Practical TCP/IP and Ethernet Networking- P7: The transmitter encodes the information into a suitable form to be transmitted over the communications channel. The communications channel moves this signal as electromagnetic energy from the source to one or more destination receivers. The channel may convert this energy from one form to another, such as electrical to optical signals, whilst maintaining the integrity of the information so the recipient can understand the message sent by the transmitter.: The transmitter encodes the information into a suitable form to be transmitted over the communications channel. The communications channel moves this signal as electromagnetic energy from the source to one or more. | 12 Practical TCP IP and Ethernet Networking Encoding methods Manchester Manchester is a bi-phase signal-encoding scheme used in Ethernet LANs. The direction of the transition in mid-interval negative to positive or positive to negative indicates the value 1 or 0 respectively and provides the clocking. The Manchester codes have the advantage that they are self-clocking. Even a sequence of one thousand 0s will have a transition in every bit hence the receiver will not lose synchronization. The price paid for this is a bandwidth requirement double that which is required by the RZ-type methods. The Manchester scheme follows these rules V and -V voltage levels are used There is a transition from one to the other voltage level halfway through each bit interval There may or may not be a transition at that start of each bit interval depending on whether the bit value is a 0 or 1 For a 1 bit the transition is always from a -V to V for a 0 bit the transition is always from a V to a -V In Manchester encoding the beginning of a bit interval is used merely to set the stage. The activity in the middle of each bit interval determines the bit value upward transition for a 1 bit downward for a 0 bit. Differential Manchester Differential Manchester is a bi-phase signal-encoding scheme used in token ring LANs. The presence or absence of a transition at the beginning of a bit interval indicates the value the transition in mid-interval just provides the clocking. For electrical signals bit values will generally be represented by one of three possible voltage levels positive V zero 0 V or negative -V . Any two of these levels are needed - for example V and -V. There is a transition in the middle of each bit interval. This makes the encoding method self-clocking and helps avoid signal distortion due to DC signal components. For one of the possible bit values but not the other there will be a transition at the start of any given bit interval. For example in a .
