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Jumbo Frames

In computer networks Jumbo Frames a so-called Ethernet frame with more than 1,500 Byte payload, the limit set by the IEEE 802.3 standard. Conventionally, the jumbo frame can carry up to 9,000 Byte payload, but there are variations – so the term should be used with some care.

Many Gigabit Ethernet switches and Gigabit Ethernet network interface cards support the Jumbo Frame. Some Fast Ethernet switches and Fast Ethernet network interface cards also support it.

Development

Each Ethernet Frame frame must be processed as it traverses a network. Processing the content of a single large frame is preferable to processing the same content divided into smaller frames, as this makes better use of available CPU time by reducing interrupts. This also minimizes the number of overheadBytes and reduces the number of frames that need to be processed. This is analogous to physically sending a paper packet instead of multiple individual envelopes, each containing one sheet. This can save envelopes and reduce sorting time.

The jumbo frame first gained notoriety when Alteon WebSystems introduced itself to its ACEnic Gigabit Ethernet adapters. Many other vendors have adopted the size as well.

Error Detection

Simple additive checksums, such as those found in UDP and TCP transports, have proven ineffective at detecting bus-specific bit errors, as these errors tend to cancel themselves out with simple summations. Tests leading to the introduction of RFC 3309 simulated error injection using real data and showed that up to 2% of these errors were not detected.

For larger errors, undetected errors are more likely to occur with simple CRC32 error detection in Ethernet frames. As packet size increases, it becomes more likely that multiple errors will cancel each otherout.

An IETF solution for adopting Jumbo Frames avoids reducing the data integrity of the service data unit by performing an additional CRC at the next network protocol layer over Ethernet. SCTP transport and iSCSI use the Castagnoli CRC polynomial.

Configuration

Some providers include headers in the size setting, while others do not. This is either the maximum frame size or the maximum transfer unit. Therefore, different values may need to be configured in devices from different vendors for the settings to match. A mixture of devices configured for this and for devices not configured for Jumbo Frames on a network can cause network performance problems.

Bandwidth Efficiency

Jumbo Frames can increase Ethernet and network processing efficiency in hosts by reducing protocol overhead.

Baby Jumbo Frames

Baby Jumbo Frames are Ethernet frames that are only slightly larger than allowed by IEEE Ethernet standards. For example, they are required for IP/MPLS to be provided over Ethernet services. In most implementations, non-jumbo user frames must be encapsulated in the MPLS frame format, which in turn can be encapsulated in an appropriate Ethernet frame format with Ether-Type values. The increased additional MPLS and Ethernet headers means that support for 1,600-Byte frames is a mandatory requirement in Carrier Ethernet networks.

Super Jumbo Frame

Super Jumbo Frames are generally considered to be frames with a payload size greater than 9,000 Byte. The relative scalability of network data throughput as a function of packet transmission rates is related in a complex way to the payload size per packet. As the power bit rate increases, the packet payload size should increase in direct proportion to maintain equivalent timing parameters. However, this implies scaling numerous intermediate logic circuits along the network path to accommodate the maximum required frame size.

Tip

By making CPU utilization independent of frame size, LSO (Large Send Offload) eliminates the per-packet overhead that Jumbo Frames is designed to reduce. LRO (Large Receive Offload), the inbound counterpart of LSO, does not completely eliminate the per-packet overhead carried by the CPU. Therefore, frames remain beneficial for inbound traffic.


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