TDC 461: Wide Area Network Services DePaul University 22 May, 2001.
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TDC 461: Wide Area Network Services DePaul University 22 May, 2001
Agenda Frame Relay –PVCs, CIR and Pricing Packetized Voice –Voice over IP Over the Internet Over Frame Relay SS7 Integrated Services Digital Networks (ISDN) –Basic Rate Interface (2B + D) –Primary Rate Interface (23B + D) DSL Cable Modems
Frame Relay Telecommunications carriers maintain networks of Frame Relay switches Customer get access line to nearest switch to get Frame Relay service Higher data rates than X.25 Lower delays, higher throughputs and better security than the Internet
Frame Relay Basics Frame Relay = “Son of X.25” – –Frame Assembler/Disassemblers (FRADs) Similar to X.25 PADs
Frame Relay Basics Frame Relay = “Son of X.25” - except: –Data only sent over Permanent Virtual Circuits (PVCs), which are set up by the carrier, not customer - always available! –Customer can access network at data rates from 56 Kbps to 45 Mbps ! –No error control done by network switches (error control is responsibility of customer)
Frame Relay Basics Frame Relay = “Son of X.25” - except: –Fixed monthly price based on “Port charge” “PVC charge” –Frame Relay is a layer 2 protocol, so
Frame Relay Setup Typically used to replace leased lines: –Customer gets one Frame Relay PVC to replace each leased line –Customer still gets guaranteed delay and throughput (CIR) similar to leased line –Customer uses one access line at each business location for all frame relay data –Customer saves money - PVCs cost less than leased lines
Leased Line Problem: Number of leased circuits (and cost!) grows very large as number of sites increases!!
The Frame Relay Solution: 1 Access Line for each site!!
Frame Relay Addressing The carrier assigns each PVC a 10-bit Data Link Connection Identifier (DLCI). Customer sets up a table in each access router that maps each possible destination to its DLCI. Router puts correct DLCI into each frame header before sending frame into network.
CIR For each PVC, customer specifies a Committed Information Rate (CIR): –CIR represents a guaranteed throughput for this PVC –Carrier also guarantees limited data delivery time if customer does not exceed CIR –Price of PVC is directly related to CIR High CIR = Low CIR =
CIR Example: –I have a T1 (1.536 Mbps) access line into the frame relay network in Chicago –I ask my carrier to create a PVC from Chicago to Dallas with CIR = 512 Kbps. –If I stay within my CIR (i.e., send less than 512,000 bps Chicago-Dallas, on average): Carrier guarantees 99.99% traffic gets through Carrier guarantees <= 20 ms. Network delay
Frame Relay Pricing Example: –4 sites, each with T1 access line –6 PVCs providing connectivity between sites, with 512 Kbps CIR on each PVC Monthly Costs: –4 x (T1 access port cost) plus –6 x (512 Kbps PVC cost)
What if I exceed my CIR? Example: –I have a T1 (1.536 Mbps) access line into the frame relay network in Chicago –I ask my carrier to create a PVC from Chicago to Dallas with CIR = 512 Kbps. –Isn’t it possible for me to exceed my CIR (send more than 512 Kbps Chicago-Dallas)? YES!!!!!
What if I exceed my CIR? Burst Rate (Br) Discard Eligible (DE) bit –
The Tradeoff Low CIR ==> High CIR ==> Note: Many customer still choose to pay lowest cost by selecting a Zero CIR option that provides no delivery guarantees
Frame Relay vs. The Internet Frame Relay advantages: – Frame Relay disadvantages –
Voice over IP Voice can be send over packet-switched networks in the following manner:
ISDN The Idea: –Provides a fully-digital interface over current telephone lines –Allows customer to do both 64 Kbps dial-up and X.25 data over same ISDN line –Provides intelligent signaling channel (D- channel) between customer equipment and Central Office
Basic Rate Interface (2B+D) 3 logical channels on one access loop: –2 B-channels (64-Kbps) used for –1 D-channel (16-Kbps) used for Low Cost:
ISDN BRI The Customer Requires: –Network Termination Type 1 (NT1) –ISDN-Compliant devices The Central Office Requires: –ISDN Line Card Terminates ISDN line at the Central Office and separates B channels and D channel –
Basic Rate Interface Up to 8 devices can connect to single BRI through an NT1 – –Central Office determines which device has control over which B-channel at any time.
BRI Applications Work-at-Home: Simultaneously use – Internet Access – Low-cost Business Videoconferencing Low-speed dial-up LAN Interconnection
Primary Rate Interface (23B+D) Primary Rate Interface is an enhanced T-1 circuit. –
PRI Advantage over T-1 Any PRI B-channel can be set up “call-by-call” to provide any service – In contrast, each DS0 channel on a T-1 must be statically allocated to carry only a single voice or data service.
PRI Applications Integrated business services. Delivery of Caller ID / ANI (D-channel). High-speed videoconferencing. Medium-speed LAN interconnection. Dial-up data channels with flexible bandwidth (N x 64 Kbps).
Digital Subscriber Lines xDSL=> Asymmetric DSL=> Hype