Understanding the network.pdf - Back to Home

ATM-specific applications would be developed, and mixed protocol
LAN and WAN implementations would be replaced with ATM operating
over different media and at different rates, depending upon the
environment's needs.
In the end, however, traditional Layer 2 LAN transmission
technologies, utilizing similar hardware switching technologies,
evolved far beyond what ATM's creators had ever envisioned. Today,
LAN protocols such as Ethernet have evolved to support more than
adequate operating speeds and with further standards development
(for example, IEEE 802.1p), can now provide Layer 2 traffic
prioritization. There have also been efforts to develop QoS services for
TCP/IP, which is used for all Internet data transport. QoS service for
TCP/IP has become increasingly important as technologies to transmit
voice over IP (VoIP) and real-time video over the Internet have
matured. The Resource Reservation Protocol (RSVP) developed by the
Internet Engineering Task Force (IETF) is one such method for
providing QoS services for TCP/IP.
Given the current state of development of QoS services for traditional
Layer 2 LAN transmission and Layer 3/4 transport technologies today,
the usefulness of ATM in the LAN environment is questionable.
Because ATM is a connection-oriented transmission protocol, it is
basically incompatible in its native form with traditional
connectionless protocol-based LANs. Because of the inherent
interoperability issues between ATM and traditional or legacy Layer 2
and Layer 3-based LAN protocol functionality, several strategies have
been developed to provide compatibility services between ATM and
the legacy LANs. The first and most widely supported solution is the
ATM Forum's LAN Emulation over ATM (LANE) protocol suite. The
LANE suite provides all the services necessary to fully incorporate ATM
connected end-stations into an existing traditional Layer 3 LAN
network segment.
The utilization of ATM as a high-speed WAN protocol is growing,
however, as the need for more and more bandwidth on the Internet
backbone increases. As we learned earlier, LAN networks traditionally
have been designed to operate using an 80/20 traffic utilization rule:
80 percent of the network traffic is within the local network, and 20
percent is outside the local network. Today, the 80/20 rule is more
like 50/50 or 40/60. The need for access to resources outside the local
network is growing annually. With this shift in network traffic
utilization, and with IP being the dominant network transport protocol,
the development of IP over ATM technology has been quite active for
some time. The first result of this effort was the development of IETF's