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Community Member

nbma, frame relay

Can anyone one tell me why frame realy is nbma, also are any other WAN services nbma ?

3 REPLIES
Community Member

Re: nbma, frame relay

Good question!

Frame-relay is layer 2 as is ethernet, for example. Therefore lets examine these 2 layer-2 addressing schemes; DLCI and MAC. DLCI addresses do not have a broadcast functionallity whereas MAC addresses do (ffff.ffff.ffff).

Both technologies are multiple access - meaning the layer 2 segment can support more than 2 hosts. So, how do you find the host you want to talk to? You build a map. ARP does this for ethernet and inverse-arp, or manual mappings, does the same for Frame-relay. Based on this map, traffic is sent directly to the relevant destination/next-hop.

Because ethernet has only one access/path on to the medium, it can basically shout and everyone will hear. FR, on the other hand, can have many logical paths onto the medium and no way of referencing 'everyone', therefore is not broadcast capable.

ATM has similar issues.

Not sure if I explained it well, or if the answer cleares it up for you, but I hope it helps a bit.

Community Member

Re: nbma, frame relay

you say frame relay is layer 2, does this mean you still have to route accross it or could you configure it like a bridge ?

Community Member

Re: nbma, frame relay

as you can see from the name of frame-relay, the meaning of relay is that the frame received from one segment will be relayed to another segment base on the map of frame-relay switching device. so you can treat frame-relay as point to point link, that is easy to understand why frame-relay can not have the broadcast ability as ethernet.

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