Frame Realay Encapsulation Question

Maybe I didn't explain myself clearly.

Router====>Frame Cloud=====>Router


I thought that only the Routers would be concerned with the encapsulation type; so it wouldn't matter what made up the "Frame Cloud". I am thinking that the frame cloud is normally made up of switches so they don't care about the encapsulation type? But, in the case of the question, the frame cloud is made up of a specific non-Cisco router. I'm not sure if this makes a difference or not.

I know that the LMI types must match between the Routers and the Frame Cloud, but I thought only the Routers cared about the encapsulation type regardless of what device makes up the frame cloud.

Thanks for the reply S0lo,

The testing program said my answer of cisco was wrong. Maybe the software has an error?

Do you remember what other answers were available ?

I found the exact question:

Your manager has given you the task of connecting the Cisco routers in several branch offices to a Frame Relay service provider. Your service provider uses StartNet routers to provide this service.

Which encapsulation type should you configure the Cisco routers to use?

a) Cisco
b) IETF
c) Q.933A
d) ANSI

As previously stated, I thought only the end-points DTEs cared about the encapsulation type and the frame cloud cared about the LMI type.

As previously stated, I thought only the end-points DTEs cared about the encapsulation type and the frame cloud cared about the LMI type.

Yup, same as what I was thinking. I guess if the question was:

Which LMI type should you configure the Cisco routers to use?

then possible answers would have been Q.933A and ANSI. Besides, I never heard of "encapsulation type", it's always either just "encapsulation" or "lmi type". May be the question needs to be revised.

The first node you hit on ingress to the provider (PER) is not a switch but a router card on a switch which acts as an access integrator muxing different subrates to get further along towards the backbone transport speed/method. It needs to know the frame header type (how the packet is encapsulated) if not it can't do proper SAR of large packets if it doesn't know which stop bits to look for to strip. Despite the transport method, the backbone is usually always ATM in legacy providers (pure IP MPLS of late in next gen networks of newer providers) which uses fixed length packets (53 bytes I think) and your larger frame packets need to be segmented into 48 byte cells with 5 byte headers (=53 bytes) and then reassembled (SAR) as they egress the other side and get encapsulated in frame again. If it isn't IETF specified, Cisco will use it's proprietary encapsulation and if the PER is a non-Cisco device it will treat the SAR differently based on what IETF specifies as the demarc for the encapsulation resulting in dropped packets.

The question is very real and very important for distinction between the two types of encapsulation in real-world practice.

Humm... still now sure why the other source said the encapsilation type only matters to the DTEs.