Making The New Public Network Happen Now
BY STEPHEN DUFFY
Any farsighted enterprise depending on the Internet for success wants a
business-class, multi-service IP network optimized for quality voice,
video, and data � a network with bandwidth quality of service (QoS)
comparable to the PSTN. Such next-generation packet networks need
platforms that can grow quickly and elegantly to meet exploding bandwidth
demand. They also must incorporate value-added, differentiated services
such as high-bandwidth allocation and high-speed transmission � and
support QoS at gigabit and terabit rates.
While QoS is used sparingly today in emerging IP networks, farsighted
network builders should recognize that surging appetite for
beyond-best-effort applications, such as VoIP service, soon will oblige
prevalent QoS for competitive survival. Designed to be the core of these
new nets, next-generation network elements (NEs), such as terabit switch
routers, will be relied upon to not only assure adequate bandwidth but
also enable QoS that can minimize management costs and add
revenue-producing service offerings.
Reliable Internet QoS is essential to developing service level
agreement (SLA) revenue models in which a business can buy only the type
of service it needs � with billing commensurate with use. A
business-centric Internet should provide QoS levels to match different
classes � akin to airlines offering coach/business/first-class service
options that will accommodate the range of typical business traffic, from
low-priority Web surfing to mission-critical voice transmissions. And as
new applications like real-time packetized voice and audio/video streaming
migrate to the Internet, the network�s operational requirements must
change to accommodate them.
Such traffic variety will challenge resources and create
revenue-enhancing opportunities. Delay-tolerant, highly elastic
applications like e-mail and file transfer protocol (FTP) are more
tolerant of network delays than real-time, delay-sensitive interactive
applications such as VoIP, which demand low loss and bounded delay and
jitter. Real-time applications must receive data within some finite period
of time or the packets essentially become worthless. This makes it
mandatory to enforce an upper bound of delay for such flows. Users should
expect to pay a premium for such guaranteed precision. Conversely, a
predictive service may deliver a fairly reliable but not guaranteed level
of service at a much lower cost.
Note that the emerging demands of next-gen networks do not necessarily
revolve around bandwidth. The strategy of deploying an increasing number
of higher data-rate channels over dense wave division multiplexing (DWDM)
fiber has not and will not quench the insatiable demand for bandwidth. In
fact, it inevitably will lead to a commoditization in the cost of
bandwidth, so the capital-intensive solution of overbuilding networks won�t
suit a world where the cost of bandwidth is dropping faster than network
transmission costs.
Over-provisioning can relieve congestion, but it can�t deliver
tightly bounded delay mechanisms for guaranteed SLAs that incorporate
delay-intolerant applications such as corporate data centers or VPNs. IP
networking in which carriers can offer �always on� types of services,
readily differentiate and prioritize traffic, and efficiently manage their
networks while minimizing infrastructure costs, will need �intelligent�
next-gen NEs that can flex new flow-based protocols and QoS mechanisms.
NEW METHODS
Differentiated services (DiffServ) and Multi-Protocol Label Switching (MPLS)
standards, developed by the networking industry�s Internet Engineering
Task Force (IETF,), are linchpins to
providing QoS over the Internet. They hand service providers the
appropriate means to control high-priority applications, like VoIP, and
guarantee quality end-to-end service.
DiffServ is an IP QoS mechanism that allows network traffic to flow
with sufficient quality to ensure successful deployment of the
application. It enables identification of the traffic class of each
packet, the primary component allowing QoS to be deployed, so traffic can
be directed without the overhead of managing each end-to-end flow.
DiffServ is based on common, configurable parameters derived from the
application�s bandwidth, delay-jitter, and loss-probability
requirements.
QoS on the Internet obliges consolidating traffic flows, which must be
summarized into aggregate groups or classes across the network (much like
routing protocols provide network summaries to the Internet�s routing
table). DiffServ aggregates individual flows and marks packets for the
appropriate level of service available from an assortment of predefined
packet treatments.
Because it affords nearly boundless combinations of services, a
differentiated-services network can easily provide the service levels
demanded by either new-age enterprises transacting business entirely over
the Internet, or traditional businesses migrating from private voice/data
networks to IP-based service provider nets.
Meanwhile, network designers must be sure the amount of high-priority
traffic put on any individual network link does not exceed its bandwidth.
MPLS virtual connections among packet switches � Label Switched Paths (LSPs)
�can be routed independently of the underlying link topology. This
dynamically computes routes for high-priority traffic flows based on a
predetermined set of network policies. Controlling traffic flows based on
such network constraints means all links share traffic load efficiently
and equally with none becoming over-committed with high-priority traffic.
The MPLS standard is based on the blending of connectionless protocols,
like IP, with virtual-circuit networking concepts. Compared to using ATM,
MPLS is a more efficient way to engineer traffic. Without it, there is no
way to ensure high-priority traffic won�t exceed the physical capacity
of any given link in the network. By using MPLS to define the physical
links that specific traffic will use, service providers can manage traffic
loads to ensure they are within any link�s ability to handle with
acceptable quality.
NEW MODELS
Internet QoS is achieved through three main processes: Queue
management within a single network element, performing things like
shaping, scheduling, weighted fair queuing, and random early detection;
controlling flow end-to-end to ensure that high-priority traffic avoids
congested nodes; and marking flows to signal different treatment, then
aggregating multiple flows into classes across the backbone.
Next-generation network elements need all of these features, which terabit
switch routers deliver.
Terabit switch routers already provide massive hardware-forwarding
capabilities and intelligent scaling capacities that can maintain internal
protocols as the network grows. Their repertoire covers QoS mechanisms
that include sophisticated tools for network-congestion management and
intelligent-buffering or congestion-avoidance. They perform admission
control, flow identification/classification, traffic policing, and scheduling to avoid network
congestion and ensure that traffic flows conform to their pre-negotiated
QoS contract. And router vendors, naturally, continue to work on creating
technology for next-generation IP networks that will take Internet QoS to
still higher levels.
Service providers can use intelligent terabit switch routers to
leverage QoS and MPLS to both gain operational network efficiencies and
enable higher value-added pricing models that are founded on network-aware
treatment of applications. Differentiating traffic by user and application
means network resources can support more granular levels of service. New
service levels, meantime, will give network operators the flexibility to
offer different pricing models, i.e., a pay-as-you-go or X+Y (flat rate
for a fixed number of hours, variable usage thereafter). The end result is
more ways for network operators to generate incremental sources of
revenue.
NET TALK
VoIP will both benefit from and rely on the QoS capabilities of the next-gen
routers which will make up the new packet-network infrastructure.
Scalable, flexible devices will allow emerging facilities-based carriers
to offer innovative services in order to compete against larger, more
established players.
In fact, �next-gen� is fast becoming �now-gen� as carriers
already are rolling out or taking to trial next-generation networks which
have IP running on top of optical cores (obviating the need for SONET
equipment in between). The trend already underway in switching � for
both the LAN and WAN markets � is the advent of multi-layer capabilities
able to provide QoS at wire rate to diverse network flows. Soon to come
will be new standards to increase interoperation of the IP service layer
and the underlying optical layer. The auto-provisioning in these next-gen
networks will need switch hardware capable of detecting network
bottlenecks and increasing service capabilities in real time, able to
dynamically add or redirect bandwidth as network loads change.
The combination of flexible, hardware-based, QoS-aware switches,
DiffServ for marketing and aggregating flows, and MPLS for traffic
engineering will be bringing sophisticated routing capabilities to packet
networks. This means such connectionless entities can behave in a
deterministic fashion. And when a network performs in a predictable and
controlled manner, applications of any priority can be supported on a
common infrastructure.
By bringing such intelligence to the Internet, terabit switch routers
enable the success of high-priority applications such as VoIP. They
provide an abundance of new traffic-engineering mechanisms and QoS
capabilities that enable policy management and application-aware traffic
forwarding. The net result is successful delivery of high-quality services
that efficiently utilize network resources, to the benefit of service
providers and end users alike.
Stephen Duffy is a product line manager with Avici Systems, Inc., of
Billerica, Mass., and can be reached at [email protected].
With its mission to build �speed of light� networks for the 21st
century, Avici is the leader in integrating packet-based technology with
carriers� optical investments to ensure highly scalable, highly
reliable, and highly cost effective networks for the future. For more
information, visit the company�s Web site at www.avici.com.
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