Practical TCP/IP and Ethernet Networking- P57: 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 | 262 Practical TCP IP and Ethernet Networking Note that datagrams as the IP packets are known may have to be broken down or fragmented into smaller packets as they pass through a router onto a network with a smaller frame size . from Ethernet with a maximum size of 1500 bytes to Arcnet with a maximum of approximately 800 bytes . The IP protocol does not guarantee delivery of any of the packets. It merely handles the routing of the packets to its destination across the different interconnected networks. Packets could be lost due to routers becoming congested and thus discarding packets or due to corruption of the packets on a network due to electrical noise for example. Hence the TCP protocol is used to guarantee delivery of the packets. Transmission control protocol or TCP Structure of TCP The TCP protocol is used to guarantee delivery of the packet. Each byte of information is given a unique sequence number. The receiver keeps track of these sequence numbers and sends an acknowledgement to indicate to the originator of the packets that it has received the datagram up to a particular defined byte number. The TCP protocol initiates the transfer of information using a three-way handshake in which it exchanges parameters with the node it is transferring this data to. TCP flow control is based on the concept of a window. The window is used to determine how much data can be outstanding . unacknowledged from the recipient of the information transfer. The amount of data that can be in transit is referred to as the bandwidth-delay product. The maximum window size is 64 kbytes but practically it is often limited to 32 kbytes . Sliding windows Obviously there is a need to get some sort of acknowledgment back to ensure that there is a guaranteed delivery service. This technique called positive acknowledgment with retransmission requires the receiver to send back an acknowledgment message. Inherent in this is the concept of a timeout where a timer is started by the
