Subject: issues in "modified TEST packet"

From: Choon Lee <[email-masked]>
Date: Wed, 13 Oct 1993 08:45:11 -0700

Several issues were raised in the recent loop prevention SIGlet meeting regarding
the "modified TEST packet" proposal:

	|                                |
	|  |-----|             |-----|   |
	|--|  J  |-------------|  K  |---|
	|  |-----|             |-----|   |
	|                                |
	|  |-----|             |-----|   |
	|--|  L  |-------------|  M  |---|
	|  |-----|             |-----|   |
	|                                |
     LAN segment A                    LAN segment B

(1) The DLSw RFC does not specify whether the CANUREACH SSP message can carry any
    data. It is thus conceivable that the TEST frame carries data 
    (i.e. MAC hdr - LLC2 hdr - data), and the data need to be replicated in the
    TEST frame generated at the remote LAN.

(2) Timing issue. X (on LAN segment A) generates a TEST frame which is received by
    both J and L. CANUREACH is sent to K and M respectively. Due to the varying
    propagation delay incurred across the WAN links (J-K and L-M), it is conceivable
    that a response (from Y on LAN segment B) can get to M before the CANUREACH
    arrives at M.

(3) Netbios UI frames. Some Netbios UI frames (e.g. ANR frames) are broadcasted (carry
    a functional address) to every LAN, and when they get picked up by the DLSw nodes, 
    no "control block" is created to "remember" the Data Link ID .
    This is different from TEST frames, or Netbios NR frames, which can be sent to
    only the LAN that has the target station (by using CANUREACH to the appropriate
    DLSw partner. 
    As a result, these UI frames can result in infinite loop.

Did I describe the issues correctly? Did I miss any other issues?

Regards,
Choon Lee

---

From: Choon Lee <[email-masked]>
Date: Thu, 13 Jan 1994 16:31:29 -0800

Hello,

I apologize for taking this much time to get back to the group on the 
topic of loop prevention.
 
To refresh our memories, I've re-listed my understanding of the issues
that were raised in the previous AIW meeting regarding the "modified
TEST packet" proposal.

I will be following this up with another email to discuss a proposal
to resolve these issues.

For those who wants to have a copy of the paper that was submitted 
to the last AIW, please contact me.

Regards,
Choon Lee

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Regards,
Choon Lee

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