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1. INTRODUCTION
The present era is the era of connectivity. Think of any sort of
information, and it can be transferred to us within question of a little time; be it
audio information, video information or any other form of data. Now talking about
transferring data between our computer and the other peripherals, the first and
foremost standard comes to our mind is Universal Serial Bus (USB). It is a medium
speed serial data addressable bus system which carry large amount of data to a
relatively short distance (up to 5m).The present version USB 3.0 promises to provide
theoretical speed of up to 5Gbps.
But Intel has unveiled a new interoperable standard called LIGHTPEAK which can
transfer data between computers and the peripherals at the speed of 10Gbps in both
the directions with maximum range of 100m (much higher than USB or any other
standard) and has potential to scale its speed high up to 100Gbps in near future.
Light Peak is the code name for a new high-speed optical cable technology designed
to connect electronic devices to each other. Light Peak is basically an optical cable
interface designed to connect devices in peripheral bus. It is being developed as a
single universal replacement for the current buses such as SCSI, SATA, USB,
FireWire, PCI express, and HDMI etc in an attempt to reduce the proliferation of
ports on computers.
Fiber-optic cabling is not new, but Intel executives believe Light Peak will make it
cheap enough and small enough to be incorporated into consumer electronics at a pr
ice point that consumers and manufacturers will accept. Thus with light peak, the
bandwidth would tremendously increase, multiple protocols could be run over single
longer and thinner cable. The prototype system featured two motherboard controllers
that both supported two bidirectional buses at the same time, wired to four external
connectors. Each pair of optical cables from the controllers is led to a connector,
where power is added through separate wiring. Intel has stated that Light Peak has
the performance to drive everything from storage to displays to networking, and it can
maintain those speeds over 100 meter runs.
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2. LIGHT PEAK TECHNOLOGY: FEATURES
Optical networking technologies have been over the last two decades
reshaping the entire telecom infrastructure networks around the world and as
network bandwidth requirements increase, optical communication and networking
technologies have been moving from their telecom origin into the enterprise and
Light Peak is one of its successful outcome.
It is basically a new high-speed optical cable technology designed to connect
electronic devices to each other. It also support multiple protocols simultaneously
with the bidirectional speed of about 10Gbps (can scale up to about 100Gbps). In
comparison to other bus standards like SATA and HDMI, it is much faster,
smaller, longer ranged, and more flexible in terms of protocol support.
Thus it basically provides:
_ Standard low cost high bandwidth optical- based interconnect.
_ Supports multiple existing I/O protocols and smooth transition between them.
_ Supports wide range of devices (handhelds, PCs, workstations etc.)
_ Connect to more devices with the same cable, or to combo devices such as
docking stations.
_ Smaller connectors.
_ Longer (up to 100m on single cable), thinner and economical.
Light peak consist of a controller chip and optical module that would be included in
platform to support this technology. The optical module performs the task of
conversion of electricity to light conversion and vice versa, using miniature lasers
and photo detectors. This transceiver can send two channels of information over an
optical cable, necessary, since pc needs at least two ports. The controller chip
provides protocol switching to support multiple protocols over single cable.
The Light Peak cable contains a pair of optical fibers that are used for
upstream and downstream traffic to provide speed of about 10Gbps in both the
directions. The prototype system featured two motherboard controllers that both
supported two bidirectional buses at the same time, wired to four external
connectors. Each pair of optical cables from the controller s is led to a connector,
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where power is added through separate wiring. It was developed as a way to reduce
proliferation of number of ports on the modern computer. Earlier USB was
developed for the same purpose and performed very well in this direction but
increased bandwidth demand and high performance has led to development of
new more efficient technologies.
Combining the high bandwidth of optical fiber with Intel’s practice to
multiplex multiple protocols over a single fiber, optical technology may change the
landscape of IO system design in the future. It’s possible that most of the legacy
IO protocols can be tunneled by optical- capable protocols, so some of the
legacy IO interfaces can be converged to one single optical interface, significantly
simplifying the form factor design of computers. This change in IO system will
definitely affect the design of systems.
Figure2.1: Abstract model of the optical-enabled system (Arrow shows that we are
looking at the system from IO to processor).
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There are four main components in this figure, the IO devices, the IO controller
which connects to the IO devices through optical fiber, the processing unit and the
interconnection between the IO controller and the processing unit, whatever it can be
implemented as.
Mobile and handheld devices are two fast growing market segments which
attract interests from processor vendors. For mobile and handheld devices, user
interface and IO are two important factors besides computing power that affect
end users’ purchase decision. Taking power into account, it’s possible that more
carefully tuned IO workload offloading engines will be integrated into the IO
controller, saving the power to move the data from IO a long way to the system
memory. It makes no sense to have a high throughput IO system with
insufficient processing power or overloaded inter connections between IO system and
the processor. The ultimate goal of system architects is to make a balanced and
efficient system, on both power and cost grounds.
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3. TODAYS CHALLENGES
In the coming future, people would be using more and more electrical
devices such as HD devices, MIDs and many more and user experience would
depend on the huge volume of data capturing, transfer, storage, and
reconstruction. But existing electrical cable technology is approaching the
practical limit for higher bandwidth and longer distance, due to the signal
degradation caused by electro-magnetic interference (EMI) and signal integrity
issues.
Higher bandwidth can be achieved by sending the signals down with more
wires, but apparently this approach increases cost, power and difficulty of PCB
layout, which explains why serial links such as SATA, SAS, and USB are becoming
the mainstream.
However optical communications do not create EMI by using photonics
rather than electrons, thus allowing higher bandwidth and longer distances. Besides,
optical technology also allows for small form factors and longer, thinner cables.
3.1 Electrons v/s Photons
The physics has a kind of inevitability about it. Electrons travel through
copper more slowly than light through fiber. The USB connectors on the smaller
devices like mobile phones have to use mini-USB or micro-USB to save on the space
taken up by the wiring and electricity through wire creates electric field interference,
but light do not create EMI since it rely over photonics. Optical connecters can
carry extremely narrow beams of light and fiber can be thinner because more
streams can pass through glass or plastic passages. Each fiber is only 125
microns wide, the width of a human hair.
In the present scenario, the devices are getting smaller, thinner, and
lighter but present connecting standards seems to hinder in their performance
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being to thicker and stiffer. So vendors turn over to new technologies providing
much better performance and Light Peak seems to be a providing a good solution.
Different protocols demands for different connectors leading to too any connectors
and cables. But in Light Peak there is the Light Peak protocol and the native protocols
such as PCI express, Display Port, USB or whatever might be running on it. The
native protocols run basically on top of the Light Peak protocol. But the Light Peak
protocol defines the speed. The protocol is running at 10 gigabits per second. So, if
the native protocols that are running on top of it are also running at 10 gigabits per
second, or something close to that, then the effective bandwidth for a device on the
other end would be equivalent to that 10Gbps.
FIG. 3.1 MULTIPLE SPECIALIZED CONNECTORS
Thus, it can be said that presently we demand for the devices and technologies that:
- Provides much higher bandwidth
- Provides more flexible designs, thinner form factor and new and better usage
models.
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- Much simpler and easier in terms of connectivities.
It’s possible that most of the legacy IO protocols can be tunneled by optical-
capable protocols, so some of the legacy IO interfaces can be converged to one single
optical interface, significantly simplifying the form factor design of computers.
Ultimately the main aim is to build an efficient and balanced system. Thus Light Peak
seems to be providing a good solution to the problems existing with the copper
connector s and provides a good platform for the high performance system.
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4. LIGHT PEAK V/S USB 3.0
4.1 USB 3.0
_ It is an electrical cable technology which transmits data using electricity
which put limitation on speed and length.
_ It consists of 9 copper wires for transfer of data between the PC and the
peripherals.
_ Theoretically it can provide maximum speed of 5Gbps which on practical
grounds get restricted to about 3Gbps.
_ It supports only USB protocol.
_ The maximum allowable cable length for USB 3.0 is only about nine meters.
4.2 LIGHT PEAK
_ It is an optical cable technology which relies over light to transmit data thus
providing much better speed and length.
_ It consists of 4 optical fiber s for both upstream and downstream traffic
simultaneously.
_ Initial proposed speed for Light Peak (LPK) [10] starts at 10Gbps and has future
potential to scale up to 100Gbps. With this speed Blu-Ray movie can be transferred in
less than 30 seconds (or in less than 3 seconds with 100Gbps).
_ It is a Universal connector supporting multiple existing protocols.
_ The maximum allowable cable length is about 100 meters and can be even
extended more.
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5. COMPONENTS OVERVIEW
Light Peak consists of a controller chip and an optical module that
would be included in platforms supporting this technology. The optical module
performs the conversion from electricity to light and vice versa using miniature
lasers ( VCSELs) and photo detectors. Intel is planning to supply the controller chip,
and is working with other component manufacturers to deliver all the Light Peak
components.
The main components are:
_ Fiber optics
_ Optical module
_ Controller chip
FIG 5.1 :Prototype view of components of light peak controller.
These are the fundamentally required components for a basic light peak
connector.
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6. OPTICAL MODULE
Light Peak is based on 10G 850nm VCSEL and PIN-diode arrays with LOMF
(Laser-optimized Multi- mode Fiber) and a new optical interface connector yet to be
determined. The optical module does the function of converting optical signals into
electrical signals and vice versa. This module contains an array of VCSEL (vertical
cavity surface emitting laser).
FIG 6.1:Schematic diagram of Optical module
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6.1 VCSEL (Vertical-Cavity Surface- Emitting Laser Diodes)
FIG 6.2:Simplified schematic for VCSEL without substrate, electrode for pumping,
structure for current confinement etc.
VCSELs are semiconductor lasers, more specifically laser diodes with a
monolithic laser resonator, where the emitted light leaves the device in a
direction perpendicular to the chip surface. The laser resonator consists of two
distributed Bragg reflector (DBR) mirrors parallel to the wafer surface with an
active region consisting of one or more quantum wells for the laser light generation
in between. The planar DBR-mirrors consist of layers with alternating high and low
refractive indices. Each layer has a thickness of a quarter of the laser
wavelength in the material, yielding intensity reflectivities above 99%.
VCSELs has low-cost potential because the devices are completed and tested
at the wafer level for material quality and processing purposes and a matrix VCSEL is
capable of delivering high power( up to few watts). VCSELs have low threshold
current value, low temperature sensitivity, high transmission speed,high fiber
coupling efficiency and circular and low divergence output beam as compared to
edge-emitters. VCSELs for wavelengths from 650 nm to 1300 nm are typically
based on gallium arsenide (GaAs) wafer s with DBRs formed from GaAs and
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aluminium gallium arsenide (AlxGa(1-x)As). The curr ent is confined in an oxide
VCSEL by oxidizing the material around the aperture of the VCSEL. As a result in
the oxide VCSEL, the current path is conf ined by the ion implant and the oxide
aperture.
The wavelength of VCSELs may be tuned, within the gain band of the
active region, by adjusting the thickness of the reflector layers. In the present
demonstrated Light Peak technology, architecture of optical interconnects is built up
on the bases of four VCSELD and two optical links where thermal effects of both the
diodes and the links are included. Nonlinear relations are correlated to investigate the
power-current and the voltage- current dependences of the four devices. The
good performance ( high speed) of interconnects are deeply and parametrically
investigated under wide ranges of the affecting parameters. The high speed
performance is processed through three different effects, namely the device 3-dB
bandwidth, the link dispersion characteristics, and the transmitted bit rate. Eight
combinations are investigated; each possesses its own characteristics. The best
architecture is the one composed of VCSELD that operates at 850 nm and the silica
fiber whatever the operating set of causes. This combination possesses the largest
device 3-dB bandwidth, the largest link bandwidth and the largest transmitted bit
rate.
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7. LIGHT PEAK TECHNOLOGY OVERVIEW
Light Peak Technology is an optical cable technology that consists of an
optical module and controller chip which allows multiple protocols to run over the
single cable. From the technical point of view, Intel’s Light Peak Technology can be
overviewed as:
- Light peak protocol
- Light Peak controller
- Light peak platforms
- Server Network
7.1 LIGHT PEAK PROTOCOL ARCHITECTURE:
Efficient transport mechanism. It uses packet switch multiplexing.
- Packetize data to transfer
- Multiplex it onto the wire
- Packets from different connections share the same link.
Each packet is composed by the payload (the data we want to transmit) and a header.
The header contains information useful for transmission, such as:
Source (sender’s) address
Destination (recipient’s) address
Packet size
Sequence number
Error checking information
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FIG 7.1:Simplified view of protocol Light Peak Networks use a similar idea of packet
switching.
All the I O devices may have their native protocols but when using Light Peak
they all run over Light Peak protocol. That is they uses their individual protocol for
data transfer but their speed is defined by light peak. Also it uses Virtual Wire
Semantics thus performs high level of isolation between high level protocols
(QoS). It provides cheap switching and establishes all routing at the setup only.
7.2 LIGHT PEAK CONTROLLER:
At the heart of Light Peak is an Intel-designed controller chip that handles
the protocols, along with an optical module that converts electrical signals to photons
and vice versa. Basic implementation unit of Light Peak Controller contains:
-A Cross bar switching unit: switches the various protocols from LPK to their
respective protocol adapter.
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- LPK Ports and Protocol Adapter ports: LPK ports to connect down to PC
using any standard and diverging it their respective protocol through protocol
adapter.
FIG 7.2: LIGHT PEAK CONTROLLER SCHEMATIC
The Host controller is typically multi protocol and has multiple ports with
a software interface unit and is optimized for host side implementation whereas
the peripheral controller could be single port and single protocol-based and is
optimized for particular usage. This is because of this controller chip that
different protocols get identified and transmitted correctly. API (Application
programming interface) helps to determine the different protocols. It places the FIS
(Flag Identification Symbol) packets in the memory, the controller access these
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packets from the memory and send these packets to the destination over the optical
link. The multi- protocol capability the controller implements is an innovative
new technology that will enable new usage models like flexible system designs
and thinner form factors, media creation and connectivity, faster media transfer and
cable simplification.
7.3 LIGHT PEAK PLATFORM:
A typical Light Peak platform can be viewed with few of these.
FIG 7.3:Mobile Platform
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7.4 DIRECT NETWORK OF SERVERS:
Goal:Build a high-bandwidth, fault- resilient, low-cost network that can
deliver performance isolation across applications.
Approach:
-Integrate low-radix switches into several platforms.
- Interconnect servers directly using multi- path topologies.
Why Light Peak to be considered as an option?
- Small buffers and tables enable cheaper switching components
- Bandwidth allocation and performance isolation
- Flexible topologies and multi-path enables better resiliency.
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8. SOFTWARE ARCHITECTURE
Light Peak employs a connection-oriented link-layer transport protocol, where
in paths must be configured prior to data transmission. Correspondingly, the notion of
connection management is a primary functionality of the control plane, to support the
data plane (sending and receiving traffic) of a Light Peak network. In addition, basic
performance and fault management functions are needed as well. The software to
provision and run a network prototype based on Light Peak has the following logical
components:
_ Connection Manager
_ Device Driver
_ Link/Switch Status Monitor
_ Failover Manager.
FIG 8.1: Key software component interactions of the prototype.
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8.1 Connection Manager
A network of interconnected Light Peak switches are grouped into a set of
“domains,” each of which is managed by a software component called “Connection
Manager.” The Connection Manager may be administratively associated with one of
the domain member interfaces (called a “Root-Switch”) and is responsible for device
enumeration, path configuration, QoS and buffer allocations at the switches in its
domain. The Light Peak protocol allows the Connection Manager of the domain to be
changed without impacting previous configuration and data transfer.Starting from the
Root Switch, the Connection Manager enumerates each switch in the domain,
building a topology graph. The Connection Manager also gets notified of topology
changes caused by hot-plug and hot-unplug events.After initial enumeration, the
Connection Manager must configure paths to enable data communication between
nodes. Path configuration may be performed at initialization time or on-demand based
on traffic patterns. Multiple domains may be interconnected in arbitrary fashion.
Light Peak configuration protocol provides primitives that enable communication
between the CMs in adjacent domains, and the Connection Managers of the
connected domains may exchange information with each other to perform inter-
domain configuration of paths.
8.2 Device Driver
A Device Driver component for the Light Peak host interface is responsible
for sending and receiving network traffic. In the prototype, the device driver is an
operating system kernel component that interacts with the TCP/IP subsystem on the
host on one side and communicates with the host interface. Also, it is responsible for
the initialization, configuration updates and shutdown of the Light Peak host interface
and associated crossbar switch. The Light Peak host interface provides access to the
device’s status registers and can read/write to areas of host’s memory using DMA.
The host interface implements support for a pair of producer-consumer queues (one
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for transmit, one for receive) for each configured path. The host interface also
presents a larger protocol data unit that can be used by software to send and receive
data.
In addition to interfacing with the operating system TCP/IP stack, the device driver
also exports a direct interface to send and receive data directly from user space.
8.3 Link/Switch Status Monitor
The Status Monitor component gets updates from the Connection Manager
with events related to the Light Peak interface and link failures within its domain. The
Status Monitor instructs the Connection Manager to implement various recovery and
rerouting strategies as appropriate.
In addition, the Status Monitor can also collect performance indicators from each
Light Peak switch for network performance monitoring and troubleshooting purposes.
8.4 Failover Manager
In general, a failure at a domain’s Root-Switch (i.e., Connection Manager
itself) does not affect traffic already in transit, but subsequent link/switch failures
require updates to path tables at every switch. The Failover Manager selects and
assigns a new Connection Manager in the event of Root Switch failures. The selection
can be administrative or based on a consensus algorithm. When multiple domains are
involved, a failure affecting inter-domain traffic requires messaging across
corresponding Connection Managers.
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9. DATA TRANSFER SPEED COMPARISION
How does Light Peak compare to the latest technologies? The slowest is
wireless. HDMI version 1.3 and higher will transfer at 10.2 Gbps, while Display Port
can go up to 10.8 Gbps. These are slightly better than Light Peak, but they are
mostly designed for video. No one is pushing the
data transfer rates of these protocols.
FIG 9.1:The chart shows how Light Peak compares to all of these other protocols.
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10. BRINGING OPT ICAL TO MAINSTREAM
Since Light Peak is developed to meet PC requirements and the telecom
ones, thus the Light Peak optical module can be designed to be lower cost than
Telecom optical modules. This is due to some modification in design considerations:
- First Intel relaxed the optical standar ds required of its components. In the
telecom market, components must meet stringent Telcordia standards, such as a 20-
year lifetime.Obviously, that kind of longevity is not required in the PC market, so
Intel lowered its requirements to a five- to seven- year lifetime.
- Requirements for the operating environment also are not as rigorous. Intel
lowered thermal requirements from the Telcordia-Zpecified range of 0° to 85° to a
more relaxed 5° to 65°. Intel had originally intended to specify a range starting at 0°
but then realized that batteries freeze at that temperature, making the operation of the
PC a moot point.
-The company also relaxed its specification for number of failures per lifetime. If
there is a failure on a trans-Atlantic cable, it’s a big deal. But the potential failure of
one of four ports on a PC, for example, is not nearly as critical.
-Because Light Peak is intended for distances of 100 m or less and dispersion
is, therefore, not an issue spectral-width requirements also can be less stringent
than Telcordia specifies. As a result vendors are able to get closer to 90% to 95%
yields on their VCSELs and photo detectors, rather than the much lower in telecom.
-Intel has also removed the traditional eye-safety requirements, which also translates
into higher yields and lower costs. The traditional telecom module is typically
launched at about 1 mW of power. But the very aggressive power management
of the Light Peak optical module features a launch power much higher than eye
safety.
-Finally, Intel designed the optical module to be high- volume manufacturer able thus
further reducing the cost of production.
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11.ADVANTAGES
- The light peak optical modules are physically much smaller than those of telecom
grade.
-The optical modules are designed to be much lower cost and higher performance.
-Light Peak can send and receive data at 10 billion bits per second.
-The thin optical fiber will enable Light Peak to transfer data over very thin,
flexible cables.
-Unlike electrical cables, Light Peak do not faces the problem of EMI, thus can be
used upto 100m.
-Light Peak also has the ability to run multiple protocols simultaneously over
a single cable, enabling the technology to connect devices such as docking stations,
displays, disk drives, and more. A simple analogy is it is like loading up many cars
onto a high-speed bullet train.
-The data transfer is bidirectional in nature thus enabling devices to transfer
simultaneously.
-Quality of service implementation
-No Operating System (OS) changes required.
-It also supports another feature known as Hot-swapping which means the PC needs
not be shut down and restarted to attach or remove a peripheral.
-Economies of scale from a single optical solution.
-Enables I/O performance for the next generation Allows for balanced
platform, with external I/O keeping up with most platform inter connects.
-Up to 100 meters on an optical-only cable. Each fiber is only 125 microns
wide, the width of a human hair.
-Supports multiple existing I/O protocols over a single cable and smooth
transition for today’s existing electrical I/O protocols.
-Can connect to more devices with the same cable, or to combo devices such as
docking stations.
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12. DEVELOPMENT STATUS
Intel is working with optical manufacturers to make Light Peak components
ready to ship in 2010. The company’s intent is to work with the industry to determine
the best way to make this new technology a standard and available on PCs,
handheld devices, consumer electronics, workstations and more.
Fig.12.1:Demonstration of connection of a HDTV with a laptop
Till date, Intel has suggested that it would be providing controller chip and had
collaborated with
different manufactures for various components.
Intel’s Light Peak suppliers include:
-Oclaro: VCSELs
-Enablence Technologies Inc.: large-area, dual-wavelength 10-Gbps photodiodes
-Avago Technologies: optical module with embedded optical engine
-SAE Magnetics: optical module
-IPtronics: driver and receiver silicon
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-Ensphere Solutions Inc.: transceiver IC
13. CONCLUSION
Light Peak is a high-speed, multi-protocol interconnect for innovative and
emerging client usage models, that complements other existing interconnects.Light
Peak is the name for a new high-speed optical cable technology designed to
connect electronic devices to each other. Light Peak deliver s high bandwidth starting
at 10Gb/s with the potential ability to scale to 100Gb/s over the next decade. At
10Gb/s, we can transfer a full-length Blu-Ray movie in less than 30 seconds.
Light peak allows for smaller connectors and longer, thinner, and more flexible
cables than currently possible. Light Peak also has the ability to run multiple
protocols simultaneously over a single cable, enabling the technology to connect
devices such as peripherals, displays, disk drives, docking stations, and more.
Intel is working with the optical component manufacturers to make
Light Peak components ready to ship in 2010, and will work with the industry to
determine the best way to make this new technology a standard to accelerate its
adoption on a plethora of devices including PCs, handheld devices,
workstations, consumer electronic devices and more. Light Peak is
complementary to existing I/O technologies, as it enables them to run together on a
single cable at higher speeds.
The goal of this new developing technology is to build a high-bandwidth,
fault-resilient, low- cost network that can deliver performance isolation across
applications. The basic approach to achieve this target is to integrate low-radix
switches into server platform and interconnect severs directly using multipath
topologies. Thus if the question WHY LIGHT PEAK?? arises, then the answer
would be because it is cheaper as it incorporates cheaper switching components,
provide better bandwidth allocation and performance isolation, uses flexible
topologies, integrate multiple protocol devices on to one cable.
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