1 Module 06 WAN Technology Chapter 18 Fundamentals of WANs 2 Table of Content 1 OSI Layer 1 for Point-to-Point WANs 2 OSI Layer 2 for Point-to-Point WANs 3 Packet-switching service 3 1. OSI Layer 1 for Point-to-Point WANs 4 Overview WAN connections  Point-to-point WAN links provide basic connectivity between two points. To get a point-topoint WAN link, you would work with a service provider to install a circuit.  A point-topoint WAN connection sometimes is called a leased circuit or leased line because you have the exclusive right to use that circuit, as long as you keep paying for it. 5 WAN Connections from the Customer Viewpoint 6 Connecting WAN interfaces 7 Clock Rates, DCE, and DTE  The terms clock rate and bandwidth both refer to the speed of the circuit. You will also hearthe speed referred to as the link speed.  The device that provides, clocking, typically the CSU, is considered to be the data communications equipment (DCE).  The device receiving clocking, typically the router, is referred to as data terminal equipment (DTE). 8 Link Speeds Offered by Telcos 9 2. OSI Layer 2 for Point-to-Point WANs 10 HDLC  HDLC defines framing that includes an address field, a frame check sequence (FCS) field, and a protocol type field.  The original HDLC standards did not include a Protocol Type field [...]... optical links 18 SONET Link Speeds Optical Carrier Speed OC-1 52Mbps OC-3 155Mbps OC-12 622Mbps OC-48 2.4Gbps OC-192 9.6Gbps OC-768 40Gbps 19 ATM  Asynchronous Transfer Mode (ATM) provides data link layer services that run over SONET Layer 1 links  ATM does not forward frames—it forwards cells  ATM cells contain 48 bytes of payload and a 5-byte header The header contains two fields that together... aids in communication between interconnecting layers  PPP provides a method for encapsulating multi-protocol datagrams over a point-to-point link, and uses the data link layer for testing the connection  PPP is made up of two sub-protocols:  Link Control Protocol – Used for establishing the point-to-point link  Network Control Protocol – Used for configuring the various network layer protocols 11... signal the beginning of a byte 12 3 Packet-Switching Services 13 Introducing Frame Relay  Frame Relay is a Consultative Committee for CCITT and ANSI standard  Frame Relay is a packet-switched, connection-oriented, WAN service  It operates at the data link layers of the OSI reference model  Originally Frame Relay was designed to allow ISDN equipment to have access to a packet-switched service on...  The sum of the CIRs will normally be greater than the port speed Sometimes this is a factor of 2 or 3 17 SONET  Synchronous Optical Network (SONET) defines an alternative Layer 1 signaling and encoding mechanism The motivation behind SONET was to allow the phone companies of the world to connect their COs with highspeed optical links SONET provides the Layer 1 details of how to pass high-speed data... tries to use the same speed as another device on the other end of a serial link However, by examining transitions between voltage states on the link, the device can notice slight variations in the speed on each end and can adjust its speed accordingly  Asynchronous: Both sides agree to the same speed, but there is no check or adjustment of the rates if they are slightly different However, because only... data link layers of the OSI reference model  Originally Frame Relay was designed to allow ISDN equipment to have access to a packet-switched service on a B channel However, Frame Relay is now a stand-alone technology 14 Frame Relay terminology: VC  The connection through the Frame Relay network between two DTEs is called a virtual circuit (VC)  Frame Relay virtual circuits fall into two categories... recovery mechanism 15 Frame Relay terminology: DLCI  May have multiple virtual circuits connecting it to various end points on a single access line  Frame Relay virtual circuits are identified by data-link connection identifiers (DLCIs) DLCI values typically are assigned by the Frame Relay service provider (for example, the telephone company)  Frame Relay DLCIs have local significance, which means... act like the DLCI for Frame Relay by identifying each VC The two fields are named Virtual Path Identifier (VPI) and Virtual Channel Identifier (VCI) 20 Summary       WAN connections HDLC PPP FRAME-RELAY SONET ATM 21 . 1 Module 06 WAN Technology Chapter 18 Fundamentals of WANs 2 Table of Content 1 OSI Layer 1 for Point-to-Point WANs 2 OSI Layer 2 for Point-to-Point WANs 3 Packet-switching service 3 1 service 3 1. OSI Layer 1 for Point-to-Point WANs 4 Overview WAN connections  Point-to-point WAN links provide basic connectivity between two points. To get a point-topoint WAN link, you would. over optical links. 19 SONET Link Speeds Optical Carrier Speed OC-1 52Mbps OC-3 155Mbps OC-12 622Mbps OC-48 2.4Gbps OC-192 9.6Gbps OC-768 40Gbps 20 ATM  Asynchronous Transfer Mode (ATM) provides