Network Layer (OSI Layer 3) The network layer is concerned with the routing of information and methods to determine paths to a destination. Information at this layer is called packets. Specifications include routing protocols, logical network addressing, and packet fragmentation. Routers operate in this layer. The CCIE lives and dies in this layer. Examples of network layer specifications are the following: | The OSI Reference Model 21 Examples of data-link layer technologies are the following Frame Relay Asynchronous Transport Mode ATM Synchronous Data Link Control SDLC High-level data-link control HDLC IEEE and IEEE Gigabit Ethernet IEEE Fast Ethernet Ethernet version 2 Integrated Services Digital Network ISDN Point-to-Point Protocol PPP Token Ring Spanning-Tree Protocol STP Network Layer OSI Layer 3 The network layer is concerned with the routing of information and methods to determine paths to a destination. Information at this layer is called packets. Specifications include routing protocols logical network addressing and packet fragmentation. Routers operate in this layer. The CCIE lives and dies in this layer. Examples of network layer specifications are the following Internet Protocol IP Routing Information Protocol RIP Open Shortest Path First OSPF Enhanced Interior Gateway Routing Protocol EIGRP Internetwork Packet Exchange IPX Connectionless Network Protocol CLNP Transport Layer OSI Layer 4 The transport layer provides reliable transparent transport of data segments from upper layers. It provides end-to-end error checking and recovery multiplexing virtual circuit management and flow control. Messages are assigned a sequence number at the transmission end. At the receiving end the packets are reassembled checked for errors and acknowledged. Flow control 22 Chapter 2 Networking Concepts Review manages the data transmission to ensure that the transmitting device does not send more data than the receiving device can process. Examples of transport layer specifications are the following Transmission Control Protocol TCP Real-Time Transport Protocol RTP Sequenced Packet Exchange SPX AppleTalk s Transaction Protocol ATP User Datagram Protocol UDP provides unreliable transport at this layer with less overhead than TCP Session Layer OSI Layer 5 The session layer provides a control structure for communication between applications. It establishes .
