In the configuration stage of PPP, IIRC, two sets of "control characters"
(which need to be escaped) are negotiated by the two sides. Each set
specifies which characters need to be escaped for that side to receive them
correctly.

It is actually quite interesting to see what a jumble of protocols a TCP/IP
stack is. PPP is like a heavily modified HDLC and includes a CRC. IP then
goes on top of that,and has no error control over the contents, only the
header. Then TCP or UDP add another layer of checksum to protect the data,
and TCP also includes indexing to the packets to ensure reassembly in the
correct order.

Sean


At 02:11 PM 9/7/99 -0700, you wrote:
>Errr... RIGHT! I knew that!! Just testing! <GRIN>
>
>If the need is for only one "escape" value for resyncing, then escape only
>one or two (infrequently used) characters and pass all the rest as binary.
>Paul is right, now that I think about it, that is what the ASCII control
>characters were designed for.
>
>Isn't this the same sort of thing that is done in PPP? (Notice how I
>cleverly remembered not to say PPP Protocol?)
>
>James Newton, webmaster http://get.to/techref
>(hint: you can add your own private info to the techref)
>mailto:jamesnewton@geocities.com
>1-619-652-0593 phone
>
>
>
>-----Original Message-----
>From: pic microcontroller discussion list
>[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Paul B. Webster VK2BZC
>Sent: Tuesday, September 07, 1999 1:44 PM
>To: PICLIST@MITVMA.MIT.EDU
>Subject: Re: Binary to ASCII
>Importance: Low
>
>
>James Newton wrote:
>
>> Why not a length byte at the beginning? Dead easiest to code.  Divide
>> longer xmitions up into 255 byte packets.
>
>  Probably because if you had a transmission error, you would never
>manage to resync.  You need flags (and escapes) to do so.
>--
>  Cheers,
>        Paul B.
>
|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
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