|  | 6.1 | Frame Relay Technology
| 6.1.5 | The fields of the F rame R elay frame format

The Frame Relay frame format is shown in the Figure. The flag fields indicate the beginning and end of the frame. Following the leading flag field are 2 bytes of address information. 10 bits of these 2 bytes make up the actual circuit ID (that is, the DLCI). The following are the Frame Relay frame fields: Flag -- Indicates the beginning and the end of the Frame Relay frame. Address -- Indicates the length of the Address field. Although Frame Relay addresses are currently all 2 bytes long, the Address bits allow for the possible extension of Address lengths in the future. The eighth bit of each byte of the Address field is used to indicate the address. The Address contains the following information: DLCI Value -- Indicates the DLCI value. Consists of the first 10 bits of the Address field. Congestion Control -- The last 3 bits in the address field, which control the Frame Relay congestion notification mechanisms. These are the FECN, BECN, and discard eligible (DE) bits. Data -- Variable-length field that contains encapsulated upper-layer data. FCS -- Frame check sequence (FCS), used to ensure the integrity of transmitted data.
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