ITPRC NEWS - June 2001
Looking Into The Crystal Ball: The
Evolving Network Architecture
By Irwin Lazar
One constant in the IT industry is rapid change.
One important way that organizations can effectively manage change is by
developing and maintaining an enterprise network architecture. A network
architecture ties an organizationís business goals into its network
planning process in order to create a strategic direction (or road-map)
of how the network will evolve over the next three to five years based
on long-term business objectives. Key to an effective network
architecture is the ability to understand what new technologies are
emerging that can be leveraged to provide a competitive advantage.
In this article, we peek into our crystal ball to
try and predict the most significant emerging technologies that will
impact network architectures over the next two to three years in three
crucial areas, Wide Area Networking, Convergence, and Quality of
The Future of the WAN
For the most part, access to the WAN is still
based on time-division-multiplexing or Frame Relay, providing access at
speeds from 56kbps (DS0) to 45Mbps (DS3) per second. In many areas, ATM
access services are available at speeds from DS3 to OC3 (155 Mbps).
Incumbent exchange carriers still tightly control access in most areas
and the competition that was envisioned as a result of the 1996
telecommunications reform act has been slow to materialize. However,
within the last year the signs of competition are beginning to emerge
and over the next two to three years the number of choices that are
available to the end-user will continue to grow.
These new choices for the last mile include such
services as xDSL, Cable Modem, Ethernet, and wireless. Additional
choices will soon be available from power companies, low-earth orbit
satellite systems and potentially even high-altitude aircraft based
systems. Depending on availability, some locations may have fiber
connected directly to their building that can provide enterprises with
even more choices such as direct connectivity to a SONET service,
Gigabit Ethernet service or even simply to lease dark fiber to build
their own point-to-point networks.
Options within the WAN core have traditionally
consisted of leased line, TDM, frame relay, or more recently, ATM. With
the rise of the Internet a new choice has emerged, public IP network
Public IP services are typically being offered by
Internet Service Providers (ISPís) that are looking to leverage their
existing networks to offer additional services. Public IP services
either replace or supplement traditional frame relay, ATM and leased
line services by tunneling private traffic within public shared networks
based on IP. The largest drawback to public IP services has been the
lack of guarantees of performance, however this is beginning to change
as carriers improve their networks. Recently carriers such as UUNET have
begun to offer service level guarantees for public IP networks that
rival those offered by leased line and frame relay networks. As more
providers improve their networks, public IP offerings should grow.
One of the keys to the future of the WAN is the
development and deployment of multi-protocol label switching (MPLS).
MPLS uses tags to mark specific IP traffic flows in order to provide
varying classes of service. Using MPLS, carriers can engineer their
networks to offer guaranteed service levels for multiple types of
traffic flowing through their networks.
More recently there has been interest among
carriers and other network service providers in using MPLS for IP-based
VPN (Virtual Private Network) services. Carriers may use MPLS to
"nail up" the equivalent of a permanent virtual circuit across
an IP routed network; separate MPLS connections may even be established
for each class of network service offered by the carrier. From the
carrier's perspective, MPLS-based VPN connections (such as AT&T's
"IP-Enabled Frame Relay") may be promoted as a replacement for
frame relay PVC services. MPLS-based VPN's can also allow service
providers to tunnel privately addressed networks through their own IP
network. This removes one of the great barriers to VPN adoption by many
large enterprises that have standardized on a private IP addressing
While only carriers and enterprises that own their
own WAN infrastructure will likely deploy MPLS, MPLS will allow carriers
to offer new services that will widen the choices available to their
Convergence and Quality of Service
Perhaps no subject has received more press
coverage in the last two years than voice, video and data integration.
As the networking world has standardized on the IP protocol, and as new
technologies have been introduced that improve network performance, it
is only logical that organizations would look to consolidate their
multiple networks for voice, video and data into a single network
infrastructure based on IP. The architects of such networks believe that
voice and video are simply data types that can be delivered over the
same packet networks used to transmit other types of data.
However, the roadblock to convergence continues to
be performance. Traditional IP data networks are based on best effort
guarantees where no guarantee of reliable transmission is made. This
type of network is fine for applications such as e-mail and web browsing
but is insufficient to support application such as voice and video where
delivery of data within a specified time range is required. In order to
support applications such as video and voice, data networks must be
converted to enable prioritization of voice and video data such that
acceptable delays and jitter are achieved.
Fortunately, many efforts to deliver guaranteed
Quality of Service (QoS) are underway. The two most important
technologies under development are Diff-Serv and the previously
Diff-Serv provides a way of using the Type of
Service bit (TOS) in the IP packet header to mark a packet for a certain
level of priority. Using Diff-Serv, a network can give higher priority
to packets marked as voice or video, and lower priority to packets
marked as web browsing or e-mail.
Both MPLS and Diff-Serv will likely be managed via
policy-based networking. In early policy management implementations,
network managers are able to centrally configure security and Quality of
Service policy for the entire network from a single console. However,
these policies are static and are not capable of changing based on
certain network criteria such as load, user location, or day of the
However, in future policy management
implementations, network managers will configure policy information for
users and/or applications that is then stored in a directory (usually
based on LDAP). Applications will request access to devices or certain
quality of service levels (usually via RSVP (Resource Reservation
Protocol). Network devices such as routers, switches (and in some
implementations, network interface cards) forward the request to the
policy manager using the COPS (Common Open Policy Services) protocol .
Windows 2000 already supports APIs for using RSVP to request quality of
service levels. The policy manager either grants or denies the request
based on information stored within the policy management directory.
It should also be noted that the policy server
model will also extend to security. In this case, the request/response
protocol might be RADIUS for network authentication, authorization, and
accounting functions. Policy servers will thus need to support multiple
request/response protocols, including COPS and RADIUS.
The Desktop Management Taskforce (DTMF) is leading
an effort to standardize how information about network objects is stored
within the directory. The Directory-Enabled Networking (DEN) standard
will attempt to create a common enterprise directory that can be shared
among a variety of applications including messaging systems, network
management systems, and network policy systems.
Technologies such as Diff-Serv and MPLS, along
with initiatives such as DEN will eventually allow todayís data
networks to deliver the guaranteed performance required for convergence
of voice, video and data into the same network infrastructure. This will
in turn lower management costs and reduce network complexity.
Within the scope of network architecture
technology is constantly changing. While the pace of change of
technology within the LAN has slowed in recent months, the pace of
change in the WAN and in voice, video and data convergence is exploding.
In order to maintain a competitive advantage, organizations must manage
their network architecture to embrace, manage and exploit these changes.
Irwin Lazar is a Senior Consultant for The Burton Group. He focuses on
strategic planning and network architecture for Fortune 500 enterprises
as well as large service providers. He is the conference director for
MPLScon and runs The MPLS Resource Center www.mplsrc.com and The
Information Technology Professional's Resource Center www.mplsrc.com.
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