Computer Communications (Networks)

Computer Communications (Networks)

  • Abdelhalim Zekry added an answer:
    Could someone explain me clearly the impact of the channel delay spread and the channel coherence bandwidth in the design of error correcting codes?

    In  the design of an error correcting code, what can be the impact of such channel parameters.

    Abdelhalim Zekry · Ain Shams University

    Dear Abraham,

    This is really a good question and it needs investigations to precisely answer it.

    In order to answer it, i will stick to the basic principles and concepts of the channel performance and the channel coding.

    Assume you have a communication channel that has multipath effects such that the delay spread of the symbols is Tau, The coherence bandwidth Bc = 1/ Tau. The consequence of this delay spread is the channel bandwidth is limited to certain bandwidth Bc which is termed the coherence bandwidth. It means that as the signal bandwidth is smaller than the channel coherence band width, the signal will suffer only from flat fading and the signal can be detected with correctly with very few errors. In case of that the bandwidth of the transmitted signal is greater than the coherent channel bandwidth the fading will be selective deep fading such that some signal frequencies will be severely attenuated. Such selective fading must be treated by frequency domain equalizers. Such that the channel response becomes flat at all signal frequencies. 

    Such frequency selective fading may be severe such that that one can not completely eliminate it by equalizers. Fast fading has also the same effect in case of

    doppler spread which can be reduced by time domain equalizers. One can additionally utilize channel coding to reduce the bit error rate by detecting and correcting the errors in the bits.

    There are two major types, the block codes and the convolutional codes. The convolutional codes are capable to correct  discrete bit errors while Reed Solomon codes are capable to correct complete symbols and therefore are capable to combat burst errors. By adding interleaves to the the convolutional encoders  they become capable to correct burst errors. To combat deep fading errors, a method capable to combat burst type error is required.

    In summary ,It is so that one can use:
    -RS encoders

    - Interleavers + convolutional encoders,

    - Turbo encoders which are composed of two recursive convolutionl encoders with inerleaver between the outer and the inner one.

    It must be said the channel coding is basically used to enhance also, the white Guassian noise channels. and consequently all types of the channels.

    Best wishes

  • Riaz Ahmed Shaikh added an answer:
    Is there a formal algorithm for detecting link failures through Passive-Acknowledgement protocol for MANETs OR Wireless Sensor Networks?

    Passive acknowledgement is a protocol originally proposed for MANETs to detect link failures. It says,that a node must overhear the channel to check whether its neighbor transmitted the packet or not.

    Riaz Ahmed Shaikh · King Abdulaziz University

    You may find the following paper useful, in which authors have discussed the issue of passive acknowledgements in zigbee wireless sensor networks.

    Sung, T. W., Wu, T. T., Yang, C. S., & Huang, Y. M. (2010). Reliable data broadcast for Zigbee wireless sensor networks. International journal on smart sensing and intelligent systems, 3(3), 504-520.  http://www-ist.massey.ac.nz/s2is/issues/v3/n3/papers/paper11.pdf

  • Walaa Ali added an answer:
    What is the benefit of representing wireless sensor network as a graph?

    Many papers that describe protocols for wireless sensor networks mention that the network can be represented as a graph such as unit disk graph. nodes are vertices of the graph and links between nodes are edges of the graph. I need to know if all nodes in the network know this graph in the beginning of the connection?  what is confusing for me , from my knowledge i know that node know information about its direct neighbors only. how can i assume in my simulation that network with thousand of sensors , all of them have the graph that represent the whole network???

    so if what i think is correct, i.e.  the graph is too big and need many communication to be constructed in the beginning of the connection that mean it can't be known to all nodes in the network, what is the benefit that papers always mention that the network represented as graph????  

    Walaa Ali · Minoufiya University

    thanks all for answering. it is now clear for me 

  • Sergo Shavgulidze added an answer:
    Why is the definition of interleaved Gabidulin codes not similar to the definition of Reed-Solomon interleaved codes ?

    interleaved Reed-Solomon codes are defined as time interleaved codes in order to benefit from the time diversity. An interleaved Gabidulin code is the direct sum of ℓ Gabidulin codes. 

    Sergo Shavgulidze · Georgian Technical University

    Rank codes (also called Gabidulin codes) are non-binary linear error-correcting codes over not Hamming (compared to Reed-Solomon codes) but rank metric.

  • Peter T Breuer added an answer:
    How can we fix problems of computer communications in a proper way?

    Last decade observed a significant research effort directed towards indoor localization utilizing location fingerprinting techniques. Fingerprinting solutions generally require a pre-deployment site survey procedure during which a radio-map is constructed by laboriously collecting signal strength samples (e.g., Wi-Fi) over the whole localization area. However, such localization efforts have certain shortcomings. For example, it is time consuming, labor intensive, vulnerable to environmental changes, and the process requires certain pedigree on the surveyor that may deem the fingerprinting techniques impractical to be deployed over large areas (e.g., shopping malls, multi-storey offices/residences, etc.). Newer emerging techniques try to bypass this expensive pre-deployment effort of fingerprinting solutions altogether. They may build the radio-map through the implicit participation of the building occupants, office employee, shoppers, visitors, etc. Apart from the traditional performance comparison criteria like accuracy, precision, robustness, scalability, algorithmic complexity based on which the localization techniques were evaluated, these newer approaches warrant some additional ones. For example, whether they require an actual geographical map of the localization area, the percentage of occasional location fix to ensure reasonable accuracy, the usage of explicit/implicit user participation to construct the radio map, the usage of building landmarks (e.g., entrance, conference room, elevator, escalator, etc.) or additional sensors (e.g., accelerometer, gyroscope, compass, etc.), whether they address device heterogeneity, etc. In this article, we survey the newer emerging fingerprinting solutions that try to relieve the pre-deployment woes. We also identify some newer performance comparison criteria based on these solutions’ inherent characteristics, and apply them together with the traditional ones in order to evaluate a number of such proposed systems.Last decade observed a significant research effort directed towards indoor localization utilizing location fingerprinting techniques. Fingerprinting solutions generally require a pre-deployment site survey procedure during which a radio-map is constructed by laboriously collecting signal strength samples (e.g., Wi-Fi) over the whole localization area. However, such localization efforts have certain shortcomings. For example, it is time consuming, labor intensive, vulnerable to environmental changes, and the process requires certain pedigree on the surveyor that may deem the fingerprinting techniques impractical to be deployed over large areas (e.g., shopping malls, multi-storey offices/residences, etc.). Newer emerging techniques try to bypass this expensive pre-deployment effort of fingerprinting solutions altogether. They may build the radio-map through the implicit participation of the building occupants, office employee, shoppers, visitors, etc. Apart from the traditional performance comparison criteria like accuracy, precision, robustness, scalability, algorithmic complexity based on which the localization techniques were evaluated, these newer approaches warrant some additional ones. For example, whether they require an actual geographical map of the localization area, the percentage of occasional location fix to ensure reasonable accuracy, the usage of explicit/implicit user participation to construct the radio map, the usage of building landmarks (e.g., entrance, conference room, elevator, escalator, etc.) or additional sensors (e.g., accelerometer, gyroscope, compass, etc.), whether they address device heterogeneity, etc. In this article, we survey the newer emerging fingerprinting solutions that try to relieve the pre-deployment woes. We also identify some newer performance comparison criteria based on these solutions’ inherent characteristics, and apply them together with the traditional ones in order to evaluate a number of such proposed systems.

    Peter T Breuer · Birmingham City University

    I think he's talking about wifi.

    Not that that incomprehensible mess says so!

    What is "indoor localization"?

    Is that trying to figure out where you are inside a building via measured signal strengths from known wifi transmiters?

    Why would anyone ever want to do that, instead of using bluetooth to map when you go through a doorway? Is this part of some fancy scheme like they have in Apple headquarters, where everyone wears a bluetooth badge, and one logs in at any terminal and it comes up with ones own desktop, just as one left it? 

  • Harekrishna Misra added an answer:
    Which region of the network witnesses the highest buffer utilization?

    As stated in the following paper,

    "Balancing buffer utilization in meshes using a “restricted area” concept, by P.-J. Chuang, J.-T. Chen, and Y.-T. Jiang, in IEEE Trans. Parallel Distrib. Syst., vol. 13, no. 8, 2002"

    the region of adaptivity tends to handle the most concentrated network load which can also be translated as the highest buffer utilization. 

    However, according to the results presented in Fig. 6, the highest buffer utilization for unbalanced routing algorithms such as West-First or North-Last occurs at the least adaptive region of the network (i.e. West half or North half, respectively) which is really confusing.

    Which one is correct, the theory or the results?

    My own results obtained using the BookSim network simulator conforms to the theory. Except from the West-First results which is the same as Fig. 6(a) of the above paper.

    Any explanation or hint is highly appreciated! 

    Harekrishna Misra · Institute of Rural Management Anand

    Could u please send this article and results of your work to share views!

  • Kashif Naseer Qureshi added an answer:
    What tool can generate random HTTP, FTP, Telnet, SMTP traffic for a test bed environment?

    what tool can generate random realistic HTTP, FTP, Telnet, SMTP traffic for a test bed environment? I need this traffic to stimulate normal working condition of my test environment. Thanks

    Kashif Naseer Qureshi · Universiti Teknologi Malaysia

    There are many tools available for this purpose. The selection is based on your knowledge and awareness about tool.  Some tools are as follows:

    1.  Apache

    2.  Postfix 

    3. Vsftpd

    4. Wireshark

  • P.K. Bansal added an answer:
    How can I design a primary and a secondary path from source to sink node?

    refer me the code for that

    P.K. Bansal

    Please mention which network ur refering?

  • Quist-Aphetsi Kester added an answer:
    What are some open challenges in cloud security at SaaS and IaaS?
    I am willing to do work on cloud security issues at SaaS and IaaS. for the same. Can anyone suggest approaches and future scopes for this?
    Quist-Aphetsi Kester · University of Cape Coast

    Data Security is the key issue as well as others below 

    Network Security

    Authentication

    Access

    Data confidentiality

    Web Application Security

  • Saeed Moradnoory added an answer:
    How do I connect native border router and cooja mote to simulated sky motes ?

    Hi,

    I am trying to connect rpl native border router to simulated sky motes., using slip radio and serial socket

    when i start the simulation the DIO packet sent by border are getting DIO ACK from nodes, but data packets send by nodes are not reaching to border router.
    Though nodes sending DAO packets for DIO from border router, border router still sending many DIO packtes

    I can see the packets received over slip radio on terminal, but in border-router.c I added lines to listen the tcpip event

    while(1) {
    PROCESS_YIELD();
    if(ev == tcpip_event)
    tcpip_handler();
    }
    that event is never triggered during simulation, though continuous data packets are sent form other nodes

    I have working code of this, It is working fine on sky platform (sink and other nodes are sky motes )

    I tried cooja mote as sink node, RPL tree is getting constructed, for every DIO from cooja mote there is DIO ACK repled from other motes, but still cooja mote sending continuously DIO packets. here also same case as with border router


    I am not able to understand what is wrong going here ?
    I tried all possible combination by changing MAC & RDC layer protocol through conf files, but still no success


    please need a help to solve this
    any one succeeded in this

    Thanks

  • Cindy Stap added an answer:
    How do I resolve a segmentation fault in my simulation after 5 second in ns-2?

    actully when i run my modified approach then my code is run only for 5 second after that i get an core dump segmentation fault error

    Cindy Stap · Dell

    sounds like a timing issue where code is trying to access the same memory... does it happen exactly the same every time?

  • Prakash Pawar added an answer:
    How do I forward packets received form neighbor motes ?,

    Hi all

    How to forward packets received form neighbor motes ?,
    consider scenario

    1-----------2------------3

    mote 1 and 3 are not in their transmission range,
    whenever mote 1 send packet, mote 2 captures it and the stores for few time, and later sends to mote 3 , i.e. mote 3 feels that the packets are coming directly from mote 1
    ------------------------------------------------------

    I am working on wormhole attack on RPL IoT,

    guidance regarding for coding above (mote 2) will helpful

    where should i focus either on contikimac or cc2420 radio chip for coding above mote ?

    Any one has experience on creation of wormhole attack on any simulator ? then please guide regarding the same


    Thanks in Advance

    Prakash Pawar · Indian Institute of Technology Hyderabad

    Hi Francisco Estevez, I did it at RDC layer sicslowmac, just adding few if else lines, without modifying any thing, just resend the packets which are hit on radio interface

    Thanks for your help

  • Saeed Moradnoory added an answer:
    How do I implement RED algorithm in ns-2?

    While implementing RED algorithm in ns2 i have already used the line "set val(ifq) Queue/RED " for using RED and set the following parameters

    Queue/RED set thresh_ 5
    Queue/RED set maxthresh_ 15
    Queue/RED set q_weight_ 0.001
    Queue/RED set bytes_ false
    Queue/RED set queue_in_bytes_ false
    Queue/RED set gentle_ false
    Queue/RED set mean_pktsize_ 1000

    but my simulation is not completed. Can anyone tell me the simulation of RED in ns2.

    Snapshot is also attached.

  • Negar Khajeddin added an answer:
    How can I define a new authentication scheme in Open IMS core?

    Hello

         I'm looking for a familiar guys with Open IMS core. Actually i wanna define a new authentifcation scheme for IMS network. so for performance evaluation purpose i'm gonna use the OPen IMS core with IMS bench SIpp.

    can any one guide me what are the main files to edit in Open IMS core in order to define a new auth scheme

    A lot of thanks

    Negar Khajeddin · Iran University of Science and Technology

    Dear Saliha

    -" I mean define my own new scheme not the existing ones"

    I don't the exact answer but one thing is for sure that you have change or add scscf and hss related files. Studying OpenIMSCore structure is a good practice. You can also ask this question in OpenIMSCore mailinglist.

    - "where cheking the HSS authentication sheme? is it in the web interface?"

    Yes, you have to use the web interface for HSS authentication scheme. In case you are registering multiple users, you have to changing the user data in add-imscore-user.sh file.

    Regards,

    Negar

  • Wan Mohd Nur Muzaaliff Wan Musa added an answer:
    What's the current advancement in network (Access Point) selection mechanism?

    I'm using Quality Function Deployment (QFD) to perform network (Access Point) prioritisation and selection, semantically (context aware). Any ideas for advancement, extension or comparison?

    Wan Mohd Nur Muzaaliff Wan Musa · Kolej Poly-Tech Mara

    Quality function deployment (QFD) is a structured method to extract quantitative parameters from qualitative user requirements. It helps to prioritise the parameters to produce justified decisions. In this case, the network selection.

    Whereas, QoS is a quantitatively measured performance of network. Specifically, the performance perceived by the users of the network.

  • Tanya Sammut-Bonnici added an answer:
    Would you know of recent cutting edge work on Network Effects and Compatible Networks?

    Shapiro, Farrell and Economides wrote about this in the 1990s and we seem to have lost our way research wise after that. Most digital networks are compatible. I am interested in the dynamics of compatible networks: communications networks, social networks, c2c/b2b networks. 

    Tanya Sammut-Bonnici · University of Malta

    Thank you!

  • Mohanchur Sarkar added an answer:
    Has anyone here worked on key management or key exchange in DTN using one simulator?

    I want to analyse the effect of key management in DTN . I would appreciate any useful idea especially using ONE simulator.

    Mohanchur Sarkar · Indian Space Research Organization

    I feel some DTN simulation codes are available for  ns2 network simulator. One may have a look into that if it helps.

  • Sirapat Boonkrong added an answer:
    Is there any way to perform manual assocation of random MAC addresses with the access point in a wireless environment?

    I wanted to know if an attacker can do manual associations of random MAC addresses with the access point.

    Can it be done in case of WPA2 encrypted networks too, i mean the complete four way handshaking involved during authentication?

    Sirapat Boonkrong · King Mongkut's University of Technology North Bangkok

    It depends what type of authentication you are doing.

    If you do "open authentication", it is possible for any attacker to fake a MAC address.

    If you do "shared-key authentication", then it becomes more difficult because authentication is done using the pre-shared secret key, rather than a MAC address.

    Bear in mind that if your wireless network uses DHCP, it is very likely that you will need to have an additional authentication layer to stop DHCP from giving out IP address automatically.

  • Tapan P Gondaliya added an answer:
    Who has some papers or documents on simulation of data link layer protocol using GO BACK N and SELECTIVE RETRANSMISSION protocols ?

    Who has some papers or documents on this title ? I plan to use java but not java applets since it  wont  be web based. I will introduce the presence of bit error probability.

    *New References
    The books

    Tapan P Gondaliya · RK University

    All the best.. 

  • Saliha Mallem added an answer:
    Does anyone know about using IMS bench SIPp with OpenIMSCOre ?

    Hello guys

    Have anyone of you already used IMS bench SIPp with OpenIMSCOre? If so how can i test the registration phase? i mean what are the steps? There is really little support about that.

    Many thanks

    Saliha Mallem · Ecole Nationale Supérieure d'Informatique

    Hi Merima

    i run these commands to compile SIPp (With TLS support)

    # ./configure --with-openssl
    # make

  • Ali Khaniki added an answer:
    How can I model a satellite network on opnet?

    i want to model a LEO satellite network on opnet.the main feature of this network is a rapid dynamically topology but predictable.if we consider each satellite as a node,the RF inter satellite links connect nodes together.my problem is that i don't know how model a network with this features on opnet.i need some help.your help can guide me a lot.

    Ali Khaniki · Iran University of Science and Technology

    which node should i use? opnet has satellite node but i don't know how use it

  • Ahmad Kamal Ramli added an answer:
    Is there any proven autonomic computing algorithm that inline with IBM autonomic computing blueprint?

    This is to understand the possible solutions for autonomic computing algorithm in Maths. At the moment , according to my own experiences , binomial heap really great in this approach compared to others. Bayesian Network , linear regression , N-Gram requires extra parameters in solving false and right alarms. Any suggestion how the algorithm can really inline with K-MAPE will be really grateful. Thanks in advanced.

    Ahmad Kamal Ramli · University of Leeds

    Thanks guys for the great input. 

  • Saliha Mallem added an answer:
    Which simulator is suitable for communication protocol assessment of performance?

    Hello everybody

    I want to test the performance of my own authentication protocol. To be more clear, my protocol is for IMS network. and i don't really know which tool should be used (omnet++ , opnet....??). Or should I use a tool related to IMS network?

    Many thanks,

    Saliha Mallem · Ecole Nationale Supérieure d'Informatique

     hi guys

    Does NS2 allow to evaluate a sip traffic ( to the best of my knowledge the traffic sources in NS2 are : FTP , CBR and telnet??)

    Does NS2 allow to interact with a database? it's import in my protocol to have a databases

    Many thanks

  • Sai R N added an answer:
    What is the role of "Agent" in NetSim WSN simulation ?

    In NetSim WSN, I can see a icon in the GUI for "agent", and also several properties for this including mobility. What is the role of this agent ?

    Sai R N · BITS Pilani

    One more question Akhilesh, how do I change the underlying data rate of 250 kbps in WSN simulations in NetSim. Can it be done via GUI or should I use command line ?

  • Hamza Kheddar added an answer:
    Can I simulate a communication based SIP protocol on Omnet++ simulator?

    I would like to know if it's easily possible to simulate a communication based SIP on the Omnet++? If not, what are the possible tools to do that? For more clarification I would like to simulate a new protocol aimed to enhance registration in IMS network.

    Many thanks

    Hamza Kheddar · University of Science and Technology Houari Boumediene

    Actually, i tried to work on it, but when i realise that my work is based on RTP flow messages (communication SIP part)  i change the software entirely and i'm using jvoiplib software. but i'm sure with OpenIMS support, you can find the solution

    Best regards.

  • Nils Ulltveit-Moe added an answer:
    How do I use Boost Graph Library in Eclipse for C++ (Windows)?

    I never used Boost libraries. I wish to know how I can use the library in my program. Do I need to install boost or use the binaries? What changes do I need to make in the Eclipse project and Eclipse settings? Thank you in advance

    Nils Ulltveit-Moe · Universitetet i Agder

    In general you will need the Boost library (.dll file) and the include files (*.h) in order to compile a C/C++ program. You can then compile your program by specifying the include path of your header file (-I dir), the include path of your libraries (-L dir) and the library itself (-lboost). You must then tell Eclipse somehow where these files reside in order to compile a Boost program in Eclipse. The Eclipse documentation should describe how to do this.

  • Philip James Hasnip added an answer:
    How can I eliminate this problem in running CASTEP within material s studio 7?

    Hi,

    Running CASTEP calculations on some structures in materials studio 7 this message appeared and persists:

    Failed to create job for the server: CASTEP. This computer was unable to communicate with the computer providing the server.

    Can someone explain this and resolve it?

    Philip James Hasnip · The University of York

    Dear Zlimann,

    Materials Studio starts Castep calculations by communicating with a special server, often called a "gateway". In order to run Castep locally, you need to start the gateway on your local machine, and then tell Materials Studio to use this.

    I can't quite remember exactly how you do this, but I think there are scripts somewhere in the Materials Studio installation to start the Gateway (I think they're called something like gwstart or perhaps gwstartservice, and there are others to configure it, restart it, stop it etc.) To get Materials Studio to use it I think you need to open the License Administrator and configure everything in there.

    Sorry this is a bit vague, I use Linux most of the time so am not too familiar with Materials Studio. You'd probably get better advice from Accelrys' customer forum:

    https://community.accelrys.com/index.jspa

    I hope that helps a bit at least.

    All the best,

    Phil Hasnip

    (Castep developer)

  • Mohammadreza Rahimizadeh added an answer:
    Is it possible to launch DHCP starvation attack in wireless network?

    According to cisco enterprise mobility, the clients are associated to Access Points using MAC address. So, can an attacker send various DHCPDISCOVER messages using spoofed random source MAC addresses in a wireless environment?

    Mohammadreza Rahimizadeh · University of Tehran

    In wired networks, port security can prevent DHCP starvation attacks. However, if attacker change the MAC address in the DHCP payload (chaddr), port security can't prevent attack. In this case, administrator can slow down attack using a DHCP rate limiter on the switch port.

    But in wireless networks, due to the 802.11 protocol definition, MAC address spoofing is prevented and this prevents clients from spoofing the source address of the frame in addition to the DHCP client field in the payload. The WLC (which terminates the user traffic) protects the network from DHCP starvation attacks because it tests DHCP requests to certify that the client MAC address matches the chaddr. If not, the DHCP request is dropped. 

About Computer Communications (Networks)

A computer network is a collection of computers and other hardware components interconnected by communication channels that allow sharing of resources and information.

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