Network Working Group P. Johansson Request for Comments: 2734 Congruent Software, Inc. Category: Standards Track December 1999 IPv4 over IEEE 1394 Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (1999). All Rights Reserved. ABSTRACT This document specifies how to use IEEE Std 1394-1995, Standard for a High Performance Serial Bus (and its supplements), for the transport of Internet Protocol Version 4 (IPv4) datagrams; it defines the necessary methods, data structures and codes for that purpose. These include not only packet formats and encapsulation methods for datagrams, but also an address resolution protocol (1394 ARP) and a multicast channel allocation protocol (MCAP). Both 1394 ARP and MCAP are specific to Serial Bus; the latter permits management of Serial Bus resources when used by IP multicast groups. TABLE OF CONTENTS 1. INTRODUCTION.....................................................2 2. DEFINITIONS AND NOTATION.........................................4 2.1 Conformance..................................................4 2.2 Glossary.....................................................4 2.3 Abbreviations................................................6 2.4 Numeric values...............................................6 3. IP-CAPABLE NODES.................................................6 4. LINK ENCAPSULATION AND FRAGMENTATION.............................7 4.1 Global asynchronous stream packet (GASP) format..............8 4.2 Encapsulation header.........................................9 4.3 Link fragment reassembly....................................11 5. SERIAL BUS ADDRESS RESOLUTION PROTOCOL (1394 ARP)...............11 6. CONFIGURATION ROM...............................................14 6.1 Unit_Spec_ID entry..........................................14 6.2 Unit_SW_Version entry.......................................14
6.3 Textual descriptors.........................................15 7. IP UNICAST......................................................16 8. IP BROADCAST....................................................17 9. IP MULTICAST....................................................17 9.1 MCAP message format.........................................18 9.2 MCAP message domain.........................................21 9.3 Multicast receive...........................................21 9.4 Multicast transmit..........................................22 9.5 Advertisement of channel mappings...........................23 9.6 Overlapped channel mappings.................................23 9.7 Transfer of channel ownership...............................24 9.8 Redundant channel mappings..................................25 9.9 Expired channel mappings....................................25 9.10 Bus reset..................................................26 10. IANA CONSIDERATIONS............................................26 11. SECURITY CONSIDERATIONS........................................27 12. ACKNOWLEDGEMENTS...............................................27 13. REFERENCES.....................................................28 14. EDITOR'S ADDRESS...............................................28 15. Full Copyright Statement.......................................29 1. INTRODUCTION This document specifies how to use IEEE Std 1394-1995, Standard for a High Performance Serial Bus (and its supplements), for the transport of Internet Protocol Version 4 (IPv4) datagrams. It defines the necessary methods, data structures and codes for that purpose and additionally defines methods for an address resolution protocol (1394 ARP) and a multicast channel allocation protocol (MCAP)---both of which are specific to Serial Bus. The group of IEEE standards and supplements, draft or approved, related to IEEE Std 1394-1995 is hereafter referred to either as 1394 or as Serial Bus. 1394 is an interconnect (bus) that conforms to the CSR architecture, ISO/IEC 13213:1994. Serial Bus permits communications between nodes over shared physical media at speeds that range, at present, from 100 to 400 Mbps. Both consumer electronic applications (such as digital VCRs, stereo systems, televisions and camcorders) and traditional desktop computer applications (e.g., mass storage, printers and tapes), have adopted 1394. Serial Bus is unique in its relevance to both consumer electronic and computer domains and is EXPECTED to form the basis of a home or small office network that combines both types of devices.
The CSR architecture describes a memory-mapped address space that Serial Bus implements as a 64-bit fixed addressing scheme. Within the address space, ten bits are allocated for bus ID (up to a maximum of 1,023 buses), six are allocated for node physical ID (up to 63 per bus) while the remaining 48 bits (offset) describe a per node address space of 256 terabytes. The CSR architecture, by convention, splits a node's address space into two regions with different behavioral characteristics. The lower portion, up to but not including 0xFFFF F000 0000, is EXPECTED to behave as memory in response to read and write transactions. The upper portion is more like a traditional IO space: read and write transactions in this area usually have side effects. Control and status registers (CSRs) that have FIFO behavior customarily are implemented in this region. Within the 64-bit address, the 16-bit node ID (bus ID and physical ID) is analogous to a network hardware address---but 1394 node IDs are variable and subject to reassignment each time one or more nodes are added to or removed from the bus. NOTE: Although the 16-bit node ID contains a bus ID, at present there is no standard method to connect separately enumerated Serial Buses. Active development of a standard for Serial Bus to Serial Bus bridges is underway in the IEEE P1394.1 working group. Unless extended by some future standard, the IPv4 over 1394 protocols specified by this document may not operate correctly across bridges. The 1394 link layer provides a packet delivery service with both confirmed (acknowledged) and unconfirmed packets. Two levels of service are available: "asynchronous" packets are sent on a best- effort basis while "isochronous" packets are guaranteed to be delivered with bounded latency. Confirmed packets are always asynchronous but unconfirmed packets may be either asynchronous or isochronous. Data payloads vary with implementations and may range from one octet up to a maximum determined by the transmission speed (at 100 Mbps, named S100, the maximum asynchronous data payload is 512 octets while at S400 it is 2048 octets). NOTE: Extensions underway in IEEE P1394b contemplate additional speeds of 800, 1600 and 3200 Mbps.
2. DEFINITIONS AND NOTATION 2.1 Conformance When used in this document, the keywords "MAY", "OPTIONAL", "RECOMMENDED", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD" and "SHOULD NOT" differentiate levels of requirements and optionality and are to be interpreted as described in RFC 2119. Several additional keywords are employed, as follows: EXPECTED: A keyword used to describe the behavior of the hardware or software in the design models assumed by this standard. Other hardware and software design models may also be implemented. IGNORED: A keyword that describes bits, octets, quadlets or fields whose values are not checked by the recipient. RESERVED: A keyword used to describe either objects---bits, octets, quadlets and fields---or the code values assigned to these objects; the object or the code value is set aside for future standardization. A RESERVED object has no defined meaning and SHALL be zeroed by its originator or, upon development of a future standard, set to a value specified by such a standard. The recipient of a RESERVED object SHALL NOT check its value. The recipient of an object whose code values are defined by this standard SHALL check its value and reject RESERVED code values. 2.2 Glossary The following terms are used in this standard: address resolution protocol: A method for a requester to determine the hardware (1394) address of an IP node from the IP address of the node. bus ID: A 10-bit number that uniquely identifies a particular bus within a group of multiple interconnected buses. The bus ID is the most significant portion of a node's 16-bit node ID. The value 0x3FF designates the local bus; a node SHALL respond to requests addressed to its 6-bit physical ID if the bus ID in the request is either 0x3FF or the bus ID explicitly assigned to the node. encapsulation header: A structure that precedes all IP data transmitted over 1394. See also link fragment. IP datagram: An Internet message that conforms to the format specified by STD 5, RFC 791.
link fragment: A portion of an IP datagram transmitted within a single 1394 packet. The data payload of the 1394 packet contains both an encapsulation header and its associated link fragment. It is possible to transmit datagrams without link fragmentation. multicast channel allocation protocol: A method for multicast groups to coordinate their use of Serial Bus resources (channels) if multicast datagrams are transmitted on other than the default broadcast channel. multicast channel owner: A multicast source that has allocated a channel for one or more multicast addresses and transmits MCAP advertisements to communicate these channel mapping(s) to other participants in the IP multicast group. When more than one source transmits MCAP advertisements for the same channel number, the source with the largest physical ID is the owner. node ID: A 16-bit number that uniquely identifies a Serial Bus node within a group of multiple interconnected buses. The most significant ten bits are the bus ID and the least significant six bits are the physical ID. node unique ID: A 64-bit number that uniquely identifies a node among all the Serial Bus nodes manufactured worldwide; also known as the EUI-64 (Extended Unique Identifier, 64-bits). octet: Eight bits of data. packet: Any of the 1394 primary packets; these may be read, write or lock requests (and their responses) or stream data. The term "packet" is used consistently to differentiate Serial Bus primary packets from 1394 ARP requests/responses, IP datagrams or MCAP advertisements/solicitations. physical ID: On a particular bus, this 6-bit number is dynamically assigned during the self-identification process and uniquely identifies a node on that bus. quadlet: Four octets, or 32 bits, of data. stream packet: A 1394 primary packet with a transaction code of 0x0A that contains a block data payload. Stream packets may be either asynchronous or isochronous according to the type of 1394 arbitration employed.
2.3 Abbreviations The following are abbreviations that are used in this standard: 1394 ARP Address resolution protocol (specific to 1394) CSR Control and status register CRC Cyclical redundancy checksum EUI-64 Extended Unique Identifier, 64-bits GASP Global asynchronous stream packet IP Internet protocol (within this document, IPv4) MCAP Multicast channel allocation protocol 2.4 Numeric values Decimal and hexadecimal numbers are used within this standard. By editorial convention, decimal numbers are most frequently used to represent quantities or counts. Addresses are uniformly represented by hexadecimal numbers, which are also used when the value represented has an underlying structure that is more apparent in a hexadecimal format than in a decimal format. Decimal numbers are represented by Arabic numerals or by their English names. Hexadecimal numbers are prefixed by 0x and represented by digits from the character set 0 - 9 and A - F. For the sake of legibility, hexadecimal numbers are separated into groups of four digits separated by spaces. For example, both 42 and 0x2A represent the same numeric value. 3. IP-CAPABLE NODES Not all Serial Bus devices are capable of the reception and transmission of 1394 ARP requests/responses or IP datagrams. An IP- capable node SHALL fulfill the following minimum requirements: - it SHALL implement configuration ROM in the general format specified by ISO/IEC 13213:1994 and SHALL implement the bus information block specified by IEEE P1394a and a unit directory specified by this standard; - the max_rec field in its bus information block SHALL be at least 8; this indicates an ability to accept block write requests and asynchronous stream packets with data payload of 512 octets. The same ability SHALL also apply to read requests; that is, the node SHALL be able to transmit a block response packet with a data payload of 512 octets;
- it SHALL be isochronous resource manager capable, as specified by IEEE P1394a; - it SHALL support both reception and transmission of asynchronous streams as specified by IEEE P1394a; and 4. LINK ENCAPSULATION AND FRAGMENTATION All IP datagrams (broadcast, unicast or multicast), 1394 ARP requests/responses and MCAP advertisements/solicitations that are transferred via 1394 block write requests or stream packets SHALL be encapsulated within the packet's data payload. The maximum size of data payload, in octets, is constrained by the speed at which the packet is transmitted. Table 1 - Maximum data payloads (octets) Speed Asynchronous Isochronous +------------------------------------+ | S100 | 512 | 1024 | | S200 | 1024 | 2048 | | S400 | 2048 | 4096 | | S800 | 4096 | 8192 | | S1600 | 8192 | 16384 | | S3200 | 16384 | 32768 | +------------------------------------+ NOTE: The maximum data payloads at speeds of S800 and faster may be reduced (but will not be increased) as a result of standardization by IEEE P1394b. The maximum data payload for asynchronous requests and responses may also be restricted by the capabilities of the sending or receiving node(s); this is specified by max_rec in either the bus information block or 1394 ARP response. For either of these reasons, the maximum data payload transmissible between IP-capable nodes may be less than the default 1500 octet maximum transmission unit (MTU) specified by this document. This requires that the encapsulation format also permit 1394 link-level fragmentation and reassembly of IP datagrams. NOTE: IP-capable nodes may operate with an MTU size larger than the default, but the means by which a larger MTU is configured are beyond the scope of this document.
4.1 Global asynchronous stream packet (GASP) format Some IP datagrams, as well as 1394 ARP requests and responses, may be transported via asynchronous stream packets. When asynchronous stream packets are used, their format SHALL conform to the global asynchronous stream packet (GASP) format specified by IEEE P1394a. The GASP format illustrated below is INFORMATIVE and reproduced for ease of reference, only. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | data_length |tag| channel | 0x0A | sy | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | header_CRC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | source_ID | specifier_ID_hi | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |specifier_ID_lo| version | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +--- data ---+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | data_CRC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 - GASP format The source_ID field SHALL specify the node ID of the sending node and SHALL be equal to the most significant 16 bits of the sender's NODE_IDS register. The specifier_ID_hi and specifier_ID_lo fields together SHALL contain the value 0x00 005E, the 24-bit organizationally unique identifier (OUI) assigned by the IEEE Registration Authority (RA) to IANA. The version field SHALL be one. NOTE: Because the GASP format utilizes the first two quadlets of data payload in an asynchronous stream packet format, the maximum payloads cited in Table 1 are effectively reduced by eight octets. In the clauses that follow, references to the first quadlet of data payload mean the first quadlet usable for an IP datagram or 1394 ARP request or response. When the GASP format is used, this is the third quadlet of the data payload for the packet.
4.2 Encapsulation header All IP datagrams transported over 1394 are prefixed by an encapsulation header with one of the formats illustrated below. If an entire IP datagram may be transmitted within a single 1394 packet, it is unfragmented and the first quadlet of the data payload SHALL conform to the format illustrated below. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | lf| reserved | ether_type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2 - Unfragmented encapsulation header format The lf field SHALL be zero. The ether_type field SHALL indicate the nature of the datagram that follows, as specified by the following table. ether_type Datagram +-------------------------+ | 0x0800 | IPv4 | | 0x0806 | 1394 ARP | | 0x8861 | MCAP | +-------------------------+ NOTE: Other network protocols, identified by different values of ether_type, may use the encapsulation formats defined herein but such use is outside of the scope of this document. In cases where the length of the datagram exceeds the maximum data payload supported by the sender and all recipients, the datagram SHALL be broken into link fragments; the first two quadlets of the data payload for the first link fragment SHALL conform to the format shown below. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | lf|rsv| datagram_size | ether_type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | dgl | reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3 - First fragment encapsulation header format
The second and subsequent link fragments (up to and including the last) SHALL conform to the format shown below. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | lf|rsv| datagram_size | rsv | fragment_offset | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | dgl | reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4 - Subsequent fragment(s) encapsulation header format The definition and usage of the fields is as follows: The lf field SHALL specify the relative position of the link fragment within the IP datagram, as encoded by the following table. lf Position +------------------------+ | 0 | Unfragmented | | 1 | First | | 2 | Last | | 3 | Interior | +------------------------+ datagram_size: The encoded size of the entire IP datagram. The value of datagram_size SHALL be the same for all link fragments of an IP datagram and SHALL be one less than the value of Total Length in the datagram's IP header (see STD 5, RFC 791). ether_type: This field is present only in the first link fragment and SHALL have a value of 0x0800, which indicates an IPv4 datagram. fragment_offset: This field is present only in the second and subsequent link fragments and SHALL specify the offset, in octets, of the fragment from the beginning of the IP datagram. The first octet of the datagram (the start of the IP header) has an offset of zero; the implicit value of fragment_offset in the first link fragment is zero.
dgl: The value of dgl (datagram label) SHALL be the same for all link fragments of an IP datagram. The sender SHALL increment dgl for successive, fragmented datagrams; the incremented value of dgl SHALL wrap from 65,535 back to zero. All IP datagrams, regardless of the mode of transmission (block write requests or stream packets) SHALL be preceded by one of the above described encapsulation headers. This permits uniform software treatment of datagrams without regard to the mode of their transmission. 4.3 Link fragment reassembly The recipient of an IP datagram transmitted via more than one 1394 packet SHALL use both the sender's source_ID (obtained from either the asynchronous packet header or the GASP header) and dgl to identify all the link fragments from a single datagram. Upon receipt of a link fragment, the recipient may place the data payload (absent the encapsulation header) within an IP datagram reassembly buffer at the location specified by fragment_offset. The size of the reassembly buffer may be determined from datagram_size. If a link fragment is received that overlaps another fragment identified by the same source_ID and dgl, the fragment(s) already accumulated in the reassembly buffer SHALL be discarded. A fresh reassembly may be commenced with the most recently received link fragment. Fragment overlap is determined by the combination of fragment_offset from the encapsulation header and data_length from the 1394 packet header. Upon detection of a Serial Bus reset, recipient(s) SHALL discard all link fragments of all partially reassembled IP datagrams and sender(s) SHALL discard all not yet transmitted link fragments of all partially transmitted IP datagrams. 5. SERIAL BUS ADDRESS RESOLUTION PROTOCOL (1394 ARP) Methods to determine the hardware address of a device from its corresponding IP address are inextricably tied to the transport medium utilized by the device. In the description below and throughout this document, the acronym 1394 ARP pertains solely to an address resolution protocol whose methods and data structures are specific to 1394. 1394 ARP requests SHALL be transmitted by the same means as broadcast IP datagrams; 1394 ARP responses MAY be transmitted in the same way or they MAY be transmitted as block write requests addressed to the
sender_unicast_FIFO address identified by the 1394 ARP request. A 1394 ARP request/response is 32 octets and SHALL conform to the format illustrated by Figure 5. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | hardware_type (0x0018) | protocol_type (0x0800) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | hw_addr_len | IP_addr_len | opcode | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +--- sender_unique_ID ---+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sender_max_rec| sspd | sender_unicast_FIFO_hi | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sender_unicast_FIFO_lo | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sender_IP_address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | target_IP_address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5 - 1394 ARP request/response format 1394 ARP requests and responses transported by asynchronous stream packets SHALL be encapsulated within the GASP format specified by IEEE P1394a (see also 4.1). The recipient of a 1394 ARP request or response SHALL ignore it unless the most significant ten bits of the source_ID field (whether obtained from the GASP header of an asynchronous stream packet or the packet header of a block write request) are equal to either 0x3FF or the most significant ten bits of the recipient's NODE_IDS register. Field usage in a 1394 ARP request/response is as follows: hardware_type: This field indicates 1394 and SHALL have a value of 0x0018. protocol_type: This field SHALL have a value of 0x0800; this indicates that the protocol addresses in the 1394 ARP request/response conform to the format for IP addresses. hw_addr_len: This field indicates the size, in octets, of the 1394-dependent hardware address associated with an IP address and SHALL have a value of 16.
IP_addr_len: This field indicates the size, in octets, of an IP version 4 (IPv4) address and SHALL have a value of 4. opcode: This field SHALL be one to indicate a 1394 ARP request and two to indicate a 1394 ARP response. sender_unique_ID: This field SHALL contain the node unique ID of the sender and SHALL be equal to that specified in the sender's bus information block. sender_max_rec: This field SHALL be equal to the value of max_rec in the sender's configuration ROM bus information block. sspd: This field SHALL be set to the lesser of the sender's link speed and PHY speed. The link speed is the maximum speed at which the link may send or receive packets; the PHY speed is the maximum speed at which the PHY may send, receive or repeat packets. The table below specifies the encoding used for sspd; all values not specified are RESERVED for future standardization. Table 2 - Speed codes Value Speed +---------------+ | 0 | S100 | | 1 | S200 | | 2 | S400 | | 3 | S800 | | 4 | S1600 | | 5 | S3200 | +---------------+ sender_unicast_FIFO_hi and sender_unicast_FIFO_lo: These fields together SHALL specify the 48-bit offset of the sender's FIFO available for the receipt of IP datagrams in the format specified by section 6. The offset of a sender's unicast FIFO SHALL NOT change, except as the result of a power reset. sender_IP_address: This field SHALL specify the IP address of the sender. target_IP_address: In a 1394 ARP request, this field SHALL specify the IP address from which the sender desires a response. In a 1394 ARP response, it SHALL be IGNORED.
6. CONFIGURATION ROM Configuration ROM for IP-capable nodes SHALL contain a unit directory in the format specified by this standard. The unit directory SHALL contain Unit_Spec_ID and Unit_SW_Version entries, as specified by ISO/IEC 13213:1994. The unit directory may also contain other entries permitted by ISO/IEC 13213:1994 or IEEE P1212r. 6.1 Unit_Spec_ID entry The Unit_Spec_ID entry is an immediate entry in the unit directory that specifies the organization responsible for the architectural definition of the Internet Protocol capabilities of the device. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x12 | unit_spec_ID (0x00 005E) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6 - Unit_Spec_ID entry format The value of unit_spec_ID SHALL be 0x00 005E, the registration ID (RID) obtained by IANA from the IEEE RA. The value indicates that the IETF and its technical committees are responsible for the maintenance of this standard. 6.2 Unit_SW_Version entry The Unit_SW_Version entry is an immediate entry in the unit directory that, in combination with the unit_spec_ID, specifies the document that defines the software interface of the unit. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x13 | unit_sw_version (0x00 0001) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 7 - Unit_SW_Version entry format The value of unit_sw_version SHALL be one, which indicates that the device complies with the normative requirements of this standard.
6.3 Textual descriptors Textual descriptors within configuration ROM are OPTIONAL; when present they provide additional descriptive information intended to be intelligible to a human user. IP-capable nodes SHOULD associate a textual descriptor with a content of "IANA" with the Unit_Spec_ID entry and a textual descriptor with a content of "IPv4" for the Unit_SW_Version entry. The figure below illustrates a unit directory implemented by an IP- capable node; it includes OPTIONAL textual descriptors. Although the textual descriptor leaves are not part of the unit directory, for the sake of simplicity they are shown immediately following the unit directory. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | directory_length (4) | CRC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x12 | unit_spec_ID (0x00 005E) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x81 | textual descriptor offset (3) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x13 | unit_sw_version | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x81 | textual descriptor offset (5) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | textual_descriptor_length (3) | CRC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +--- zeros ---+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | "I" | "A" | "N" | "A" | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | textual_descriptor_length (3) | CRC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +--- zeros ---+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | "I" | "P" | "v" | "4" | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 9 - Sample unit directory and textual descriptors
7. IP UNICAST A unicast IP datagram may be transmitted to a recipient within a 1394 primary packet that has one of the following transaction codes: tcode Description Arbitration +--------------------------------------+ | 0x01 | Block write | Asynchronous | | 0x0A | Stream packet | Isochronous | | 0x0A | Stream packet | Asynchronous | +--------------------------------------+ Block write requests are suitable when 1394 link-level acknowledgement is desired but there is no need for bounded latency in the delivery of the packet (quality of service). Isochronous stream packets provide quality of service guarantees but no 1394 link-level acknowledgement. The last method, asynchronous stream packets, is mentioned only for the sake of completeness. This method SHOULD NOT be used for IP unicast, since it provides for neither 1394 link-level acknowledgment nor quality of service---and consumes a valuable resource, a channel number. Regardless of the IP unicast method employed, asynchronous or isochronous, it is the responsibility of the sender of a unicast IP datagram to determine the maximum data payload that may be used in each packet. The necessary information may be obtained from: - the SPEED_MAP maintained by the 1394 bus manager, which provides the maximum transmission speed between any two nodes on the local Serial Bus. The bus manager analyzes bus topology in order to construct the speed map; the maximum transmission speed between nodes reflects the capabilities of the intervening nodes. The speed in turn implies a maximum data payload (see Table 1); - the sender_max_rec field in a 1394 ARP response; or - other methods beyond the scope of this standard. The maximum data payload SHALL be the minimum of the largest data payload implemented by the sender, the recipient and the PHYs of all intervening nodes (the last is implicit in the SPEED_MAP entry indexed by sender and recipient).
NOTE: The SPEED_MAP is derived from the self-ID packets transmitted by all 1394 nodes subsequent to a bus reset. An IP-capable node may observe the self-ID packets directly. Unicast IP datagrams whose quality of service is best-effort SHALL be contained within the data payload of 1394 block write transactions addressed to the source_ID and sender_unicast_FIFO obtained from a 1394 ARP response. If no acknowledgement is received in response to a unicast block write request it is uncertain whether or not the data payload was received by the target. NOTE: An acknowledgment may be absent because the target is no longer functional, may not have received the packet because of a header CRC error or may have received the packet successfully but the acknowledge sent in response was corrupted. Unicast IP datagrams that require quality of service other than best-effort are beyond the scope of this standard. 8. IP BROADCAST Broadcast IP datagrams are encapsulated according to the specifications of section 4 and are transported by asynchronous stream packets. There is no quality of service provision for IP broadcast over 1394. The channel number used for IP broadcast is specified by the BROADCAST_CHANNEL register. All broadcast IP datagrams SHALL use asynchronous stream packets whose channel number is equal to the channel field from the BROADCAST_CHANNEL register. Although 1394 permits the use of previously allocated channel number(s) for up to one second subsequent to a bus reset, IP-capable nodes SHALL NOT transmit asynchronous stream packets at any time the valid bit in their BROADCAST_CHANNEL register is zero. Since the valid bit is automatically cleared to zero by a bus reset, this prohibits the use of 1394 ARP or broadcast IP until the IRM allocates a channel number. 9. IP MULTICAST Multicast IP datagrams are encapsulated according to the specifications of section 4 and are transported by stream packets. Asynchronous streams are used for best-effort IP multicast; quality of service other than best-effort is beyond the scope of this standard.
By default, all best-effort IP multicast SHALL use asynchronous stream packets whose channel number is equal to the channel field from the BROADCAST_CHANNEL register. In particular, datagrams addressed to 220.127.116.11 and 18.104.22.168 SHALL use this channel number. Best-effort IP multicast for other IP multicast group addresses may utilize a different channel number if such a channel number is allocated and advertised prior to use, as described below. IP-capable nodes may transmit best-effort IP multicast only if one of the following two conditions is met: - the channel number in the stream packet is equal to the channel number field in the BROADCAST_CHANNEL register and the valid bit in the same register is one; or - for other channel number(s), some source of IP multicast has allocated and is advertising the channel number used. The remainder of this section describes a multicast channel allocation protocol (MCAP) employed by both IP multicast sources and recipients whenever a channel number other than the default is used. MCAP is a cooperative protocol; the participants exchange messages over the broadcast channel used by all IP-capable nodes on a particular Serial Bus. CAUTION: This document does not define facilities and methods for shared use of a single channel number (other than the default channel number specified by the BROADCAST_CHANNEL register) by more than one IP multicast address. 9.1 MCAP message format MCAP messages, whether sent by a multicast channel owner or recipient, are transported as the data portion of a GASP packet and have the format illustrated below. The first four octets of the message are fixed; the remainder consists of variable-length tuples, each of which encodes information about a particular IP multicast group. Individual MCAP messages SHALL NOT be fragmented and SHALL be encapsulated within a stream packet as ether_type 0x8861.
1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length | reserved | opcode | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + message data + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 10 - MCAP message format Field usage in an MCAP message is as follows: length: This field SHALL contain the size, in octets, of the entire MCAP message. opcode: This field SHALL have one of the values specified by the table below. opcode Name Comment +----------------------------------------------------------------+ | 0 | Advertise | Sent by a multicast channel owner to | | | | broadcast the current mapping(s) from one | | | | or more group addresses to their | | | | corresponding channel number(s). | | 1 | Solicit | Sent to request multicast channel owner(s) | | | | to advertise the indicated channel | | | | mapping(s) as soon as possible. | +----------------------------------------------------------------+ message data: The remainder of the MCAP message is variable in length and SHALL consist of zero or more group address descriptors with the format illustrated below.
1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length | type | reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | expiration | channel | speed | reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | bandwidth | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + group_address + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 11 - MCAP group address descriptor format length: This field SHALL contain the size, in octets, of the MCAP group address descriptor. type: This field SHALL have a value of one, which indicates a group address descriptor. expiration: The usage of this field varies according to opcode. For solicit messages the expiration field SHALL be IGNORED. Otherwise, for advertisements, this field SHALL contain a time- stamp, in seconds, that specifies a future time after which the channel number specified by channel may no longer be used. channel: This field is valid only for advertise messages, in which case it SHALL specify an allocated channel number, in the range zero to 63 inclusive. All other values are RESERVED. speed: This field is valid only for advertise messages, in which case it SHALL specify the speed at which stream packets for the indicated channel are transmitted. Table 2 specifies the encoding used for speed. bandwidth: This field SHALL be zero; it is allocated in the group address descriptor to accommodate future extensions to MCAP that specify quality of service and utilize the isochronous capabilities of Serial Bus. group_address: This variable length field SHALL specify the IP address of a particular IP multicast group. The length of group_address, in octets, is derived from the length of the group address descriptor by subtracting 12 from the length field.
9.2 MCAP message domain MCAP messages carry information valid only for the local Serial Bus on which they are transmitted. Recipients of MCAP messages SHALL IGNORE all MCAP messages from other than the local bus, as follows. The source_ID of the sender is contained in the GASP header that precedes the encapsulated MCAP message. A recipient of an MCAP message SHALL examine the most significant ten bits of source_ID from the GASP header; if they are not equal to either 0x3FF or the most significant ten bits of the recipient's NODE_IDS register, the recipient SHALL IGNORE the message. Within an MCAP message domain, the owner of a channel mapping is identified by the source_ID field in the GASP header of an MCAP advertisement. The owner is the node with the largest physical ID, the least significant six bits of source_ID. 9.3 Multicast receive An IP-capable device that wishes to receive multicast data SHALL first ascertain the channel mapping (if any) that exists between a group address and a channel number other than the default channel specified by the BROADCAST_CHANNEL register. Such a device may observe the MCAP advertisements on the broadcast channel for the desired channel mapping(s). An intended multicast recipient may transmit MCAP solicitation requests in order to request multicast channel owner(s) to broadcast advertisements sooner than the next ten second interval. Originators of MCAP solicitation requests SHALL limit the rate at which they are transmitted. Subsequent to sending a solicitation request, the originator SHALL NOT send another MCAP solicitation request until ten seconds have elapsed. In either case, if a mapping exists for the group address for other than the default channel, an MCAP advertise message is EXPECTED within ten seconds. Upon receipt of an MCAP advertise message that describes one or more channel mappings, the intended multicast recipient may receive IP datagrams on the indicated channel number(s) until the expiration time. If multiple MCAP advertise messages are observed that specify the same group address, the channel number SHALL be obtained from the advertisement message with the largest physical ID, which SHALL be obtained from the least significant six bits of source_ID from the GASP header.
If no MCAP advertise message is received for a particular group address within ten seconds, no multicast source(s) are active for channel(s) other than the default. Either there is there is no multicast data or it is being transmitted on the default channel. Once a multicast recipient has observed an advertisement for the desired group address, it MAY receive multicast data on either the default broadcast channel or the channel number(s) indicated but it SHALL continue to monitor the default broadcast channel for MCAP advertisements for the same group address in order to refresh the expiration time of channel number(s) in use. 9.4 Multicast transmit An IP-capable device that wishes to transmit multicast data on other than the default channel SHALL first ascertain whether or not another multicast source has already allocated a channel number for the group address. The intended multicast source may transmit an MCAP solicitation request with one or more group address descriptors. Whether or not a solicitation request has been transmitted, the intended multicast source SHALL monitor the broadcast channel for MCAP advertisements. If a channel mapping already exists for the group address, an MCAP advertisement SHOULD be received within ten seconds. In this case the intended multicast source may commence transmission of IP datagrams on the indicated channel number(s) and may continue to do so until their expiration time. The multicast source SHALL monitor MCAP advertisements in order to refresh the expiration time of channel number(s) in use. When no other multicast source has established a channel mapping for the group address, the intended multicast source may attempt to allocate a channel number from the isochronous resource manager's CHANNELS_AVAILABLE register according to the procedures described in IEEE P1394a. If the channel number allocation is successful, the multicast source SHALL advertise the new channel mapping(s) as soon as possible. Once 100 ms elapses subsequent to the initial advertisement of a newly allocated channel number , the multicast source may transmit IP datagrams using the channel number advertised. Multicast IP datagrams may be transmitted on the default channel until the sender observes (or transmits) an advertisement that specifies non- default channel mapping(s) for the multicast addresses. This permits the smooth transition of multicast from the default channel to an explicitly allocated channel.
Once a multicast source has advertised a channel mapping, it SHALL continue to transmit MCAP advertisements for the channel mapping unless it either a) transfers ownership to another multicast source, b) permits the channel mapping to expire without transfer or c) in the case of overlapped channel mappings, relinquishes control of the channel mapping to another multicast source. 9.5 Advertisement of channel mappings Each multicast source SHALL periodically broadcast an advertisement of all IP multicast group addresses for which it has allocated a channel number different from the default multicast channel number. An advertisement SHALL consist of a single MCAP message with an opcode of zero that contains one or more group address descriptors (one for each group address assigned a channel number other than that specified by the BROADCAST_CHANNEL register). Within each group address descriptor, the group_address and channel fields associate an IP multicast group address with a Serial Bus channel number. The speed field specifies the maximum 1394 speed at which any of the senders within the IP multicast group is permitted to transmit data. The expiration field specifies the current time or a future time after which the channel mapping(s) are no longer valid. Except when a channel owner intends to relinquish ownership (as described in 9.7 below), the expiration time SHALL be at least 60 seconds in the future measured from the time the advertisement is transmitted. No more than ten seconds SHALL elapse from the transmission of its most recent advertisement before the owner of a channel mapping initiates transmission of the subsequent advertisement. The owner of a channel mapping SHOULD transmit an MCAP advertisement in response to a solicitation as soon as possible after the receipt of the request. 9.6 Overlapped channel mappings When two intended multicast sources wish to transmit to the same IP multicast group and no channel mapping exists for the group address, there is a chance that both will allocate channel numbers and both will advertise the channel mappings. These channel mappings overlap, i.e., the same group address is mapped to more than one channel number in MCAP advertisements with nonzero expiration times. Multicast channel owners SHALL monitor MCAP advertisements in order to detect overlapped channel mappings. MCAP advertisements whose expiration field has a value less than 60 SHALL be ignored for the purpose of overlapped channel detection. When an overlapped channel
mapping is detected, the owner with the largest physical ID (as determined by the least significant six bits of source_ID from the GASP header) is NOT REQUIRED to take any action. The channel numbers advertised by owners with smaller physical IDs are invalid; their owners SHALL cease transmission of both IP datagrams and MCAP advertisements that use the invalid channel numbers. As soon as these channel mappings expire , their owners SHALL deallocate any unused channel numbers as described in 9.8 below. Recipients of MCAP advertisements that detect overlapped channel mappings SHALL ignore the advertisements from multicast channel owner(s) with the smaller physical IDs and SHALL NOT transmit IP datagrams that use the invalid channel number. It is possible for some channel mappings in a single MCAP advertisement to be valid even if others SHALL be IGNORED as a result of overlap. 9.7 Transfer of channel ownership The owner of a channel mapping may cease multicast transmission on a particular channel, in which case it SHOULD invalidate the channel mapping and in some cases deallocate the channel number. Because other multicast sources may be using the same channel mapping, an orderly process is defined to transfer channel ownership. The owner of an existing channel mapping that wishes to release the mapping SHALL commence a timer to measure the time remaining before the anticipated release of the mapping and its associated channel. Until the timer counts down to zero, the owner SHOULD continue to transmit MCAP advertisements for the affected channel but SHALL adjust expiration in each advertisement to reflect the time remaining until the channel is to be deallocated. If the owner is unable to transmit MCAP advertisements until the timer reaches zero, it SHALL initiate a bus reset. Otherwise, the sequence of expiration times transmitted by the owner intending to release the mapping SHALL decrease with each succeeding advertisement. If other multicast source(s) are using the same channel mapping and observe an expiration time less than or equal to 60 seconds, they SHALL commence transmitting MCAP advertisements for the channel mapping with refreshed expiration times greater than or equal to 60 seconds that maintain the channel mapping. Any contention that occurs between multiple sources that attempt to claim ownership of the channel mapping SHALL be resolved as described in 9.8. If the original owner observes an MCAP advertisement for the channel to be relinquished before its own timer has expired, it SHALL NOT deallocate the channel number.
Otherwise, if the owner's timer expires without the observation of a MCAP advertisement by another node, the owner of the channel number SHALL subsequently deallocate the channel as described in 9.8. If the intended owner of the channel mapping observes an MCAP advertisement whose expiration field is zero, orderly transfer of the channel(s) from the former owner has failed. The intended owner SHALL either stop reception and transmission on the expired channel number(s) or allocate different channel number(s) as specified by 9.4. 9.8 Redundant channel mappings When ownership of a channel mapping is transferred from one multicast source to another, it is possible for more than one device to claim ownership. This results in redundant MCAP advertisements, transmitted by different sources, each of which specifies the same multicast group address and channel. A procedure similar to that of 9.6 SHALL resolve the contention for channel ownership. Multicast channel owners SHALL monitor MCAP advertisements in order to detect redundant channel mappings. MCAP advertisements whose expiration field has a value less than 60 SHALL be ignored for the purpose of redundant channel detection. When a redundant channel mapping is detected, the owner with the largest physical ID (as determined by the least significant six bits of source_ID from the GASP header) is NOT REQUIRED to take any action. The owner(s) with smaller physical IDs SHALL cease transmission of MCAP advertisements for the redundant channel number but SHALL NOT deallocate the channel number. 9.9 Expired channel mappings A channel mapping expires when expiration seconds have elapsed since the most recent MCAP advertisement. At this time, multicast recipients SHALL stop reception on the expired channel number(s). Also at this time, the owner of the channel mapping(s) SHALL transmit an MCAP advertisement with expiration cleared to zero and SHALL continue to transmit such advertisements until 30 seconds have elapsed since the expiration of the channel mapping. Once this additional 30-second period has elapsed, the owner of the channel mapping(s) SHALL deallocate the channel number(s) and indicate their availability in the isochronous resource manager's CHANNELS_AVAILABLE register. If an IP-capable device observes an MCAP advertisement whose expiration field is zero, it SHALL NOT attempt to allocate any of the channel number(s) specified until 30 seconds have elapsed since the most recent such advertisement.
9.10 Bus reset A bus reset SHALL invalidate all multicast channel mappings and SHALL cause all multicast recipients and senders to zero all MCAP advertisement interval timers. Prior owners of multicast channel mappings may reallocate a channel number from the isochronous resource manager's CHANNELS_AVAILABLE register and resume broadcast of MCAP advertisements as soon as a channel is allocated. If channel reallocation is attempted, the prior owner SHOULD use the same channel number allocated prior to the bus reset and may commence reallocation immediately upon completion of the bus reset so long as the same channel number is reused. If the prior owner elects to allocate a different channel number, it SHALL wait until at least one second has elapsed since the completion of the bus reset before attempting to allocate a new channel number. Intended or prior recipients or transmitters of multicast on other than the default channel SHALL NOT transmit MCAP solicitation requests until at least ten seconds have elapsed since the completion of the bus reset. Multicast data on other than the default channel SHALL NOT be received or transmitted until an MCAP advertisement is observed or transmitted for the IP multicast group address. Intended or prior transmitters of multicast on other than the default channel that did not own a channel mapping for the IP multicast group address prior to the bus reset SHALL NOT attempt to allocate a channel number from the isochronous resource manager's CHANNELS_AVAILABLE register until at least ten seconds have elapsed since the completion of the bus reset. Subsequent to this ten second delay, intended or prior transmitters of multicast may follow the procedures specified by 9.4 to allocate a channel number and advertise the channel mapping. 10. IANA CONSIDERATIONS This document necessitates the creation and management of a new name space (registry) by IANA. The need for such a registry arises out of the method by which protocol interfaces are uniquely identified by bus standards compliant with ISO/IEC 13213:1994, CSR Architecture. This is explained in more detail in section 6; the essence is that a globally unique 48-bit number SHALL identify the document that specifies the protocol interface. The 48-bit number is the concatenation of 0x00 005E (a registration ID, or RID, granted to IANA by the IEEE Registration Authority) and a second 24-bit number administered by IANA.
The IEEE RA RECOMMENDS that the policy for management of the second 24-bit number be chosen to maximize the quantity of usable numbers with the range of possible values. In particular, the IEEE RA RECOMMENDS that the assignment scheme not apply a structure to the number (e.g., the allocation of a version field within the number) since this would tend to waste large portions of the range. The new name space is "CSR Protocol Identifiers". The values zero and 0xFF FFFF are reserved and SHALL NOT be allocated by IANA. The value one is allocated to this document. The remaining numbers SHALL be managed by IANA and allocated as necessary to identify Internet- Drafts that become IESG standards track documents. Regardless of the assignment method elected by IANA, a registry of all assigned version numbers SHOULD be maintained at one or more Internet sites and should clearly identify the relevant standard identified by the combination of the RID and version number. 11. SECURITY CONSIDERATIONS This document specifies the use of an unsecured link layer, Serial Bus, for the transport of IPv4 datagrams. Serial Bus is vulnerable to denial of service attacks; it is also possible for devices to eavesdrop on data or present forged identities. Implementers who utilize Serial Bus for IPv4 SHOULD consider appropriate counter- measures within application or other layers. 12. ACKNOWLEDGEMENTS This document represents the efforts of the IP/1394 Working Group. The editor wishes to acknowledge the contributions made by all the active participants, either on the reflector or at face-to-face meetings, which have advanced the technical content.
13. REFERENCES Normative reference to standards under development at the time of this document's publication shall utilize the most current draft until such time as it is replaced by an approved standard.  IEEE Std 1394-1995, Standard for a High Performance Serial Bus  ISO/IEC 13213:1994, Control and Status Register (CSR) Architecture for Microcomputer Buses  IEEE Project P1394a, Draft Standard for a High Performance Serial Bus (Supplement)  IEEE Project P1394b, Draft Standard for a High Performance Serial Bus (Supplement)  Postel, J., "Internet Protocol Darpa Internet Program Protocol Specification", RFC 791, September 1981.  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. 14. EDITOR'S ADDRESS Peter Johansson Congruent Software, Inc. 98 Colorado Avenue Berkeley, CA 94602 Phone: (510) 527-3926 Fax: (510) 527-3856 EMail: firstname.lastname@example.org
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