In table format explain the ISDN LAPD frame structure. And the answer
should include columns for Information, Supervisory and Unnumbered
frames and should not only describe the function of individual fields
but give an indication of their comparative sizes.

Hello Kevin9327,

The Link Access Procedure - D (LAPD) is used as the data link protocol
(layer 2) for an ISDN connection. A good summary of the data formats
used at layer 2 to define opening flag, address, control, information,
frame check sequence, and closing flag fields is at...
  http://www.cis.upenn.edu/~kimbong/tcom501/isdn.html

Go down to section 4 - there are illustrations as well as explanations
for the field definitions. Item 3 (Control Field) describes the
modifiers for Information, Supervisory and Unnumbered frames.

There is an explanation of the same information from the point of view
of a protocol analyzer. Look at
  http://www.acacia-net.com/wwwcla/Events/q921.htm
and scroll down to various tables that layout the data in each field.

A good library reference would be
  ISDN: Concepts, Facilities, and Services (4th ed.), Gary C. Kessler
and Peter V. Southwick, McGraw-Hill, 1998, ISBN 0-07-034437-X
You can review the table of contents here...
  http://www.garykessler.net/library/isdnbook.html

Let me know if you need some additional information with a
clarification request. I will check later tonight and tomorrow.

--Maniac