This chapter provides an overview of IRIS Frame Relay (IFR), including a description of how it works, what it needs to run, and some examples of how it is commonly used.
Frame Relay is software that allows two LANs to be connected via a synchronous communication line. Frame Relay software manages the interface between the IP protocol and the lower-level synchronous communications board driver, as shown in Figure 1-1.
Frame Relay, residing at the data link layer, passes frames of data through a synchronous line to another site. The frames of data are managed by the configuration parameters that are chosen and contained in the configuration files.
Frame Relay is accessed by Link Access Procedures for Frame Relay (LAPF). LAPF conveys Data Link Service Data Units (DLSDUs) between DL-Service Users across the user-network interface over synchronous lines. Frame mode bearer connections are established using procedures specified in either Recommendation Q.933 or (for PVCs) by subscription.
The key features of Frame Relay are:
symmetric procedural behavior with respect to the User Network Interface (UNI), allowing direct user-to-user internetworking with the network side being passive (or only supporting the DL-CORE protocol)
DL-CORE subset of LAPF
use within a layered protocol suite, which allows internetworking between frame relaying, frame switching, and IP-based services
MFE—Multiprotocol over Frame Relay Encapsulation according to RFC 1490, FRF.3, and T1.617 Annex F
congestion control
PVC status procedures (T1.617 Annex D/Q.933 Annex A/Original Group of Four)
Frame Relay requires the following hardware and software:
IRIX 6.2
synchronous interface driver
synchronous communications board
Frame Relay can be used to connect two LANs. The LANs may be connected by a Point-to-Point dedicated leased line, as shown in Figure 1-2, or through the Internet, as shown in Figure 1-3. The connection, using a synchronous communications board, supports several lines, each allowing data to be passed at speeds from 56 Kbps to a maximum of 2 Mbps. Frame Relay's high-speed data rate might be beneficial in connecting two Web servers.
The following acronyms are used throughout this guide.
| ANSI | American National Standards Institute | |
| BECN | Backward Explicit Congestion Notification | |
| CEI | Connection endpoint identifier | |
| CLNP | Connectionless Network Protocol | |
| DE | Discard Eligible | |
| DLCI | Data Link Connection Identifier | |
| DLPI | Data Link Provider Interface | |
| DLSAP | Data Link Service Access Point | |
| DLSDU | Data Link Service Data Unit | |
| DL-CORE | Core aspects of LAPF | |
| FECN | Forward Explicit Congestion Notification | |
| FR | Frame Relay | |
| FRF | Frame Relay Forum | |
| IFR | The Frame Relay DL-CORE (Frame Relay Service) driver | |
| IP | Internet Protocol | |
| ITU-T | International Telecommunications Union - Telecommunications | |
| LAPF | Link Access Procedures for Frame Mode Bearer Services | |
| MC | Communication between layer management and DL-CORE | |
| MDL | Communication between layer management and the data link layer | |
| MFE | Multiprotocol over Frame Relay Encapsulation | |
| NLPID | Network Layer Protocol Identifier | |
| OUI | Organizationally Unique Identifier | |
| PDU | Protocol Data Unit | |
| PID | Protocol Identifier | |
| PPA | Physical Point of Attachment | |
| PVC | Permanent (or semi-permanent) Frame Relay connection | |
| RFC | Request For Comments | |
| SNAP | Subnetwork Access Protocol | |
| SNID | Subnetwork Identifier | |
| UI | Unnumbered Information | |
| VC | Virtual Circuit | |
| VCID | VC Identifier | |
| WAN | WAN driver | |
| XID | Exchange Identification |