IPX/SPX PROTOCOL SUITE

IPX/SPX Protocol Suite

Novell Inc. developed this protocol suite in early 1980s. Although, officially this protocol is referred as the Netware protocol suite, but due to the immense popularity of two protocols, Internetwork Packet Exchange (IPX) and Sequential Packet Exchange (SPX), this protocol suite is commonly referred to as the IPX/SPX protocol suite.

The following figure shows the IPX/SPX protocol suite mapped to the seven layers of the OSI reference model:

In the preceding figure, the IPX/SPX protocol suite consists of the following protocols:


Service Advertisement Protocol (SAP): This protocol is used by various servers, such as file and print servers, to publicize their IPX addresses and services.
Netware Core Protocol (NCP): This protocol is used to make server functions, such as file and print sharing, available to clients.
Internetwork Packet Exchange (IPX): This protocol provides fast but connectionless communication service. For this purpose, it uses datagrams, which are not acknowledged. In addition to providing logical addressing on the network, IPX also provides routing services.
Sequential Packet Exchange (SPX): This protocol is connection-oriented and guarantees the error-free delivery of data packets.
Netware Link Service Protocol (NLSP): This protocol works with the IPX protocol to find the appropriate route between communicating networks.
Routing Information Protocol (RIP): This protocol provides routing-related information to the Network layer.
Link Support Layer (LSL): This protocol provides the interface between network cards and upper layer protocols.
Multiple Link Interface Driver (MLID): This protocol enables the integration of network cards with upper layer protocols.
       

NETWORK PROTOCOL SUITES: TCP/IP SUITE

Network Protocol Suites

A protocol suite is a hierarchical collection of protocols. Similar to individual protocols, protocol suites can either be developed by a standards organization or a vendor.
Some of the protocol suites are:

• TCP/IP protocol suite
• IPX/SPX protocol suite
• NetBEUI protocol suite
• AppleTalk protocol suite
• DLC protocol suite
• SNA protocol suite

TCP/IP Protocol Suite

Department of Defense (DOD) developed this protocol suite in collaboration with a number of research organizations and universities in the 1970s. Initially, this protocol suite was referred to as the Internet protocol suite because it evolved with the Internet. However, with the emergence of two of its protocols, TCP and IP, this suite is better known as the TCP/IP protocol suite.

The following figure shows the TCP/IP protocol suite mapped to the seven layers of the OSI reference model:

In the preceding figure, the TCP/IP protocol suite consists of the following protocols:


File Transfer Protocol (FTP): This protocol enables the transfer of files from one computer or node to another.
Telnet: This terminal emulation protocol enables access to remote nodes and works on the node as if you were working on it locally.
Simple Mail Transfer Protocol (SMTP): This protocol enables the exchange of electronic mails (e-mails) between two nodes.
Routing Information Protocol (RIP): This protocol provides routing-related information to the Network layer.
Open Shortest Path First (OSPF): This protocol helps the Network layer to discover the shortest available path across networks between two communicating nodes.
Transmission Control Protocol (TCP): This protocol enables reliable, connection-oriented data transfers between two nodes.

User Datagram Protocol (UDP): This protocol enables fast but unreliable connectionless data transfers between two nodes.
Internet Protocol (IP): This protocol moves data between the intermediate networks that lie between the source and destination nodes.
Domain Name Service (DNS): This protocol resolves the names of hosts to their corresponding logical addresses, known as IP addresses.
Internet Control Message Protocol (ICMP): This protocol generates control messages related to any error in connection or flow control.
Address Resolution Protocol (ARP): This protocol resolves the MAC address of a node given its logical address.

     

OSI LAYERS INTERACTIONS

OSI Layer Interactions

Various protocols are implemented at each of the seven layers defined in the OSI reference model. The protocols function based on the guidelines defined for each layer.
In the OSI model, a layer at one end of the communication can interact with a peer layer at the other end. The message travels down the layer of the sending end through the transmission medium to the peer layer of the receiving end.
The following figure shows the communication between the Transport layers of two peers:

Communication Between Transport Layers Of Two Peers

In case two peers need to communicate with each other, the Application layer initiates the message for the recipient end. However, the two Application layers cannot communicate directly. As a result, the message is passed to the Presentation layer at the sender end, which adds its own header to the message and passes it to the Session layer. The Session layer, in turn, adds its own header and passes it to the next lower layer, the Transport layer. In this manner, each layer at the sender end receives the message, adds its own header, and passes the message to the next lower layer. This is because the message is converted into bits and placed on the transmission medium at the Physical layer. The Physical layer does not append any header.
When the recipient's Physical layer receives the message, it passes the message to the Data Link layer. The header added by the peer Data Link layer is stripped and passed to the Network layer, which, in turn, strips its own header. In this manner, each time the message is passed to the upper layer, the corresponding header is stripped off. When the message reaches the Application layer, it is read and interpreted.
The following figure shows the communication between the layers of two communicating ends:

     

OPEN SYSTEM INTERCONNECTION REFERENCE MODEL

The Open System Interconnection (OSI)  Reference Model

The International Standards Organization Open System Interconnection (ISO OSI) reference model first achieved the International standardization of the protocols. ISO developed the standards for connecting systems that are open to communication with other systems.
The OSI reference model has seven layers. The following figure shows the seven-layer OSI reference model:

OSI Seven Layers

The seven layers of the model are listed as follows in the bottom-to-top approach:

• Physical Layer
• Data Link Layer
• Network Layer
• Transport Layer
• Session Layer
• Presentation Layer
• Application Layer

Physical Layer
The Physical layer is responsible for the transmission of data over a communication channel or the transmission medium. This transmission medium is the physical path over which the data is transmitted in the form of signals. During a transmission, the Physical layer converts the data into series of bits and places these bits on the transmission medium. This layer is also responsible for specifying the physical structure or topology of the network. Although the Physical layer deals with transmission media, the transmission medium is not specified.


Data Link Layer
The Data Link layer is responsible for the following aspects of communication:

1. Providing unique identification to each node on the network
2. Transforming data bits from the Physical layer into groups called frames
3. Detecting errors that occur during a transmission
4. Managing the flow of data packets or frames

The Data Link layer provides unique identity to each node on the network. It uses the network address, which is hard-coded into the network card of each node for this purpose. Although the Data Link layer is responsible for the detection of transmission errors, it is not responsible for the correction of errors.

The Data Link layer is divided into two sublayers. These are:

1. Media Access Control (MAC): This sublayer helps the nodes on a network to communicate with each other as it provides information about physical address of the node or the MAC address.
   
2. Logical Link Control (LLC): This sublayer establishes and manages a logical link between two communicating devices on the network. It provides error control and flow control within a network

Network Layer
The Network layer is responsible for the following functions:

1. Providing a unique network address to each node on the network
2. Transmitting data across networks
3. Controlling network traffic

The Network layer provides a unique address to each node on a network. The addresses are different from Data Link layer addresses because Data Link layer addresses can only be used for communication within a single local network. However, if a node on a network A, needs to communicate with a node on network B, it would not be able to do so using Data Link layer addresses.

For communication among different networks, a special Network layer-addressing scheme known as logical addressing is used. When two nodes that are located on two separate networks need to communicate with each other, they need the logical address provided by the Network layer.

The Network layer is also responsible for determining all the possible routes to the destination network and selecting the best path to the network where the destination node is located. This process is known as routing.


Transport Layer
The Transport layer is responsible for the following functions:

1. Organizing messages into segments or breaking large segments into smaller segments 
2. Delivering segments to recipients
3. Providing error control

The Transport layer segments and reassembles data. In case the upper layers generate large data packets, the Transport layer breaks the large packets into smaller segments that can be handled by lower layers. Similarly, when lower layers pass small segments to the Transport layer, it combines multiple segments to form large packets. Because the Transport layer deals with segmentation and reassembly, it is also responsible for correctly sequencing the segments so that the entire data can be reconstructed correctly.

The Transport layer is also responsible for the unreliable or reliable delivery of segments with the help of connectionless or connection-oriented services, respectively. The recipient acknowledges a transmission in connection-oriented services. If the sender does not receive an acknowledgement from the recipient within a specific interval, it retransmits the unacknowledged packets. In connectionless services, the sender continues to transmit packets without receiving acknowledgements.

The Transport layer also provides error control services. When a packet is lost during transmission, the Transport layer retransmits it after a specific interval. In addition, the Transport layer adds checksums to the segments before transmission. The recipients use these checksums to determine whether the segment was corrupted during the transmission or not. If the segment is corrupted, the Transport layer retransmits the appropriate segments.


Session Layer
The Session layer establishes, manages, and synchronizes the communication between two communicating nodes. The two nodes can exchange information only after a session has been established between them. In this case, session is defined as a logical connection between the two nodes.

The Session layer can also control the direction in which data flows. Based on this direction of data flow, a session can be any one of the following:

1. Simplex: Only one node can transmit data at a time.
2. Half duplex: One node can transmit while the other node can receive data. However, both nodes cannot transmit data at the same time.
3. Duplex: Both nodes can transmit as well as receive data at the same time.

Presentation Layer
The Presentation layer encodes and decodes data in a mutually agreeable format. As a result, this layer plays an important role in facilitating data exchange between heterogeneous hardware and software platforms that use different data formats. For example, if one node uses one byte to represent a character and the other node uses two bytes to represent a character, the Presentation layer plays a significant role in facilitating successful data exchange between the two nodes.

If required, the Presentation layer also compresses and decompresses data packets. As a result, the network traffic is less, preventing congestion. The Presentation layer also plays an important role in the encryption and decryption of data. This ensures high data security during transmission.


Application Layer
The Application layer provides an interface between the user and the network. It supports a number of software programs and end-user processes that act as a link between the user and the network. As a result, all network applications and protocols reside on this layer. This is the reason for the name Application layer. Some of the common applications and protocols that operate on this layer include e-mail, FTP, and Telnet.

      

BASICS OF NETWORK PROTOCOLS

Understanding the Need for Protocols

Apart from network components and transmission media, protocols are also basic building blocks of networks.Due to the immense popularity of networks, many vendors offer the network components and software solutions required for a network. However, the problem is that each vendor uses their own specifications to develop their network solutions and products. The specifications might not be compatible with each other.

In everyday life, we follow some rules while communicating. For example, in a phone transaction, one person speaks at a time. If both people speak at the same time, neither of them will be able to understand what the other person is saying.

Similar to the example discussed above, a set of established and agreed-upon rules is required to enable effective communication on a network. The set of standards, rules, or conventions are called protocols.
Either a vendor or a networking standard organization can develop protocols.
After a protocol is conceived, developed, and tested, it must be approved by a standardization organization.

Understanding the Need For OSI Reference Model

A protocol model or reference model is a set of guidelines followed by vendors to develop protocols. The models also explain the services that are required to transfer data from one computer to another. In addition, reference models also help understand complex network functions.

The International Standards Organization Open System Interconnection (ISO OSI) reference model first achieved the International standardization of the protocols. ISO developed the standards for connecting systems that are open to communication with other systems.
      

COLLABORATIVE NETWORK COMPUTING MODEL

Network Computing Models

A network can be designed for processing information by either the client or the server. The network model can also be structured in a way that both the client and the server can process information. Depending on this flexibility, network computing models can be of three types:

Centralized network computing model

Distributed network computing model

Collaborative network computing model

Collaborative Network Computing Model

The collaborative network computing model is an advanced distributed computing model. In this model, nodes also share processing capabilities apart from sharing data, resources, and other services. In other words, processes can run on two or more computers. The following figure shows the collaborative network computing model:

Advantages
The advantage of the collaborative network computing model is:
Increased processing speed: The nodes on the collaborative network share the task of processing the request. This reduces the processing time and increases the overall network performance.
      

DISTRIBUTED NETWORK COMPUTING MODEL

Network Computing Models

A network can be designed for processing information by either the client or the server. The network model can also be structured in a way that both the client and the server can process information. Depending on this flexibility, network computing models can be of three types:

Centralized network computing model

Distributed network computing model

Collaborative network computing model

Distributed Network Computing Model

The distributed network computing model allows all network computers to take part in processing but at their respective ends, separately. This model allows sharing data and services but does not help the other network computers in processing.

In this network model, a processing-intensive task is broken into a subset of tasks and distributed among multiple nodes. The nodes work on their individual subsets of tasks. The following figure shows the distributed network computing model:

Advantages

Some of the advantages of the distributed network computing model are:

• Faster data access: The distributed network model allows a node to store the information locally. As a result, data can be accessed faster than in the centralized network model.
• High reliability: In the distributed network model, no single point of failure exists because the network does not entirely depend on a single node. This ensures lower network downtime.
• Customized network setup: The distributed network model offers the flexibility of treating different computers as clients and servers. It allows the optimized use of resources because the roles of the server and the client are interchangeable.

    

CENTRALIZED NETWORK COMPUTING MODELS

Network Computing Models

A network can be designed for processing information by either the client or the server. The network model can also be structured in a way that both the client and the server can process information. Depending on this flexibility, network computing models can be of three types:
Centralized network computing model
Distributed network computing model
Collaborative network computing model

Centralized Network Computing Model

In the centralized network computing model, the clients use the resources of high-capacity servers to process information. In this model, the clients are also referred to as dumb terminals with very low or no processing capability. The clients only connect to the server and not to each other. The following figure shows the centralized network computing model:

Advantages
Some of the advantages of the centralized network computing model are:

• Centralized data management: In a centralized network computing model, data is stored on the server. This increases the reliability of data because all data modifications are stored at a central location.
  
• High level of security: The centralized network computing model is a highly secure network model. This is because network security can be implemented and monitored centrally from the server.
  
• Cost effectiveness: High-end investment is required for establishing a high-capacity and secure server. On the other hand, clients require very low investment. This reduces the overall cost of setting up a centralized network.

Limitations
The centralized network computing model is a conventional model that is used only by a few network setups due to the following limitations:

• Low performance and network speed: The centralized network computing model consists of a server that manages numerous requests, simultaneously. This increases network traffic, consequently reducing the speed and performance of the network.
  
• Central point of failure: The server is the central place for storing data and processing all client requests. If the server fails, the functioning of the entire network is disrupted.

     

WIDE AREA NETWORK AND INTERNET CONCEPTS

WIDE AREA NETWORK AND INTERNET CONCEPTS

Wide Area Network Concepts

A wide area network (WAN) is very similar in concept to a widely distributed client/server LAN. In a wide area network, some distances typically separate computers. A typical WAN is a local city- or countywide network, like the one in the following figure. This network links network members together through a Bulletin
Board Service (BBS). Users can access the bulletin board’s server with a simple telephone call.

A Country-Wide Network

Several types of communication systems connect WANs together. These communication paths are referred to as links. In some areas, high-speed intermediate-sized networks, referred to as Metropolitan Area Networks (MANs), are coming up. These networks typically cover areas up to 30 miles or 50 kilometers in diameter and are operated to provide access to regional resources. They are like LANs in speed and operation, but use special high-speed connections and protocols to increase the geographic span of the network, like a WAN.

Internet Concepts

The most famous WAN is the Internet. The Internet is actually a network of networks, working together. The main communication path for the Internet is a series of networks, established by the U.S. government, to link supercomputers together at key research sites. This pathway is referred to as the backbone and is affiliated with the National Science Foundation (NSF). Since the original backbone was established, the Internet has expanded around the world. It offers access to computer users in every part of the globe.

The TCP/IP protocol divides the transmission into packets of information, suitable for retransmission across the Internet. Along the way, the information passes through different networks that are organized at different levels. Depending on the routing scheme, the packets may move through the Internet using different routes to reach the intended address. At the destination, the packets are reassembled into the original transmission.
The packets movement around the Internet is shown in the following figure.

Data Packet Moving Through Internet

As a message moves from the originating address to its destination, it may pass through LANs, mid-level networks, routers, repeaters, hubs, bridges, and gateways.
A mid-level network is simply another network that does not require an Internet connection to carry out communications.
A router receives messages, amplifies them, and retransmits them to prevent the messages from deteriorating as they travel.
Hubs are used to link networks together, so that nodes within them can communicate with each other.
Bridges connect networks together, so that data can pass through them as it moves from one network to the next. A special type of bridge, called a gateway translates messages as they pass through, so that they can be used on different types of networks, such as Apple
networks and PC networks.