diff --git a/lib/ably/models/channel_options.rb b/lib/ably/models/channel_options.rb
new file mode 100644
index 000000000..ec23f0be4
--- /dev/null
+++ b/lib/ably/models/channel_options.rb
@@ -0,0 +1,97 @@
+module Ably::Models
+  # Convert token details argument to a {ChannelOptions} object
+  #
+  # @param attributes (see #initialize)
+  #
+  # @return [ChannelOptions]
+  def self.ChannelOptions(attributes)
+    case attributes
+    when ChannelOptions
+      return attributes
+    else
+      ChannelOptions.new(attributes)
+    end
+  end
+
+  # Represents options of a channel
+  class ChannelOptions
+    extend Ably::Modules::Enum
+    extend Forwardable
+    include Ably::Modules::ModelCommon
+
+    MODES = ruby_enum('MODES',
+      presence: 0,
+      publish: 1,
+      subscribe: 2,
+      presence_subscribe: 3
+    )
+
+    attr_reader :attributes
+
+    alias_method :to_h, :attributes
+
+    def_delegators :attributes, :fetch, :size, :empty?
+    # Initialize a new ChannelOptions
+    #
+    # @option params [Hash] (TB2c) params (for realtime client libraries only) a  of key/value pairs
+    # @option modes [Hash] modes (for realtime client libraries only) an array of ChannelMode
+    # @option cipher [Hash,Ably::Models::CipherParams]   :cipher   A hash of options or a {Ably::Models::CipherParams} to configure the encryption. *:key* is required, all other options are optional.
+    #
+    def initialize(attrs)
+      @attributes = IdiomaticRubyWrapper(attrs.clone)
+
+      attributes[:modes] = modes.to_a.map { |mode| Ably::Models::ChannelOptions::MODES[mode] } if modes
+      attributes[:cipher] = Ably::Models::CipherParams(cipher) if cipher
+      attributes.clone
+    end
+
+    # @!attribute cipher
+    #
+    # @return [CipherParams]
+    def cipher
+      attributes[:cipher]
+    end
+
+    # @!attribute params
+    #
+    # @return [Hash]
+    def params
+      attributes[:params].to_h
+    end
+
+    # @!attribute modes
+    #
+    # @return [Array<ChannelOptions::MODES>]
+    def modes
+      attributes[:modes]
+    end
+
+    # Converts modes to a bitfield that coresponds to ProtocolMessage#flags
+    #
+    # @return [Integer]
+    def modes_to_flags
+      modes.map { |mode| Ably::Models::ProtocolMessage::ATTACH_FLAGS_MAPPING[mode.to_sym] }.reduce(:|)
+    end
+
+    # @return [Hash]
+    # @api private
+    def set_params(hash)
+      attributes[:params] = hash
+    end
+
+    # Sets modes from ProtocolMessage#flags
+    #
+    # @return [Array<ChannelOptions::MODES>]
+    # @api private
+    def set_modes_from_flags(flags)
+      return unless flags
+
+      message_modes = MODES.select do |mode|
+        flag = Ably::Models::ProtocolMessage::ATTACH_FLAGS_MAPPING[mode.to_sym]
+        flags & flag == flag
+      end
+
+      attributes[:modes] = message_modes.map { |mode| Ably::Models::ChannelOptions::MODES[mode] }
+    end
+  end
+end
diff --git a/lib/ably/models/idiomatic_ruby_wrapper.rb b/lib/ably/models/idiomatic_ruby_wrapper.rb
index ce3e2c3ce..a9e964a1e 100644
--- a/lib/ably/models/idiomatic_ruby_wrapper.rb
+++ b/lib/ably/models/idiomatic_ruby_wrapper.rb
@@ -94,6 +94,10 @@ def size
       attributes.size
     end
 
+    def empty?
+      attributes.empty?
+    end
+
     def keys
       map { |key, value| key }
     end
diff --git a/lib/ably/models/protocol_message.rb b/lib/ably/models/protocol_message.rb
index 1534a135e..b07e1e64f 100644
--- a/lib/ably/models/protocol_message.rb
+++ b/lib/ably/models/protocol_message.rb
@@ -66,6 +66,14 @@ class ProtocolMessage
       auth:         17
     )
 
+    ATTACH_FLAGS_MAPPING = {
+      resume: 32, # 2^5
+      presence: 65536, # 2^16
+      publish: 131072, # 2^17
+      subscribe: 262144, # 2^18
+      presence_subscribe: 524288, # 2^19
+    }
+
     # Indicates this protocol message action will generate an ACK response such as :message or :presence
     # @api private
     def self.ack_required?(for_action)
@@ -185,6 +193,10 @@ def has_correct_message_size?
       message_size <= connection_details.max_message_size
     end
 
+    def params
+      @params ||= attributes[:params].to_h
+    end
+
     def flags
       Integer(attributes[:flags])
     rescue TypeError
@@ -218,27 +230,27 @@ def has_transient_flag?
 
     # @api private
     def has_attach_resume_flag?
-      flags & 32 == 32 # 2^5
+      flags & ATTACH_FLAGS_MAPPING[:resume] == ATTACH_FLAGS_MAPPING[:resume] # 2^5
     end
 
     # @api private
     def has_attach_presence_flag?
-      flags & 65536 == 65536 # 2^16
+      flags & ATTACH_FLAGS_MAPPING[:presence] == ATTACH_FLAGS_MAPPING[:presence] # 2^16
     end
 
     # @api private
     def has_attach_publish_flag?
-      flags & 131072 == 131072 # 2^17
+      flags & ATTACH_FLAGS_MAPPING[:publish] == ATTACH_FLAGS_MAPPING[:publish] # 2^17
     end
 
     # @api private
     def has_attach_subscribe_flag?
-      flags & 262144 == 262144 # 2^18
+      flags & ATTACH_FLAGS_MAPPING[:subscribe] == ATTACH_FLAGS_MAPPING[:subscribe] # 2^18
     end
 
     # @api private
     def has_attach_presence_subscribe_flag?
-      flags & 524288 == 524288 # 2^19
+      flags & ATTACH_FLAGS_MAPPING[:presence_subscribe] == ATTACH_FLAGS_MAPPING[:presence_subscribe] # 2^19
     end
 
     def connection_details
diff --git a/lib/ably/modules/channels_collection.rb b/lib/ably/modules/channels_collection.rb
index 113fdbdb3..aa9c14214 100644
--- a/lib/ably/modules/channels_collection.rb
+++ b/lib/ably/modules/channels_collection.rb
@@ -13,14 +13,21 @@ def initialize(client, channel_klass)
     # Return a Channel for the given name
     #
     # @param name [String] The name of the channel
-    # @param channel_options [Hash] Channel options including the encryption options
+    # @param channel_options [Hash, Ably::Models::ChannelOptions] A hash of options or a {Ably::Models::ChannelOptions}
     #
     # @return [Channel]
     #
     def get(name, channel_options = {})
       if channels.has_key?(name)
         channels[name].tap do |channel|
-          channel.update_options channel_options if channel_options && !channel_options.empty?
+          if channel_options && !channel_options.empty?
+            if channel.respond_to?(:need_reattach?) && channel.need_reattach?
+              raise_implicit_options_update
+            else
+              warn_implicit_options_update
+              channel.options = channel_options
+            end
+          end
         end
       else
         channels[name] ||= channel_klass.new(client, name, channel_options)
@@ -70,6 +77,19 @@ def each(&block)
     end
 
     private
+
+    def raise_implicit_options_update
+      raise ArgumentError, "You are trying to indirectly update channel options which will trigger reattachment of the channel. Please use Channel#set_options directly if you wish to continue"
+    end
+
+    def warn_implicit_options_update
+      logger.warn { "Channels#get: Using this method to update channel options is deprecated and may be removed in a future version of ably-ruby. Please use Channel#setOptions instead" }
+    end
+
+    def logger
+      client.logger
+    end
+
     def client
       @client
     end
diff --git a/lib/ably/realtime/channel.rb b/lib/ably/realtime/channel.rb
index 6781b1071..2b16276c2 100644
--- a/lib/ably/realtime/channel.rb
+++ b/lib/ably/realtime/channel.rb
@@ -36,6 +36,7 @@ class Channel
       include Ably::Modules::MessageEmitter
       include Ably::Realtime::Channel::Publisher
       extend Ably::Modules::Enum
+      extend Forwardable
 
       # ChannelState
       # The permited states for this channel
@@ -92,17 +93,20 @@ class Channel
       # @api private
       attr_reader :manager
 
+      # ChannelOptions params attrribute (#RTL4k)
+      # return [Hash]
+      def_delegators :options, :params
+
       # Initialize a new Channel object
       #
       # @param  client [Ably::Rest::Client]
       # @param  name [String] The name of the channel
-      # @param  channel_options [Hash]     Channel options, currently reserved for Encryption options
-      # @option channel_options [Hash,Ably::Models::CipherParams]   :cipher   A hash of options or a {Ably::Models::CipherParams} to configure the encryption. *:key* is required, all other options are optional.  See {Ably::Util::Crypto#initialize} for a list of +:cipher+ options
+      # @param  channel_options [Hash, Ably::Models::ChannelOptions]     A hash of options or a {Ably::Models::ChannelOptions}
       #
       def initialize(client, name, channel_options = {})
         name = ensure_utf_8(:name, name)
 
-        update_options channel_options
+        @options       = Ably::Models::ChannelOptions(channel_options)
         @client        = client
         @name          = name
         @queue         = []
@@ -309,6 +313,16 @@ def __incoming_msgbus__
         )
       end
 
+      # Sets or updates the stored channel options. (#RTL16)
+      # @param channel_options [Hash, Ably::Models::ChannelOptions]     A hash of options or a {Ably::Models::ChannelOptions}
+      # @return [Ably::Models::ChannelOptions]
+      def set_options(channel_options)
+        @options = Ably::Models::ChannelOptions(channel_options)
+
+        manager.request_reattach if need_reattach?
+      end
+      alias options= set_options
+
       # @api private
       def set_channel_error_reason(error)
         @error_reason = error
@@ -319,13 +333,6 @@ def clear_error_reason
         @error_reason = nil
       end
 
-      # @api private
-      def update_options(channel_options)
-        @options = channel_options.clone.freeze
-      end
-      alias set_options update_options # (RSL7)
-      alias options= update_options
-
       # Used by {Ably::Modules::StateEmitter} to debug state changes
       # @api private
       def logger
@@ -336,7 +343,12 @@ def logger
       # #transition_state_machine must be used instead
       private :change_state
 
+      def need_reattach?
+        !!(attaching? || attached?) && !!(options.modes || options.params)
+      end
+
       private
+
       def setup_event_handlers
         __incoming_msgbus__.subscribe(:message) do |message|
           message.decode(client.encoders, options) do |encode_error, error_message|
diff --git a/lib/ably/realtime/channel/channel_manager.rb b/lib/ably/realtime/channel/channel_manager.rb
index 4e61a19ca..5cec145be 100644
--- a/lib/ably/realtime/channel/channel_manager.rb
+++ b/lib/ably/realtime/channel/channel_manager.rb
@@ -38,6 +38,8 @@ def attached(attached_protocol_message)
         if attached_protocol_message
           update_presence_sync_state_following_attached attached_protocol_message
           channel.properties.set_attach_serial(attached_protocol_message.channel_serial)
+          channel.options.set_modes_from_flags(attached_protocol_message.flags)
+          channel.options.set_params(attached_protocol_message.params)
         end
       end
 
@@ -64,6 +66,7 @@ def duplicate_attached_received(protocol_message)
         end
 
         channel.properties.set_attach_serial(protocol_message.channel_serial)
+        channel.options.set_modes_from_flags(protocol_message.flags)
 
         if protocol_message.has_channel_resumed_flag?
           logger.debug { "ChannelManager: Additional resumed ATTACHED message received for #{channel.state} channel '#{channel.name}'" }
@@ -199,14 +202,18 @@ def channel_retry_timeout
       end
 
       def send_attach_protocol_message
-        send_state_change_protocol_message Ably::Models::ProtocolMessage::ACTION.Attach, :suspended # move to suspended
+        message_options = {}
+        message_options[:flags] = channel.options.modes_to_flags if channel.options.modes
+        message_options[:params] = channel.options.params if channel.options.params.any?
+
+        send_state_change_protocol_message Ably::Models::ProtocolMessage::ACTION.Attach, :suspended, message_options
       end
 
       def send_detach_protocol_message(previous_state)
         send_state_change_protocol_message Ably::Models::ProtocolMessage::ACTION.Detach, previous_state # return to previous state if failed
       end
 
-      def send_state_change_protocol_message(new_state, state_if_failed)
+      def send_state_change_protocol_message(new_state, state_if_failed, message_options = {})
         state_at_time_of_request = channel.state
         @pending_state_change_timer = EventMachine::Timer.new(realtime_request_timeout) do
           if channel.state == state_at_time_of_request
@@ -227,7 +234,8 @@ def send_state_change_protocol_message(new_state, state_if_failed)
               next unless pending_state_change_timer
               connection.send_protocol_message(
                 action:  new_state.to_i,
-                channel: channel.name
+                channel: channel.name,
+                **message_options.to_h
               )
               resend_if_disconnected_and_connected.call
             end
@@ -237,7 +245,8 @@ def send_state_change_protocol_message(new_state, state_if_failed)
 
         connection.send_protocol_message(
           action:  new_state.to_i,
-          channel: channel.name
+          channel: channel.name,
+          **message_options.to_h
         )
       end
 
diff --git a/lib/ably/realtime/channels.rb b/lib/ably/realtime/channels.rb
index 9b06dea26..ef52e8d3d 100644
--- a/lib/ably/realtime/channels.rb
+++ b/lib/ably/realtime/channels.rb
@@ -13,7 +13,7 @@ def initialize(client)
       # Return a {Ably::Realtime::Channel} for the given name
       #
       # @param name [String] The name of the channel
-      # @param channel_options [Hash] Channel options, currently reserved for Encryption options
+      # @param channel_options [Hash, Ably::Models::ChannelOptions] A hash of options or a {Ably::Models::ChannelOptions}
       # @return [Ably::Realtime::Channel}
       #
       def get(*args)
diff --git a/lib/ably/rest/channel.rb b/lib/ably/rest/channel.rb
index 2a187fe2e..972dcb217 100644
--- a/lib/ably/rest/channel.rb
+++ b/lib/ably/rest/channel.rb
@@ -29,13 +29,12 @@ class Channel
       #
       # @param client [Ably::Rest::Client]
       # @param name [String] The name of the channel
-      # @param channel_options [Hash] Channel options, currently reserved for Encryption options
-      # @option channel_options [Hash,Ably::Models::CipherParams]   :cipher   A hash of options or a {Ably::Models::CipherParams} to configure the encryption. *:key* is required, all other options are optional.  See {Ably::Util::Crypto#initialize} for a list of +:cipher+ options
+      # @param channel_options [Hash, Ably::Models::ChannelOptions]     A hash of options or a {Ably::Models::ChannelOptions}
       #
       def initialize(client, name, channel_options = {})
         name = (ensure_utf_8 :name, name)
 
-        update_options channel_options
+        @options = Ably::Models::ChannelOptions(channel_options)
         @client  = client
         @name    = name
         @push    = PushChannel.new(self)
@@ -164,14 +163,16 @@ def presence
         @presence ||= Presence.new(client, self)
       end
 
-      # @api private
-      def update_options(channel_options)
-        @options = channel_options.clone.freeze
+      # Sets or updates the stored channel options. (#RSL7)
+      # @param channel_options [Hash, Ably::Models::ChannelOptions]  A hash of options or a {Ably::Models::ChannelOptions}
+      # @return [Ably::Models::ChannelOptions]
+      def set_options(channel_options)
+        @options = Ably::Models::ChannelOptions(channel_options)
       end
-      alias set_options update_options # (RSL7)
-      alias options= update_options
+      alias options= set_options
 
       private
+
       def base_path
         "/channels/#{URI.encode_www_form_component(name)}"
       end
diff --git a/lib/ably/util/crypto.rb b/lib/ably/util/crypto.rb
index 06fae0d19..d8202812a 100644
--- a/lib/ably/util/crypto.rb
+++ b/lib/ably/util/crypto.rb
@@ -30,7 +30,7 @@ class Crypto
     #    crypto.decrypt(decrypted) # => 'secret text'
     #
     def initialize(params)
-      @fixed_iv = params.delete(:fixed_iv) if params.kind_of?(Hash)
+      @fixed_iv = params[:fixed_iv]
       @cipher_params = Ably::Models::CipherParams(params)
     end
 
diff --git a/spec/acceptance/realtime/channel_spec.rb b/spec/acceptance/realtime/channel_spec.rb
index 8f437aad6..38953e986 100644
--- a/spec/acceptance/realtime/channel_spec.rb
+++ b/spec/acceptance/realtime/channel_spec.rb
@@ -117,6 +117,75 @@ def disconnect_transport
           end
         end
 
+        context 'context when channel options contain modes' do
+          before do
+            channel.options = { modes: %i[publish] }
+          end
+
+          it 'sends an ATTACH with options as flags (#RTL4l)' do
+            connection.once(:connected) do
+              client.connection.__outgoing_protocol_msgbus__.subscribe(:protocol_message) do |protocol_message|
+                next if protocol_message.action != :attach
+
+                expect(protocol_message.has_attach_publish_flag?).to eq(true)
+                stop_reactor
+              end
+
+              channel.attach
+            end
+          end
+        end
+
+        context 'context when channel options contain params' do
+          let(:params) do
+            { foo: 'foo', bar: 'bar'}
+          end
+
+          before do
+            channel.options = { params: params }
+          end
+
+          it 'sends an ATTACH with params (#RTL4k)' do
+            connection.once(:connected) do
+              client.connection.__outgoing_protocol_msgbus__.subscribe(:protocol_message) do |protocol_message|
+                next if protocol_message.action != :attach
+
+                expect(protocol_message.params).to eq(params)
+                stop_reactor
+              end
+
+              channel.attach
+            end
+          end
+        end
+
+        context 'when received attached' do
+          it 'decodes flags and sets it as modes on channel options (#RTL4m)'do
+            channel.on(:attached) do
+              expect(channel.options.modes.map(&:to_sym)).to eq(%i[subscribe])
+              stop_reactor
+            end
+
+            channel.transition_state_machine(:attaching)
+            attached_message = Ably::Models::ProtocolMessage.new(action: 11, channel: channel_name, flags: 262144)
+            client.connection.__incoming_protocol_msgbus__.publish :protocol_message, attached_message
+          end
+
+          it 'set params as channel options params (#RTL4k1)' do
+            params = { param: :something }
+
+            channel.on(:attached) do
+              expect(channel.params).to eq(channel.options.params)
+              expect(channel.params).to eq(params)
+              stop_reactor
+            end
+
+            channel.transition_state_machine(:attaching)
+            attached_message = Ably::Models::ProtocolMessage.new(action: 11, channel: channel_name, params: params)
+            client.connection.__incoming_protocol_msgbus__.publish :protocol_message, attached_message
+          end
+        end
+
         it 'implicitly attaches the channel (#RTL7c)' do
           expect(channel).to be_initialized
           channel.subscribe { |message| }
@@ -1950,6 +2019,64 @@ def fake_error(error)
       end
     end
 
+    describe '#set_options (#RTL16a)' do
+      let(:modes) { %i[subscribe] }
+      let(:channel_options) do
+        { modes: modes }
+      end
+
+      shared_examples 'an update that sends ATTACH message' do |state|
+        it 'sends an ATTACH message on options change' do
+          attach_sent = nil
+
+          client.connection.__outgoing_protocol_msgbus__.subscribe(:protocol_message) do |protocol_message|
+            if protocol_message.action == :attach && protocol_message.flags.nonzero?
+              attach_sent = true
+              expect(protocol_message.flags).to eq(262144)
+            end
+          end
+
+          channel.once(state) do
+            channel.options = channel_options
+          end
+
+          channel.on(:attached) do
+            client.connection.__incoming_protocol_msgbus__.subscribe(:protocol_message) do |protocol_message|
+              next if protocol_message.action != :attached
+
+              expect(attach_sent).to eq(true)
+              stop_reactor
+            end
+          end
+
+          channel.attach
+        end
+      end
+
+      context 'when channel is attaching' do
+        it_behaves_like 'an update that sends ATTACH message', :attaching
+      end
+
+      context 'when channel is attaching' do
+        it_behaves_like 'an update that sends ATTACH message', :attached
+      end
+
+      context 'when channel is initialized' do
+        it "doesn't send ATTACH message" do
+          client.connection.__outgoing_protocol_msgbus__.subscribe(:protocol_message) do |protocol_message|
+            raise "Unexpected message" if protocol_message.action == :attach
+          end
+
+          channel.options = channel_options
+          expect(channel.options.modes.map(&:to_sym)).to eq(modes)
+
+          EventMachine.next_tick do
+            stop_reactor
+          end
+        end
+      end
+    end
+
     context 'channel state change' do
       it 'emits a ChannelStateChange object' do
         channel.on(:attached) do |channel_state_change|
diff --git a/spec/acceptance/realtime/channels_spec.rb b/spec/acceptance/realtime/channels_spec.rb
index 992aeecb3..9d385da7c 100644
--- a/spec/acceptance/realtime/channels_spec.rb
+++ b/spec/acceptance/realtime/channels_spec.rb
@@ -10,17 +10,56 @@
     end
 
     it 'returns channel object and passes the provided options' do
-      expect(channel_with_options.options).to eql(options)
+      expect(channel_options).to be_a(Ably::Models::ChannelOptions)
+      expect(channel_options.to_h).to eq(options)
       stop_reactor
     end
   end
 
   vary_by_protocol do
+    let(:client_options) do
+      { key: api_key, environment: environment, protocol: protocol }
+    end
     let(:client) do
-      auto_close Ably::Realtime::Client.new(key: api_key, environment: environment, protocol: protocol)
+      auto_close Ably::Realtime::Client.new(client_options)
     end
     let(:channel_name) { random_str }
-    let(:options)      { { key: 'value' } }
+    let(:options) do
+      { params: { key: 'value' } }
+    end
+
+    subject(:channel_options) { channel_with_options.options }
+
+    context 'when channel supposed to trigger reattachment per RTL16a (#RTS3c1)' do
+      it 'will raise an error' do
+        channel = client.channels.get(channel_name, options)
+
+        channel.on(:attached) do
+          expect { client.channels.get(channel_name, { modes: [] }) }.to raise_error ArgumentError, /use Channel#set_options directly/
+          stop_reactor
+        end
+
+        channel.attach
+      end
+
+      context 'params keys are the same but values are different' do
+        let(:options)      do
+          { params: { x: '1' } }
+        end
+
+        it 'will raise an error' do
+          channel = client.channels.get(channel_name, options)
+
+          channel.on(:attached) do
+            expect { client.channels.get(channel_name, { params: { x: '2' } }) }.to raise_error ArgumentError, /use Channel#set_options directly/
+
+            stop_reactor
+          end
+
+          channel.attach
+        end
+      end
+    end
 
     describe 'using shortcut method #channel on the client object' do
       let(:channel) { client.channel(channel_name) }
@@ -35,26 +74,39 @@
     end
 
     describe 'accessing an existing channel object with different options' do
+      let(:client_options)  { super().merge(logger: custom_logger_object) }
+      let(:custom_logger_object) { TestLogger.new }
       let(:new_channel_options) { { encrypted: true } }
-      let(:original_channel)    { client.channels.get(channel_name, options) }
+      let!(:original_channel)    { client.channels.get(channel_name, options) }
 
       it 'overrides the existing channel options and returns the channel object' do
-        expect(original_channel.options).to_not include(:encrypted)
+        expect(original_channel.options.to_h).to_not include(:encrypted)
         new_channel = client.channels.get(channel_name, new_channel_options)
         expect(new_channel).to be_a(Ably::Realtime::Channel)
         expect(new_channel.options[:encrypted]).to eql(true)
         stop_reactor
       end
+
+      it 'shows deprecation warning' do
+        client.channels.get(channel_name, new_channel_options)
+
+        warning = custom_logger_object.logs.find do |severity, message|
+          message.match(/Using this method to update channel options is deprecated and may be removed/)
+        end
+
+        expect(warning).to_not be_nil
+        stop_reactor
+      end
     end
 
     describe 'accessing an existing channel object without specifying any channel options' do
       let(:original_channel) { client.channels.get(channel_name, options) }
 
       it 'returns the existing channel without modifying the channel options' do
-        expect(original_channel.options).to eql(options)
+        expect(original_channel.options.to_h).to eq(options)
         new_channel = client.channels.get(channel_name)
         expect(new_channel).to be_a(Ably::Realtime::Channel)
-        expect(original_channel.options).to eql(options)
+        expect(original_channel.options.to_h).to eq(options)
         stop_reactor
       end
     end
diff --git a/spec/acceptance/rest/channels_spec.rb b/spec/acceptance/rest/channels_spec.rb
index 8f82d5bb3..6b6485e6d 100644
--- a/spec/acceptance/rest/channels_spec.rb
+++ b/spec/acceptance/rest/channels_spec.rb
@@ -5,11 +5,11 @@
   shared_examples 'a channel' do
     it 'returns a channel object' do
       expect(channel).to be_a Ably::Rest::Channel
-      expect(channel.name).to eql(channel_name)
+      expect(channel.name).to eq(channel_name)
     end
 
     it 'returns channel object and passes the provided options' do
-      expect(channel_with_options.options).to eql(options)
+      expect(channel_with_options.options.to_h).to eq(options)
     end
   end
 
@@ -32,12 +32,29 @@
       it_behaves_like 'a channel'
     end
 
+    describe '#set_options (#RTL16)' do
+      let(:channel) { client.channel(channel_name) }
+
+      it "updates channel's options" do
+        expect { channel.options = options }.to change { channel.options.to_h }.from({}).to(options)
+      end
+
+      context 'when providing Ably::Models::ChannelOptions object' do
+        let(:options_object) { Ably::Models::ChannelOptions.new(options) }
+
+        it "updates channel's options" do
+          expect { channel.options =  options_object}.to change { channel.options.to_h }.from({}).to(options)
+        end
+      end
+    end
+
     describe 'accessing an existing channel object with different options' do
       let(:new_channel_options) { { encrypted: true } }
       let(:original_channel)    { client.channels.get(channel_name, options) }
 
       it 'overrides the existing channel options and returns the channel object (RSN3c)' do
-        expect(original_channel.options).to_not include(:encrypted)
+        expect(original_channel.options.to_h).to_not include(:encrypted)
+
         new_channel = client.channels.get(channel_name, new_channel_options)
         expect(new_channel).to be_a(Ably::Rest::Channel)
         expect(new_channel.options[:encrypted]).to eql(true)
@@ -48,10 +65,10 @@
       let(:original_channel) { client.channels.get(channel_name, options) }
 
       it 'returns the existing channel without modifying the channel options' do
-        expect(original_channel.options).to eql(options)
+        expect(original_channel.options.to_h).to eq(options)
         new_channel = client.channels.get(channel_name)
         expect(new_channel).to be_a(Ably::Rest::Channel)
-        expect(original_channel.options).to eql(options)
+        expect(original_channel.options.to_h).to eq(options)
       end
     end
 
diff --git a/spec/lib/unit/models/channel_options_spec.rb b/spec/lib/unit/models/channel_options_spec.rb
new file mode 100644
index 000000000..1d9d16a8d
--- /dev/null
+++ b/spec/lib/unit/models/channel_options_spec.rb
@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Ably::Models::ChannelOptions do
+  let(:modes) { nil }
+  let(:params) { {} }
+  let(:options) { described_class.new(modes: modes, params: params) }
+
+  describe '#modes_to_flags' do
+    let(:modes) { %w[publish subscribe presence_subscribe] }
+
+    subject(:protocol_message) do
+      Ably::Models::ProtocolMessage.new(action: Ably::Models::ProtocolMessage::ACTION.Attach, flags: options.modes_to_flags)
+    end
+
+    it 'converts modes to ProtocolMessage#flags correctly' do
+      expect(protocol_message.has_attach_publish_flag?).to eq(true)
+      expect(protocol_message.has_attach_subscribe_flag?).to eq(true)
+      expect(protocol_message.has_attach_presence_subscribe_flag?).to eq(true)
+
+      expect(protocol_message.has_attach_resume_flag?).to eq(false)
+      expect(protocol_message.has_attach_presence_flag?).to eq(false)
+    end
+  end
+
+  describe '#set_modes_from_flags' do
+    let(:subscribe_flag) { 262144 }
+
+    it 'converts flags to ChannelOptions#modes correctly' do
+      result = options.set_modes_from_flags(subscribe_flag)
+
+      expect(result).to eq(options.modes)
+      expect(options.modes.map(&:to_sym)).to eq(%i[subscribe])
+    end
+  end
+
+    describe '#set_params' do
+      let(:previous_params) { { example_attribute: 1 } }
+      let(:new_params) { { new_attribute: 1 } }
+      let(:params) { previous_params }
+
+      it 'should be able to overwrite attributes' do
+        expect { options.set_params(new_params) }.to \
+          change { options.params }.from(previous_params).to(new_params)
+      end
+
+      it 'should be able to make params empty' do # (1)
+        expect { options.set_params({}) }.to change { options.params }.from(previous_params).to({})
+      end
+    end
+end
diff --git a/spec/unit/models/protocol_message_spec.rb b/spec/unit/models/protocol_message_spec.rb
index 53c7a20a6..44d6e2fe2 100644
--- a/spec/unit/models/protocol_message_spec.rb
+++ b/spec/unit/models/protocol_message_spec.rb
@@ -223,6 +223,24 @@ def new_protocol_message(options)
       end
     end
 
+    context '#params (#RTL4k1)' do
+      let(:params) do
+        { foo: :bar }
+      end
+
+      context 'when present' do
+        specify do
+          expect(new_protocol_message({ params: params }).params).to eq(params)
+        end
+      end
+
+      context 'when empty' do
+        specify do
+          expect(new_protocol_message({}).params).to eq({})
+        end
+      end
+    end
+
     context '#has_connection_serial?' do
       context 'without connection_serial' do
         let(:protocol_message) { new_protocol_message({}) }
diff --git a/spec/unit/realtime/channels_spec.rb b/spec/unit/realtime/channels_spec.rb
index 6382a9f51..9fbc70b6f 100644
--- a/spec/unit/realtime/channels_spec.rb
+++ b/spec/unit/realtime/channels_spec.rb
@@ -3,39 +3,77 @@
 
 describe Ably::Realtime::Channels do
   let(:connection) { instance_double('Ably::Realtime::Connection', unsafe_on: true, on_resume: true) }
-  let(:client) { instance_double('Ably::Realtime::Client', connection: connection, client_id: 'clientId') }
+  let(:client) do
+    instance_double('Ably::Realtime::Client', connection: connection, client_id: 'clientId', logger: double('logger').as_null_object)
+  end
   let(:channel_name) { 'unique' }
-  let(:options) { { 'bizarre' => 'value' } }
+  let(:options) do
+    { params: { bizarre: 'value' } }
+  end
 
   subject { Ably::Realtime::Channels.new(client) }
 
   context 'creating channels' do
     context '#get' do
-      it 'creates a channel if it does not exist (RSN3a)' do
-        expect(Ably::Realtime::Channel).to receive(:new).with(client, channel_name, options)
-        subject.get(channel_name, options)
+      context "when channel doesn't exist" do
+        shared_examples 'creates a channel' do
+          it 'creates a channel (RTS3a)' do
+            expect(Ably::Realtime::Channel).to receive(:new).with(client, channel_name, channel_options)
+            subject.get(channel_name, channel_options)
+          end
+        end
+
+        describe 'hash' do
+          let(:channel_options) { options }
+          it { expect(channel_options).to be_a(Hash) }
+
+          include_examples 'creates a channel'
+        end
+
+        describe 'ChannelOptions object' do
+          let(:channel_options) { Ably::Models::ChannelOptions.new(options) }
+          it { expect(channel_options).to be_a(Ably::Models::ChannelOptions) }
+
+          include_examples 'creates a channel'
+        end
       end
 
       context 'when an existing channel exists' do
-        it 'will reuse a channel object if it exists (RSN3a)' do
-          channel = subject.get(channel_name, options)
-          expect(channel).to be_a(Ably::Realtime::Channel)
-          expect(subject.get(channel_name, options).object_id).to eql(channel.object_id)
+        shared_examples 'reuse a channel object if it exists' do
+          it 'will reuse a channel object if it exists (RTS3a)' do
+            channel = subject.get(channel_name, channel_options)
+            expect(channel).to be_a(Ably::Realtime::Channel)
+            expect(subject.get(channel_name, channel_options).object_id).to eql(channel.object_id)
+          end
+        end
+
+        describe 'hash' do
+          let(:channel_options) { options }
+          it { expect(channel_options).to be_a(Hash) }
+
+          include_examples 'reuse a channel object if it exists'
+        end
+
+        describe 'ChannelOptions object' do
+          let(:channel_options) { Ably::Models::ChannelOptions.new(options) }
+          it { expect(channel_options).to be_a(Ably::Models::ChannelOptions) }
+
+          include_examples 'reuse a channel object if it exists'
         end
 
         it 'will update the options on the channel if provided (RSN3c)' do
           channel = subject.get(channel_name, options)
-          expect(channel.options).to eql(options)
-          expect(channel.options).to_not include(:encrypted)
+          expect(channel.options.to_h).to eq(options)
+          expect(channel.options.to_h).to_not include(:encrypted)
           subject.get(channel_name, encrypted: true)
-          expect(channel.options[:encrypted]).to eql(true)
+          expect(channel.options[:encrypted]).to eq(true)
         end
 
         it 'will leave the options intact on the channel if not provided' do
           channel = subject.get(channel_name, options)
-          expect(channel.options).to eql(options)
+          expect(channel.options.to_h).to eq(options)
           subject.get(channel_name)
-          expect(channel.options).to eql(options)
+          expect(channel.options.to_h).to eq(options)
         end
       end
     end
diff --git a/spec/unit/rest/channels_spec.rb b/spec/unit/rest/channels_spec.rb
index 1a6221ac2..5b4eba0dd 100644
--- a/spec/unit/rest/channels_spec.rb
+++ b/spec/unit/rest/channels_spec.rb
@@ -2,30 +2,97 @@
 require 'spec_helper'
 
 describe Ably::Rest::Channels do
-  let(:client)       { instance_double('Ably::Rest::Client') }
+  let(:client)       { instance_double('Ably::Rest::Client', logger: double('logger').as_null_object) }
   let(:channel_name) { 'unique'.encode(Encoding::UTF_8) }
-  let(:options)      { { 'bizarre' => 'value' } }
+  let(:options)      do
+    { params: { 'bizarre' => 'value' } }
+  end
 
   subject { Ably::Rest::Channels.new(client) }
 
-  context 'creating channels' do
-    it '#get creates a channel' do
-      expect(Ably::Rest::Channel).to receive(:new).with(client, channel_name, options)
-      subject.get(channel_name, options)
-    end
+  describe '#get' do
+    context "when channel doesn't exist" do
+      shared_examples 'creates a channel' do
+        it 'creates a channel (RSN3a)' do
+          expect(Ably::Rest::Channel).to receive(:new).with(client, channel_name, options)
+          subject.get(channel_name, options)
+        end
+      end
 
-    it '#get will reuse the channel object' do
-      channel = subject.get(channel_name, options)
-      expect(channel).to be_a(Ably::Rest::Channel)
-      expect(subject.get(channel_name, options).object_id).to eql(channel.object_id)
+      describe 'hash' do
+        let(:channel_options) { options }
+        it { expect(channel_options).to be_a(Hash) }
+
+        include_examples 'creates a channel'
+      end
+
+      describe 'ChannelOptions object' do
+        let(:channel_options) { Ably::Models::ChannelOptions.new(options) }
+        it { expect(channel_options).to be_a(Ably::Models::ChannelOptions) }
+
+        include_examples 'creates a channel'
+      end
     end
 
-    it '[] creates a channel' do
-      expect(Ably::Rest::Channel).to receive(:new).with(client, channel_name, options)
-      subject.get(channel_name, options)
+    context 'when an existing channel exists' do
+      shared_examples 'reuse a channel object if it exists' do
+        it 'will reuse a channel object if it exists (RSN3a)' do
+          channel = subject.get(channel_name, channel_options)
+          expect(channel).to be_a(Ably::Rest::Channel)
+          expect(subject.get(channel_name, channel_options).object_id).to eql(channel.object_id)
+        end
+      end
+
+      describe 'hash' do
+        let(:channel_options) { options }
+        it { expect(channel_options).to be_a(Hash) }
+
+        include_examples 'reuse a channel object if it exists'
+      end
+
+      describe 'ChannelOptions object' do
+        let(:channel_options) { Ably::Models::ChannelOptions.new(options) }
+        it { expect(channel_options).to be_a(Ably::Models::ChannelOptions) }
+
+        include_examples 'reuse a channel object if it exists'
+      end
+
+      context 'with new channel_options modes' do
+        shared_examples 'update channel with provided options :modes' do
+          it 'will update channel with provided options modes (RSN3c)' do
+            channel = subject.get(channel_name, channel_options)
+            expect(channel.options.modes).to eq(modes)
+
+            subject.get(channel_name, channel_options)
+            expect(channel.options.modes).to eq(modes)
+          end
+        end
+
+        let(:modes) { %i[subscribe] }
+        let(:new_options) { { modes: modes } }
+
+        describe 'hash' do
+          let(:channel_options) { new_options }
+          it { expect(channel_options).to be_a(Hash) }
+
+          include_examples 'update channel with provided options :modes'
+        end
+
+        describe 'ChannelOptions object' do
+          let(:channel_options) { Ably::Models::ChannelOptions.new(new_options) }
+          it { expect(channel_options).to be_a(Ably::Models::ChannelOptions) }
+
+          include_examples 'update channel with provided options :modes'
+        end
+      end
     end
   end
 
+  it '[] creates a channel' do
+    expect(Ably::Rest::Channel).to receive(:new).with(client, channel_name, options)
+    subject.get(channel_name, options)
+  end
+
   context '#fetch' do
     it 'retrieves a channel if it exists' do
       channel = subject.get(channel_name, options)