Bridge & Switch Pietro Nicoletti Piero[at]studioreti.it Bridge-Switch-Engl - P. Nicoletti: see note pag.
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Bridge Called also MAC Bridge operate at layer use simple forwarding algorithm forwarding technique based on MAC destination address are normally used for local connections Bridge-Switch-Engl - 3 P. Nicoletti: see note pag.
Bridge model Upper Upper Layers BRIDGE Layers MAC MAC Relay MAC MAC Physical Physical Physical Physical Bridge-Switch-Engl - 4 P. Nicoletti: see note pag.
Bridge architecture Bridge Processing Port B LAN # Port A LAN # Forwarding Data Base Bridge-Switch-Engl - 5 P. Nicoletti: see note pag.
Forwarding Forwarding table is calculated by: backward learning looking the Source MAC address Backward learning work only over LAN with tree topology other topologies are transformed to tree topology by spanning tree algorithm Spanning tree algorithm operate periodically (any second) decide which port set to forwarding state and which port set to blocking state Bridge-Switch-Engl - 6 P. Nicoletti: see note pag.
Transparent Bridge IEEE standardized the bridge functions by 80.D standard The bridge 80.D work in transparent mode, for this reason are also called transparent bridge: are derived from Ethernet have a local forwarding table The main functions of the bridge are: frame forwarding Singlecast frames forwarding based on Destination MAC Address Broadcast frames are forwarded in every ports except the port where as been received stations auto-learning loop detection by spanning tree algorithm Bridge-Switch-Engl - 7 P. Nicoletti: see note pag.
Transparent Bridge PC PORT A PC BRIDGE PC3 PORT B PC4 Bridge-Switch-Engl - 8 P. Nicoletti: see note pag.
Bridge physical architecture CPU ROM Flash Memory RAM BUS Network Interface Network Interface Network Interface Network Interface Network Interface Bridge-Switch-Engl - 9 P. Nicoletti: see note pag.
Bridge logical architecture Higher Layer Entities Bridge Management (bribge control functions) LLC Entities MAC Service MAC Entity Bridge Protocol Entity (BLAN topology computation) MAC Relay Entity (Media Access Method Indipendent Functions) Internal Internal Sublayer Sublayer Service Service LLC Entities MAC Service MAC Entity (Media Access Method Dependent Functions) (Media Access Method Dependent Functions) LAN Port Port LAN Bridge-Switch-Engl - 0 P. Nicoletti: see note pag.
Bridge functions MAC Relay Entity Bridging Process Forwarding Sub-Process Spanning Tree Process Learning Sub-Process Bridge Protocol Entity Bridge-Switch-Engl - P. Nicoletti: see note pag.
Filtering data base Entry fields MAC address Destination port Ageing time (default expire after 300 s) Port status (depending by spanning tree protocol) Entry type dynamic Updated by learning process Max entries: 04 65 K static Not updated by learning process 56 entries typically Lookup by CAM (Content Addressable Memory) Bridge-Switch-Engl - P. Nicoletti: see note pag.
Filtering database example filtering database show command Switch-> show cam dynamic * = Static Entry. + = Permanent Entry. # = System Entry X = Port Security Entry Dest MAC Address Ports Age ------------------ ----- --- 00-00-86-a-a6-44 / 00-00-c9-0-b3-0f / 0 00-00-f8-3-c-3b / 4 00-00-f8-3-f7-a0 / 00-0-e7-00-e3-80 / 0 00-0-a5-84-a7-a6 / 00-0-b3-e-b4-aa / 5 00-0-b3-e-da-da /5 00-0-b3-e-dc-fd /4 Stations MAC address Modular switcth: slot/port Ageing time Bridge-Switch-Engl - 3 P. Nicoletti: see note pag.
Bridge Forwarding Begin Frame received without error on port x Destination found in forwarding data base? N Discart Frame Y Y Direction equal to port x? N Forward Frame to correct LAN Forward Frame in all LAN except X Bridge-Switch-Engl - 4 P. Nicoletti: see note pag.
Bridge Learning From Bridge forwarding Source found in forwarding data base? Y Update direction and timer N Add Source to DB with timer and direction Finished Bridge-Switch-Engl - 5 P. Nicoletti: see note pag.
Forwarding frame to unknown destination Station 08-00-b-6-50-a0 Station 08-00-b-0-0-56 Port MAC adress Ageing time LAN A Flooding 08-00-b-6-50-a0 0 B LAN B 3 Stazion 3 08-00-5a-0-40-e LAN C Station 5 08-00-b-c4-e6-aa Station 4 08-00-5a-00-00-06 Bridge-Switch-Engl - 6 P. Nicoletti: see note pag.
Forwarding frame to known address destination June 006 Station 08-00-b-6-50-a0 Station 08-00-b-0-0-56 Port MAC adress Ageing time LAN A B Selective forwarding to port LAN B 08-00-b-6-50-a0 5 3 08-00-b-c4-e6-aa 0 3 Station 3 08-00-5a-0-40-e LAN C Station 5 08-00-b-c4-e6-aa Station 4 08-00-5a-00-00-06 Bridge-Switch-Engl - 7 P. Nicoletti: see note pag.
Traffic limitation Station 08-00-b-6-50-a0 Station 08-00-b-0-0-56 Port MAC adress Ageing time LAN A 3 B Discarded frame LAN B 08-00-b-6-50-a0 3 08-00-b-c4-e6-aa 3 08-00-b-0-0-56 0 Stazion 3 08-00-5a-0-40-e LAN C Station 5 08-00-b-c4-e6-aa Station 4 08-00-5a-00-00-06 Bridge-Switch-Engl - 8 P. Nicoletti: see note pag.
Station 5 move and Filtering Data Base update Station 5 08-00-b-c4-e6-aa Station 08-00-b-6-50-a0 Station 08-00-b-0-0-56 Port MAC adress Ageing time LAN A 3 B Discarded Frame LAN B 08-00-b-6-50-a0 40 3 08-00-b-c4-e6-aa 0 08-00-b-0-0-56 0 Station 3 08-00-5a-0-40-e LAN C Station 4 08-00-5a-00-00-06 Bridge-Switch-Engl - 9 P. Nicoletti: see note pag.
Station move and forwarding error Station 08-00-b-6-50-a0 LAN A Frame for Station Forwarded on wrong port Port MAC adress Ageing time 08-00-b-6-50-a0 50 B LAN B 3 08-00-b-c4-e6-aa 5 3 08-00-b-0-0-56 40 Station 3 08-00-5a-0-40-e 08-00-5a-0-40-e 0 LAN C Station 5 08-00-b-c4-e6-aa Station 4 08-00-5a-00-00-06 Station 08-00-b-0-0-56 Bridge-Switch-Engl - 0 P. Nicoletti: see note pag.
Fault Tolerant network and Filtering Data Base Update 6 5 3 4 Primary Link Sencodary Link Bridge-Switch-Engl - P. Nicoletti: see note pag.
LAN 6 Loop on the network Broadcast are not filtered: broadcast storm 3 LAN B Bp=3768 00-00-0C-0-A0-30 LAN 3 Bp=3768 00-00-0C-0-5-04 B 3 LAN Bp=3768 00-00-0C-0-0-03 B5 LAN 7 3 B3 Bp=3768 08-00-B-5-- LAN 4 LAN 5 B4 Bp=867 08-00-B-AA-50-30 Bridge-Switch-Engl - P. Nicoletti: see note pag.
Solution: cut the loops LAN Bp=3768 00-00-0C-0-5-04 B 3 LAN 6 3 B Bp=3768 00-00-0C-0-A0-30 LAN 3 LAN Bp=3768 00-00-0C-0-0-03 B5 LAN 7 3 B3 Bp=3768 08-00-B-5-- LAN 4 LAN 5 B4 Bp=867 08-00-B-AA-50-30 Bridge-Switch-Engl - 3 P. Nicoletti: see note pag.
Spanning Tree All bridge in the network must be IEEE 80.D spanning tree compliant The spanning tree algorithm operate with the following steps: Root Bridge election Root Port selection Designated/Blocking Port selection The spanning tree protocol use the BPDU (Bridge Protocol Data Unit) Bridge-Switch-Engl - 4 P. Nicoletti: see note pag.
Spanning tree protocol result June 006 LAN 6 LAN 4 Bp=3768 00-00-0C-0-5-04 Costo 0 3 Designated Port Root Port Designated Port LAN Root Port B Bp=3768 B 00-00-0C-0-A0-30 Costo 0 LAN 7 Root Path Cost 0 (0 di B+ 0 di B) 3 Costo 0 3 Bp=867 08-00-B-AA-50-30 B3 B4 Costo 0 Bp=3768 08-00-B-5-- Costo 0 Root Path Cost 0 LAN 3 LAN 5 B5 Bp=3768 00-00-0C-0-0-03 Costo 0 Designated Port LAN Bridge-Switch-Engl - 5 P. Nicoletti: see note pag. Root Port Designated Port Root Bridge Designated Port Root Port
Bridge Protocol Data Unit (BPDU) Configuration BPDU Topology Change Notification BPDU Dest. Addr. Multicast 0-80-C 00-00-00 Source Addr. Singlecast MAC Bridge Address Length XY DSAP SSAP Control BPDU 04H 04H XID Configuration BPDU or Topology Change Notification BPDU FCS BPDU: Bridge Protocol Data Unit DSAP: Destination Service Access Point SSAP: Source Service Access Point Bridge-Switch-Engl - 6 P. Nicoletti: see note pag.
Configuration BPDU Root Identifier bridge identifier of root bridge Root Path Cost Cost to reach the root bridge Zero on BPDU transmitted by root bridge Bridge Identifier Port Identifier Byte 3 4 5 6 3 4 7 8 5 6 7 Protocol Identifier: 00-00 Protocol Version Identifier: 00 BPDU Type: 00 TC Flags Root Identifier TCA TCA First byte = Bridge Priority Last 6 byte = Root Bridge MAC Address Root Path Cost Bridge Identifier First byte = Bridge Priority Last 6 byte = Bridge MAC Address witch transmit BPDU Port Identifier First byte = Port Priority second byte = port number 8 9 30 3 3 33 34 35 Message Age Max Age Hello Time Forward Delay Bridge-Switch-Engl - 7 P. Nicoletti: see note pag.
Bridge Identifier MAC Address assigned to the Bridge Priority assigned to the Bridge: bridge priority Configuration Default value to guarantee plug&play operation Became root bridge the bridge with less bridge identifier Less bridge priority determine the root bridge election If Bridge priority is the same in every bridge the lowest MAC address determine the root bridge election Bridge Identifier or Root Identifier Bridge Priority (default 3.768) Bridge MAC Address Bridge-Switch-Engl - 8 P. Nicoletti: see note pag.
Port Identifier Identify the port witch transmit the BPDU on connected LAN Port Priority (default 8) Port number Port Identifier Bridge-Switch-Engl - 9 P. Nicoletti: see note pag.
The algorithm principle Root Bridge election Is selected as root bridge the bridge with lowest Bridge Identifier Root port The port (only one) connection to the root bridge Designated Port The port that forwards frames from that LAN towards the Root A bridge may one or more designated ports Bridge-Switch-Engl - 30 P. Nicoletti: see note pag.
The algorithm principle: Root & Designated Port selection Rule for Root and Designated Port selection Lowest Root Path Cost In case of equal Root Path Cost the algorithm look for Lowest Bridge Identifier In case of equal Root Path Cost and equal Bridge Identifier the algorithm look for Lowest Port Identifier If there is only one port to connect a LAN that port is immediately elected as Designated Port All the active port of the root Bridge are selected as Designated Port The ports that are not been selected as root or designated go to Blocking State Bridge-Switch-Engl - 3 P. Nicoletti: see note pag.
Port State Listening Receive frames Do not forward frames Do not update the forwarding data base Compute received BPDU Transmit BPDU Forwarding Receive frames Forward frames Update the forwarding data base Compute received BPDU Transmit BPDU Learning Receive frames Do not forward frames Update the forwarding data base Compute received BPDU Transmit BPDU Blocking Receive frames Do not forward frames Do not update the forwarding data base Compute received BPDU DO not transmit BPDU Bridge-Switch-Engl - 3 P. Nicoletti: see note pag.
Port state diagram () Disabled () () () (,) Listening (3) (5) (4) Blocking (4) Learning (4) (5) Forwarding (,) (,) ) Port enabled, by management or initialization ) Port disabled, by management or failure 3) Algorithm selects as Designated or Root Port 4) Algorithm selects as Alternate Port 5) Protocol timer expiry (Forwarding Timer) Bridge-Switch-Engl - 33 P. Nicoletti: see note pag.
Topology Change If a bridge detect a topology change send a Topology Change Notification BPDU trough root port A bridge that receive a TCN BPDU forward that frame trough root port Root bridge answer with a Configuration BPDU with topology change bit set The bridge receiving that BPDU from root port forward a BPDU with topology change acknowledgment bit set A bridge detecting or informed about a topology change set a short time to remove the entries equal to forward delay timer Byte 3 4 Protocol Identifier: 00-00 Protocol Version Identifier: 00 BPDU Type: 80 TCN Bridge-Switch-Engl - 34 P. Nicoletti: see note pag.
Timers values Hello time Configuration BPDU generation interval Range: - 0 seconds - Recommended: seconds Forward delay timer Delay port state change: from listening to learning, from learning to forwarding state short time to remove the entries from filtering database Range: 4-30 seconds - Recommended: 5 seconds Max age The maximum age of received protocol information before it is discarded (unblocking timer port). Range: 6-40 seconds - Recommended: 0 secondi The timers are announced by the root bridge on the configuration BPDU Bridge-Switch-Engl - 35 P. Nicoletti: see note pag.
Timers limit The recommended timers assure a STP convergence of 50 seconds The recommended timers assure a correct STP operation with a maximum bridge diameter up 7 bridge The maximum bridge diameter of the Bridge LAN is the maximum number of Bridges between any two points of attachment of end stations. Changing the timers may: Increase or decrease the STP convergence Increase or decrease the maximum bridge diameter Bridge-Switch-Engl - 36 P. Nicoletti: see note pag.
STP Configuration parameters The bridges are plug&play They may work with default configuration parameters Bridge priority Range: 0-6440 Default/recommended: 3768 Suggested increment (IEEE 80.t): 4096 Port priority Range: 0-40 Default/recommended: 8 Suggested increment (IEEE 80.t): 6 Port Path cost Range: 0-65535 Recommended (IEEE 80.D): 000/(Speed in Mb/s) Bridge-Switch-Engl - 37 P. Nicoletti: see note pag.
Recommended Port Path Cost by IEEE 80.D rev998 June 006 Port Recommended Recommended Accepted speed values range values range values 4Mb/s 50 00-000 - 65535 0 Mb/s 00 50-600 - 65535 6 Mb/s 6 40-400 - 65535 00 Mb/s 9 0-60 - 65535 Gb/s 4 3-0 - 65535 0 Gb/s - 5-65535 Bridge-Switch-Engl - 38 P. Nicoletti: see note pag.
IEEE 80.t: new STP parameters adopted by 80.w e 80.s standards Extended Port Path Cost in a range from to 00.000.000 Extended System Identifier Bridge Identifier o Root Identifier 4 bit bit Bridge MAC Address Bridge Priority (default 3.768) STP Instance Bridge-Switch-Engl - 39 P. Nicoletti: see note pag.
Path Cost IEEE 80.t & 80.w June 006 Port Recommended Recommended Accepted speed value range range values <= 00 Kb/s 00.000.000 0.000.000-00.000.000-00.000.000 Mb/s 0.000.000.000.000-00.000.000-00.000.000 0 Mb/s.000.000 00.000-0.000.000-00.000.000 00 Mb/s 00.000 0.000 -.000.000-00.000.000 Gb/s 0.000.000-00.000-00.000.000 0 Gb/s 000 00-0.000-00.000.000 00 Gb/s 00 0-000 - 00.000.000 Tb/s 0-00 - 00.000.000 0 Tb/s -0-00.000.000 Bridge-Switch-Engl - 40 P. Nicoletti: see note pag.
Rapid Spanning Tree Protocol (RSTP) 80.w Fast convergence Spanning tree: Less than second Interoperable with STP IEEE 80.D Without fast convergence Modern solution for mission critical BLAN Operate only on point-to-point links Direct connections (no hub) June 006 Bridge-Switch-Engl - 4 P. Nicoletti: see note pag.
Port rules Blocking state substitute by Alternate & Backup port rules Alternate Port that offers an alternate path in the direction of the Root Bridge to that provided by the Bridge s own Root Port. Backup Acts as a backup for the path provided by a Designated Port in the direction of the leaves of the Spanning Tree. Backup Ports exist only where there are two or more connections from a given Bridge to a given LAN. Root Designated Disabled Bridge-Switch-Engl - 4 P. Nicoletti: see note pag.
Edge Port Edge port is a terminating that connect a end-station Edge port do not work as other port: As soon detect a Link Integrity Test go immediately to Forwarding state without Listening e Learning state A port changing state do not cause a TCN BPDU transmission trough root port Bridge-Switch-Engl - 43 P. Nicoletti: see note pag.
Diagrammatic conventions Legenda Graphic Symbol Bridge Identifier Port Identifier & Port Cost p, c p, c p, c p, c BBB RRR,c p, c p, c BRIDGE p, c p, c Root Identifier Root Path Cost A LAN Bridge-Switch-Engl - 44 P. Nicoletti: see note pag.
Diagrammatic conventions Port rule Port state Legenda Designated Edge Port Root Port Alternate Backup Disabled Discarding Learning Forwarding Forwarding Discarding Learning Forwarding Discarding Discarding ----- Designated Designated Proposal Root Root Agreement BPDU trasmesse Bridge-Switch-Engl - 45 P. Nicoletti: see note pag.
The algorithm principle Same as STP Root Bridge election Root port Designated Port The port not selected as root or designated are selected as: Alternate if connected to a port on different bridge Backup if connected to a different port of the same bridge Bridge-Switch-Engl - 46 P. Nicoletti: see note pag.
Physical redundant star topology 4 3 A B 3 4 C F D E 6 333 3 5 4 6 444 3 5 4 G I H K J M L N 555 4 3 666 4 3 777 4 3 888 4 3 Bridge-Switch-Engl - 47 P. Nicoletti: see note pag.
RSTP active topology Root,0 4 3 A B,0 3 4 C F D E 6 333,0 3 5 4 6 444,0 3 5 4 G I H K J M L N 555,0 4 3 666,0 4 3 777,0 4 3 888,0 4 3 Bridge-Switch-Engl - 48 P. Nicoletti: see note pag.
RSTP tree & port state Root A,0,0 4 3 B 3 4 C F D E 6 333,0 3 5 4 6 444,0 3 5 4 G I H K J M L N 555,0 4 3 666,0 4 3 777,0 4 3 888,0 4 3 Bridge-Switch-Engl - 49 P. Nicoletti: see note pag.
Backup port example,0 4 3 Root A B,0 3 4 C F D E 6 333,0 3 5 4 6 444,0 3 5 4 G I H K J M L N 555,0 4 3 666,0 4 3 777,0 4 3 888,0 4 3 O Bridge-Switch-Engl - 50 P. Nicoletti: see note pag.
Ring topology A Root,0 3 B,0 C 3 L D K 3 666,0 333,0 E 3 J F I 3 555,0 H 3 444,30 G Bridge-Switch-Engl - 5 P. Nicoletti: see note pag.
Fault recovery based on physical level fault detection If the switch loose a root port activate immediately the alternate port that became a new root port Fault detection and recovery based on physical layer fault Bridge-Switch-Engl - 5 P. Nicoletti: see note pag.
Fault detection and flush entry Local flush entries The bridge flush immediately the entries that have a faulty port as destination port Local flush entries on bridge ports at end of faulty link A bridge that change an Alternate Port to a Root Port send a Topology Change Notification (TCN) BPDU trough root port A bridge that receive a TCN BPDU: Flush the entries on every ports except the port were the TCN as been received Forward TCN on every ports in forwarding state except the port were the TCN as been received Bridge-Switch-Engl - 53 P. Nicoletti: see note pag.
Flush entry example: initial configuration,0,0,0 333,0 444,0,0 333,0 444,0 555,0 666,0 555,0 666,0 777,30 Tree represantation 777,30 Bridge-Switch-Engl - 54 P. Nicoletti: see note pag.
Flush entry: step The link 555-777 fails, and both 555 and 777 notice. It can be seen that all the Ports indicated will need to be flushed.,0 333,0,0 444,0 555,0 666,0 Legenda Addresses learnt on these Ports need to be flushed. Addresses learnt on these Ports have been flushed. TCN transmitted in the direction of the arrow 777,30 Bridge-Switch-Engl - 55 P. Nicoletti: see note pag.
Flush entry: step 555 and 777 flush addresses for their failed Ports. 777 change the port state from alternate to root 777 sends a TCN message (an RSTP BPDU with TC set).,0 333,0,0 444,0 555,0 666,0 Legenda Addresses learnt on these Ports need to be flushed. 777,30 Addresses learnt on these Ports have been flushed. TCN transmitted in the direction of the arrow Bridge-Switch-Engl - 56 P. Nicoletti: see note pag.
Flush entry: step 3 666 receives the TCN message, flushes addresses on all other Ports, and forwards a TCN.,0 333,0 3 4,0 444,0 555,0 666,0 3 Legenda Addresses learnt on these Ports need to be flushed. Addresses learnt on these Ports have been flushed. TCN transmitted in the direction of the arrow 777,30 Bridge-Switch-Engl - 57 P. Nicoletti: see note pag.
Flush entry: step 4 333 receives the TCN message, flushes, and forwards the TCN to and 555.,0 3,0 3 333,0 4 444,0 555,0 666,0 Legenda Addresses learnt on these Ports need to be flushed. 777,30 Addresses learnt on these Ports have been flushed. TCN transmitted in the direction of the arrow Bridge-Switch-Engl - 58 P. Nicoletti: see note pag.
Flush entry: step 5 receives the TCN, flushes and sends TCN messages on all other Ports.,0 3,0 3 Receipt of the TCN will cause and 444 to flush their Ports. 333,0 444,0 3 4 555,0 666,0 Legenda Addresses learnt on these Ports need to be flushed. 777,30 Addresses learnt on these Ports have been flushed. TCN transmitted in the direction of the arrow Bridge-Switch-Engl - 59 P. Nicoletti: see note pag.
DSAP SSAP Length DSAP SSAP Multicast 0-80-C-00-00-00 Singlecast Bridge Address Control June 006 XY 04H 04H XID Configuration message Proposal Port role Unknown Alternate/Backup Root Designated 00000000 = STP 0000000 = RSTP 3 4 5 6 0 0 0 0 Agreement RSTP Configuration BPDU Byte Protocol Identifier 00-00 Protocol Ver. Identifier 00 BPDU Type 00 TC Flags TCA Root Identifier First bytes = Bridge Priority Lasti 6 bytes = Root Bridge MAC Address Root Path Cost Bridge Identifier First bytes = Bridge Priority Last 6 byte = Bridge MAC Address witch transmit BPDU Port Identifier First byte = Port Priority Second byte = port number Message Age Max Age Hello Time Forward Delay Bridge-Switch-Engl - 60 P. Nicoletti: see note pag. 3 4 5 6 3 4 7 8 5 6 7 8 9 30 3 3 33 34 35
Ring topology and fast recovery Fault on the ring If the bridge have an alternate port change immediately the state from alternate to root state Recovery based physical layer If the bridge don t have an alternate port propose it self as Root Bridge Recovery based on new protocol handshaking Fast BPDU Proposal and Agreement type handshaking Sync & Agree operations Port receiving BPDU with Designated Proposal flag execute a Sync operation Discard all packet received on non-edge ports Port discarding packet (Sync) go immediately on Forwarding State when receive a BPDU with Designated Agreement flag Bridge-Switch-Engl - 6 P. Nicoletti: see note pag.
Ring topology fault: step,0 3 4 B 333,0 4 3,0 3 4 B 333,0 4 3 A C fault C,0 3 D 444,0 3 4,0 3 D 444,0 3 4 E F E F Bridge-Switch-Engl - 6 P. Nicoletti: see note pag.
Ring topology fault and new Root proposal,0 3 4 B 333,0 4 3,0 3 4 B 333,0 4 3 fault C fault C,0 3 Root Bridge? D BPDU as root bridge with flag Designated Proposal 444,0 3 4 E F,0 3 D 444,0 3 4 E F Sync operation Bridge-Switch-Engl - 63 P. Nicoletti: see note pag.
Ring topology fault: Sync Operation,0 3 4 B 333,0 4 3,0 3 4 B 333,0 4 3 fault,30 3 D BPDU containing new route to the root bridge with Flag Designated Proposal C 444,0 3 4 E BPDU flag Root Proposal F fault,30 3 BPDU flag Root Agreement D BPDU with Designated Agreement flag set C 444,0 3 4 E F Bridge-Switch-Engl - 64 P. Nicoletti: see note pag.