Using the example given is the TCP/IP guide, I made a comparison of normal PPP and Multilink PPP (just to have some fun).
Original frame size = 32 bytes = 256 bits
Stripped down frame size = 24 bytes = 192 bits
MP Frame size = 158 bits X 3
Size difference = |256 bits - 474 bits| = 218 bits
Time to transfer orginal on 64,000bps = 0.004s .....(1)
Time to transfer MP in 64,000bps X 2 = [(158X2)bits over 128kbps = 0.00246875s] + [158bits over 64,000bps = 0.00246875s] = 0.0049375s .....(2)
From (1) and (2), time taken my MP is more.
However, the Information field of PPP frames is variable. So when a larger amount of data is to be carried, MP is obviously more efficient.
A PPP frame starts and ends with a Flag with value 0x7E. The Flag (start) is followed by Address and Control fields, with are not needed for PPP, but are present for compatibility with High Level Data Link Control Protocol (HDLC). Default values are 0xFF for Address (broadcast) and 3 for Control. The fields are suppressed when using Field compression. (0xFF03 is not a valid Protocol field, and thus the difference is made).
The Protocol field ranges from 0x0000 to 0xFFFF, each used for a particular protocol. Some values are not used (see above). The first octet is even and the second octet is odd. The value when encapsulating an IP packet is 0x0021. When using IPCP, the value is 0x8021. (Add 8 to first digit for getting corresponding NCP value).
The Information Field has the Network Layer data encapsulated. It may be followed by Padding.
This is followed by FSC (Frame Check Sequence), which is a CRC code of the data. It is 2(default) or 4 bytes in size.
The last byte is, ofcourse, the Flag, 0x7E.
Link dead -> Link Establishment -> (Authentication) -> Network Layer Protocol -> Link Open -> Link Termination.
IP Datagram broken into bytes. Each packet starts and ends with END character (C0h).
If END character is present in data, it is converted into DB-DC (DBh is escape character)
If ESC character is present in data, it is converted into DB-DD
Named for telegraphy pioneer Jean Maurice Emile Baudot (1845-1903), this is a unit that measures the number of changes, or transitions, that occur in a signal in each second. So, if the signal changes from a “one” value to a “zero” value (or vice-versa) one hundred times per second, that is a rate of 100 baud.
Modern modems use advanced modulation techniques that encode more than one bit of data into each transition. A 28,800 bps modem typically encodes nine bits into each transition; it runs at 3,200 baud, not 28,800 baud (the latter number being the product of 3,200 and 9)
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