Similarly, as traffic increases, the number of collisions and retransmissions also increases and Ethernet performance deteriorates, making Ethernet less suitable also for networks that frequently carry heavy traffic. Switched Ethernet The desire to operate local area networks at higher speed and with longer ranges also makes hub-based Ethernet unusable in many

Instead, switched Ethernet permits the point-to-point connection of any pair of nodes. Multiple pairs can be connected simultaneously. Modern switches even provide a buffer to hold frames destined for a receiver already in use. Switching thus prevents collisions, and there is no need to implement CSMA/CD in switched Ethernet systems. Switched Ethernet has two additional advantages: (1) it is possible to connect nodes together in full-duplex mode, which is not possible with a single bus connection, and (2) each pair of connections can operate at the maximum bit rate of the network. Wireless Ethernet is similar to hub-based Ethernet because of the nature of the medium. A variation on CSMA/CD is used for Wi-Fi. Wi-Fi protocols are presented in 14. 13.6 QUALITY OF SERVICE Certain types of data are dependent on reliable end-to-end transport where packets arrive at the receiving host in order, with sufficient throughput, with minimum, or at least, consistent, delay, at precise

, even time intervals, and with a low probability of errors and missing packet failures. These necessary qualities are particularly important for streaming audio and video applications, such as IPTV and VoIP, and for online gaming and virtual reality applications. In contrast, IP offers unreliable, best-effort service that provides limited support for any of these qualities. Similarly, the basic Ethernet specifications do not indicate any level of quality support, although a number of alternative data link layer protocols do include such methods and measures in their specifications. These include Frame Relay, ATM, and MLSP, among others, as well as certain variants on Ethernet. There is no simple, effective measure of the quality of packet switched delivery. Instead, Quality of Service (QoS) focuses on two parameters: (1) methods to reserve and prioritize channel capacity to favor packets that require special treatment, and (2) service guarantees from contracted carrier services that s

Throughput is important to assure that the network can deliver the entire stream at the required data rate. (Picture a favorite song that gets slower and slower as you listen to itnot entirely accurate, but you get the idea.) Jitter is defined as the variation in delay from packet to packet. It is a particularly important parameter in the transmission of