As per Relevance of the word encapsulating, we have this rfc below:
Network Working Group B.
Request for Comments: 2143 Compucat
Category: Experimental May 1997
Encapsulating IP with the Small Computer System
Status of this
This memo defines an Experimental Protocol for the
community. This memo does not specify an Internet standard of
kind. Discussion and suggestions for improvement are requested
Distribution of this memo is unlimited
Table of
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 1
2. Brief background to the Small Computer System Interface . 2
3. Link Encapsulation . . . . . . . . . . . . . . . . . . . . 3
4. An Address Resolution Protocol . . . . . . . . . . . . . . 4
5. Scalability . . . . . . . . . . . . . . . . . . . . . . . 4
6. Possible applications . . . . . . . . . . . . . . . . . . 5
7. Security considerations . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . 5
9. Author's Address . . . . . . . . . . . . . . . . . . . . . 5
1.
As the capacity of local area networks increases to meet the
of high volume application data, there is a class of
intensive problems which may be applied to small clusters
workstations with high bandwidth interconnection
A general observation of networks is that the bit rate of the
path typically decreases as the distance between hosts increases.
is common to see regional networks connected at a rate of 64Kbps
office networks connected at 100Mbps, but the inverse is far
common
The same is true of peripheral and memory interconnection.
close to a CPU's core may run at speeds equivalent to a
network. More importantly, devices such as disks may connect
number of metres away from its host at speeds well in excess
current local area network capacity
Elliston Experimental [Page 1]
RFC 2143 Encapsulating IP with the SCSI May 1997
This document outlines a protocol for connecting hosts running
TCP/IP protocol suite over a Small Computer System Interface (SCSI
bus. Despite the limitation in the furthest distance between hosts
SCSI permits close clusters of workstations to communicate
each other at speeds approaching 360 megabits per second
The proposed introduction of newer SCSI implementations such
serial SCSI will bring much faster communication at
distances
2. Background to the Small Computer System Interface (SCSI
SCSI defines a physical and data link protocol for
peripherals to hosts. Devices connect autonomously to a bus and
synchronous or asynchronous messages to other devices
Devices are identified by a numeric identifier (ID). For
original SCSI protocol, devices are given a user-selectable SCSI
between 0 and 7. Wide SCSI specifies a range of SCSI IDs between 0
and 15. The most typical SCSI configuration comprises of a
adapter and one or more SCSI- capable peripherals responding
asynchronous messages from the host adapter
The most critical aspect of the protocol with respect to its use as
data link for the Internet protocols is that a SCSI device must
as an "initiator" (generator of SCSI commands/requests) or a "target
(a device which responds to SCSI commands from the initiator).
model is correct for a master/slave relationship between host
and devices. The only time an initiator receives a message
to it is in response to a command issued by it in the past and
target device always generates a response to every command
receives
Clearly this is unsuitable for the peer-to-peer model required
multiple host adapters to asynchronously send SCSI commands to
another without surplus bus traffic. Furthermore, some host
may refuse to accept a message from another adapter as it expects
only initiate SCSI commands. This restriction to the
requires that SCSI adapters used for IP encapsulation support what
known as "target mode", with software device driver support to
these messages up to higher layer modules for processing
Elliston Experimental [Page 2]
RFC 2143 Encapsulating IP with the SCSI May 1997
3. Link
The ANSI SCSI standard defines classes of peripherals which may
interconnected with the SCSI protocol. One of these is the class
"communication devices" [1].
The standard defines three message types capable of carrying
general-purpose payload across communication devices. Each of
are known as the "SEND MESSAGE" message type, but the size and
structure of the message header differs amongst them. The
forms of message header are six (6), ten (10) and twelve (12)
long
It was decided that the ten byte header offers the
flexibility for encapsulating version 4 IP datagrams for
following reasons
a. The transfer length field is 16 bits in size which is
matched to the datagram length field in IP version 4.
Implementations of IP will run efficiently as datagrams
never be fragmented over SCSI networks
b. The SCSI "stream select" field, which was designed to
a device to specify the stream of data to which a
belongs, may be used to encode the payload type (in a
manner to the Ethernet frame type field). For consistency,
lowest four bits of the "stream select" field should match
set of values assigned by the IEEE for Ethernet protocol types
Encapsulating an IP datagram within a SCSI message
straightforward
+------------------+-----------------------------------+
| SCSI header | IP datagram |
+------------------+-----------------------------------+
The fields of the SCSI header should be completed as follows
Byte 0: 0x2A (SEND_MESSAGE(10) opcode
Byte 1: Logical unit number encoded into top 3 bits | 0x00
Byte 2: 0x00
Byte 3: 0x00
Byte 4: 0x00
Byte 5: Protocol type encoded into lowest 4 bits | 0x00
Byte 6: 0x00
Bytes 7/8: IP datagram length, big endian
Byte 9: 0x00
Elliston Experimental [Page 3]
RFC 2143 Encapsulating IP with the SCSI May 1997
4. An Address Resolution
When IP decides that the next hop for a datagram will be onto a
network supported by a SCSI IP network interface implementation,
is necessary to acquire a data link address to deliver the datagram
Network interfaces such as Ethernet have well-known methods
acquiring the media address for an Internet protocol address,
most common being the Address Resolution Protocol (ARP). In
implementations, the forwarding host "yells" using a broadcast
address and expects the named host to respond
The SCSI protocol does not provide a broadcast data link address.
acceptable solution to the address resolution problem for a
network is to simulate a broadcast by performing a series of round
robin transmissions to each target. Depending on the SCSI
being used, this would require upward of seven independent
accesses. This is not grossly inefficient, however, if combined
an effective ARP caching policy. A further possible optimisation
negative ARP caching, whereby incomplete ARP bindings are not
for some period in the future
5.
While the utility of a network architecture based around a
network which can span less than ten metres and support only
hosts may be questionable, the flexibility of IP and in particular
IP routing, improves the scalability of this architecture
Consider a network of eight hosts connected to a SCSI bus in
each host acts as a multi-homed host with a second host
connecting another seven hosts to it. When configured with IP
routing capability, each of the 64 total hosts may communicate
one another at high speed in a packet switched manner
Depending on the I/O bus capabilities of certain workstations, it
also be possible to configure a multi-homed host with a
number of SCSI host adapters, permitting centralised
configurations to be constructed
It should be apparent that for little expense, massively
virtual machines can be built based upon the IP protocol running
the high-bandwidth SCSI protocol
Elliston Experimental [Page 4]
RFC 2143 Encapsulating IP with the SCSI May 1997
6. Possible
Research has been made into the capability of "networks
workstations", and their performance compared to supercomputers.
observation that has been made thus far is that bottlenecks exist
the channels by which executable code is transported between
for execution. A very high-speed network architecture based
the Internet protocol would permit a seamless transition of
application software to a high-bandwidth environment
Other applications that have been considered are server clusters
fault-tolerant NFS, World-Wide Web and database services
7. Security
Transmitting IP datagrams across a SCSI bus raises similar
issues to other local area networking architectures. The scale
security problems relating to protocols above the data link
should be obvious to a reader current in Internet security
8.
[1] ANSI X3T9 Technical Committee, "Small Computer
Interface - 2", X3T9.2, Project 375D, Revision 10L,
1993.
9. Author's
Ben
Compucat Research Pty
Box 7305 Canberra Mail
Canberra ACT 2610
Phone: +61 6 295 1331
Fax: +61 6 295 1855
Email: ben.elliston@compucat.com.
Elliston Experimental [Page 5]
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
RFC documents can be found at I.E.T.F.
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