Network Technologies and Standards

• Distributed systems rely on networking and internetworking
• Coulouris, Dollimore, Kindberg, and Blair wrote "Distributed Systems: Concepts and Design" in its 5th Edition, published by Addison-Wesley in 2012

Introduction to Networks

• A network enables computers and devices to exchange data
• Each device on a network is a node
• Nodes used for communication are called hosts
• Every node has a unique address, a series of bytes
• Address assignments vary depending on the network type

Internetworking

• Internetworking connects different networks using intermediary devices like routers or gateways
• It allows data communication among different entities using a common protocol like the Internet Routing Protocol (IRP)

Network Components in Distributed Systems

• Networks use a range of transmission media like wires, cables, fiber optics, and wireless channels
• Hardware devices in networks include routers, switches, bridges, hubs, repeaters, and network interfaces
• Software components consist of protocol stacks and network device drivers
• The functionality and performance of systems and applications are affected by all of these components

Communication Subsystems

• A communication subsystem includes hardware and software, and offers communication for a distributed system
• The Internet serves as a single communication subsystem, connecting all hosts
• The Internet comprises many subnets
• A subnet represents a routing unit, with nodes reachable over the same physical network

Networking Issues for Distributed Systems

• Network performance is affected by factors impacting message transmission speed between interconnected computers, such as network latency
• Network Latency is the delay after a send operation before data arrives, measured by the time to transfer an empty message, and determined mostly by software overheads and routing delays
• Data Transfer Rate measures how fast data can transfer between two computers once a transmission has started, usually in bits per second, and determined by network physical characteristics

Message Transmission Time

• Following defined parameters, the time required for a network to transfer a message is the message transmission time
• The message transmission time = latency + (message length / data transfer rate)
• This applies to messages smaller than the technology's maximum length
• Longer messages need segmentation, and the transmission time becomes the sum of each segment's time
• Since distributed systems often transfer small messages, latency can be equally or more significant than transfer rate in determining performance

Scalability

• Estimating the real size of networks now and in the future can be difficult
• The potential size of the Internet could be equivalent to the population of the planet, including billions of nodes and hundreds of millions of active hosts

Reliability

• Many applications are designed to recover from communication failures, so error-free communication is not always needed
• Typical errors happen from software errors in sender or receiver – such as failure by the receiving computer to accept a packet, buffer overflow or network errors

Other Networking Considerations

• Security is addressed using firewall technology and cryptographic technology
• Mobility is supported, through mechanisms have been adapted, the growing number of mobile devices will continue to push the need for future development
• Quality of Service handles multimedia data transmission
• Multicasting allows one-to-many communication, delivering messages to multiple recipients at once

Types of Networks

• Networks can be personal area networks, local area networks, wide area networks, or metropolitan area networks
• Internetworks consist of interconnected networks, integrating to provide a single data communication medium

PANs (Personal Area Networks)

• PANs are a subset of local networks where a user's digital devices connect on a low-cost, low-energy network
• Wireless Personal Area Networks (WPANs)
• Gaining importance because of mobile phones, PDAs, music players, digital cameras, and similar gadgets
• The Bluetooth WPAN is an example

LANs (Local Area Networks)

• LANs transmit messages at high speed between computers using media like coaxial cable or optical fiber
• A segment is a cable section serving a department or floor in a building, with many computers attached
• Routing of messages is not required within a segment because the medium provides direct connections
• Larger buildings or campuses are made of segments interconnected by switches or hubs

WANs (Wide Area Networks)

• WANs transmit messages at lower speeds between nodes of different organizations, which are separated by large distances in different cities, countries, or continents
• The communication medium uses a set of communication circuits, linking a set of dedicated computers called routers
• Routers route network communication and route messages or packets to their destinations

MANs (Metropolitan Area Networks)

• MANs use high-bandwidth copper and fiber optic cabling installed in some towns and cities
• MANs transmit data over distances of up to 50 kilometers
• A MAN is optimized for an area larger than a LAN, which can be blocks of buildings to entire cities and depends on communications channels of moderate-to-high data rates
• A MAN is owned or operated by single entities, such as public utilities, as well as networking local networks
• Metropolitan area networks can span up to 50km, devices used are modem and wire/cable, and run IEEE 802-2001 standard

Wireless Network Standards

• Metropolitan area networks (MANs) are based on high-bandwidth copper and fiber optic cabling with distances up to 50 km, with technology ranging from Ethernet to ATM (Asynchronous Transfer Mode)
• Wireless local area networks (WLANs) operate on IEEE 802.11 (WiFi) (a, b, and now g) with a bandwidth near 54Mbps and over 150m
• Wireless metropolitan area networks (WMANs) operate on IEEE 802.16 WiMAX standard
• Wireless wide area networks (WWANs) operate on GSM (3G, 4G); UMTS (Universal Mobile Telecommunication System) with rates up to 100 Mbps

Network Principles

• Interconnecting networks is essential for scalability and distributed system openness
• Local and wide area networks can provide each specific group of users with the required networking capabilities
• In global networks, information transmits from one node to another through transit nodes
• This is called switching, where network interconnection occurs via switching nodes like routers, gateways and using software that supports global addressing and data transmission

Basis Of Computer Networks

• The principles are use a layered model of network protocols, routing, and support for the streaming model of data transmission, in addition to packet switching
• Networking enables the integration of various heterogeneous networks
• Internet addressing and routing schemes accommodate new applications requiring security, mobility, and quality of service

Switching

• Networks connect many devices
• From the invention of the telephone to now, circuit switching has been the dominant technology for voice communications
• Packet switching has evolved substantially for digital data since 1970
• It was designed to provide a more efficient facility than circuit switching for burst data traffic

Packet Switching

• Packet switching (developed in 1960s) is a method for transferring data in a network as a single stream
• Packet switching transfers files quickly/efficiently over a network, and minimize transmission latency
• Data is broken into small, variable-length pieces called Packets
• Each packet contains Source and destination address, and they independently travel through networks
• Packets belonging to the same file may or may not travel through the same path

Packet Transmission

• Asynchronous communication means messages arrive after a variable delay, based on packet travel time
• Transmitted messages are subdivided into packets
• Each packet contains binary data of a limited length, as well as source and destination computer information
• A switching scheme facilitates information transmission between two nodes

Data Streaming

• Data streaming is the transmission and display of audio and video in real time
• Streaming video requires 1.5 Mbps if the data is compressed or 120 Mbps if uncompressed
• Channel streams from the source to destination of a multimedia stream
• This involves predefined routes, reserved resources, and buffering for smoothness
• IPv6 now include feature for real-time separate IP stream treatment

Switching Schemes

• There are four methods typically used, Broadcast, Circuit switching, Packet switching, and Frame relay

Switching Scheme: Broadcasting

• Broadcasting is a transmission technique that involves no switching
• Everything transmits to every node
• Potential receivers must notice transmissions addressed to their device
• Some LAN technologies, including Ethernet, is based on broadcasting
• Wireless networking is always broadcasting, and nodes grouped where broadcasts are arranged to reach

Switching Scheme: Circuit Switching

• For two processes to communicate, a permanent, dedicated, and not-shared physical link (or circuit, or path) is established
• The packets transmit over this dedicated path
• The link is allocated for the communication duration, and no other process can use that link during the period.
• A telephone is a great example. Once a line is opened, no one else can use the circuit until communication is terminated

Switching Scheme: Packet Switching

• Each packet is sent to its destination separately
• The destination requires the Source and address with its data
• Each packet may take a different path through the network
• The packets must be reassembled into messages as they arrive

Switching Scheme: Circuit vs Packet Switching

• Circuit Switching uses a physical path between the source and destination, and all packets use the same path. Bandwidth usage has store and forward transmission and reserves the bandwidth in advance
• Packet Switching has no physical path, packets travel independently, and bandwidth wastage depends on the destination

Explore various network types, standards like IEEE 802.11 (WiFi), and technologies such as GSM and packet switching. Understand network interconnection, information transmission in global networks, and the advantages of packet switching.