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From: rmora@coasin.co.cr
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Date: Thu, 2 Nov 2000 20:27:01 -0500
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Cc: <rmora@coasin.co.cr>
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The original URL of this article is:
http://www.tmcnet.com/articles/itmag/0400/0400ii.htm.
Message from sender:
Estimado Francisco:
Adjunto copia del artículo sobre las diferencia
entre IP y ATM para el core de una red.
Como podrá observar en el artículo se habla de
lo que conversamos sobre la eficiencia
de ATM o IP y como se recomienda que un
carrier tradicional como el ICE se oriente
hacia ATM en el Core a pesar de la supuesta
eficiencia del IP/PPP
Gracias
-------------------------
April 2000
IP Versus ATM: It's No Debate
BY JIM MACHI
At least once every week someone asks my opinion on when IP will replace
ATM. Since I'm getting a bit tired of the question, let's set this
straight. While ATM and IP do offer some competing methods to packetize
voice, they co-exist in most networks -- and will continue to for some
time.
The real debate is this: Which is the better solution? Packets over SONET
(POS)? Or IP over ATM? Today this debate is mainly among network engineers
working for service providers. But it will become an increasingly
important issue as more voice traffic migrates to IP.
As in most debates, both sides have some advantages and there is no one
best answer. The right solution will depend on the operating environment
and business model where the technology will be used.
Getting Down To Basics
To understand some of the points being argued, it's essential to
understand some basic technical issues. SONET (Synchronous Optical
NETwork) is the underlining transport mechanism of both POS and IP over
ATM. SONET is a standard for transporting and multiplexing data over
optical media between two points. This technology has been deployed in all
carriers' networks.
A scalable technology, SONET has a hierarchy of optical signals defined
from an OC-3 (155 Mbps) to OC-192 (9.6 Gbps). Each optical signal maps
into the next highest layer. SONET also has a low overhead rate of about
3.7 percent, making it a very efficient transport technology.
POS is technically simple. SONET provides a point-to-point connection
between two routers. IP packets can be mapped directly into SONET using a
point-to-point link protocol (PPP). At each node, the IP packets are
wrapped into PPP frames. When they get to the next node, they are
unwrapped. The destination address is examined, routed to the correct
path, and re-wrapped as new PPP frames. This is a very efficient way to
transport IP. But it leaves the network management and control to the
routers.
IP over ATM is more complex. It is important to have a basic understanding
of ATM. This standards-based multiplexing and switching technology is
built on a fixed-cell length of 53 bytes. ATM is a connection-oriented
technology. For two end points to communicate, a virtual circuit must be
established between them. The virtual circuit concept is crucial to ATM.
Each virtual circuit is assigned a traffic or service class, which
provides the quality of service (QoS).
There are several ways to place IP directly over ATM. These include
classical IP over ATM and LAN emulation. The most effective method is
multiple protocols over ATM (MPOA), which basically provides for a
distributed virtual router. In simple terms, it allows an increase in
efficiency and higher throughput compared to other IP over ATM methods.
While the technical issues are always interesting to debate, their impact
can be seen in some of the network attributes including cost, performance,
and management.
Bandwidth Issues
POS is a very efficient way to transport IP. IP can achieve up to 95
percent of the available line rate when running over PPP compared to 80
percent of the available line rate when running IP over ATM. The
difference is the overhead required to support ATM.
IP over ATM has the advantage on bandwidth management. The virtual
circuits allow you to assign flexible bandwidth to each virtual circuit
(VC). This allows differential service levels among multiple users. A VC
carrying VoIP can be assigned a high priority compared to one that is
strictly data, so higher quality of services levels can be easily
achieved.
PPP has no mechanisms providing bandwidth management, which is the
responsibility of the IP layer. The IP layer must schedule its packet
transmissions to ensure each flow receives its fair share of link
bandwidth. MPLS (MultiProtocol Label Switching) will provide some
bandwidth management feature; however, in the near term it will not match
IP over ATM.
Quality Of Service
QoS is related to packet loss, throughput, end-to-end packet delay, and
jitter. ATM traffic/service classes and management functions can help
mitigate the first three problems. Since ATM is connection-oriented,
jitter is less of an issue. However, IP over ATM can only offer these
advantages between the ATM switches. If the quality of service is crucial
and most of the problems occur in the WAN, IP over ATM is a good choice.
Otherwise, neither technology has an advantage.
It's The Environment That Matters
While POS and IP over ATM offer different features, the operating
environment and business model are essential to determining the best
solution.
Traditional carrier networks usually own the fiber, making bandwidth cost
less of an issue. However, bandwidth management and QoS are crucial. These
companies need to provide high-quality voice services to customers paying
10 cents per minute, deal with legacy services that might not fit into a
pure IP network, and provide Internet service. IP over ATM is a good fit
for these customers. While IP may be the network layer of choice, ATM
allows them to integrate legacy services and to offer differentiated
services.
ISPs and emerging carriers are not encumbered by legacy services.
Data-based services generate a large portion of their revenues compared to
traditional carriers. Many ISPs and emerging carriers lease the fiber,
making bandwidth cost an issue. They are usually more concerned with
routing large numbers of packets between their backbone routers than in
offering differentiated voice services. POS is a good choice for them.
Enterprises have a blend of the challenges facing ISPs and traditional
carriers. They must lease bandwidth from the carriers. They need to
provide different level of service to intranet traffic and intra-company
voice traffic, and to deal with legacy data communications traffic. Many
of these companies are migrating from frame relay to ATM-based services,
allowing them to minimize their cost while providing the level of services
end users require.
MPLS may solve many of the today's QoS and bandwidth management problems.
Newer technologies like IP directly over DWDM, or DTM, might replace POS.
However, in the future, please don't ask me about the great ATM versus IP
debate. There just isn't a clear answer. Ultimately, the winner depends on
the operating environment and business model of whoever's asking the
question. c
Jim Machi is director of product marketing, Internet Telephony, for
Dialogic Corporation (an Intel company). Dialogic is a leading
manufacturer of high-performance, standards-based computer telephony
components. Dialogic products are used in fax, data, voice recognition,
speech synthesis, and call center management CT applications. For more
information, visit the Dialogic Web site at www.dialogic.com.
Copyright 2000 Techonology Marketing Corporation (TMC) - All rights
reserved