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This chapter is from the book

This chapter is from the book

Chapter Summary

Many important functions occur at the Data Link layer of the OSI model. Different technologies can be implemented at Layer 2 to transmit data across the network. Token ring and FDDI networks use token-passing to send frames, whereas ethernet uses the 802.3 frame standard with 802.2 LLC specifications. Ethernet framing and ethernet addressing are both significant topics for the CCNA exam. Other key ethernet functions include error detection and arbitration. Although the FCS field of the 802.3 frame detects errors on a LAN, the CSMA/CD algorithm arbitrates how data is transmitted on a LAN.

Data Link layer devices include bridges and switches. Switches are really multi-port bridges, so they share the same general functionalities. New networks are most likely to use a Layer 2 switch in place of a bridge. Switches have been improved upon over the years and offer more options for the consumer, such as dedicated bandwidth and full-duplex communications.

Although the Data Link layer uses frames to transmit data, the Network layer uses Internet Protocol or IP addresses to route traffic. Chapter 4 discusses IP addressing and subnetting at length. Both topics are imperative for the CCNA exam.

Key Terms

  • token-passing
  • token ring
  • 802.5
  • MSAU
  • RI
  • RO
  • FDDI
  • ANSI X3T9.5
  • unicast
  • multicast
  • broadcast
  • frame
  • 802.2
  • MAC
  • LLC
  • SAP
  • DSAP
  • SSAP
  • SNAP
  • 802.3
  • 10BASE-2
  • 10BASE-5
  • 10BASE-T
  • 10BASE-FL
  • 802.3u
  • 100BaseT4
  • 100BaseTX
  • 100BaseFX
  • 802.3ab
  • 1000BaseT
  • 802.3z
  • 1000BaseCX
  • 1000BaseSX
  • 1000BaseLX
  • 802.3ae
  • 10GbE
  • baseband
  • broadband
  • LRE
  • EMI
  • coaxial cable
  • unshielded twisted-pair cable
  • shielded twisted-pair cable
  • fiber-optic cable
  • multimode
  • single-mode
  • switch
  • ASIC
  • bridge
  • transparent bridges
  • Spanning Tree Protocol
  • duplex
  • microsegmentation
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