RE: Re: iSCSI Marker questions

["Somesh Gupta" <somesh_gupta@silverbacksystems.com>]

Julian,

 

Should the marker interval be counted from the begining of 1 marker to the

begining of the next, or from the end of one marker to the begining of the next.

Having the marker interval counted from the begining of 1 marker to the begining

of the next makes it easier for the receiver to determine where the next marker

will be.

 

Somesh

-----Original Message-----
From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of Julian Satran
Sent: Tuesday, December 11, 2001 4:54 PM
To: ips@ece.cmu.edu
Subject: Fw: Re: iSCSI Marker questions

----- Forwarded by Julian Satran/Haifa/IBM on 12-12-01 02:39 -----

Julian Satran 11-12-01 14:44

To:        IPS List         cc:                 Subject:        Re: iSCSI Marker questionsLink

Dean,



owner-ips@ece.cmu.edu wrote on 11-12-2001 03:09:11:

> The iSCSI Draft 9 Appendix C makes the following statements about
> Markers and the Initial Marker-less Interval:
>
>      "The offset to the next iSCSI PDU header is counted in terms
>       of the TCP stream data. Anything counted in the TCP
>       sequence-number is counted for the offset. Specifically this
>       includes any bytes "inserted" in the TCP stream by an UFL and
>       it excludes any other markers inserted between the one we are
>       examining and the next PDU header."...
>
>      "To enable the connection setup including the login phase
>       negotiation, marking (if any) is started only at the first
>       marker interval after the end of the login phase."
>
> I understand that markers are not inserted until after login phase.
> Am I correct to assume that the placement of the first marker
> determined by the TCP sequence numbers on the final Login Request/
> Response PDUs, or is initial marker position determined by the
> TCP sequence numbers at connection establishment?
>
> Assume the following interaction:
>
> I->  SYN     (TCP sequenceNum=1000)  -- irrelevant to this discussion?
>
> T->  SYN-ACK (TCP sequenceNum=2000)  -- irrelevant to this discussion?
>
> I->  Login Request PDU, T=0,CSG=1,NSG=0:
>      InitiatorName=xxx
>      TargetName=yyy
>      SessionType=normal
>      ...
>      FMarker=send-receive
>      RFMarkInt=512,1024
>
> T->  Login Response PDU, T=0,CSG=1,NSG=0:
>      ...
>      FMarker=send-receive
>      SFMarkInt=1024
>      RFMarkInt=1024
>
> I->  Login Request PDU, T=1,CSG=1,NSG=3:
>      SFMarkInt=1024
>      (64-byte PDU... TCP sequenceNum=1301-1364)
>
> T->  Login Response PDU, T=1,CSG=1,NSG=3:
>      (48-byte PDU... TCP sequenceNum=2201-2248)
>
> The above interaction designates a 1024 x 4 = 4096-byte marker
> interval in both directions. The first PDU byte sent by the
> intitiator in full-feature mode will have sequenceNum=1365, and
> the first byte sent by the target will have sequenceNum=2249.
>
> Assuming the markerless interval starts at the end of login
> phase, the first two markers in each direction will have the
> following TCP sequence numbers:
>
>                TCP SeqNum of    TCP SeqNum of
>                First Marker     Second Marker
>                ------------     -------------
> Initiator:     5461-5468        9565-9572
> Target:        6345-6352        10449-10456
>
No - the correct numbers are dependent only on the marker interval (not the length of the login phase) and are:

Initiator        5096-5103        9200-9201
Target           6096-6103        10200-10201
 
 
> Is this the correct interpretation of marker usage in iSCSI
> Draft 9, or does marker placement depend on the connection's
> initial sequence numbers?
>
> Also, is "RFMarkInt=..." always considered an offer, and "SFMarkInt="
> considered a reply to that offer? If an offer is sent with "FMarker=..."
> and "RFMarkInt=...", MUST the reply contain either "FMarker=no" or
> BOTH "FMarker=yes" and "SFMarkInt=..."?
>

Fmarker is not boolean - legal values are no, send, receive, send-receive
The sender and receiver must set the interval it wants/is ready to use
otherwise the responder can't answer.
I assume a normal dialogue may go like:

I->FMarker=send-receive,RFMarkInt=1,4,SFMarkInt=1,512
T->FMarker=send-receive,RFMarkInt=8, SFMarkInt=2

Please observe that target answers with RFMarkInt to the initiators SFMarkInt and viceversa.

I will attempt an example in draft 10 (last?).


 
> Thanks,
> Dean Scoville
> QLogic Corp.