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uniqs
9805

thanksforthehelp
@stvincent.org

thanksforthehelp

Anon

preamble

what is the impact does disabling short preamble ? we have handheld devices that we are piloting on our wireless network and this is a setting the manufacturer is recommending. how could this potentially affect other devices such as wireless muse carts that transmit ekgs ?
LLigetfa
join:2006-05-15
Fort Frances, ON

LLigetfa

Member

The theory is that a short preamble leaves more room for data but not all devices play well with it short. A longer preamble means that there is less time for data.

awolfpup
Premium Member
join:2001-01-18
Belleville, IL

awolfpup

Premium Member

What? Where did you pull that from?

Preamble is a pre-set time to live with regard to access points. Settings are long & short or automatic...

Preamble setting determines how long a wireless device will wait for a response back from a wireless access point. If a response is not received before that time expires, the wireless card will hop to another wap[if it has the same SSID] or may hop to another different wap or drop the wireless connection.

By default, wireless waps[WAP/wireless routers/etc] are usually set by the manufacturer to long.
LLigetfa
join:2006-05-15
Fort Frances, ON

1 edit

LLigetfa

Member

Really?
I offer into evidence the following:
»forskningsnett.uninett.n ··· put.html

Take notice of the author's comment on preamble.
quote:
There are two types of PLCP headers. One for long preamble and one for short preamble. One downside to the PLCP is that the PLCP preamble and header is ALWAYS transmitted at 1Mbps, regardless of the transmit rate for the rest of the data. This means that the transfer time is constant at 192 Usec (microseconds) for the PLCP with long preamble. The short preamble version does a bit better, transmitting the shorter preamble at 1Mbps and the header at 2Mbps, shortening the transmit time to 96 Usec.

Lasko
@cox.net

Lasko to thanksforthehelp

Anon

to thanksforthehelp
quote:
Preamble is a pre-set time to live with regard to access points.
Where did that come from. Certainly no 802.11 spec or technical resource.

Short/long preamble applies only to 802.11b or 802.11b/g mixed networks. 802.11a and 802.11g only networks use a different type of preamble.

The preamble is the first thing sent at the very beginning of a data transmission. It is used to allow the receiver to "setup" (Automatic Gain Control adjustment for example) for reception and to synchronize the receiver's clock to the transmitter. Basically it is there to tell the receiver "get ready, there is a message coming".

awolfpup
Premium Member
join:2001-01-18
Belleville, IL

awolfpup

Premium Member

Reference taken from:
»www.intel.com/support/wi ··· 5317.htm

No_Strings

join:2001-11-22
The OC

No_Strings

The cited source confirms the other two definitions offered, not a time-to-live as you suggested.

awolfpup
Premium Member
join:2001-01-18
Belleville, IL

awolfpup

Premium Member

said by No_Strings:

The cited source confirms the other two definitions offered, not a time-to-live as you suggested.
Quoted from the link i notated above:

"The preamble allows the receiver to acquire the wireless signal and synchronize itself with the transmitter."

What do you think happens with the wireless connection, when that "sychronizing" process fails? Although the words are not "time to live" that is exactly the process that is occuring.

======

I work with several brands of wireless devices, and most do not offer a "time to live" option... Preamble is only usually the only option listed on most wireless cards[although the name varies by OEM].

win-xp menu:
start-control panel-network connections- Rt click on your wireless network connection, select properties, click on the configure button, select advanced, more than likely you will not see a "time to live" property entry. Preamble or [PLSC header on most dell laptops] is what is used for the "time-to-live".

No_Strings

join:2001-11-22
The OC

No_Strings

You're confusing me. You said:
Preamble is a pre-set time to live with regard to access points. Settings are long & short or automatic...

Preamble setting determines how long a wireless device will wait for a response back from a wireless access point.
If the preamble is part of the 802.11b/g/whatever standard and most wireless devices do not offer a time to live option (again, your words), how is it that the preamble is used for a time to live?

Additionally, I looked through several write-ups on it and while I am not a whiz at any of this stuff, I didn't find any documents that support your assertion that the client "will hop to another wap[if it has the same SSID] or may hop to another different wap or drop the wireless connection" based on the preamble setting.

I'm not trying to pick a fight or challenge your experience, just trying to get an accurate definition for the next person who happens along and reads this.
LLigetfa
join:2006-05-15
Fort Frances, ON

1 recommendation

LLigetfa

Member

said by No_Strings:

You're confusing me.
Don't feel bad, I too am confused. While awolfpup attempted to discredit my explanation with some "time-to-live" malarky, in the end, his/her link to the Intel document only reinforced what I said.

NotTTL
@cox.net

NotTTL to awolfpup

Anon

to awolfpup
quote:
What do you think happens with the wireless connection, when that "sychronizing" process fails?
The receiver, being broken, may fail to receive the message. The message is sent, of course. Depending on the underlying protocol which caused the message to be sent it may be resent at a later time or just forgotten. Either way it has no effect on the transmission or reception of any other messages.
quote:
Although the words are not "time to live" that is exactly the process that is occuring.
No it is not the process which is occurring. Please read the various definitions of "time to live" and how it is used in networking and RF transmission/reception.
stevech0
join:2006-09-17
San Diego, CA

1 edit

stevech0

Member

The preamble is also when the w-router's AP function decides which antenna to use - switched diversity.

awolfpup
Premium Member
join:2001-01-18
Belleville, IL

awolfpup to LLigetfa

Premium Member

to LLigetfa
said by LLigetfa:

While awolfpup attempted to discredit my explanation with some "time-to-live" malarky..
From the other posts I've seen of yours in this forum, your credibility was already thin...an your calling my information malarky... you just lost what little cred you had remaining with me...
said by LLigetfa:

in the end, his/her link to the Intel document...
At least I cited a source of information from a wireless manufacturer, Intel; as in Intel Pro Set Wireless cards. I looked over that link of yours, not much information regarding wap's, or any hardware for that matter.
said by NotTTL :

The receiver, being broken, may fail to receive the message.
What? The reciever in this case is the wireless card that is on person's laptop. I highly doubt that with the 1,000's of wireless using customers I have worked with over the years that their wireless card were defective when it failed to maintain a wireless connection to the wap.

Especially, when changing their preamble setting to Long Only, which matches the setting of the wireless WAPs and wireless routers default setting. This stabalized their wireless connection to the wap and were able to use the internet connection in their guest room.

An yes, if the wireless card does not receive a response within the set amount of time[on the long setting = 192 usec (microseconds) or if using the short setting = 96 usec (microseconds)], the wireless card will jump to another wap[if any in range] or drop the connection altogether.

Which brings us back to the original reason of this person's posting. What will be the impact of using short or long preamble.

The impact will be, that since most[if not all] WAP's currently on the market transmit on the long preamble setting[by default], if a laptop/PDA/or any other wireless device may lose its wireless connection easier due to the shorter span of time 96 usec as opposed to the longer 192 usec. By using the Long Preamble, when interference is encountered between the transmitting wap and the wireless receiving device; there will be greater leeway of the wap/or wireless device to not drop the signal during transmission of data.
Tom Blue
join:2007-09-17
MN, USA

Tom Blue to thanksforthehelp

Member

to thanksforthehelp
Whose preamble is bigger?
LLigetfa
join:2006-05-15
Fort Frances, ON

LLigetfa

Member

Dunno... lost all my cred. If mine lasts more than four hours, I'm calling my doctor.

I still stand by my first post. The OP wanted to know what the effect was on existing clients when switching from short to long. The long preamble will consume more of the timeslot so there will be a slight reduction in overall efficiency. I haven't seen anything to the contrary to discredit that.

Killer Max
@sunwave.com.br

Killer Max to awolfpup

Anon

to awolfpup
said by awolfpup:

By using the Long Preamble, when interference is encountered between the transmitting wap and the wireless receiving device; there will be greater leeway of the wap/or wireless device to not drop the signal during transmission of data.
That's one impact. There is a tradeoff here. With a long preamble, more time is taken by the preamble. Given that the AP and clients are sharing the channel, each AP has less time to transmit the data. Less time to transmit = lower bandwidth.

nobody7
join:2001-01-30
Mayer, MN

nobody7 to thanksforthehelp

Member

to thanksforthehelp
Wow, has turned to a huge ballywho hasn't it? From my understanding everyone is right on this. The PLCP preamble (128 vs 56bytes) size does indeed effect the overall throughput on the RF channel since it takes up more room on the overall packet size. However in 802.11b systems it is used as a "listen before talk" collision aviodance. For those in the RF world the preamble sets up the resources for a client to transmit data. All other radios that can hear the preamble will not transmit to the AP during this time to avoide packet collision in the RF channel.

I think Lasko's answer was the best one so far. This really only matters where you have mix B/G networks. B radios MUST support long preamble. I think latency may be the one thing to worry about especially since you are working in a hosptial. Defaulting to Long Preamble will give you a slight increase in latency. Have you contacted your GE rep to see what preambles are used on the MUSE/MobileLink ECG carts? The whole point of those devices is to quickly get patient data to doctors. Also what is your wireless solution? Some commerical solutions deal with mixed B/G networks differently so that should be taken into account as well.