Dsl what is atm

The ATM network was contiguous - it started at the customer's DSL interface, continued through the DSLAM and through the service provider's network in fact, the service provider's network was based on ATM up to the BRAS where the customer's packets were first inspected and either kept in the same service provider's network, or tunneled away to a different internet service provider.

Nowadays, ATM is not used anymore inside service provider's networks. IP packets are chopped up to pieces of at most 48 bytes this is the size of the payload portion of an ATM cell and are carried in multiple ATM cells. You can read more about AAL5 here but it is admittedly a fairly involved reading:.

More complex environments used dynamic helper protocols to set up these mappings automatically. View solution in original post. ATM does not have its own physical and transport and application layers? Even though ATM itself has a fairly complex reference model consisting of 4 layers plus additional planes, it was most often treated just like a sophisticated data link layer technology. ATM provides virtual circuits between attached hosts, allowing them to talk to each other directly as immediate neighbors, and this would be exactly what OSI Layer2 does.

However, ATM also had its own addressing model and was capable of searching for best paths between any two end hosts, which is a Layer3 function. So from this point of view, ATM was also capable of running as a Layer3 technology.

In any case, ATM had numerous physical layer implementations. Then there is the ATM layer that is roughly equivalent to the data-link layer in that it concerns with carrying "frames" called ATM cells between attached devices. Our common networks and data-link layer technologies do not usually have a layer similar to AAL, but because the operations of AAL are so closely tied to the process of carrying useful data in ATM cells, AAL and ATM together provide services we're used to seeing in the data-link layer, and that is what is also suggested in the picture above.

It simply has the 4th layer saying "higher protocols", and that's where all higher protocols are. ATM - as a technology - can provide a virtual circuit between a subscriber and his service provider, but there is a lack of other features a service provider needs to do: authenticating the subscriber, performing the accounting, negotiating what higher protocols will be carried over the virtual circuit such as IPv4 or IPv6 , what settings should those higher protocols use, etc.

The virtual circuit provided by ATM was just a raw data conduit, and some other protocol offering all these services was required to carry customer's data over this conduit. PPP was the natural choice here. It provides easy framing, authentication, accounting properties, it is able to carry multiple packet types itself, it provides mechanisms to negotiate which higher level protocols will be used and how they should be configured, so from this point of view, it was just perfect. AAL5 is capable of carrying segmenting and reassembling upper-layer datagrams of up to roughly 64 KiB which is far beyond the usual IP packet sizes.

However, in the beginnings of DSL, such integrated routers were extremely rare or did not exist at all. This posed another problem - if the PC can be connected to the DSL modem over an Ethernet interface only, how should the PPP frames created on the PC be delivered to the DSL modem so they can be ultimately forwarded to the service provider, and vice versa? PPPoE encapsulation consumes additional 8 bytes in its headers that need to fit into the Ethernet payload.

However, whether you can use either PPPoE or PPPoA depends on your service provider; some of them support both modes while others support only one of these and you need to discuss with your service provider which mode should be used. This is, however, done to meet the provider's expectations. The service provider does not care where does the subscriber run his PPP driver - whether it is on his PC or on his integrated router.

This gives the service provider the flexibility to communicate in the same way with any kind of customer, either those using simple DSL modems and running PPP software on their PCs, or those using integrated DSL routers.

Yes, among others. Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer. Add a comment.

Active Oldest Votes. Improve this answer. Martin Rosenau Martin Rosenau 2, 4 4 silver badges 9 9 bronze badges. English wikipedia also describes the byte payload as a political compromise between and byte, proposed by different groups, and describes 5-byte header as what was considered reasonable.

This is, indeed, why ATM exists and yes, 53byte cells were a level-the-playing-field compromise to make everyone build new hardware, vs. There are systems that use frame-relay, btw. RickyBeam I updated my answer — Martin Rosenau. PPP was there because it grew out of dialup and was an existing means of authentication. Zac67 Zac67 Sign up or log in Sign up using Google. Sign up using Facebook.

Sign up using Email and Password. Post as a guest Name. The functionality provided by the PPP LCP protocols allows for the authentication and identification of users of a service.

PPP allows the negotiation of the use of encryption on a link. PPP supports the assignment and management of IP addresses, network protocol multiplexing, link configuration, error detection, and data-compression negotiation.

Although originally defined for use over point-to-point connection, such as those provided by analog modem over the dial telephone network, the protocol has been adapted for use over broadband connections such as those provided by DSL services.

Two such adaptations of PPP have been defined:. The configuration of the ATM network is therefore quite simple when PPP over Ethernet is supported; a single VC can support multiple simultaneous users of multiple services without the complexity or expense of a router on the customer's premises. It is possible to use the PPP negotiation process to select access to a particular service.

Previous page. Table of content. Next page. This Interface is the interface that carries the DSL physical layer between the customer's premises and the network. Session multiplexing ATM provides intrinsic support for multiple sessions via the use of multiple virtual circuits between a network and the customer's premises. Multiprotocol support An ATM virtual circuit can support many different protocol stacks. Autoconfiguration and management The integrated local management interface ILMI provides a method of configuring the ATM service at the customer premises.

Service selection Although the use of permanent virtual circuits PVCs requires preconfiguration , the use of switched virtual circuits SVCs allows communication between the users' premises and the service providers to be set up in real time as needed.

Security and AAA The support of VCs end to end keeps communications for different users and services separated, which provides some security enhancements. Error detection Errors to cell headers introduced during transmission can be detected. Service selection This is a function of higher-layer protocols. Security and AAA AAL5 neither enhances nor degrades the security function of protocols above or below it in the stack.

Bridged Ethernet Figure Bridged Ethernet directly transporting IP. IP directly on AAL5. Multiprotocol support This protocol stack is meant to support IP and protocols that run over IP other routed protocols such as IPX can also be supported.

Service selection This is a not a function of this stack. Security and AAA This function is not inherent in this stack. Session multiplexing As PPP can support multiple simultaneous protocols, multiple sessions can be implemented. Multiprotocol support PPP allows the support of multiple protocols over each session.