Transaction Log - Communication Protocol Definition

Got protocol messaging pretty much v1 done:

/**
 * The communication protocol between a subscriber
 * and a publisher
 */
message ReplicationCommunicationPacket
{
  enum Command
  {
    REQUEST_PING = 1; /* ping/heartbeat */
    RESPONSE_PING = 2;
    REQUEST_CHANNEL_APPLIED = 2; /* get last transaction ID applied on a channel */
    RESPONSE_CHANNEL_APPLIED = 3; /* response the last transaction ID a publisher applied */
    REQUEST_TRANSACTION = 4; /* sent by subscriber to request a stream of transactions */
    RESPONSE_TRANSACTION_HEADER = 5; /* information about transaction messages to be sent */
  }
  message RequestChannelApplied
  {
    required uint32 channel_id = 1; /* the channel in question */
  }
  message ResponseChannelApplied
  {
    required uint32 channel_id = 1; /* the channel in question */
    required uint64 transaction_id = 2; /* the transaction ID last applied on the publisher */
  }
  message RequestTransaction
  {
    required uint32 channel_id = 1; /* the channel in question */
    required uint64 transactions_after_id = 2; /* subscriber is requesting transactions AFTER this ID. */
    required uint32 max_number_transactions = 3; /* response no more than this number of transaction messages in response */
  }
  message ResponseTransactionHeader
  {
    required uint32 channel_id = 1; /* the channel in question */
    required uint64 min_transaction_id = 2; /* first transaction ID of transaction messages to be sent */
    required uint64 max_transaction_id = 3; /* last transaction ID of transaction messages to be sent */
    required uint32 num_transactions = 4; /* total number of transactions to be sent */
  }
  required Command command = 1; /* the type of command in this packet */
  optional RequestChannelApplied request_channel_applied = 2;
  optional ResponseChannelApplied response_channel_applied = 3;
  optional RequestTransaction request_transaction = 4;
  optional ResponseTransactionHeader response_transaction_header = 5;
}