📄 rfc1223.txt
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Network Working Group J. Halpern
Request for Comments: 1223 NSC
May 1991
OSI CLNS and LLC1 Protocols on Network Systems HYPERchannel
Status of this Memo
The intent of this document is to provide a complete discussion of
the protocols and techniques used to transmit OSI CLNS and LLC1
datagrams (and any associated higher level protocols) on Network
Systems Corporation's HYPERchannel equipment. This document is
intended for network planners and implementers who are already
familiar with the OSI protocol suite and the techniques used to carry
OSI traffic on standard networks such as 802.3.
This memo provides information for the Internet community. It does
not specify an Internet standard. Distribution of this memo is
unlimited.
Table of Contents
Goals of this Document . . . . . . . . . . . . . . . . . . . . . 1
HYPERchannel Network Messages . . . . . . . . . . . . . . . . . . 2
Message Proper Header . . . . . . . . . . . . . . . . . . . . . 3
TO Addresses and Open Driver Architecture . . . . . . . . . . . 8
Broadcasting . . . . . . . . . . . . . . . . . . . . . . . . . . 9
ES-IS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Security Considerations . . . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
Goals of this Document
In this document, we have three major technical objectives:
1. To standardize the encapsulation of LLC1 packets over
HYPERchannel. The format will be used for OSI CLNS and for
any other protocols using LLC1 over HYPERchannel. (Note
that if one desires to use the LLC1/SNAP combination for
TCP/IP, this is the format to use. This represents an
alternative to the native mode for TCP/IP over HYPERchannel,
allowing for sharing the medium at the LLC1 layer.)
Halpern [Page 1]
RFC 1223 OSI and LLC1 on HYPERchannel May 1991
2. To describe how multicast protocols such as ES-IS and IS-IS shall
operate over HYPERchannel. As a medium, HYPERchannel does not
support either broadcast or multicast. Therefore, special
techniques are needed to handle these protocols. Note that these
techniques do not allow general multicast, although any specific
problem may be solved by a generalization of these methods.
3. To make use of a standardized "message type" field in bytes
8 and 9 of the HYPERchannel network message. To permit better
interoperability, NSC maintains a "network protocol registry"
where any interested party may obtain a unique value in byte 8
(or bytes 8 and 9) for their own public, private, commercial or
proprietary protocol. Lists of assigned protocol type numbers
and their "owners" would be periodically published by NSC and
are available to interested parties.
HYPERchannel Network Messages
Unlike most datagram delivery systems, the HYPERchannel network
message consists of two parts:
Message Proper
+--------------------+
| |
| |
| |
| 16-64 bytes |
| |
| |
| |
+--------------------+
Associated Data
+----------------------------------------------------+
| |
| |
| |
| |
| |
| |
| Unlimited length |
| |
| |
| |
| |
| |
| |
+----------------------------------------------------+
Halpern [Page 2]
RFC 1223 OSI and LLC1 on HYPERchannel May 1991
The first part is a message header that can be up to 64 bytes in
length. The first 16 bytes contain information required for the
delivery of the entire message, and the remainder can be used by
higher level protocols. The second part of the message, the
"Associated Data," can be optionally included with the message
proper. In most cases (transmission over HYPERchannel-50 trunks) the
length of the associated data is literally unlimited. Others (such
as HYPERchannel-10 or transmission within a local HYPERchannel-50
A400 adapter) limit the size of the Associated Data to 4K bytes. If
the information sent can be contained within the Message Proper, then
the Associated Data need not be sent.
HYPERchannel lower link protocols treat messages with and without
Associated Data quite differently; "Message only" transmissions are
sent using abbreviated protocols and can be queued in the receiving
network adapter, thus minimizing the elapsed time needed to send and
receive the messages. When associated data is provided, the
HYPERchannel-50 adapters free their logical resources towards driving
the host interface and coaxial trunks at maximum speed, so that data
can flow through the transmitting channel, the coaxial cable, and the
receiving channel concurrently. Thus HYPERchannel-50 can approach
the nominal burst speed of the computer host interface when sending
large data blocks over an extended period.
Message Proper Header
The first 16 bytes of the network Message Proper are examined by the
network adapters to control delivery of the network message. The
message format is as follows:
Halpern [Page 3]
RFC 1223 OSI and LLC1 on HYPERchannel May 1991
byte Message Proper
+------------------------------------------------------------+
0 | Trunks to Try | Message Flags |
| TO trunks | FROM trunks | |A/D|
+--------------+---------------+-------------------------+---+
2 | TO Domain # | TO Network # |
| | |
+------------------------------+-----------------------------+
4 | TO Unit # | Logical To |
| | (port number) |
+------------------------------+-----------------------------+
6 | From Unit # | Logical From |
| | (port number) |
+------------------------------+-----------------------------+
8 | Message type |
| 0x0B01 |
+------------------------------+-----------------------------+
10 | FROM Domain # | FROM Network # |
| | |
+------------------------------+-----------------------------+
12 | True Unit | age count |
| | |
+------------------------------+-----------------------------+
14 | Header End Offset | Next Header Offset |
| (16) | (16) |
+------------------------------+-----------------------------+
16 | LLC1 destination SAP | LLC1 source SAP |
| (0xFE for CLNP) | (0xFE for CLNP) |
+------------------------------+-----------------------------+
18 | LLC1 function code | |
| (0x03 for normal data) |Start of upper layer protocol|
+------------------------------+ +
20 | from bytes 19-63 of the message proper |
| and continuing in the associated data |
| (For OSI this is CLNP, then transport etc.) |
+------------------------------+-----------------------------+
Trunks to Try
Consists of two four bit masks indicating which of four possible
HYPERchannel-50 coaxial data trunks are to be used to transmit the
message and to return it. If a bit in the mask is ON, then the
adapter firmware will logically AND it with the mask of installed
trunk interfaces and use the result as a candidate list of
interfaces.
Whenever one of the internal "frames" are sent to communicate with
Halpern [Page 4]
RFC 1223 OSI and LLC1 on HYPERchannel May 1991
the destination adapter, the transmission hardware electronically
selects the first non-busy trunk out of the list of candidates. Thus
selection of a data trunk is best performed by the adapter itself
rather than by the host. Dedicating trunks to specific applications
only makes sense in very critical real time applications such as
streaming data directly from high speed overrunable peripherals.
A second Trunk mask is provided for the receiving adapter when it
sends frames back to the transmitter, as it is possible to build
asymmetric configurations of data trunks where trunk 1 on one box is
connected to the trunk 3 interface of a second. Such configurations
are strongly discouraged, but the addressing structure supports it if
needed.
The "trunks to try" field is only used by HYPERchannel-50. To assure
maximum interoperability, a value of 0xFF should be placed in this
field to assure delivery over any technology. The newer DX series
units determine the trunk mask on their own, but this field is
preserved for use with A series equipment.
Message Flags
Contains options in message delivery. There are several bits defined
by the hardware. However, only the A/D bit will be described here.
Other bits are used only for special diagnostic or management
purposes. If there is a need to set them, check the specific Network
Systems manuals on their meanings. In the absence of such need, all
bits other than A/D shall be set to zero on transmission, and not
examined upon receipt of a message.
ASSOCIATED DATA PRESENT (A/D) is ON if an Associated Data block
follows the Message Proper. 0 if only a message proper is present in
the network message. The value of this bit is enforced by the
network adapter firmware.
TO Domain Number
This is the most significant byte of the four byte hyperchannel
address. It selects an NSC addressing domain, among a set of
domains. If this and the network number both refer to the local
domain and network, they may be set to 0.
TO Network Number
This is the destination network number. It identifies the network
within the selected domain, where the destination unit resides. If
the destination is in the local domain and network, both the TO
domain and TO network numbers may be set to zero.
Halpern [Page 5]
RFC 1223 OSI and LLC1 on HYPERchannel May 1991
TO Unit
Upon arrival at the destination domain and network, this is the unit
number of the destination HYPERchannel adapter. The combination of
Domain, Network, and Unit uniquely identify a single adapter in a
HYPERchannel network. For compatibility with existing HYPERchannel
equipment, when sending a message to a destination outside the local
domain and network, set this byte to 0, and store the actual
destination unit number in the True Unit field.
Logical To
This field further identifies which process the message is intended
for. With some hardware, the bottom bits select a machine from among
several. When sending a message to an N400, the bottom two bits of
this field select which of four attached hosts the message is
destined for. Within a host, the logical to field selects a
destination process. This is used in conjunction with the Message
Type field to insure that messages are delivered to the correct
place. The Logical TO field identifies a process, which then checks
the Message Type to insure that it understands the message. This
also allows for running two processes, both of which understand the
same protocol.
From Unit
This identifies the Unit number from which this message was sent.
Logical From
This identifies the host and process who originated this message.
Message Type
The following two bytes are reserved for NSC. Users have been
encouraged to put a zero in byte 8 and anything at all in byte 9 so
as to not conflict with internal processing of messages by NSC
firmware. In the past, this field has been loosely defined as
carrying information of interest to NSC equipment carrying the
message and not as a formal protocol type field. For example, an
0xFF00 in bytes 8 and 9 of the message will cause the receiving
adapter to loop back the message without delivering it to the
attached host.
NSC now uses both bytes 8 and 9 as a formal "protocol type"
designator. Major protocols will be assigned a unique value in byte
8 that will (among good citizens) not duplicate a value generated by
a different protocol. Minor protocols will have 16 bit values
Halpern [Page 6]
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