hdlc

Answered Question
Aug 2nd, 2009

Hi every body.

I have few questions .

Let say we have following scenario:

pc1--e0(R1)s0------s0(R2)e0----pc2

Let say pc1 pings pc2. Following will occur:

1) pc1 sends ping frame using R1 e0's mac as destination.

2)R1 receives the frame ,processes it then remove the ethernet headers and encapsulates the ping packet in hdlc header.

Now my question is what address would R1 use in the address field of hdlc header before sending the frame to R2?

My understanding is we need address only when there are muliple recipents on the link. But when there is only one possible receiver as is the case in point to point link, we don't need to specify the receiver .

But then why has designer of hdlc put address field in the hdlc header if there is no purpose for address field ?

thanks a lot.

I have this problem too.
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Correct Answer by Peter Paluch about 7 years 4 months ago

Hello,

The HDLC was actually designed for a point-to-multipoint style of communication on a shared bus. The address field made sense then, as it was necessary to address different stations across the bus. However, in todays applications, the HDLC is almost exclusively used on point-to-point type links, therefore the address field may appear largely useless.

The Wikipedia article about the HDLC (not about Cisco HDLC which is a derivative of the original HDLC) explains all the history and the principles behind the HDLC very nicely. I recommend reading it.

http://en.wikipedia.org/wiki/HDLC

Best regards,

Peter

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Correct Answer
Peter Paluch Mon, 08/03/2009 - 01:51

Hello,

The HDLC was actually designed for a point-to-multipoint style of communication on a shared bus. The address field made sense then, as it was necessary to address different stations across the bus. However, in todays applications, the HDLC is almost exclusively used on point-to-point type links, therefore the address field may appear largely useless.

The Wikipedia article about the HDLC (not about Cisco HDLC which is a derivative of the original HDLC) explains all the history and the principles behind the HDLC very nicely. I recommend reading it.

http://en.wikipedia.org/wiki/HDLC

Best regards,

Peter

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