tech-invite   World Map     

IETF     RFCs     Groups     SIP     ABNFs    |    3GPP     Specs     Glossaries     Architecture     IMS     UICC    |    search

RFC 1221

 
 
 

Host Access Protocol (HAP) specification: Version 2

Part 2 of 3, p. 17 to 46
Prev RFC Part       Next RFC Part

 


prevText      Top       Page 17 
6. The Service Agent

   Allocation of network resources, such as streams and groups, is
   accomplished via an exchange of datagram messages, called Setup
   messages, between the user host and the Service Agent (network
   address zero).  Setup operations include reserving, allocating,
   modifying, freeing, and deallocating resources.  The Service Agent
   causes the requested action to be carried out and serves as the
   intermediary between the user and the rest of the network.  In the
   process of implementing the requested action, various network data
   bases are updated to reflect the current state of the referenced
   resource.  The Service Agent also permits a host to inquire about
   resources it owns using Information Request and Information Reply
   messages.

   A setup interaction initiated by a host involves a 3-way exchange
   where: (1) the requesting host sends a Setup Request to the Service
   Agent, (2) the Service Agent returns a Setup Reply to the requesting
   host, and (3) the requesting host returns a Setup Acknowledgment to
   the Service Agent.  This procedure is used to ensure reliable
   transmission of Setup Requests and Replies.  In order to allow more
   than one Setup Request message from a host to be outstanding, each
   Request is assigned a unique Request ID.  The associated Reply and
   subsequent Acknowledgment are identified by the Request ID that they
   contain.  The requesting host should receive a reply to a setup
   request within 3 seconds.  The actual delay will depend on the nature
   of the request and the topology of the network.  For simple networks,
   the delay will often be less than one second.  The requesting host
   should respond to a Reply with a Setup Acknowledgment within one
   second.

   Setup exchanges initiated by the Service Agent involve a two-way
   exchange where: (1) the Service Agent sends a Notification to

Top       Page 18 
   affected hosts, and (2) the hosts return a Setup Acknowledgment to
   the Service Agent.  Notifications are used to inform a host of
   changes in the status of a network resource.  In order to allow more
   than one Notification to be outstanding, each is assigned a unique
   Notification ID.  The Setup Acknowledgment returned by the notified
   host to the Service Agent must contain the Notification ID.  The host
   should respond within one second.

   An information query is initiated by a host and involves a two-way
   exchange where: (1) the host sends an Information Request message to
   the Service Agent, and (2) the Service Agent sends back an
   Information Reply.  There is no acknowledgment mechanism, since this
   request does not change any resource allocation.  Furthermore, if
   there is an error in the request, only one response will be sent by
   the WPS, and the WPS will make no effort to check for or retransmit
   lost responses.  It is the responsibility of the host to wait a
   certain amount of time and then determine that an unanswered
   information request has been lost and to resend it.  (The time
   necessary to answer such a request is usually much less than one
   second.)  The WPS will return the message ID of the information
   request in the information reply message.

          The general format of all Service Agent messages is:

                         <DATAGRAM MESSAGE HEADER>
                          <SERVICE AGENT HEADER>
                              <MESSAGE BODY>

   The Protocol ID field in the datagram message header must be
   HAP_PROTO_SETUP (1) (see Appendix C) for messages sent to the Service
   Agent and will be HAP_PROTO_SETUP in messages received from the
   Service Agent.  The Service Agent does not recognize or support use
   of other higher level protocols (e.g., IP), in setup messages, and
   will discard messages containing such headers.

   Illustrations of message formats below show only the Service Agent
   Header header and message body and do not include the datagram
   message header.  As a reminder that the datagram header is not
   included, word offsets are prefixed with an "S".

   The format of the Service Agent Header is illustrated in Figure 6.
   The body of the message will depend on the particular message type.
   Stream Request and Reply messages are described in Section 6.1.
   Group Request and Reply messages are described in Section 6.2.  The
   format of Notifications is described in Section 6.3, and Setup
   Acknowledgments are described in Section 6.4.  Information Request
   and Reply messages are described in Section 6.5.

Top       Page 19 
                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |     MESSAGE TYPE      |          CODE         |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                    CHECKSUM                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                   MESSAGE ID                  |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                           SERVICE AGENT HEADER
                                 Figure 6


     S0[0-7]   Message Type.  This field determines the type of
               message.

                    0 = Setup Acknowledgment
                    1 = Setup Request
                    2 = Setup Reply
                    3 = Notification
                    4 = Information Request
                    5 = Information Reply

     S0[8-15]  Code.  For Setup Requests, this field identifies the
               request type.

                    1 = Create group (multicast) address
                    2 = Delete group address
                    3 = Join group
                    4 = Leave group
                    5 = Create stream
                    6 = Delete stream
                    7 = Change stream
                    8 = Create shared stream
                    9 = Delete all streams owned by this host
                   10 = Add member to group
                   11 = Remove member from group

               For Setup Replies, this field provides the Reply Code.
               Some of the Reply Codes can be returned to any setup
               request and others are request specific.

                    0 = Group or stream created
                    1 = Group or stream deleted
                    2 = Host added to group
                    3 = Host deleted from group
                    4 = Stream changed

Top       Page 20 
                    5 = (Reserved)
                    6 = Request type invalid or unsupported
                    7 = (Reserved)
                    8 = Network trouble
                    9 = Bad group key
                   10 = Group address/stream ID nonexistent
                   11 = Not member of group/not creator of stream
                   12 = Stream precedence not being accepted
                   13 = (Reserved)
                   14 = (Reserved)
                   15 = (Reserved)
                   16 = Unable to add all the new hosts
                   17 = Insufficient network resources
                   18 = Requested bandwidth too large
                   19 = (Reserved)
                   20 = (Reserved)
                   21 = Maximum messages per interval too small
                   22 = Reply lost in network
                   23 = Illegal priority or precedence value
                   24 = Invalid address provided

               For Notifications, this field contains the Notification
               Type.  (See Section 6.3.)

               For Setup Acknowledgments, this field contains the
               Acknowledgment Type.  (See Section 6.4.)

               For Information Requests, this field contains the
               request type.  (See Section 6.5.)

               For Information Replies, this field contains the reply
               type.  (See Section 6.5.)

     S1[0-15]  Checksum.  The checksum is the 2's-complement of the
               2's-complement sum of the words in the Service Agent
               Header (excluding the checksum word itself) and the
               message body.  Messages received with bad checksums
               must be discarded.

     S2[0-15]  Message ID.  This field is assigned by the host to
               uniquely identify outstanding requests (Request ID) and
               by the Service Agent to uniquely identify outstanding
               notifications (Notification ID).

6.1. Stream Setup Messages

   Streams provide a means of reserving network resources for the
   delivery of traffic at a specified maximum throughput to a specified

Top       Page 21 
   list of recipients.  Traffic sent via a stream has priority over all
   non-stream traffic, and is delivered with the minimum end-to-end
   delay possible.  Hosts use streams to support applications that have
   predictable traffic loads (such as packet voice or video or other
   continuous media traffic) or that require minimum transmission delay
   and lowest delay variance.  Streams are typically used for traffic
   flows of moderate to long duration, where the cost of performing a
   stream Setup is acceptable.

   Streams must be set up before stream data messages can flow.  The
   stream setup messages, each of which has a Request and a Reply, are
   Create Stream, Delete Stream, Change Stream, and Delete All Streams.
   (Create Shared Stream Request is a planned future addition to the
   protocol.)  The use of these messages is illustrated in the scenario
   of exchanges between a host and the Service Agent shown in Figure 7
   where the host establishes a stream, sends some data, modifies the
   stream characteristics, sends some more data, and finally closes down
   the stream.  Not illustrated, but implicit in this scenario, are the
   optional A/R indications associated with each of the stream Setup
   messages.


                                              Service     Other
                                     Host      Agent      hosts

          Create Stream Request        ---------->
          Create Stream Reply          <----------
          Reply Acknowledgment         ---------->
          Stream Messages              --------------------->
             :   :
          Change Stream Request        ---------->
          Change Stream Reply          <----------
          Reply Acknowledgment         ---------->
          Stream Messages              --------------------->
             :   :
          Delete Stream Request        ---------->
          Delete Stream Reply          <----------
          Reply Acknowledgment         ---------->

                              STREAM EXAMPLE
                                 Figure 7

   Streams have eight characteristic properties which are selected at
   stream setup time.  These properties are: (1) data words per time
   interval, (2) time interval, (3) reliability, (4) reliability length,
   (5) precedence, (6) maximum messages per interval, (7) the list of
   recipients, and (8) the set of other streams with which this stream
   shares resources.  To establish a stream, the host sends the Create

Top       Page 22 
   Stream Request message (Figure 8) to the Service Agent.  After the
   network has processed the Create Stream Request, the Service Agent
   will reply with a Create Stream Reply message (Figure 9).  If the
   reply code in the Create Stream Reply indicates that the stream has
   been created successfully, the host may proceed to transmit stream
   data messages after sending a Reply Acknowledgment.

   During the lifetime of a stream, the host which created it may decide
   that some of its characteristic properties should be modified.  All
   but one of the properties can be modified using the Change Stream
   Request message (Figure 10).  The one property that cannot be changed
   is whether or not the stream is willing to share its resources with
   other streams.  After the network has processed the Change Stream
   Request, the Service Agent will respond by sending a Change Stream
   Reply (Figure 11) to the host.  A host requesting a reduced channel
   allocation should decrease its sending rate immediately without
   waiting for receipt of the Change Stream Reply.  A host requesting an
   increased allocation should not proceed to transmit according to the
   new set of parameters without first having received a Reply Code
   indicating that the requested change has taken effect.

   When the host no longer needs the stream it created, it should first
   stop sending traffic via the stream and then send the Service Agent a
   Delete Stream Request message (Figure 12).  After the network has
   processed the Delete Stream Request, the Service Agent will respond
   by sending a Delete Stream Reply (Figure 13) to the host.

   If the host has crashed or restarted, it may no longer know what
   streams it owns.  The host may use an Information Request (see
   Section 6.5) to determine what streams it owns, or the host may use a
   Delete All Streams Request (Figure 14) to discard whatever stream
   resources it may own.  The format for the Delete All Streams Reply is
   shown in Figure 15.

   Note that streams, like all other resources allocated by the Service
   Agent, may be reclaimed by the network if unused.  Currently, if no
   traffic is sent to a stream in a 6 minute interval, and if the owner
   of the steam is down or unreachable, the stream may be deleted.

Top       Page 23 
                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           1           |           5           |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S3        |  MAX MES  | PRE | INT | RLY |      RLEN       |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S4        |            DATA WORDS PER INTERVAL            |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S5        |                 INTERVAL                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S6        |           0           |  ADDRESS LIST LENGTH  |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               |                                               |
     S7-SN     :            DESTINATION ADDRESS LIST           :
               |                                               |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                           CREATE STREAM REQUEST
                                 Figure 8



     S0[0-7]   Setup Type = 1 (Request).

     S0[8-15]  Request Type = 5 (Create Stream).

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

     S3[0-3]   Maximum Messages Per Interval (1-15).  This field
               specifies the maximum number of stream messages the
               host will deliver to the WPS in any single stream
               interval.

     S3[4-5]   Precedence.  This field specifies the precedence of the
               stream.  When there are insufficient network resources
               to support all the requested streams, requests for
               higher precedence streams will preempt existing lower
               precedence streams, and requests for streams with
               insufficient precedence will be rejected.  Medium
               precedence is recommended as the default choice.

Top       Page 24 
                    0 = Low Precedence
                    1 = Medium Precedence
                    2 = High Precedence

     S3[6-7]   Interval.  This field specifies the interval, in
               multiples of 21.22 milliseconds.  (For backward
               compatibility only.  New applications should use 3.
               Use of this field to specify an interval is being
               phased out.)

                    0 =  21.22 milliseconds
                    1 =  42.44 milliseconds
                    2 =  84.88 milliseconds
                    3 =  use interval in word S5

     S3[8-9]   Reliability.  This field specifies the basic bit-error
               rate requirement for the data portion of all messages
               in the stream.  The exact error rate obtained by each
               choice is not specified.

                    0 = Low Reliability
                    1 = Medium-Low Reliability
                    2 = Medium-High Reliability
                    3 = High Reliability

     S3[10-15] Reliability Length.  This field specifies how many
               words beyond the stream message header should be
               transmitted at maximum reliability for all messages in
               the host stream.

     S4[0-15]  Data words per interval.  This field specifies the
               maximum number of 16-bit words of this stream's data
               the network will need to carry during each interval,
               not counting HAP stream message header words.  The
               stream data may be carried in however many messages (up
               to MAX MES) in each interval the host chooses.

     S5[0-15]  Interval (125 microsecond units).  This field specifies
               the time interval over which the <data words per
               interval> data in <max mes> messages will be sent.  For
               backward compatibility, an interval of 0 selects an
               interval of 169.76 milliseconds.  This field is ignored
               unless the INT field is 3.

     S6[0-7]   Reserved.  Must be zero.

     S6[8-15]  Destination address list length.  This field specifies
               the number of entries in the Destination Address List

Top       Page 25 
               field.  Allowed values are 1-8.

     S7-SN     Destination address list.  This list must specify, at
               least indirectly, all the intended recipients of this
               stream's traffic.  At least one destination address
               must be supplied.  Any valid network address,
               specifically including group addresses, may be used
               (except the Service Agent's address, 0).  Messages sent
               in the stream are not limited to using the HAP
               addresses listed.  E.g., if the list consists of only
               group address G, and host A is a member of G, a stream
               message may be sent to A, which was not in the list.

   Caution: Group membership is only evaluated at setup time.  Changes
   in group membership do not cause the stream to be modified.

   Caution: Stream creation involves allocation of specific network
   resources along specific routes for delivery of that traffic.  A
   stream message sent to hosts other than those specified via Setup
   will probably be undeliverable.  A stream message to a group address
   that has gained new members since the stream's last Setup may be
   undeliverable to the new members.


                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           2           |      REPLY CODE       |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S3        |        0        |         STREAM ID           |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S4        |        0        |     ADDRESS LIST LENGTH     |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               |                                               |
     S5-SN     :                 ADDRESS LIST                  :
               |                                               |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                            CREATE STREAM REPLY
                                 Figure 9



     S0[0-7]   Setup Type = 2 (Reply).

Top       Page 26 
     S0[8-15]  Reply Code.  Any reply other than "Stream created"
               means the stream was not created.

                    0 = Stream created
                    8 = Network trouble
                   12 = Stream precedence not being accepted
                   17 = Insufficient network resources
                   18 = Requested bandwidth too large
                   21 = Max. messages per interval too small
                   22 = Reply lost in network
                   23 = Illegal precedence value
                   24 = Invalid destination address in list

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

     S3[0-5]   Reserved.  Must be zero.

     S3[6-15]  Stream ID.  This field contains a stream ID assigned by
               the network.  It must be included in all stream data
               messages sent by the host to allow the WPS to associate
               the message with stored stream characteristics and the
               resources reserved for that stream's traffic.

     S4[0-5]   Reserved.  Must be zero.

     S4[6-15]  Address list length.  The number of entries in the
               Address List field.

     S5-SN     Address list.  This contains the destination addresses
               from the Create Stream Request that were invalid or
               unreachable.  Unreachable destinations are listed as a
               group if every member of the group was unreachable, or
               individually otherwise; i.e., group addresses are
               expanded and the unreachable members are included in
               the list.  The list of unreachable destinations will be
               truncated, if needed, to limit this Reply to a single,
               maximum length HAP message.

Top       Page 27 
                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           1           |           7           |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S3        |        0        |         STREAM ID           |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S4        |  MAX MES  | PRE | INT | RLY |      RLEN       |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S5        |            DATA WORDS PER INTERVAL            |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S6        |                   INTERVAL                    |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S7        |           0           |  ADDRESS LIST LENGTH  |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               |                                               |
     S8-SN     :            DESTINATION ADDRESS LIST           :
               |                                               |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                           CHANGE STREAM REQUEST
                                 Figure 10



     S0[0-7]   Setup Type = 1 (Request).

     S0[8-15]  Request Type = 7 (Change Stream).

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

     S3[0-5]   Reserved.  Must be zero.

     S3[6-15]  Stream ID.

     S4[0-3]   New Maximum Messages Per Interval.

     S4[4-5]   New Precedence.

     S4[6-7]   New Interval selection.

     S4[8-9]   New Reliability.

Top       Page 28 
     S4[10-15] New Reliability Length.

     S5[0-15]  New Data Words Per Interval.

     S6[0-15]  New Interval (ignored unless INT = 3).

     S7[0-7]   Reserved.  Must be zero.

     S7[8-15]  Destination Address List length.  This field specifies
               the number of entries in the new Destination Address
               List.  Allowed values are 0-8.  Use zero (indicating no
               addresses in the list) to avoid changing the list of
               recipient hosts.

     S8-SN     New Destination Address List.  The new, complete, list
               of recipient hosts.  Membership of group addresses is
               evaluated at setup execution time.  Subsequent changes
               in group membership do not cause the stream to be
               modified.  Note that using the same destination address
               list in the Change Stream Request as was used in the
               Create Stream Request can result in a change in the
               list of recipient hosts if membership in a group has
               changed.


                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           2           |      REPLY CODE       |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S3        |        0        |     ADDRESS LIST LENGTH     |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               |                                               |
     S4-SN     :                 ADDRESS LIST                  :
               |                                               |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                            CHANGE STREAM REPLY
                                 Figure 11



     S0[0-7]   Setup Type = 2 (Reply).

Top       Page 29 
     S0[8-15]  Reply Code.  The number in parentheses indicates the
               processing phase at the time of the error (see Caution
               below).  Phase zero and phase one errors leave the
               stream unchanged; errors from later phases may leave
               the stream partially modified.

                    4 = Stream changed
                    8 = (1) Network trouble
                   10 = (0) Stream ID nonexistent
                   11 = (0) Not creator of stream
                   12 = (0) Stream precedence not being accepted
                   16 = (3) Unable to add all the new recipients
                   17 = (2) Insufficient network resources
                   18 = (2) Requested bandwidth too large
                   21 = (0) Maximum messages per interval too small
                   22 = (2) Reply lost in network
                   23 = (0) Illegal precedence value
                   24 = (0) Invalid destination address in list

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

     S3[0-5]   Reserved.  Must be zero.

     S3[6-15]  Address list length.  This field specifies the number
               of addresses in the Address List.

     S4-SN     Address list.  This contains the destination addresses
               from the Change Stream Request that were invalid (phase
               0 errors) or unreachable (phase 3 errors).  Unreachable
               destinations are listed as a group if every member of
               the group was unreachable, or individually otherwise;
               i.e., group addresses are expanded and the unreachable
               members are included in the list.  The list of
               unreachable destinations will be truncated, if needed,
               to limit this Reply to a single, maximum length HAP
               message.

     Caution: The Change Stream Reply will indicate failure if any
     aspect of the requested changes did not occur.  However, the
     stream may have been partially modified.  Processing is performed
     in the following phases:
         0: check for invalid requests;
         1: drop former recipients that are not in the latest list;
         2: increase or decrease the stream's bandwidth allocation
             (decreases are normally successful); then
         3: extend the stream to any new recipients.

Top       Page 30 
     If phase 2 fails, phase 3 is not performed, the Reply Code will
     indicate an error and the stream parameters will be unchanged.
     If phase 3 fails, the Address List will contain the destinations,
     if any, from the latest list that the stream does not reach.
     Phase 1 only fails if the stream has been suspended (see
     Notifications) or the WPS is experiencing network connectivity
     problems.


                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           1           |           6           |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S3        |        0        |         STREAM ID           |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                           DELETE STREAM REQUEST
                                 Figure 12




     S0[0-7]   Setup Type = 1 (Request).

     S0[8-15]  Request Type = 6 (Delete Stream).

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

     S3[0-5]   Reserved.  Must be zero.

     S3[6-15]  Stream ID.

Top       Page 31 
                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           2           |      REPLY CODE       |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                            DELETE STREAM REPLY
                                 Figure 13


     S0[0-7]   Setup Type = 2 (Reply).

     S0[8-15]  Reply Code.  If the request was valid, the Service
               Agent will have marked the stream for deletion even if
               the stream resources have not actually been deleted
               yet.

                    1 = Stream deleted
                   10 = Stream ID nonexistent
                   11 = Not creator of stream

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.


                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           1           |           9           |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                        DELETE ALL STREAMS REQUEST
                                 Figure 14



     S0[0-7]   Setup Type = 1 (Request).

     S0[8-15]  Request Type = 9 (Delete All Streams).

Top       Page 32 
     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.


                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           2           |      REPLY CODE       |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                         DELETE ALL STREAMS REPLY
                                 Figure 15


     S0[0-7]   Setup Type = 2 (Reply).

     S0[8-15]  Reply Code.  The Service Agent will have marked all of
               the host's streams for deletion, even if the stream
               resources have not actually been deleted yet.

                    1 = Streams deleted

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

6.2. Group Setup Messages

   Group (multicast) addressing allows a host to send the same message
   to N different hosts without having to send N copies of the message.
   The network duplicates the message as required.  In addition to
   reducing the burden on the originating host, multicasting reduces the
   load on the network because the network no longer has to carry the
   duplicates along the common portions of the paths between the source
   and destinations.  Multicasting is particularly recommended for
   multi-site conferencing and distributed simulations.

   Group addresses are dynamically created and deleted via setup
   messages exchanged between the hosts and the Service Agent.
   Membership in a group may be any arbitrary subset of the network
   hosts.  A datagram message or stream message addressed to a group is
   delivered to all hosts that are members of that group (exception:
   stream messages sent to a group address that includes hosts the

Top       Page 33 
   stream was not set up to reach).  The group setup messages, each of
   which has a Request and a Reply, are Create Group, Delete Group, Join
   Group, Leave Group, Add Group Member, and Remove Group Member.

   Figure 16 shows a typical use of group setup messages.  The figure
   illustrates a scenario of exchanges between three hosts and the
   Service Agent.  In the scenario one host, Host A, creates a group
   which is joined by hosts B and C.  The hosts then exchange some data
   messages using the group address.  Note that multicast messages are
   not returned to their originator.  Hosts A and C then leave the
   group, and Host B decides to delete the group.  As in the scenario in
   Section 6.1, A/R indications have been omitted for clarity.

   Part of the group creation procedure involves the Service Agent
   returning to the creating host a 48-bit key along with the 16-bit
   group address.  The creating host must pass the key along with the
   group address to other hosts that want to join the group.  These
   other hosts must supply the key along with the group address in their
   Join Group Requests.  The key is used by the network to authenticate
   these operations and thereby minimize the probability that unwanted
   hosts will deliberately or inadvertently become members of the group.
   The procedure used by a host to distribute the group address and key
   is not within the scope of HAP.

   In the figure below, the network Service Agent is pictured as a
   single entity for simplicity.

Top       Page 34 
                                   Service   Host  Host  Host
                                    Agent     A     B     C

        Create Group Request         |<-------|
        Create Group Reply           |------->|
        Reply Acknowledgment         |<-------|
           :   :
        Distribute Group Adr & Key            |---->|
        Distribute Group Adr & Key            |---------->|
           :   :
        Join Group Request (C)       |<-------------------|
        Join Group Reply             |------------------->|
        Reply Acknowledgment         |<-------------------|
        Join Group Request (B)       |<-------------|
        Join Group Reply             |------------->|
        Reply Acknowledgment         |<-------------|
           :   :
        Data Message 1 (A to B and C)         |---->|---->|
        Data Message 2 (B to A and C)         |<----|---->|
        Data Message 3 (C to A and B)         |<----|<----|
           :   :
        Leave Group Request (C)      |<-------------------|
        Leave Group Reply            |------------------->|
        Reply Acknowledgment         |<-------------------|
        Leave Group Request (A)      |<-------|
        Leave Group Reply            |------->|
        Reply Acknowledgment         |<-------|
        Delete Group Request         |<-------------|
        Delete Group Reply           |------------->|
        Reply Acknowledgment         |<-------------|

                               GROUP EXAMPLE
                                 Figure 16

   An alternative method of adding and removing group members is the use
   of Add Group Member and Remove Group Member.  These setup requests
   allow hosts that are already members of the group to add or delete
   other hosts.

   The Setup requests Join Group, Leave Group, Add Group Member, Remove
   Group Member, and Delete Group are authenticated using the 48-bit
   key.  Leave Group and Remove Group Member will remove a host from the
   group membership list but will not alter the existence of the group.
   Delete Group expunges all knowledge of the group from the network.
   HAP permits any host with the proper key to delete the group at any
   time.  Thus, group addresses can be deleted even if the host which
   originally created the group has left the group or has crashed.
   Moreover, groups may exist for which there are currently no members

Top       Page 35 
   because each member has executed a Leave while none has executed a
   Delete.  It is the responsibility of the hosts to coordinate and
   manage the use of group addresses.

   Note that group addresses, like all other resources allocated by the
   network, may be reclaimed by the network if unused for too long.
   Currently, if no traffic is sent to the group address in a 6 minute
   interval, the network may delete the group and notify all members
   that the group no longer exists.

   The Create Group Request (Figure 17) is used to establish a multicast
   address.  After the network has processed the Create Group Request,
   the Service Agent will respond by sending a Create Group Reply
   (Figure 18) to the host.

   A host may become a member of a group, once it knows the group
   address and the 48-bit key, by sending the Service Agent the Join
   Group Request message (Figure 19).  The Service Agent will respond to
   the Join Group Request with a Join Group Reply (Figure 20).  The host
   which creates a group automatically becomes a member of that group
   without any need for an explicit Join Group Request.

   A member host may add another host to the group by sending the
   Service Agent the Add Group Member Request message (Figure 21).  The
   Service Agent will respond with an Add Group Member Reply (Figure
   22).

   At any time after becoming a member of a group, a host may choose to
   drop out of the group.  To do this, the host sends the Service Agent
   a Leave Group Request (Figure 23).  The Service Agent will respond
   with a Leave Group Reply (Figure 24).

   One member host may expel another member of the group by sending the
   Service Agent the Remove Group Member Request message (Figure 25).
   The Service Agent will respond with a Remove Group Member Reply
   (Figure 26).

   A host can delete an existing group via a Delete Group Request
   (Figure 27).  The Service Agent will respond with a Delete Group
   Reply (Figure 28).  The Service Agent will also send the other
   members of the group, if any, a notification that the group has been
   deleted (see Section 6.3).

Top       Page 36 
                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           1           |           1           |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                           CREATE GROUP REQUEST
                                 Figure 17



     S0[0-7]   Setup Type = 1 (Request).

     S0[8-15]  Request Type = 1 (Create Group).

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.


                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           2           |      REPLY CODE       |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S3        |                 GROUP ADDRESS                 |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S4        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S5        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S6        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                            CREATE GROUP REPLY
                                 Figure 18



     S0[0-7]   Setup Type = 2 (Reply).

Top       Page 37 
     S0[8-15]  Reply Code.

                    0 = Group created
                    8 = Network trouble
                   17 = Insufficient network resources
                   22 = Reply lost in network

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

     S3[0-15]  Group Address.  This field contains the 16-bit
               multicast address that any group member may use to
               reach the other group members.  Multicast addresses are
               dynamically assigned by the network.

     S4-S6     Key.  This field contains a 48-bit key assigned by the
               network which is associated with the group address.  It
               must be provided for subsequent Join Group, Leave
               Group, Add Group Member, Remove Group Member, and
               Delete Group requests which reference the group
               address.


                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           1           |           3           |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S3        |                 GROUP ADDRESS                 |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S4        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S5        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S6        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S7        |                     0                   | MGP |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                            JOIN GROUP REQUEST
                                 Figure 19

Top       Page 38 
     S0[0-7]   Setup Type = 1 (Request).

     S0[8-15]  Request Type = 3 (Join Group).

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

     S3[0-15]  Group Address.  This is the group that the host wishes
               to join.  Upon successfully joining the group, the host
               may send messages to the group and will receive
               messages sent to the group when those messages have a
               priority of MGP or higher.

     S4-S6     Key.  This is the key associated with the group
               address.

     S7[0-13]  Reserved.  Must be zero.

     S7[14-15] Minimum group message priority.  The host will not
               receive messages sent to the group that have a message
               priority less than MGP.  Send another Join Group
               Request message to change the minimum priority.


                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           2           |      REPLY CODE       |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                   REQUEST ID                  |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                             JOIN GROUP REPLY
                                 Figure 20



     S0[0-7]   Setup Type = 2 (Reply).

     S0[8-15]  Reply Code.

                    2 = Host added to group
                    9 = Bad key
                   10 = Group address nonexistent
                   17 = Insufficient network resources

Top       Page 39 
     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.


                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           1           |           10          |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                   REQUEST ID                  |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S3        |                 GROUP ADDRESS                 |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S4        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S5        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S6        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S7        |                  HOST ADDRESS                 |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                         ADD GROUP MEMBER REQUEST
                                 Figure 21



     S0[0-7]   Setup Type = 1 (Request).

     S0[8-15]  Request Type = 3 (Join Group).

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

     S3[0-15]  Group Address.  This is the group the host will join.
               Upon successfully joining the group, the host may send
               messages to the group and will receive messages sent to
               the group by other hosts (the initial minimum priority
               will be 0).

     S4-S6     Key.  This is the key associated with the group
               address.

     S7[0-15]  Host address.  The network address of the host to add

Top       Page 40 
               to the group.


                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           2           |      REPLY CODE       |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                          ADD GROUP MEMBER REPLY
                                 Figure 22



     S0[0-7]   Setup Type = 2 (Reply).

     S0[8-15]  Reply Code.

                    2 = Host added to group (or was already a member)
                    9 = Bad key
                   10 = Group address nonexistent
                   11 = Requestor is not a member of the group
                   17 = Insufficient network resources
                   22 = Reply lost in network
                   24 = Host address was invalid

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

Top       Page 41 
                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           1           |           4           |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                   REQUEST ID                  |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S3        |                 GROUP ADDRESS                 |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S4        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S5        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S6        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                            LEAVE GROUP REQUEST
                                 Figure 23



     S0[0-7]   Setup Type = 1 (Request).

     S0[8-15]  Request Type = 4 (Leave Group).

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

     S3[0-15]  Group Address.  This is the group that the host wishes
               to cease being a member of.  After leaving the group,
               the host will cease receiving messages sent to the
               group and will be unable to send to the group.

     S4-S6     Key.  This is the key associated with the group
               address.

Top       Page 42 
                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           2            |     REPLY CODE       |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                             LEAVE GROUP REPLY
                                 Figure 24



     S0[0-7]   Setup Type = 2 (Reply).

     S0[8-15]  Reply Code.

                    3 = Host deleted from group
                    9 = Bad key
                   10 = Invalid group address
                   11 = Not member of group
                   17 = Insufficient network resources

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

Top       Page 43 
                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           1           |           11          |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                   REQUEST ID                  |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S3        |                 GROUP ADDRESS                 |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S4        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S5        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S6        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S7        |                  HOST ADDRESS                 |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                        REMOVE GROUP MEMBER REQUEST
                                 Figure 25



     S0[0-7]   Setup Type = 1 (Request).

     S0[8-15]  Request Type = 4 (Leave Group).

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

     S3[0-15]  Group Address.  This is the group from which the host
               should be removed.  After leaving the group, that host
               will cease receiving messages sent to the group and
               will be unable to send to the group.

     S4-S6     Key.  This is the key associated with the group
               address.

     S7[0-15]  Host address.  The network address of the host to
               remove from the group.

Top       Page 44 
                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           2            |     REPLY CODE       |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                         REMOVE GROUP MEMBER REPLY
                                 Figure 26



     S0[0-7]   Setup Type = 2 (Reply).

     S0[8-15]  Reply Code.

                    3 = Host deleted from group (or was not a member)
                    9 = Bad key
                   10 = Invalid group address
                   11 = Requestor is not a member of the group
                   17 = Insufficient network resources
                   22 = Reply lost in network
                   24 = Host address was invalid

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

Top       Page 45 
                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           1           |           2           |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                   REQUEST ID                  |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S3        |                 GROUP ADDRESS                 |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S4        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S5        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S6        |                      KEY                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                           DELETE GROUP REQUEST
                                 Figure 27



     S0[0-7]   Setup Type = 1 (Request).

     S0[8-15]  Request Type = 2 (Delete Group).

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.

     S3[0-15]  Group Address.  This is the multicast address to
               delete.  If the group is deleted, the other remaining
               members of the group, if any, will be notified of the
               group's deletion.

     S4-S6     Key.

Top       Page 46 
                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S0        |           2           |      REPLY CODE       |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S1        |                 SETUP CHECKSUM                |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     S2        |                  REQUEST ID                   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                            DELETE GROUP REPLY
                                 Figure 28



     S0[0-7]   Setup Type = 2 (Reply).

     S0[8-15]  Reply Code.

                    1 = Group deleted
                    8 = Network trouble
                    9 = Bad key
                   10 = Invalid group address
                   17 = Insufficient network resources
                   22 = Reply lost in network

     S1[0-15]  Setup Checksum.  (See setup header description.)

     S2[0-15]  Request ID.




(page 46 continued on part 3)

Next RFC Part