Explanation/Reference:
Section: Enterprise Network Design Explanation
Explanation:
The best-effort model is the Quality of Service (QoS) model that is primarily used on the Internet. No QoS mechanisms are used when the best-effort model is implemented; all packets are treated with equal priority. The best-effort model is very scalable and easy to implement. However, since bandwidth is not guaranteed for any packet types the best-effort model can be a key limitation when considering an Internet circuit as a backup connection for an enterprise wide area network (WAN).
The Integrated Services (IntServ) model is not the QoS model primarily used on the Internet. IntServ, which was the first QoS model, provides end-to-end reliability guarantees for bandwidth, delay, and packet loss. However, IntServ is not very scalable, since its signaling overhead can consume a lot of bandwidth.
IntServ uses Resource Reservation Protocol (RSVP) as the signaling protocol.
The Differentiated Services (DiffServ) model is also not the QoS model primarily used on the Internet.
DiffServ does not provide end-to-end reliability guarantees. Instead, it provides per-hop QoS mechanisms.
Because end-to-end signaling is not required, bandwidth is not consumed by signaling overhead?
therefore, DiffServ is more scalable than IntServ. However, the QoS mechanisms employed by DiffServ must be configured consistently at each hop.
AutoQoS is not a QoS model. AutoQoS automates the configuration of QoS on Cisco devices, enabling consistent configurations throughout a large network.
Reference:
CCDA 200-310 Official Cert Guide, Chapter 7, WAN Backup over the Internet, pp. 263-264 Cisco: QoS Fact or Fiction