Welcome to Jenny's Switches Page
Congested Networks
Today's Networks are becoming congested and sluggish because
they weren't designed to handle the extreme amount of inter-subnet
traffic currently crossing the enterprise.
Ethernet switching devices increase overall network performance by
decreasing the amount of extraneous traffic on the individual network
segments attached to the switch. When the packet arrives at the switch
the packet's destination address is inspected to determine which segment
it is destined for. If it is destined for a node residing on a different segment
than that on which it arrived, the packet is then forwarded to that destination
segment only.
Switches beging monitoring network traffic immediately upon powerup
and automatically filters packet by the source and destination addresses
as soon as a network map can be constructed (a matter of a few minutes).
Additionally, all bad or misaligned packets are filtered anytime they are
found.
Front panel of a switch
Toward a New Architecture
Adopting switching technology to solve bandwidth, scalability, and
manageability problems can be as easy or as difficult as the network planner,
makes it. Switches can be seamlessly slipped into the network to fix a trouble
spot - or the network may be re-designed around switching as the core
technology. Although using switching as a point-solution is often an easy
win, this approach misses an opportunity to take advantage of switching
technology on an enterprise scale. In order to get maximum value for an IT
dollar, network owners must plan the evolution to a switched enterprise
network. To do this the Network Planner must ask these questions. What
type of switching should be used? Where should it be deployed? What should
you do to prepare to adopt switching? How much planning is needed?
Developing a Network Architecture
Planning means developing a network architecture. An
architecture is more than a laundry list of the boxes and topologies
scattered throughout closets, floors and buildings--more than
routers and hubs and star topologies. An architecture sets forth
both the strategies and blueprints which define major network
elements and the relationship between them. There is either a
documented, well-conceived design, or there isn't. And the
difference between an enterprise infrastructure and meshes of
loosely connected networks is an architecture plan.
Architecture provides the high level design, specific subnetwork
technologies, network concentration, switching and interconnection
schemes, carrier services, wiring, management systems, and
protocols from which implementation flows. Architecture
establishes the key points of stability in networks through which
next generation technology is integrated into the installed base of
systems. The rigorous definition of these interfaces permits
operational flexibility. An architectural framework for the network
allows organizations to cope with rapid unforeseen changes in
technology or business practices.
Switching Technology Is Rapidly Changing Networking
The networking industry--and by extension, network owners--are caught
in a period of radical change right now. Switching technology in general,
and ATM in particular, represents a discontinuous (rather than continuous, or
incremental) change in networking. These technologies are not just somewhat
faster than existing networks--they are two orders of magnitude greater. Such
large, discontinuous change is defining. With the arrival of switching,
networking has evolved into something entirely new. Although switching
technology can be made to behave like the installed base internetworking
devices, its power, and the compelling reasons to adopt switching, come from
its ability to transform the way networks are designed, built, and run.
Successful network planners will get out in front of the wave of change and
begin planning now to adopt switching technology.
Picture of a Switch
Fitting The Pieces Together
Many roads lead to the enterprise switched network. This is necessary,
largely because of the variability in networking technology across companies.
Fundamentally, the high level structure of a switched network is simple:
A high speed point-to-point switched core providing at least 100 Mbps
links to aggregate and forward traffic across an enterprise network;
High-speed frame switching (either Ethernet or Token Ring) providing
dedicated links to desktops, servers, and workgroup-level resources;
and
Mechanisms which integrate existing broadcast-based, shared access
LANs into the heart of the switched environment.
What Is A Switched Enterprise Network?
This figure provides a conceptual overview of how the various switching
technologies fit together to form an enterprise network.
Anatomy of an Enterpriser Network
The core of the network (the backbone and select workgroups) is driven
by high speed ATM connections. Attached to the ATM core are devices and
workgroups connected via switched Ethernet and switched Token Ring. The
world of legacy shared access LANs is in turn connected to the switched
infrastructure through traditional bridges and routers.
A Fine Sauce; Not Dessert
The capable enterprise network must successfully combine an array of
technology, old and new--including routers, frame switches, shared access
Ethernet and Token Ring, bridges, cell switches, VLANs, hubs, NICs,
protocols and repeaters. The resulting network architecture is not defined by
a single element. Instead, it is rather like a fine sauce, blending many
elements into a creation better than any of its ingredients. Individual
technologies are combined in a complementary manner, each leveraging other
building blocks in the network.
Store and Forward versus Cut-through Design
To decrease the amount of time to process packets, some switches use a
procedure known as a "cut-through". Only the first few bytes of the Ethernet
packet are read for the destination and source addresses; these switches then
route the packets ahead without examining the remaining bytes for any
possible problems. This procedure allows for fast processing, but allows
misaligned or packets being jammed because of late collisions to be
forwarded on to other network segments.
The "store and forward" approach examines the entire packet. Devices using
the store and forward technique filter out any bad or misaligned packets and
then filter or forward the remaining valid packets to their correct destinations.
The store and forward approach offers a solution which is very
"network-safe" and allows for additional features such as selective filtering
schemes. Store and forward technology is now nearly as fast as cut-through
designs, with the added benefit of bad packet filtering. The LSB4 combines
these features to offer high performance switching between Ethernet
segments with maximum filtering options and Spanning Tree Algorithm
Support.
Should You Build a Switched Enterprise Network?
A switched enterprise network -- built around ATM, switched LANs, and
VLANs -- offers the broad set of capabilities required to meet the demands of
a new generation of application technology and organizations pushing that
technology to the limit. But what are the decision criteria that indicate
whether you should consider switching technology as the foundation for your
enterprise network? Any enterprise that meets three of the following six
criteria should begin a serious evaluation of switching technology.
Consider switching if (the):
Number of end stations in your enterprise is growing at the rate of 25
percent per year. In expanding the network, switching technology must be
considered. Frame switching may be adopted at the floor or building
backbone level, perhaps in place of workgroup class routers. Existing power
users and servers might be connected with switched Ethernet or Token Ring,
passing down existing repeated network connections to new users less likely
to need high-bandwidth links.
Client/server computing applications are a success. The next killer
application is probably no further away than the next scheduled client/server
application rollout. Although client/server is a faster, cheaper environment for
developing applications, these systems require at least an order of magnitude
greater bandwidth than do terminal/ host applications.
Building backbones need more than 100 Mbps. When FDDI runs out
of gas, it is time to consider switched 100 Mbps Fast Ethernet or ATM.
Think about switching technology before segmenting that FDDI backbone
again.
Some servers need more than 20 Mbps (shared) bandwidth. When
servers with multiple shared Ethernet or Token Ring interfaces cannot
support aggregate workgroup or server bandwidth demands, it is time to
begin investigating 100 Mbps Fast Ethernet or ATM interfaces.
Some desktops need more than shared 10 Mbps. When advanced
applications increase bandwidth requirements, it is time to consider switched
LANs for high-performance workgroups. In the extreme case, for users of
scientific visualization applications, or users who live in the world of
multimedia or delay-sensitive applications (options trading, for example),
ATM interfaces will replace existing or planned FDDI network adapters.
Servers are being centralized, increasing the amount of traffic that
traverses building or campus backbones. Experience shows that as soon as
more than about one-third of client/ server traffic leaves an individual
workgroup, the workgroup link to the backbone must be doubled in capacity.
Incorporating Switches into your network
Switching Technology For Everyman
Switched networks offer something for everyone. New twists on
venerable Ethernet provide dedicated 10 Mbps connections to every
endstation on the network--users and servers alike. Links to critical shared
resources are built with Ethernet delivering 100 Mbps. These links aggregate
traffic streams from many desktops to workgroup file or database servers.
Switched Token Ring is also making an appearance, alleviating congestion in
the largest ring networks while working with the installed base of NIC cards,
just as switched Ethernet does today.
Switching technology and products offer network planners the
opportunity to solve networking problems with a better set of tools.
Switching promises higher performance, greater scalability, and improved
manageability. To capitalize on these benefits, network owners must evaluate
the existing network, determine where the troublespots lay, and decide how
and where to use new technology to overcome existing weaknesses.
Answering these questions is the heart of the architecture planning exercise.
Good answers are not easy to come by, but are proof that planning pays.
THE END
Any questions?
© 1997
