<commit_before>::

  ZIP: ???
  Title: Network Upgrade Zero ("OverWinter") Transaction Format
  Author: <NAME> <<EMAIL>>
  Comments-Summary: No comments yet.
  Category: Process
  Created: 2018-01-10
  License: MIT

Terminology
===========

The key words "MUST", "MUST NOT", "SHOULD", and "MAY" in this document are to be interpreted as described in RFC 2119.

"Legacy" - pre-NU0

"NU0" - Network upgade zero

"Overwinter" - Code-name for NU0

Abstract
========

This proposal defines a new transaction format required for Network Upgrade Activation Mechanism [#zip-0???]_
and Transaction Expiry [#zip-0???]_.

Related to [#zip-0143]_

Motivation
==========

A new transaction format is required to:

* support safe network upgrades as specified in Network Upgrade Activation Mechanism [#zip-0???]_.
* provide replay protection between Legacy and Overwinter network upgrade.
* provide replay protection between different branches post-Overwinter e.g. Overwinter and Sapling upgrade.
* enable soft forks of transactions within a branch i.e. forwards compatibility, where a node will accept a newer transaction version format.
* enable a branch to support multiple transaction version formats
* support transaction expiry as specified in the Transaction Expiry [#zip-0???]_

Specification
=============

Zcash launched with support for upstream Bitcoin version 1 transactions and a custom version 2 transaction format which added fields required for shielded transactions.

======== =============== =========================== =======
Version  Field           Description                 Type<commit_msg>Remove point about sort forks<commit_after>::

  ZIP: ???
  Title: Network Upgrade Zero ("OverWinter") Transaction Format
  Author: <NAME> <<EMAIL>>
  Comments-Summary: No comments yet.
  Category: Process
  Created: 2018-01-10
  License: MIT

Terminology
===========

The key words "MUST", "MUST NOT", "SHOULD", and "MAY" in this document are to be interpreted as described in RFC 2119.

"Legacy" - pre-NU0

"NU0" - Network upgade zero

"Overwinter" - Code-name for NU0

Abstract
========

This proposal defines a new transaction format required for Network Upgrade Activation Mechanism [#zip-0???]_
and Transaction Expiry [#zip-0???]_.

Related to [#zip-0143]_

Motivation
==========

A new transaction format is required to:

* support safe network upgrades as specified in Network Upgrade Activation Mechanism [#zip-0???]_.
* provide replay protection between Legacy and Overwinter network upgrade.
* provide replay protection between different branches post-Overwinter e.g. Overwinter and Sapling upgrade.
* enable a branch to support multiple transaction version formats
* support transaction expiry as specified in the Transaction Expiry [#zip-0???]_

Specification
=============

Zcash launched with support for upstream Bitcoin version 1 transactions and a custom version 2 transaction format which added fields required for shielded transactions.

======== =============== =========================== =======
Version  Field           Description                 Type
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