COS 140: Foundations of C Networks Fall 2017 Copyright c 2002 2017 UMaine School of Computing and Information S 1 / 21
Homework, announcements New chapter (23) online No homework assigned today, sorry! Copyright c 2002 2017 UMaine School of Computing and Information S 2 / 21
What are C Networks? What are they? Types of Networks Multiple cs that are connected in some way Directly Via hubs, bridges, gateways, relays, routers,... The connected cs can communicate with each other Communication protocol Formal or ad hoc Idiosyncratic or standard Copyright c 2002 2017 UMaine School of Computing and Information S 3 / 21
Why have c networks? What are they? Types of Networks General public: WWW, e-mail, e-commerce... Business: e-commerce, b-to-b transactions, data sharing, communication, synchronization of business processes... S: data sharing, communication (formal, informal), CPU sharing/grids... Military: data sharing, synchronization, communication, control of assets... Copyright c 2002 2017 UMaine School of Computing and Information S 4 / 21
Origins What are they? Types of Networks Hard to imagine 1st-world life w/o Internet & Web But networks very young: 1st remote login in 1969 The Internet is even younger: public use in late 80s The Web is younger still: mid-90s Why did c scientists invent them? Resource sharing: programs, data, equipment Increase reliability: alternate sources of supply (CPU, disk) Economics: Make full use of expensive mainframes Later: network of small cs cheaper than single, powerful machine (e.g., Beowulf cluster) Communication between c scientists Copyright c 2002 2017 UMaine School of Computing and Information S 5 / 21
From networks the Internet What are they? Types of Networks DoD: Better communication within military National security demands nationwide communication, even in face of nuclear war Existing communication infrastructure: vulnerable Develop a distributed communication scheme that can survive attack ARPANET (early 70s) Academics/NSF CSNET, NSFNET (early to mid-80s) The Internet /Commercial access (early to mid-90s; ARPANET, NSFNET retired) Copyright c 2002 2017 UMaine School of Computing and Information S 6 / 21
Types of Networks What are they? Types of Networks One extreme: Local Area Networks (LAN) Cs are in the same building Have control over the way the cs are set up Can have dedicated lines which connect the cs The other: Wide Area Networks (WAN) Great phys. distance might separate cs May not have a lot of control over all of the cs (may be from several companies, universities, etc.) Creating the connection can be much more expensive Between the two: Intranets Metropolitan Area Networks Copyright c 2002 2017 UMaine School of Computing and Information S 7 / 21
What is a network, really? What is a network, really? Interfacing with the Network Store-and-Forward Networks Network Topology Broadcast & point-to-point Buses and Broadcast Channels A network is a set of cs connected by communication channels Physical channel may be: wires (twisted pair, coax), fiber, radio (Wi-Fi, e.g.), other One c communicates with another via causing changes to the channel such that the other can detect them. Examples: Voltages Properties of the voltage (e.g.) in the wire: amplitude, frequency Light pulses Properties of radio waves Copyright c 2002 2017 UMaine School of Computing and Information S 8 / 21
Interfacing with the Network What is a network, really? Interfacing with the Network Store-and-Forward Networks Network Topology Broadcast & point-to-point Buses and Broadcast Channels Cs on the network hosts A host is connected to the network (to the channel) via its network controller e.g., a network card Controller puts information from host into the network (by modulating something about the channel) and getting information from the network Originally, several hosts might share their connection to the network; now single host per network controller card Copyright c 2002 2017 UMaine School of Computing and Information S 9 / 21
Beyond the controller What is a network, really? Interfacing with the Network Store-and-Forward Networks Network Topology Broadcast & point-to-point Buses and Broadcast Channels Hubs: connect group of cs to network repeater, or with an internal network Bridge: between LANs of same type (e.g., Ethernets) Router (original ARPANET name: Interface Message Processors, IMPS): route information packets between hosts or LANs Copyright c 2002 2017 UMaine School of Computing and Information S 10 / 21
Store-and-Forward Networks What is a network, really? Interfacing with the Network Store-and-Forward Networks Network Topology Broadcast & point-to-point Buses and Broadcast Channels A unit of information to be transferred is called a packet Packet arrives at router, which stores it until the output line is free and it can be forwarded to the next router Ultimately, final router delivers it to the recipient host Also called point-to-point or packet switched. Copyright c 2002 2017 UMaine School of Computing and Information S 11 / 21
Network Topology What is a network, really? Interfacing with the Network Store-and-Forward Networks Network Topology Broadcast & point-to-point Buses and Broadcast Channels Which hosts and routers are connected to each other. Possible topologies include: bus, ring, tree, complete, irregular possibly with hub topology overlaid In LANs, often can design the topology so hosts are connected for maximum efficiency. In WANs, have irregular topologies because may have little control over connections, or may add in subnets eliminating ability to make a global design. Difference between internets and the Internet Copyright c 2002 2017 UMaine School of Computing and Information S 12 / 21
Broadcast vs Point-to-Point Channels What is a network, really? Interfacing with the Network Store-and-Forward Networks Network Topology Broadcast & point-to-point Buses and Broadcast Channels Broadcast channel (or protocol): All hosts get all of the messages. Messages marked with intended recipient so can be ignored by others. Point-to-point: targeted toward particular host Multicast: subscribers get all packets Copyright c 2002 2017 UMaine School of Computing and Information S 13 / 21
Buses and Broadcast Channels What is a network, really? Interfacing with the Network Store-and-Forward Networks Network Topology Broadcast & point-to-point Buses and Broadcast Channels Networks with broadcast channels can be buses They are different from what we have studied about system buses because: Routers and host cs linked to bus, not devices associated with cs. They are like what we have studied about system buses because: Need to protect against more than one c trying to communicate at a time. Copyright c 2002 2017 UMaine School of Computing and Information S 14 / 21
Protocols Protocols Example: Business Correspondence Layered Architectures for Networks ISO OSI Standard TCP/IP TCP/IP Layers Standards Specifications for interaction between entities. If two cs use the same protocols, they can interact. Allows the processing of the cs to be hidden. Abstracts a c to the protocol. What is sent/received and when: defined by protocol How the c implements the protocol solely responsibility of c/os designer Copyright c 2002 2017 UMaine School of Computing and Information S 15 / 21
Example: Business Correspondence Protocols Example: Business Correspondence Layered Architectures for Networks ISO OSI Standard TCP/IP TCP/IP Layers Standards Several levels of interaction on both sides: Correspondents Secretaries Post offices/mail rooms Can consider each level to be communicating with the same level in other correspondent. Communication really goes to bottom layer and then back up. At each level, communication happens in a way particular to that level. Communication between layers is also specified. Copyright c 2002 2017 UMaine School of Computing and Information S 16 / 21
Layered Architectures for Networks Protocols Example: Business Correspondence Layered Architectures for Networks ISO OSI Standard TCP/IP TCP/IP Layers Standards Way to modularize the problem so can focus on a section at a time and ignore other details. Separate protocols for each layer, so the same layer appears to communicate between machines. Interfaces between layers are also specified so the proper information is passed up and down the hierarchy. Physical layer at the bottom actually passes the bits. Copyright c 2002 2017 UMaine School of Computing and Information S 17 / 21
ISO OSI Standard Protocols Example: Business Correspondence Layered Architectures for Networks ISO OSI Standard TCP/IP TCP/IP Layers Standards Application layer - provides user with services that are needed, such as e-mail, file transfer, remote job entry Presentation layer - Concerned with syntax and semantics of the bits; interpret the bits as characters, etc.; data compression Session layer - Allows users on a different machine to establish a session which has some services like file transfer or remote log in Transport layer - prepare data for the network layer and make sure it arrives error-free Network layer - operation of subnet; packet routing Data link layer - find data intended to be sent; remove errors from transmissions Physical layer - transmitting bits over the communication channel Copyright c 2002 2017 UMaine School of Computing and Information S 18 / 21
TCP/IP Protocols Example: Business Correspondence Layered Architectures for Networks ISO OSI Standard TCP/IP TCP/IP Layers Standards Started in USA; DoD model The major worldwide protocol the Internet protocol Missing some of the layers in ISO/OSI Copyright c 2002 2017 UMaine School of Computing and Information S 19 / 21
TCP/IP Layers Protocols Example: Business Correspondence Layered Architectures for Networks ISO OSI Standard TCP/IP TCP/IP Layers Standards Application layer Same as OSI s Sometimes considered as part of TCP/IP Ex: HTTP, FTP,... Transport layer OSI s transport and session layers Transport Control Protocol (TCP) connection-oriented Guarantees packets arrive in order, retransmitting as needed Also User Datagram Protocol (UDP; connectionless), others Internetwork layer OSI s network layer Internet Protocol, or IP Link layer Corresponds to OSI s physical and data link layers E.g.: Ethernet, Wi-Fi Copyright c 2002 2017 UMaine School of Computing and Information S 20 / 21
A Word About Standards Protocols Example: Business Correspondence Layered Architectures for Networks ISO OSI Standard TCP/IP TCP/IP Layers Standards Especially important when have issues of interoperability Often have de facto standards that are set by large groups of users of corporations Standards need to be set between research and industry interest groups Copyright c 2002 2017 UMaine School of Computing and Information S 21 / 21