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Networking Theory

Chapter 1

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Chapter 1 Outline• What Is a Network? • How Do Networks Communicate?• Network Components

- Data flow- Addressing

• Network Layers– TCP/IP Protocol Suite Layers– OSI Layers

• Internet Architecture – IP Datagram format– ICMP

• Major protocols1. IP2. ICMP3. TCP4. UDP

• Security Issues– Firewalls– Proxy Servers

• Chapter 1 Highlights

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What Is a Network ?

• Data communication is the transfer of data from one device to another via some form of transmission medium.

• A Network: is a set of communication devices connected by media links.

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What Is 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

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How Do Networks Communicate?

Connections between computers and devices:

1. Wires and cables – electricity sent

2. Infrared and RF (wireless)

3. 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”)

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Network Components

• Components: message, sender, receiver, medium, and protocol.

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Data flow

• Data flow between two devices can occur in one of three ways: simplex, half-duplex, or full-duplex.

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Simplex

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Half-duplex

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Full-duplex

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Addressing

• Each node represented by an address just as home address

• Manufacturer of NIC installed in every devices connected to network is responsible to ensure that no two card carry the same address and chooses a suitable addressing scheme

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Addressing

• Commonly used term for physical address:– Hardware address– Ethernet address– MAC address– NIC address

• Addresses are used to send information to the appropriate node

• Ethernet network cards are assigned a unique 48-bit number

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Sending a letter

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Data Transmission Using Packets

• 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

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Data Transmission Using Packets

• 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

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OSI model

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Advantages of Layering

The Advantages of layering:1. Simplify networking protocol by breaking them into

smaller and manageable 2. Offers better flexibility

The protocols that make up the TCP/IP suite have been carefully designed with the following major achievement:

1. Resource sharing between networks2. Hardware and software independence3. Reliability and robustness4. “Good” protocols that are efficient and simple

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Internet layers

The five-layer model provides guidelines for the development of universally compatible networking protocols.

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Summary of duties

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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

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IPv4 Datagram Format

Back

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IP Address

• To map between a physical network address and an IP address, Address Resolution Protocol (ARP) is used

• Four-byte (32 bits) address expressed in dotted decimal format192.10.1.1

• Classful IP Addresses (first octet)– Class A (1 - 126) – Class B (128 – 191)– Class C (192 - 223)

• 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 (Domain Name System)

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Major Protocols

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.

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ICMP• ICMP defines five error messages

1. Destination Unreachable2. Parameter Problems3. Redirect4. Source Quench5. 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

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Major Protocols3. 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

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Major Protocols4. 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.

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TCP/IP Suite

HTTPSMTPFTPPOP3

TCPUDPICMP

Internet Protocol

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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)• Network News Transport Protocol (NNTP) (port 119)

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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

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Chapter Highlights

In this chapter, you have learned:• What a network is• How networks transmit information using packets and

addresses• The layers of the OSI Reference Model• The major protocols of the Internet, including the Internet

Protocol (IP),• Internet Control Message Protocol (ICMP), Transmission

Control Protocol• (TCP), and User Datagram Protocol (UDP)• The effect of firewalls and proxy servers on users and

developers