Communication and Networking

Communication and Networking

1. Communication Methods

   • Serial
     • Bits are sent via an interface one bit at a time over a single wire.
   • Parallel
     • Transmitting several bits simultaneously over a number of parallel wires
     • Due to differences in properties in the wires, the arrival time of each bit may be different causing a skew
     • Reliable over short distances
   • Advantages of serial over parallel transmission
     • Significant reduction in the size and complexity of connectors
     • Cheaper costs
     • Crosstalk isn't an issue
       • Lower chance of corruption
     • More reliable over greater distances
     • Can be transmitted at higher frequencies due to reduced chance of crosstalk/corruption

2. Bit Rate

   • The speed at which data is transmitted serially
   • Bit rate is directly proportionate to bandwidth

3. Baud Rate

   • The rate at which the signal changes
   • Bit rate can be higher than baud rate if more than one bit is encoded in each signal change

4. Bit rate of channel = baud rate * number of bits per signal

5. Bandwidth

   • The range of frequencies that a transmission medium can carry

6. Latency

   • The time delay between the moment that transmission of the first byte or packet and the moment it is recieved

7. Synchronous transmission

   • Data is transferred at regular intervals that are timed by a clocking signal

8. Asynchronous transmission

   • Data is sent one byte at a time preceded by start and stop bits

9. Wireless Communications and Networks

   • Components required
     • Wireless network adaptor
     • Station
     • Wireless access point
     • Router
   • Securing wireless networks
     • Wi-Fi Protected Access (WPA) and Wi-Fi Protected Access II (WPA2)
     • Encrypts the data transmitted with 128 bit key for each package
     • SSID to identify the network
       • Up to 32 bits
   • Whitelists
     • Controls which MAC addresses can be on the network

10. CSMA/CA with RTS/CTS

11. Internet

    • Packet Switching
      • Method of communicating packets of data across a network on which other similar communications are happening simultaneously
    • Routers
      • Connects LANs and WANs together or a LAN to its ISP's network
      • Job of the router is to read the recipient's IP address in each packet and forward it to the recipient via the fastest and least congested route to the next router
    • Gateways
      • Routing packets between routers requires the use of protocols
      • The the packet and the routers use different protocols, gateways strip the packet to the raw data and adds a new header to format the networks protocols
    • Security
      • Firewalls
        • A firewall is a security checkpoint designed to prevent unauthorised access between two networks
        • Typical firewalls are separate computers with two Network interface cards. One on the private network the other on the external.
          • Each data packet is analysed against packet filter and then accepted or rejected
      • Packet filtering
        • Also known as static filtering
        • Control network access according to network rules and policies by examining the source and destination IP addresses in the packet header.
        • Packets can also be blocked or accepted if they used a certain port
      • Stateful inspection
        • Inspects the payload of the packet to better assess it for safety
        • It can also create temp context rules which are designed to ensure all the aceptable packet come from the same IP address, through the same port
      • Proxy Servers
        • Intercepts all packets entering or leaving a network, hiding the true network address of the source recipient.
      • Encryption
        • Symmetric encryption
          • The data is encrypted and decrypted using a private key
          • This means that the key must also be transferred/ key exchange
        • Asymmetric encryption
          • Digital Signatures
            • A mathematical value designed to ensure the entgrity of the document. Producing a hash total
            • The hash total is encrypted with the senders private key. Then the document + the signiture is encrypted using the recievers public key. The reciever decrypts the data using their private key and then uses the senders public key to decrypt the signature to produce the hash total. If the hash total matches, the document hasn't been interferred with
          • Digital Certificates
            • Issued by Certificate Authorites to verfiy the trustworthiness of the a message sender or website
    • Malware and Vulnerabilities
      • Viruses and Worms
        • Virus are files which self replicate with malicious intent. They require the use of other host files to run. Any open files running when the virus is run gets infected
        • Worms are a subclass of virus which don't require host files
          • They will replicate and send the copies to other computer. E.G: via email
      • Trojans
        • It manifests inside any file you want to install onto your computer. Once installed, the payload is released. Often creating a back door for the attacker to access their files
          • Unlike virus and worms, they cannot self replicate
      • System Vulnerabilities
        • Malware exploit system vulnerabilities and poor code quality.
        • Many forms of malware exploit the buffer overflow phenomenon where the program accidently writes values to locations too small to handle. This causes the overwrite of neighboring locations
    • TCP/IP
      • Transmission Control Protocol/Internet Protocol
      • Application Layer uses protocols relating to the application.
      • Transport Layer uses TCP to establish an end-to-end connection with the recipient computer. The data is split into packets and labelled with the packet number, total number of packet and the port number. If any packets go astray during the connection, the transport layer request retransmission of lost packets, Receipt of packets is acknowledged
      • Network layer adds the source and destination IP addresses. Router operate on this layer. IP address and port number forms a socket.
      • The Link layer is the physical connection between nodes and adds the MAC addresses of the NICs of the source and destination devices. The MAC addresses are changed at each hop. The first destination MAC address is usually the networks router's MAC address
    • DHCP
      • Dynamic Host Configuration is the process when a server assigns an IP address on public networks.
    • Network Address Translation
      • Private IP addresses are not routable so need to become public IPs to contact devices outside their network
      • Network Address Translators convert Private IP into Public IP's
      • Port Forward is a product of network address translation.

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