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WAN and LAN

Posted on 2004-04-10
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Would you expect queueing delays, access delays, and propagation delays to be longer on a LAN or on a WAN?  Please explain the answer.
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Question by:rnr333
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by:pseudocyber
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WAN.  Wide Area Networks cover longer distances and are usually over slower media than Local Area Networks.

A LAN can typically send and receive traffic up to a theoretical maximum of 100Mbps.  However, when that data stream reaches a WAN device, such as an Internet Router - speeds typically drop to between 10Mbps and 1Mbps or even lower.  Therefore, the data stream must be queued for transmission onto the slower WAN medium.
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Beachdude67 earned 200 total points
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I'd expect longer delays over a WAN than over a LAN. Over a LAN (local area network) you can pretty much expect that the media is going to run at 100Mbps (100megabits per second) or faster. You might find the odd 10 mbps card here or there, but for the most part you'll have either cat 5 cable running over the LAN or wireless capable of comparable speeds. There are few factors within an office that will cause real propagation or queing delays, and those factors are usually rooted out by the IT staff in short order (things like fans, refridgerators, etc being too close to network cabling can cause problems)

However, WANs often tend to connect via slower internet links. It isn't uncommon to find an office on a WAN connecting at 56k over a modem and logging into a Windows 2000 or Netware server remotely. Even if the company spends the big bucks and gives broadband connections of one form or another to all the branches of the WAN, the fasted they tend to connect is 10 mbps - and that is in idea conditions. Those speeds usually hit around 500k because everyone has to share them.

To further answer this question, consider a Netware network spread out across a WAN. User A logs in to a local server via NDS, which is connected to 9 other netware servers. The login process locally is fast, but in order to keep the NDS database consistent, it has to send updates to the other servers. If the tree is well designed, it might send the updates to just two or three other servers. But over a big WAN with a lot of servers, all of which are sending updates every time someone logs in, out, changes their password, etc - well, it can get hairy - especially if one or more of the servers has to use a 56k connection to update the database. The same principle applies to Active Directory in Windows 2000.

LANs rarely have this sort of problem, even a large LAN. The bandwidth is generally sufficient to take care of mess, and if it isn't the admin can always upgrade his bandwidth by installing gigabit cards and switches.

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