P1394 Mail Archive: P1394> SBP-2 vs. DPP 0.71 Cheat Sheet (?)

P1394 Mail Archive: P1394> SBP-2 vs. DPP 0.71 Cheat Sheet (?)

P1394> SBP-2 vs. DPP 0.71 Cheat Sheet (?)

Greg Shue (gregs@sdd.hp.com)
Fri, 20 Feb 1998 16:46:07 -0800 (PST)

Hi all,

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

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

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

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