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Much of the core business logic of sending and recieving tokens between chains is unchanged between IBC Classic and IBC v2. Some of the key differences to pay attention to are detailed below.

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No Channel Handshakes, New Packet Format and Encoding Support

  • IBC v2 does not establish connection between applications with a channel handshake. Channel identifiers represent Client IDs and are included in the Payload
    • The source and destination port must be "transfer"
    • The channel IDs must be valid client IDs of the format {clientID}-{sequence}, e.g. 08-wasm-007
  • The Payload contains the FungibleTokenPacketData for a token transfer.
The code snippet shows the Payload struct. 
/ Payload contains the source and destination ports and payload for the application (version, encoding, raw bytes)

type Payload struct {
	/ specifies the source port of the packet, e.g. transfer
	SourcePort string `protobuf:"bytes,1,opt,name=source_port,json=sourcePort,proto3" json:"source_port,omitempty"`
	/ specifies the destination port of the packet, e.g. trasnfer
	DestinationPort string `protobuf:"bytes,2,opt,name=destination_port,json=destinationPort,proto3" json:"destination_port,omitempty"`
	/ version of the specified application
	Version string `protobuf:"bytes,3,opt,name=version,proto3" json:"version,omitempty"`
	/ the encoding used for the provided value, for transfer this could be JSON, protobuf or ABI
	Encoding string `protobuf:"bytes,4,opt,name=encoding,proto3" json:"encoding,omitempty"`
	/ the raw bytes for the payload.
	Value []byte `protobuf:"bytes,5,opt,name=value,proto3" json:"value,omitempty"`
}
The code snippet shows the structure of the Payload bytes for token transfer 
/ FungibleTokenPacketData defines a struct for the packet payload
/ See FungibleTokenPacketData spec:
/ https://github.com/cosmos/ibc/tree/master/spec/app/ics-020-fungible-token-transfer#data-structures
type FungibleTokenPacketData struct {
	/ the token denomination to be transferred
	Denom string `protobuf:"bytes,1,opt,name=denom,proto3" json:"denom,omitempty"`
	/ the token amount to be transferred
	Amount string `protobuf:"bytes,2,opt,name=amount,proto3" json:"amount,omitempty"`
	/ the sender address
	Sender string `protobuf:"bytes,3,opt,name=sender,proto3" json:"sender,omitempty"`
	/ the recipient address on the destination chain
	Receiver string `protobuf:"bytes,4,opt,name=receiver,proto3" json:"receiver,omitempty"`
	/ optional memo
	Memo string `protobuf:"bytes,5,opt,name=memo,proto3" json:"memo,omitempty"`
}

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Base Denoms cannot contain slashes

With the new Denom struct, the base denom, i.e. uatom, is seperated from the trace - the path the token has travelled. The trace is presented as an array of Hops. Because IBC v2 no longer uses channels, it is no longer possible to rely on a fixed format for an identifier so using a base denom that contains a ”/” is dissallowed.

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Changes to the application module interface

Instead of implementing token transfer for port.IBCModule, IBC v2 uses the new application interface api.IBCModule. More information on the interface differences can be found in the application section.
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