process.

To be able to do an “acceptable” job the codec needs the data items (the digitized voice data) presented to it in an evenly spaced (in time) stream hence the term “real-time streaming”. The nature of time as we humans perceive it is an analogue continuum (that is to say time is a linear progression).

If the transport protocol is unable to present the data as and when the codec expects it, the codec, has no choice but to assume silence or make a “best guess”. Either way is unacceptable where voice is concerned as the conversation rapidly becomes untenable and the message does not get through.

If the data arrives late then the time sequence relating to that part of the data-stream will have passed and the codec will simply drop it. Once again, this is unacceptable for IP telephony. Remember that time is analogue by nature and once a “time window” elapses, the “lost” time becomes unrecoverable.

Queue Delay and Jitter

Asynchronous Transfer Mode (ATM) carries data from a multitude of sources and variable sizes including voice, audio and many other variable sized files. When combined with standard queuing strategies, maximum queuing delays were common.

Because ATM was designed to implement a low-jitter network interface this situation is intolerable whenever voice and video communications are to take place. The answer was to use small-fixed size cells (packet) to overcome the effects of queue delay.

With small fixed-sized cells, ATM is able to transport both large datagrams while still maintaining short/minimal queuing delays.

Asynchronous Transfer Mode (ATM) Cell Structure

ATM breaks all packets, data, and voice streams into 48-byte chunks, adding a 5-byte routing header to each one. The 5-byte header is essential for later reassembly.

The reason for the header being 5-bytes in length is that 10% of the payload of every cell is considered to be more than enough to dedicate to routing information.

ATM multiplexed these 53-byte cells instead of packets and in so doing reduced the worst-case queuing jitter by a factor of almost 30, removing the need for echo cancellers.

ATM defines two different cell formats the Network-Network Interface (NNI) and the User-Network Interface (UNI). Most ATM links use the UNI cell format.

Asynchronous Transfer Mode (ATM) Adaption Layers (AAL)

ATM Adaptation Layers (AAL) are the rules for segmenting and reassembling packets and streams into cells. It is the AALs that provide the support for the various services delivered by ATM.

Currently there are five different AALs and which one is in use for each cell is not included in the cell. Instead, it is negotiated by or configured at the endpoints on a per-virtual-connection basis.

• AAL1 - Constant Bit Rate (CBR) Services, Circuit Emulation
• AAL2 - Variable Bit Rate (VBR) Services
• AAL3 - Variable Bit Rate (VBR) Services
• AAL4 - Variable Bit Rate (VBR) Services
• AAL5 - Data Transport

Asynchronous Transfer Mode (ATM) Connectivity

Being a connection-oriented channel-based technology means that ATM needs to establish a “logical” connection between the two endpoints prior to commencement of data exchange.

Virtual Circuits (VC)

By including an 8-bit or 12-bit Virtual Path Identifier (VPI) and a 16-bit Virtual Channel Identifier (VCI) pair in the ATM frame's header each Virtual Circuit (VC) is uniquely identifiable. Virtual Circuits (VC) are admirably suited to multiplexing scenarios.

Virtual Channel

An ATM Virtual Channel represents the basic means of communication between two end-points. Cells are given a unique identifier called the Virtual Channel Identifier (VCI) which is placed into the ATM cells' header. All ATM cells containing identical VCIs are transported in the same Virtual Channel.

Virtual Path (VP)

A Virtual Path (VP) denotes the transport of ATM cells belonging to virtual channels which share a common identifier called a Virtual Path Identifier (VPI) which is included in the header of every ATM frame. In other words a Virtual Path (VP) is a bunch of Virtual Channels (VC) connecting the same end-points, and have a common traffic allocation.

Virtual Path Idetifier (VPI)

The Virtual Path Idetifier's (VPI) length varies depending on the interface it is sent on (inside the nework or on the edge of the network.

Asynchronous Transfer Mode (ATM) Traffic Contracts

When an ATM circuit is set up each switch is informed of the traffic class of the connection. These ATM contracts constitute part of ATM's Quality of Service (QoS) mechanisms. There are four basic types of contracts:

1. Constant Bit Rate (CBR) - A constant specified Peak Cell Rate (PCR) is set
2. Variable Bit Rate (VBR) - An average cell rate is specified. This may peak at a certain predefined maximum level for a certain length of time before becoming problematic
3. Available Bit Rate (ABR) - A minimum guaranteed rate is specified
4. Unspecified Bit Rate (UBR) - Traffic is allocated all remaining transmission capacity

Traffic Shaping

The objective of traffic shaping is to ensure that cell flow will meet its traffic contract and is usually done at the entry point to an ATM network.

Traffic Policing

To maintain network performance it is possible to police virtual circuits against their traffic contracts. If a circuit is exceeding its traffic contract, the network can either drop the cells or mark the Cell Loss Priority (CLP) bit (to identify a cell as discardable farther down the line).

Basic policing works on a cell by cell basis, but this is sub-optimal for encapsulated packet traffic (as discarding a single cell will invalidate the whole packet).

Asynchronous Transfer Mode (ATM) Deployment Scenarios

ATM has proved very successful in the Wide Area Network (WAN) scenario and numerous telecommunication providers have implemented ATM in their Wide Area Network (WAN) cores.

For slow links less than 2Mb/s, ATM still makes sense, which is why many ADSL systems use ATM as an intermediate layer between the physical link layer and a Layer 2 protocol like PPP or Ethernet.

Interest in using native ATM for carrying live video and audio has increased recently. In these environments, low latency and very high quality of service are required to handle linear audio and video streams.

Asynchronous Transfer Mode (ATM) the Future

Currently the future for ATM does not look very bright as it seems that in all likelihood gigabit Ethernet implementations (10Gbit-Ethernet, Metro Ethernet) will replace ATM as a technology of choice in new WAN implementions.

At the time ATM was designed, 155 Mbit/s (135 Mbit/s payload) over fiber-optic cable was fast in comparison to other technologies but since then networks have become much faster. A 1500 byte (12000-bit) full-size Ethernet packet takes only 1.2 µs to transmit on a 10 Gbit/s optical network, removing the need for small cells to reduce jitter.

The complexity of ATM is another factor that makes deployment of ATM unsuitable in many of the scenarios that its creators had originally intended.

The speed and traffic shaping requirements of converged networks also challenges ATM.

This tutorial will give you a good idea on how to create a simple ball and make it move across the screen, maybe you think that this is to simple for you, well when I first began I thought the same as you, however we all must start with the basics to progress to much bigger animation such as bone structures, ik handles and even vertex animation.

So to begin with open up maya 7 and let’s make a start,

I have drawn a arrow to the tool we will use to create a sphere quickly, first of all if you don’t see this tool bar I will show you why,

Make sure you have the polygons tool bar open and not one of the other tool bars, right now click the tool that the arrow points to this will create a sphere with what ever default settings your sphere options have, don’t worry if your sphere looks different to this one it doesn’t really matter for this tutorial.

Next step, lets make sure the animation setting are perfect for us, click the tool that the arrow points to below,

This is called the animation preference, it will open this pop up,

Now if your options don’t look like this don’t worry, we need to set it up, change the playback and the animation start/end to 25 we are only going to make this animation 1 second long, (now if you are in America set this to 30).

Make sure that the playback speed is set to real time [numbers], if your real time [25 fps] isn’t 25 do not worry we will set this up next.

Click where the arrow points to Setting and you should have a different screen facing you like the one below.

Change the time to PAL [25 fps] if you live in England or Europe if you live in America or else where change it to NTSC or your local setting that you know.

It is important that you do this every time you start an animation to make sure that the play back speed is perfect for your region, this is very important if you get a job in the industry.

Now click save and the box will go away, now in your time line located at the bottom of the screen, if you have something lie this going on,

1.04 we need to change it to one as it’s not a whole number, in the white box where the longer arrow points select the number and type in 1.0 to reset it back to 1, this as changed because we have changed the settings, but everything is back to normal now.

Select the ball and make sure the time line is on one still and press S, now if you look at your time line you should see that a blue line as appeared on the selected frame like below,

Click on the frame two and you should see something like the image next to it, if you don’t , reselect frame one, press S again, if no luck make sure you don’t have caps lock on and repress S it will work now.

Right now select frame 25 (or 30), once you’re in frame 30 select the ball and press W (making sure caps lock is not on) and move the ball to a new location, once you have moved it press S to create a animation frame.

Once again you will have a red line in frame 25 (or 30) this will tell you that both of these frames are animated, now time to watch the animation click on frame 1 and press the play button, and there you have it a simple move animation, now you know how to do this you can move on to bigger and better animations.