Cisco line cards include interfaces optimized for desktops, branch office backbones, and servers for enterprise and commercial switching solutions, and service provider metropolitan Ethernet networks. These line cards are functionally transparent; all the packet processing, queuing, buffering, and quality of service (QoS) occur in the supervisor engine. The simple design of the line cards results in a very high mean time between failures (MTBF), helping ensure high availability for a single connection to an end user.