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BIRLA INSTITUTE OF TECHNOLOGY & SCIENCE, PILANI HYDERABAD CAMPUS Second Semester 2011-2012 Adv. Computer Networks (CS G525)

Comprehensive Examination Time: 3 hours Date: 12.05.2012(AN) Type: Part Open Weightag e: 35% Marks: 140 Note: Read the following instructions carefully. 1. Manage your time as per the weightage of each question and write precisely. 2. Assume suitable data if necessary. 3. Paper consists of two parts. Part A is closed book and objective. Part B is open book. 4. It is up to you to manage time between Part A and Part B. It is suggested that you do not spend more than 120 minutes on part A. 5. Answer Part A first. After returning Part A, you may take Part B answer sheet and textbook, and/or reference books, computers etc.

Part A (Closed Book): 90 Marks To be answered neatly in the attached paper

Q.1 Select the most appropriate choice for the below mentioned questions. [2Mx6 = 12M] A. Which of the following is least likely to be modified for a TCP packet that passes though firewalls / proxies a. Source IP b. Port Number . Destination IP d. TCP Window Size B. The most differentiating factor for Wireless communication (w.r.t. wired) is a. Latency b. c. Error rate d. Segment size C. Mobility Binding Table contains ______address a. Home b. Home Agent c. Media d. Corresponding Address Address Address address D. Mobile IP mandates authentication between (MN – Mobile Node, CN – Corresponding node, HA – Home agent, FA – Foreign agent) a. MN - CN b. HA – MN c. HA - FA d. FA - MN E. Media Independent Handover is implemented in a. Physical Layer b. Across multiple layers c. MAC layer d. Network Layer F. Which of the following is not used for NAT traversal a. TURN b. IPSEC c. STUN d. ICE

Q.2 Provide precise and objective answers for following. [3Mx9 = 27M] A. What are the three management layers that operate on top of “Network Elements”? B. List three common approaches for implementing QOS in IP network. C. For SIP, list three header fields and their usage. D. IPv6 uses Router Solicitation (RS) for Network Discover Protocol (NDP). List three other ICMPv6 packet types that are used in NDP. E. List three non-proactive AdHoc routing protocols. F. What are the three broad categories of RFID devices? G. List three primary drivers for wireless network convergence. H. List three decentralized and three centralized (super-peer etc. based) P2P networks / protocols for file . I. List six SNMP command/message types. You can include both SNMPv1 and SNMPv2 protocols.

Page 1/3 Q.3 Provide precise and objective answers for following. [2Mx9 = 18M] A. List two major topics that should be should be included in initial baseline report for a new network deployment. B. List two major surprises in network planning. C. List two surrogate placement approaches in CDN. D. What are the two coordination approaches to solving hidden terminal problem in 802.11 netwroks? E. List two flavors of TCP other than TCP-Reno for congestion avoidance. F. List two common operations of either or . G. Some of the IPv4 header fields have been dropped from IPv6 header fields. List two of those. H. What is the use of bootstrapping in P2P? I. What is the role of “Media Gateway” in context of PSTN and VoIP?

Q4. Answer as True / False. [1Mx12 = 12M] A. Forking Proxy approach is used in H323 to locate users. B. Ferrying and Throw-boxes are most likely to be used in Mesh Networks. C. Routing decisions in DTN using Independent Mobile Nodes can be based on flooding and/or knowledge. D. MIMO relies on FFT (Fast Fourier Transform) and IFFT (Inverse FFT). E. MPLS is a network layer protocol. F. Mobile IP does not require changes to software of non-mobile hosts/routers. G. For P2P, logarithmic mesh with prefix routing is faster than CAN topologies. H. Mobile IP requires modifications to IP addresses / IP address format. I. Power law graph is more optimized than PRR (logarithmic mesh with prefix routing). J. SIP message body can have any protocol. K. iBGP sessions are going over routes that are set up by an Intradomain routing protocol. L. Random Early Detection drops TCP packets even if the buffers are not full.

Q5. ConnectTel plans to offer services in Hyderabad/Secunderabad. It has divided the area into 19 cells as captured in Figure 1 of attached answer sheet. Each cell has a base station that needs a frequency band of 800 KHz. It is advised to have inter-band gap of 200 kHz. [3Mx3 = 9M] A. What is the minimum required spectrum for ConnectTel to offer cellular service? B. If ConnectTel purchases license for 9.5 MHz starting at 881.8 MHz, list how the frequency sub- bands will be created. C. Using sub bands in step ‘Q5.B’ number the cells in Figure 1. Ensure maximum physical separation among similar band Base Stations.

Q6. Answer the following concisely [3Mx4 = 12M] A. IGMP is not defined for IPv6. Why? B. What is the benefit of “soft state” in RSVP? C. What is the similarity between PMTUD (path maximum transmission unit discovery) and traceroute? D. What is meant by TCP-Offload? How is it beneficial?

Page 2/3 Part B (Open Book): 50 Marks Q1.A. What are the disadvantages of DSR? How does AODV resolve some of them? In what scenarios will you prefer DSR over AODV? [3 + 3 +2 = 8M] B. IP-Mobility can have heavy load on the home agent with “binding updates” if mobile node(s) are frequently moving across different foreign agents. Suggest a solution for the same using illustrations / examples. What are the drawbacks of your solution? [4M] Q2.A. SNMP in v2 included a new approach in the way notifications are sent by network elements. What is the new approach and why was it needed? [4M] B. Is SNMP v2c secure? If yes how, if not – why was it allow to be deployed without security? [4 M]

Q3. The cooperative society of fishermen of a coastal town in AP plans to deploy a network infrastructure for effective communication among them. Between them they have a fleet of around 60 boats. Their primary goals are: - Find location of other boats when at sea. - information about their catch with approximately 20 buyers who stay in the town. o Buyers are not on this network deployment, but have IP connectivity through BSNL. o Buyers can provide rate information using which certain fishes can be dumped at sea in order to have storage space for higher priced varieties. - Share weather and catch quality related updates with other boats. - Bandwidth permitting, they would like to do voice/video communication with other boats in neighborhood. Assumptions: a. Exiting radio transmitters in most of the boats have following bandwidth: @1 KM 1 mbps, @2KM 128 kbps, @3 KM 8 kbps, @ 4KM – almost 0. b. Though the radio transmitters are used primarily for voice communication, they are free 90% of the time and the team wants to reuse the same for digital communication. c. Fishermen do understand that they will need to add some hardware and possibly lease a broadband connection at the jetty/dock. d. The fishermen stay in sea for a max of 8 hours, and travel as deep as 10 kms from the coast. e. Maximum speed of their boats is 10 kmph. f. During fishing the boats maintain a minimum gap of 500 meters. g. Most of the boats leave between 6 AM – 11- AM and return between 2 PM – 5 PM with uniform distribution of departure and arrival frequency. h. There are on an average 50 boats that travel daily in a 25sq. KM area in the sea. This stretch is approximately a rectangle of 2.5 KM x 10 KM. i. When boats are away from jetty, between 30 min to 60 minutes delay are tolerable for them when communicating with traders. Between the boats in their vicinity they prefer real time connectivity. j. Using compression, the information on fishermen’s catch can be compressed in 400 bytes. Similarly rate information from each buyer can be compressed to 410 bytes. k. Typical operational cost for each boat is two lacs annually and they do not want the investments for the network to exceed 15% of this. Equipping each boat with a computer that works under humid and saline environment is around Rs. 20,000/= l. BSNL offers broadband connectivity at 2 mbps for 2,000/- p.m. and 10 mbps at 5,000/- p.m. VSNL offers satellite based communication at 32 kbps for 500/- p.m. and at 2 mbps at 5,000/- p.m. Installation cost for VSAT infrastructure is 25,000/- m. Renting a boat for facilitating communication for 12 hours costs approximately 2,000/- for travel up to 40 kms roundtrip. 3 hour rental costs 500/- for 15 kms roundtrip.

Questions: A. What type of will you suggest to use in this scenario? [4 M] B. Neatly draw a diagram to capture your solution at 10 AM, 12:30 PM and 4:00 PM [9 M] C. Do a costing for you solution (hardware elements, operational expenses, maintenance etc.) [4 M] D. What will your Maximum PDU size be? What routing protocols will you use? [4 M] E. What will be the biggest limitation / challenge for the network you have designed? [4 M] F. If it was possible to bring in extra investments of 20,000 per boat after a year of operating this network, what changes will you propose to your solution. [5 M]

Page 3/3 Advanced Computer Networks: Part A (90M) Marks:______

Name:______ID No.:______

Q.1 A. B. C. D. E. F. Q.2 A B C D E F G

H

I

Q.3 A B C D E F G H ______

______I

Q.4 A B C D E F G H I J K L

Q.5 A. (Min. Spectrum) = C. Figure 1 B. (frequency sub-bands)

Q.6 A______B______

C______D______

Advanced Computer Networks: Part A (90M) SOLUTIONS

Name:______ID No.:______

Q.1 A. d. TCP Win. Size B. c. Error Rate C.a. Home Address D. b HA-MN E.b. across multiple layers F. b IPSec A Element Mgmt System/Layer Network Mgmt System/Layer Operation Support System (service / Q.2 Business Mgt Layer) B MPLS – label distribution IntServ RSVP – Path/RESV DSCP/DiffServ – Policies C Any 3 of: Accept, Authorization, Call-ID, Contact, Content-Length, Content-Type, CSeq, Encryption, Expires, From, Max- Forwards, Priority, Record-Route, Require, Response-Key, Retry-After, Route, Subject, To, Via, Warning, Unsupported D Router Advertisement Neighbor Solicitation Neighbor Advertisement E Any 3 of: AODV (Ad hoc On-Demand Distance Vector), DSR (Dynamic Source Routing), Geographical Routing (DREAM, GPSR, LAR), Hierarchical Routing F Active Passive Semi-Active G Voice over IP/Voice Voice and Data Multimedia Apps H Centralized: CuteMX Direct Connect Advanced Direct Connect Opennap Decentralized:Advanced Direct Connect Applejuice Ares BitTorrent eDonkey FastTrack GNUnet Gnutella Kad OpenFT WASTE WinMX get Getnext, getbulknext Set I response Trap Inform

A Multiple answers: e.g. performance benchmark, stress report, deployment diagram Q.3 B Multiple answers: e.g. technology shift, user/usage shift, application servers/accelerator placements C Any two of: tree, greedy, random, hot-spot, hot-zone D Point CF Distributed CF E Any two of: Tahoe, Vegas, New Reno, Hybla, BIC, RUBIC etc. F GnuTella: Ping, Pong, Query, QueryHit, BitTorrent: Choke, Unchoke, Interested, Have, Push, Bye BitField, Request, Cancel, G Any of: Header Length, Identification, Header Checksum, Flags, Fragment Offset H Bootstrapping provides initial configuration information to newly joining nodes so that they may successfully join the

I Media gateway converts the audio from digital encoded formats to the format suitable for PSTN and vice versa.

Q.4 A False B False C True D False E False F True G False H False I False J True K True L True

Q.5 A. (Min. Spectrum) = approx. 3 MHz C. Figure 1 1 B. (frequency sub-bands) 4 8 7 2 6 Band 1: 882.0 – 882.8 Band 2: 883.0 – 883.8 5 9 Band 3: 884.0 – 884.8 Band 4: 885.0 – 885.8 8 3 4 6 7 Band 5: 886.0 – 886.8 Band 6: 887.0 – 887.8 9 1 5 Band 7: 888.0 – 888.8 Band 8: 889.0 – 889.8 4 8 2 Band 9: 890.0 – 890.8

Q.6 A IPv6 was designed with multicast in B Soft states: RSVP reservations expire periodically, unless mind. ICMP-v6 includes all the renewed. The resources consumed by expired can be functionality of IGMP. automatically cleaned up. Renewals can be refused if other higher QOS app demands. Adapts well to route changes.

C Intermediate routers generate D TCP Offload allows processing of TCP packets including response for both PMTUD and congestion and flow control to be done in NIC, thus freeing up traceroute. Both approaches have the host CPU from continuous interrupts etc. response coming back as ICMP

Part B: Q1.A Disadvantage of DSR protocol is that the route maintenance mechanism does not locally repair a broken link. Stale route cache information could also result in inconsistencies during the route reconstruction phase. The connection setup delay is higher than in table-driven protocols. Even though the protocol performs well in static and low-mobility environments, the performance degrades rapidly with increasing mobility. Also, considerable routing overhead is involved due to the source-routing mechanism employed in DSR. This routing overhead is directly proportional to the path length.

In AODV, the source node and the intermediate nodes store the next-hop information corresponding to each flow for data packet transmission. The source node floods the RouteRequest packet in the network when a route is not available for the desired destination. It may obtain multiple routes to different destinations from a single RouteRequest. The data flow need not include the path information; it just needs to have destination address. DSR will be preferred over AODV if communication happens between same/similar pair of nodes over very small distances (2-5 hops). AODV in such scenarios may consume lot of memory on intermediate links and add other overheads like information stored during flooding for discovery etc.

Q1.B Foreign agents can be clustered and a hierarchy built around them. E.g. a person with home agent as Vodafone AP could be travelling to US and roaming on T-Mobile’s network across the state boundaries. T- Mobile could provide a root-foreign agent in one of the state’s and Home agent from Bangalore forwards the packets to this. As the mobile node moves and comes across new FA, it sends the binding updates to root- foreign agent instead of ending the update to home agent.

Q2.A SNMP Traps have been replaced by Inform requests. SNMP commonly runs over UDP where delivery is not assured and dropped packets are not reported, delivery of a Trap was not guaranteed.InformRequest fixes this by sending back an acknowledgement on receipt. Receiver replies with Response parroting all information in the InformRequest. If the sender does not get a response, it resends the Inform message.

Q2.B SNMP v2c is not a secure protocol. It is especially prone to sniffing and replay attacks. The target of SNMP was to keep the implementation simple so that even extremely portable devices with small footprint can implement it. In general the deployment of SNMP happens over a physically separate LAN (sometimes using separate virtual LAN / VLAN). The security and access to this LAN is controlled to ensure that SNMP is not compromised.

Q3. Multiple solutions possible. AdHoc network is the most likely scenario. When all 50 boats are at sea and the try to go as far out as possible, they will cover an area of 50 * 0.25 sq. km => 12.5 sq. KM. i.e. the closest boat in this scenario is 5 km away from the dock. For communicating with traders a DTN approach may be used. A hired boat will provide the option of Message Ferrying (mule) – the boat can travel up to 3.5 KM into the sea, come back to 2.5 KM, go back to 3.5 Km and finally return to dock; thus it can provide a DTN connectivity. A. What type of network topology will you suggest to use in this scenario? AdHoc networks using AODV or similar routing working on top of the wireless infrastructure available in the boats. Possibly a computer with specialized NIC / adapter is also needed. At the dock, we will need to have a high power station (new infra) with possibly a transmit capacity to reach larger distances.

B. Neatly draw a diagram to capture your solution at 10 AM, 12:30 PM and 4 PM.

C. Do a costing for you solution (hardware elements, operational expenses, maintenance etc.) Computer with interface communication equipment: ~20K – 60 boats => 12 Lacs. Base station at the Jetty – approximate cost 3 lacs. Leasing a boat between 11:15 AM – 1:45 PM to connect distant boats by travelling up to 4 km into the sea- 500 per day => 1.8 Lacs. D. What will your typical packet size be? What routing protocol will you use? Typical packet size will be 512 bytes. Most of the communication is in the vicinity or with base station. Maximum hops to base station is 2-5 KMs. For MANET either of DSR/AODV or geographical routing can be used as we do not have power constraints. For DTN part, “knowledge based” approach can be used such that returning ships help complete the communication. E. What will be the biggest limitation / challenge for the network you have designed? Between 11 AM to 2 PM when the ships are away from the dock / base station, communication tends to become “delayed”. Also the available bandwidth of 64 kbps is quite low, when we add the fact that packets take around 5 hops to reach the base station, a 512 byte packet may see significant delay latency. Moreover at higher distances bit-errors imply that the content will need to be retransmitted or have adequate FEC provided. F. If it was possible to bring in extra investments of 20,000 per boat after a year of operating this network, what changes will you propose to your solution. Multiple answers: e.g. o Rather than ferry, we can deploy 4-5 throw boxes, which are always at sea and possibly use higher power communication with base station or deploy VSAT technology. o Upgrade the communication system in the boats such that range is increased and bit error rates drop. NOTE: VSAT is not a cost/performance feasible option especially because the geographical distance is quite small.