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Core Networking 2110472 Computer Networks Natawut Nupairoj, Ph.D. Department of Computer Engineering Chulalongkorn University Outline Overview Network infrastructure: from core to terminal. Telecommunication. Broadband communication. Basic terminologies. Gigabit Network Cores Frame Relay. ATM. Overview Communication networks Voice network: telephone, RF, 1G mobile. Data over voice: fax, modem, 2G mobile. Data network: broadband (DSL), 3G mobile, VoIP. The topology of the connection ? 1876 - Voice over Wire Central Office (CO) PSTN: Network of Local COs Inter-Exchange Carrier (IEC) • CO • End Office • Local Exchange Carrier (LEC) Local Loop Internet: Global Data Network Founded by Department of Defense (DOD) and National Science Foundation (NFS) ARPANET + MILNET. Network of networks Build the whole network from several subnetworks. High-performance core network switching Carry large traffic. Similar to highway interconnecting Bangkok and regional provinces. ARPANET – Internet’s Daddy! Core Network Switching Switching Technologies Packet Switching. Circuit Switching. Message Switching. Cell Switching. Core Networking (WAN) Technology Frame Relay. ATM. X.25 Use to be a dominate core networking delivery. Designed to send Data over Voice communication (in 1970) Error prone. Link is not for data. X.25 Philosophy Make sure that every transmission is correct. Tight error and flow control. X.25 Exchange Frame Relay Problem with X.25 Very slow…..w. Much better data link: Fiber optic Low error rate. Designed for data transmission. How to improve speed ? Simplify the protocol Thinner protocol stack. Simple switching node = faster and better throughput. No error or flow control Error and loss recovery is application responsibility. Frame Relay Exchange Frame Relay Characteristics PDU is called “Frame” Variable sizes … up to 1600 bytes. Virtual Circuit and Connection Oriented. Multiplex several VC in a link Using Datalink Control Identifier (DLCI) DLCI is translated along the route (different for each link). DLCI Frame Relay Characteristics If detect error, discard the frame. Congestion control Congestion avoidance. Prevent the congestion by controlling the transmission rate at the source. Committed Information Rate (CIR). Congestion Control Too many packets … poor performance. Why? Senders send very fast (increase the utilization). Switches/Receivers are not fast enough. Queue at the switches are getting longer. More delay … poor performance. Not enough queue, discard (or control). Retransmission = more packets. More delay … poor performance. Congestion Control Techniques There are several approaches to handle the congestion Discard data. Congestion recovery. Congestion avoidance. Congestion Recovery Start handling when congestion happens. Good utilization. Bad when network is overloaded Bangkok traffics. TCP/IP Mostly initiated by receiver. Sending source-quench to the sender. Reduce window-size. Slow-start algorithm. Frame Relay CIR Congestion avoidance Control how fast a source can send. CIR = agreements between user and network. If transmitting over CIR, the “over-CIR” frames are marked Likely to be dropped during congestion occurs. Leaky-Bucket algorithm Smooth the Bursty traffic. A bucket of tokens and control the “dropping rate”. Burst Transmission Leaky Bucket Algorithm ATM Problems Frame relay is still too slow. Need to support multimedia traffic Data traffic is delay tolerance but not error tolerance. Multimedia is the opposite. Delayed too long = packet lost. ATM = Asynchronous Transfer Mode. ATM Characteristics Philosophy Simple data transmission: simple = fast. Fixed-length PDU = Cell. Low processing overhead. Minimal error and flow controls. QOS – quality of service. Connection oriented. Congestion control Congestion avoidance: similar to Frame Relay. Traffic policing Not allow a new connection if the bandwidth is not enough. ATM Characteristics 5 Bytes Fixed-size cell 53 octets 5 octets header 48 octets data low processing overhead higher data rate 155.52 and 622.08 Mbps 48 Bytes ATM Protocol Layers Voice Cell Data Cell Video Cell ATM Protocol Layers Physical Layer Optical fiber ATM Layer Cell-based SDH/SONET-based Service independent Only define cell + logical connection AAL Layer Service dependent AAL Layer 4 classes (5 types) class A: circuit emulation class B: multimedia traffics class C: data (connection oriented) class D: data (connectionless) What are the differences ? Cell loss ratio Cell transfer delay Cell delay variation Summary Core Networking Frame Relay. ATM. References J. Kurose and K. Ross, Computer Networking: A Top-Down Approach Featuring the Internet, Addison Wesley, 2001. A. Tanenbaum, Computer Networks, 2nd edition, Prentice Hall International, 1996. And many more.