OSI Model

Network equipment manufacturers have proposed and developed network architectures specific to their devices. For instance, IBM has developed SNA, DEC has developed DNA… These architectures have all the same defect: as they are manufacturer-specific systems, it is difficult to interconnect them, unless manufacturers agree on a common architecture. Consequently, in order to avoid the development of hundreds of solution for the interconnection of these heterogeneous architectures, the ISO (International Standards Organisation), body that depends on the UNO and composed of 140 national normalisation bodies, has developed a reference model called the OSI model (Open Systems Interconnection model). This model describes the fundamental concepts and the approach used to normalize the interconnection of open systems (a network is made up of open systems when modifying, adding or removing one of these systems does not modify the global working of the network).

When designing this model, taking the heterogeneity of the equipment into account was a fundamental issue. Indeed, this model was designed to allow the interconnection of heterogeneous systems for historical and economic reasons. Besides, it should not support a particular provider. Lastly, it should make it possible to adapt to the evolution of data to process without calling into question the investments. Thus, all this led the adoption of common communication and co-operation rules between the equipment, i.e. this model should logically carry out to an international standardization of protocols.

The OSI model is not a real network architecture, because it does not really specify the services and protocols each layer should use. It rather describes what the layers must do. Nevertheless, the ISO has developed its own standards for each layer, and this independently of the OSI model, i.e. as does any manufacturer.

The first works related to the OSI model date from 1977. They were based on the experience gained in the area of wide area networks and local private networks; the OSI model was indeed supposed to be valid for any type of network. In 1978, the ISO proposed this model as the standard ISO IS7498. In 1984, 12 European manufacturers, joined in 1985 by the main American manufacturers, adopted this standard.

The different layers of the OSI model

The 7 layers

The OSI model is composed of 7 layers:

The principles that led to these 7 layers were the following:

• A layer must be created every time a new level of abstraction is necessary,
• every layer has well defined functions,
• the functions of each layer must be chosen in the objective of the international standardization of protocols,
• boundaries between layers must be chosen so as to minimize the flows of data through interfaces,
• the number of layers must be such as there is no cohabitation of completely different functions within the same layer and such as it is not too difficult to control the architecture.

The low layers (1, 2, 3 and 4) are necessary to the routing of information between the two concerned ends and depend on the physical medium. The higher layers (5, 6 and 7) are responsible for the data processing relative to the management of exchanges between information processing systems. In addition, layers 1 to 3 intervene between close machines, but not between ending machines that can be separated by several routers. On the contrary, layers 4 to 7 intervene only between distant hosts.

The physical layer

This layer is in charge of the raw transmission of bits over a communication channel. This layer must guarantee the perfect transmission of the data (a bit set to 1 must be received as a bit set to 1). Concretely, this layer must standardize the electrical characteristics (for instance, a bit set to 1 is represented by a voltage of 5V), the mechanical characteristics (the shape of the connectors, topology…), the functional characteristics of the circuits of data and the procedures of establishment, maintenance and release of the circuit of data.

The typical information unit for this layer is the bit, represented by a given voltage.

The data link layer

Its has a role of “binder”: it will transform the physical layer into a connection a priori freefrom transmission errors for the network layer. It splits the input data of the sender into frames, sends these frames in sequence and manages the acknowledgement frames sent back by the receiver. To remind, for the physical layer, the data do not have any particular meaning. The data link layer must therefore be able to recognize the limits of frames. This can actually pose problems, since the sequences of bits used to identify boundaries may also appear in the data.

The data link layer must be able to signal a transmission problem by sending an appropriate frame. In a general way, an important role of this layer consists in detecting and correcting errors that occured on the physical layer. This layer integrates also a flow control function to avoid the blocking of the receiver.

The information unit for this layer is the frame made up of a few hundreds to a few thousands of bytes maximum.

The network layer

This layer is in charge of the sub-network, i.e. the routing packets over the sub-networks and the interconnection of the various sub-networks. When designing it, it is very important to determine the routing mechanism and calculation of the routing tables (static or dynamic tables…).

The network layer also controls sub-network congestions. It is also possible to complete it with accounting functions for invoicing on volume, but this may be delicate.

The information unit for this layer is the packet.

The transport layer

This layer is responsible for the good delivery of messages to the recipient. Its main role is to take the messages of the session layer, split them into smaller units and give them to the network layer, while checking pieces arrive correctly. Therefore, this layer also re-assembles the initial message when it receives the pieces.

This layer is also responsible for the optimization of the network resources: normally, the transport layer should create a network connection for every transport connection required by the session layer, but it is able to create several network connections by session layer’s process, for example to improve the bit rate. Conversely, this layer can use one network connection to transport several messages at the same time, using multiplexing. In any case, all this must transparent for the session layer.

This layer is also responsible for the type of service to provide to the session layer, any finaly to the users of the network: connection-oriented or connectionless service, with or without guarantee of the delivery order, broadcast… Thus, this layer is also responsible for opening and closing network connections.

One of its latest role is flow control.

It is one of the most important layers, because it provides the basic service to the user and controls the whole connection process, with all the related constraints.

The information unit for this layer is the message.

The session layer

This layer sets up and synchronizes the exchanges between distant processes. It binds logical addresses to physical addresses for distributed tasks. It also binds two application programs that must cooperate control their dialogue (which one should speak, which is currently speaking…). In this latter case, the service of set up is called the token management. The session layer also makes it possible to insert recovery points in the data flow in order to resume dialogue after a failure.

The presentation layer

This layer deals with the syntax and semantics of the transmitted data: it processes the data so as to make it compatible between communicating tasks. It will ensure the independance between the user and the data transport.

Typically, this layer can convert, format, crypt and compress the data.

The application layer

This layer is the point of contact between the user and the network. Therefore, it brings the basic network services to the user, such as file transfer, electronic mail…

TCP/IP Model

TCP/IP commonly refers to a network architecture, but this acronym also refers to 2 protocols that are closely bound: a transport protocol, TCP (Transmission Control Protocol) we use “above” a network protocol, IP (Internet Protocol). What we designate by “TCP/IP model” is actualy a network architecture of 4 layers in which the TCP and IP protocols have a major role, since they constitute the official and most common implementation. Consequently, TCP/IP means two different things: the 4-layer network architecture, and the set of 2 protocols, TCP and IP.

As we will see later on, the TCP/IP model has become the model of reference on place of the OSI model. This is due to its story. Indeed, contrary to the OSI model, the TCP/IP model was first implemented before being specified. This particular story makes TCP/IP’s characteristics, its advantages and drawbacks.

TCP/IP dates from the the ARPANET network. ARPANET is a telecommunication network developed by the ARPA (Advanced Research Projects Agency), the research agency of the American ministry of defence (the DOD: Department Of Defense). Besides the possibility to interconnect heterogeneous networks, this network was supposed to resist to a possible nuclear war, contrary to the telephon network usually used for telecommunication but considered as too vulnerable. It was then decided that ARPANET would use a standing out and promising new technology: packet switching (datagram mode). It is to meet this context that the TCP and IP protocols were invented in 1974. The ARPA then signed several agreements with manufacturers (especially BBN) and the Berkeley University, where a Unix system was under development, to impose this standard, and that was done.

Description

A 4-layer model

The TCP/IP model can indeed be described as a 4-layer network architecture:

The OSI model was added to ease the comparison between these two major models.

The host-network layer

It is a pretty strange layer. Indeed, it seems to comprise both physical and data link layers of the OSI model. Actually, this layer has not been really specified; the only constraint of this layer, is to allow a host to send IP packets of a network. The implementation of this layer is free. In more concrete terms, this implementation is typical of the technology used to build the local network (LAN). For example, LANs use Ethernet; Ethernet is an implementation of the host-network layer.

The internet layer

This layer is the key of the architecture. It realizes the interconnection of remote (heterogeneous) networks without establishing a connection. Its role is to inject packets into any network and deliver them to the destination independently to one another. As no connection is established first, packets may not be received in order; the delivery order control process is the responsability of the upper layers.

Because of the major role of this layer in the packet delivery process, the critical point of this layer is routing. For this reason, we may compare this layer to the network layer of the OSI model.

This internet layer has an offical implementation: the IP protocol (Internet Protocol).

We may notice that the name of this layer (”internet”) is written with a small i, for the simple reason that we consider here internet as an interconnection of networks, even if the Internet (with a big I) uses this layer.

The transport layer

It has the same role as the transport layer of the OSI model: it is used to make peer entities dialog with one another.

Officialy, this layer only has two possible implementations: the TCP protocol (Transmission Control Protocol) and the UDP protocol (User Datagram Protocol). TCP is a reliable and connection-oriented protocol that delivers packets without error from a machine of an internet to another machine of the same internet. Its role is to split up the message to be transmitted into a form the internet layer can handle. Conversely, on the receiving machine, TCP places fragments into order to reconstruct the initial message. TCP is also in charge of the flow control of the connection.

On the other hand, UDP is a very simple protocol: it is a non-reliable and connectionless protocol. Using it presupposes that we do not need flow control, either preserving the order of packets. For instance, we use it when the application layer is supposed to control the order of delivery. I remind you that in the OSI model, several layers were in charge of this order delivery control. It is an advantage of the TCP/IP model, but we will see this later on. We also use UDP to transmit voice. Indeed, inverting two sounds does not compromise the comprehension of the final message. In the more general way, we use UDP whenever it is more important to deliver packets on time.

The application layer

Contrary to the OSI model, this layer is immediately bound to the transport layer, simply because the session and presentation layers are useless. Indeed, with use, we have discover that network software hardely use these layers, and finally, the OSI model without these 2 layers is really close to the TCP/IP model

This layer holds all high level protocols, such as Telnet, TFTP (trivial File Transfer Protocol), SMTP (Simple Mail Transfer Protocol), HTTP (HyperText Transfer Protocol). The main issue for this layer is that it can use both TCP or UDP protocols. For example, TFTP (mainly used over LANs) uses UDP, because we consider that physical links on a LAN are rather reliable and transmission times are short enough to avoid packets to be inverted. This makes TFTP faster than FTP, which uses TCP. On the contrary, SMTP uses TCP, because we want mails to be perfectly delivered, without any error.

Comparaison with the OSI model and criticism

Comparaison with the OSI model

First of all, let’s start with the common points. The TCP/IP and OSI models are both based on the concept of independent protocols stacks. Then, taken as a whole, functions are the same.

About the differences, we can notice the following issue: the OSI model makes clearly the difference between 3 main concepts, although TCP/IP does not make this distinction. These 3 concepts are services, interfaces and protocole. Indeed, TCP/IP does not make a clear difference between these concepts, in spite of the efforts of designers to bring the TCP/IP model closer to the OSI model. This is due to the fact that, for the TCP/IP model, protocols appear first, before specifications. The model is finally a theoretical justification of protocols, without making them independent to each other.

finally, the last important difference comes from the mode of connection. Indeed, connection-oriented modes and connectionless modes are available in both models, but not at the same layer: in the OSI model, these modes are only available at the network layer (at the transport layer, only the connection-oriented mode is available), though they are available at the transport layer in the TCP/IP model (the internet layer only offers the connectionless mode). Therefore, the TCP/IP has an advantage, compared to the OSI model: applications (that directly use the transport layer) have the choice between both modes.

Criticism

First, we can say that the TCP/IP model does not make the distinction between specifications and implementation: IP is a protocl that is an integral part of the specifications of the model.

We can also speak about the host-network layer: Indeed, it is not a real abstraction layer, insofar as its specification is not accurate enough. Manufacturers are then obliged to propose solutions to fill in the lacks. Finally, we notice that the physical and data link layers are as important as the transport layer. From this fact, we may propose a hybrid model with 5 layers, which would gather the good points of every model:

Hybrid model of reference Finaly, this model is the real reference in the Internet world. We have kept most layers of the OSI model (all but the session and presentation layers) because they are well specified. On the other hand, OSI’s protocols have no success and finally, we have kept those from the TCP/IP model.

Computer Networking Definition

Computer Networking Definition
Definition of "Computer networking" is the engineering discipline concerned with communication between computer systems. Such communicating computer systems constitute a computer network and these networks generally involve at least two devices capable of being networked with at least one usually being a computer. The devices can be separated by a few meters (e.g. via Bluetooth) or nearly unlimited distances (e.g. via the Internet). Computer networking is sometimes considered a sub-discipline of telecommunications, and sometimes of computer science, information technology and computer engineering. Computer networks rely heavily upon the theoretical and practical application of these scientific and engineering disciplines.
A computer network is any set of computers or devices connected to each other. Examples of networks are the Internet, a wide area network that is the largest to ever exist, or a small home local area network (LAN) with two computers connected with standard networking cables connecting to a network interface card in each computer.
Networking Methods
Networking is a complex part of computing that makes up most of the IT Industry. Without networks, almost all communication in the world would cease to happen. It is because of networking that telephones, televisions, the internet, etc. work.
There are two (broad) types of networks in existence at the moment. These are:
Local Area Network (LAN)
A Local Area Network is a network that spans a relatively small space and provides services to a small amount of people. Depending on the amount of people that use a Local Area Network, a peer-to-peer or client-server method of networking may be used. A peer-to-peer network is where each client shares their resources with other workstations in the network. Examples of peer-to-peer networks are: Small office networks where resource use is minimal and a home network. A client-server network is where every client is connected to the server and each other. Client-server networks use servers in different capacities. These can be classified into two types: Single-service servers, where the server performs one task such as file server, print server, etc.; while other servers can not only perform in the capacity of file servers and print servers, but they also conduct calculations and use these to provide information to clients (Web/Intranet Server). Computers are linked via Ethernet Cable, can be joined either directly (one computer to another), or via a network hub that allows multiple connections.
Wide Area Network (WAN)
A Wide Area Network is a network where a wide variety of resources are deployed across a large domestic area or internationally. An example of this is a multinational business that uses a WAN to interconnect their offices in different countries. The largest and best example of a WAN is the Internet, which is the largest network in the world.
Wireless Networks (WLAN, WWAN)
A wireless network is basically the same as a LAN or a WAN but there are no wires between hosts and servers. The data is transfered over sets of radio trancievers. These types of networks are beneficial when it is to costly or inconvenient to run the necessary cables. For more information, see Wireless LAN and Wireless wide area network
In order for communication to take place between computers, mediums must be used. These mediums include Protocols, Physical Routers and Ethernet, etc. This is covered by Open Systems Interconnection which comprises all the processes that make information transport possible.

Easy Steps to Prevent Mesothelioma

Mesothelioma is a rare cancer that attacks the body's mesothelial cells around the organs. The mesothelium provides a protective membranous lining for the internal organs and allows moving organs (i.e. the heart and the lungs) to glide easily against adjacent structures. The names of the three regions of mesothelial cells that provide protective coating are 1) pleura, the sac which surrounds the lungs; 2) peritoneum, the lining which protects the abdominal cavity; and 3) pericardium, the sac which surrounds the heart. Three different types of mesothelioma cancer attack these three different regions.
Pleural mesothelioma: A type of lung cancer which attacks the pleura surrounding the lungs, this is the most common type of mesothelioma, affecting approximately two-thirds of all mesothelioma patients. Symptoms include horseness, fever, blood in sputum, swollen arms and face, coughing, loss of weight, difficulty breathing, chest pain, weak muscles, and reduced tactile sensitivity.

Peritoneal mesothelioma: A cancer of the abdomen which attacks the peritoneum lining the abdominal cavity. This affects approximately one-third of all mesothelioma patients. Symptoms include abdominal bloating, impaired bowl function, fever, swollen feet, and nausea.

Pericardial mesothelioma: This form of mesothelioma which attacks the pericardium surrounding the heart is extremely rare. Symptoms include chest pain, dyspnea, cough, and palpitations. Mesothelioma has been linked to asbestos exposure. Asbestos is a type of building material used in thermal insulation products and ceiling tiles. In the United States, asbestos usage peaked during the 1950s - 1970s. During the late 1960s, concerns over the health consequences of asbestos exposure began to arise, thereby decreasing the amount of asbestos manufactured in next two decades. By the 1980s, a new industry of asbestos abatement began to flourish. But according to the United States Environmental Protection Agency (EPA), as many as 733,000 schools and public buildings still contain asbestos.
Small asbestos fibers that enter the air do not evaporate and can remain suspended in the air for a long time. These fibers, when breathed into the body, are toxic. There are three types of asbestos exposure.

Occupational asbestos exposure: People working in factories that manufacure asbestos are likely to have a high exposure to asbestos and are most at risk of developing asbestosis or mesothelioma.

Paraoccupational asbestos exposure: Family members of workers exposed to asbestos in the workplace are susceptible to exposure from asbestos dust brought home by the worker on his clothes or skin.

Neighborhood asbestos exposure: Those who live in the vicinity of an asbestos manufacturing plant are also at risk.
Mesothelioma is still a relatively rare form of cancer. There are an estimated 2,000 - 3,000 new cases per year in the United States. Approximately 7-13 per one million male patients with a history of asbestos exposure contract mesothelioma. Diagnosis usually occurs 20-40 years after initial exposure to asbestos.

About the author:
Amie Perlowski writes about mesothelioma and other asbestos-related diseases. Learn more at http://www.lsasbestoslaw.com/results.html.

Asbestos Cancers

About Asbestos Cancers

Asbestos cancer is a general term for a variety of cancers caused by exposure to asbestos. Malignant mesothelioma, a rare cancer of the membranes that line the chest (pleural mesothelioma) and abdomen (peritoneal mesothelioma), is nearly always attributable asbestos exposure. Lung cancer may also be asbestos related.

Mesothelioma is sometimes mistakenly referred to as a lung cancer because almost two-thirds of the diagnosed cases affect the pleural lining, which predomenantly surrounds the lungs. In actuality, this cancer resides outside the lungs, but may affect their functioning, as it is the job of the pleural lining to permit movement between the lungs, diaphragm and other organs as they function (think of the expansion and contraction of the lungs as the breath in and expel air).

What is asbestos?

Asbestos is a fibrous mineral that has been used widely in everyday products because it won't conduct electricity and is heat- and chemical- resistant. These asbestos fibers, when loose, can easily be inhaled or swallowed, and remain in the body for years, eventually resulting in an asbestos-related cancer.

Symptoms and Diagnosis

Symptoms

Because asbestos fibers remain in the body so long, symptoms of asbestos-related diseases may only appear decades after the asbestos has been inhaled. Common symptoms of an asbestos-related cancer include:

• Shortness of breath
• A cough or a change in cough pattern
• Blood in the sputum (fluid) coughed up from the lungs
• Pain in the chest or abdomen
• Difficulty in swallowing or prolonged hoarseness
• Significant weight loss

If any of these symptoms develop and you believe you may have worked with--or been around someone who has worked with--asbestos, make an appointment to see your doctor immediately.

Diagnosis

Once you have contacted your physician and explained your symptoms, the doctor may perform a complete physical examination. This may include a chest x-ray and lung function tests. While a chest x-ray cannot determine whether there are asbestos fibers in the lungs, it can help determine whether your lungs may have changed due to asbestos exposure. A x-ray specialist in asbestos-related diseases may be required to examine and interpret your x-rays.

If an abnormal area is found through the x-ray, you may need to have a biopsy to learn if that area is cancerous. In a biopsy, a surgeon or a medical oncogolgist (a doctor who specializes in diagnosing and treating cancer) removes a tissue sample. Then this sample is examined under a microscope by a pathologist.

Because asbestos fibers can be found in urine, feces, mucus, or material from the lungs, you may have to undergo additional testing to determine the scope of your condition.

Treatment of Mesothelioma

Treatment of MM using conventional therapies has not proved successful and patients have a median survival time of 6 - 12 months after presentation. The clinical behaviour of the malignancy is affected by several factors including the continuous mesothelial surface of the pleural cavity which favours local metastasis via exfoliated cells, invasion to underlying tissue and other organs within the pleural cavity, and the extremely long latency period between asbestos exposure and development of the disease.

Surgery
Surgery, either by itself or used in combination with pre- and post-operative adjuvant therapies has proved disappointing with a 5 year survival rate of less than 10%. A pleurectomy/decortication is the most common surgery, in which the lining of the chest is removed. Less common is an extrapleural pneumonectomy (EPP), in which the lung, lining of the inside of the chest, the hemi-diaphragm and the pericardium are removed. It is not possible to remove the entire mesothelium without killing the patient.

Radiation

For patients with localized disease, and who can tolerate a radical surgery, radiation is often given post-operatively as a consolidative treatment. The entire hemi-thorax is treated with radiation therapy with radiation often times being given simultaneously with chemotherapy. This approach of using surgery followed by radiation with chemotherapy has been pioneered by the thoracic oncology team at Brigham & Women's Hospital in Boston. Delivering radiation and chemotherapy after a radical surgery has led to extended life expectancy in selected patient populations with some patients surviving more than 5 years. As part of a curative approach to mesothelioma, radiotherapy is also commonly applied to the sites of chest drain insertion, in order to prevent growth of the tumor along the track in the chest wall.

Although mesothelioma is generally resistant to curative treatment with radiotherapy alone, palliative treatment regimens are sometimes used to relieve symptoms arising from tumor growth, such as obstruction of a major blood vessel. Radiation therapy when given alone with curative intent has never been shown to improve survival from mesothelioma. The necessary radiation dose to treat mesothelioma that has not been surgically removed would be very toxic.

Chemotherapy

In February 2004, the Food and Drug Administration approved pemetrexed (brand name Alimta) for treatment of malignant pleural mesothelioma. Pemetrexed is given in combination with cisplatin. Folic acid is also used to reduce the side-effects of pemetrexed.

Immunotherapy

Treatment regimens involving immunotherapy have yielded variable results. For example, intrapleural inoculation of Bacillus Calmette-Guérin (BCG) in an attempt to boost the immune response, was found to be of no benefit to the patient (while it may benefit patients with bladder cancer). Mesothelioma cells proved susceptible to in vitro lysis by LAK cells following activation by interleukin-2 (IL-2), but patients undergoing this particular therapy experienced major side effects. Indeed, this trial was suspended in view of the unacceptably high levels of IL-2 toxicity and the severity of side effects such as fever and cachexia. Nonetheless, other trials involving interferon alpha have proved more encouraging with 20% of patients experiencing a greater than 50% reduction in tumor mass combined with minimal side effects.

Heated Intraoperative Intraperitoneal Chemotherapy

A procedure known as heated intraoperative intraperitoneal chemotherapy was developed by Paul Sugarbaker at the Washington Cancer Institute.The surgeon removes as much of the tumor as possible followed by the direct administration of a chemotherapy agent, heated to between 40 and 48°C, in the abdomen. The fluid is perfused for 60 to 120 minutes and then drained.

This technique permits the administration of high concentrations of selected drugs into the abdominal and pelvic surfaces. Heating the chemotherapy treatment increases the penetration of the drugs into tissues. Also, heating itself damages the malignant cells more than the normal cells.

What Is Mesothelioma

Malignant mesothelioma is an uncommon, but no longer rare, cancer that is difficult to diagnose and poorly responsive to therapy. Malignant mesothelioma is the most serious of all asbestos-related diseases.

A layer of specialized cells called mesothelial cells lines the chest cavity, abdominal cavity, and the cavity around the heart. These cells also cover the outer surface of most internal organs. The tissue formed by these cells is called mesothelium.

The mesothelium helps protect the organs by producing a special lubricating fluid that allows organs to move around. For example, this fluid makes it easier for the lungs to move inside the chest during breathing. The mesothelium of the chest is called the pleura and the mesothelium of the abdomen is known as the peritoneum. The mesothelium of the pericardial cavity (the "sac-like" space around the heart) is called the pericardium.

Tumors of the mesothelium can be benign (noncancerous) or malignant (cancerous). A malignant tumor of the mesothelium is called a malignant mesothelioma. Because most mesothelial tumors are cancerous, malignant mesothelioma is often simply called mesothelioma.

Mesothelioma was recognized as a tumor of the pleura, peritoneum and pericardium in the late 1700's. However it was not until much later, in 1960, that this particular type of tumor was described in more detail and even more importantly, its association with asbestos exposure was recognized. The first report linking mesothelioma to asbestos exposure was written by J.C.Wagner, and described 32 cases of workers in the "Asbestos Hills" in South Africa. Since then, the relationship between mesothelioma and asbestos exposure has been confirmed in studies around the world.

The incidence of mesothelioma in the United States remains very low, with 14 cases occurring per million people per year. Despite these numbers, the noticed threefold increase in mesothelioma in males between 1970 and 1984, is directly associated with environmental and occupational exposure to asbestos, mostly in areas of asbestos product plants and shipbuilding facilities.

Although the disease is much more commonly seen in 60-year-old men, it has been described in women and early childhood as well. The cause of the disease is not so well understood in these latter two groups, but there is some evidence of possible asbestos exposure for some of these cases as well.

Malignant mesothelioma is divided into three main types. About 50% to 70% of mesothelioma occurrences are the epithelioid type. This type has the best prognosis (outlook for survival). The other two types are the sarcomatoid type (7%-20%), and the mixed/biphasic type (20%-35%). Treatment options for all three types are the same.

About three-fourths of mesothelioma occurrences start in the chest cavity and is known as pleural mesothelioma. Another 10% to 20% begin in the abdomen and is called peritoneal mesothelioma. Pericardial mesothelioma, starting in the cavity around the heart, is very rare. The covering layer of the testicles is actually an outpouching of peritoneum into the scrotum. Mesothelioma that affects this covering of the testicles is quite rare.