7.1 Networking Overview pdf

Networking Session 7.1 Topics  Signals on Networks  Data and Packets  Message Addressing  Routing  Networks and Protocols  Host addressing  Ports and Processes Windows Phone Starting with the Signal  If we wanted to talk to a friend next door we could this by flashing our bedroom light  In this case the data media would be light  We can send a (light on) and a (light Windows Phone Signals in Windows Phone Windows Phone Programs Internet Programmer Interface WIFI Cellular USB  When a Windows Phone communicates over a network it uses a variety of methods  But the program always uses the same software interface to send data Windows Phone The Network Information classes using Microsoft.Phone.Net.NetworkInformation;  This namespace holds classes that can be used to determine the connections available to an application when it is running  The libraries are already loaded, we can add the namespace to make it easier to use Windows Phone Getting Network Information if (DeviceNetworkInformation.IsWiFiEnabled) { // Got Wifi }  An application can test the DeviceNetworkInformation class properties to determine connection state  There are a number of properties available to be tested Windows Phone Phones and Networks  It is important that a Windows Phone application is written with network failure in mind  The user might put the phone into “Aircraft” mode and turn off all connections  Or they might drive their car into a tunnel  An application must respond sensibly to this Windows Phone Demo Demo 1: Network Status Windows Phone Building up Packets  Just a single bit does not give us much data transfer capabilities  In real life we would assign meaning to certain patterns  “Three flashes means ‘Bring Pizza’” Windows Phone Networks and Octets  Modern networks send everything around in terms of bit data items  In network terms these are called “octets”  An octet can hold 256 different possible values  0000000 to 11111111  We can send larger ranges of data by sending a number of octets together to form a packet Windows Phone Routing and Packets  Note that when a packet is “routed” in this way it is not actually passed on  You can’t say that a packet is like a physical envelope which is handed from one person to another  Instead the packet is re-sent with the new destination address Windows Phone Networks and Media  A given local area network could actually use a number of different physical media  You can have a wired network at home, along with a WIFI connection  Your phone can also make use of GPRS data connections  A single local area network can share a number of different media types at the physical level Windows Phone Networks and Protocols  The Internet is based on a number of protocols  These are rules that set out how different parties in a connection should collaborate to pass data between them  There are protocols at a range of different levels to manage addressing of systems and the routing of data between them Windows Phone Stations and Addressing  The network address of a station is a set of numeric values that identify that machine on the internet  However, it is useful to address a station by more meaningful name  The Domain Naming System (DNS) provides a way that a system can request the network address of a station with a particular name Windows Phone Name Resolution  Stations on the network each have a unique internet address:  150.237.176.24  This is the internet address of our web server  However we would like to use DNS names  www.hull.ac.uk  A station can send a name to a special system on the internet which will look up Windows Phone Domain Name System  When a system first connects to a local network it will broadcast a request for information about that network  Part of the reply will identify the DNS server for that network  The system then knows who to ask  The DNS server will also forward requests for addresses if it doesn’t have the required address Windows Phone Addresses and Subnets  Systems on a particular physical network may be placed in a subnet  These systems will not be directly addressable from outside the network, but the router will perform address translation when the systems on the subnet connect out to the internet  Many cellular networks are organised like this  Phones can originate connections but cannot Windows Phone Conversation Topics  When we talk to our friends we might have a number of different topics  Sports  TV  We could expand a packet to include “topic” information Windows Phone Networks and Ports  The internet has a similar arrangement  When we connect to a remote system we are really connecting to a process on that system  Web server  Mail server  A process will sit behind a particular port number Windows Phone Well Known Ports  The internet has reserved some port numbers for “well known” services  The web server is behind port 80  We can use port numbers of our own for services that we create  However these might not be transferred onto the network  A router may act as a firewall and restrict use of certain port numbers by not forwarding their Windows Phone Connections and Datagrams  Networks can pass two kinds of data  Datagram  We send the package and don’t care if it was received or not  Connection  It is important to us that the entire packet is Windows Phone Datagrams  Datagrams are used in situations where we don’t want/need each packet to be acknowledged  If we are sending a video stream there is no time to re-transmit missing data, we just have to live with a small degradation in the picture if data is missing  The important thing with a datagram is that you want to send data as fast as possible Windows Phone Connection  A connection sets up a data path between two processes that makes sure that data sent in one end arrives at the other  This requires more work to set up and manage, but is useful when we are sending data that must arrive complete and undamaged  Web pages  Images Windows Phone UDP and TCP  Datagrams can be sent over the internet using the User Datagram Protocol (UDP)  Connections can be set up between processes using the Transmission Control Protocol (TCP)  In either case the packets are sent and routed in exactly the same way, but are marked as being part of different kinds of conversation Windows Phone Review  A network allows for packets of data to be sent between stations  An internetwork provides for routing of packets between different networks  A station has an address that identifies it on the local network and the inter-network  Stations can send unacknowledged datagrams or set up connections that ensure delivery of data Windows Phone ... Windows Phone Name Resolution  Stations on the network each have a unique internet address:  150.2 37.17 6.24  This is the internet address of our web server  However we would like to use DNS names