A Frame Relay frame is primarily composed of three main parts: the header and address area, the user-data portion, and the frame check sequence (FCS).
Key Components of a Frame Relay Frame
According to the provided reference, the Frame Relay frame is made up of three primary components:
- The Header and Address Area: This is the initial part of the frame.
- The User-Data Portion: This section carries the actual information being transmitted.
- The Frame Check Sequence (FCS): This is used for error detection.
Let's look at these components in more detail:
The Header and Address Area
This crucial part of the frame is responsible for routing the data to the correct destination circuit.
- Length: The address area is 2 bytes in length.
- Contents: This 2-byte area is specifically comprised of:
- 10 bits: Representing the actual circuit identifier. This identifier, known as the Data Link Connection Identifier (DLCI), specifies the virtual circuit the frame belongs to.
- 6 bits: Fields related to congestion management. These bits signal network conditions like congestion experienced by the frame.
Here's a simple breakdown of the address area:
| Field | Size (bits) | Purpose |
|---|---|---|
| Actual Circuit Identifier | 10 | Identifies the virtual circuit |
| Congestion Management | 6 | Network condition signals |
The User-Data Portion
This is the part of the frame that carries the payload – the actual data from the higher-layer protocols (like IP packets) that the end-users want to send across the network. Frame Relay is designed to simply transport this data transparently, without inspecting its contents.
The Frame Check Sequence (FCS)
Located at the end of the frame, the FCS is used for error detection. It's a calculated value based on the contents of the frame's header and data. The receiving device recalculates the FCS upon receiving the frame. If the calculated value doesn't match the FCS sent in the frame, it indicates that an error occurred during transmission, and the frame is typically discarded.
