the destination address is established prior to trans- mission, and there are no intermediate stops. A connectionless environment worries about getting a packet one step closer to the destination (see Figure 3.6). It doesn't worry about having an end-to-end view of the path over which the message will flow; this is the fundamental differ- ence between connection-oriented and connectionless environments, and, hence, between infrastructures such as the PSTN and the Internet. Examples of connec- tionless packet-switched networks include the public Internet, private IP back- bones or networks, Internet-based VPNs, and LANs. Again, each packet (referred to as a datagram transmission) is an independent unit that contains the source and destination addresses, which increases the overhead. That's one of the issues with connectionless packet-switched networks: If we have to address each packet, the overall percentage of control information relevant to the actual data being trans- ported rises. Each router performs a path calculation function independently, and each makes use of various routing protocols (e.g., OSPF, IS-IS, BGP). Each router calcu- lates the appropriate next hop for each destination, which is generally based on the smallest number of hops (although some routing protocols use an abstract notion of cost, as defined by the network administrator, in making decisions). Packets are forwarded on a hop-by-hop basis rather than as part of an end-to-end connection. IP-based network backbone Routing tables at each (e.g., the Internet, packet node determine IP backbones, LANs) the best path at that moment Routing table Packet Figure 3.6 A connectionless network Establishing Connections: Networking Modes and Switching Modes Each packet must be individually routed, which increases delays (due to queuing delays), and the more hops, the greater the delay. Therefore, connectionless envi- ronments provide less control over ensuring QoS because of unknown latencies, unknown retransmissions, and unknown sequences in which the