EC1009 HIGH SPEED NETWORKS (ELECTIVE) (2 marks Questions and answers)

Transcription

1 DEPARTMENT OF ECE EC1009 HIGH SPEED NETWORKS (ELECTIVE) (2 marks Questions and answers) FINAL YEAR 7 th SEMESTER

2 UNIT I HIGH SPEED NETWORKS 1) What is common channel signaling? The data s and control signals of a user are transmitted on separate channel. The control signals of all the user are passed through a single common channel. 2) What is inband signaling? If the data s and control signals of a user are transmitted on same channel with same frequency then it is called inband signaling. 3) Define cell sequence integrity? It is the characteristic of virtual channel to preserve sequence of transmitted cells. 4) What is the purpose of cell loss priority bit in ATM cell format? It provides guidance to the network in the event of congestion. A value of ) indicates a cell of higher priority which should not be discarded unless no other alternatives is available. A value of 1 indicates that this cell is subject to discard with in the network. 5) what are the AAL services? Handling of transmission errors Segmentation and Reassembly to enable large blocks of data to be carried in the information field. Handling of lost and misinserted cell condition. Flow control and timing control. 6) What are the two types of sublayer used in ATM adaptation layer? 1. Convergence sub layer 2. Segmentation and Reassembly sub layer. 7) Define sustainable cell rate? The SCR is the average cell rate over a long time interval. The actual cell rate may be lower or higher than this value, but the average should be equal to or less than SCR. 8) Define peak cell rate? The PCR defines the sender s maximum cell rate. The user s cell rate can sometimes reach this peak as long as the SCR is maintained.

3 9) Define fabric in fiber channel communication. The fiber channel communication network consists of one or more switching elements which are collectively called as fabrics. 10) Define collision domain? The maximum distance that data can travel between two station is called collision domain in Ethernet. 11) Define DTE? 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. 12) Define DCE? 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 transmit data through the WAN. In most cases, these are packet switches. Figure 10-1 shows the relationship between the two categories of devices. 13) What is Virtual channel? 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. 14) What are the 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 15) What are the Requirements of Wireless LAN?

4 Throughput Number of nodes Connection to backbone Service area Battery power consumption Transmission robustness and security 16)What are IEEE Services? Association Reassociation Disassociation Authentication Privacy 17) What are the functions of 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). 18) Define Basic Service Set? IEEE defines the BSS as the building block of a wireless LAN. It consists of stationary or mobile stations and a possible central base station known as Access Point. 19) What is PCF? Point Co-ordinate Function is a centralized MAC algorithm used to provide contention free service. This is done by polling stations in turn. Higher priority traffic makes use of PCF. 20) What are the topologies used in Fiber channel? 1. Switched topology 2. Point-to-point topology

5 3. Arbitrated loop topology UNIT II CONGESTION AND TRAFFIC MANAGEMENT 1) When queue will be formed in a network? Queue will be formed if the current demand for a particular service exceeds the capacity of service provider. 2)what are the characteristics of queuing process? 1. Arrival pattern 2.Service pattern 3.Number of server 4.System capacity 5.Queue discipline 3) What is meant by implicit congestion signaling? When network congestion occurs packets get discard and acknowledgement will be delayed. As a result source understand that there is congestion implicitly. 4) What are the Congestion-Control Mechanisms? Backpressure Request from destination to source to reduce rate Useful only on a logical connection basis Requires hop-by-hop flow control mechanism Policing Measuring and restricting packets as they enter the network Choke packet Specific message back to source E.g., ICMP Source Quench Implicit congestion signaling Source detects congestion from transmission delays and lost packets and reduces flow

6 5) What is meant by FECN? The FECN bit is part of the Address field in the Frame Relay frame header. The FECN mechanism is initiated when a DTE device sends Frame Relay frames into the network. If the network is congested, DCE devices (switches) set the value of the frames' FECN bit to 1. When the frames reach the destination DTE device, the Address field (with the FECN bit set) indicates that the frame experienced congestion in the path from source to destination. 6) What is meant by BECN? The BECN bit is part of the Address field in the Frame Relay frame header. DCE devices set the value of the BECN bit to 1 in frames traveling in the opposite direction of frames with their FECN bit set. This informs the receiving DTE device that a particular path through the network is congested. 7) What is the use of Discard Eligibility (DE) bit? The Discard Eligibility (DE) bit is used to indicate that a frame has lower importance than other frames. The DE bit is part of the Address field in the Frame Relay frame header. 8) What is the error checking mechanism used in Frame Relay? Frame Relay uses a common error-checking mechanism known as the cyclic redundancy check (CRC). The CRC compares two calculated values to determine whether errors occurred during the transmission from source to destination. Frame Relay reduces network overhead by implementing error checking rather than error correction. 9) What are the Considerations for Traffic Management in Congested Network? Fairness Quality of Service Reservations 10) Advantages of Frame Relay Congestion Control Minimize frame discard Maintain QoS (per-connection bandwidth) Minimize monopolization of network

7 Simple to implement, little overhead Minimal additional network traffic 11) What are the Frame Relay Traffic Rate Management Parameters? Committed Information Rate (CIR) Average data rate in bits/second that the network agrees to support for a connection Data Rate of User Access Channel (Access Rate) Fixed rate link between user and network (for network access) Committed Burst Size (Bc) Maximum data over an interval agreed to by network Excess Burst Size (Be) Maximum data, above Bc, over an interval that network will attempt to transfer 12) Define committed Burst size(bc)? This is maximum number of bits in a predefined period of time that the network is committed to transfer without discarding any frames. 13) Define access rate? For every connection in frame relay network, an access rate is defined. The access rate actually depends on bandwidth of channel connecting user to network. 14) What are the steady state performance measures to be determined in Queueing models? Queueing models allow a number of useful steady state performance measures to be determined, including: the average number in the queue, or the system, the average time spent in the queue, or the system, the statistical distribution of those numbers or times, the probability the queue is full, or empty, and the probability of finding the system in a particular state.

8 15)Write Kendall s notation. (a/b/c): (d/e) is Kendall s notation a distribution of inter arrival time b distribution of service time c number of server d maximum number of allowed items in a system e queuing discipline used 16) Compare single server and multi server queue Single server model Congestion statistics for this model are : M/M/1, M/D/1, M/G/1 Arrival rate=λ Multi server model Congestion statistics for this model is : M/M/N Arrival rate for each server=λ/n 17) What is meant by traffic intensity in queuing analysis? Traffic intensity ρ=λ/µ =Arrival rate/service rate 18) Write Little s formula. ρ = λt s r = λt r w = λt w

9 UNIT III TCP AND ATM CONGESTION CONTROL 1)What are retransmit policies used in TCP traffic control? 1. First only 2. Batch 3. Individual 2) State the condition that must be met for a cell to conform. In case of ATM, the information flow on each logical connection is organized into fixed size packets called cells. Cells should arrive within theoretical arrival time but with in CDVT. 3)What are the mechanisms used in ATM traffic control to avoid congestion condition? 1.Resource management 2.Connection admission control 3.Usage parameter control 4.Traffic shaping 4) What are the TCP congestion control mechanisms? 1.Retransmission Timer Management 2.Window Management 5) What are the Three Techniques to calculate retransmission timer (RTO): RTT Variance Estimation Exponential RTO Backoff Karn s Algorithm 6) What is reactive congestion control? Whenever a packet discard takes place due to severe congestion some control mechanism is needed to recover from network collapse, these mechanism is reactive congestion control.

10 7) What are the requirements for ATM Traffic and Congestion Control? Most packet switched and frame relay networks carry non-real-time bursty data No need to replicate timing at exit node Simple statistical multiplexing User Network Interface capacity slightly greater than average of channels Congestion control tools from these technologies do not work in ATM 8) Why congestion control is difficult to implement in TCP? The end system is expected to exercise flow control upon the source end system at a higher layer.thus it is difficult to implement congestion control in TCP. 9)What is meant by silly window syndrome? If data s are send as small segments frequently, the response will be speed in the sender side, but it cause degradation in performance. This degradation is called silly window syndrome. 10) What is meant by cell insertion time and allowed cell rate? Cell insertion time: It is the time taken to insert a single cell on to the network. Allowed cell rate: The current rate at which the source is permitted to send or transmit cell in ABR mechanism is called allowed cell rate. 11) Define Behavior Class Selector (BCS). BCS enables an ATM network to provide different service levels among UBR connections by associating each connection with one of a set of behavior class. 12)What are the Objectives of ATM layer traffic and congestion control Support QoS for all foreseeable services Not rely on network specific AAL protocols nor higher layer application specific protocols

11 Minimize network and end system complexity Maximize network utilization 13)What is meant by Open Loop Control and Closed Loop Control? Open loop control: If there is no feedback to the source concerning congestion then this approach is called as open loop control. Closed Loop Control: If there is feedback to the source concerning congestion then this approach is called as closed loop control. 14)What are the accept policies used in TCP traffic control? 1.In-order policy 2.In-window policy 15) What are the techniques of Window management? 1.Slow start 2.Dynamic window sizing on congest 3.Fast retransmit 4.Fast recovery 5.Limited transmit 16) What does awnd and cwnd refers to? awnd refers to allowed window. This is window size allowed by TCP to send without waiting for acknowledgement. cwnd refers to congestion window. This is window used by TCP during startup and to reduce flow during congestion. 17) Two techniques to reduce the transmission of useless cells? 1. Partial packet discard 2. Early packet discard

12 18) What are the QoS parameters? 1. Peak to peak cell delay variation 2. Maximum cell transfer delay 3. Cell loss ratio 19) What is Buffer Management? This mechanism provides the way in which cells are treated that have been buffered at network switch. When congestion occurs, the buffer occupancy becomes maximum. Now tagged cells are discarded to give preference to untagged cells. 20) What is self clocking? TCP automatically senses the network bottleneck and regulates the flow at source. This is called self clocking. UNIT IV 1. What is meant by elastic traffic? Give example. Elastic traffic can adjust over wide ranges to changes in delay and throughput across an internet and still meet the needs of its applications. Example: File transfer Web access 2. What is meant by inelastic traffic? Give example. Inelastic traffic cannot adjust to changes in delay and throughput across an internet. Example: Voice chat Tele conferencing 3. Define Delay Jitter. The delay jitter is the maximum variation in delay experienced by packets in a single session. 4. What is meant by best effort service? Flows that are not reserving resources are provided with best effort service. The network will put best effort to deliver the packet but if congestion occurs severely discard the packet.

13 5. What is meant by guaranteed service? Flows that are reserving resources are provided with guaranteed service. The service provides assured capacity levels. 6. Define global synchronization. Due to packet discard during congestion, many TCP connections entered slow start at the same time. As a result, the network is unnecessarily under utilized for some time. The TCP connections which entered into slow start, will come out of slow start at about time causing congestion again. This phenomenon is called global synchronization. 7. What are the design goals of RED algorithm? 1. Congestion avoidance 2. Global synchronization avoidance 3. Round on average queue length 8. Define behavior aggregate in per hop behavior. A set of packets with the same Ds code point crossing a link in particular direction is called behaviour aggregate. 9. Define DS code point. A specified value of 6 bit DS code point portion of the 8 bit DS field in the IP header which indicate to which class packet belongs and its drop precedence. 10. What is meant by traffic conditioning agreement? An agreement that specify rules that are to apply for packets selected by the classifier. Control functions performed in TCA are metering, marking, shaping and dropping. 11. Define DS boundary node. A DS node that connects one Ds domain to the node in another domain. 12. Define DS interior node. A node in DS domain, which is not the boundary node is called Ds interior node. 13. Define Ds node. A router that supports DS policies is called as DS node. A host system that use DS for application is called as DS node. 14. What is meant by differentiated service? It does not attempt to view the total traffic demand in integrated sense. It does not reserve network capacity in advance.

14 It provides differential level of QOS to different traffic flows. 15. What is meant by integrated services? The Is provider Views the total of current traffic demand. Limits the demand with respect to the current capacity handled by the network. Reserve resources with in the domain to provide a particular QOS guaranteed. UNIT V 1. What is meant by soft state in RSVP? RSVP use connectionless approach, each intermediate router maintain state information about nature of flow, that will be refreshed by end system at predetermined amount of time. This is called soft state. 2. Why receiver is responsible to initiate reservation in RSVP? Each member (destination) in multicast may require different resources to be reserved depending on QOS it needs. So it is therefore better for receiver to make resource reservation. 3. Define session in RSVP? Once a reservation is made to the router by a particular destination, the router considers this as a session and allocates resources for the life of that session. Session is defined by Session: Destination IP address IP protocol identifier Destination port 4. Define flow specification in RSVP. The flow specification of RSVP specifies a desired QOS and is used to set parameters in a node s packet scheduler. Flow spec is defined by Flow spec: Service class R spec T spec R spec is Reserve Specification T spec is Traffic Specification 5. Define filter specification in RSVP. Filter spec in RSVP defines the set of packets or flow, for which a reservation is requested.

15 Filter spec is defined by Filter spec: Source address UDP/TCP source port 6. What are the types of reservation style used in RSVP? Wild card filter reservation style. Fixed filter reservation style. Shared explicit reservation style. 7. What is meant by label merging and frame merging? Label merging: The replacement of multiple incoming labels for a particular equivalent class with a single outgoing label is called label merging. Frame merging: Label merging, when it is applied to operation over frame based media, then it is called as frame merging. 8. Define label swapping in MPLS. The basic operation of looking up an incoming label to determine the outgoing label and forwarding is called label swapping. 9. Define Label switched hop in MPLS. The hop between two MPLS nodes on which forwarding is done using labels is called label switched loop. 10. What is meant by ingress edge and egress edge in MPLS domain? Ingress edge: Label switched router through which packets from internet router enters into MPLS domain is called ingress edge. Egress Edge LSR: LSR through which packets leaves the MPLS domain is called egress edge. 11. Define Label switched router in MLPS An MPLS network consists of a set of nodes called label switched router (LSR) capable of switching and routing packets on the basis of which a label has been added to each packets. 12. What is purpose of time to live field in label format? The value of this field is decremented at each router and the packet is dropped if the count falls to zero. 13. What is meant by integrated layer processing in RTP?

16 In TCP/IP each layer processed sequentially, whereas in integrated layer processing, adjacent layers are tightly coupled and they function parallely. 14. What is the function of RTP relays and give its types? A relay operating at a given protocol layer is an intermediate system that acts as both a destination and a source in a data transfer. 15. What is the function of mixer and translator in RTP? Mixer: It is source of synchronization. It receives stream of RTP packets from one or more sources. Combines these streams and forwards a new RTP packet stream to one or more destinations. Translator: It produces one or more outgoing RTP packets for each incoming packets. It change the format of the data that suite to transfer from one domain to another.