4 WAN ServicesA WAN is the communications network that connects LANs through a WAN Service Provider (e.g. RBOC)WANs operate at the first three layers of the OSI, but focus mainly on the physical and data link layers.Examples of WAN Services include….Call-setupSS7 used for telephone callsISDNA circuit-switched service using TDM, which allocates bandwidth to different sources on the same mediaFrame RelayA packet-switched service using statistical multiplexing
5 WAN Physical Structure Toll Network – collection of switches/trunks in WAN cloudCO Switch – nearest point of presence for the WSP’s serviceLocal loop – extends from the CPE (at the demarc) to the COCPE – devices located on premises, either owned or leased
6 DTE/DCE InterfaceThe transfer of responsibility for service between the ISP and the customer occurs at the DTE/DCE interface.The DTE generates the data and passes them, along with any necessary control characters to a DCE.The DCE converts the signal to a format appropriate to the transmission medium and introduces it into the network link.(Reverse process at the receiving end)
7 WAN Virtual CircuitsSwitched Virtual Circuits (SVCs) are WAN paths to the destination established and terminated on demand.Three phases:Circuit establishment – creates the virtual circuitData transfer – sending and receiving user dataCircuit termination – tearing down the virtual circuitTelephone service and ATM use SVCsIncreased use of bandwidth but decreased costPermanent Virtual Circuits (PVCs) are permanently established circuits with one mode: data transferX.25 and Frame Relay use PVCsDecreased use of bandwidth but increased cost
9 WAN DevicesIn order to connect to a leased line, the customer must have…Access to the service provider’s circuitAn appropriate router port availableAn a CSU/DSU, modem or ISDN Terminal Adapter
10 Routers Routers offer many services including: Internetworking WAN serial interfacesRouters can operate as...Internal RoutersBackbone RoutersArea Border RoutersAutonomous System Boundary Routers
11 ModemsAlso called CSU/DSUs (channel service units/digital service units)Interface with voice-grade connection in order to convert analog signal to digital.Represents the DCE side of the DTE/DCE connection.Leased lineRouterCSU/DSU
13 WAN Standards What layers of the OSI model do WAN standards describe? Physical and Data Link Layers
14 WAN Physical LayerProtocols that describe how to provide electrical, mechanical, operational, and functional connections for WAN services.These services are most often obtained from WAN service providers such as RBOCs, alternate carriers, post, telephone and telegraph (PTT) agencies.Describes the interface between the data terminal equipment (DTE) and the data circuit-terminating equipment (DCE).
15 WAN Physical LayerTypically, the DCE is the service provider and the DTE is the attached device.In this model, the services offered to the DTE are made available through a modem or a CSU/DSU.
16 WAN Physical LayerSeveral physical layer standards specifying this interface between the DTE & DCE are...EIA/TIA-232EIA/TIA-449V.24V.35X.21G.703EIA-530
17 WAN Data-Link LayerWAN data link protocols describe how frames are carried between systems on a single data link.They include protocols designed to operate over dedicated point-to-point, multipoint, and multi-access switched services.WAN standards are defined and managed by a number of recognized authorities, including the following agencies: ITU-T, ISO, IETF, & EIA
19 WAN Data-Link Encapsulations PPP (Point-to-Point Protocol)Developed by IETF; replacing SLIPContains a field to identify the network layer protocolPPP can check for link quality during connection establishmentSupports PAP (Password Authentication Protocol) & CHAP (Challenge Handshake Authentication Protocol)
20 WAN Data-Link Encapsulations High-Level Data Link Control (HDLC)Cisco default encapsulation; typically used between routers running Cisco IOS; replacing SDLCStreamlined: no windowing or flow controlmay not be compatible with different vendors because of the way each vendor has chosen to implement it.HDLC supports both point-to-point and multipoint configurations with minimal overhead
21 WAN Data-Link Encapsulations Frame Relayuses high-quality digital facilities;uses simplified framing with no error correction mechanisms (connectionless!!);it can send Layer 2 information much more rapidly than other WAN protocols
23 WAN Link Options Dedicated Switched T1, E1, T3, E3 xDSL SONET Circuit SwitchedPacket/Cell SwitchedPOTSISDNX.25Frame RelayATM (cell)SMDS (cell)
24 WAN Link Options Dedicated Switched T1, E1, T3, E3 xDSL SONET Circuit SwitchedPacket/Cell SwitchedPOTSISDNX.25Frame RelayATM (cell)SMDS (cell)
25 Dedicated Digital Services Dedicated Digital Services provide full-time connectivity through a point-to-point linkT series in U.S. and E series in EuropeUses time division multiplexing to “slice up” data and assign time slots for transmissionsT1 = MbpsT3 = MbpsE1 = MbpsE3 = MbpsUses twisted pair & fiberExtremely popularModerate cost
26 Dedicated Digital Services Digital Subscriber Lines (xDSL); the x stands for a family of technologiesWAN Technology for home use; decreasing bandwidth with increasing distance from the phone companies CO.Data rates as high as Mbps but more common to be in the 100s of KbpsVarieties include HDSL, SDSL, ADSL, & VDSLModerate expense and getting cheaper
27 Dedicated Digital Services Synchronous Optical Network (SONET)Specialized high bandwidth technology for use at various Optical Carrier speeds (OC) ranging from Mbps (OC-1) to 9,952 Mbps (OC-192)Uses lasers to divide the wavelength of the light into sections that can carry large amounts of data (Wave Division Multiplexing)Very expensive; used by large ISPs and other Internet backbone entities.
28 WAN Link Options Dedicated Switched T1, E1, T3, E3 xDSL SONET Circuit SwitchedPacket/Cell SwitchedPOTSISDNX.25Frame RelayATM (cell)SMDS (cell)
29 Circuit Switched Services Plain Old Telephone System (POTS)Not a computer data service but...POTS is an important component of our communication infrastructure andIt is still the standard for designing reliable networks
30 Circuit Switched Services Integrated Services Digital Network (ISDN)Historically important--first dial-up digital serviceProvides both voice & data transmission over existing phone linesCost is moderate; max. bandwidth = 128 kbps for BRI (Basic Rate Interface)2 B 64kps and 1 D 16kpsB channels are voice/data channels; D for signalingBD
31 WAN Link Options Dedicated Switched T1, E1, T3, E3 xDSL SONET Circuit SwitchedPacket/Cell SwitchedPOTSISDNX.25Frame RelayATM (cell)SMDS (cell)
32 Packet Switched Services X.25 (Connection-oriented)Older WAN technology developed in 1970sReliable--X.25 has been extensively debugged and is now very stable--literally no errors in modern X.25 networksStore & Forward--Since X.25 stores the whole frame to error check it before forwarding it on to the destination, it has an inherent delay (unlike Frame Relay) and requires large, expensive memory buffering capabilities.
33 Packet Switched Services Frame Relay (Connectionless)More efficient and much faster than X.25Packet switched version of ISDN (which is circuit switched); data rates up to Mbps with 56kbps and 384kbps being the most popularUsed mostly to forward LAN IP and IPX packets but can be used to forward other types of trafficPrimary competitive advantage is its low cost
34 Cell Switched Services Asynchronous Transfer Mode (ATM)Relatively new WAN Technology related to broadband ISDN; max. bandwidth = 622 MbpsDeveloped in order to provide one technology for both WANs and LANs to transport data, video, and voice. (High Cost)Key Benefits:One network for all traffic--voice, data, videoCompatible with current wiring infrastructure (cable plant)Very flexible and scalableSimplifies network management
35 Cell Switched Services Switched Multimegabit Data Service (SMDS)Closely related to ATM; SMDS is the MAN (Metropolitan Area Network) implementation of ATMHigh Cost with max. bandwidth Mbps