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January 19, 2015 17:16
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eva hladka questions + answers of examinations 2015
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| //1 describe first layer, functions, what protocols? | |
| PHYSICAL LAYER: | |
| interacts with transmision media (wire, fibre, air) | |
| functions: - transform bits to analog signals, | |
| - bit rate control, | |
| - multiplexing to logical channels | |
| - circuit switching : old telephones, two network nodes establish communication channel which guarantees | |
| the full bandwidth | |
| - bit syncronisation | |
| algs: | |
| IEEE 802.x | |
| rs232 | |
| //1 describe second layer, functions, what protocols, graph algorithm it use? | |
| DATA LINK LAYER: | |
| functions: - framing (received packed gets into frame) | |
| - error control (CRC) | |
| - addressing (MAC address, frame has source and dest. address) | |
| - flow control (prevent congestions) | |
| - MEDUIM ACESS CONTROL: multiple devices on shared media. point is to Eliminate collisions | |
| protocols: * random-access: Aloha, CSMA/CD, CSMA/CA | |
| * controlled-access: tokens, reservations, | |
| * channelization: FDMA, TDMA | |
| graph algorithms: | |
| - Distributed Spanning Tree Algorithm: prevent loops | |
| * root bridge selection phase (the lowest address gets root) | |
| * root ports selection phase (select path tho root bridge) | |
| * active/inactive ports selection phase | |
| topologies: star, bus, circle | |
| //1 discribe L3 of OSI model, protocols it uses, addressing and graph algorithm? | |
| functions: - packetizing (transform segments to packets) | |
| - logically joins independent LAN networks | |
| - provide UNIQUE addres for every device on internet | |
| - ensures packets routing | |
| - fragmenting | |
| addressing protocols: | |
| ARP, RARP, IPv4 (32 bit), IPv6 (128 bit), IGMP | |
| control protocol: | |
| ICMP, ICMPv6, IGMP (for multicast) | |
| graph algorithms: | |
| DISTANCE VECTOR: (metric = hops, usefull for small network, Bellman-ford algorithm, info just about neighbours) | |
| * RIP (Routing Information Protocol) protocol | |
| * IGRP | |
| * EIGRP | |
| LINK STATE (metric = cost, dijkstra for shortest path, routers maintain complete info about network topology): | |
| * OSPF (Open shortest path first) protocol | |
| * IS-IS | |
| //1 discribe L4 of OSI model, protocols it uses, addressing and graph algorithm? | |
| transport layer | |
| functions: - transform data in segments | |
| - transmission relibility (illusion of direct physical interconnections) | |
| - connection reliablity (flow control, error control) | |
| - connection control : | |
| * connectionless | |
| - un numbered packets, | |
| * connection-oriented services: | |
| - numbered packets | |
| - ACK delivery | |
| - addressing (ports 16bits) | |
| - Qos | |
| protocols: | |
| UDP: - connectionless | |
| - unreliable | |
| - minimal overhead / simplicity | |
| - DNS, multicast, real-time transfers, | |
| TCP: - connection-oriented | |
| - reliable | |
| - handshake | |
| - no multicast | |
| - flow control (protects receiver) | |
| - congestion control (protects network, congestion window ) | |
| //traditional tcp protocols and iproved | |
| traditional | |
| tahoe | |
| reno | |
| vegas | |
| improved:; | |
| multi-stream TCP | |
| web100 | |
| H-TCP | |
| BIC-TCP | |
| CUBIC-TCP | |
| //TCP extensions | |
| GridDT = a collection of ad-hoc modification | |
| Scalable TCP | |
| High Speed TCP | |
| //TCP alternatives | |
| - udp for data, tcp for control | |
| tsunami | |
| RBUDP (Reliable Blast UDP) | |
| XCP (feedback from every router) | |
| //2 Home Mobility in IPv6 & scheme | |
| home agents (router at home) | |
| correspondent node (peer node (foreign node)) | |
| mobile node | |
| mobile node can have | |
| home address or | |
| care-of address | |
| it has to prove that has both of them | |
| steps: home test init, home test | |
| care of test init, care of test | |
| binding update, binding ack | |
| //2 security in IPv6 | |
| IPSec is mandatory | |
| = transport mode | |
| = tunnel mode (complete encapsulated datagram) | |
| AH authentication header not uses so much computational power as ESP (encapsulating security payload), | |
| but authenticate whole datagram | |
| ESP stronger encryption | |
| //3 packet classification and filtering, why we use it? | |
| * to provide different service garantees for different type of traffic | |
| * flexibility for ISP billing | |
| * preventing attacks | |
| algorithms: | |
| Naive | |
| Two-dimensional solutions | |
| d-dimensional solutions | |
| divide and Conquer | |
| Decision tree | |
| //4 what is Multiprotocol Label Switching (MPLS) and GMPLS | |
| Multiprotocol Label Switching (MPLS) is packet forwarding mechanism to improve speed of core ip routers | |
| - it is based on labels instead of IP | |
| - requare prtocol to destribute label Information | |
| - connection-oriented and packets are routed on preconfigured label switched paths | |
| * edge label-switched router | |
| ingress: packet is analysed and based on class; given a proper label | |
| egress: remove label, decreased TTL | |
| * core label-switched router | |
| packet is not analysed, modified | |
| GMPLS: Generalized Multiprotocol Label Switching | |
| generilized not just for packets but for | |
| Time-division multiplexing cable | |
| fibre-switch | |
| lambda-switch | |
| G^2 grid eneblaed multiprotocol label switching | |
| grid-resource computing | |
| 5 what is Reliable Blast UDP (RBUDP) | |
| protocol which uses TCP for control and UDP for data transmission | |
| proposed for disk to disk transmission | |
| 6 Heuristic-Based Routing Strategies in P2P | |
| - Iterative Deepening | |
| use DFS to one limit and then increase that limit | |
| - Directed BFS | |
| dont send to all neigbours, choose inteligently to which | |
| - Local Indices Search | |
| proces the nodes on radius of k hops | |
| - Random-walk | |
| - Adaptive Probabilistic Search (APS) | |
| - Interest-Based Shortcuts | |
| //p2p architecture | |
| Application layer | |
| - file sharing | |
| - messageing | |
| - distributed computing | |
| Middleware | |
| responsible for: | |
| - security | |
| - groups | |
| - service/resource discovery | |
| Base Overlay layer | |
| - over tcp | |
| - discover new peers; | |
| - forward messages | |
| - maintain network | |
| underlying network | |
| // structure of P2p algorithms | |
| - Distributed hash table system | |
| * chord | |
| * CAN (area division) | |
| * pastry (use PRR tree) | |
| - skip list based system | |
| skip list | |
| skip graph (many lists at each level) | |
| skip net | |
| - tree based system | |
| p-grid (each peer is responsible for all data items whose prefix is equal to the peer identifier ) | |
| p-tree (based on chord ring) | |
| BATON (data is in leaf and internal nodes) | |
| //7 routing P2p PRR tree | |
| - Distributed hash table system | |
| pastry (prefix) alghoritm and tapestry (suffix) uses PRR tree | |
| node wich id prefix is the most simmilar to data id holds the data. | |
| each node has routing table and data. | |
| //8 Wireless Sensor Ad-hoc (WSN) | |
| ad hoc network is network constructed on demand | |
| wirelesss sensor network are focused on enviroment not on human interaction | |
| used in: | |
| * agriculture (when to use pesticide) | |
| * emergency operation (droping sensors on fire) | |
| * intelligent buildings (reduce energy waste) | |
| - protocols should be optimised for using LESS ENERGY | |
| - low PROCESSING POWER | |
| - MEMORY correlate with size | |
| - small BANDWIDTH due to low power consuption | |
| - usually not global unique ADDRESS | |
| //manet & vanet | |
| - MANET Mobile ad-hoc network | |
| - VANET Vehicular ad-hoc network (moving cars in organized way) | |
| 9 Proactive vs Reactive Protocol (Ad-hoc routing) | |
| ad-hoc routing: | |
| nodes need to find route so routing protocol is tightly connected with Medium Acess Control | |
| * address based routing | |
| * data-centric | |
| ============================= | |
| proactive protocols: | |
| * discover route before needed | |
| * small latency | |
| * use distance vector or link state | |
| -Destination Sequence Distance Vector | |
| -Optimized Link State Routing | |
| reactive protocols: | |
| * route on demand | |
| * small routing overhead | |
| * high latency | |
| -Dynamic Source Routing | |
| -Ad Hoc on Demand Distance Vector | |
| -Dynamic MANET On Demand | |
| =================================== | |
| ----------------------------------- | |
| table driven (distance vector): | |
| * each node knows next hop | |
| * might have loops | |
| * small overhead | |
| source routing: | |
| * node knows complete route to destination | |
| ----------------------------------------- | |
| ========================================== | |
| flat: | |
| * all nodes same alghoritm | |
| hierarchical: | |
| * some nodes have greater responsibility | |
| =========================================== | |
| //10 Autonomous system and purpose | |
| (ISP) | |
| Purpose: - a reduction of routing overhead | |
| - simplification of network management | |
| * addressing = 16 bit | |
| * routers inside a single AS are managed by a single organization/institution | |
| * interior routing (IGP interior gateway protocol) === RIP, OSPF | |
| * exteror routing (BGP border gateway protocol (path vector routing)) among Autonomous systems: | |
| //. 2 what is traffic engineering TE? what/where/how (I don’t remember) technique used in that? | |
| -traffic engineering is discovering new; paths and links available in networks, monitor what current traffic usage is | |
| and direct traffic to routes other then shortest path so optimal use of resource is made. | |
| it is used in interior routing | |
| methods to collect network usage: | |
| - simple network management protocol | |
| - net flow | |
| - sflow | |
| usually calculated once per day, peak of traffic data is considered as traffic for TE | |
| // . 3 Coexistence IPv4 and IPv6 need a way how to go across one network to another. Please describe possible solutions | |
| dual stack = device support ipv4 and ipv6 at the samte time: | |
| * flexible | |
| * 2 protocols to maintain | |
| tunneling = | |
| * single point of failure | |
| * security | |
| translators = | |
| * the worst, try to avoid | |
| * no support for ipv6 features | |
| * single point of failure | |
| //. 4 What is the router, what is its main functionality, describe router abstract schema | |
| router is networking device which: | |
| main functionality: | |
| - routing | |
| compute best path | |
| - packet forwarding | |
| moves packet from input interface; to apporpriate output interface; | |
| other functions: | |
| * calc checksum | |
| * change ttl | |
| * IP header validation | |
| * fragmentation | |
| * traffic prioritization | |
| * packet classification | |
| * queue manager | |
| // address lookup with CIDR algorithms | |
| - Naive O(n) | |
| - Trie-based | |
| * binary | |
| * multibit | |
| * compressed multibit | |
| //. 5 VANETs and differences with sensor Wireless network… | |
| Vehicular ad-hoc network | |
| - simmilar: | |
| * rely on self organisation | |
| * limited energy in device | |
| * usually multi-hop communication | |
| - differences: | |
| * energy | |
| * processing power | |
| * memory | |
| * mobility | |
| //. 6 What is multimedia how can we classify it? | |
| // Please provide protocols used in multimedia transportation in IP network and its function. | |
| multimedia is data composed of different type | |
| text, image, video, audio, | |
| classification: | |
| media types: | |
| - real time | |
| * continuous | |
| = delay tolerant (audio/video streaming) | |
| = delay intolerant (interactive audio/video , remote desktop(error intolerant)) | |
| * discrete (text, weather update) | |
| - non real time (text image) | |
| /*protocols: | |
| - Real-Time Transport Protocol (RTP) | |
| * session identification | |
| - Real-Time Control Protocol (RTCP) | |
| * syncronisation | |
| - Real-Time Streaming Protocol (RTCP) | |
| &*/ | |
| protocols: | |
| FEC forward error corrcection | |
| * repair data is added to stream | |
| Interleaving | |
| * fix small gaps | |
| Automatic Retransmission Request (ARQ) | |
| * error intolerant applications | |
| Error Concealment | |
| //. 7 describe Chord in detail (searching strategy) in P2P | |
| chord works to use hash function to map each node and data item to an m-bit identifier | |
| searching strategy: | |
| - simple lookup (O(n)) | |
| node check if has an item, if not, check to next neigbour. | |
| if node identifier exceed data identifier there is no result | |
| - scalable lookup (O(logN)) | |
| instead of neighobour it saves finger table | |
| // 8 how to digitize audio, name 3 or more formats of audio | |
| with sampling and quantization | |
| mp3 | |
| GSM | |
| G.722 | |
| G.726 | |
| G.729 | |
| wav | |
| flagg | |
| // 9 IGRP and EIGRP | |
| distance vector routing | |
| metric: composite | |
| develop by cisco | |
| IGRP: interior gateway route protocol | |
| * 5 different metrics for each route | |
| * multiple paths for one route for load balancing | |
| * no suport for variable lenght subnet masking | |
| * slow convergence | |
| EIGRP: enhanced interior gateway protocol | |
| * loop free routing | |
| * allow variable length subnet masking | |
| * reliable delivery | |
| // OSPF and IS-IS | |
| belongs to link state family. uses dijkstra for shortest path. | |
| metric: cost | |
| Open shortest path first: most used LS protocol | |
| * message authentication | |
| * load balancing using equal cost multi path | |
| * routing areas divided in subdomains (hierarchy) | |
| * packet encapsulated in IP datagrams | |
| IS-IS: intermediate system to intermediate system | |
| * packet encapsulated in link layer frames | |
| * run on top of 2 layer so its safer from spoofing | |
| * less chatty and can scale better | |
| * easier support for ipv6 | |
| // path vector routing protocol | |
| BGP protocool | |
| Border gateway protocol deals with more complex topologies | |
| * loops, redundant topologies, | |
| * uses hop as count metric | |
| * used in Autonomous systems for exterior routing. | |
| * provides infos about adjacent Autonomous system. | |
| //. 10 IPv6 Header, how fragmentation in IPv6 | |
| -fixed size header (40B) | |
| -fregmentation and checksum not included. | |
| -fregmentation is now done via extension headers | |
| //2. How works autoconfiguration in IPv4 and Ipv6? | |
| in ipv 4 dhcpv4 | |
| in ipv 6 we have statefull autoconfiguration: | |
| DHCPv6 simmilar to DHCPv4 | |
| stateless autoconfiguration: | |
| * node generate Link-local address. | |
| * Test if it is unique | |
| * if is unique it is used on LAN only | |
| * now contact router for more Information | |
| * with new info node might get DHCP or stateless configuration | |
| * if is stateless global Address is created | |
| during autoconfiguration duplicate address is detected; | |
| //3. Scalable TCP and Hign Speed TCP | |
| - based on MIMD (Multiplicative increase Multiplicative decrease) | |
| - emulates the behavior of traditional TCP for small window sizes and/or higher packet loss rates in the network | |
| in this case switches into AIMD (Additive Increase Multiplicative Decrease) mode | |
| -They both dont deal with the slow-start phase.!! | |
| //5. What is QoS and how is solved in IPv6? Is there any relationship with the flow and flow labeling? | |
| quality of service is packet prioritization | |
| - baseod on flow | |
| - based on packet markup == simple, scalable | |
| ipv6 has flow label (sequence number 20bit) | |
| there is releation, flow label allows flow classification | |
| qos algorithms: | |
| source-based | |
| (source tell all routers in path how to handle) not scalable | |
| hop-by-hop | |
| every router knows just for next hop, not scalable, loops problem | |
| hierarchical Routing alg. - | |
| scalable | |
| //PNNI private network network interface | |
| protocol for ATM networks | |
| Asynchronous transfer mode | |
| //8. Vanet and differences with P2P… | |
| simmilarity: | |
| * self organizing | |
| * dynamic topology | |
| * routing in distributed enviroment | |
| differences P2P vs vanet: | |
| * fixed medium and direct vs wifi | |
| * high connection confidence vs low | |
| * any internet point vs restricted area | |
| * fixed position vs mobile | |
| * reactive routing vs proactive and reactive | |
| //Middleware in P2P | |
| middleware provide access to the services for application layer. it is risponsible for | |
| - security | |
| - peer group discovery | |
| - service discovery | |
| Compare multimedia application | |
| - real time | |
| * continuous | |
| = delay tolerant (audio/video streaming) | |
| = delay intolerant (interactive audio/video , remote desktop(error intolerant)) | |
| * discrete (text, weather update) | |
| - non real time (text image) | |
| //IPv6 neighbour discovery protocol: | |
| in ipv4 == arp | |
| - autoconfiguration | |
| - duplicate detection | |
| protocol: | |
| Router advertisment: | |
| router solicitation: | |
| neighbour solicitation: send to descover neigbours | |
| neigbour advertisement: answer back with advertisment message | |
| ICMP redirect |
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