12002 M. T. Harandi and J. HouStudent Notes Pages 2002, M. T. Harandi and J. Hou (modified: I. Gupta)Lecture 11-1Lecture 11-1Computer Science 425Distributed SystemsComputer Science 425Distributed SystemsLecture 11NETWORKINGReading: Chapter 3 2002, M. T. Harandi and J. Hou (modified: I. Gupta)Lecture 11-2Lecture 11-2Our Distributed System DefinitionOur Distributed System DefinitionA distributed system is a collection of entities, each of which is autonomous, programmable, asynchronous and failure-prone, and communicating through an unreliablecommunication medium.• Our interest in distributed systems involves – design and implementation, maintenance, study, algorithmics• Entity=a process on a device (PC, PDA)• Communication Medium=Wired or wireless networkFocus of next 2 lectures 2002, M. T. Harandi and J. Hou (modified: I. Gupta)Lecture 11-3Lecture 11-3So far…So far…• Abstract distributed system – collection of processes over a communication medium• Protocols/algorithms for synchronization, snapshots, multicast, election, mutual exclusion, failure detectors• Will work in any distributed group of processes1. E.g., Group of processes on computer hosts2. E.g., Group of processes on PDAs• For most of this course, we’ll focus on (1): computer hosts over the Internet 2002, M. T. Harandi and J. Hou (modified: I. Gupta)Lecture 11-4Lecture 11-4The Internet (Internet Mapping Project, color coded by ISPs)PCs,routers,switches…=nodeslinks=edges 2002, M. T. Harandi and J. Hou (modified: I. Gupta)Lecture 11-5Lecture 11-5Types of NetworksTypes of NetworksRange Bandwidth Latency Local Area 1 - 2km10-1000Mbps1-10msNetwork (LAN) Wide Area large regions0.01- 600 100 - 500 Network (WAN) Metro Area2 - 50 1 - 150 10Network (MAN) Wireless LAN0.15 - 1.5 2 – 11 5 - 20 Wireless WANworldwide 0.01 - 2 100 - 500 Internetworkworldwide 0.01 - 2 100 - 500 2002, M. T. Harandi and J. Hou (modified: I. Gupta)Lecture 11-6Lecture 11-6♣♣♣♣ Performance: consider two routers connected by a link– Latency over the communication link» Propagation delay (Lt): the time it takes for the first bit of a packet to reach the destination» Data transfer rate (Tr)packet delay = Lt + packet size / Tr– Other components of latency» Processing delay: the time it takes for the OS to process/send/ receive the message.» Queuing delay: the time it takes a message to be queued either at end hosts or intermediate nodes while waiting for transmission.– Bandwidth: the total amount of information that can be transmitted over a given time. Expressed as messages/second or bytes per secondNetworking Issues for DSNetworking Issues for DS22002 M. T. Harandi and J. HouStudent Notes Pages 2002, M. T. Harandi and J. Hou (modified: I. Gupta)Lecture 11-7Lecture 11-7Networking PrinciplesNetworking Principles Switching Schemes Broadcast (over a LAN) E.g., IEEE 802.3 - CSMA/CD (Carrier Sense Multiple Access with Collision Detection) E.g., IEEE 802.11{a,b,g} - WLAN Circuit Switching: a physical circuit is established from the caller to the callee before communication takes place. E.g., POTS – Plain Old Telephone System Packet Switching (a.k.a. store-and-forward): packets that arrive at a node are first stored at the node and then forwarded towardtheir destinations. E.g., IPv4/IPv6 - Internet Protocol Circuit and Packet switching incur the Lt+pkt size/Tr cost on each hop (because each hop stores and forwards entire packet) 2002, M. T. Harandi and J. Hou (modified: I. Gupta)Lecture 11-8Lecture 11-8Networking PrinciplesNetworking Principles Switching Schemes Frame Relay: Similar to store-and-forward, but intermediate nodes route frames based on their first few bits. Frames as a whole are not stored at nodes but pass through the nodes as short streams of bits.E.g., ATM Networks (Asynchronous Transfer Mode)Frame Relay incurs only additional Lt latency on each hop. Packetsize/Tr cost incurred over entire path (with Tr=minimum of link transmission speeds along the path) 2002, M. T. Harandi and J. Hou (modified: I. Gupta)Lecture 11-9Lecture 11-9OSI 7-Layer Protocol ModelOSI 7-Layer Protocol Model Protocol Specifies the sequence of messages to be exchanged Specifies the format of data in messagesApplicationPresentationSessionTransportNetworkData linkPhysicalMessage SentMessage ReceivedCommunication ChannelOSI Layered Protocol ModelOSI=Open Systems InterconnectionHeader added at each layerHeader stripped at each layer 2002, M. T. Harandi and J. Hou (modified: I. Gupta)Lecture 11-10Lecture 11-10OSI 7-Layer Protocol SummaryOSI 7-Layer Protocol SummaryLayer Description ExamplesApplication Protocols that are designed to meet the communication requirements ofspecific applications, often defining the interface to a service.HTTP, FTP, SMTP,CORBA IIOPPresentation Protocols at this level transmit data in a network representation that isindependent of the representations used in individual computers, which maydiffer. Encryption is also performed in this layer, if required.Secure Sockets(SSL),CORBA DataRep.Session At this level reliability and adaptation are performed, such as detection offailures and automatic recovery.Transport This is the lowest level at which messages (rather than packets) are handled.Messages are addressed to communication ports attached to processes,Protocols in this layer may be connection-oriented or connectionless.TCP, UDPNetwork Transfers data packets between computers in a specific network. In a WANor an internetwork this involves routing the message throughrouters (based on IP addresses). In a single LAN no routing is required.IP, ATM virtualcircuitsData link Responsible for transmission of packets between nodes that are directlyconnected by a physical link. Uses MAC addresses. Between pairs of routers or pairs of hosts. Ethernet MAC,ATM cell transfer,PPPPhysical The circuits and hardware that drive the network. It transmits sequences ofbinary data by analogue signalling, using amplitude or frequency modulationof electrical signals (on cable circuits), light signals (on fibre optic circuits)or other electromagnetic signals (on radio and microwave circuits).Ethernet base- bandsignalling, ISDN 2002, M. T. Harandi and J. Hou (modified: I. Gupta)Lecture 11-11Lecture 11-11Why such a
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