Re: [WISPA] PAcket loss with CSMA/CA

2006-12-28 Thread Jack Unger

Tom,

After making several retransmission attempts and still not getting a 
packet through, the radio will discard the packet and move on to sending 
the next packet. In other words, the packet is lost. Often, depending on 
the radio or the operating system, the number of retransmission attempts 
made before the packet is discarded is software-configurable. One 
typical default value for the number of retransmission attempts is eight.


jack


Tom DeReggi wrote:

I just installed a PTP 900Mhz Atheros SR9 StarOSV3 link that had 5% 
packet loss that I could not get rid of.

(Set 12mbps modulation, and averaged greater than 20db SNR.)

In theory, CSMA/CA should not get PAcket loss, like a TDD system might, 
as the CSMA waits for acknowledment and re-transmits if it does not get 
it, Wifi's built-in native ARQ.


I was not surprices to see Latency skyrocket, or retransmisson to sky 
rocket, but I was surprised to see uncorrectable 5% packetloss.
Any ideas on why it occured.  Meaning why 802.11 MAC didn't self correct 
the packet loss with its native re-transmission?


Tom DeReggi
RapidDSL  Wireless, Inc
IntAirNet- Fixed Wireless Broadband


- Original Message - From: Charles Wu [EMAIL PROTECTED]
To: 'WISPA General List' wireless@wispa.org
Sent: Thursday, December 28, 2006 4:47 PM
Subject: RE: [WISPA] Alvarion Comnet Radios have arrived - 
regardinginterference - Part 1



I go to see Mickey Mouse for a few days and look where this thread has
gone...wow

So, my 2 cents...

One of the largest concerns in the license-exempt world is the question 
of a

system's interference robustness.  However, before we can get into further
detail on the pros and cons of Alvarion VL vs Canopy, CSMA/CA vs GPS, 
etc --

it is necessary to realize that interference as a term is extremely broad
and vague, and can mean just about anything to anyone.  Heck, all radios in
the market have some sort of interference robustness / avoidance
capability -- the trick to understanding a system's capabilities is 
knowing

what TYPE of interference the system can actually handle.  Read on...I'll
talk more about each particular platform when I get some time to write Part
2 =)



WHAT IS INTERERENCE?

In the wireless world, interference, by definition, is a situation where
unwanted radio signals operate in the same frequency channels or bands -
i.e. they mutually interfere, disrupt or add to the overall noise 
level in

the intended transmission.

Interference can be divided into two forms, based on whether it comes from
your own network(s) or from an outside source.  If the interfering RF
signals emanate from a network under your control, whether it is on the 
same

tower or several miles away, it is termed self-interference.  If the
opposing signals come from a network, device or other source that is not
under your control, it is termed outside interference.  Thus, the
definition of what type of interference is being combated is not based on
technology, but ownership.

In licensed bands, where spectrum is relatively scarce (due to high costs)
self-interference alone must be taken into account; however given a more or
less known operating environment (the radio spectrum will only have signals
transmitting that are under control by a single entity) proper product
design and network deployment can reduce these interferes to a level where
they do not impact network performance.

Self-interference is not a phenomenon that is confined to licensed band
operations; license-exempt bands must address the same issues.  The
techniques and design elements of a given product that serve to reduce and
tame self-interference in licensed band operations can be applied directly
to license-exempt systems.

THE LICENSE-EXEMPT CHALLENGE OF INTERFERENCE

In the license-exempt bands, not only must self-interference be accounted
for, but, given the nature of the regulations governing these bands,
external interference must be designed for as well.  This can be extremely
challenging, as there is no way of knowing in advance where these outside
signals may be or will be sourced from, or even how strong the interfering
transmissions will be relative to the desired transmission.  This aspect of
the license-exempt bands represents the possible downside of
license-exempt network operation.

Yet as potentially damaging and unpredictable as external interference can
be in license-exempt networks, a properly designed and implemented 
broadband

wireless system can make a significant difference in the performance of a
network under siege from unwanted external radio transmissions.

DEALING WITH COCHANNEL INTERFERENCE: PHY LAYER

1. Modulation  the C/I Ratio

At the most fundamental level, an interfering RF source disrupts the 
digital

transmission by making it too difficult for the receiving station to
decode the signal.  How much noise or interference a digital RF
transmission can tolerate depends on the modulation used.

Fundamentally, modulation is the method 

RE: [WISPA] PAcket loss with CSMA/CA

2006-12-28 Thread Gino A. Villarini
Imho, packet loss on your system is happening when the latency or retrans is
exceeding the tcp timeout ..?

Gino A. Villarini
[EMAIL PROTECTED]
Aeronet Wireless Broadband Corp.
tel  787.273.4143   fax   787.273.4145

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Tom DeReggi
Sent: Thursday, December 28, 2006 8:11 PM
To: WISPA General List
Subject: [WISPA] PAcket loss with CSMA/CA

I just installed a PTP 900Mhz Atheros SR9 StarOSV3 link that had 5% packet 
loss that I could not get rid of.
(Set 12mbps modulation, and averaged greater than 20db SNR.)

In theory, CSMA/CA should not get PAcket loss, like a TDD system might, as 
the CSMA waits for acknowledment and re-transmits if it does not get it, 
Wifi's built-in native ARQ.

I was not surprices to see Latency skyrocket, or retransmisson to sky 
rocket, but I was surprised to see uncorrectable 5% packetloss.
Any ideas on why it occured.  Meaning why 802.11 MAC didn't self correct the

packet loss with its native re-transmission?

Tom DeReggi
RapidDSL  Wireless, Inc
IntAirNet- Fixed Wireless Broadband


- Original Message - 
From: Charles Wu [EMAIL PROTECTED]
To: 'WISPA General List' wireless@wispa.org
Sent: Thursday, December 28, 2006 4:47 PM
Subject: RE: [WISPA] Alvarion Comnet Radios have arrived - 
regardinginterference - Part 1


I go to see Mickey Mouse for a few days and look where this thread has
gone...wow

So, my 2 cents...

One of the largest concerns in the license-exempt world is the question of a
system's interference robustness.  However, before we can get into further
detail on the pros and cons of Alvarion VL vs Canopy, CSMA/CA vs GPS, etc --
it is necessary to realize that interference as a term is extremely broad
and vague, and can mean just about anything to anyone.  Heck, all radios in
the market have some sort of interference robustness / avoidance
capability -- the trick to understanding a system's capabilities is knowing
what TYPE of interference the system can actually handle.  Read on...I'll
talk more about each particular platform when I get some time to write Part
2 =)



WHAT IS INTERERENCE?

In the wireless world, interference, by definition, is a situation where
unwanted radio signals operate in the same frequency channels or bands -
i.e. they mutually interfere, disrupt or add to the overall noise level in
the intended transmission.

Interference can be divided into two forms, based on whether it comes from
your own network(s) or from an outside source.  If the interfering RF
signals emanate from a network under your control, whether it is on the same
tower or several miles away, it is termed self-interference.  If the
opposing signals come from a network, device or other source that is not
under your control, it is termed outside interference.  Thus, the
definition of what type of interference is being combated is not based on
technology, but ownership.

In licensed bands, where spectrum is relatively scarce (due to high costs)
self-interference alone must be taken into account; however given a more or
less known operating environment (the radio spectrum will only have signals
transmitting that are under control by a single entity) proper product
design and network deployment can reduce these interferes to a level where
they do not impact network performance.

Self-interference is not a phenomenon that is confined to licensed band
operations; license-exempt bands must address the same issues.  The
techniques and design elements of a given product that serve to reduce and
tame self-interference in licensed band operations can be applied directly
to license-exempt systems.

THE LICENSE-EXEMPT CHALLENGE OF INTERFERENCE

In the license-exempt bands, not only must self-interference be accounted
for, but, given the nature of the regulations governing these bands,
external interference must be designed for as well.  This can be extremely
challenging, as there is no way of knowing in advance where these outside
signals may be or will be sourced from, or even how strong the interfering
transmissions will be relative to the desired transmission.  This aspect of
the license-exempt bands represents the possible downside of
license-exempt network operation.

Yet as potentially damaging and unpredictable as external interference can
be in license-exempt networks, a properly designed and implemented broadband
wireless system can make a significant difference in the performance of a
network under siege from unwanted external radio transmissions.

DEALING WITH COCHANNEL INTERFERENCE: PHY LAYER

1. Modulation  the C/I Ratio

At the most fundamental level, an interfering RF source disrupts the digital
transmission by making it too difficult for the receiving station to
decode the signal.  How much noise or interference a digital RF
transmission can tolerate depends on the modulation used.

Fundamentally, modulation is the method whereby zeros and ones are
communicated by varying one of three