Migrating To High-speed LANs

Corporate LANs are facing explosive
growth in traffic, driving the need for higher and higher bandwidths. A number of
technologies are available for increasing the speed and bandwidth of these LANs. However,
a number of factors have to be considered to decide on the technology option as well as
implementation of the same. Some of these are: type of application and data, size of data,
impact on the network bandwidth, network performance requirements, cost, reliability,
flexibility for upgrading in phases, scalability for future growth, and availability of
tools for management and support.

An understanding of the applications that
are driving the need for a higher bandwidth play a critical role in planning and
implementing network upgrades. Any upgrade without a proper analysis of these factors
would not yield the desired results, leading to wasted investments. Following are the
applications driving the need for higher bandwidths:

These applications involve 3D modeling/visualization of scientific
or complex objects. They often require creation and transfer of data files of the sizes of
100 MB to 100 GB. They need higher bandwidth for desktop, server, and backbone.

Magazines, brochures, and other full-color publications created on the
desktop are often transmitted directly to the printing centers. Similarly, many medical
applications involve transfer of complex images over network between hospitals/doctors/
and clinical/diagnostic centers. These files are also of GB sizes and require higher
bandwidth for desktops, servers, and backbone.

Many enterprises are building private intranets and deploying applications that go beyond
email involving static information publishing/dissemination, groupware, workflow, and 2/3
tier client server applications on the intranets. The information exchanged for these
applications would be compound documents comprising data, text, audio, video, and images.
The browser would be the universal user interface from which any information from anywhere
in the corporate network can be accessed from the desktop.

Large files of 1 MB to 100 MB typically get
transferred in real-life transactions that take place on corporate intranets. These online
transaction applications have different type of networking needs. In addition to high
network bandwidth, they need faster transfer rates and low transmission latency.

datawarehousing applications for business intelligence often involve extraction and
transfer of Giga to Terrabytes of data from the operational databases from all over the
enterprise to the central datawarehouse database. The extracted information in the
warehouse is often accessed by thousands of users. There is also a need to constantly
update the databases to provide users near-real-time data for critical business analysis
and decisions. These applications need low latency for faster search and access to data
and higher bandwidth for servers and backbones.

enterprises, backup of servers and storage systems is often done for archival purposes.
Such backups are usually taken after office hours and require large amounts of bandwidth
during a fixed amount of time. The backup involves GBs or Terrabytes of data distributed
over hundreds of servers and storage systems throughout an enterprise. These applications
require higher bandwidth for servers and backbone, and low latency.

going to be an increase in the desktop applications involving video e.g.
videoconferencing, education/training etc. These typically involve datastream transfers at
1.5-3.5 Mbps at the desktops. They not only need higher bandwidth for servers and
backbones but also need low and predictable latency.

These are the various types of emerging
applications that are driving the need for high-performance networks. We have also found
that each type of application has a different type of requirement.

Selecting Technology
In addition to understanding the application requirements one also needs to keep in view
the following common issues while planning a network upgrade.

  • Easy and straight forward migration without
    disruption to the current work
  • Scalability to higher performance levels
  • Low cost of ownership-both purchase cost and
    support cost
  • Flexibility to new applications and data
  • Reliability
  • Availability of management and support

Any upgradation to higher speed should
ideally be done transparently to the current users without disrupting their work. Also,
depending on the application”s need and types of data, sizes of data etc., the individual
segments have to be taken up for upgradation. For instance, backbone upgrades,
desktop-to-switch upgradation, switch-to-server upgradation etc.

Technology should be properly chosen while
optimizing the investments already made in the current networks. Technology selected
should offer scalability to take care of future growth. Cost of ownership is a major
factor for network administrators. Here, the one-time purchase cost as well as ongoing
support for training and maintenance tools need to be taken into account. Network
reliability is very crucial to the success of an enterprise. The network topology and the
internetworking schemes should be so chosen that the ultimate network built becomes highly

The most important of the criteria is the
flexibility to handle new type of applications and data. Increasingly, the emerging
applications need the network to handle various type of data comprising audio, text, data
image, and video. The loading and traffic patterns may also vary according to the
application. The network technology should have capabilities to handle these requirements.

Lastly, availability of tools for support
and management is critical. Whether the upgrade needs a different set of tools for support
and maintenance or whether the existing tools would be adequate, needs to be examined. For
new technologies their availability itself may be an issue.

High-speed Network Technologies
Above mentioned was the new applications that are driving the need to high speed
networking and the criteria for choosing a proper technology. Here are the various
technology options for high-speed networking.

Ethernet is an extension to the highly successful 10 Mbps and 100 Mbps IEE 802-3 Ethernet
standards offering a raw bandwidth of 1000 Mbps. It supports new full duplex operation
modes for switch-to-switch and switch-to-end station connection and half duplex operating
modes for shared connections, using repeaters and the CSM/CD access method.

Initially, operational over optical fiber,
Gigabit Ethernet would also use category 5 Unshielded Twisted Pair (UTP) cabling and Coax.
It can be switched, routed, or shared depending upon cost and bandwidth requirements.

ATM: Asynchronous Transfer
Mode (ATM) technology has been developed to provide scalable high-speed networking for
both data and voice. Starting with speeds of 150 Mbps it can be scaled for a speed of up
to 622 Mbps. It can support a wide range of data services including standard voice
telephony, TDM network trunks, compressed voice and video, connection-oriented datacom
protocols such as Frame relay, TCP, SNA, and X.25. It also supports connectionless
datagram-based communication protocols.

ATM networks can be built by connecting
devices to an ATM switch. Simple networks might be star configured with one multi-ported
ATM switch at the center of the star. Larger ATM networks are tree-structured with an ATM
switch at each branch. The following table gives a summary of ATM and Gigabit features:

A comparison of the two technologies i.e.
ATM and Gigabit Ethernet reveals that ATM is advantageous in terms of scalability,
guaranteed quality of service (at hardware level), fault tolerance, and availability of
products from multiple vendors in the market. However, it is expensive, complex in
technology, and requires retraining of staff. Standards are also still in the evolving
stage. The Gigabit Ethernet is relatively inexpensive and compatible with existing
Ethernet tools management. However, Gigabit Ethernet does not offer quality service
support at hardware level. It requires new switching and routing hardware, and has severe
distance limitations over copper and shared nets. Its standards will also not be ready
till March 1998.

These two technologies are similar in some
ways and different in others. They have to be viewed as complementary rather than
competing technologies. In terms of speed required to eliminate backbone congestion, any
one of them can be chosen. They differ mainly in terms of applications. ATM is designed to
support multimedia traffic and is best technology to support time-sensitive data, voice,
and video. Moreover, ATM provides a seamless connection of LAN and WAN without protocol
conversion. A major shortcoming of ATM is its high cost. This is mainly due to its quality
of service guarantees and advanced congestion control features.

Gigabit Ethernet maintains full
compatibility with the huge installed base of Ethernet networks. The current investment in
management and maintenance tools can be fully leveraged. It is simple to connect the
existing low-speed Ethernet users and devices using LAN switches or routers. As the frame
format and sizes are same for Ethernet technologies, no other network changes are
necessary. As far as high-speed LANs are concerned, the choice between ATM and Gigabit
Ethernet has to be based on the factors described above.

Network Migration
After choosing the proper technology, the actual migration has to be planned keeping in
mind the application need and traffic patterns. The most likely user upgrade scenarios
would be:

  • Upgrading switch to server connections: This
    will enable high-speed access to application and file servers.
  • Upgrading switch-to-switch connections: This
    will facilitate high-speed Gigabit pipes between switches.
  • Upgrading a switched Fast Ethernet backbone:
    This will upgrade the Ethernet switches to Gigabit speed.
  • Upgrading a shared FDDI backbone: This will
    enable upgrading of the current FDDI switches.
  • Upgrading desktop: This will upgrade the
    desktops with Gigabit NICs.

Depending on the application need, a phased
upgrade program can be taken up for specific segments of the enterprise network.

The emerging applications are creating
incredible growth of traffic on corporate LANs, driving the need for high-speed,
high-bandwidth LANs. We need to consider the nature of the application, the data type and
volumes, cost, reliability, disruption, maintenance tools, and TCO factors before deciding
about the technology.

The two technologies-ATM and Gigabit
Ethernet-offer complementary features and hence the user need to select either one of them
or a combination depending on his need. Finally a phased approach need to be taken for
upgrading the network segments gain depending on the requirements.

Group VP, IS, (Software Quality & Technology)
Wipro Infotech.

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