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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 THUNDERBOLT(Light Peak)
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 thunderbolt technology, a new high-speed optical cable
technology designed to connect electronic devices to each other.
It 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, PCIExpress, and HDMI etc in an attempt to reduce the proliferation of ports
on computers.
Fiber-optic cabling is not new, but Intel executives believe Thunderbolt will make it cheap
enough and small enough to be incorporated into consumer electronics at a price point that
consumers and manufacturers will accept.
Thus with thunderbolt, 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. The physical connector used on the prototype system looks similar to the existing
USB or FireWire connectors.
Intel has stated that this technology has the performance to drive everything from storage to
displays to networking, and it can maintain those speeds over 100 meter runs.
Thunderbolt began at Intel Labs with a simple concept: create an incredibly fast input/output
technology that just about anything can plug into. After close technical collaboration between
Intel and Apple, Thunderbolt emerged from the lab to make its first appearance in
MacBook Pro.
Intel co-invented USB and PCI Express, which have become widely adopted technologies for
data transfer. Apple invented FireWire and was instrumental in popularizing USB. Their
collective experience has made Thunderbolt the most powerful, most flexible I/O technology
ever in a personal computer.
Intel introduced Thunder bolt at the 2009 Intel Developer Forum (IDF), using a prototype
MacPro motherboard to run two 1080p video streams plus LAN and storage devices over a
single 30-meter optical cable with modified USB ends. The system was driven by a prototype
PCI Express card, with two optical buses powering four ports. At the show, Intel claimed that
Thunder bolt-equipped systems would begin to appear in 2010.
On 4 May 2010, in Brussels, Intel demonstrated a laptop with a Thunder bolt connector,
indicating that the technology had shrunk small enough to fit inside such a device, and had
the laptop send two simultaneous HD video streams down the connection, indicating that at
least some fraction of the software/firmware stacks and protocols were functional. At the
same demonstration, Intel officials said they expected hardware manufacturing to begin
around the end of 2010.
In September 2010, some early commercial prototypes from manufacturers were
demonstrated at Intel Developer Forum 2010.
Developed by Intel (under the code name Light Peak), and brought to market with technical
collaboration from Apple. Thunderbolt technology is a new, high-speed, dual-protocol I/O
technology designed for performance, simplicity, and flexibility. This high-speed data
transfer technology features the following:
Dual-channel 10 Gbps per port
Dual-protocol (PCI Express* and Display port*)
Compatible with existing Display Port devices
Daisy-chained devices
Electrical or optical cables
Low latency with highly accurate time synchronization
Uses native protocol software drivers
Power over cable for bus-powered devices
Intel's Thunderbolt controllers interconnect a PC and other devices, transmitting and
receiving packetized traffic for both PCIe and DisplayPort protocols. Thunderbolt technology
works on data streams in both directions, at the same time, so users get the benefit of full
bandwidth in both directions, over a single cable. With the two independent channels, a full
10 Gbps of bandwidth can be provided for the first device, as well as additional downstream
FIG 3.1 PCI Express and DisplayPort transported between Thunderbolt controllers over a
Thunderbolt cable.
Thunderbolt is an interface for connecting peripheral devices to a computer via an expansion
bus. Thunderbolt was developed by Intel and brought to market with technical collaboration
from Apple Inc. It was introduced commercially on Apple's updated MacBook Pro line up on
February 24, 2011, using the same port and connector as Mini Display Port. Though initially
registered with Apple Inc., full rights of the Thunderbolt technology trademark belong to
Intel Corp., and subsequently led to the transfer of the registration.
Thunderbolt essentially combines PCI Express and Display Port into a new serial data
interface that can be carried over longer and less costly cables. Because PCI Express is
widely supported by device vendors and built into most of Intel's modern chipsets,
Thunderbolt can be added to existing products with relative ease. Thunderbolt driver chips
fold the data from these two sources together, and split them back apart again for
consumption within the devices. This makes the system backward compatible with existing
Display Port hardware upstream of the driver.
The interface was originally intended to run on an optical physical layer using components
and flexible optical fiber cabling developed by Intel partners and at Intel's Silicon Photonics
lab. The Intel technology at the time was marketed under the name Light Peak,[6] today
(2011) referred to as Silicon Photonics Link.[7] However, conventional copper wiring turned
out to be able to furnish the desired 10 Gb/s Thunderbolt bandwidth at lower cost. Later
versions of Thunderbolt are still planned to introduce an optical physical layer based on Intel
silicon photonics technology.
Thunderbolt is a revolutionary I/O technology that supports high-resolution displays and
high-performance data devices through a single, compact port. It sets new standards for
speed, flexibility, and simplicity. And it makes its debut in the new MacBook Pro.
FIG 3.2 Thunderbolt
Thunderbolt began at Intel Labs with a simple concept: create an incredibly fast input/output
technology that just about anything can plug into. After close technical collaboration between
Intel and Apple, Thunderbolt emerged from the lab to make its first appearance in
MacBook Pro.
Intel co-invented USB and PCI Express, which have become widely adopted technologies for
data transfer. Apple invented FireWire and was instrumental in popularizing USB. Their
collective experience has made Thunderbolt the most powerful, most flexible I/O technology
ever in a personal computer.
FIG 3.3 Thunderbolt connector
Thunderbolt I/O technology gives you two channels on the same connector with 10 Gbps of
throughput in both directions. That makes it ultra fast, and ultra flexible. You can move data
to and from peripherals up to 20 times faster than with USB 2.0 and more than 12 times faster
than with FireWire 800. You also have more than enough bandwidth to daisy-chain multiple
high-speed devices, without using a hub or switch. For example, you can connect several
high-performance external disks, a video capture device, and even a Mini Display Port
display to a single Thunderbolt chain while maintaining maximum throughput.
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 Thunderbolt 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
Smaller connectors.
Longer (up to 100m on single cable), thinner and economical.
Thunderbolt 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 Thunderbolt 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 controllers is led to a connector, where power is added through separate
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 the
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.
FIG 3.1.1 Abstract model of the optical-enabled system (Arrow shows that we are looking at
the system from IO to processor)
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 interconnections between IO system and the
The ultimate goal of system architects is to make a balanced and efficient system, on both
power and cost grounds.
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.
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 being to thicker and stiffer. So
vendors turn over to new technologies providing much better performance and Thunderbolt
seems to be a providing a good solution.
FIG 4.1 Connections using Thunderbolt
Different protocols demands for different connectors leading to too many connectors and
cables. But in Thunderbolt there is the Thunderbolt protocol and the native protocols such as
PCI Express, DisplayPort, USB or whatever might be running on it. The native protocols run
basically on top of the Thunderbolt protocol. But the Thunderbolt 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.
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
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. This change in IO
system will definitely affect the design of systems. It makes no sense to have a high
throughput IO system with insufficient processing power or overloaded interconnections
between IO system and the processor. Ultimately the main aim is to built an efficient and
balanced system.
Thus Thunderbolt seems to be providing a good solution to the problems existing with the
copper connectors and provides a good platform for the high performance system.
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
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
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 fibers for both upstream and downstream traffic
Initial proposed speed for Thunderbolt (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.
Thunderbolt 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 Thunderbolt components. The main components are:
 Fiber optics
 Optical module
 Controller chip
FIG 6.1 Prototype view of components of Thunderbolt controller
These are the fundamentally required components for a basic Thunderbolt connector. The
description for each would be given in forgoing discussion.
A basic optical communication link consists of three key building blocks: optical fiber, light
sources, and light detectors.
The silica-based optical fiber structure consists of a cladding layer with a lower refractive
index than the fiber core it surrounds. This refractive index difference causes a total internal
reflection, which guides the propagating light through the fiber core with an attenuation less
than 20 dB/km, necessary threshold to make fiber optics a viable transmission technology.
For telecommunications, the fiber is glass based with two main categories: SMF (Singlemode fiber) and MMF (Multi-mode fiber)
SMFs typically have a core diameter of about 9 μm, while MMFs typically have a core
diameter ranging from 50 to 62.5 μm.
Optical fibers have two primary types of impairment: optical attenuation and dispersion
The fiber optical attenuation, which is mainly caused by absorption and the intrinsic Rayleigh
scattering, is a wavelength dependent loss with optical losses as low as 0.2 dB/km around
1550 nm for conventional SMF (SMF-28).
The optical fiber is a dispersive waveguide. There are three primary types of fiber
Modal dispersion
It depends on both core diameter and transmitted wavelength. For a single-mode
transmission, the step-index fiber core diameter (D) must satisfy the following condition:
where λ is the transmitted wavelength and n1 and n2 are the refractive indices of fiber
core and cladding layer, respectively.
Chromatic dispersion
It is due to the wavelength-dependent refractive index with a zero-dispersion
wavelength occurring at 1310 nm in conventional SMF. When short duration optical
pulses are launched into the fiber, they tend to broaden since different wavelengths
propagate at different group velocities, due to the spectral width of the emitter.
Optical transmission systems operating at rates of 10 Gbps or higher and distances
above 40 km are sensitive to this phenomenon.
Polarization-mode dispersion
It is caused by small amounts of asymmetry and stress in the fiber core due to the
manufacturing process and environmental changes such as temperature and strains.
This fiber core asymmetry and stress leads to a polarization-dependent index of
refraction and propagation constant, thus limiting the transmission distance of high
speed (≥ 10 Gbps) over SMF in optical communication systems
Optical fiber is never bare. The fiber is coated with a thin primary coating to protect the
inner glass fiber from environmental hazards.
Thunderbolt is based on Laser-optimized Multi-mode fiber (LOMF). By laser optimized it
just means that the fiber was designed to be used with lasers, and in the case of MMF,
typically VCSELs.
The internal diameter of each Thunderbolt fiber is 62.5 microns (around half the size of a
human hair, but thicker than the fiber used in telecoms). The beam expander moulded into the
lens expands that to 700 microns, so that dust — usually around 100 microns — may
interrupt the beam partially but the connection will still work. The beam expander also
compensates for distortion or movement in the connector after been used for a while.
Thunderbolt fiber has a 3-micron coating to prevent cracking, it can be bend to a radius of
3mm and it won't break.
It is mixed with copper wires for power and fiber optic cables for data. The commercial
version of the connector has not been released to the public, but it would be possible to create
a Thunderbolt port that is backwards compatible with USB. The fiber optic connection could
be deep in the connector so it would be undamaged by a standard USB cable. Electrical
connections could be provided for a standard USB 1.1/2.0 cable so that the connector could
provide both fiber optic and electrical connections.
The light source is often the most costly element of an optical communication system. It has
the following key characteristics: (a) peak wavelength, at which the source emits most of its
optical power, (b) spectral width, (c) output power, (d) threshold current, (e) light vs. Current
linearity, (f) and a spectral emission pattern.
There are two types of light sources in widespread use: the Laser Diode (LD) and the Light
Emitting Diode (LEDs).
Both LEDs and LDs use the same key materials: Gallium Aluminum Arsenide (GaAIAs) for
short-wavelength devices and Indium Gallium Arsenide Phosphide (InGaAsP) for longwavelength devices.
Semiconductor laser diode structures can be divided into the so-called edge-emitters, such as
Fabry Perot (FP) and Distributed Feedback (DFB) lasers and vertical-emitters, such as
Vertical Surface Emitting Lasers (VCSELs).
For Thunderbolt optical modules, VCSELs are used as light source.
In optical networks, binary digital modulation is typically used, namely on (light on) and off
(no light) to transmit data. These semiconductor laser devices generate output light intensity
which is proportional to the current applied to them, therefore making them suitable for
modulation to transmit data.
Modulation schemes can be divided into two main categories: a direct and an external
In a direct modulation scheme, modulation of the input current to the semiconductor laser
directly modulates its output optical signal since the output optical power is proportional to
the drive current. In an external modulation scheme, the semiconductor laser is operating in a
Continuous-Wave (CW) mode at a fixed operating point. An electrical drive signal is applied
to an optical modulator, which is external to the laser. Consequently, the applied drive signal
modulates the laser output light on and off without affecting the laser operation.
The direct modulation of a laser diode has several limitations, including limited propagation
distance due to the interaction between the laser, frequency chirp and fiber dispersion. This is
not an issue for enterprise networks which are short distance and thus lasers can be
modulated directly.
Light detectors convert an optical signal to an electrical signal. It operates on the principle of
the p-n junction.
There are two main categories of photo detectors: a p-i-n (positive- intrinsic-negative)
photodiode and an Avalanche Photodiode (APD), which are typically made of InGaAs or
The key parameters for photodiodes are: (a) capacitance, (b) response time, (c) linearity, (d)
noise, and (e) responsivity.
Amplifier is needed to amplify the electric current to a few mA.
Thunderbolt modules uses pin photodiodes as light detectors since these are more
To enable the reliable operation of laser diodes and photodiodes devices, an optical package
is required. There are many discrete optical and electronic components, which are based on
different technologies that must be optically aligned and integrated within the optical
package. Optical packaging of laser diodes and photodiodes is the primary cost driver. These
packages are called as Optical Sub-Assemblies (OSAs).
Tunable 10 Gbps lasers use a similar butterfly optical package. The butterfly package design
uses a coaxial interface for passing broadband data into the package, which requires the use
of a coaxial interface to the host Printed Circuit Board (PCB). To operate with highperformance, uncooled designs must be implemented with more advanced control systems
that can adjust the laser and driver parameters over temperature.
TO-can-based designs are now maturing to support high performance 10 Gbps optical links.
These designs being produced in high volumes will further reduce the cost of optical
The optical transmitter and receiver modules are usually packaged into a single package
called an optical transceiver.
There are several form factors for this optical transceiver depending on their operating speed
and applications.
FIG 7.4.1 PCB of transceiver
Above figure shows an example of the printed circuit board of a transceiver. The industry
worked on a Multi-Source Agreement (MSA) document to define the properties of the optical
transceivers in terms of their mechanical, optical, and electrical specifications. Optical
transponders operating at 10 Gb/s, based on MSA, have been in the market since circa 2000,
beginning with the 300-pin MSA, followed by XENPAK, XPAK, X2, and XFP.
7.5 VCSEL (Vertical-Cavity Surface- Emitting Laser Diodes)
FIG7.5.1 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) wafers with DBRs formed from GaAs and aluminium gallium arsenide (AlxGa(1x)As).
The current 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 confined 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 Thunderbolt 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 powercurrent 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.
The Thunderbolt module detects when cables are cut or unplugged and automatically turns
off the laser.
The Thunderbolt optical module is only12mm by 12mm and drives two optical ports.
A single-chip solution will be in demand for Thunderbolt as well, but to date Intel has simply
suggested that it will be providing the controller chip and is working with industry partners to
provide other various components.
Thunderbolt is based on 10G 850nm VCSEL and PIN-diode arrays with LOMF (Laseroptimized 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 8.1 Schematic diagram of Optical module
Thunderbolt 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 Thunderbolt Technology can be overviewed as:
Thunderbolt protocol
Thunderbolt controller
Thunderbolt platforms
Server Network
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
Common Transport
Cable and
FIG 9.1.1 Simplified view of protocol
Thunderbolt Networks use a similar idea of packet switching.
All the IO devices may have their native protocols but when using Thunderbolt they all run
over Thunderbolt protocol. That is they uses their individual protocol for data transfer but
their speed is defined by Thunderbolt.
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.
At the heart of Thunderbolt 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 Thunderbolt Controller contains:
A Cross bar switching unit: switches the various protocols from LPK to their
respective protocol adapter.
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 9.2.1Thunderbolt controller schematic
FIG 9.2.2 Thunderbolt controller chip
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 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.
A typical Thunderbolt platform can be viewed with few of these examples:
FIG 9.3.1Workstation
Build a high-bandwidth, fault- resilient, low-cost network that can deliver performance
isolation across applications.
Integrate low-radix switches into several platforms.
Interconnect servers directly using multi- path topologies.
Why Thunderbolt 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.
FIG 9.4.1 Network of servers
How does Thunderbolt 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 Thunderbolt, but they are mostly designed for video. No one is
pushing the data transfer rates of these protocols.
FIG 10.1 Performance of Thunderbolt
The chart shows how Thunderbolt compares to all of these other protocols. At 10 Gbps, it can
cover a whole range of transfer protocols. The magic of Thunderbolts is that it can become
the cable of choice for all these protocols with no significant loss in transfer speed.
Since Thunderbolt is developed to meet PC requirements and the telecom ones, thus the
Thunderbolt 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 standards 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-specified 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 Thunderbolt 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
Thunderbolt optical module features a launch power much higher than eye safety.
Finally, Intel designed the optical module to be high-volume manufacturable thus
further reducing the cost of production.
The Thunderbolt optical modules are physically much smaller than those of telecom
The optical modules are designed to be much lower cost and higher performance.
Thunderbolt can send and receive data at 10 billion bits per second.
The thin optical fiber will enable Thunderbolt to transfer data over very thin, flexible
Unlike electrical cables, Thunderbolt do not faces the problem of EMI, thus can be
used up to 100m.
Thunderbolt 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 highspeed bullet train.
The data transfer is bidirectional in nature thus enabling devices to transfer
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 interconnects.
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.
Thunderbolt is a high-speed, multi-protocol interconnect for innovative and emerging client
usage models, that complements other existing interconnects
Thunderbolt is the name for a new high-speed optical cable technology designed to connect
electronic devices to each other. Thunderbolt delivers 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.
Thunderbolt allows for smaller
connectors and longer, thinner, and more flexible cables than currently possible. Thunderbolt
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
Intel is working with the optical component manufacturers to make Thunderbolt 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. Thunderbolt is
complementary to existing I/O technologies, as it enables them to run together on a single
cable at higher speeds.
At the present time, Intel has conducted three successful public demonstrations of the
Thunderbolt technology and confirmed that the first Thunderbolt-enabled PCs should begin
shipping next year.
The goal of this new developing technology is to build a high-bandwidth, fault-resilient, lowcost 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 THUNDERBOLT?? 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.
Intel CEO Paul Otellini called Thunderbolt “the I/O performance and connection for the next
generation,” and confirmed that both Nokia and Sony have publicly announced their support.
Victor Krutul, director of Intel’s optical development team and founder of the Thunderbolt
program, is even more effusive, calling Thunderbolt “the biggest thing to happen to the
optical industry ever, or at least since the creation of the laser.”
© Electronicsforu magazine, Oct 10