FIX Protocol Tag 789: NextExpectedMsgSeqNum

Next sequence number the sender expects to receive, sent in a Logon so both sides can detect and recover gaps. It was added in FIX 4.4.

Tag number: 789
Data type: SEQNUM
FIX versions: FIX 4.4 to 5.0 SP2 and FIXT 1.1
Used in: 1 message type

Practical notes on NextExpectedMsgSeqNum

NextExpectedMsgSeqNum on the Logon states the next sequence number the sender expects to receive, so both sides can see a gap at logon.

When the counterparty sees a value lower than its own next outgoing number, it knows its earlier messages were lost and can replay or gap-fill them without waiting for a ResendRequest.
It only helps when both sides support it, so agree its use in the rules of engagement.

Changes between FIX versions

Added to the Logon in FIX 4.4.

Tag 789 in each FIX version

Values and message usage as defined in a specific version.

Data type

SEQNUM: A positive integer message sequence number.

Example

789=1024

Illustrative value. In a message, fields are separated by the SOH character (0x01), often shown as | or ^ in logs.

Decode a message with this tag

Message types that use tag 789

Logon 35=A

Covers every version from FIX 4.0 to 5.0 SP2, including fields reached through components and repeating groups. The version pages above show whether the tag is required in each message.

Field and message data comes from the QuickFIX data dictionaries for FIX 4.0 to 5.0 SP2 and FIXT 1.1, used under the QuickFIX Software License. This product includes software developed by quickfixengine.org (http://www.quickfixengine.org/). Enumerated value names are converted to plain text for reading.