Newbie: async mode dedicated versus async mode interactive!!

Hi Pink,

~ I have been trying to understand the difference between async mode ~ dedicated and async mode interactive and have searched the group for ~ some answers. I have also read Cisco's documentation and have gained ~ little understanding from it. I would appreciate your time and effort ~ if you could please help me clarify the issue. ~ ~ One chain of thought indicates that if we use async mode dedicated, ~ then the interface starts functioning in framed mode (SLIP / PPP).

This is so.

~ If ~ we use async mode interactive, then the user has the liberty to use ~ TELNET.

This is so.

~ Now SLIP / PPP are L2 protocols while TELNET is an L4 protocol

This is so.

~ So I found this explanation hard to follow. ~ ~ My understanding is that if we use the interactive mode, then the end ~ user has the option of accessing the exec prompt. Am I correct?

You are.

~ Also, ~ what is the significance of the dedicated mode?

As you way, in dedicated mode, when the interface comes up, it is in framed mode (SLIP/PPP). When the interface comes up, it is in UNFRAMED async mode.

So what you may be missing is an understanding of what unframed async mode is. Perhaps it would be more helpful to describe it as "character-at- a-time mode"? When a line is operating in unframed async mode, then when the router receives a character from the line, it will not treat it as part of a layer 2 frame, but as a character to be input to the exec process.

For example, let's say that the line is operating in unframed async mode, and that it receives the following data pattern from the line:

7368 6f77 2076 6572 7369 6f6e 0d

Let's say that the exec process on the line is sitting at the exec mode prompt ("router#"). Then, when the router receives that data pattern from the line, it will parse it as ASCII, so it will see it as: "show version\\r" and so it will respond by transmitting the "show version" output.

Now, let's say that the line is operating in framed async (let's say, PPP) mode, and receives the same data pattern. It will attempt to parse this pattern as an async PPP frame - but since this is an invalid frame, the receiver will discard the data, and one of the input error counters in "show interface async" will increment.

Does this make it clearer?

Aaron

Hi Aaron,

Good Evening!!

Thank you for your help on the issue.

Yes your answer did help me to understand the difference.

However, I have one question that lingers in my mind.

Even if the line is configured to interpret stuff in character mode, won't my PC send stuff through Layer 2 which will eventually be encapsulated appropriately? (Thus even if I used TELNET, it would eventually be encapsulated that L2 protocol.)

Please advise.

Regards,

- P> Hi Pink,

Nope! If the PC is operating in character mode, then it doesn't use any framing protocol.

I guess a picture might help ...

[TELNET server]-----{IP network}-----[router [TELNET client]]--async line--[PC] || ||||| |||||

Does this help?

Aaron

Hi Aaron,

Apologies for the delayed reply.

Yes that indeed helped.

Thank you for your time and effort in helping me out.

Warm Regards,

- P>

framing protocol.