Frame Relay
Frame Relay is a packet-switching technology that fragments data into transmission units called frames and sends them in high-speed bursts through a digital network. It establishes an exclusive connection during the transmission period called a virtual connection.
Key Features of Frame Relay
- Fast Packet Technology: Error checking does not occur at any intermediate node but is done at the ends, making it more efficient than X.25 and achieving higher process speeds (up to 2,044 Mbps).
- Efficient Use of Resources: Requires less powerful switching centers (nodes) and less memory capacity than X.25.
- High Performance: Performance is superior to X.25 for heavy traffic with a large number of small packets. For large file transfers at high speeds, the price/performance ratio is higher than X.25.
- Supports Multiple Users: Can support multiple users over the same line and establish a permanent virtual circuit or a switched virtual circuit.
Evolution from X.25
Frame Relay evolved from X.25 packet switching to reduce network delays, protocol overheads, and equipment costs. Unlike X.25, which guarantees data integrity and network-managed flow control, Frame Relay switches packets end-to-end faster but without any guarantee of data integrity.
Characteristics of Frame Relay
| Feature | Description |
|---|---|
| Connectionless | Each data packet passing through the network contains address information. |
| Variable Speeds | Supports speeds from 56 Kbps up to 25 Mbps. |
| Variable Length Frames | Frames can vary in length up to 4,096 bytes. |
| Broadband ISDN Service | Considered a Broadband ISDN service. |
| No Flow Control | Only detects errors, no flow control or error correction. |
| Large Frame Size | Can accommodate all local area network frame sizes. |
Frame Format
| Field | Description |
|---|---|
| DLCI Length | 10 bits |
| EA Locations | First set to 0, second set to 1 |
| DE (Discard Eligibility) | Indicates part that can be discarded first when congestion occurs |
| Data Size | Up to 4096 bytes |
Frame Relay Layers
Frame Relay operates on two layers: the physical layer and the data link layer.
Physical Layer
- Supports ANSI standards.
- No specific protocol is defined; any protocol recognized by ANSI can be used.
Data Link Layer
- Employs a simplified version of HDLC (High-Level Data Link Control).
- No flow control or error correction; only error detection is performed.
Need for Frame Relay
Higher Data Rates
Frame Relay can handle data rates up to T-3 transmission (44.376 Mbps). It allows the transfer of burst data and can efficiently connect LANs located at physically distant places.
Handling Bursty Data
Frame Relay supports bursty data, meaning large amounts of data are sent suddenly, followed by periods of very little or no data. It supports a minimum average data rate and can handle bursty data efficiently.
Lower Overheads
Frame Relay reduces overheads by eliminating acknowledgments from switches to the sender, intermediate error checks, and storage of packet copies at intermediate hosts. This saves memory space and increases efficiency.