Sna Responses; Lu-Lu Session Error Reporting - IBM 3708 Description

SNA Responses
The SNA response header (RH) contains indicators that describe the type of
response given. The indicators are Definite Response 1 (DRl) or Definite Response
2 (DR2). The RH also contains an Exception Response (EX) indicator that is used
when describing the response protocol. Definite response protocol (DRl or DR2)
specifies that a response, either positive or negative, must be given. Exception
response protocol specifies that only a negative response may, or need be, returned.
The PLU must adhere to the response type specified in the BIND. If definite
response is specified by the BIND, then requests sent with ERI is rejected by the
3708. If exception response is selected by the BIND, then requests sent with DR2 is
rejected.
The only definite response type requested by the 3708 is Definite Response 1 (DRl).
The response protocol requested by the 3708 (definite response and/or exception
response) is defined in the BIND.
The 3708 responds to a message from the host with any requested response type
(DRl, DR2, or both). The 3708 supports definite response and exception response
protocols. A no response request is treated as an exception response request.
LU-LU Session Error Reporting
When the host program or the 3708 SLU is the receiving LU, errors are reported by
returning a negative response to the sending LU with descriptive sense data included.
The format of the 4-byte sense data RU sent with a negative response is as follows:
1
2 and 3
System Sense User
Major Code
Modifier Sense
Byte 0 of the sense data RU is bit-encoded to reflect one of six transmission error
categories:
Byte 0 Major Code
X'80' Path Error
X'40' RH Error
X'20' State Error
X'lO'
Request Error
X'08' Request Reject
X'OO' User-Defined Error
Byte 1 of the sense data RU is a binary modifier that further defines the error
condition. The modifier encoding is unique to each major code.
Bytes 2 and 3 are zeros for all negative responses sent by the 3708. Section "SNA
Sense Codes" defines the modifier encoding for each major code of system sense
data that is issued by the 3708.
Note that the 3708 does not examine the sense data in a negative response from the
host. All negative responses on the LU-LU session cause the 3708 to enter RCV
state and await further action by the host.
Chapter 3. SDLC and SNA Communication
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