Clouding

Chapter 4: Networks Collaboration, and Sustainability Contributors: John Richardson, Stella Porto, Kim Wandersee, Les Pang This chapter presents an overview of the Internet and other telecommunication networks, business applications, and trends and reviews technical telecommunications alternatives. Network Basics

Each of the past three centuries has been dominated by a single technology. The 18th Century was the time of the great mechanical systems accompanying the Industrial Revolution. The 19th Century was the age of the steam engine. During the 20th Century, the key technology was electrical information gathering, processing, and distribution. What will we say about the 21st Century? Due to rapid technological progress, these areas are rapidly converging, and collecting, processing, storing, and transporting information are quickly becoming just elements of a single information system.

Although the computer industry is young compared to other industries such as automobiles and air transportation, computers have made spectacular progress in a short time. During the first two decades of their existence, computer systems were highly centralized, usually within a single large room. Not infrequently, this room had glass walls, through which visitors could gawk at the great electronic wonder inside. A medium sized company or university might have had one or two computers, while large institutions had at most a few dozen. The idea that within 20 years equally powerful computers smaller than postage stamps would be mass produced by the millions was pure science fiction.

The merging of computers and communications has had a profound influence on the way computer systems are organized. The concept of the "computer center" as a room with a large computer to which users bring their work for processing is now totally obsolete. The old model of a single computer serving all the organization's computational needs has been replaced by one in which a large number of separate but interconnected computers do the job -- the computer networks.

A data network transfers data from one point to another without changing it. In fact, the network does not contain any facilities to process information. Instead, all data processing is performed by applications programs. When applications use a network, they do so in pairs -- the pair uses the network merely to exchange messages. This is the concept of the dumb network and the smart terminals. That is, the intelligence is at the edges of the network. Indeed, many think that this is the genius of the Internet: the network and its owners place no restrictions on traffic, so that the users at the edges are free to experiment and innovate with technology and applications.

Proponents of the current political issue called Network Neutrality seek to preserve this concept. Opponents seek to charge differentially for high volume, high quality, and high priority transmission to provide capital for further investment in network facilities. Analysis of the merits of these positions is important but beyond the scope of these lecture notes.

Consider, as an example, a distributed database service that allows remote users to access a central database. Such service requires two applications, one running on the computer that has the database and the other running on the remote computer. The application on the remote computer sends a request to the application running on the database computer. When the request arrives, the application running on the database computer consults the database and returns a response. Only the two applications understand the meaning and the format of the message. The way these two computers find each other in a large network such as the Internet follows a straightforward mechanism: one application starts first and waits for the other application to contact it. The second application must know the location where the first application is waiting. This arrangement is known as the client-server paradigm or as client-server computing. In this scheme, the program that waits for contact is called a server and the program that initiates contact is known as a client. To initiate contact, a client must know where the server is running, and must specify its location to the network software.

Protocols represent the language used for two computers to “talk” to each other. Protocols are used in a layered communication representation called Open Systems Interconnection (OSI) model.  A tutorial for understanding the OSI model is found at this site . Protocols are used to enable a computer in one system to interact with a corresponding computer at the same layer in another system. Network Types

Computer networking is a complex subject. Many technologies exist, and each technology has features that distinguish it from the others. Multiple organizations have created networking standards independently, which are not all compatible. Many companies have created commercial networking products and services that use the technologies in unconventional ways. Finally, networking is complex because multiple existing technologies can be used to interconnect two or more networks. As a result, many combinations of networks are possible.

Networking can be especially confusing because there is no single underlying theory that explains the relationship among all parts. In fact, various organizations and research groups have attempted to define conceptual models that can be used to explain the differences and similarities among network hardware and software systems. The lack of an underlying theory has produced a situation where there is no uniform terminology for networking concepts, resulting in multiple terms for the same concept. To master this complexity, one must look beyond the details, concentrate on understanding concepts, and be able to identify them in distinct contexts and situations.

There is no generally accepted taxonomy into which all computer networks fit, but two dimensions stand out as important: transmission technology and scale. Transmission technology, broadly speaking, exhibits two types:

· Point-to-point networks

· Broadcast networks

Point-to-point networks consist of many connections between individual pairs of machines. In this type of network to go from the source to the destination, short messages, called packets, may have to go to one or more intermediate machines. Often multiple routes of different lengths are possible, so routing algorithms play an important role in point-to-point networks. Broadcast networks, by contrast, have a single communication channel that is shared by all the machines on the network. Packets sent by any machine are received by all others. An address field within the packet specifies for whom it is intended. Upon receiving a packet, a machine checks the address field. If the packet is intended for itself, it processes the packet; if the packet is intended for some other machine, it is just ignored.

Broadcast systems generally also allow the possibility of addressing a packet to all destinations by using a special code in the address field. When a packet with this code is transmitted, it is received and processed by every machine on the network. This mode of operation is called broadcasting. Some broadcast systems also support transmission to a subset of the machines, something known as multicasting. One possible scheme is to reserve a 1 bit to indicate multicasting. The remaining n-1 address bits can hold a group number. Each machine can "subscribe" to any or all of the groups. When a packet is sent to a certain group, it is delivered to all machines subscribing to that group.

As a general rule (although there are many exceptions), smaller, geographically localized networks tend to use broadcasting, whereas larger networks usually are point-to-point. Scale is an alternative criterion for classifying networks. One may classify networks based on interprocessor distance. At one end of this classification, with an interprocessor distance of around 0.1 m, we have highly parallel computers (called in this context data flow machines), with many functional units all working on the same program. Next, at a scale of around 1 meter, come the multicomputers, systems that communicate by sending messages over very short, very fast buses. Beyond the multicomputers are the true networks, computers that communicate by exchanging messages over longer cables at scales of one to thousands of kilometers. These can be divided into local, metropolitan, and wide area networks, although few use the designation "metropolitan" anymore. Finally, the connection of two or more networks is called an internetwork. The worldwide Internet is a well known example of an internetwork. Distance is important as a classification metric because different techniques are used at different scales.

Wired Networks

Local Area Networks

Local area networks, generally called LANs, are privately owned networks within a single building or campus of up to a few kilometers in extent. They are widely used to connect personal computers and workstations in company offices and factories to share resources and exchange information. LANs are distinguished from other kind of networks by three characteristics: (1) their size, (2) their transmission technology, and (3) their topology.

LANs are restricted in size, which means that the worst-case transmission time is bounded and known in advance. Knowing this bound makes it possible to use certain designs that would not otherwise be possible. It also simplifies network management. LANs often use a transmission technology consisting of a single cable, to which all the machines are connected.

Most LANs use broadcast transmission technology, with an arbitration mechanism to resolve conflicts when two or more machines want to transmit simultaneously. Another kind of LAN is built using point-to-point lines where individual lines connect a specific machine with another specific machine. Traditional LANs run at speeds of ten to hundreds of megabits per second (Mb/s), have low delay (tens of microseconds), and make very few errors. Newer LANs may operate at higher speeds, up to several gigabits per second (Gb/s). Ethernet is a common transmission technology, in which speeds have increased to 1 Gb/s and even 10 Gb/s.

Various topologies are possible for broadcast LANs. Two common types are the bus and the ring. In a bus network, in which all the machines are connected to one linear cable. At any instant one machine is the master and is allowed to transmit. A second type of broadcast system is the ring, in which all the machines are connected to a cable that closes back on itself. In a ring, each bit propagates around on its own, not waiting for the rest of the packet to which it belongs. Typically, each bit circumnavigates the entire ring in the time it takes to transmit a few bits, often before the complete packet has even been transmitted. Wide Area Networks A Wide Area Network (WAN) technology can be used to form networks that span an arbitrarily long distance and connect arbitrarily many computers. A typical WAN consists of electronic devices called packet switches interconnected by communication lines. A packet switch is implemented with a special purpose computer that is dedicated to the task of providing communication. Although an individual computer connects to a single switch, the system is configured to allow a computer to transfer packets to or from any other computer on the network.

Packet switching networks use a store-and-forward approach in which an arriving packet is placed in the memory of a packet switch until the processor can forward the packet to its destination. Under normal conditions, a packet does not remain in memory long. However, if multiple computers attempt to send packets at the same time, delays increase.

Forwarding relies on a data structure known as a routing table. The table contains an entry for each destination, and it specifies the next hop used to reach that destination. To save space, a routing table usually lists packet switches as destinations instead of individual computers. Examples of WAN technologies include ARPANET, X.25, Frame Relay, Switched Multimegabit Data Service (SMDS), and Asynchronous Transfer Mode (ATM).

Wireless Networks

Mobile computers, such as notebook computers and personal digital assistants (PDAs), are the fastest-growing segment of the computer industry. Many of the owners of these computers have desktop machines on LANs and WANs back at the office and want to be connected to their home base even when away from home or en route. The answer is the wireless network.

Wireless networks have many uses. A common one is the portable office. People on the road often want to use their portable electronic equipment to send and receive telephone calls, faxes, and electronic mail; read remote files; login on remote machines; access the Internet; and so on, and do this from anywhere on land, sea, or air. Wireless networks are of great value to fleets of trucks, taxis, buses, and repair persons for keeping contact with the home base. Another use is for rescue workers at disaster sites where the telephone system has been destroyed.

Computers there can send messages and keep records. Finally, wireless networks are important to the military. If you have to be able to fight a war anywhere on earth on short notice, counting on using the local networking infrastructure is probably not a good idea.

Although wireless networking and mobile computing are often related, they are not identical, as the table below shows. Portable computers are sometimes wired. For example, if a traveler plugs a portable computer into the telephone or Ethernet jack in a hotel, we have mobility without a wireless network. On the other hand, some wireless computers are not portable. An important example here is a company (or a homeowner) that owns an older building that does not have network cabling installed and wants to connect its computers. Installing a wireless LAN may require little more than buying a small box with some electronics and setting up some antennas. This solution may be cheaper than wiring the building. But of course, there are also the true mobile, wireless applications, ranging from portable office to people walking around a store with a PDA doing inventory.

Application	Wireless	Mobile
Stationary workstations in offices	No	No
Using a portable in a hotel Ethernet jack	No	Yes
LANs in older, unwired buildings	Yes	No
Portable office	Yes	Yes

Although wireless LANs are easy to install, they have some disadvantages. Typically they are much slower than wired LANs--say, up to 50 Mb/s for shared Wi-Fi compared with 100 Mb/s for Ethernet. The error rates are often higher, too, and the transmission from different computers can interfere with one another. Security requires special attention.

Wireless networks come in many forms. Some universities are already installing antennas all over the campus. Even entire cities, such as Philadelphia and San Francisco, are building wireless networks accessible anywhere in the city. Here the computers communicate directly with wireless LANs in digital form. Wi-Fi (IEEE 802.11) is an example. WiMAX (IEEE 802.16) is another, with greater range. Another possibility is using a newer 3G (third generation) cellular telephone with data rates of 300 kb/s to 700 kb/s,

Finally, it is possible to have different combinations of wired and wireless networking. As an example, we would have a "fly-LAN" in a plane. Each seat is equipped with a wired Ethernet connection into which passengers can plug their computers. A single router on the aircraft maintains a radio link with some router on the ground, changing routers as it flies along. This configuration is just a traditional LAN, except that its connection to the outside world happens to be a radio link instead of a hardwired line.

Current Trends

IPv6 Although the current version of IP has worked well for many years, exponential growth of the Internet means that the 32-bit address space will be exhausted soon. The Internet Engineering Task Force IETF has designed a new version of IP that uses 128 bits to represent each address. The new address space is so large that it will not be exhausted for many decades. The addresses can be used for any addressable device, whether it is a computer or a home thermostat.

To distinguish the new version of IP from the current version, the two protocols are named using their version number. The current version of IP is IPv4, and the new version is IPv6. IPv6 retains many of the concepts from IPv4, but changes all the details. For example, like IPv4, IPv6 provides a connectionless service in which two computers exchange short messages called datagrams. However, unlike an IPv4 datagram in which the header contains fields for each function, IPv6 defines separate headers for each function. Each IPv6 datagram consists of a base header followed by zero or more extension headers, followed by data.

Like IPv4, IPv6 defines an address for each network connection. Thus, as in IPv4, a computer that connects to multiple physical networks (e.g., a router) has multiple addresses. However, special addresses are completely changed in IPv6. Instead of IPv4's notion of network broadcast, IPv6 defines multicast and anycast (cluster) addresses, both of which correspond to a set of computers. A multicast address corresponds to a set of computers at multiple sites that are treated as a single entity -- each computer in the set will receive a copy of any datagram sent to the set. A cluster permits replication of services -- a datagram sent to a cluster address will be delivered to exactly one member of the cluster (e.g., the member that is the closest to the sender), which will replicate it to the other members.

To make IPv6 addresses easier for people to use, the designers use colon hexadecimal notation. Colon hexadecimal notation expresses an address in eight groups of 16 bits in hexadecimal, with a colon separating groups. The resulting is more compact that the dotted decimal form used in IPv4.

The transition from IPv4 to IPv6, although necessary, is proceeding very slowly because of cost, hardware, software, and training obstacles. In the meantime, several workarounds have been devised to keep the Internet working. Cloud Computing and Virtualization

Networks make cloud computing possible. Obviously, we need fast and reliable networks to carry the data back and forth between the user and the cloud computing provider. Less obviously, networks internal to the cloud computing provider continually distribute processing and storage among the provider's machines to accommodate all the many users of the service. These internal networks and machines use virtualization—processing applications on a virtual machine instead of a particular physical machine—to achieve the efficiency and flexibility needed to meet user requirements. Cloud computing must provide rigorous security and privacy safeguards because the great amounts of user data that they handle are vulnerable to loss or disclosure.

Here is a short introductory video, Cloud Computing vs. Virtualization at http://www.youtube.com/watch?v=6pdL4aefX6Y

Sensor Networks Sensor networks consists of a distribution of sensor units are that linked wirelessly.  Data pertaining to physical or environmental conditions (temperature, pressure, vibration, pollutants, etc.) are transmitted among the sensors to a base location. Originally used for military battlefield locations, they are finding applications in the industrial, medical health and consumer market.

More than 230,000 people died because of an earthquake and tsunami in the Indian Ocean in 2004. As result, Japan, the U.S. and other countries implemented a network of sensors called the Deep-ocean Assessment and Reporting of Tsunamis (DART) at tsunami-prone locations worldwide. The sensor network consists of acoustic and pressure-sensitive buoys and sensors anchored to the ocean floor that can detect seismic activity as well as the size and height of waves. Sensors send data at regular intervals to nearby buoys mounted with a GPS, which in turn transmit data to satellites. Emergency official can be alerted through this system if there is unusual wave behavior and the public can be warned well ahead of a tsunami. (Source: Gartner)

Collaboration Technologies

E-mail and calendaring serve as the bare minimum for achieving collaboration, but more is needed in terms of satisfying the communication and coordination requirements of the entire organization. Video conferencing and group meeting systems go well beyond e-mail in effectiveness. Specialized tools are available to support specific roles and responsibilities in an organization such as those for financial specialists, engineers, and sales executives. These tools include unified communications and collaboration (UCC) tools and enterprise social software. (Source: Gartner)

Conclusions

Computer networks have been growing explosively. Two decades ago, few people had access to a network. Now, computer communications have become an essential part of our infrastructure. Networking is used in every aspect of business, including planning, production, shipping, advertising, marketing, billing, and accounting. Consequently, most corporations, educational institutions, government offices at all levels, and military organizations have multiple networks.

These networks have a profound effect on business operations.  In the future, these networks will continue to improve the effectiveness and efficiency of the organizations involved and improve the quality of decision making.