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ICE VITA 49.0 Radio Transport Ethernet Packet Specification

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In compliance with the ANSI VITA 49.0 standard, this document outlines the ICE VRT packet lengths, fields, and contents which are supported for UDP Multicast transport over ethernet interfaces (1Gbit/sec and 10Gbit/sec) by the ­VITA 49-compliant I/O modules. In order to achieve the highest possible throughput on both dedicated hardware and commercial computing platforms, certain options within the VITA 49.0 standard have been specified as mandatory.

Ethernet Frame Description

The raw ethernet frame transmitted by the ICE­ ­VITA 49-compliant I/O modules is shown in Figure 1 – Ethernet Frame Description Primary Payload. The Primary payload size is 1440 Bytes. An Ethernet Frame Description for the Alternate Payload size (1024 Bytes) is shown in Figure 2 – Ethernet Frame Description Alternate Payload In order to allow commercial network switches to segregate, prioritize, and efficiently route VRT packets, IEEE 802.1Q (VLAN) tagging of packets is supported. Additionally, the total raw IP packet size is kept below the 1542 byte maximum (1500 byte payload MTU) in order to prevent packet fragmentation and orphaned payloads. Many COTS routers and switches cannot support jumbo frames and will fragment IP packets which exceed the 1542 byte length.

ICE VRT Packet Description

The bitwise definition of the ICE VRT packet is shown in Figure 3 – ICE VRT Packet Definition. The packet definition specifies a default fixed-length VRT packet size of 1472 bytes. Using the VITA 49.0 definition of 32-bit words, each VRT packet contains the following fields: Header (1 word), Stream Identifier (1 word), Class Identifier (2 words), Timestamp (3 words), Payload (360 words), Trailer (1 word). Each of these fields are mandatory for the ICE VRT packets. By requiring all eight words of the VRT header and trailer fields (Header, StreamID, ClassID, Timestamp, Trailer), and by carefully selecting the payload size to be 360 words, eight byte alignment is maintained. This alignment is critical to the throughput of network cards and DMA interfaces on modern COTS computers. (Non-aligned memory moves on modern CPU architectures are very inefficient and can introduce significant performance bottlenecks.)

This content is also available as a datasheet: Pdf icon.gif ICE-VRT-PACKET-Description.pdf

ICE VRT Packet – Header

BITS Field Value Description
31-28 Type 0x0001 IF Data Packet Type containing a Stream Identifier
27 C 0x1 Packet contains a Class Identifier
26 T 0x1 Packet contains a Trailer
25-24 RSV N/A Reserved
23-22 TSI 0xX Packet contains a timestamp of type = {0x01, 0x10, 0x11}
21-20 TSF 0xX Fractional timestamp of type = {0x01, 0x10, 0x11}
19-16 PKTCNT 0xX Modulo-16 packet sequence counter
15-0 PKTSIZE 0x0170 VRT Header + 360 word payload

ICE VRT Packet – Stream Identifier

BITS Field Value Description
31-0 Stream ID 0xXXXXXXXX Unique 32-­bit stream identifier for each data stream

ICE VRT Packet – Class Identifier (Word 1)

BITS Field Value Description
31-24 RSV 0x00 Reserved
23-0 OUI 0x104D77 IEEE Organizationally Unique Identifier for ICE

ICE VRT Packet – Class Identifier (Word 2)

BITS Field Value Description
31-16 ICC 0x0000 Information Class Code
15-0 PCC 0xXXXX Packet Class Code

ICE VRT Packet – Class Identifier (Word 2, PCC Breakout)

BITS Field Value Description
15 Packing 0x1 Processor or link efficient packing
14-13 ComplexMode 0x0 Real, complex, polar data mode
12-8 DIF 0x0 Data Item Format (enumerated list from VITA 49.0 spec)
7-6 RSV N/A Reserved
5-0 DIS 0xX Data Item Size (bits_per_item - 1)

Appendix: Figures

Figure 1 – Ethernet Frame Description Primary Payload

EthernetFramePrimary.png

Figure 2 – Ethernet Frame Description Alternate Payload

EthernetFrameAlt.png

Figure 3 – ICE VRT Packet Definition

ICEVRTPacketDef.png