ATM Distinguished Service Record

To do this I will present a short summary style review of ATM as a protocol and then discuss the implications of this technology as it applies to the end-user (consumer).

The reason I have elected to use ATM to demonstrate and illustrate these contentious issues is that most consumer ADSL2+ implementations offer PPPoE or PPPoA as their transport protocols (at least here in Australia). PPPoA stands for Point-to-Point Protocol over Asynchronous Transfer Mode while PPPoE means Point-to-Point Protocol over Ethernet.

ATM has a long and distinguished service record for voice communications, is ideally suited to multiplexing environments and can be readily configured to carry VoIP traffic streams. Now for a little background about ATM and all will become clear.

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.

Asynchronous Transfer Mode (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.

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. AALs may provide constant bit rate services, circuit emulation, variable bit rate services or general data transport services.

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.

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: constant bit rate, variable bit rate, available bit rate and unspecified bit rate.

ATM Traffic Shaping and Policing

Now we get to a couple of the basic underpinning capabilities of ATM that ISPs can use at their “godly” discretion to put the brakes on your Internet Surfing and downloading pleasures.

Firstly however; I must point out that when ATM was being developed the developers may have been viewing the world through rose-colored glasses as their primary reasons for incorporating these particular aspects in the ATM protocol were all about network service, performance and quality of service. High ideals indeed but none-the-less crucial for real-time voice and video communications along with many of today's streaming media applications.

Unfortunately, as is so often the case, many a good intention/idea has been later subverted. Let us have a quick look at them here:

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.

Remember traffic contracts are negotiated between customer and service provider on a service-by-service basis. The customer requires a certain amount of bandwidth and pays the service provider accordingly. The service provider for their part agrees to make available and deliver that agreed minimum bandwidth.

For example if a customer required a certain minimum data bandwidth the service provider could ensure that this was met by electing to implement a set specific constant bit rate traffic contract. The ATM switches at either end are configured appropriately and the automatic traffic policing should ensure that this is the way things are.

Service level delivery guarantees are thus monitored automatically and any undesired anomalies or variations can be dealt with by the ATM switches logic. No prizes for guessing that this is not a labor-intensive activity and hence is a favorite with ISPs.

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). In instances where that part of the ISP's network carrying the traffic contract bandwidth exceeding traffic is not very busy the ISP can elect not to drop those cells with the CLP bit marked on. Similarly if network traffic is high the ISP can elect to drop said cells.

The problem here is that basic policing works on a cell-by-cell basis. When transferring most data packets ATM will as discussed above chop the frames into 48 byte size chunks, add its 5 byte header and then multiplex them all as a stream. This means that large frames will be carried as a very large number of uniformly-sized 53 byte cells.

Failure of any one of these cells to arrive at the destination will be interpreted as a corrupt frame upon analysis or reassembly at the recipient end and hence the entire frame will be automatically dropped. Simple CRC checking mechanism at the Data Link layer will pick up these errors and automatically drop the frame, even before the entire frame has been received by the Layer 2 device (switches for example).

Thus discarding a single cell will invalidate the whole packet of which the single cell is but one component. The implications are enormous. Traffic policing of the bandwidth constricting type can be effectively and efficiently enforced with a minimum of processing and filtering overheads on the part of those performing the traffic policing (ISP). It also means that cells can be marked as droppable by many different organizations at various points as it travels the Internet.

If you are into conspiracy theories then there is considerable food for thought here.

Another point worthy of consideration here is that ATM uses ATM switches and once the virtual circuits and traffic contracts have been established and configured by the service provider it is pretty much auto-pilot from there on. This means that network traffic policing; from the ISP's point of view, occurs automatically as part of the normal functional processes of the hardware (the ATM switch). This is most definitely a cost-effective minimal labor required solution.

Your problems start when errors occur in the administrative functionalities particularly between ISP peers. For example, you may decide to upgrade your service traffic contract or are experiencing data transfer corruption problems. Some of these data transfer issues can be the result of a Denial-of-Service attack (DoS) that is not necessarily directed against you specifically. You are just being caught in the backwash.

Unfortunately, another scenario that may adversely be affecting you is if an ATM switch on another network is marking some of the cells comprising your packets as droppable by turning on the CLP bit as they pass through that carrier's network.

This could arise from one of their customers exceeding their specific traffic contracts and since you are trying to upload or download from that customer traffic intended for you that was initiated by you is adversely affected. Keep in mind that it only takes one cell to be dropped to invalidate the entire frame.

Final Thoughts

One final word is that if you are in the situation of implementing a VoIP solution using a broadband modem router with inbuilt LAN switch via an ADSL2+ service that offers both PPPoE and PPPoA you may be best advised to implement a traffic segmentation solution by using PPPoE for standard data traffic and PPPoA for voice.

My home D-Link DSL-504 ADSL modem/router has been doing precisely this without any troubles for neigh on six months now. I guess just sometimes the world was meant to be easy. I will present another article shortly showing precisely how this is done. Screen shots will be included as I have just decided that I will make it a walk-through style presentation.

Although, to use voice over IP away from your computer requires a paid service it is inexpensive compared to standard services VoIP can cut international calls costs down by virtually 90 percent. VoIP helps to simplify and organize and individual's life. It gives a person the ability to access their office from home using voice over IP. This new technology was originally developed to provide communication in any place around the world. People are using VoIP at home and in their businesses. VoIP can eliminate your need of a fax machine because it is so productive. VoIP is capable of combining different data types simplifying routing and signaling to be more flexible. VoIP is a great technolgy based method of improving communication.

Voice over IP has five major abilities that add to the reason of its growing popularity. The first major ability of voice over IP is that it allows you to transmit more than one telephone call down the same broadband-connected telephone line. You can add an extra telephone line to any home or office with VoIP. This can increase many VoIP users productivity without increasing their monthly bills. The second ability voice over IP has is extra features without the extra costs. VoIP extra features include 3-way calling, call forwarding, automatic redial, and caller ID. Traditional phone companies charge users extra for these kind of features unlike VoIP.

The third ability voice over IP has is to make secure calls using standardized protocols. VoIP can easily encrypt and authenticate the data stream giving you a strong transmission. The fourth ability voice over IP has is its location independence. You are not limited with voice over IP like you are with standard phone companies. It only requires an internet connection to gain access to a VoIP provider. Vocie over IP phones can practically function from anywhere with a stable internet connection. The fifth major ability voice over IP has is integration with other services. You can integrate a number of other services available over the Internet including message or data file exchange during conversation, video conversation, audio conferencing, address book managing, and passing information about friends or colleagues availability online to others.

History of the Problem

Phone service was created in the early part of the 20 th century in the US. Quickly, people learned they could call neighbors, businesses, and if they were budgeted carefully, [at over $4 a minute] they could call relatives in different states via long distance. In 1995, after the world had become used to the amazing internet, researchers learned they could “piggy back” long distance calls on top of their regular internet service lines. What makes this both amazing and logical is that most users of the net do not realize that when they are researching things outside of their city, they are in fact, making legal long distance calls but without the liability of being charged for one-since a fantastic component [a server] connects computers around the world. [A server is a specialized computer with software that connects computers. It can be modified by using different software to act like a regular PC-as this paper's author has done with one of his computers.]

Problem

A major weakness of VOIP is that it is using one phone line for two purposes; interconnecting to different computers via their software and using phone software. When one uses a device designed for a different purpose, one gets a hodge-podge result; like using rubber bands to connect things where scotch tape should be used, or tape when screws should be, etc.

When calling customer service now, this author almost never gets a clear reception. He has been conditioned to ask “are you in India or the Philippines? And nine times out of ten, the person admits that they are. When this occurs, the sound going back and forth echos and bounces and makes “normal” communication almost impossible.

The physical laws of science and physics intrude; the more “stuff” that lies between the sender and receiver, the poorer the reception on a phone call.

Effective, clear communication is the fabric of excellent customer service and VOIP, unfortunately, becomes a major weakness leading to poor customer service. It is true, however, that if one uses specific phone services, filters and software, VOIP can sound almost identical to regular phone service. And it is true that anyone can convert their computers to become VOIP receivers too. The results can not be good, clear communications UNLESS the special, specific matrix of service, filters and software in installed and in almost all cases, it is not.

Significance of the Problem

It is a fact that when a customer [a business or a home owner] finds conducting business over the phone difficult, the customer quickly seeks an alternative produce/service provider.

Prior to 1995, merchants had clear phone communication but had often surly staffers. Often bosses treated the lowest pay scale staff poorly and that attitude on the part of management leaked over to the way the employee treated others.

The way weak managers tried to solve this problem was by “sending the problem overseas.”

It is a fact that customer service staffing costs money since all business processes cost money.

When the “bean counters” get so involved that they inform their bosses that customer service costs are increasing "x" percent, the boss too often feels the best remedy is to send the problem to the least expensive customer service staff-and that means off-shore and that means using VOIP.

When one checks out customer service complaints on the internet, one of the most frequent is hearing complains about India, the Philippines and elsewhere, answering the phone.

There is no reasonable way that, try as they might, a foreigner has any clue as to what we, in the US, are asking for. While the teachers of English and “American ways” do their best, it is illogical to expect that the customer service offered in Asia can equal what Americans have received [when good] over a period of 200 years within American business and thus, have come to expect.

American corporations are losing business to other nations for many reasons with the first one being business myopia; the inability to see what the American customer wants and to promptly provide it. Instead, the American business CEO too often is only interested in earning the highest bonuses he can during the short run even though smart business profit growth is strictly a long run proposition!

Until American companies bring back to America, its “shipped overseas” jobs originally done JUST to cut costs, American customers will slow down--if not stop entirely--being happy with American businesses.

This author found that the internet service provider, Earthling, no longer permits customers to contact anyone at corporate headquarters. Also, all their CS staff is off-shore and in 12 calls this author has made, not one of the CS agents understood one request-or-when they did, they said, “we are not authorized to answer or help in that field, you must send in an email-even though their web site stated the opposite; “that can not be answered by email, you must contact a phone customer service agent. They lost ½ of my business and later this year, will lose the other ½.

Methodology

The author, a business consultant and college business teacher, has done primary research, and reviewed secondary literature regarding customer service and has taught customer service skills in college.

Suggested Solutions

This is a no brainer. American companies tried and tested the hypothesis “cut costs any way you can, and forget about any long range con sequences.”

American businesses are losing market share because of this myopic behavior.

Interestingly, the “young pups” of American industry and graduates of America colleges, are realizing that they could perhaps either buy a dinosaur firm and bring it back to life or....for negligible costs in many circumstances, start up a new firm that uses American products, American service and American positive PR.

There are three ways of using VoIP:

1. ATA: Analog Telephone Adaptor

   This is a device that connects to a normal home phone and a computer. It is very easy to set up however compared to the other ways it is the bulkiest.

2. IP Phone

   This is just a normal phone but instead of having a normal phone connector it has an Internet connector. These phones connect straight to a router. They are harder to set up but there better then an ATA if you use computers a lot.

3. Computer to Computer

   Works pretty much the same way as a chat website. Not a good phone replacement but its better then nothing.

VoIP has a few advantages. One is VoIP uses packet switching instead of the normal circuit switching, this is the main advantage. Packet switching is much more efficient then circuit switching and allows a lot more calls to be made at the 1 time. This makes it cheaper for phone companies and governments.

VoIP isn't a miracle but. It has its disadvantages. Normal home phones don't use house power they use phantom power. This phantom power comes from the phone line, so when there is a black out the phone will go as well as the power.

Since VoIP is an internet based connection there is the usual problems associated with the internet. It's completely normal for an internet site to stop working for a while but it's unusual for the phone to loose a connection.

With VoIP the phone will stop working for what seems like no reason just like the WWW. The last major disadvantage is that VoIP calls are not traceable. Emergency companies will not be able to see the location that the call was made.

What is VoIP?

VoIP stands for Voice-over Internet Protocol. It means that you use your Internet connection to send your voice to anywhere in the world.

This is similar to using MSN Messenger or Yahoo Messenger, where you type on your computer and your friend on another computer receives it instantly.

How is VoIP different from MSN or Yahoo Messenger?

One difference is that instead of typing on your keyboard, you talk on your microphone and your friend hears you on his or her earphone, instantly. Also, while Yahoo already offers voice, you can only talk to friends who also have a computer and have the same program loaded in their computer.

VoIP lets you call a friend on a regular phone. VoIP also lets you talk on the Internet without a computer.

How do I make free calls with VoIP?

You can make free calls if:

• you and your friend use your computer to talk, and
• you are using the same VoIP program on your computer.

How do I save money with VoIP?

Compared to your regular phone company, VoIP charges you much less for your long-distance and mobile phone calls. That's because they use your existing Internet connection to receive your phone call and send it to the person you are calling.

Also, features like call waiting, call forwarding, call barring, conference calls, user ID and other paid phone features are usually free on VoIP.

The call rates differ with different providers, though. Call prospective companies to find out their rates.

What is a VoIP service provider?

These are the companies that receive your phone calls through the Internet and transfer them to regular phone lines so your friends without VoIP can receive your calls.

So I can call friends even if they have no VoIP?

Absolutely. They will receive it like a regular call on their regular phone.

Can they call me too?

Yes. They simply dial your VoIP number, which looks just like a regular phone number, and your computer or VoIP phone will ring to let you know somebody is calling.

Your incoming calls are free. Your friends will be charged by their phone company in just the same way that they will be charged if they called a regular phone.

What is a VoIP phone?

It is a phone with a modem and software installed inside so that you can connect to your Internet directly and make online calls without turning on your computer.

Does a VoIP phone sound as clear as a regular phone?

Yes - if your Internet connection is good. Most companies require a speed of at least 100 kbps. The recommended speed is 250 kbps or faster. A reputable company will never install VoIP on a dial-up connection.

Can I choose my VoIP phone number?

It depends on your service provider. Some will let you:

• choose your phone number
• keep your old number
• even choose your area code! (This is great if your business clients or family all live in a different state. This will let them call you and be charged as if they were making a local call. On the other hand, if your neighbors call you, they will be charged long distance.)

Can I get rid of my regular phone line?

Technically, yes, because VoIP only needs your Internet connection.

However, keep in mind that if you use VoIP to call 911, they will not be able to track your location automatically, as when you are using your regular phone. The connection of VoIP to 911 is also rather unreliable. If you get rid of your regular landline, use your mobile phone to call 911.

Also, your VoIP will not work in a power outage. But then again, your regular phone might not either.

Can I use my Internet on the computer while calling on my VoIP phone?

Yes, although it may affect your connection speed, which will affect the sound quality of your call.

What do I need to use VoIP?

1. a high-speed Internet connection
2. a VoIP service provider
3. a VoIP phone, or a computer with a headset, or a regular phone with a VoIP adapter

Is VoIP for me?

• Are you always online anyway?
• Do you make many long-distance or mobile phone calls?
• Would you or people important to you benefit from your having a phone number with an area code different from where you actually live?
• Do you want to get phone features like caller ID, call waiting, call forwarding, conference calls or call barring for free?

If you answer “yes” to two or more of these questions, VoIP is probably for you.

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