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Download Forward without ACK - SIUE - Southern Illinois University Edwardsville
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CS 447 Networks and Data Communication Frame Relay Networks Department of Computer Science Southern Illinois University Edwardsville Fall, 2013 Dr. Hiroshi Fujinoki E-mail: [email protected] FrameRelay-Intro/000 CS 447 Networks and Data Communication What is “Frame Relay”? • Frame Relay (FR) is a VC (Virtual Circuit) data transmission network • FR evolved from X.25 VC packet-switching network • FR was introduced with two primary motivations: Provide inexpensive virtual WAN network for corporate users (i) Security (dedicated network for high security) (ii) Speed (high volume data transmission in a short time) (iii) Low cost (branch-to-branch long distance connection at low price) (i), (ii) (iii) in a trade-off relationship Low delay data transmission for real-time voice transmission FrameRelay-Intro/001 - Eliminate point-to-point error control from X.25 CS 447 Networks and Data Communication What is “Frame” in “Frame Relay”? • Reserved (dedicated) resources • Expensive • Low variance in delay • Shared resources • Inexpensive • High variance in delay • High quality • Low quality (best-Effort) Circuit Switching Cell Relay • Fixed size • No “packet” • Continuous stream • Small units Public analog Telephone networks FrameRelay-Intro/002 ATM Frame Relay • Variable size • Large data units Frame Relay Packet Switching • Variable size • Large data units IP Networks CS 447 Networks and Data Communication Low delay transmission in Frame Relay Digital Tx Analog Tx D/A Digital to Analog Converter A/D Analog to Digital Converter X.25 VC Packet Switching Fix Errors D/A A/D High error rate D/A Fix Errors A/D High error rate Frame Relay Low error rate FrameRelay-Intro/003 Low error rate D/A A/D CS 447 Networks and Data Communication Low delay transmission in Frame Relay • Error Control • Flow Control • Switching • Error Control • Flow Control • Switching For human conversation this delay < 400ms FrameRelay-Intro/004 X.25 VC Packet Switching CS 447 Networks and Data Communication Low delay transmission in Frame Relay Frame Relay • Switching • Switching Short RTT delay • Switching • Switching FrameRelay-Intro/005 CS 447 Networks and Data Communication Inexpensive virtual WAN network N(N-1) 2 Problem Scalability links required Branch B Branch C Branch A Branch E FrameRelay-Intro/006 Branch D CS 447 Networks and Data Communication Inexpensive virtual WAN network Problem Single point of network disconnection Branch B Branch C Branch A Branch E FrameRelay-Intro/007 Branch D CS 447 Networks and Data Communication Inexpensive virtual WAN network A long distance carrier WAN network Dedicated Subscriber Loop Contract to a long distance carrier Branch B Branch C Branch A VC1 You install only the subscriber loops Branch E Branch D Problem Developing a nation-wide is too expensive FrameRelay-Intro/008 CS 447 Networks and Data Communication Inexpensive virtual WAN network A long distance carrier WAN network Dedicated Subscriber Loop Branch B Branch C Branch A VC2 Branch E FrameRelay-Intro/009 Branch D CS 447 Networks and Data Communication Inexpensive virtual WAN network A long distance carrier WAN network Dedicated Subscriber Loop Branch B Branch C VC3 Branch A Branch E FrameRelay-Intro/010 Branch D CS 447 Networks and Data Communication Inexpensive virtual WAN network What is VC supposed to do? Provide guaranteed transmission rate - No matter how busy the network is, your paid quota should be reserved - Called CIR (Committed Information Rate) Preserve pre-defined VCs - You pre-define VCs - No need for creating VCs when you transmit data Short end-to-end delay transmission - All resources are reserved - Upper bound for end-to-end is also guaranteed FrameRelay-Intro/011 CS 447 Networks and Data Communication Circuit Switching Frame Relay X.25 Virtual Circuit Data Network Today’s Topic Packet Switching Datagram ARPANET FrameRelay-Intro/012 IP Network CS 447 Networks and Data Communication 1. IP Network (Store & Forward transmission) Data Packet R1 ACK Data Packet R2 ACK Transmitter Data Packet R3 Data Packet ACK ACK Receiver Router 2. Frame Relay (Forward without ACK) Data Packet ACK R1 Data Packet ACK Router FrameRelay-Intro/013 R2 Data Packet ACK R3 Data Packet ACK CS 447 Networks and Data Communication Router Operation for IP Network (Store and Forward) Router Incoming Link Store Forward Outgoing Link ACK Memory Buffer Perform: • Switching • Error Check (CRC Check Sum) • Flow Control FrameRelay-Intro/014 CS 447 Networks and Data Communication Router Operation for Frame-Relay Network Router Incoming Link Store Forward Outgoing Link Cut-through After switching Temporary Buffer Perform: Switching FrameRelay-Intro/015 CS 447 Networks and Data Communication Frame Relay Data Transfer (Forward without ACK) Data as a collection of frames Data Packet ACK R1 Data Packet ACK R2 Data Packet R3 ACK Data Packet ACK ACK (= Error/Flow Control) Messages Router Intermediate routers just relay frames and ACK messages between two end hosts FrameRelay-Intro/016 CS 447 Networks and Data Communication Router Operation for IP Network (Store and Forward) Memory Copy Application Packeting Routing Routing Network Layer Flow Control Framing Storing Transmission Transmitting Host FrameRelay-Intro/017 Error Check Receiving De-Framing Framing Storing Link Layer Transmission Physical Layer First-Hop Router CS 447 Networks and Data Communication Router Operation for Frame Relay Memory Copy Application Network Layer Framing Storing Routing Link Layer Transmission Transmitting Host FrameRelay-Intro/018 Receiving Transmission First-Hop Router Physical Layer CS 447 Networks and Data Communication Frame Relay Network LAN E LAN B LAN D Frame Relay Router LAN C Frame Relay as a network backbone LAN A FrameRelay-Intro/019 CS 447 Networks and Data Communication
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