Today, there’s much talk about information highways and Asynchronous
Transfer Mode (ATM). Just as the Internet revolutionized worldwide communication,
ATM brings new meaning to high-speed networking. However ATM is emerging
as the primary networking technology for next-generation, multimedia communication.
Besides, the ATM protocol designed to handle isochronous (time critical)
data such as video and telephony (audio), in addition to more conventional
data communications between computers.
ATM can define as the transport protocol. It’s a way of transmitting
data, voice and video from one place to another. However, ATM gives you
more than a basic transmission capability such as
1) It support both private and public networks
2) Uses the same technology for Local and Wide Area Network
3) Transports voice, video, and data traffic on a common circuit
4) Delivers bandwidth on demand
However, it comes at a low price. Contrary to common misconceptions,
ATM is a very complex technology, perhaps the most complex ever developed
by the networking industry. While the structure of ATM cells and cell switching
do facilitate the development of hardware intensive, high performance ATM
switches, the development of ATM network requires the overlay of a highly
complex, software intensive, protocol infrastructure. This infrastructure
is required to both allow individual ATM switches to be linked into a network,
and for such networks to inter-networking with the vast installed base
of existing local and wide area network.
ATM is the networking technology that satisfies these requirements.
For LAN users, you’ll get more bandwidth with ATM than with many of today’s
LANs. You can begin to use new applications and improve the performance
of existing applications. ATM also provides more flexible bandwidth for
your Wide Area Network (WAN). WAN users can expect enchanted bandwidth
management and bandwidth on demand, which can reduce the cost.
Furthermore, the advantages of the ATM network are ATM is a very
flexible bandwidth allocation and It simple routing due to connection oriented
technology. Besides, It is the high bandwidth utilization due to statistical
multiplexing.
However the disadvantages of the ATM are overhead of cell header and complex mechanisms for achieving Quality of Service. Finally, it very congestion and it may cause cell losses.
Nowadays, there are many reasons why ATM will be the networking technology for the near future and beyond. The success of this technology has not been left to chance, because ATM technology is been engineered in a manner to proactively address the problems that will be encountered with next-generation networks. One of the reason it successes is that ATM technology is designed to handle all aspects of multimedia (video, audio and data) for the LAN, MAN, and WAN. However there are few basic concept for the ATM how it be the next generation networking.
(Figure 1)
Various services and provide service specific functions. This AAL specific information is contained in the information field of the ATM cell.
Routing: ATM is a connection-oriented mode. The header values (i.e. VCI and VPI etc.) are assigned during the connection set up phase and translated when switched from one section to other. Signaling information is carried on a separate virtual channel than user information. In routing, there are two types of connection i.e. Virtual channel connection (VCC) and Virtual path connection (VPC). A VPC is an aggregate of VCCs. Switching on cells is first done on the VPX and then on the VCC. We will discuss these two connections later.
Following we will discuss about why we using ATM Network as our next generation network? The following is the benefit of using ATM network:
In this part, I will discuss the architecture of ATM networks, ATM
connection and ATM connection type.
An ATM network, it consist of a set of ATM switches interconnected
by point-to-point ATM links or interfaces. ATM switch support two kinds
of interfaces, there are User-Network Interface (UNI) and network-node
interfaces (NNI). Before I go in detail I will differential what is UNI
and NNI. Actually, the UNI is the network interface, but the different
is subtle and unimportant. However, the NNI is a cell. It unlike the UNI
cells, because there is no Generic Flow Control (GFC) field, and the first
four bits of the cell are used by an expanded (12-bit) VPI field. Since
the GFC is rarely used, so that there are no difference functional between
UNI and NNI cells, other than in the fact that the latter can support a
larger VPI space.
From the figure 2 below the UNI connect ATM end-system which included hosts, router and so on to an ATM switch, while an NNI may be imprecisely defined as an interface connection two ATM switches together; slightly different cell formats are defined across UNI and NNI. More precisely, however, an NNI is any physical or logical link across which two ATM switches exchange the NNI protocol. So that, for this reason the connection between a private ATM switch and public ATM switch is a UNI – known as a Public UNI – since these switches do not typically exchange NNI information.
(Figure 2 ATM Network Interface)
ATM networks are fundamentally connection oriented. This means that a virtual circuit needs to be set up across the ATM network prior to any data transfer. ATM circuits are of two types: virtual paths, identified by virtual path identifiers (VPI); and virtual channels identified by the combination of VPI and of virtual channel identifier (VCI). A virtual path is a bundle of virtual channels, all of which are switched transparently across the ATM network on the basis of the common VPI. All VCI and VPI, however, have only local significance across a particular link, and are remapped, as appropriate, at each switch. In normal operation, switches allocate all UNI connections within VPI=0; the use of other virtual paths is discussed later in this paper.
The basic operation of an ATM switch is very simple: to receive a cell across a link on a know VCI or VPI value; to look up the connection value in a local translation table to determine the outgoing port (or ports) of the connection and the new VPI/VCI value of the connection link with the appropriate connection identifiers such as the figure 3.
(Figure 3)
The switch operation is simple such as the following diagram (Figure 4) because external mechanisms set up the local translation tables prior to the transmittal of any data. The manner in which in which these tables are set up determine the two fundamental types of ATM connection :
( Figure 4 Virtual Circuit and Vritual Path Switching)
On the other hand, the ATM routing protocols is route ATM connection
requests across the ATM network such as the figure 5. There are two fundamental
types of ATM connections:
(Figure 5 Types of ATM Connection)
What is notably missing from these types of ATM
connections is an analog to the multicasting or broadcasting capability
common in many shared medium LAN technologies such as Ethernet or Token
Ring. In such technology multicasting allows multiple end systems to both
receive data from other multiple systems, and transmit data to these multiple
systems. Such capabilities are easy to implement in shared media technologies
such as LANs, where all nodes on a single LAN segment must necessarily
process all packets sent on that segment. The obvious analog in ATM to
a multicast LAN group would be a (bi-directional) multipoint-to-multipoint
connection. Unfortunately, this obvious solution cannot be implemented
when using AAL5; the most common ATM Adaptation Layer (AAL) used to transmit
data across ATM network.
As a conclusion ATM will offer significantly greater bandwidth, flexibility and quality of service support than is possible on today's networks built with shared media hubs and routed internetworks. The most important reason for impending success of ATM is that this technology is standards-based. Standards and interpretability are the most important factors behind Internet worked communications. Networking standard that is technically sound and rigidly followed are more important than much technical limitation within a system.
[MAIN] [ABOUT ME] [Secondary Classmate] [S3S CLUB ] [BIT MEMBERS]
[PHOTO GALLERY] [BIT's PHOTO GALLERY] [DATA COMMUNICATION]
Prepare by Wang Fook Weng
28th September 1997