MAHALAKSHMI ENGINEERING COLLEGE TIRUCHIRAPALLI

Transcription

1 MAHALAKSHMI ENGINEERING COLLEGE TIRUCHIRAPALLI UNIT I HIGH SPEED NETWORKS Part A (2 Marks) 1. Differentiate Frame relay and X.25 packet-switching service. -> Call control signaling is carried on a separate logical connection from user data. Thus, intermediate nodes need not maintain state tables or process messages relating to call control on an individual per-connection basis -> Multiplexing and switching of logical connections takes place at layer2 instead of layer3, eliminating one entire layer of processing ->There is no hop-by-hop flow control and error control. End-to-end flow control and error control are the responsibility of a higher layer, if they are employed at all. 2. What is jitter? The packets between a given source and destination may vary in length, may take different routes, may be subject to varying delays in the switches they encounter, the overall packet delay can vary substantially. This phenomenon, called JITTER may not be desirable for some application; for example in real-time applications including telephone voice and real-time video. 3. List out some of the control functions of LAPF core. Frame delimiting, alignment and transparency Frame multiplexing/demultiplexing using the address field Detection of transmission errors Congestion control functions. 4. What is called a cell in ATM? In ATM, the information flow on each logical connection is organized into fixed size packets called cells. 5. What are the planes in protocol reference model? User plane Control plane Management plane. 6. What are the advantages of virtual paths? Simplified network architecture Increased network performance and reliability Reduced processing and short connection setup time Enhanced network services. 7. What is VPI? The Virtual path identifier constitutes a routing field for the network. It is 8 bits at the user-network interface and 12 bits at the network-network interface. The latter allows support for an expanded number of VPCs internal to the network, to include

2 those supporting subscribers and those required for network management. 8. What is CLP? The cell loss priority bit is used to provide guidance to the network in the event of congestion. A value of 0 indicates a cell of relatively higher priority, which should not be discarded unless no other alternative is available. A value of 1 indicates that this cell is subject to discard within the network. 9. What are the services of ATM The ATM services are: Real time services: Constant Bit Rate (CBR) Real Time Variable Bit Rate (rt-vbr) Non Real time services: Non Real Time Variable Bit Rate (nrt-vbr) Available Bit Rate (ABR) Unspecified Bit Rate (UBR) Guaranteed Frame Rate (GFR) 10. What is Frame Relay network? A form of packet switching based on the variable length link layer frames. There is no network layer. Many of the basic functions have been streamlined and eliminated to provide great throughput. 11. What are the message types needed for Frame relay call control? SETUP CONNECT RELEASE RELEASE COMPLETE. 12. What are the AAL services? Handling of transmission errors. Segmentation and reassembly, to enable larger blocks of data to be carried in the information field of ATM cells. Handling of lost and misinserted cell conditions. Flow control and timing control. 13. What are the applications of AAL? Circuit emulation VBR voice and video General data services IP over ATM Multiprotocol encapsulation over ATM LAN emulation. 14. What is SNP? The sequence Number Protection field is an error code for detection and possibly correction on the sequence number field. It consists of a 3 bit cyclic redundancy check, calculated over the 4 bit SN field, and a parity bit. The parity bit is set so that the parity of the 8 bit SAR header is even.

3 15. Differentiate bridge and layer2 switch. Bridge Frame handling alone in software Analyze & forward one frame at at a time. Store and forward. Layer2Switch Frame handling in hardware Multiple data paths & can handle multiple frames at a time. Can do cut through.

4 16. What are the benefits of 10 Gbps Ethernet over ATM? ->No expensive, bandwidth consuming conversion between Ethernet packets and ATM cells. ->Network is Ethernet end to end. ->IP plus Ethernet offers QoS and traffic policing capabilities approach that of ATM. ->Wide variety of standard optical interfaces for 10Gbps Ethernet. 17. What is the purpose of Fiber channel? Fiber channel is designed to combine the best features of both technologies the simplicity and speed of channel communication with the flexibility and interconnectivity that characterize protocol based network communication. 18. List some of the requirements of Wireless LAN. Throughput Number of nodes Connection to backbone LAN Service area Handoff/roaming Dynamic configuration. 19. What are the IEEE services? Association Reassociation Disassociation Authentication Privacy. 20. What are the physical medias defined in ? ->Direct sequence spread spectrum operating in the 2.4 GHz ISM band, at data rates of 1 Mbps and 2 Mbps -> Frequency hopping spread spectrum (FHSS) operating in the 2.4GHz ISM band at data rates of 1Mbps and 2Mbps -> Infrared at 1 Mbps and 2 Mbps operating at a wavelength between 850 and 950nm. 21. Define ISDN? The integrated services digital network is to provide a unique user network interface (UNI) for the support of the basic set of narrow band(nb) services that is voice and low speed data thus providing a narrowband integrated access. 22. What are the features of an ISDN? 1. Standard user network interface (UNI) 2. Integrated digital transport 3.Service integration 4. Intelligent network services 23. What is constant bit rate (CBR)? CBR is used to provide circuit emulation services. The corresponding bandwidth allocated on the peak of the traffic sources so that a virtually loss free communication service is obtained with prescribed targets of cell transfer delay (CTD) and cell delay variation (CDV)

5 24. What is available bit rate (ABR)? It is used to support data traffic sources. In this class a minimum bandwidth can be required by the source that is guaranteed by the network. The service is supported with the guarantee of CLR or CTD. 25. What is unspecified bit rate (UBR)? It is used to support data sources willing to use just the capacity left available by all the other without any objective on CLR and CTD. 26. Define ATM adaptation layer (AAL)? A collection of standardized protocols that provide services to higher layers by adapting user traffic to a cell format. 27. Define AAL1 (AAL type 1)? An AAL used for the transport of constant bit rate (CBR) traffic (ie. Audio and video) and for emulating TDM based circuits. 28. Define AAL2 (AAL type2)? An AAL used for supporting time dependent variable bit rate (VBR-RT) connection oriented traffic (ie.packetized video and audio). 29.What is AAL3/4(AAL type 3 and 4)? An AAL used for supporting both connectionless and connection oriented variable bit rate (VBR) traffic.it is also used to support SMDS. 30.What is AAL5 (AAL type5)? The most common AAL type used for the transport of data packets. 31. Define ATM? A broadband switching and multiplexing, connection-oriented, high performance and cost effective integrated technology for supporting BISDN services. 32. What are the features of SDH? 1. Provision of single worldwide transmission network 2. Easy multiplexing and demultiplexing 3. Flexibility in adapting internal signal structure 4. Provision of operation and maintenance functions. 33. What are the layers present in SDH? 1. Circuit layer 2.path layer 3.transmission layer 34. Give the SDH multiplexing elements? Container, virtual container, tributary unit, tributary unit group, administrative unit, administrative unit group, synchronous transport module.

6 35. What is meant by floating mode of multiplexing? Pointer information allows a VC to float within its TU is called mode of multiplexing. 36. What are the elements present in VC? A VC consists of a Container and the path overhead processed in the SDH multiplexer. 37. What are the functions of a tributary unit group? It performs the function of assembling together several TU s without further overhead. 38. What is path overhead? The header needed to perform the functions at the path layer is path overhead. 39. What is the need for plesiochronous digital hierarchy? The need is to develop a step-by-step hierarchical multiplexing in which higher level multiplexing are needed. 40. What is SS7? SS7 defines a signaling network features and the protocol architecture of the common channel signaling used in ISDN. 41. Define frame relay. A form of packet switching based on the use of variable-length link-layer frames. There is no network layer, and many of the basic functions have been streamlined or eliminated to provide for greater throughput. 42. Define ATM. ATM is a connection-oriented packet switching technique that generalizes the notion of a virtual connection to one that Provides quality-of-service guarantees. (Or) A form of packet transmission using fixed size packets, called cells. ATM is the data transfer interfaces for B-ISDN. Unlike X.25, ATM does not provide error control and flow control mechanisms. 43. Write down the advantages of packet switching network over circuit switching. a). Line efficiency is greater, because a single node-to-node link can be dynamically shared by many packets over time. b). A packet-switching network can carry out data-rate conversion. c). Priorities can be used. 44. What are the main features of ATM? The service is connection-oriented, with data transfer over a virtual circuit. The data is transferred in 53 byte packets called cells.

7 Cells from different VCs that occupy the same channel or link are statistically multiplexed. ATM switches may treat the cell streams in different VC connections unequally over the same channel in order to provide different qualities of services (QOS). 45. What are the traffic parameters of connection-oriented services? a. Peak Cell Rate (PCR) b. Sustained Cell Rate (SCR) c. Initial Cell Rate (ICR) d. Cell Delay Variation Tolerance (CDVT) e. Burst Tolerance (BT) f. Minimum Cell Rate (MCR) 46. What are the quality service (QoS) parameters of connection-oriented services? a. Cell Loss Ratio (CLR) b. Cell Delay Variation (CDV) c. Peak-to-Peak Cell Delay Variation (Peak-to-Peak CDV) d. Maximum Cell Transfer Delay (Max CTD) e. Mean Cell Transfer Delay (Mean CTD) 47. Types of ATM network interface. Two most important interfaces are: 1. User-network interface (UNI) 2. Network-network interface or network-node interface (NNI). 48. What are the two sub layers of AAL? f. Convergence Sub layer (CS) g. Segmentation and Reassembly Sub layer (SAR). 49. What is the function of CS? The Convergence Sublayer (CS) converts the information stream into four types of packets streams, called AAL Type1, Type2, Type3/4, and Type5.The packet formats match the requirements of the information stream.

8 50. What are the subdivisions of CS? a. Upper, service-specific or SSCS sub layer b. Lower, common part or CPCS sub layer. 51. What do you mean by Type1 traffic? Type1 traffic is a traffic generated at constant bit rate, and it is required to be delivered at the same rate (with a fixed delay). 52. What are the functions of management and control? 1. Fault management 2. Traffic and congestion control 3. Network status monitoring and configuration 4. User/network signaling. 53. What are the functions of user plane? It compromise the functions required for the transmission of user information for instance, for an internet protocol over ATM, these layers could be HTTP/TCP/IP/AAL What are the two basic tasks required for internetworking over ATM? The first is encapsulation of the protocol data units, and the second is Routing or Bridging of these PDUs. 55. Define fast Ethernet Fast Ethernet refers to a set of specifications developed by the IEEE committee to provide a low-cost, Ethernet-compatible LAN operating at 100 Mbps. 56. Define gigabit Ethernet? Gigabit Ethernet, which has a data rate of 1000 Mbps (Or) 1 Gbps. In which collision domain is reduced. Gigabit Ethernet is mainly designed to use optical fiber, although the protocol does not eliminate the use of twisted pair cables. There are four implementations have been designed for gigabit Ethernet: a) 1000Base-LX b) 1000Base-SX c) 1000Base-CX d) 1000Base-T

9 57.List requirements for WLAN? a). Throughput b). Number of nodes c). Connection to backbone LAN d). Service area e). Battery power consumption f). Transmission robustness and security g). Collocated network operation h). License-free operation i). Handoff/roaming j). Dynamic configuration 58. List out the important services of IEEE ? a) Association b) Reassociation c) Disassociation d) Authentication e) Privacy 59. Mention the requirements for fibre channels? a. Full duplex links with two fibers per link. b. Performance from 100 Mbps TO 800 Mbps on a single line. c. Small connectors d. Support for distances up to 10 km. e. High capacity utilization with distance insensitivity. f. Broad availability. g. Small systems h. Interface and network protocols.

10 60. List out the fibre channel elements? a. Node: The key elements of a fibre channel network are the end systems. b. Fabric: The collection of switching elements 61.What is the datalink control functions provided by LAPF? LAPF core provides a minimal set of datalink control functions consisting of the following (i)frame delimiting, alignment & transparency. (ii)frame multiplexing/demultiplexing using the address field. (iii)inspection of the frame to ensure that it consist of an integer no. of octets prior to zero bit insertion or following zero bit extraction. (iv)inspection of the frame to ensure that it is neither too long nor too short. (v)detection of transmission errors. (vi)congestion control functions. 62. List the levels of fiber channel & the function of each level? FC-0 PHSICAL MODE Includes optical fiber for long distance application, co-axial for high speeds over short distances & shielded twisted pair for lower speeds over short distance. FC-1 TRANSMISSION POROTOCOL Defines the signal encoding scheme. FC-2 FRAMING PROTOCOL Deals with defining topologies, frame format, flow & error control & grouping of frames into logical entities called sequences & exchanges. FC-3 COMMON SERVICES Include multicasting. FC-4 MAPPING Defines the mapping of various channel & network protocol to fiber channel, including IEEE 802, ATM, IP & the Small Computer System Interface (SCSI). 63. What is meant by SAR & CS? The AAL layer is organized in two logical sub layers: SAR & CS SAR: Segmentation And Reassembly sub layer is responsible for packing information at the other end. CS: The Convergence Sublayer provides the function needed to support specific application using AAL.

11 64. Difference b/w AAL ¾ & AAL 3/5 AAL ¾ AAL 3/5 (i)in this MID field is used to multiplex diff streams of data on the same virtual ATM connection. (ii)a 10 bit CRC is provided for each SAR PDU. (iii)in this 8 octets per AAL SDU, 4 octets per ATM cell. (i)in this MID field is assumed to that the higher layer software takes care of such multiplexing. (ii)a 32 bit CRC protects the entire cpu s PDU, provides strong protection against bit errors. (iii)8 octets per AAL SDU, 0 octets per ATM cell. 65. Give the data rates for frame relay & X.25? The lower bit rate for X.25 is 64 kbps. The fixed data for frame relay is 1.544mbps. The higher data rate for frame relay is mbps. 66. Define Ethernet. As packet switching has dominated wide area data networking, Ethernet dominates local area networking. The original experimental Ethernet operated at 3mbps over coaxial cable. This remarkable over twisted pair & optical fiber as well as coaxial cable. It was released commercially at 10 mbps & then was scaled up first to 100bps & none 1 & 10 gbps. Part B (16 Marks) 1.Explain Frame relay Networks in detail. Frame relay Networks Frame Relay often is described as a streamlined version of X.25, offering fewer of the robust capabilities, such as windowing and retransmission of last data that are offered in X.25. Frame Relay Devices Devices attached to a Frame Relay WAN fall into the following two general categories: Data terminal equipment (DTE) Data circuit-terminating equipment (DCE) DTEs generally are considered to be terminating equipment for a specific network and typically are located on the premises of a customer. In fact, they may be owned by the customer. Examples of DTE devices are terminals, personal computers, routers, and bridges. DCEs are carrier-owned internetworking devices. The purpose of DCE equipment is to provide clocking and switching services in a network, which are the devices that actually

12 transmit data through the WAN. In most cases, these are packet switches. Figure 10-1 shows the relationship between the two categories of devices. Standard Frame Relay Frame Standard Frame Relay frames consist of the fields illustrated in Figure Figure Five Fields Comprise the Frame Relay Frame Each frame relay PDU consists of the following fields: 1. Flag Field. The flag is used to perform high level data link synchronization which indicates the beginning and end of the frame with the unique pattern To ensure that the pattern does not appear somewhere inside the frame, bit stuffing and destuffing procedures are used. 2. Address Field. Each address field may occupy either octet 2 to 3, octet 2 to 4, or octet 2 to 5, depending on the range of the address in use. A two-octet address field comprising the EA=ADDRESS FIELD EXTENSION BITS and the C/R=COMMAND/RESPONSE BIT. 3. DLCI-Data Link Connection Identifier Bits. The DLCI serves to identify the virtual connection so that the receiving end knows which information connection a frame belongs to. Note that this DLCI has only local significance. A single physical channel can multiplex several different virtual connections. 4. FECN, BECN, DE bits. These bits report congestion: o FECN=Forward Explicit Congestion Notification bit o BECN=Backward Explicit Congestion Notification bit o DE=Discard Eligibility bit 5. Information Field. A system parameter defines the maximum number of data bytes that a host can pack into a frame. Hosts may negotiate the actual maximum frame length at call set-up time. The standard specifies the maximum information field size (supportable by any network) as at least 262 octets. Since end-to-end protocols typically operate on the basis of larger information units, frame relay recommends that the network support the maximum value of at least 1600 octets in order to avoid the need for segmentation and reassembling by end-users. Frame Check Sequence (FCS) Field. Since one cannot completely ignore the bit error-rate of the medium, each switching node needs to implement error detection to avoid wasting bandwidth due to the transmission of erred frames. The error detection mechanism used in frame relay uses the cyclic redundancy check (CRC) as its basis. Congestion-Control Mechanisms Frame Relay reduces network overhead by implementing simple congestion-notification mechanisms rather than explicit, per-virtual-circuit flow control. Frame Relay typically is

13 implemented on reliable network media, so data integrity is not sacrificed because flow control can be left to higher-layer protocols. Frame Relay implements two congestionnotification mechanisms: Forward-explicit congestion notification (FECN) Backward-explicit congestion notification (BECN) FECN and BECN each is controlled by a single bit contained in the Frame Relay frame header. The Frame Relay frame header also contains a Discard Eligibility (DE) bit, which is used to identify less important traffic that can be dropped during periods of congestion. Frame Relay versus X.25 The design of X.25 aimed to provide error-free delivery over links with high error-rates. Frame relay takes advantage of the new links with lower error-rates, enabling it to eliminate many of the services provided by X.25. The elimination of functions and fields, combined with digital links, enables frame relay to operate at speeds 20 times greater than X.25. X.25 specifies processing at layers 1, 2 and 3 of the OSI model, while frame relay operates at layers 1 and 2 only. This means that frame relay has significantly less processing to do at each node, which improves throughput by an order of magnitude. X.25 prepares and sends packets, while frame relay prepares and sends frames. X.25 packets contain several fields used for error and flow control, none of which frame relay needs. The frames in frame relay contain an expanded address field that enables frame relay nodes to direct frames to their destinations with minimal processing. X.25 has a fixed bandwidth available. It uses or wastes portions of its bandwidth as the load dictates. Frame relay can dynamically allocate bandwidth during call setup negotiation at both the physical and logical channel level. 2.Explain ATM architecture, Logical connections and its services. Asynchronous Transfer Mode (ATM) Asynchronous Transfer Mode (ATM) is an International Telecommunication Union- Telecommunications Standards Section (ITU-T) standard for cell relay wherein information for multiple service types, such as voice, video, or data, is conveyed in small, fixed-size cells. ATM networks are connection-oriented. ATM is a cell-switching and multiplexing technology that combines the benefits of circuit switching (guaranteed capacity and constant transmission delay) with those of packet switching (flexibility and efficiency for intermittent traffic). It provides scalable bandwidth from a few megabits per second (Mbps) to many gigabits per second (Gbps). Because of its asynchronous nature, ATM is more efficient than synchronous technologies, such as timedivision multiplexing (TDM). With TDM, each user is assigned to a time slot, and no other station can send in that time slot. If a station has much data to send, it can send only when its time slot comes up, even if

14 all other time slots are empty. However, if a station has nothing to transmit when its time slot comes up, the time slot is sent empty and is wasted. Because ATM is asynchronous, time slots are available on demand with information identifying the source of the transmission contained in the header of each ATM cell. ATM transfers information in fixed-size units called cells. Each cell consists of 53 octets, or bytes. The first 5 bytes contain cell-header information, and the remaining 48 contain the payload (user information). Small, fixed-length cells are well suited to transferring voice and video traffic because such traffic is intolerant of delays that result from having to wait for a large data packet to download, among other things. Figure illustrates the basic format of an ATM cell. Figure :An ATM Cell Consists of a Header and Payload Data ATM Protocol architecture: ATM is almost similar to cell relay and packets witching using X.25and framerelay.like packet switching and frame relay,atm involves the transfer of data in discrete pieces.also,like packet switching and frame relay,atm allows multiple logical connections to multiplexed over a single physical interface. in the case of ATM,the information flow on each logical connection is organised into fixed-size packets, called cells. ATM is a streamlined protocol with minimal error and flow control capabilities :this reduces the overhead of processing ATM cells and reduces the number of overhead bits required with each cell, thus enabling ATM to operate at high data rates.the use of fixed-size cells simplifies the processing required at each ATM node,again supporting the use of ATM at high data rates. The ATM architecture uses a logical model to describe the functionality that it supports. ATM functionality corresponds to the physical layer and part of the data link layer of the OSI reference model.. the protocol referencce model shown makes reference to three separate planes: user plane provides for user information transfer,along with associated controls (e.g.,flow control,error control). control plane performs call control and connection control functions. management plane includes plane management,which performs management function related to a system as a whole and provides coordination between all the planes,and layer management which performs management functions relating to resource and parameters residing in its protocol entities.

15 The ATM reference model is composed of the following ATM layers: Physical layer Analogous to the physical layer of the OSI reference model, the ATM physical layer manages the medium-dependent transmission. ATM layer Combined with the ATM adaptation layer, the ATM layer is roughly analogous to the data link layer of the OSI reference model. The ATM layer is responsible for the simultaneous sharing of virtual circuits over a physical link (cell multiplexing) and passing cells through the ATM network (cell relay). To do this, it uses the VPI and VCI information in the header of each ATM cell. ATM adaptation layer (AAL) Combined with the ATM layer, the AAL is roughly analogous to the data link layer of the OSI model. The AAL is responsible for isolating higher-layer protocols from the details of the ATM processes. The adaptation layer prepares user data for conversion into cells and segments the data into 48-byte cell payloads. Finally, the higher layers residing above the AAL accept user data, arrange it into packets, and hand it to the AAL. Figure :illustrates the ATM reference model.

16 Structure of an ATM cell An ATM cell consists of a 5 byte header and a 48 byte payload. The payload size of 48 bytes was a compromise between the needs of voice telephony and packet networks, obtained by a simple averaging of the US proposal of 64 bytes and European proposal of 32, said by some to be motivated by a European desire not to need echo-cancellers on national trunks. ATM defines two different cell formats: NNI (Network-network interface) and UNI (Usernetwork interface). Most ATM links use UNI cell format. Diagram of the UNI ATM Cell GFC VPI VPI VCI VCI VCI PT CLP HEC Diagram of the NNI ATM Cell VPI VPI VCI VCI VCI PT CLP HEC Payload (48 bytes) Payload (48 bytes) GFC = Generic Flow Control (4 bits) (default: 4-zero bits) VPI = Virtual Path Identifier (8 bits UNI) or (12 bits NNI) VCI = Virtual channel identifier (16 bits) PT = Payload Type (3 bits) CLP = Cell Loss Priority (1-bit) HEC = Header Error Correction (8-bit CRC, polynomial = X 8 + X 2 + X + 1)

17 The PT field is used to designate various special kinds of cells for Operation and Management (OAM) purposes, and to delineate packet boundaries in some AALs. Several of ATM's link protocols use the HEC field to drive a CRC-Based Framing algorithm, which allows the position of the ATM cells to be found with no overhead required beyond what is otherwise needed for header protection. The 8-bit CRC is used to correct single-bit header errors and detect multi-bit header errors. When multi-bit header errors are detected, the current and subsequent cells are dropped until a cell with no header errors is found. In a UNI cell the GFC field is reserved for a local flow control/submultiplexing system between users. This was intended to allow several terminals to share a single network connection, in the same way that two ISDN phones can share a single basic rate ISDN connection. All four GFC bits must be zero by default.the NNI cell format is almost identical to the UNI format, except that the 4-bit GFC field is re-allocated to the VPI field, extending the VPI to 12 bits. Thus, a single NNI ATM interconnection is capable of addressing almost 2 12 VPs of up to almost 2 16 VCs each (in practice some of the VP and VC numbers are reserved). A Virtual Channel (VC) denotes the transport of ATM cells which have the same unique identifier, called the Virtual Channel Identifier (VCI). This identifier is encoded in the cell header. A virtual channel represents the basic means of communication between two endpoints, and is analogous to an X.25 virtual circuit. A Virtual Path (VP) denotes the transport of ATM cells belonging to virtual channels which share a common identifier, called the Virtual Path Identifier (VPI), which is also encoded in the cell header. A virtual path, in other words, is a grouping of virtual channels which connect the same end-points. This two layer approach results in improved network performance. Once a virtual path is set up, the addition/removal of virtual channels is straightforward

18 ATM Classes of Services ATM is connection oriented and allows the user to specify the resources required on a perconnection basis (per SVC) dynamically. There are the five classes of service defined for ATM (as per ATM Forum UNI 4.0 specification). The QoS parameters for these service classes are summarized in Table 1. Service Class Quality of Service Parameter This class is used for emulating circuit switching. The cell rate is constant constant bit rate with time. CBR applications are quite sensitive to cell-delay variation. (CBR) Examples of applications that can use CBR are telephone traffic (i.e., nx64 kbps), videoconferencing, and television. variable bit rate This class allows users to send traffic at a rate that varies with time depending on the availability of user information. Statistical multiplexing non-real time is provided to make optimum use of network resources. Multimedia e- (VBR NRT) mail is an example of VBR NRT. variable bit rate This class is similar to VBR NRT but is designed for applications that are real time (VBR sensitive to cell-delay variation. Examples for real-time VBR are voice RT) with speech activity detection (SAD) and interactive compressed video. available bit rate (ABR) This class of ATM services provides rate-based flow control and is aimed at data traffic such as file transfer and . Although the standard does not require the cell transfer delay and cell-loss ratio to be guaranteed or minimized, it is desirable for switches to minimize delay and loss as much as possible. Depending upon the state of congestion in the network, the source is required to control its rate. The users are allowed to declare a minimum cell rate, which is guaranteed to the connection by the network. unspecified rate (UBR) bit This class is the catch-all, other class and is widely used today for TCP/IP. Technical Parameter Definition cell loss ratio CLR is the percentage of cells not delivered at their destination (CLR) because they were lost in the network due to congestion and buffer

19 overflow. The delay experienced by a cell between network entry and exit cell transfer points is called the CTD. It includes propagation delays, queuing delay (CTD) delays at various intermediate switches, and service times at queuing points. cell variation (CDV) delay CDV is a measure of the variance of the cell transfer delay. High variation implies larger buffering for delay-sensitive traffic such as voice and video. peak cell (PCR) rate The maximum cell rate at which the user will transmit. PCR is the inverse of the minimum cell inter-arrival time. sustained rate (SCR) cell This is the average rate, as measured over a long interval, in the order of the connection lifetime. burst (BT) This parameter determines the maximum burst that can be sent at tolerance the peak rate. This is the bucket-size parameter for the enforcement algorithm that is used to control the traffic entering the network. Benefits of ATM The benefits of ATM are the following: high performance via hardware switching dynamic bandwidth for bursty traffic class-of-service support for multimedia scalability in speed and network size common LAN/WAN architecture opportunities for simplification via VC architecture international standards compliance

20 3. Explain ATM adaptation layer in detail ATM Adaptation Layers (AAL) The use of Asynchronous Transfer Mode (ATM) technology and services creates the need for an adaptation layer in order to support information transfer protocols, which are not based on ATM. This adaptation layer defines how to segment and reassemble higher-layer packets into ATM cells, and how to handle various transmission aspects in the ATM layer. Examples of services that need adaptations are Gigabit Ethernet, IP, Frame Relay, SONET/SDH, UMTS/Wireless, etc. The main services provided by AAL (ATM Adaptation Layer) are: Segmentation and reassembly Handling of transmission errors Handling of lost and misinserted cell conditions Timing and flow control The following ATM Adaptation Layer protocols (AALs) have been defined by the ITU-T. It is meant that these AALs will meet a variety of needs. The classification is based on whether a timing relationship must be maintained between source and destination, whether the application requires a constant bit rate, and whether the transfer is connection oriented or connectionless. AAL Type 1 supports constant bit rate (CBR), synchronous, connection oriented traffic. Examples include T1 (DS1), E1, and x64 kbit/s emulation. AAL Type 2 supports time-dependent Variable Bit Rate (VBR-RT) of connectionoriented, synchronous traffic. Examples include Voice over ATM. AAL2 is also widely used in wireless applications due to the capability of multiplexing voice packets from different users on a single ATM connection. AAL Type 3/4 supports VBR, data traffic, connection-oriented, asynchronous traffic (e.g. X.25 data) or connectionless packet data (e.g. SMDS traffic) with an additional 4-byte header in the information payload of the cell. Examples include Frame Relay and X.25. AAL Type 5 is similar to AAL 3/4 with a simplified information header scheme. This AAL assumes that the data is sequential from the end user and uses the Payload Type Indicator (PTI) bit to indicate the last cell in a transmission. Examples of services that use AAL 5 are classic IP over ATM, Ethernet Over ATM, SMDS, and LAN Emulation (LANE). AAL 5 is a widely used ATM adaptation layer protocol. This protocol was intended to provide a streamlined transport facility for higher-layer protocols that are connection oriented. AAL 5 was introduced to: reduce protocol processing overhead. reduce transmission overhead. ensure adaptability to existing transport protocols.

21 T AAL1 PDU The structure of the AAL1 PDU is given in the following illustration: SN SNP CSI SC CRC EPC SAR PDU Payload 1 bit 3 3 bits 1 bit 47 bytes bits AAL1 PDU SN Sequence number. Numbers the stream of SAR PDUs of a CPCS PDU (modulo 16). The sequence number is comprised of the CSI and the SN. CSI Convergence sublayer indicator. Used for residual time stamp for clocking. SC Sequence count. The sequence number for the entire CS PDU, which is generated by the Convergence Sublayer. SNP Sequence number protection. Comprised of the CRC and the EPC. CRC Cyclic redundancy check calculated over the SAR header. EPC Even parity check calculated over the CRC. SAR PDU payload 47-byte user information field. AAL2 AAL2 provides bandwidth-efficient transmission of low-rate, short and variable packets in delay sensitive applications. It supports VBR and CBR. AAL2 also provides for variable payload within cells and across cells. AAL type 2 is subdivided into the Common Part Sublayer (CPS ) and the Service Specific Convergence Sublayer (SSCS ). AAL2 CPS Packet The CPS packet consists of a 3 octet header followed by a payload. The structure of the AAL2 CPS packet is shown in the following illustration.

22 CID LI UUI HEC Information payload 8 bits 6 bits 5 bits 5 bits 1-45/64 bytes AAL2 CPS packet CID Channelidentification. LI Length indicator. This is the length of the packet payload associated with each individual user. Value is one less than the packet payload and has a default value of 45 bytes (may be set to 64 bytes). UUI User-to-user indication. Provides a link between the CPS and an appropriate SSCS that satisfies the higher layer application HEC Header error control. AAL2 The structure of the AAL2 SAR PDU is given in the following illustration. Start field CPS-PDU payload OSF SN P AAL2 PDU payload PAD 6 bits 1 bit 1 bit 0-47 bytes AAL2 CPS PDU OSF Offset field. Identifies the location of the start of the next CPS packet within the CPS-PDU. SN Sequence number. Protects data integrity. P Parity. Protects the start field from errors. SAR PDU payload Information field of the SAR PDU.

23 PAD Padding. AAL2 SSCS Packet The SSCS conveys narrowband calls consisting of voice, voiceband data or circuit mode data. SSCS packets are transported as CPS packets over AAL2 connections. The CPS packet contains a SSCS payload. There are 3 SSCS packet types. Type 1 Unprotected; this is used by default. Type 2 Partially protected. Type 3 Fully protected: the entire payload is protected by a 10-bit CRC which is computed as for OAM cells. The remaining 2 bits of the 2-octet trailer consist of the message type field. AAL2 SSCS Type 3 Packets: The type 3 packets are used for the following: Dialled digits Channel associated signalling bits Facsimile demodulated control data Alarms User state control operations. The following illustration gives the general sturcture of AAL2 SSCS Type 3 PDUs. The format varies and each message has its own format according to the actual message type. Redundancy Time Message Message CRCstamp dependant type 10 information bits AAL2 SSCS Type 3 PDU Redundancy Packets are sent 3 times to ensure error correction. The value in this field signifies the transmission number. Time stamp Counters packet delay variation and allows a receiver to accurately reproduce the relative timing of successive events separated by a short interval.

24 Message dependant information Packet content that varies, depending on the message type. Message The message type code. type CRC-10 The 10-bit CRC. AAL3/4 AAL3/4 consists of message and streaming modes. It provides for point-to-point and pointto-multipoint (ATM layer) connections. The Convergence Sublayer (CS) of the ATM Adaptation Layer (AAL) is divided into two parts: service specific (SSCS ) and common part (CPCS ). This is illustrated in the following diagram: AAL3/4 packets are used to carry computer data, mainly SMDS traffic. AAL3/4 CPCS PDU The functions of the AAL3/4 CPCS include connectionless network layer (Class D), meaning no need for an SSCS; and frame relaying telecommunication service in Class C. The CPCS PDU is composed of the following fields: Header Info Trailer CPI Btag Basize CPCS Pad 0 Etag Length SDU bytes AAL3/4 CPCS PDU CPI Message type. Set to zero when the BAsize and Length fields are encoded in bytes. Btag Beginning tag. This is an identifier for the packet. It is repeated as the Etag. BAsize Buffer allocation size. Size (in bytes) that the receiver has to allocate to capture all the data.

25 CPCS Variable information field up to bytes. SDU PAD Padding field which is used to achieve 32-bit alignment of the length of the packet. 0 All-zero. Etag End tag. Must be the same as Btag. Length Must be the same as BASize. AAL3/4 SAR PDU The structure of the AAL3/4 SAR PDU is illustrated below: ST SN MID Information LI CRC bits 2-byte header 44 bytes 2-byte trailer 48 bytes AAL3/4 SAR PDU ST Segment type. Values may be as follows: SN Sequence number. Numbers the stream of SAR PDUs of a CPCS PDU (modulo 16). MID Multiplexing identification. This is used for multiplexing several AAL3/4 connections over one ATM link. Information This field has a fixed length of 44 bytes and contains parts of CPCS PDU. LI Length indication. Contains the length of the SAR SDU in bytes, as follows:

26 CRC Cyclic redundancy check. Functions of AAL3/4 SAR include identification of SAR SDUs; error indication and handling; SAR SDU sequence continuity; multiplexing and demultiplexing. AAL5 The type 5 adaptation layer is a simplified version of AAL3/4. It also consists of message and streaming modes, with the CS divided into the service specific and common part. AAL5 provides point-to-point and point-to-multipoint (ATM layer) connections. AAL5 is used to carry computer data such as TCP/IP. It is the most popular AAL and is sometimes referred to as SEAL (simple and easy adaptation layer). AAL5 CPCS PDU The AAL5 CPCS PDU is composed of the following fields: Info Trailer CPCS payload Pad UU CPI Length CRC bytes AAL5 CPCS PDU CPCS The actual information that is sent by the user. Note that the information comes before any length indication (as opposed to AAL3/4 where the amount of memory required is known in advance). Pad Padding bytes to make the entire packet (including control and CRC) fit into a 48-byte boundary. UU CPCS user-to-user indication to transfer one byte of user information. CPI Common part indicator is a filling byte (of value 0). This field is to be used in the future for layer management message indication. Length Length of the user information without the Pad.

27 CRC CRC-32. Used to allow identification of corrupted transmission. AAL5 SAR PDU The structure of the AAL5 CS PDU is as follows: Information PAD UU CPI Length CRC bytes AAL5 SAR PDU 8-byte trailer 4.Explain Fast Ethernet and Gigabit Ethernet in detail. Emergence of High-Speed LANs 2 Significant trends Computing power of PCs continues to grow rapidly Network computing Examples of requirements Centralized server farms Power workgroups High-speed local backbone Classical Ethernet Bus topology LAN 10 Mbps CSMA/CD medium access control protocol 2 problems: A transmission from any station can be received by all stations How to regulate transmission Solution to First Problem Data transmitted in blocks called frames: User data Frame header containing unique address of destination station CSMA/CD Carrier Sense Multiple Access/ Carrier Detection If the medium is idle, transmit. If the medium is busy, continue to listen until the channel is idle, then transmit immediately. If a collision is detected during transmission, immediately cease transmitting. After a collision, wait a random amount of time, then attempt to transmit again (repeat from step 1).

28 Medium Options at 10Mbps <data rate> <signaling method> <max length> 10Base5 10 Mbps 50-ohm coaxial cable bus Maximum segment length 500 meters 10Base-T Twisted pair, maximum length 100 meters Star topology (hub or multipoint repeater at central point) Hubs and Switches Hub Transmission from a station received by central hub and retransmitted on all outgoing lines Only one

29 transmission at a time Layer 2 Switch Incoming frame switched to one outgoing line Many transmissions at same time

30 Bridge Frame handling done in software Analyze and forward one frame at a time Store-and-forward Layer 2 Switch Frame handling done in hardware Multiple data paths and can handle multiple frames at a time Can do cut-through Layer 2 Switches Flat address space Broadcast storm Only one path between any 2 devices Solution 1: subnetworks connected by routers Solution 2: layer 3 switching, packet-forwarding logic in hardware Benefits of 10 Gbps Ethernet over ATM No expensive, bandwidth consuming conversion between Ethernet packets and ATM cells Network is Ethernet, end to end IP plus Ethernet offers QoS and traffic policing capabilities approach that of ATM Wide variety of standard optical interfaces for 10 Gbps Ethernet.

31 5. Explain Fiber channel in detail. Fibre Channel 2 methods of communication with processor: I/O channel Network communications Fibre channel combines both Simplicity and speed of channel communications Flexibility and interconnectivity of network communications

32 I/O channel Hardware based, high-speed, short distance Direct point-to-point or multipoint communications linkdata type qualifiers for routing payload Link-level constructs for individual I/O operationsprotocol specific specifications to support e.g. SCSI Fibre Channel Network-Oriented Facilities Full multiplexing between multiple destinations Peer-to-peer connectivity between any pair of ports Internetworking with other connection technologies Fibre Channel Requirements Full duplex links with 2 fibres/link 100 Mbps 800 Mbps Distances up to 10 km Small connectors high-capacity Greater connectivity than existing multidrop channels Broad availability Support for multiple cost/performance levels Support for multiple existing interface command sets Fibre Channel Protocol Architecture FC-0 Physical Media FC-1 Transmission Protocol FC-2 Framing Protocol FC-3 Common Services FC-4 Mapping. 6.Explain IEEE WLAN in detail. Wireless LAN Requirements Throughput Number of nodes Connection to backbone Service area Battery power consumption Transmission robustness and security Collocated network operation License-free operation Handoff/roaming Dynamic configuration IEEE Services Association Reassociation Disassociation Authentication Privacy

33

34