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The TCP/IP network access layer is the equivalent of the OSI data link
layer (Layer 2) and the physical layer (Layer 1).
 The OSI physical layer provides the means to transport the bits that make
up a data link layer frame across the network media.
 The physical layer standards address three functional areas: physical
components, frame encoding technique, and signaling method.
 Using the proper media is an important part of network communications.
Without the proper physical connection, either wired or wireless,
communications between any two devices will not occur.
 Wired communication consists of copper media and fiber cable.
 There are three main types of copper media used in networking:
unshielded-twisted pair (UTP), shielded-twisted pair (STP), and coaxial
cable. UTP cabling is the most common copper networking media.
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 69
Network Access
Summary (cont.)
 Optical fiber cable has become very popular for interconnecting
infrastructure network devices. It permits the transmission of data over
longer distances and at higher bandwidths (data rates) than any other
networking media.
 Wireless media carry electromagnetic signals that represent the binary
digits of data communications using radio or microwave frequencies.
 The data link layer is responsible for the exchange of frames between
nodes over a physical network media. It allows the upper layers to access
the media and controls how data is placed and received on the media.
 Among the different implementations of the data link layer protocols, there
are different methods of controlling access to the media. These media
access control techniques define if and how the nodes share the media.
 The actual media access control method used depends on the topology
and media sharing. LAN and WAN topologies can be physical or logical.
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 70
Network Access
Summary (cont.)
 WANs are commonly interconnected using the point-to-point, hub and
spoke, or mesh physical topologies.
 In shared media LANs, end devices can be interconnected using the star,
bus, ring, or extended star (hybrid) physical topologies.
 All data link layer protocols encapsulate the Layer 3 PDU within the data
field of the frame. However, the structure of the frame and the fields
contained in the header and trailer vary according to the protocol.