Re: HDLC frames delivered over PWs

Hello Javi,

Please see inline.

On 9/12/2006 1:01 PM, Javi allegedly said the following:
> Hello Carlos,
> 
> Thanks again.
> 
> Thinking your explanation, I understand all HDLC frames are delivered 
> over HDLCPWs in order to maximize transparency, so that they any 
> protocol that has HDLC-like framing may utilize the HDLCPW mode, 
> including PPP, Frame-Relay ("port to port" Frame-Relay  transport), X.25 
> (LAPB), etc. This is an advantage, but delivering all frames (including 
> RR, RNR, ...) is less efficient for the bandwidth.
> 
> On the other hand, in FRPW is necessary to inspect a frame incoming on 
> the AC.

Note that FRPWs operate at the DLCI level, taking care of end-to-end
characteristics like status by terminating local management and using
SLIs with Circuit Status AVP between LCCEs. The FR specification points
to the HDLC one to operate in a port-to-port fashion.

> 
> So, if you need a solution for a particular scenerio (i.e. LAPB over 
> IP), would it be better (more efficient) to define an specific PW for 
> this particular protocol that has HDLC-like framing?. For instance, a 
> LAPB PW which only deliveres over PWs the necessary frames (usually, I 
> frames).

Yes, but if flow-control packets (RR, RNR, Rej) are not sent over the PW
then this specific PW extension needs to take care of local flow-control
for example (see the discussion in rfc1613 section 6.2). Interested
people can define this specific PW Type by submitting an I-D.

Thanks,

--Carlos.

> 
> Carlos Pignataro escribió:
>> Hello Javi,
>>
>> Please see inline.
>>
>> On 9/7/2006 6:40 AM, Javi allegedly said the following:
>>   
>>> Hello Carlos,
>>>
>>> Thanks, I agree with you.
>>>
>>> Howerver, my question tried to evaluate the efficiency of the method. If 
>>> PWs deliver all HDLC frames, it means all RR/RNR frames (which are 
>>> continuously transmitted)
>>>
>>> So, HDLCPW would use too much resources in the IP network. Is it 
>>> neccesary?. Perhaps, delivering only "I" frames may be enough if we use 
>>> polling in LCCEs (so that, they answer to RR/RNR frames).
>>>     
>> The HDLCPW encapsulation does not inspect a frame incoming on the AC
>> beyond HDLC flags and FCS, to maximize transparency.
>>
>> This for instance allows what's described in the rfc:
>>
>>    Since all packets are passed in a largely transparent manner over the
>>    HDLCPW, any protocol that has HDLC-like framing may utilize the
>>    HDLCPW mode, including PPP, Frame-Relay ("port to port" Frame-Relay
>>    transport), X.25 (LAPB), etc.  In such cases, the negotiations and
>>    signaling of the specific protocols transported over the HDLCPW take
>>    place between the Remote Systems.
>> ...
>>    In addition
>>    to the transport of HDLC frames, a natural application of HDLCPWs
>>    allows for the transport of any protocol using an HDLC-like framing.
>> ...
>>       o HDLC data and control fields are transported transparently (see
>>         Section 4.1).  The specific negotiations and signaling of the
>>
>> This is in turn in line with the PWE3 Architecture in rfc3935.
>>
>> Thanks,
>>
>> --Carlos.
> 

-- 
--Carlos Pignataro.
Escalation RTP - cisco Systems