interface to the service provider is dependent on the type of connection; the connector could be
RJ-11, RJ-48, RJ-45, or possibly coax.
shown in the figure. Depending on the expected type of line, a variety of physical interfaces are
used. These interfaces are the same as those used for external CSU/DSU devices.
TIA works with the ITU on international standards. For more information on these standards
bodies, and for the opportunity to spend money to get copies of the standards, you can refer to
the Web sites www.tiaonline.org or www.itu.int.
Other than point-to-point links, Frame Relay is the WAN protocol most typically seen by
CCNAs. This section reviews the details of how Frame Relay accomplishes its goal of delivery
of frames to multiple WAN-connected sites.
Layer 2. The term frame is generally associated with a collection of data bits that includes an
OSI Layer 2 equivalent header. For example, an Ethernet frame includes the Ethernet header/
trailer. Frame Relay uses addresses, but that addressing does not attempt to create a logical
address structure that could be used over a variety of media; therefore, Frame Relay addressing
is closer to OSI Layer 2 addressing standards and is considered to be a Layer 2 protocol. (Refer
to Chapter 3 for a review of OSI layers.)
the exam.
on Interface