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TOPIC: Question about 802.3 LAN connected to 802.5 LAN , need help

Question about 802.3 LAN connected to 802.5 LAN , need help 13 years 2 days ago #1869

  • ckcheong2
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I have a question below, and need the answer fast .. pls help

Suppose a bridge connects an 802.3 (Ethernet) LAN to an 802.5 (Token Ring) LAN as shown in the figure below. Of the bridge forwards a frame from the Token Ring to the Ethernet, answer the following questions:

1. Does the bridge need to recalculate the value of the CRC field? How?

2. How is the priority before the Token Ring set?
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Re: Question about 802.3 LAN connected to 802.5 LAN , need help 13 years 2 days ago #1870

  • sahirh
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I think your image didn't embed..
Sahir Hidayatullah.
Firewall.cx Staff - Associate Editor & Security Advisor
tftfotw.blogspot.com
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Re: Question about 802.3 LAN connected to 802.5 LAN , need help 13 years 2 days ago #1872

  • tfs
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First of all, I can't find the figure below - I guess you forgot. But that doesn't matter here.

First of all, I don't know how much you know about token ring, but it is a completely different protocol from ethernet, which is why you need a bridge or router to handle the conversion.

In the token ring case, you have one token (actually you can have many, but they will be in order) that goes around a virtual ring (because of the MAU - which is like a switch - but not really), and each station gets a look at the token in order. If you are using a router, it will become part of the ring. It isn't like ethernet where you can just hook up and start shouting "here I am - can I use the wire now". You only get to talk on the wire when the token gets to you.

I am not sure why you are worrying about the CRC or priorty flag, here are a couple of articles on the differences. There are a lot of others, but I am not sure what you are looking for.

www.ibiblio.org/mdw/HOWTO/Token-Ring/qanda.html

www.faqs.org/faqs/LANs/token-ring-faq/

If you go to google and use: bridge "token ring" ethernet - you should see quite a bit there.

When we converted our system from Token ring to Ethernet, it was quite easy as we used our Cisco router that had a token ring port and an ethernet port. Worked like a charm.
Thanks,

Tom
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Re: Question about 802.3 LAN connected to 802.5 LAN , need help 13 years 2 days ago #1886

  • ckcheong2
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I cann't find any of the information , either regarding the recalculating the value of CRC field or The priority of the token ring.
this is a assignment question ... I have try to search the net under "Internetworking" , "802.3 to 802.5" and "token Ring & Ethernet" .. but non of the site talking about these of give much info on these .

for question 1 on the CRC fields , if the bridge forwards a frame from the token ring to the ethernet, that's mean the bridge received the frame from Token Ring and then forward it to Ethernet , is the ethernet side need to do the error checking or the bridge itself also need to strip off the frame and do the checking ???? Is the bridge need to recalculated the value of the CRC field from the token ring before the bridge forward it to the ethernet ??

For question 2 on the priority set , same case , if the bridge forwards a frame from the token ring then forward it to the ethernet, how is the priority before the Token Ring set ? is that mean the priority that a frame have before the token ring set the priority on it ??

I cann't understand what is the question asking about... and I try to find the infomation in the net but I can find any so far .... The question is asking about Token Ring/Ethernet or asking about Bridging (the function of the bridge) ??? Pls help ...
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