This article lists protocols, categorized by the nearest layer in the Open Systems Interconnection model. This list is not exclusive to only the OSI protocol family. Many of these protocols are originally based on the Internet Protocol Suite (TCP/IP) and other models and they often do not fit neatly into OSI layers. Layer 1 (physical layer) Telephone network modems IrDA physical layer USB physical layer EIA RS-232, EIA-422, EIA-423, RS-449, RS-485 Ethernet physical layer 10BASE-T, 10BASE2, 10BASE5, 100BASE-TX, 100BASE-FX, 1000BASE-T, 1000BASE-SX and other varieties Varieties of 802.11 Wi-Fi physical layers DSL ISDN T1 and other T-carrier links, and E1 and other E-carrier links ITU Recommendations: see ITU-T IEEE 1394 interfaces TransferJet Etherloop ARINC 818 Avionics Digital Video Bus G.hn/G.9960 physical layer CAN bus (controller area network) physical layer Mobile Industry Processor Interface physical layer Infrared Frame Relay FO Fiber optics X.25 Layer 2 (data link layer) ARCnet Attached Resource Computer NETwork ARP Address Resolution Protocol ATM Asynchronous Transfer Mode CHAP Challenge Handshake Authentication Protocol CDP Cisco Discovery Protocol DCAP Data Link Switching Client Access Protocol Distributed Multi-Link Trunking Distributed Split Multi-Link Trunking DTP Dynamic Trunking Protocol Econet Ethernet FDDI Fiber Distributed Data Interface Frame Relay ITU-T G.hn HDLC High-Level Data Link Control IEEE 802.11 WiFi IEEE 802.16 WiMAX LACP Link Aggregation Control Protocol LattisNet LocalTalk L2F Layer 2 Forwarding Protocol L2TP Layer 2 Tunneling Protocol LLDP Link Layer Discovery Protocol LLDP-MED Link Layer Discovery Protocol - Media Endpoint Discovery MAC Media Access Control Q.710 Simplified Message Transfer Part Multi-link trunking Protocol NDP Neighbor Discovery Protocol PAgP - Cisco Systems proprietary link aggregation protocol PPP Point-to-Point Protocol PPTP Point-to-Point Tunneling Protocol PAP Password Authentication Protocol RPR IEEE 802.17 Resilient Packet Ring SLIP Serial Line Internet Protocol (obsolete) StarLAN Space Data Link Protocol, one of the norms for Space Data Link from the Consultative Committee for Space Data Systems STP Spanning Tree Protocol Split multi-link trunking Protocol Token Ring a protocol developed by IBM; the name can also be used to describe the token passing ring logical topology that it popularized. Virtual Extended Network (VEN) a protocol developed by iQuila. VTP VLAN Trunking Protocol VLAN Virtual Local Area Network Network Topology Asynchronous Transfer Mode (ATM) IS-IS, Intermediate System - Intermediate System (OSI) SPB Shortest Path Bridging MTP Message Transfer Part NSP Network Service Part TRILL (TRansparent Interconnection of Lots of Links) Layer 2.5 ARP Address Resolution Protocol MPLS Multiprotocol Label Switching PPPoE