NBMA protocols, per se, do not carry protocol type information in the
same that Ethernet does. On the other hand, neither do 802.3, 802.5,
or FDDI. The protocol type information for 802.3 is carried inside
an 802.2 LLC/SNAP header at the start of the data field.
And there are similar mechanisms for WANs:
RFC 2427 Multiprotocol Interconnect over Frame Relay. C. Brown, A. Malis.
September 1998.
RFC 2684 Multiprotocol Encapsulation over ATM Adaptation Layer 5. D.
Grossman, J. Heinanen. September 1999.
It isn't always necessary, however, to identify the payload protocol.
When there is only one protocol in use, or there is little additional
cost to each VC so you can configure one VC per protocol, most
implementations allow you to configure both ends of a VC to support a
single fixed payload protocol type. Saves 5 bytes per frame, which
might even be significant on a slow FR link.
>Hi all,
>
>As I understand it the frame header has stuff like the addresses,
>BECN's, FECN's and the like but no place to indicate upper layer
>protocols even exist. The upper layer stuff is in the data envelope
>portion of the frame packet(frame) therfore the frame relay service
>cannot directly push the details to the next (upper) layer. A
>device must be used to strip the frame header off then read the
>packet and find where it goes from there.
>
>Int this way frame is different to ethernet or token ring in that
>they have a field that points directly to the upper layers.
>
>Just my way of viewing it
>
>Teunis,
>Hobart, Tasmania
>Australia
>
>
>n Thursday, February 01, 2001 at 04:34:56 PM, Pierre-Alex wrote:
>
>> Understood but there must be a field in a frame relay packet that let Layer
>> 2 know which Layer 3 protocol should receive the data. Something like a
>> service access point. Don't you agree? Or maybe that is the role of the
>> command frame-relay map ip ...
>>
>> -----Original Message-----
>> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
>> Rik Guyler
>> Sent: Thursday, February 01, 2001 8:29 AM
>> To: Cisco Groupstudy (E-mail)
>> Subject: RE: Frame Relay
>>
>>
>> Layer 2
>>
>> Seriously, FR is a Layer 2 protocol, as is Ethernet, Token Ring, etc. As
>> those other protocols support numerous Layer 3 (or higher) protocols, so
>> will FR. The beauty of the OSI model is that there is separation of the
>> layers without too much interaction between them. In other words, the Layer
>> 4 datagrams get encapsulated into the Layer 3 packets, which in turn get
>> encapsulated into Layer 2 frames. FR doesn't care for the most part what is
>> "inside" the Layer 3 stuff coming down the pipe. ;-}
>>
>> Rik
>>
>> -----Original Message-----
>> From: Pierre-Alex [mailto:[EMAIL PROTECTED]]
>> Sent: Thursday, February 01, 2001 8:41 AM
>> To: [EMAIL PROTECTED]
>> Subject: Frame Relay
>>
>>
>> What element in a frame relay packet allows support for multiple protocols?
>>
>> Pierre-Alex
>>
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