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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 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
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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.
Powerful technology from a powerful collaboration. 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.
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THUNDERBOLT 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 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 stations.
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.
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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 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.
•
Fig. 2.1: 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
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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 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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TODAYS CHALLENGES In the coming future, people would be using more and more electrical deices 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.
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So vendors turn over to new technologies providing much better performance and Thunderbolt seems to be a providing a good solution.
Fig.3.1 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 models. 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
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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. THUNDERBOLT V/S USB 3.0 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 THUNDERBOLT 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 simultaneously.
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.
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COMPONENTS OVERVIEW 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
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FIG 3.2: 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.
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FUNDAMENTALS OF OPTICAL COMPONENTS A basic optical communication link consists of three key building blocks: optical fiber, light sources, and light detectors. OPTICAL FIBER: 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 (Single-mode 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 dispersions: 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.
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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.
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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. LIGHT SOURCE: 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 long-wavelength 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 modulation. 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
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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: 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 germanium. 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 economical. PACKAGING: OPTICAL SUBASSEMBLY AND TRANSEIVERS 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 SubAssemblies (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
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requires the use of a coaxial interface to the host Printed Circuit Board (PCB). To operate with high- performance, 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 modules. OPTICAL TRANSEIVERS: 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. 3.3: 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. OPTICAL MODULE
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Thunderbolt 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 3.4: Schematic diagram of Optical module
VCSEL (Vertical-Cavity Surface- Emitting Laser Diodes):
FIG 3.5: 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.
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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(1-x)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 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 3dB 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.
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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.
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THUNDERBOLT TECHNOLOGY OVERVIEW 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
THUNDERBOLT 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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IO
Applicati on specific Protocol LIGH T PEAK
IO Pro toc ol
Pro toc ol
IO pro toc ol
Common Transport Electrical/Optical PHY Cable and connectors
FIG 4.1: 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. THUNDERBOLT CONTROLLER: 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:
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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.
PROTOCOL ADAPTER
PORTS
THUNDERBOL T PORTS
Adapte Adapter r
Crossbar Switch
LPK
Adapter Adapte r Adapte Adapter r
LPK
LPK
LPK
FIG 4.2: THUNDERBOLT CONTROLLER SCHEMATIC
Fig. 4.3: 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
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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.
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THUNDERBOLT PLATFORM: A typical Thunderbolt platform can be viewed with few of these examples:
PCIe
dGF X
CPU
DMI
Mem
FIG PCH 11 Mobile Platform
Displ ay Displa y PCIe
Thunderb olt
Controller
CPU
PCIe dGF X PCI e DM I QPI
Mem
IOH
ICH
PCIe Thunder bolt Contoller
Displa y
FIG 4.4: Entusiast/Workstation
Thunder bolt Controll er
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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 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.
SERVER
SERVER
SERVER
SERVER
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DATA TRANSFER SPEED COMPARISION
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 5.1 Performance of Thunderbolt FIG 5: 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.
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BRINGING OPTICAL TO MAINSTREAM 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.
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ADVANTAGES • • • • • •
The Thunderbolt optical modules are physically much smaller than those of telecom grade. 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 cables. 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 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 interconnects.
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•
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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CONCLUSION
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 more. 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, faultresilient, low-cost network that can deliver performance isolation across applications.
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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.”
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http://science.howstuffworks.com
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techresearch.intel.com/ProjectDetails.aspx?Id=143 en.wikipedia.org/wiki/Light_Peak news.cnet.com/8301-13924_3-20025559-64.html www.lightpeakinfo.com/ http://opticalcomponents.blogspot.com/2010/07/laser-optimized-multi-modefiber-lomf.html http://www.technewsworld.com/story/68231.html http://optics.org/indepth/1/3/6 http://arstechnica.com/apple/news/2009/09/apple-inspiration-behind-lightpeak-optical-connection-standard.ars http://www.lightwaveonline.com/about-us/lightwave-current-issue/Intel-plotsLight-Peak-interconnect-revolution.html http://www.computer.org/portal/web/csdl/doi/10.1109/HOTI.2010.13
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©
http://www.intel.com/thunderbolt
© http://www.apple.com/thunderbolt
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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
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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.
Powerful technology from a powerful collaboration. 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.
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THUNDERBOLT 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 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 stations.
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.
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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 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.
•
Fig. 2.1: 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
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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 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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TODAYS CHALLENGES In the coming future, people would be using more and more electrical deices 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.
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So vendors turn over to new technologies providing much better performance and Thunderbolt seems to be a providing a good solution.
Fig.3.1 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 models. 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
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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. THUNDERBOLT V/S USB 3.0 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 THUNDERBOLT 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 simultaneously.
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.
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COMPONENTS OVERVIEW 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
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FIG 3.2: 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.
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FUNDAMENTALS OF OPTICAL COMPONENTS A basic optical communication link consists of three key building blocks: optical fiber, light sources, and light detectors. OPTICAL FIBER: 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 (Single-mode 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 dispersions: 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.
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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.
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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. LIGHT SOURCE: 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 long-wavelength 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 modulation. 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
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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: 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 germanium. 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 economical. PACKAGING: OPTICAL SUBASSEMBLY AND TRANSEIVERS 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 SubAssemblies (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
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requires the use of a coaxial interface to the host Printed Circuit Board (PCB). To operate with high- performance, 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 modules. OPTICAL TRANSEIVERS: 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. 3.3: 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. OPTICAL MODULE
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Thunderbolt 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 3.4: Schematic diagram of Optical module
VCSEL (Vertical-Cavity Surface- Emitting Laser Diodes):
FIG 3.5: 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.
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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(1-x)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 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 3dB 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.
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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.
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THUNDERBOLT TECHNOLOGY OVERVIEW 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
THUNDERBOLT 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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IO
Applicati on specific Protocol LIGH T PEAK
IO Pro toc ol
Pro toc ol
IO pro toc ol
Common Transport Electrical/Optical PHY Cable and connectors
FIG 4.1: 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. THUNDERBOLT CONTROLLER: 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:
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•
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.
PROTOCOL ADAPTER
PORTS
THUNDERBOL T PORTS
Adapte Adapter r
Crossbar Switch
LPK
Adapter Adapte r Adapte Adapter r
LPK
LPK
LPK
FIG 4.2: THUNDERBOLT CONTROLLER SCHEMATIC
Fig. 4.3: 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
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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.
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THUNDERBOLT PLATFORM: A typical Thunderbolt platform can be viewed with few of these examples:
PCIe
dGF X
CPU
DMI
Mem
FIG PCH 11 Mobile Platform
Displ ay Displa y PCIe
Thunderb olt
Controller
CPU
PCIe dGF X PCI e DM I QPI
Mem
IOH
ICH
PCIe Thunder bolt Contoller
Displa y
FIG 4.4: Entusiast/Workstation
Thunder bolt Controll er
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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 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.
SERVER
SERVER
SERVER
SERVER
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DATA TRANSFER SPEED COMPARISION
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 5.1 Performance of Thunderbolt FIG 5: 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.
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BRINGING OPTICAL TO MAINSTREAM 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.
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ADVANTAGES • • • • • •
The Thunderbolt optical modules are physically much smaller than those of telecom grade. 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 cables. 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 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 interconnects.
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•
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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CONCLUSION
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 more. 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, faultresilient, low-cost network that can deliver performance isolation across applications.
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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.”
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