ATM UNI Cell Structure

The currently defined structure of an ATM cell at the user-network 
interface is indicated in the diagram below:

                         BIT
     8     7     6     5     4     3     2     1
    |-------------------------------------------|
    |        GFC          |          VPI        | 1    
    |-------------------------------------------|
    |        VPI          |          VCI        | 2
    |-------------------------------------------|
    |                    VCI                    | 3
    |-------------------------------------------|     OCTET
    |        VCI          |      PT      | CLP  | 4
    |-------------------------------------------|
    |                    HEC                    | 5
    |-------------------------------------------|
    |         Cell Payoad (48 Octets)           | 6-53
    |-------------------------------------------|

CFC - Generic Flow Control
VCI - Virtual Channel Indentifier
CLP - Cell Loss Priority
VPI - Virtual Path Indentifier
PT  - Payload Type
HEC - Header Error Check

Keywords: ATM, UNI, GFC, VCI, CLP, VPI, PT, HEC, cell