Advances of WAN Technologies
Zhangxi Lin
ISQS 6341
About SONET
Not dead yet
Some companies carry IP, ATM, frame relay and Gigabit
Ethernet on a SONET transport structure
Main beef against SONET: End users can't scale up gradually to
get--and pay for--just what they need. Another annoyance is that
it traditionally took weeks and a couple of truck rolls to add to
any customer's capacity.
There is a way to provision bandwidth over SONET in seconds,
and at increments of just 1.5 Mbps.
The mistake most competitive carriers made is strictly focusing
on customer touch--having facilities in the ground--rather than
on the profit per megabit. Value-added voice--that's high
revenue. Video is high revenue
- May 29, 2001
IP Over SONET
A SONET ring provides point-to-point
connections between routers. IP
packets must, therefore, map to a pointto-point link, for which the most popular
solution is using the Point-to-Point
Protocol (PPP), defined by the IETF in
RFC 1661.
– (the technology in 1997)
IP Over SONET
IP over DWDM
IP over DWDM is the concept of transmitting raw IP
packets over an optical layer, using DWDM for its
capacity and other operations.
This new technical solution can increase the capacity
of existing networks without the need for expensive
re-cabling and can tremendously reduce the cost of
network upgrades. This creates a vision of an alloptical network where all management is carried out
in the photonic layer.
Transmitting IP directly over DWDM holds the key to
the bandwidth glut and opens the frontier of terabit
Internets.
– http://www.ari.vt.edu/ece5516/OpticalNetworks/ipdwdm.htm
DWDM (Dense wavelength division
multiplexing)
A technology that puts data from different sources together on an optical
fiber, with each signal carried on its own separate light wavelength.
Up to 80 (and theoretically more) separate wavelengths or channel of data
can be multiplexing into a lightstream transmitted on a single optical fiber.
In a system with each channel carrying 2.5 Gbps (billion bits per second),
up to 200 billion bits can be delivered a second by the optical fiber.
Sometimes called wave division multiplexing (WDM). Since each channel is
demultiplexed at the end of the transmission back into the original source,
different data formats being transmitted at different data rates can be
transmitted together. Specifically, Internet (IP) data, Synchronous Optical
Network data, and asynchronous transfer mode data can all be traveling at
the same time within the optical fiber.
Promises to solve the "fiber exhaust" problem and is expected to be the
central technology in the all-optical networks of the future.
Replaces time-division multiplexing (Time-Division Multiplexing) as the most
effective optical transmission method. Although TDM is the primary
approach in today's networks, DWDM systems were tested and deployed in
late 1998 and 1999.
DWDM – The Solution for the
next generation Internet (NGI)
If one million families decide they want to see video on Web
sites and sample the new emerging video applications, then
network transmission rates of terabits (trillions of bits per second
[Tbps]) are required. With a transmission rate of one Tbps, it is
possible to transmit 20 million simultaneous 2-way phone calls
or transmit the text from 300 years–worth of daily newspapers
per second.
For some applications the time sensitivity is so important that
minimum delay is the overriding factor for all protocol and
equipment design decisions. So, there is a need for Burst mode
optical data switching.
Many transmission protocols require that data packets traverse
the network only after a circuit has been established. For some
applications, such as periodic transmission of sensor data, this
may be an unnecessary overhead to impose.
Multi-layer Stack
Disadvantages of Multi-layer Stack
The multi-layer stack has more problems
than advantages:
•
•
•
•
Every layer now runs at its own speed. So, low
speed devices cannot fill the wavelength
bandwidth.
Increasing Bandwidth, due to this technological
revolution, Core technologies are pushed to the
edges.
Functional overlap: So many layers are doing
the same thing, e.g. routing.
A failure affects many layers
IP and DWDM - A Winning
Combination
The good news about optical networking is
that it lets carriers deliver huge amounts of
bandwidth. The bad news is that it's hard to
get money out of those fat pipes. But now,
with ATM and SONET/SDH out of the way
revenue generating services (which were
struggling till now) like IP virtual private
networks (VPN) and voice over IP (VOIP) will
gain direct access to DWDM resources, and
will finally become practical.
Advantages of IP over DWDM
Less latency
Automatic provision
Unified bandwidth service
Improved QoS
Challenges
Any pair of photonic transmission paths cannot use
the sane wavelength on a shared fiber link. An
algorithm needs to be devised which could route
more than 1 line on the same wavelength.
There is limited address space arising from
physical addressing i.e. there is a finite number of
accessible wavelengths.
Multi-Protocol Lambda Switching
(MPLambdaS)
Lambda switching is derived from Multi-Protocol
Label Switching (MPLS). We can assume
MPLambdaS to be just implementing Label Switching
in the Optical domain.
A DWDM network (implementing Lambda switching)
is analogical to an ATM network in the aspects of
switching. ATM networks perform packet switching
based on the virtual circuit number, while the optical
channel layer performs switching based on the
wavelength of the signal (or packet). Hence the name
"Lambda Switching" is applied to the optical network.
The Way to All-Optical Network
DWDM is just the first step on the road to full optical
networking and the realization of the optical layer.
The concept of an All-optical network implies that the
service provider will have optical access to traffic at
various nodes in the network, much like the SONET
layer for SONET traffic. Optical wavelength add/drop
(OWAD) offers that capability, where wavelengths are
added or dropped to or from a fiber, without requiring
a SONET terminal. Combined with OWAD and
DWDM, the optical cross-connect (OXC) will offer
service providers the ability to create a flexible, highcapacity, efficient optical network with full optical
bandwidth management.
Conclusions
The future holds many challenges to the All-optical networks.
But, the commercial implementations for IP over DWDM are not
far away. It provides the backbone to support existing and
emerging technologies with almost limitless amounts of
bandwidth capacity and opens the pathway to Terabit
networking.
The trend of IP/DWDM solutions over the last few years seems
to have taken an exponential growth. All-optical networking (not
just point-to-point transport) enabled by Optical Cross-Connects,
Optical programmable add/drop multiplexers, and Optical
switches provides a unified infrastructure capable of meeting the
telecommunications demands of today and tomorrow.
Transparently moving trillions of bits of information efficiently
and cost effectively will enable service providers to maximize
their embedded infrastructure and position themselves for the
capacity demand of the future.
References
ATM tutorial at IEC proforum www.iec.org/tutorials/atm_fund/index.html
Describes at length ATM technology, ATM classes of services; Highspeed local-area network (LAN) interconnection; ATM standards, ATM
multimedia applications in voice, video etc.
Sonet tutorial at IEC proforum www.iec.org/tutorials/sonet
This Primer provides an introduction to the SONET standard, based on
the latest information available from the Bellcore and International
Telecommunications Union–Telecommunications Standardization
Sector (ITU–T) standards organizations.
DWDM tutorial at IEC proforum www.iec.org/tutorials/dwdm
This tutorial addresses the importance of scalable DWDM systems in
enabling service providers to accommodate consumer demand for
ever-increasing amounts of bandwidth.
Talk by Dr.Raj Jain on IP over DWDM www.netlab.ohiostate.edu/talks/h_aipwd.htm
This streaming video lecture discusses a gamut of issues starting from
the need for IP over DWDM to the requirements for creating an all
optical networks based on Multi- protocol lambda switching(MPLS).