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NIC Full-Duplex Operation (FDX)

Adapter Support
Full-Duplex Operation

Sources:
Token-Ring Adapter FDX Drivers/Microcode ("Adapter Support" - archived)
Token-ring migration to switched LAN interconnect ("FDX Operation" - 1997, archived)

Adapter Support

Token Ring Adapters

• Auto 16/4 MC - Unknown (Early pages say 1997, then "Contact IBM for more information")
  10H4710
  50G7028 Token Ring front end

• LANStreamer MC 16 - No FDX
  50G8180 Token Ring protocol chip "Huntingdale"
  National Semiconductor 93F2932 Token Ring front end

• LANStreamer MC 32 - No FDX
  50G8180 Token Ring protocol chip "Huntingdale"
  National Semiconductor 93F2932 Token Ring front end

• Auto LANStreamer MC 32 - FDX Capable
  73G2692 or 38H6302 Multi-Protocol Chip (MPC)
  50G7028 Token Ring front end

• Dual LANStreamer MC 32 - FDX Capable
  73G2692 Multi-Protocol Chip (MPC)
  50G7028 Token Ring front end

Ethernet Adapters

• EtherStreamer MC 32 - FDX Capable
  60G0663 or 73G2692 Multi-Protocol Chip (MPC)
  National Semiconductor DPADP10 Ethernet front end

• Dual EtherStreamer MC 32 - FDX Capable
  73G2692 Multi-Protocol Chip (MPC)
  National Semiconductor DPADP10 Ethernet front end

Full-Duplex Operation

The classical operation mode of Ethernet and Token Ring is referred to as half-duplex (HDX) here, meaning that a station can either transmit or receive data but not both simultaneously. Also, in the shared LANs, only one station can transmit at a time. A server with a single network interface connection (NIC) is limited to the amount of bandwidth that it can acquire in a shared-network environment as network loading increases. Priority access schemes in both Token Ring and FDDI systems can reduce access delays for selected stations, thus making them well suited for many types of multimedia applications.

FDX is a well-known mode of operation in communication networks. However, it is only with recent advances in switching technology that it is now practical to consider switching and FDX operation at speeds of 10, 16, or even 100 Mbps. In FDX operation, separate transmit and receive paths are dedicated on a point-to-point link rather than repeating the incoming data signals (See Figure 1).

Figure 1: Full-Duplex Adapter Operation (Reference 3)

There are no collisions or tokens to regulate media access, because dedicated transmit and receive paths exist. Each station simply transmits data once it has been correctly formatted within the adapter. This greatly simplifies the MAC protocol (Reference 1). The switch and adapter designs ensure that there are adequate buffers to receive the incoming frames. Data loss can occur during periods of bursty traffic if inadequate buffer capacity is provided (Reference 2). Some limited flow-control schemes were designed for the connection-oriented link-level protocols for relieving congestion in intermediate bridges and are also applicable to switched environments. The best example is the dynamic-window algorithm defined for IEEE 802.2 Type 2 (connection-oriented) service (Reference 3).

Figure 2: Dedicated FDX vs Shared-Bandwidth Performance

The most compelling reason to migrate to FDX operation and a switched environment is the significant gain in bandwidth that is available to each individual station (References 1 and 3). With shared networks, such as token ring and Ethernet, the amount of bandwidth available to each station decreases in proportion to the number of stations that share the link (See Figure 2). This has been sufficient for the past 10 years due to the limited bandwidth requirements of existing applications. However, emerging multimedia applications could require as much as 4 to 6 Mbps per session. This bandwidth can be provided by simply dedicating to each station the full bandwidth of the LAN adapter. However, once the link has been dedicated to one station, FDX operation then essentially doubles the available bandwidth while also decreasing end-to-end latency.

References

1. Saunders, S., "Traffic Jam at the LAN Switch," Data Communications, 21 November 1994, 53-58.
2. Bux, W. and Grillo, D., "Flow Control in LANs of Interconnected Token Rings," IEEE Transactions on Communications, COM-33 (October 1985), 1058-1066.
3. Tolly, K., "Token Ring Switching: The Design Challenge," Data Communications, February 1995, 97-104.