cisco semester 4 chapter 2 wans. technologies not covered in semester 4 dsl cable modem atm sonet...
TRANSCRIPT
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Cisco Semester 4 Chapter 2
WANS
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Technologies Not Coveredin Semester 4
• DSL
• Cable Modem
• ATM
• SONET
• SMDS
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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
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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 router DCE – converts user
data into WAN acceptable format
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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
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WAN Line Types and Bandwidth
• 56 DSO 56b kbps• 64 DSO 64 kbps• T1 DS1 1.544 Mbps• E1 ZM 2.048 Mbps• E3 M3 34.068 Mbps• J1 Yi 2.048 Mbps• T3 DS3 44.736 Mbps• OC 1-48 Sonet 51.84 to 2488.32 Mbps
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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
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Modems
• Interprets digital and analog signals – Enable data to be transmitted over voice-grade
telephone lines
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Leased Lines
• Router Port
• CSU/DSU
• Service Provider Circuit
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ISDN
• TA - device used to connect ISDN BRI connection to other interfaces
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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
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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 612-3 HSSI– ITU-T V.24 and .35– X.21 – used in Europe and Japan
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WAN Data Link Layer
• Encapsulation Protocols– HDLC high-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
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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
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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
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WAN FORMATS
• Common Fields– Flag, Address, Control, Data, FCS , Flag
• Different Fields– PPP uses Protocol field; HDLC has proprietary
field
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PPP
• Described in RFC 1661
• Specifies Layer 3 protocol type
• Is a link control protocol
• Provides Authentication– PAP Password Authentication Protocol– CHAP Challenge Handshake
Authentication Protocol
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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
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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
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Packet Switched Connections
• Network devices share PVC – permanent virtual circuit– Like a point-to-point link
• Frame Relay, SMDS, and X.25
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Frame Relay
• Types of Service– DLCI (Data-Link Connections Identifier)
– CIR (Committed Information Rate)
– Access Rate 56, 65 kbps or 1.544 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
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Circuit Switched Connections
• Connection on Demand
• Relatively low bandwidth
• Uses– Remote users– Mobile users– Backup lines
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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
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ISDN
• Three channels – 2 64 kbps B (bearer) and 1 16 kbps D (signaling
• Connections– TE1 connects to NT (Type 1 or 2– TE2 designates device not compatible– TA converts standard signal to ISDN– NT1 Connects 4-wire ISDN wiring– NT2 Directs 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