Understanding the network.pdf - Back to Home

hardware-based routers is essentially to "route" Layer 3 datagrams at
wire speed by developing a hardware chip to perform the same
functionality that is achieved with software-based traditional routers.
At the present time, several vendors are developing and marketing
Layer 3 switches. Some of the more notable solutions are Cabletron
Systems'SmartSwitch routers, Foundry Networks BIG Iron and
ServerIron switches, and PacketEngines PowerRail routing switch.
Cisco Systems, the undeniable king of software-based routers, is also
marketing and developing ASIC-based switch router products in the
form of their Routing Switch Modules (RSMs) on their Catalyst 4000,
5000, 6000, and 8000 series switches. However, Cisco's and all the
other "switch router" vendors still have a ways to go before software
routers become "a thing of the past."
This is largely due to the limitations intrinsic to hardware-based
anything; there is only so much that can fit into a chip. So, although
advances have been made in Layer 2 switching ASICs, the technology
to develop a complete multiprotocol router chipset is still not available.
Today, most Layer 3 switch routers offer IP and IPX, and some core
filtering and packet processing functions. AppleTalk and the older
legacy Layer 3 protocols have yet to make it into a production switch
router (as of this writing). The switch routers in the marketplace today
provide enough functionality to route IP/IPX network traffic, but few
have developed a hardware-based routing suite that even comes
close to providing the feature set the Cisco Internetwork Operating
System offers. In reality, most vendors have had to move to
software-based solutions for the majority of routing features, leaving
only packet routing to be handled in hardware.
This is not to say that Layer 3 switch routing will not come into its own
and deliver on its promise of wire rate routing. It just is not here today.
Not to mention the fact that most Layer 3 routers have little to nothing
in terms of any sort of WAN support (this is also changing somewhat).
ATM Switches
When ATM was introduced, its distinction from traditional LAN and
WAN transmission protocols was immediately noticed. Its support of a
diverse range of operating speeds, optimization towards multimedia
applications through the use of small MTU size and Quality of Service
(QoS) transport contracts, and dependency on switches for
implementation made ATM stand out from the crowd. It was also
believed by some of its strongest early advocates that ATM would
evolve into the "all in one" LAN/WAN networking solution.