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bharathi says...

In one of my previous blog entry, I shared my understanding about the minimum Ethernet Frame Size. In this entry, I am sharing my understanding about the relationship between the Minimum Ethernet Frame/Packet Size and the Ethernet Cable Length.

Now We are going to find the maximum cable length for the old 10Mbps (10Base5) Ethernet network:

Minimum Ethernet Frame size = 64bytes = 512bits

Propagation Delay/ Signal speed on cable = 200m/us

Time to transmit one bit in 10Mbps = (1000ms * 1000us * 1000ns) / 10000000 bits = 100ns

Time to transmit the minimum Frame = (100ns * 512bits) = 51.2us

Length of the cable = speed * min frame TX time = 200m * 51us = 10200m = 10Km.

The maximum Ethernet cable length is 10Km. Is it right?? NO!!. Why?? The 51.2us is the Round Trip Delay(RTD). So the 10Km is Round Trip Distance and the actual length is 10Km/2 = 5Km.

The new maximum cable length is 5KM. Is it right?? NO!!. Why?? To answer this Qus, we will see more details. The maximum length of the one segment of old 10Base5 cable is only 500m. To make an 1Km cable, 2 segments can be connected (500 + 500) using a repeater. The repeater device in the middle will also introduce some delay. Old repeater will add 3us delay in the one way and 6us is the two way delay.

To make a 5Km cable, we need 10 cable segments and 9 repeaters. The repeaters alone add nearly 54us delay in the path, which is more then the time to transmit the minimum frame. For us, the total round trip delay should be with-in 51us. The available options are, reduce the total length of the cable and reduce the number of repeaters in the middle. In the total delay, delay introduced by repeaters should not be greater then 50%. So the new formula is (25us + 25us) = 50us.

No of repeaters that introduce 25us delay = 25/6 = 4 Repeaters

Cable length that introduce 25us RTD = (25 * 200m) / 2 = 2500m = 2.5Km

The maximum cable length for the 10Mbps Ethernet network is 2.5Km, which can be made using 5 cable segments and 4 repeaters.

In the recent years, Ethernet device speed is increased by 10 and 100 times. Due to this, the sender transmits the frame faster. As per CSMA/CA, the collision will be detected only before the end of the packet transmission. So if we maintain the same frames size and cable length, then a station will transmit a frame too fast (very much less then 50us), and not detect a collision occurs at the other end of the cable. To avoid this, we have to maintain the maximum cable length and increase the minimum frame size OR maintain the slot time same and decrease the maximum cable length OR both increase the slot time and decrease the maximum cable length. For example, in 100Mbps network, the cable length is reduced to 500m and in 1Gbps network, minimum Ethernet frame/packet size is increased to 256 or 512 bytes.

Let see the calculation behind the length reduction in 100Mbps network:

Time to transmit one bit in 100Mbps = (1000ms * 1000us * 1000ns) / 100000000 bits = 10ns

Time to transmit the minimum Frame = (10ns * 512bits) = 5.12us

Length of the cable = speed * min frame TX time = 200m * 5us = 1000m = 1Km (Round Trip Length).

The one way length is 500m. But the practical limit is around  200m.

Effect of Duplex Mode in Cable Length:

The old Ethernet network was using the coaxial cable and all systems are connected in that cable. In this transmission and reception is on the same medium, but on the same time. Because it is not an collision free environment. This is called Half-Duplex mode and in this CSMA/CD will help to detect the collisions.

The new Ethernet device with IEEE 802.3x standard are having capability to transmit and receive in a independent point to point link (PC to PC or PC to Hub/Switch) on CAT UTP cables. This made the link as collision free and the need of CSMA/CD protocol is removed. This mode of transmission is called Full-Duplex. In this, throughput of the link is doubled, time wasted due to the collision is removed and cable can be increased.

Let see how the cable length can be increased in Full-Duplex mode:

In half-duplex mode, after transmission of a packet, device should change to receive mode. So there was hard limit in the timing requirements to ensure collisions are propagated to all system within the required 512 bit times. In Full-Duplex mode this limitation is removed, because Tx and Rx independent. So larger diameter area (1~2Km) can be covered.

Filed under: network

Browny says...

Filed under: car, network, tech

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David Hanscom's Reflection Video Series #6 features former NFL Pro Bowl Kicker Mike Hollis. Mike shares his story of achieving success even when you are not sure you have what it takes to make it.

Filed under: david, dreams, friendship, goals, hanscom, hollis, marketing, mike, network, passion, relationships, social

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David Hanscom's Reflection Video Series #6 features former NFL Pro Bowl Kicker Mike Hollis. Mike shares his story of achieving success even when you are not sure you have what it takes to make it.

Filed under: david, dreams, friendship, goals, hanscom, hollis, marketing, mike, network, passion, relationships, social

(download)

David Hanscom's Reflection Video Series #6 features former NFL Pro Bowl Kicker Mike Hollis. Mike shares his story of achieving success even when you are not sure you have what it takes to make it.

Filed under: david, dreams, friendship, goals, hanscom, hollis, marketing, mike, network, passion, relationships, social

D says...

Today was the Internet Anniversary celebration at its birthplace, UCLA. This celebratory event was co-organized by Brad Fidler. Read his press release here. There were several great ones, (see them), but here is DARPA director, Dr. Regina E. Dugan's talk.

She speaks of: women of science are going to save the day & changing the image of science ('we're smokin' hot. so that is progress, real progress'); challenges; iconic discovery; going viral; networking; these being serious times that require the best of all of us. And best, in my opinion, we need the wonder. A History of Science perspective: this.is.gold. The call-to-serve article she cites is attached.

http://www.darpa.mil/directorbio.html

Filed under: DARPA, discovery, history of science, IA40, internet, network, privacy, talks, UCLA, viral, women in science, wonder

Min ven Jakob har bedt mig dele følgende med mit netværk:

Pga. sygdom søger vi til øjeblikkelig besættelse en vikar til vores Film-team i YouSee's Produktudviklingsafdeling. Stillingen er fuldtid frem til nytår og lønnen er 150 kr. eller lignende i timen. Vi kan som udgangspunkt ikke tilbyde en ansættelse efterfølgende, men omvendt er det jo altid en fordel at have fået en fod indenfor døren. Derudover vil man få chancen for at stifte bekendtskab med produktudviklingsafdelingen i Danmarks største tv-distributør.

Arbejdsopgaverne består i at lægge de nye film på vores IPTV, Digital Kabel-TV og web-tv platform, inklusiv covers og meta-data (beskrivelser, genrer etc.). Hvis man har en smule erfaring med at anvende et CMS eller lignende vil det være til at lære ganske hurtigt.

Jakob kan kontaktes på

js@yousee.dk
30788452

Filed under: film, friend, friends, job, network, YouSee

Google Social Search is an experimental feature that helps you find relevant public web content from people in your social circle, when you're signed in to your Google Account. For example, search for [ restaurants ], and restaurant reviews by your friends and other contacts may appear more prominently in your results. Join the Social Search experiment at http://www.google.com/experimental

Social Search adds relevant content from your contacts to your results.

When you join the Social Search experiment, Google may bring up results from your friends and other contacts. These special results appear at the bottom of the search results page, in a section labeled "Results from people in your social circle."

Today brings news of the experimental launch of Google Social Search within Google Labs. According to Google:

With Social Search, you'll be able to more easily find relevant public content from your social circle, such as the following:

  • Websites, blogs, public profiles, and other content linked from your friends' Google profiles. 
  • Web content, such as status updates, tweets, and reviews, from social services that your friends have listed in their Google profiles. 
  • Relevant articles from your Google Reader subscriptions.

In the video example above, Google suggests that if, for example, I'm trying to decide whether to get an iPhone or a Bla ckBerry, Social Search can help me by providing relevant content from my friends (or friends of friends). After all, this is typically how we make purchases in real life - relying on the judgments of people we trust.

What potential implications for privacy does this feature have? Does Google retain some knowledge of your social graph after the search has been completed? I'm not sure as of yet, but if anyone knows, please feel free to comment.

Filed under: experimental, google, labs, network, privacy, search, social, socialsearch

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David Hanscom's Reflections Video Series #5 is about Rolling Up Your sleeves and getting to work so you don't loose your shirt. Work hard and make it a Successful Day!

Filed under: david, dreams, friendship, goals, hanscom, marketing, network, passion, relationships, social

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David Hanscom's Reflections Video Series #4 is about being a Bright shining Candle and not being afraid to help your team be bright shining candles as well. "A candle loses nothing by lighting another candle."

Filed under: david, dreams, friendship, goals, hanscom, marketing, network, passion, relationships, social