1. What are the main driving applications for traffic growth in today’s networks?

Supercomputer Interconnections Multimedia Interactive TV Telemedicine Applications GRID Computing Storage Area Networks Distance Learning Video Conferencing Audio and Video Broadcasting etc.

2. Which technologies and components can be used to implement high-performance network elements? Only itemize the main classes of electrical, optical and optoelectronic components and the applications in which they can be used.

Electric componentso Integrated circuitso Microprocessorso Memoryo Transistors (MESFET, HEMT, HBT)

Optical componentso Optical Fibreso Optical Couplerso Optical Isolatorso Optical Filters

Optoelectronic componentso Optical Sources (LEDs, LDs)o Photodetectorso Optical Amplifierso Optical Switches

3. What technologies and semiconductor materials are used to manufacture integrated circuits for communications applications?

CMOS nMOS, pMOS Bipolar (analogue) ECL TTI GaAs InP AlGaAs

4. What are the main trends in semiconductor electronics and in particular in integrated circuits?

decreasing feature size increasing chip area increasing clock frequency efficient micro structures better design strategies and tools

5. How can integrated circuits be classified according to their flexibility and performance?

Standard Circuits, such as a standard processor, are the most flexible integrated circuits. They are normally produced in high quantity and have a relatively low price. Full-custom and semi-custom circuits are usually used to implement user specific functions or customized blocks. Therefore they are produced in a specific quantity and are more expensive.

6. Describe methods that can be used to increase performance of a CPU? Pipelining Application specific ISA (Instruction Set Architecture) extensions Multiple ALUs and control units Superscalar Very Long Instruction Word (VLIW) Multithreading Memory hierarchy design

7. What is a content addressable memory (CAM)? Describe at least three applications of CAMs.CAM is an extension of ordinary memory (e.g. SRAM). Read and write operations are performed as usual. Content itself or parts of it function as key to search data. CAMs compare in parallel input search data to all contents of memory and return the address of the data. Tasks that benefit from CAMs are search-intensive, such as the following applications:

Routing address translation Real-time compression and encryption Cache memory in microprocessors Mapping tables and translation buffers in microprocessors Pattern recognition in artificial intelligence robotic systems

8. Draw a block diagram of a basic CAM structure.

9. What is a ternary CAM (TCAM)? Highlight differences between basic (binary) CAMs and ternary CAMs. What is the main networking application of TCAMs?While binary CAMs store only two states (0, 1) ternary CAMs store an additional state (don’t care state, X). When a don’t care is stored in the cell, a match occurs for that bit regardless of the search data. TCAM devices are favoured by most network component and equipment vendors due to the fast and deterministic lookup performance afforded by their use of massive parallelism.

10. What types of fibres are used in optical communications? How are the transmission windows of standard single-mode fibres defined? Are there any new fibre types and what are the trends in optical communications?An optical glass fibre consists of a fibre core made of highly pure glass with a high refractive index. A middle layer (cladding) is made of glass with a lower refractive index. An outer polymer jacket is added to protect the fibre from damage.There are three different kinds of optical fibre:

Multimode step-index Multimode graded-index Single-mode (step-index)

The attenuation characteristic offers three “windows” or bands for transmission.

The first window (800-900nm) has indeed a relatively high attenuation but allows using low cost optical sources and detectors.The second window (around 1310nm) offers zero dispersion on single-mode fibres. The attenuation is lower than in the first window, but sources and detectors are more costly.The third window (1500-1600nm) has the lowest attenuation but sources and detectors are more costly. Additionally the fibre disperses the signal in this band.New types of fibres are AllWave (no attenuation peak around 1400nm) and Photonic Crystal Fibres (PCF) that offer unique properties impossible to achieve in classical fibres.

11. How can chromatic dispersion in single-mode fibres be effectively compensated? Describe briefly the nonlinear effects that occur in single-mode fibres.Chromatic dispersion describes the tendency for different wavelengths to travel at different speeds in a fibre. In general, it consists of the material and waveguide dispersion. The waveguide dispersion components refer to the tendency that the effective refraction index of a mode changes with frequency. If the area occupied by the mode in relation to the fibre’s refractive index profile is large, the change of the refractive index with frequency is also large. As the core diameters in single-mode fibres are small, the waveguide contribution to the chromatic dispersion becomes comparable to the material contribution in such fibres. The waveguide contribution shifts the zero-dispersion wavelength slightly towards longer wavelengths. This is used to adjust the zero-dispersion wavelength of the fibre by adjusting fibre-design parameters such as core diameters and core-cladding index difference. By using multiple cladding layers, so called dispersion-flattened fibres (DFF) can be designed.

12. Describe the main parameters and applications of optical filters. What types of optical filters are used in communication networks?Main filter parameters are:

Filter bandwidth Centre wavelength Insertion loss Spectral shape Contrast (ration between maximum values of transmission and reflection)

Filters used in communication networks: Fabry-Perot filter (fixed and tuneable when mounted on piezoelectric crystals) Diffraction Gratings Fibre Bragg Gratings Arrayed Waveguide Grating Acusto-optic tunable Filters Dielectric Thin-Film Filters Mach-Zender Interferometer

13. Describe the differences between the gain-guided and the index-guided laser diode structure. What are the main differences between a Fabry-Perot (FP) laser and a distributed feedback (DFB) laser? What structures can be used to produce short optical pulses?The Fabry-Perot Laser is built up like a LED, but with a pair of mirrors at the ends. The mirrors are necessary to create the right condition for lasing to occur. The active layer is very thin and the refractive index difference between the material of the active layer and the surrounding material is not great. Thus you don’t get lasing in the vertical (transverse) mode. Lasing in the lateral mode is minimized by an anti-reflection material or just rough sides. Lasing in the longitudinal mode across the full width of the device is a problem as the device will tend to produce many different localised areas of lasing at different wavelengths. It is additionally a significant problem to guide the light into a fibre. To get rid of this problem gain-guidance and index-guidance have been developed.

Gain-guidance is achieved by limiting the area of the electrical contact on the surface of the device. Power is delivered into the active layer in a long stripe. There will be sufficient gain along this path for lasing to occur but outside the region there will not be sufficient gain to sustain lasing. Thus one gets narrow beam of light issuing from the centre of the active region.Index-guidance is achieved by using a lower refractive index in the active region than the material surrounding it. In this situation the light is guided out of the cavity.

14. Draw the schematic of an erbium-doped fibre amplifier (EDFA). Are there any other optical amplifiers that can be used in fibre communications? Describe the operational principle of these optical amplifiers and in which applications they can be used.Erbium-Doped Fibre Amplifier

An Erbium-doped fibre amplifier consists of a short section of fibre which has a small controlled amount of Erbium added to the glass. The Erbium ions are able to exist in several energy states. The erbium ions are excited into a high-energy state by a pump-laser at an appropriate wavelength. These ions in the excited state are then available for stimulated emission and amplify the signal.

Fibre Raman Amplifier

The relatively large bandwidth makes them attractive for fibre-optical communication applications. Moreover due to the distributed amplification the signal to be amplified remains in the linear amplification region, so that the impact of nonlinear effects and the accumulation of noise are reduced.

Semiconductor Optical Amplifier

SOAs are basically semiconductor laser diodes with antireflection coated sides that prevent oscillations in the cavity.In communication systems, SOAs are used for a wide spectrum of applications such as high-speed optical switching, wavelength conversion, in-line amplification for metro networks, per-amplification in optical receivers, and optical amplification and reshaping (2R), & retiming (3R) regenerators for long haul transmission systems.

15. How does a thermo-optic switch work? What are micro-electro-mechanical system (MEMS) switches? Why are interferometric structures used for optical switches?Thermo-optic switches are interferometric switches (usually Mach-Zender interferometers) where the phase in changed in the arms by changing the refractive index of the waveguide material by changing the temperature. This is done by varying the voltage applied to thin metal heating electrodes. Switching speed is low at about several microseconds.

Micro-electro-mechanical system (MEMS) switches consist of small mirrors that are moved as desired for switching. They have low insertion loss, low crosstalk, are optically transparent, and polarization intensity, and can scale up to high port counts. But they are often bulky and require a complex optical alignment and assembly.

16. Describe evolution of interconnection technologies during the last decades.

17. What types of interconnects do you know? How can interconnects be classified? Describe benefits and drawbacks of three typical interconnection solutions.In general, interconnects can be divided into tree main categories:

Intra-module (backplane) interconnects Chip-to-chip interconnects Data-path (in-chip) interconnects

Typical interconnection solutions are: Peripheral Component Interconnect (PCI, PCI-X, PCI Express) Small Computer System Interface (SCSI, SAS, iSCSI) HyperTransport (HT) Rapid I/O Infiniband Common Switch Interface (CSIX) SONET/SDH Ethernet ATM Fibre Channel

18. Describe PCI Express layered architecture. What are the main features of the three lower layers?The PCI Express architecture is specified in layers.

The software layers will generate read and write requests that are transported by the transaction layer to the I/O devices using a packet-based split-transaction protocol. The link layer adds sequence numbers and CRC to these packets to create a highly reliable data transfer mechanism. The basic layer consist of a dual-simplex channel that is implemented as a transmit pair and a receive pair.

19. Describe the main features of Serial Attached SCSI (SAS). Draw a typical configuration of a SAS system.Serial Attached SCSI (SAS) is a point-to-point architecture in which all storage devices connect directly to an SAS port rather than sharing a common bus as traditional SCSI devices do. Point-to-point links increase data throughput and improve the ability to locate and fix disk failures. SAS inherits its command set from parallel SCSI, frame formats from Fibre Channel, and physical characteristics from Serial ATA. SAS is defined for full-duplex operations. Point-to-point configurations provide for high bandwidth, but require intermediary devices between initiator devices (or hosts) and target devices (or peripheral devices) to provide a topology where there may be more than two devices in a system. Inexpensive expanders are the intermediary devices defined for SAS. Using SCSI protocol and architecture, it is possible to bridge from a SYS system to other systems using Infiniband, iSCSI or Fibre Channel, which also use the same SCSI objects.

20. What is Internet SCSI (iSCSI)? Describe encapsulation of storage data into TCP/TP packets by using the iSCSI protocol. There are three options for implementing iSCSI host bus adapters (HBA). Describe these implementation options. What option can provide the highest performance?Internect SCSI (iSCSI) is an standard that defines the encapsulation of SCSI packets in TCP which allows them to be routed using IP. The storage data is encaplulated into TCP/IP packets as shown in the picture.

There are three classes of iSCSI host adapters iSCSI in Software: is a very economical, low-performance block I/O solution, iSCSI drivers can

be run on an off-the-shelf Ethernet card or interface. Software implementation of iSCSI offers advantages in terms of costs. However it must be balanced with the penalty it imposes in performance and CPU overhead.

iSCSI in Software with TCP off-load: TCP incurs significant processing overhead on the host CPU. Off-loading this processing to a host network interface card frees host CPU cycles and enables much higher performance solutions.

iSCSI in silicon with TCP off-load: High performance iSCSI adapters off-load both TCP and iSCSI processing to the interface card. While this adds costs to the adapter, it provides both wire-speed iSCSI transport and minimal CPU overhead.

21. What is HyperTransport (HT)? Describe HyperTransport connections and device configurations. Can large data packets be transmitted directly over a HyperTransport channel (without need for segmenting the packet)? What is the difference between host-reflected routing and device-to-device routing in HyperTransport?HyperTransport defines direct connection to the CPU or several CPUs via high bandwidth, very low latency links. The HyperTransport daisy-chain topology includes a required “host” device, at least one end-point or “cave”, optional “tunnel” devices that connect the link to other HyperTransport devices and optional “bridge” devices that interface with non-HyperTransport interconnect technologies.HyperTransport allows transmitting packets of the size of 4-64 bytes directly in a single HyperTransport data packet. If it is longer than 64 bytes it can be placed in a sequence of data packets by breaking it up into segments of 64 bytes.In HyperTransport there are two different routing mechanisms specified:

Host reflected routing: requires that all traffic passes through the host in order to maintain PCI compatibility. All traffic passes through the host device of the daisy chain. Thus, in order to replicate the ordering properties of PCI, all base HyperTransport transactions are reflected through the host.

Device-to-device routing: allows two devices to communicate directly, greatly reducing link traffic and off-loading the host from reflecting the traffic.

22. What are the main characteristics of RapidIO?RapidIO architecture is an electronic data communication standard for interconnection chips on a circuit board and circuit boards using a backplane. It is a packet-switched interconnect architecture conceptually similar to IP. However it is designed to be used for the processor and peripheral interface where high bandwidth and low latency are necessary. RapidIO is specified in a 3-layer architectural hierarchy:

Logical layer: defines the overall protocol and packet formats. This is the information necessary for end points to initiate and complete transactions

Transport layer: provides the necessary route information for a packet to move from end point to end point.

Physical layer: describes the device level interface specifics such as packet transport mechanisms, flow control, electrical characteristics, and low-level error management.

This partitioning provides flexibility to add new transaction types to the logical layer without requiring modifying the other layers.The main characteristics of RapidIO are:

Packet switching: point-to-point interconnect to connect processors, co-processors, memory and memory mapped I/O

Low overhead and low latency Small silicon footprint: can be implemented in ASICs and even FPGAs Software transparent: an extension of microprocessor bus that allows direct, physical memory

mapping of the entire machine Reliable delivery of packets: error detection and recovery in hardware Layered architecture Standard I/O technology

23. What are the main components of an InfiniBand subnet? Describe the functions of a local (LID) and a global (GID) identifiers.The InfiniBand architecture (IBA) is an industry-standard architecture for server I/O and inter-server communications. The elements of a subnet are endnodes, switches, links and a Subnet Manager. Endnodes, such as hosts and devices, send messages over links to other endnodes. The messages are routed by switches. Routing is defined, and subnet discovery performed, by the Subnet Manager. Channel Adapters (CAs) connect endnodes to links.Every IBA subnet must contain a single master Subnet Manger, residing on an endnode or a switch. It discovers and initializes the network, assigning Local IDs (LIDs) to all elements, determining path maximum transfer units (MTUs), and loading the switch routing tables that determine the paths from endnode to endnode. Each endnode has one or more CAs and each CA has one or more ports. Each port has a unique 16-bit LID and at least one IPv6 address (Global ID, GID). Three types of quantities are important to IBA addressing: LIDs, GUIDs and GIDs.

LIDs are subnet unique 16-bit identifiers used within a network by switches for routing. GUIDs are Global unique IDs are identifiers for elements in a subnet. GIDs are 128-bit global identifiers used for routing across subnets.

24. What are the main applications for Common Switch Interfaces (CSIX)? Describe the main functions of the physical, interconnection, and logical message CSIX levels. What is a CFrame?CSIX is a detailed interface specification between port/packets processor logic and interconnect fabric logic. It is a scalable parallel interface with separate data and control paths. It is e generic specification to promote the deployment and development of highly scalable network switches. There are three levels in CSIX:

Logical or Message Level: ensures that data or control message protocol exchanged over the interface are properly understood by each end and properly processed by the appropriate function

Interconnection Level: defines all the signals with specific functions, meanings, and bit widths, input or output, signal handshake protocols, etc.

Physical Level: specifies the electrical characteristics such as voltage levels, capacitance, drive strengths, timings, etc.

A CFrame is the base information unit transferred between traffic managers and a CSIX fabric. It consists of a base header, an optional extension header, and optional payload, optional padding bits and a 16-bit vertical parity field. The payload is variable in length and is passed by CSIX fabric from incoming traffic manager to the outgoing traffic manager.

25. What technologies can be used to implement high-capacity backplanes?There are two types of backplanes: active and passive. Active backplanes contain bus control bridges; however they do not contain processor complex components such as the CPU, chipset or cache. Passive backplanes contain circuitry for bus connectors and, in some cases, buses and drivers.To avoid single point failure, switching function can be distributed over the line cards. Thus, in case each card implements a switching element, and therefore, no active backplane is needed. A drawback of this solution is that the line cards become more complex and more costly. Advanced switching should provide a standard backplane for interface for line cards, switch cards and control cards used in communication system applications.

26. Describe the SONET/SDH interfaces developed by the Optical Internetworking Forum (IOF). What are the main differences between System Packet Interface (SPI) and DERDES Frame Interface (SFI)?The OIF developed the System Packet Interface (SPI), the SERDES Framer Interfaces (SFI) and the TDM Framer Interface (TFI).The SPI is between the Physical Layer device(s) and the rest of the SONET/SDH System. This interface separates the synchronous PHY layer from the asynchronous packet-based processing performed by the higher layers. As such, the SPI supports transmit and receive data transfers at clock rates independent of the actual line bit rate. It is designed for the efficient transfer of both variable-sized packet and fixed-sized cell data.The SFI defines an electrical interface between a SONET/SDH Framer and the high speed Parallel-to-Serial/Serial-to-Parallel (SERDES) logic. This permits the SERDES and framer to be implemented in different speed technologies, allowing a cost-effective multiple chip solution for the SONET/SDH physical layer.The TFI defines the backplane interface (either electrical or optical) between a SONET based TDM framer and the switch fabric. Traffic between the framer and the fabric is modelled after a SONET/SDH frame, and operates at the STS-48/STM-16 equivalent bit rate.

27. Describe functional layering of a typical SONET/SDH framer device. What kinds of interfaces are usually used as Layer 2 (L2) interface in SONET/SDH framer devices?

28. Describe the media options for Ethernet systems. Which cable types and coding methods are used in Ethernet? Describe the coding methods used in Gigabit Ethernet over twisted pair cables and optical fibres.

Gigabit Ethernet over twisted pair uses 4D PAM-5 Code.

29. What are the main functions of the Gigabit Ethernet physical layer?The Physical Layer is subdivided into three sublayers:

Physical Coding Sublayer: auto-negotiation, synchronisation at byte level, carrier sense as well as transmit and receive functions (including coder and decoder blocks

Physical Medium Attachment Physical Medium Dependent

30. Draw a block diagram of the 10GBASE-R (10 Gigabit Ethernet) physical coding sublayer (PCS). Describe the main functions of the blocks. What coding scheme is used in 10GBASE-R?

31. Itemize at least five Ethernet interfaces. Which interface replaces the Attachment Unit Interface (AUI) in Fast Ethernet? How is the physical layer connected to Media Access Control (MAC) layer in Gigabit Ethernet?Ethernet Interfaces:

MAU (Medium Attachment Unit) MDI (Medium Dependent Interface) AUI (Attachment Unit Interface) TBI (Ten-Bit Interface) RTBI (Reduced Ten-Bit Interface) MII (Medium Independent Interface) GMMI (Gigabit Medium Independent Interface) RGMII (Reduced Gigabit Medium Independent Interface) GBIC (Gigabit Interface Converter) XAUI (10 Gigabit Attachment Unit Interface) XSBI (10 Gigabit Sixteen-Bit Interface) XGMII (10 Gigabit Medium Independent Interface)

The Medium Independent Interface (MII) replaces the Attachment Unit Interface (AUI) in Fast Ethernet. The physical layer is connected to the Media Access Control via the Gigabit Medium Independent Interface (GMII) in Gigabit Ethernet and via the 10 Gigabit Medium Independent Interface (XGMII) in 10 Gigabit Ethernet respectively.

32. What are the main features and applications of the 10 Gigabit Attachment Unit Interface (XAUI)? What is the maximum distance possible by using XAUI interface?XAUI is a full duplex interface that uses four self-clocked serial differential links in each direction to achieve 10 Gbit/s data throughput.

33. Describe the main features of the Universal Test & Operations PHY Interface for ATM (UTOPIA). What are the differences between four levels of UTOPIA interface?UTOPIA is defined by the ATM Forum to provide a standard interface between ATM devices and ATM PHY or SAR (segmentation and Reassembly) devices.

34. Describe the transmission hierarchy and the concept of flow control used in Fibre Channel (FC). How many classes of services are there in FC? Which components can be used in FC systems?Basically every byte of data that is to be transmitted is first converted into a 10-bit value called Transmission Character. All information in Fibre Channel is transmitted in groups of four Transmission Characters called Transmission Words. Together with 36 bytes of overhead and several full Transmission Words are transmitted in a FC frame (word in the analogy). A series of one or more related frames is called a Fibre Channel Series (sentence in the analogy). A Fibre Channel Exchange (conversation in the analogy) is a series of one or more non-concurrent sequences between two ports.

A device can transmit frames to another device only when the other device is ready to accept them. Before the devices can send data, they must login to each other. Thereby credit is established which refers to the number of frames a device can receive at a time. After credit runs out, no more frames can be transmitted until the destination device grants more credit. In FC two types of flow-control are used: buffer-to-buffer and end-to-end.

There are 6 numbers of classes (communication strategies) in FC, depending on the type of data to be transmitted.Components that can be used in FC systems are:

FC Hubs Switches & Directors Host Bus Adapters (HBA) Bridges