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RFC1661 - часть 40


A more

optimistic procedure (in the case of a looped-back link) is to

begin transmitting LCP Echo-Request packets until an appropriate

Echo-Reply is received, indicating a termination of the looped-

back condition.

A summary of the Magic-Number Configuration Option format is shown

below. The fields are transmitted from left to right.

0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Type | Length | Magic-Number

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Magic-Number (cont) |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

5

Length

6

Magic-Number

The Magic-Number field is four octets, and indicates a number

which is very likely to be unique to one end of the link. A

Magic-Number of zero is illegal and MUST always be Nak'd, if it is

not Rejected outright.

Simpson [Page 47]

RFC 1661 Point-to-Point Protocol July 1994

6.5. Protocol-Field-Compression (PFC)

Description

This Configuration Option provides a method to negotiate the

compression of the PPP Protocol field. By default, all

implementations MUST transmit packets with two octet PPP Protocol

fields.

PPP Protocol field numbers are chosen such that some values may be

compressed into a single octet form which is clearly

distinguishable from the two octet form. This Configuration

Option is sent to inform the peer that the implementation can

receive such single octet Protocol fields.

As previously mentioned, the Protocol field uses an extension

mechanism consistent with the ISO 3309 extension mechanism for the

Address field; the Least Significant Bit (LSB) of each octet is

used to indicate extension of the Protocol field. A binary "0" as

the LSB indicates that the Protocol field continues with the

following octet. The presence of a binary "1" as the LSB marks

the last octet of the Protocol field. Notice that any number of

"0" octets may be prepended to the field, and will still indicate




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