RE: [smartBridges] RTS / CTS

[Seeni Mohamed]

Even though the multipath reflections can be resolvable by changing the polarization or rotate the antenna to the certain degree or moving the radio to another location, the RTS/CTS settings may help in certain environment conditions.   Kind regards, Seeni sB Tech Support     -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of shoffman Sent: Wednesday, November 26, 2003 9:41 PM To: [EMAIL PROTECTED] Subject: RE: [smartBridges] RTS / CTS   Seeni,   Are you not talking about Frag level when you are talking fixing the Multi-path problem?  I mean, all that RTS is going to do is to ask the AP to shut everyone else up while I transmit.. but my transmission will still be multi-pathed, so guess what.. I still get failure and have to re- transmit.  With your description, reducing the packet size, thus giving a better chance for a packet to get there without the multi-path interference, would be increased...   I guess I am missing something here too..   Scott     -----Original Message----- From: "Seeni Mohamed" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Date: Wed, 26 Nov 2003 21:17:48 +0800 Subject: RE: [smartBridges] RTS / CTS   > Hi Brian, > > Multipath is a form of RF interference that occurs when a radio signal > has more than one path between the receiver and the transmitter. > Multipath propagation occurs when RF signals take different paths when > traveling from a source to a destination. A portion of the signal might > go directly to the destination, while another part might bounce off an > obstruction or ceiling, then on to the destination. As a result, some > of > the signal encounters delay and travels longer paths to the > destination. > > If the delays are great enough, bit errors in the packet occur. The > receiver can't distinguish the packets and interpret the corresponding > bits correctly. The receiving station detects the error in the packets. > It means, the cyclic redundancy check (CRC) checksum does not compute > correctly, indicating that there is error in the packet. In response to > the bit errors, the receiving station does not send an acknowledgment > to > the sending station. The sender eventually retransmits the signal after > regaining access to the medium. Because of the re-transmissions, users > encounter lower throughput when Multipath interference is significant. > > Due to multiple re-transmissions, the default value (RTS/CTS) may not > able to deliver the packet with original size. In such condition, > adjusting or reducing the RTS/CTS value will improve the efficiency in > the data transmission. > > You can use the RTS/CTS adjustment to overcome the effects of HIDDEN > NODE. The default value works great in the environment where all the > clients can hear each other such as indoor wireless LAN. However, in an > outdoor environment, not all the clients can hear from one each other. > If the clients located far away, neither one can hear the other. For > example, if the clients are uploading/downloading large file size at a > same time. That means data being transmitted simultaneously, which > results in a COLLISION. Whenever there is a collision, both clients > have > to re-transmit at a same time. > > That is the reason the hidden node is a problem when there is many > clients talking to the same AP at same time. None of them knows when > the > others are talking, so it will end of with collisions all over the > place. A lot of collisions results in a lot of re-transmissions which > will reduce the overall throughput at the CPE end. > > Due to multiple re-transmissions, the RTS/CTS adjustment is necessary > to > overcome the packet loss and throughput problem. > > I hope above info helps to understand the RTS/CTS adjustment for the > Multipath interference and Hidden node issues. > >  > >  > > Kind regards, > > Seeni > > sB Tech Support > >  > >  > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Brian Winter > Sent: Wednesday, November 26, 2003 7:30 PM > To: [EMAIL PROTECTED] > Subject: Re: [smartBridges] RTS / CTS > >  > > Hi Seeni, > >  > > Could you please explain how rts/cts combats multipath or any other > interference (ie not my or other users real traffic).  I thought it was > used to tell the far end (AP), and subsequently other in range clients > (by cts) to shut up while I get on with my transmission and hear the > ack.  I understood that it temporarily stops real traffic, useful on a > busy contentious system, - not interference.  Efficiency is only > improved as collisions are reduced.   Am I missing something ? > > ----- Original Message ----- > > From: Seeni <mailto:[EMAIL PROTECTED]>  Mohamed > > To: [EMAIL PROTECTED] > > Sent: Wednesday, November 26, 2003 10:35 AM > > Subject: RE: [smartBridges] RTS / CTS > >  > > The RTS/CTS adjustment is required ONLY in the CPE devices when there > is > poor performance due to MULTIPATH INTERFERENCE and many HIDDEN NODES > which will result in packet loss. Sometimes when we deal with higher > interference then we need to lower down the RTS/CTS values to improve > the efficiency in the packet transmission which avoids the packet loss. > > Normally, RTS/CTS adjustment is NOT required in the AP side. RTS/CTS > only comes into play when a client is transmitting and it does nothing > for the receive traffic. > >  > > Kind regards, > > Seeni > > sB Tech Support > >  > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of TJ Burbank > Sent: Wednesday, November 26, 2003 9:18 AM > To: [EMAIL PROTECTED] > Subject: [smartBridges] RTS / CTS > >  > > I am curious what the best values for a network with 30 bridges per AP, > and a 1.5MB backbone would be.  > >  > > I guess I am not certain if changing the RTS / CTS values on customer > bridges will help in increasing netork load and capacity. > >  > > If you change the RTS / CTS values on the CPE is is neccesary to change > them on the AP? > >  > > Thanks, > >  > > -TJ > > Last Mile Wireless > >   The PART-15.ORG smartBridges Discussion List To Join: mailto:[EMAIL PROTECTED] (in the body type subscribe smartBridges <yournickname> To Remove: mailto:[EMAIL PROTECTED] (in the body type unsubscribe smartBridges) Archives: http://archives.part-15.org