N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 7 - LAN, WAN, VPN, WLAN, MAN, FDDI and Optical MANS                                                      Slide 17 of 45 _________________                                                                                  __________

                                  OSI Model and IEEE LAN Model

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Layer 2 of OSI model is split into two sub-layers in IEEE 802 model: Logical Link Control (LLC) and Media Access Control. Two basic services are provided by LLC layer: Type 1 service -  Connectionless operation, whereby a source station can send  a message to another station without establishing a logical connection for sequencing and acknowledging messages. Type 2 service - connection-orientated, logical connections are set up for complete and accurate deliveries of messages. The LLC specifications are covered in IEEE 802.2 standard. The IEEE 802.3 standard defines the Media Access Control sublayer for CSMA / CD and a corresponding physical layer for connection to a baseband coax cable.