Chapter 1 Networking Theories

What is a network? A collection of devices that share a common communication protocol and a common communication medium. Trend : to move from computing-centric to network-centric paradigm. Devices and services can be added and removed from the network easily

Elements of a Network. Network card – hardware needed for a computer to talk to a network. The most common network card in use is the Ethernet card Router – machines that act as switches. Direct packets of data to the next “hop” across a network Hub – provides connections that allow multiple computers to access a network Gateway – connects one network to another

Cont. Programmers usually do not need to be concerned with the implementation details of a network and its underlying architecture However, it is important for programmers to be aware of the various elements making up the network.

How Do Networks Communicate? Connections between computers and devices Mostly physical connections like wires and cables – electricity sent Other media available – infrared and RF (wireless) Fiber-optics cable – use light Through this connection, data is carried between one point in the network to another Data represented as bits of information (“on” or “off”)

Addressing Each node is represented by an address just as a home address. Manufacturer of NIC(N/w Interface Card) installed in every device connected to the network is responsible to ensure that no two cards carry the same address and chooses a suitable addressing scheme. Address must be stored permanently hence it must be fixed to avoid illegal alteration – can cause conflict.

Cont. Ethernet network cards are assigned a unique 48-bit number Manufacturers are allocated batch of numbers Strictly regulated by industry

Cont. Commonly used term for physical address: Hardware address Ethernet address MAC address NIC address Addresses are used to send information to the appropriate node

Cont. Safety measures in case conflict of address occurs include: Machines have more than one type of address A server may have a physical Ethernet address as well as IP address Or more than one network cards

Data Transmission Using Packets Also known as packet-switching as opposed to circuit-switching Effective way of sending information Packets consist of header and data segment Header contains addressing information, checksum to ensure no error and other useful information needed for transmission over the network

Cont. Data will be divided into smaller packets and sent through network to reach its destination Packets may take different routes to reach the destination depending on the routing approach and congestion level of the network Mechanism to ensure no packets lost is available depending on the protocol used to send the data

Cont. The choice of protocol used depends on the type application is running Packet transmission and transmission of raw bits of information is low level processes Network programming on the other hand deals with high level transmission of data OSI model was introduced

Communication across layers Application Presentation Session Transport Network Data link physical

Advantages of Layering Simplify networking protocol by breaking them into smaller and manageable Offers better flexibility Protocol can be designed for interoperability

Internet Architecture Great evolution! From non-commercialization to both domains Read again the history of Internet. An open system, built on common network, transport and application layer protocols Internet has the flexibility to connect variety of computers, devices and operating system

Design of Internet Is the result of many decades of innovation and experimentation The protocols that make up the TCP/IP suite have been carefully designed Major achievement: Resource sharing between networks Hardware and software independence Reliability and robustness “Good” protocols that are efficient and simple

Major protocols 1. Internet Protocol (IP) Layer 3 protocol (network layer) Used to transmit data packet over the Internet The most widely used networking protocol in the world All networking hardware support IP Acts as a bridge between networks of different types Packet-switching network protocol – no “connections between” machines Information exchanged between 2 host in the form of IP packets – IP datagrams (format)format

IP Address Applications require a way to deliver packets to specific machines and to identify the sender Each host machine under the Internet Protocol has unique address – IP address Four-byte (32 bits) address expressed in dotted decimal format (e.g ) Typically one machine one IP address Machines connected to the Internet can send data to that IP address and routers and gateways ensure delivery of the message

Cont. To map between a physical network address and an IP address, Address Resolution Protocol (ARP) is used Classful IP Addresses (first octet) Class A ( ) Class B (128 – 191) Class C ( )

Host Name What are IP addresses for yahoo/google/metalab? IP address are not designed with people in mind. Imagine textual-based name vs number-based name Mechanism to associate an easy-to- remember textual name with an IP address – hostname DNS

Major Protocol (cont.) 2. Internet Control Message Protocol (ICMP) ICMP (RFC 792) is used by hosts and routers to communicate network-layer information  Error reporting  Router signaling One of the mechanisms to ensure Internet Protocol runs error-free since IP provides no guarantee of datagram delivery. Example:  “Destination network unreachable” is a message sent when a host with a certain IP address cannot be found.  This message originated from a router and is sent when it was not able to find a path to the host.

Cont. ICMP defines five error messages 1. Destination Unreachable 2. Parameter Problems 3. Redirect 4. Source Quench 5. Time Exceeded ICMP also supports informational message: Echo Request/Echo Reply ICMP is a useful protocol, however only few network application make use of it since its functionality is limited to diagnostic and error notification Famous application is ping which is used to determine if host is alive or inaccessible and the delay between sending a packet and receiving a response

Major Protocols (cont.) 3. Transmission Control Protocol Layer 4 protocol that provides guaranteed delivery and ordering of bytes Uses IP to send TCP segments Contains additional information that allows it to order packets and resend them if error occurs Has extra layer of abstraction, by using a communication port Communication port – a numerical value ( 0 – 65535) used to distinguish one application or service from another Advantages vs disadvantages

Major Protocols (cont.) 4. User Datagram Protocol (UDP) Layer 4 protocol to send packets of data Raw access to IP datagram is not really easy to determine which application a packet is for Supports port number Does not guarantee delivery of packets or will arrive in the correct order Faster data delivery but without error checking feature Video streaming etc.

Internet Application Protocols Telnet (port 23) File Transfer Protocol (port 20 & 21) Post Office Protocol Version 3 (POP3) (port 110) Internet Message Access Protocol (IMAP) (port 150) Simple Mail Transfer Protocol (SMTP) (port 25) HyperText Transfer Protocol (HTTP) (port 80) Finger (port 79) Network News Transport Protocol (NNTP) (port 119) WHOIS (port 43)

TCP/IP Suite HTTPSMTPFTPPOP3 TCPUDPICMP Internet Protocol

LAN vs WAN Coverage IP address Local/Private IP address Class A ( ) – 1 network Class B ( – ) – 16 networks Class C ( – ) – 256 networks Global Network Layout Cable type Bandwidth

Security Issue: Firewalls and Proxy Servers Network security is an important topic for network administrator and programmer producing network software Two approaches: Firewalls Proxy server

Firewalls for Developers Firewalls good for network administrators but not to network developers Most corporate firewalls block direct UDP and TCP access and making these protocol unusable Hence, developers must make a choice – either use standard Internet protocols and ignore user who work behind firewalls or adapt software to proxy requests using protocols such a HTTP

Chapters highlight You have learned: What a network is How networks transmit information using packets and addresses The layers of OSI The major protocols LAN vs WAN The effect of firewalls and proxy servers on users and developers

IPv4 Datagram Format Back