ATM Networks

We are moving towards a digital revolution where every aspect of life will be pondered by the computer networks, reading books, watching film, collecting photographs, paying bills or buying a real state. Computer systems are very complex and are able of linking astonishingly millions of computers and billions of telephone lines. The clicking mouse is more powerful and swift than any other mean of communication. The valiant explorer in an isolated corner of the earth can contact his or her family with the help of a satellite or a cellular telephone. How these marvelous webs of interconnectivity are buildup? What lies at the foundation of a computer system and why they work the way they do?
We are in these posts studying the underlying principles of internet, telephone networks and asynchronous transfer mode networks. ATM networks are the future of computer networking. They are interesting as they base on experience with the telephone network and the Internet to construct an incorporated services network that gives end to end quality of service. The goal leads to an exclusive set of design decisions that have impressed the products of networking research and commercial networking products.

Many of you will mingle this ATM with Automatic Teller Machine that is used by banks to transect money. Asynchronous Transfer Mode (ATM), a dedicated connection switching technology, uses digital signal technology to manage digital data into 53 byte cell units and to transmit on a physical medium. A cell is individually asynchronously processed relative to other adjacent cells. Before being multiplexed over the transmission, the call is queued. ATMs are designed by keeping in mind that they can be easily used by the hardware instead of software. Its processing is faster where switch speed is also possible. An ATM network may have a speed of 10 Gbps. The pre-defined bit rate could be 155.520 Mbps or 622.080 Mbps. ATM is a vital part of ISDN (BISDN) along with SONET (Synchronous Optical Network) and several other technologies.

Types of ATM Networks Connection:

There are two ways in which ATM connections between endpoints can be distinguished by the Quality of Service parameters and formats of their addressing schemes. The type of ATM is determined by ATM signaling. The signaling components situates at the end station and at the ATM switch. The creation, management and termination of SVCs (switched virtual circuits) are determined by the signaling layer of ATM’s software. UNI (User Network Interface) is the ATM standard wire protocol applied by the signaling software. The manner in which an ATM switch signals another ATM switch is composed of a second signaling standard known as NNI (Network Network Interface). ATM has two types:  

• Point to point connections
• Point to multipoint connections
Point-to-Point Connection: If an ATM-aware process wants to connect to another process on some other network then it needs to establish an SVC which can be asked from signaling software. The signaling software sends request of creating a SVC by the virtue of ATM adapter and the reserved signaling VC to the ATM switch.
The TAM switches keep forwarding the request until it reaches to its destination. Considering the ATM address for the connection and the internal network database of the switch (routing table), ATM switch ahs the right to determine which switch to propagate the request next. It is determined by each switch whether the service category and Quality of Service needs of the request are achieved. If the request of virtual circuit is supported by all the switches, the end station of the destination receives a packet that has VC number. From now onwards, the ATM-aware process can directly interact with the destination by sending packets to the VPI/VCI that recognize the specified VC.
Point-to-Multipoint Connection: Contrary to a LAN environment, ATM has no innate capability to broadcast or multicast packets. It is a connection oriented medium. To make it capable, the sending node can produce a VC to all destinations and send a copy of the data on each virtual circuit. It is highly ineffective. Point to multi point connections is an efficient way to achieve the target. It connects a single source endpoint called root node to multiple destination endpoints called leaves. On splitting into two or more branches, the ATM switches copy cells to multiple destinations. The process is unidirectional. The root can transmit to the leaves but leaves are unable to transmit to the roots or to each other on same connection. Leaf to node and node to leaf transmission needs a unique connection. The reason behind this limitation is AAL5’s simplicity and the incapability to interleave cells from multiple payloads on a single connection. Although complex but they play vital role in boosting networks, ATM is changing the way we communicate and are probably the future of our digital world.