Results 1 to 4 of 4

Thread: Broadcast Forwarding Methodology

  1. #1
    atevewr
    Guest

    Broadcast Forwarding Methodology

    Can somebody please explain me how the broadcasts work in multihop
    wireless networks. Are the packets unicast forwarded or broadcast
    forwarded. For e.g. A,B,C,D are four nodes, (A&B) in each other's
    range & (B,C & D) in the other range. When A broadcasts a packet, how
    will B forward the packet to C & D ?
    Unicast forwarding or it too will broadcast?
    If it will be broadcasted, it creates a broadcast storm, How will that
    be handled?
    Thanks in advance.

  2. #2
    Jeff Liebermann
    Guest

    Re: Broadcast Forwarding Methodology

    On Mon, 15 Feb 2010 09:54:03 -0800 (PST), atevewr <atevewr@gmail.com>
    wrote:

    >Can somebody please explain me how the broadcasts work in multihop
    >wireless networks. Are the packets unicast forwarded or broadcast
    >forwarded. For e.g. A,B,C,D are four nodes, (A&B) in each other's
    >range & (B,C & D) in the other range. When A broadcasts a packet, how
    >will B forward the packet to C & D ?
    >Unicast forwarding or it too will broadcast?
    >If it will be broadcasted, it creates a broadcast storm, How will that
    >be handled?


    It depends on the mesh network wireless bridge implimentation. Most
    early versions were your worst nightmare, where any packet without a
    destination MAC address is treated like a broadcast and is sprayed all
    over the network. STP (spanning tree) will eliminate loops, but
    there's still quite a bit of broadcast (and sometimes multicast)
    traffic.

    Monitoring one local municipal mesh network, all I saw were continuous
    ARP requests from all over the internet. This is one of the first
    things that mesh software and firmware has to fix. I don't know how
    it's done without looking at the code, but my guess(tm) is that they
    might cheat and insert the destination MAC address in the IP header,
    thus preventing the broadcast from propogating more than one hop. The
    routers might also cache ARP requests. Dive into some of the open
    source mesh networking code and see what (if anything) they do about
    the problem.
    <http://opensourcemesh.org> (Meraki based)
    More code:
    <http://opensourcemesh.org/links.html>

    --
    Jeff Liebermann jeffl@cruzio.com
    150 Felker St #D http://www.LearnByDestroying.com
    Santa Cruz CA 95060 http://802.11junk.com
    Skype: JeffLiebermann AE6KS 831-336-2558

  3. #3
    atevewr
    Guest

    Re: Broadcast Forwarding Methodology

    On Feb 15, 11:54*pm, Jeff Liebermann <je...@cruzio.com> wrote:
    > On Mon, 15 Feb 2010 09:54:03 -0800 (PST), atevewr <atev...@gmail.com>
    > wrote:
    >
    > >Can somebody please explain me how the broadcasts work in multihop
    > >wireless networks. Are the packets unicast forwarded or broadcast
    > >forwarded. For e.g. A,B,C,D are four nodes, (A&B) in each other's
    > >range & (B,C & D) in the other range. When A broadcasts a packet, how
    > >will B *forward the packet to C & D ?
    > >Unicast forwarding or it too will broadcast?
    > >If it will be broadcasted, it creates a broadcast storm, How will that
    > >be handled?

    >
    > It depends on the mesh network wireless bridge implimentation. *Most
    > early versions were your worst nightmare, where any packet without a
    > destination MAC address is treated like a broadcast and is sprayed all
    > over the network. *STP (spanning tree) will eliminate loops, but
    > there's still quite a bit of broadcast (and sometimes multicast)
    > traffic.
    >
    > Monitoring one local municipal mesh network, all I saw were continuous
    > ARP requests from all over the internet. *This is one of the first
    > things that mesh software and firmware has to fix. *I don't know how
    > it's done without looking at the code, but my guess(tm) is that they
    > might cheat and insert the destination MAC address in the IP header,
    > thus preventing the broadcast from propogating more than one hop. *The
    > routers might also cache ARP requests. * Dive into some of the open
    > source mesh networking code and see what (if anything) they do about
    > the problem.
    > <http://opensourcemesh.org> *(Meraki based)
    > More code:
    > <http://opensourcemesh.org/links.html>
    >
    > --
    > Jeff Liebermann * * je...@cruzio.com
    > 150 Felker St #D * *http://www.LearnByDestroying.com
    > Santa Cruz CA 95060http://802.11junk.com
    > Skype: JeffLiebermann * * AE6KS * *831-336-2558


    Thank you sir,
    I tried to find some info for some protocols:
    While BATMAN keeps on forwarding the broadcasts
    "OGMs are send
    and repeated as UDP broadcasts, therefore OGMs are flooded until
    every node has received it at least once, or until they got lost
    due
    to packet loss of communication links, or until their TTL (time to
    live) value has expired. "
    OLSR anyways has its MPR's which take the responsibility of doing so.
    Though i am still pondering over how the opportunistic protocols
    handles them. The broadcast information is overheard, so whether the
    broadcasts should be forwarded or not.
    I think i should read a little more.
    Thanks again.

  4. #4
    Jeff Liebermann
    Guest

    Re: Broadcast Forwarding Methodology

    On Tue, 16 Feb 2010 12:26:50 -0800 (PST), atevewr <atevewr@gmail.com>
    wrote:

    >While BATMAN keeps on forwarding the broadcasts
    >"OGMs are send
    > and repeated as UDP broadcasts, therefore OGMs are flooded until
    > every node has received it at least once, or until they got lost
    > due
    > to packet loss of communication links, or until their TTL (time to
    > live) value has expired. "


    <http://tools.ietf.org/html/draft-wunderlich-openmesh-manet-routing-00>
    OGM's (Originator Messages) are just one type of broadcast packet. The
    simply announce that the node is alive and well, which is picked up by
    neighboring nodes in order to establish a (dynamic) route. Section 5
    deals with "Flooding Mechanism" which doesn't mean generating a
    broadcast storm, but instead has something to do with announcing the
    arrival of a new node.
    <http://docwiki.cisco.com/wiki/Internetwork_Design_Guide_--_UDP_Broadcast_Flooding#UDP_Broadcast_Flooding>

    If you drop down to Section 8, there is a list of value ranges.
    Doesn't look like TTL is used to restrict broadcast repropagation.
    Otherwise, there's nothing in the BATMAN spec that talks about other
    types of broacasts.

    >OLSR anyways has its MPR's which take the responsibility of doing so.



    >Though i am still pondering over how the opportunistic protocols
    >handles them. The broadcast information is overheard, so whether the
    >broadcasts should be forwarded or not.
    >I think i should read a little more.


    Sorry, I don't have an instant answer. How it handles broadcasts has
    to be in the code somewhere. However, if you don't find a specific
    mechanism to limit broadcast retransmission (other than STP to prevent
    loops), I think it may default to handling broadcasts exactly as in
    the wired ethernet model, where each packet goes to ALL nodes on the
    network.


    --
    # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
    # 831-336-2558
    # http://802.11junk.com jeffl@cruzio.com
    # http://www.LearnByDestroying.com AE6KS

Similar Threads

  1. Port forwarding problems !!! Please help
    By danial in forum Wireless Networks & Routers
    Replies: 0
    Last Post: 06-20-09, 05:30 AM
  2. Port Forwarding - WebSTAR DPC 2100
    By sharpium64 in forum Wireless Networks & Routers
    Replies: 2
    Last Post: 05-30-09, 03:03 AM
  3. Problem in Port Forwarding for Windows Remote Desktop or VNC
    By Alterego in forum Networking Forum
    Replies: 4
    Last Post: 09-17-08, 09:22 AM
  4. How do I "break" my cable modem (or if I need to)?
    By thepcguy in forum General Broadband Forum
    Replies: 3
    Last Post: 08-11-08, 05:58 AM
  5. my cable modem dissconnects all the time?
    By cableguy2k7 in forum General Broadband Forum
    Replies: 9
    Last Post: 08-01-08, 07:30 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •