The more I look at DPP 0.71, the more similar it looks
to SBP-2. So, I put together a concept "cheat sheet"
to see how the two really compared. I thought you
might be interrested, so here it is... What do you think?
- Greg Shue
===============================
SBP-2 vs. DPP v0.71 Cheat Sheet
===============================
There are many similar concepts between SBP-2 and DPP v0.71 which
may not be well understood. The main difference between the
protocols revolves around the a/symmetry of the protocol stacks.
This "cheat sheet" is intended on laying the groundwork for a
direct comparison of the protocol stacks.
SBP-2 Model of Use for Comparison
---------------------------------
In order to get a reasonable comparison of the protocols, then
a Command Set and Model-of-use must be outlined for SBP-2. Many
of the details can be left out of the outline as long as the
essence of the profile is maintained.
Model of Use
------------
- cross-logins are established between the two devices.
(This avoids a merged target/initiator driver)
- each device provides a fetch engine and a task list.
- each task list contains commands to transfer data in one direction
(we'll choose it such that only WRITE transactions occur for
moving the ORB data block)
- each ORB allows one "data unit" to be processed.
Command Set Provides For
------------------------
- cross-login information
- negotiated max data block size per task per direction.
- indicating byte-size of completed packet
- carrying of Command IDs in CDB (2 bytes)
- carry "SDU segmentation number" in CDB (4 bytes)
- carry "SDU end of segment flag" in CDB (1 bit)
- carry routing info in CDB (2 byte Dest PID, 2 bytes Src PID)
Cheat Sheet
===========
CSR structures Thin Protocol SBP-2
-----------------------------------------------------------------------
Access Control i/f Connection Reg Mgmt Agent Reg
Response Space SDU Response Space Fetch Agent Regs
Completion status SDU Control Space Status FIFO
Transfer block SDU Register data block referenced by ORB
Functional layers Thin Protocol SBP-2
-----------------------------------------------------------------------
Connection mgmt Thin Session Management Agent
Data Transfer eng Thin Transaction Fetch Agent
Session Mgmt Thin Protocol SBP-2
-----------------------------------------------------------------------
Access Request S_Connect login
Reconnect T_Reconnect reconnect
Execute App Cmd S_Command ORB exists on task list
Access Release S_Disconnect logout
Error Notification <none> Mgmt-ORB specified Status FIFO
completion notification
Data Transfer Thin Protocol SBP-2
-----------------------------------------------------------------------
Transfer Space SDUAck ORB exists on task list
Available (write implies avail) (existance implies available)
Transfer completion SDUComp Notification write to
notification Status FIFO
Transfer Abort from SDUStop Abort Task (Set)
data receiver
Transfer Abort from SDUStop Notification write to implicit
data sender Status FIFO - Abort
Error Notification T_error Notification write to implicit
Status FIFO - error ind.
Feature Comparison
==================
Feature Thin Protocol SBP-2
-----------------------------------------------------------------------
Each node can send/rcv Yes Yes
data
Dynamically allocates Yes Yes
CSR Reg space when
estab. connect
Selectable Transfer Yes Yes, requires Create Stream
Mode request and separate
task list
Symmetric Structure Yes Yes
Negotiated Data Unit Yes Yes
size independently
per direction
Isochronous Support Yes Yes
Multiple Cmd Support Yes Yes
Bidirectional Cmds Yes Yes
Multiple Independent Unspecified (possible Yes, via Multiple LUNs &
Connection Support w/ multiple UNIT Dirs) multiple UNITS
Session segmentation Yes Yes, in CDB
support
Distinctive differences:
Feature Thin Protocol SBP-2 w/ proposed profile
-----------------------------------------------------------------------
Reconnect Support 2 sec window; 1 sec window, proposal made
either end may for programmable extension;
establish both ends must reestablish
SDU Available SDU Ack timeout exists None (?)
timeout Does this imply a real-
time processing req. on
whatever data is sent
in an SDU?
Connection Process 2 block writes 6 block writes (probably)
(2 logins @ 2 per login,
2 for negotiated params)
Shared memory buffer Fixed location during Relocatable, partitionable
connection
Data Transfer more efficient for More flexible and standardized
data < MTU size
data < MTU size SDUAck + WR Agent Reset + WR ORB ptr +
SDUComp + ORB prefetch + data xfer +
SDUAck Completion Notify
(3 transactions vs. 5 transactions)
MTU size << data < SDUSend + WR Agent Reset + WR ORB ptr +
SDU size SDUComp + ORB prefetch + page table +
data xfer +
SDUAck Completion Notify
(SBP-2 costs 3 extra transactions,
but a small overhead
-- Greg Shue Hewlett-Packard Company Office Products Division gregs@sdd.hp.com ----------------------------------------------------------------