Cisco Semester 4 Chapter 2 WANS

Technologies Not Covered in Semester 4 DSL Cable Modem ATM SONET SMDS

WAN Services Layer 1 –CSU/DSU connects to WAN to CSU/DSU to other route Service Providers –POTS, X.25/Frame Relay, TDM or T1/E1, Call setup, e.g. SS7 –Frame Relay LMI Allows DLCI to become unique network addresses DLCI value placed in frame header

DCE/DTE CPE – customer premises equipment –On customer premises – owned and leased Demaraction – point where CPE ends and local loop service begins, e.g. POP Local Loop – last mile – CAT 5 – goes from demarc to WAN provider central office CO – nearest point of presence for provider’s WAN Toll Network – inside WAN provider cloud DTE – typically routerDCE – converts user data into WAN acceptable format

Virtual Circuits Pathway through a packet-switched network that appears to be dedicated physical circuit –Can be connection-oriented (like TCP) –PVC - Customer and carrier negotiate end points and characteristics of virtual circuit Constantly available –SVC – virtual circuit availably only on demand

WAN Line Types and Bandwidth 56DSO56b kbps 64DSO 64 kbps T1DS Mbps E1ZM2.048 Mbps E3M Mbps J1Yi2.048 Mbps T3DS Mbps OC 1-48Sonet51.84 to Mbps

WAN Devices Router – both LAN and WAN WAN Switches – connect to WAN bandwidth –Layer 2 (but distinct); mostly in WAN cloud –Frame Relay, X.25, SMDS Modems- CSU/DSU and TA/NT1 devices that interface ISDN services Communication servers to concentrate dial-in and dial-out communications

Modems Interprets digital and analog signals –Enable data to be transmitted over voice-grade telephone lines

Leased Lines Router Port CSU/DSU Service Provider Circuit

ISDN TA - device used to connect ISDN BRI connection to other interfaces

WAN and OSI Model WANS focus on physical and data link layers –Standards describe physical-layer delivery methods and data-link layer requirements Addressing, flow control, encapsulation Agencies –ITU-T, ISO, IETF, EIA, TIA

WAN Physical Layer Protocols EIA/TIA 232- common standard Supports up to 64 kbps; resembles V.24; was RS-232 V.35 and X.21 HSSI DTE-DCE Modem Standards –EIA/TIA 449 up to 2 Mbps –EIA/TIA 612-3HSSI –ITU-T V.24 and.35 –X.21 – used in Europe and Japan

WAN Data Link Layer Encapsulation Protocols –HDLChigh-level data link control Cisco has its own proprietary version –PPP point to point – standard Supports several router protocols Replaced SLIP WAN Technologies –Frame Relay- simplified HDLC Packet Switched –ISDN – data-link signal Circuit Switched

WAN Data Link Layer Dedicated Point to Point –Cisco HDLC, PPP, and LAPB (ISDN) Packet Switched –Frame Relay (IETF) X.25, Frame Relay Circuit Switched –ISDN D channel LAPD –ISDN B channel

WAN Data Link Detail Frame Relay – simple encapsulation, no error correction, rapid data transmission PPP (RFC 1661) developed by IETF – contains field to identify network layer protocol ISDN – digital; uses existing telephone lines LAPB- used to encapsulate packets in the X.25 stack; provides reliability and flow control Cisco/IETF – encapsulates Frame Relay traffic HDLC – implemented differently by vendors

WAN FORMATS Common Fields –Flag, Address, Control, Data, FCS, Flag Different Fields –PPP uses Protocol field; HDLC has proprietary field

PPP Described in RFC 1661 Specifies Layer 3 protocol type Is a link control protocol Provides Authentication –PAPPassword Authentication Protocol –CHAPChallenge Handshake Authentication Protocol

HDLC Derived from SDLC encapsulation (Synchronous Data Link Control) Cisco default for serial lines –No windowing or flow control –Allows only point to point connections –Address field set to 1s –20byte type code – not interoperable NOTE: Use PPP with devices not running Cisco IOS software

Dedicated/Switched Lines Dedicated –Leased Lines Fractional T1/E1 T1/E1 T3/E3 Switched –Circuit POTS, ISDN, Switched 56 –Packet/Cell Switched X.25, Frame Relay, SMDS, ATM

Packet Switched Connections Network devices share PVC – permanent virtual circuit –Like a point-to-point link Frame Relay, SMDS, and X.25

Frame Relay Types of Service –DLCI (Data-Link Connections Identifier) –CIR (Committed Information Rate) –Access Rate 56, 65 kbps or Mbps –Two topologies Fully meshed – every device has PVD to every other device Partially meshed – star topology LMI global addressing allows DLCIs to become unique address for DTE device

Circuit Switched Connections Connection on Demand Relatively low bandwidth Uses –Remote users –Mobile users –Backup lines

DDR –Dial on Demand Routing Router can dynamically initiate and close circuit-switched sessions –Used as backup link when primary fails –Source of extra bandwidth when traffic on primary link reaches a threshhold –Substitute for dedicated lines when full-time circuit availability is not required

ISDN Three channels – 2 64 kbps B (bearer) and 1 16 kbps D (signaling Connections –TE1connects to NT (Type 1 or 2 –TE2designates device not compatible –TAconverts standard signal to ISDN –NT1Connects 4-wire ISDN wiring –NT2Directs traffic to and from difference subscriber devices and NT1 –S/T defines TE1 and NT; R is TE2 and TA U is NT and ISDN cloud