rfc2734.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

   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.






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   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



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   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.






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   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.




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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.





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   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 co