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-   -   What are short range link and long range links in routing? (http://www.linuxquestions.org/questions/linux-networking-3/what-are-short-range-link-and-long-range-links-in-routing-735163/)

mq15 06-23-2009 11:52 PM

What are short range link and long range links in routing?
 
Hello friends,
Please get me understand the short range and the long range links from routing (and routing protocols') point of view.
Regards.

JulianTosh 06-24-2009 01:25 AM

Can you please rephrase the question? It's difficult to understand.

mq15 06-25-2009 07:13 AM

Thank you Admiral Beotch for taking consideration..
Actually I am studying an RFC of a routing protocol and there is discussed how to implement link metric to the protocol. The author says:
Quote:

Consider a network with short and long links. Blah blah blah..

JulianTosh 06-25-2009 07:25 AM

Gotcha..

With dynamic routing protocols, you can assign different costs to routes.

Consider having two routes out of your network. Route A is fiber to your ISP. Route B is a DSL line for backup in case the fiber goes down.

In your router config, you can assign a low cost to Route A so that most or all of the traffic goes through that route. Similarly, you can assign a high cost to the DSL line so that relatively little or none goes that way.

Perhaps you have a contract with a carrier that limits your bandwith. Going over a given amount will cost you more per month so you want to make sure you're only using that route when absolutely necessary. A weight/cost assigned to that route keeps packets flowing over the least expensive routes.

Perhaps another route has many hops to a destination which causes some unwanted latency... A weight/cost assingned to that link will make the router decide to avoid that route unless it's main route goes down...

Is that what you were looking for?

mq15 06-26-2009 08:50 PM

Thanks a lot dear Admiral Beotch for your sincere efforts.
Someone said that 802.15.4 might be a simple example for short range links and 802.11 for long range links. I hope this will help you to make me understand the concept.

JulianTosh 06-26-2009 09:46 PM

I think what's needed here is a review of the OSI model... at least my interpretation the first 3 layers.

Layer 1 defines specifications for the medium for transmission of electrical signals. Consider these as examples:
* Cat 5 cabling: send/receive wire pairs, twisted once every x unit
* wireless: 10 channels in the 800-800MHz range

Layer 2 defines frames of information to be transmitted over the lower layer. For example, a frame might contain a total of 128 bits. The first 8 bits are the source device, second 8 bits are the destination device, etc. Each protocol will have it's own definition for the way the information is formatted in it's frame.

This is the extent of what 802.15.4 defines. There is no context for a network under 802.15.4. It only defines a medium of transmission and host addressing.

Layer 3 defines networks which allows for the context of routing. This is something that zigbee is trying to do for 802.15.4 by extending the specification. I dont know anything about zigbee, but I would guess that it defines a network space and methods for moving a packet from one network to another.

Here is a link on encapsulation that might help you understand how short/long range frames interact with higher layer routing: http://en.wikipedia.org/wiki/Encapsulation_(networking)

mq15 06-26-2009 11:16 PM

Thanks a lot Admiral Beotch...
very well explained.


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