Lecture 19: Routing Protocols Part 2

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  • May 7, 2021
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Talha Ibn Aziz – Lecturer at Department of CSE, IUT
Transcript

Hello everyone so this is the   last lecture of the course and this is   lecture 19th   uh which covers the second part of the   different routing protocols that we’re   supposed to cover   so in the last lecture we learned   about two different routing protocols   and in this one we’re going to learn   uh two new ones and also about uh   vanet or vehicular ad hoc   network okay so let’s start   so the first protocol that we’re going   to learn is dsdv destination sequence   distance vector routing and this is also   table driven   route our routing protocol for ad hoc   mobile networks but it’s based on   belmont ford algorithm   and tsd primarily contributes to solving   the routing loop problem   so if you remember the bellman fold ford   algorithm was   uh can actually detect uh cycles or   loops uh by you know and also it can   understand uh negative edges in   the you know network so if there are   negative edges and   uh there are loops so even in those   scenarios the bezel and forward   algorithm works   well and uh it can you know detect those   things okay so these are the   positive aspects of the bellman ford f4   algorithm   but the negative aspect was that it it   is very   uh it has a very high complexity because   it needs to in a relaxed   every link so   it’s it has very high complexity but uh   it can detect those things which other   you know algorithms cannot so this   belmont   4 algorithm can be used to you know   solve the routing   loop problem which is why it is used in   dsgb   so each entry of the routing table   contains the following columns   one is the destination then then the   next hop   uh in the path from the you know   source to destination then the number of   hops the sequence number and the install   time okay   so if you remember in the last lecture   we learned   a protocol uh which had three uh   let’s say uh three and three entries or   sorry three columns in each entry   uh the next top the number of hops and   the sequence number   so those three are also present here but   extra values are   or extra uh columns are the install time   and the destination   so the next top uh you know suggest uh   which hop the packet will be forwarded   to for a specific source to destination   and number of hubs tells us the number   of hops required to reach the   destination   and here the sequence number is not um   you know not only representing the   freshness but   also it represents whether there is a   link present or not   so if the sequence number is an odd   number it   it means that there is no link present   and   if it is an even number that means there   is a link present okay   so uh the destination uh keeps the   information on the address of the next   uh sorry of the destination and it is   used to determine the route for this   node okay so this is sort of   uh what is used for matching the entry   so matching means whenever we   uh compare a packet   uh the packet has a header which you   know   which i which identifies the shows where   the   destination is or what the destination   is so that is   compared to this part of the f of each   entry to   understand uh where to go   so install time uh reflects how   recent the current entry is okay so   these are the five   uh columns of each entry so this is an   example of the five   uh columns of the entries the   destination here represents   uh the node so as   it is shown in short but usually it   contains the addresses okay   instead of you know just a b and c and   the next top column represent to go for   the next   destination so as uh this table is   for the node a so to go to the   destination a the next hop is also a   because   it itself is the destination and the   number of hops required is zero   so the sequence number is just around   our number   shown here and the sequence number   usually also   uh keeps the destination information so   as you can see for the   next row the destination is b so the   sequence number is b36   and for the next uh line the destination   is c and the sequence number is also   c26 so all these are even numbers that   means   all the links are present and at the   right we can see the install time okay   so it basically stores the time   and during which the entry was uh let’s   say   kept in the table so for the destination   b   the next hop is b okay because uh b   is itself the destination and number of   hops required   to go there is one and for the   destination c the next hop is also b   and the number of hops required is two   so we can clearly understand that a is   connected to b   and b is in turn connected to c so   uh if if a requires to send the packet   to b   it just directly forwards it to b and if   it requires   to send to c then it will uh forward the   packet to b and b will forward it to c   so this is how you can understand uh who   to forward the next   of the packet to and what is the final   destination   so the distance routing vector uh   distance vector routing uses bellman   ford as we   as you have already uh learned about the   reform in previous courses and i have   also   uh talked about it in short so the   sequence number generated   is generated by destination and it keeps   the destination information   and emitted that means that let’s say if   there is an update   uh or let’s say if some node you know   detects an anomaly   regarding that path or regarding that   route then it must also use   this specific sequence number to send   updates   so that everyone else can you know   verify whether it is actual   whether it is an actual update or not   and routing information is distributed   between nodes using full   information but that is done very   infrequently that means it is not done   regularly because sending the full   information   is not necessary all the time and   smaller incremental updates are done   frequently okay so these are the two   ways the information is let’s say   forwarded   to other nodes so   according to the dsdb protocol if a   router receives   new information it uses the latest   sequence number to decide whether to   select or whether to receive uh the new   info or not   just like uh aodv right and if both the   sequence numbers   are same then route the route with   better performance   based on a routing metric for example it   can be a hop count   is selected as a new route okay so if if   the sequence numbers   are not same that means the latest   sequence number is selected and if   they’re same   then the route with the better   performance is selected   so entries without any update for a long   time are deleted along with other routes   which have   the same nodes okay why because if there   is no update regarding a specific route   or specific entry that means that there   is   a problem in that route and this is why   no updates are received so that route is   deleted for deleted from the memory and   every other route which has those   specific   nodes are deleted okay because they   might because we don’t know which   uh node has failed or which link has   failed   so all the related nodes needs to be   deleted so that a new   route can be found or it can be checked   whether a newer route is present or not   so this this protocol is a bit old but   it has multiple advantages and   disadvantages   and this protocol is you know used or   actually many protocols   take lessons from this protocol okay so   if   so the advantages can be if there is a   path available to all network   destinations   the path setup process has less delivery   so the precondition is there has to be a   path   to all the destinations and existing   wired protocols can also be   adapted to ad hoc wireless networks   using incremental updates using   sequence number levels if you remember   the incremental updates were done   frequently and they use sequence number   labels to verify or to to   you know make all the other notes   understand   that the update is valid okay so this   technique can be used for wireless   networks as well   and wired protocols can be made   effective in wireless   networks using this uh technique so it   requires a regular update of its routing   table so uses more bandwidth and power   okay even if the nodes   are ideal so this is one of the   disadvantages because of those   frequent and infrequent updates or   broadcasts   so for topology changes new sequence   numbers are necessary   every time so it is not suitable for   highly dynamic or large scale networks   because in those scenarios there there   is either a large number of nodes   for large scale networks or the routes   might be changing very frequently if the   network is highly dynamic okay   so the sequence numbers or the limit of   the sequence   numbers might be very quickly reached if   every time the sequence numbers are   changed   or if the topology is changed okay   because that’s how the   this protocol works so although the   protocol is not used the techniques are   still used in   recent protocols an example is a or dv   okay so aodv uses   some of the techniques that is used here   so it’s not actual top   other way around instead aodb learns   from this one okay   so this is another protocol and we’re   just going to learn about this in   very short or in very brief so this is   the hybrid   wireless mesh protocol or hwmp and the   name   clearly suggests that this is also used   for wireless mesh protocols and it is   defined in ieee 802.11s okay so if you   remember we   we had already gone through this   protocol right and it is a basic routing   protocol for wireless mesh network   okay the 802.11s so hwmp is actually   used for   uh that uh specific protocol   so it is based on aodv and it is a tree   based character okay so   what it does is it discovers and tracks   the neighboring nodes using a peer   link management protocol so peer usually   means the   ones of the same level so it suggests   that   it’s talking about the neighbors okay so   neighboring   link management protocol that’s that’s   also how we can   you know term it or phrase it so it is   hybrid   or the name says that it’s hybrid   because it supports two kinds of math   selection protocols   and both are actually uh used in ieh   2.11 s   and it uses mac addresses instead of ip   addresses so if you remember   uh mac addresses are addresses based on   the data link layer   and ip addresses are based on the   network layer   so um this protocol uses the mac   addresses instead of the ip address   so uh the two kinds of path selection   protocols   that it uses is one is   one of those is based on aodv and is on   demand that means   it only searches for routes if there is   a packet   which does not match any entry in the   routing table   and the other protocol   is proactive okay so that is productive   tree building means it does not wait for   a new packet or does not wait   for a packet which does not match with   any entry in the table   it automatically keeps searching for you   know   destinations or how to reach different   destinations   so it is hybrid because it can use both   simultaneously or both modes   simultaneously okay   so that’s it about this one uh next   we’re going to see some   uh vanity routing protocols okay so the   vanity is different from   mana because uh man it means mobile ad   hoc network so it just   means that the notes are ad hoc and   mobile so they will be moving and   obviously there   will be wireless but when it means   vehicular ad hoc network   so they are not only just mobile there   they move very quickly compared to   other mobile ad hoc networks okay and   the mobility might be sudden   so it might be that the car is you know   parked and it is there for a long time   but again it might suddenly start and it   might quickly you know   change its location so there are   different kinds of routing protocols for   vanets   and they can be categorized into broadly   five   so as you can see here position based   topology based   broadcast based cluster based and   geocast based okay   and there they can also be again   classified into different you know   categories   for example topology based can be   classified into   proactive reactive and hybrid and the   others are examples of the routing   protocols   so let’s see each category one by one   the first one is position based okay so   in this protocol   uh the geographical position is shared   along with the network location   so for routing we need network location   right but in this scenario along with   the network location it also shares the   geographical position   so beacons are transmitted regularly to   uh let everyone know about   the position of the node and there are   three main components of this   protocol one is beaconing which is you   know letting the everyone know   uh the current position and the location   services   so in order to let everyone know the   current position of a node   the node itself has to know its position   okay so this is why the location   services is required   and also forwarding capabilities so   without forwarding actually it’s not a   network   so it requires global global positioning   system or gps assistance   to decide the location of the various   nodes and examples of this starting   protocol can be distance routing effect   algorithm for mobility or dream   and greedy stateless routing or gpsr   so we can see a figure on the left which   you know shows an example   so the left vehicle is actually sending   a query message   and it’s a query about the   identification sequence number and hop   limit of another node and the node   is replying with a location reply   message okay   and before that it also has to check   whether it’s a duplicate message or not   otherwise for every message it gets it   it might keep on you know flooding the   network   so after the duplicate check is done it   replies with   the message the current position and   the time stamp okay so this is how you   know uh the position based   uh networks communicate or nodes in the   network communicate   so next to the topology based uh   protocol so this uses the available   information about the link of the   network to forward packet from source to   destination okay so this is only you   know possible if   the topology information is known which   is usually not the case because   vehicular ad hoc networks   have you know nodes which move very   quickly   so there are mainly three categories of   topology based shouting   one is proactive reactive and hybrid as   we have already seen in the previous   figure   so in the previous to previous   figure so the proactive routing usually   depends on the shortest path algorithms   because those algorithms actually   calculate the   uh distance to the destinations to   all possible destinations without you   know waiting for any   query and uses standard distance vector   routing protocols like dsdv   which use those you know shortest path   algorithms and   reactive writing on the other hand only   performs routing when you know a packet   arrives so it’s   sort of like on-demand routing and it   decreases the protocol overhead because   it only   uh you know searches the entire network   when required otherwise   it only maintains the already existing   routing paths   so examples of reactive routing can be   dynamic supply routing or dsr   hybrid ad hoc routing combines these two   proactive and reactive routing so it   divides the network into local and   global regions   so the local regions are following   proactive routing   and the global regions are following   reactive routing protocols together   for example zone routing protocol or zrp   the next category is broadcast based so   this sort of protocol   floods the packet over the entire   network in a broadcast domain and hence   the name   broadcast based routing so whenever the   node is outside the transmission range   this method is used because uh the   exact location or the exact uh path is   not   known so it forwards the packets to   everyone   who is in close proximity and they in   turn forward the packet so that the   intended   uh you know user or intended vehicle can   get the message   so this is mainly used for safety   related applications   for example climate traffic road   conditions etc okay   so these are of these uh messages are   very   important because they are safety   applications so   instead of taking risks the broadcast   method works very well here   because the broadcast is almost certain   to reach the destination   and this is the kind of information   which   every vehicle needs to know so the   broadcast   uh based protocol is the best used here   and example of this category are   distributed vehicular broadcast protocol   or dv   cast the next protocol is   our category is cluster based so   vehicles having similar characteristics   for example let’s say cars having the   similar velocity   and maybe they’re going in the same   direction or they’re you know going   together or grouped together so in those   scenarios the cluster based   uh protocol is used and each group   of vehicles forms a cluster and   communication is managed by the cluster   head of that cluster   so if a packet is in the same cluster or   the source and the destination both are   in the same cluster   then it can be directly sent that means   the source can directly send the data   packet to the destination however when   the destination is   outside the cluster that means it’s   let’s say in another cluster   so in this scenario the cluster head   provides a scalable system   so this means that it can it can be a   different   uh kinds of uh you know scenarios or   it can be a different kinds of system   for example the vehicle   might carry or the cluster it might   carry that data packet until it reaches   a place where it can forward it to   someone of another cluster   or it can you know uh you probably send   with the high power signal if the other   cluster is nearby   so examples of this uh category is   clustering for opening vehicular   communication network or coin   so this is the last uh you know category   which is   geocast based routing okay or   geocast based uh vehicle routing   for vanet so it uses mobicus messages to   communicate with vehicles   so mobicus is a specific type of   multicast   technique which can be used to   communicate with multiple   nodes at the same time so there are two   kinds of mobicast actually so do not   confuse them   uh this is one of those types   so communication happens at a specific   time and in a specific   region okay and though that region is   called the zone of relevance or z-o-r   so whenever the vehicles are in the zone   of relevance   then they communicate with each other so   if the destination is not in   the specific zor the communication is   done using   the zone of forwarding or zof okay   so whenever a vehicle you want to send   that means the destination vehicle and   the source vehicle and not in   the same zorr it has to be done   by you know going to another uh region   which is called the zof   and any any car in the zof has the   responsibility to forward the packet to   other zors okay so like this uh the   packet from the source can you know move   from   z to r to zof and then again to zero r   and like this until it reaches the   destination   so example protocols are ivg   dg caster etc okay so these were the   different categories of   you know vanet routing and there are   some references here as well so that you   can look up those   uh protocols uh one for the destination   sequence   distance vector routing or dsdv and the   second one is for hybrid wireless mesh   protocol or hwmp   and the third one is uh for hybrid   that the same as before but instead of   wikipedia   this is a research paper and the last   one is for vanet routing protocols   the last you know five categories that   we read you can be found here okay   so that was about it and if you have any   questions regarding this   lecture or any other lecture before this   you can   ask and i guess   this is the end of the course and it’s   the last lecture of the course   so yeah okay then   so i’m welcome everyone 




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