IFSM - Final Assessment Essay

6/25/2020 Module 4 Commentary, part 1 - IFSM 370 6381 Telecommunications in Information Systems (2205)

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Module 4: Telecommunications and Network Planning, Design, and Management

Commentary

Topics

1. Telecommunications and Network Design Strategies 2. Logical and Physical Diagrams 3. Network Planning

1. Telecommunications and Network Design Strategies

Designing telecommunications networks requires methodical procedures and strategies by design engineers and managerial stakeholders. First and foremost, the outcome of the design must support business objectives and goals. Understanding the design requirements is most important prior to designing the enterprise networks. Management has its business goals to achieve, and the network must support the business operations. Therefore, network designers must communicate and accurately translate the design requirements to network engineers to design and implement the network accurately and properly to support business objectives.

A. Layering, Layered Network Architectures, and Multiplexing Physical and Virtual Connections

Device-based multiplexing provides benefits for co-located or closely located devices that can share a single transmission medium. In short, this type of multiplexing consists of the physical connection of multiple devices with virtual point-to-point connections between pairs of devices. Software-based multiplexing, on the other hand, is what makes computer networking possible. Networking differs from simple multiplexing in that it provides virtual connections between large numbers of devices over multiple shared physical connections.

Figure 4.1 Multiplexing

Specifically, networking is rooted in statistical time-division multiplexing (STDM or statistical TDM, also known more simply asstatistical multiplexing). In STDM, each block of data transmitted over the physical connections is preceded by control information that determines the device or port to which the receiver delivers the data. Similarly, in networking, each block of data transmitted over the physical connections is preceded by control information that helps the receiving device determine what to do with the data. The control information consists of a channel number or virtual connection identifier (VCI). Depending on which packet switching technology is used, the virtual connection is configured and routed differently.

B. Virtual Ports and Devices

Once you have made the leap to the concept of virtual connections, as in STDM, you do not have to go much further to accept the possibility of having multiple virtual connections in a single physical device and sharing the connection hardware as well as the transmission hardware. A PC on a LAN may have only one physical networking port that is connected to only one physical wire, but when loaded with appropriate software, the PC may be maintaining active virtual data connections with many other machines on the network, apparently simultaneously. All virtual connections are kept separate from each other because each is assigned to a virtual port with associated tables of control data that are updated based on the contents of the control information in the header of each received block.

Keeping all of this straight requires fairly complex software. Initially, complex networking subsystems were built to address networking unique to each implementation. The developers who built these early subsystems had to be highly skilled in many areas (these areas correspond to the layers in the layered architecture) to address this level of complexity.

When faced with a complex problem, a good system designer tries to break the problem into small, simple pieces that are easier to comprehend. Using this approach, which is sometimes referred to as modularization or divide-and-conquer, the data is hidden with a module, and each module or group of modules has an implementation secret, which means that the details of how the module performs its task are not public. The internal data structure and the algorithm used, for example, are thereby hidden from the calling modules, hence the name information hiding. The advantage to such an approach is that these details can be changed without modifying the calling modules. This is also called information hiding, and supports the concept of divide-and-conquer.

Similarly, the approach used for communications and networking—using a layered architecture for the communications subsystem or network—applies the divide-and-conquer approach to the problem of transferring data reliably and quickly. Each layer of the architecture, just like each module of a complex system, needs to have a well-defined job of manageable size for this approach to work.

The following basic principles apply to a layered communications architecture:

In general, a layer is a piece of software or hardware, or a combination of the two. Each sender layer communicates control information to its matching receiver layer via an agreed-upon protocol. A sender layer requests services from the next (sending) layer below it in the protocol stack. A receiver layer delivers a communicated entity to the (receiving) layer directly above it. Layers are functionally independent. The choice of a protocol at one layer should not affect layers above or below it.

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A layer may be null if it is not required for the full interconnection session. When a layer is null, that means that no attempt is made to provide the services that this layer should provide.

C. Layer-to-Layer Interface

Each layer in a layered architecture introduces the need for more overhead in transmission. By networking overhead, we mean those bits in the data transmission that do not appear in the original data input into the protocol stack by the user/application. The concept of layered architecture is similar to that of an envelope within an envelope. If designers and implementers are willing to tolerate a large amount of overhead, there must be some benefit to offset the accompanying large cost—and there is. A layered architecture provides a great deal of functional modularity. If the architecture is properly designed, making changes to one module (at one layer) does not have a ripple effect on the operation of other layers (modules). Other less obvious benefits are associated with the reduced complexity of standard specifications and development based on smaller modules.

The layers in network architectures are structured in several different ways. For all such architectures in use today, the closer you are to the bottom of the protocol stack, the more hardware-oriented you are, and the more standardized the hardware is.

The key to a layered architecture is the concept that each module/layer communicates with only three other entities, as shown in figure 4.2:

1. the layer/module above it in the protocol stack—for service information for the current layer and data 2. the layer/module below it in the protocol stack—for service information for the subsidiary layer and data 3. its logical peer layer/module in the protocol stack on the remote host—for data and control specifications

Figure 4.2 Layered Protocol Stacks

D. The Open Systems Interconnection (OSI) Model

The Open Systems Interconnection or OSI model, developed by the International Organization for Standardization (ISO) and thus international in scope, is the logical structure on which to base the discussion and standardization of data communications. For more on the OSI model, see http://www.inetdaemon.com/tutorials/basic_concepts/network_models/osi_model. It is a layered communications architecture consisting of seven layers:

Figure 4.3 OSI Model

OPEN SYSTEMS INTERCONNECTION (OSI)

OSI Welcome

Welcome to the Open Systems Interconnection (OSI) model. In this presentation, you will learn about the seven layers of the OSI model and the security issues at each layer.

You will begin by clicking on the OSI Overview button on the top left. After you read some general information about the model, be sure to click on the Information Assurance tab to read about the five pillars of information assurance, as this topic forms the basis of the discussion about security concerns and issues at each layer.

Next, you will investigate each layer. You will do this by selecting the names of the layers from the menu on the left. When you click on a layer, you will see two tabs: Description and Information Assurance. These tabs will lead you to information about the layer and its associated security issues.

6/25/2020 Module 4 Commentary, part 1 - IFSM 370 6381 Telecommunications in Information Systems (2205)

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The layers are numbered from a communication's viewpoint in that the first layer, physical, is the one that actually reaches out and touches the communications environment. You can read more about each layer's functionality by clicking on each layer in figure 4.3.

But what does open systems interconnection model mean? The model allows different utilities and protocols the ability to communicate together. For example, an e-mail sent from one mail system such as Hotmail will be delivered to a Gmail account in a user-readable format. The current OSI environment seems to have been significantly expanded with an emphasis on open systems. The objective has been widened to include any computer and/or process that has been designed according to a set of open system specifications (some of which are national and international standards, others of which are proprietary standards where the sponsor has made them open). When a standard is "open," it is made publicly available and has various rights to use associated with it. TCP/IP is an example of an open standard.

Other changes have occurred since the OSI model was originally conceived:

The data link layer has been defined as having two sublayers: media access control (MAC) and logical link control (LLC). The MAC sublayer determines who is allowed to access the media at any one time. The LLC multiplexes protocols running on top of the data link layer and can provide flow control, acknowledgement, and error notification. The network layer has been defined as having three sublayers (to support internetworking):

subnetwork independent convergence subnetwork dependent convergence subnetwork dependent access

Network management is now considered part of the reference model environment. This model has five functional areas: fault (to recognize, isolate, correct, and log faults that occur in the network) configuration (to gather, set, and track configurations of the devices) accounting (to gather usage statistics of users) performance (to improve and determine the efficiency of the network) security (to control access to assets)

Changes to the model are likely to continue, but no radical changes are anticipated. Although the forces that brought the OSI model into existence appear to have been well-intentioned and well-supported, few pure OSI implementations seem to exist. The networking architecture is the TCP/IP suite. Mixed OSI/TCP/IP networks also exist, as it is fairly easy to replace ISO layers 5-7 with TCP/IP application-layer entities.

On a given computer (host), several networks may be attached and several protocol stacks may actually be in parallel use. For example, your e-mail installation may be running SMTP (simple mail transfer protocol) from the TCP/IP suite, but be attached to both a TCP/IP network and an OSI network. In this case, the application would fan-out, selecting the appropriate transport protocol with which to communicate to a specific computer's e-mail connection. Were this an OSI-only situation, the session layer would be responsible for properly managing the required mail connection. If, on the other hand, you had two e-mail applications (e.g., X.400 and SMTP) running in parallel over a single network connection, there might be a fan-in to the single transport layer entity.

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E. The TCP/IP Suite

The TCP/IP model, the result of many years of evolution and experience, is remarkably parallel to the OSI model. The primary difference is that the top three layers of the OSI model are represented in the single application layer in the TCP/IP model. Much of the same functionality is present in both. Another major difference is that most TCP/IP applications are defined for a single data representation, whereas the presentation layer in the OSI model makes it possible for applications to operate in a fashion independent of the data representation.

Applications are generally connection-oriented rather than connectionless, which means that the first thing your application agent program needs to do to send Internet mail, transfer a file, or emulate terminal services (or any of the other application services) is to establish a connection through which data will pass to a remote host. The destination host typically has listener applications (frequently called daemons) running for all of the services it is willing to provide to requesting hosts. On the Internet, these listeners are most often assigned to and monitor specific virtual port addresses known as well-known ports. Thus, if a given host does not support the application for which a well-known port has been designed, no listener monitors that port number, and requests destined for the associated port end up being ignored (alternatively, a listener may be monitoring and send back a "reset" packet indicating that the request was heard but is being rejected). Additionally, listener applications can be replicated to a different port number (normally outside the "well-known" range), and that application can be made available to clients who know the uncustomary port assignment. Commonly used well-known ports and associated protocols include Telnet on port 23, SMTP (e-mail) on port 25, SSH (secure shell) on port 22, HTTP on port 80, and FTP on ports 20 (data) and 21 (control).

When a request is received using the appropriate protocol with the proper virtual port address, the listener sets up an application of the proper type and assigns an unused virtual port address outside the well-known range that will be used by the session. It then sends a reply to the requesting host (to the virtual port address from which the request was received) including the virtual port address assigned to the application it just set up. In special circumstances, the listener application can handle all requests itself. The web is an example of such stateless operation. For example, with SMTP on port 25, the e-mail system being used (like Hotmail) has a setting for an SMTP server. When an e-mail is sent, a connection is created to that SMTP server over port 25, the message is transferred, and the connection is closed. After that, the SMTP server looks up the destination host for the e-mail

Please click on the OSI Overview button to begin.

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(the part of the e-mail address after the @ sign) and connects to that SMTP server, also over port 25. The mail is transferred to this new server and delivered to the appropriate user.

When both sides of client and server applications establish a port connection, the communication has been established in a socket connection. A socket connection is established when both Internet Protocols (IP) and their port connections are connected to communicate between those two communication nodes. Every communication connection starts in this fashion to exchange any communication data. The receiving node always has to have an open and listening port to accept a connection request from the sending node. While both of these nodes establish a TCP/IP connection, a three-way handshake (SYN, SYN-ACK, ACK) takes place to properly ensure that it is a connection-oriented establishment prior to transmitting any data. In a three-way handshake, the originator of the connection sends a packet that flags the TCP as SYN (for synchronize) set. This is called a SYN packet. The server will reply with a SYN/ACK packet, and the connection originator replies with an ACK (for acknowledge) packet. For example, this handshake process is similar to our own conversations with another person:

Me: Hello? Are you there? (SYN) Other person: Yes, I'm here. (SYN/ACK) Me: Good! I need to talk to you about …(ACK)

Figure 4.4 The Handshake Process

When transmitting data in this fashion, it ensures data integrity and delivery guarantee, since TCP will retransmit until the receiver acknowledges the reception of the packet. You can see that there is a fair amount of preparation prior to transmitting any real data in order to establish a guaranteed delivery. The data guarantee is the reason why the Internet is using the TCP/IP connection for most of its routing protocols, and why the growth of the Internet has been exponential.

Note that the protocols used at the lower layers may be either connection-oriented or connectionless. Certainly, the message to the listener application, because of the simplicity of the job the listener performs and the minimal amount of data required to perform it, does not need to have a pre- established connection. TCP is actually the connection-oriented protocol at the transport or host-to-host layer. The connectionless protocol at the same layer is known as UDP (User Datagram Protocol).

TCP/IP has an architectural difference from the OSI model that should be mentioned: Layers can be bypassed. The OSI model has a strict rule that a layer (or sublayer) must always be present, even if all the service requests result in duplication of the request to the next lower layer—essentially a null layer. TCP/IP's architecture permits bypassing unnecessary layers and delivering service requests directly to the module that can act on them.

Figure 4.5 OSI and TCP/IP Protocol Stacks

Figure 4.5 depicts the correlation between the OSI and TCP/IP models and how they correspond to each other when discussing each layer of protocols. Each layer protocol data unit also explains what kind of data is being transmitted in each layer. For example, the first physical layer deals with bits and bytes of raw data on the physical media, such as Ethernet or fiber optic. The data link layer forwards frames of information to other switching topologies. Switching devices run in this data link layer, which is a very popular layer in the local and wide area networks. One of the reasons that layer is popular in the switching technology is that layer 2 technology is very efficient in forwarding frames of information to other switching technologies. Layer 2 technology is proficient in moving data from one network node to the next, since we are dealing with layer 2 rather than layer 3 routing. Moving messages up and down protocol stacks can take processing overhead and time; therefore, using layer 2 is more efficient in speed and quality of service.

Layer 3 deals with the popular protocol data unit, the packets. Routing devices route packets of information based on the routing table and the data packet header information. Routing devices review each packet that arrives and determine where the next hop of network routing will be. Routers keep

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updating their routing table to properly route the packets that arrive at each router. Routers communicate with each other with routing protocols such as Open Shortest Path First (OSPF), Interior Gateway Routing Protocol (IGRP), or Enhanced Interior Gateway Protocol (EIGRP) to keep their routing tables up to date. Using these routing protocols, routers communicate with other routers to exchange their routing tables and make routing decisions based on the current routing tables in each device. There will be constant communication among routing devices to keep all their routing tables up to date. Each organization will manage its own routing zone to establish a routing architecture prior to sending packets to the Internet backbone.

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2. Logical and Physical Diagrams

Logical and physical diagrams of a network depict two distinctive views of network topology. Each diagram will convey the network architecture, but in different views and perspectives in relation to other interconnected network components. Both diagrams will explain how data will be transferred from one network node to the next. In a logical diagram, you will find a conceptual view of the network in a holistic perspective. You will have the entire organizational network design perspective and understand how the network components are interrelated. The device types and network subnets will be shown in a logical diagram. The IPs for the subnet and devices will be labeled, and this logical diagram will not directly match the physical device configuration in the network. Virtual devices will be noted, but should not be drawn as physical devices. In the logical diagram, however, you would not find physical details of the network components and their interconnected relationships with other network devices.

The physical diagram will show you each network component's physical connection and view of each interface. Each device's physical view and its interconnectivity with other network components will be drawn in the diagram.

Table 4.1 Differences between Logical and Physical Diagrams

Differences and Requirements

Physical diagram

Indicates actual devices; the cables, including the cable colors that are connecting devices together; ports that are used; etc.

Logical diagram

Generally more useful than a physical diagram.

The device types and network subnets will be shown in a logical diagram. The IPs for the subnet and devices will be labeled, and this logical diagram will not directly match the physical device configuration in the network. Virtual devices will be noted, but they should not be drawn as physical devices.

Building a telecommunications network requires an understanding of many different technical concepts and components. Now that you have a basic understanding of those concepts and components, we can begin to bring everything together into a logical design and then a physical architecture. The logical telecommunications network design describes the relationship and interdependencies between the various concepts and protocols we have discussed. It will also contain the communication flow throughout the network. The physical architecture will describe the actual components that will be needed to build the network, including media selection, topology, and routing and switching.

Figure 4.6 Logical Network Diagram

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The physical architecture for your telecommunications network will need to be planned, installed, maintained, and diagnosed for any issues that may arise. As we have discussed, a telecommunications network consists of highly complex technologies, and trial and error alone may be insufficient to diagnose a communication and network problem. Rather, specialized tools are required to ascertain the network's health and identify any problem. In addition to maintaining the functionality of the network, you will need to track key performance indicators and metrics to ensure that the network is running at its optimal performance level. Capacity management will be critical to ensure that the network continues to grow as the business requirements continue to change.

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Figure 4.7 is an example of a physical diagram. Each physical component shows its connected endpoints and the actual physical representation. Engineers should be able to trace each component's interconnection and diagnose any communication issues.

Figure 4.7 Physical Network Diagram

Think About It . . .

How would you show your network operations in a conceptual way?

On many occasions, network engineers must be able to show their management and customers what business processes are running within their networks in a graphical depiction. In order to show symbolically what operations are performed in each network, you would represent them symbolically in a logical network diagram. For example, if you are running an e-mail server in a demilitarized zone (DMZ), you would show an e-mail server symbol after the DMZ firewall to show the logical separation between the server and the production network. For another example, to show a biometric authentication in a network, you would draw a biometric symbol in an Active Directory diagram. These conceptual representations may be difficult to convey in a physical diagram.

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3. Network Planning

Any organization planning to design a network will first address its network design goals and objectives. It will determine the network requirements that must be met within the network design. Examples of network requirements include application availability, response time, reliability requirements, and cost. The network design must support the organization's business processes and enhance work productivity. Once the business objectives are laid out, the network must be designed to support those objectives. Business managers and network design engineers will then communicate what will be necessary to complete network planning. Typically, business stakeholders will draft network requirements in order to support their business goals and objectives prior to approving their network planning. The network requirements will specify the technical, functional, and operational criteria necessary in order for the network to support the organization. The stakeholders will then communicate with the network designer to ensure that the organizational network objectives and goals are translated correctly and accurately.

Network designers will then take the network design planning and ensure that all business goals and objectives are met in terms of network design and architecture. The designers will ensure that all business aspects are accommodated by the network design and planning.

Once the network design is completed, it will need to be tested and implemented. The network implementation plan consists of determining how to implement the network design and ensuring that the design layout is correctly implemented without any discrepancies from the design. While testing, network engineers may find errors in the network design and will need to correct them prior to implementation. Design engineers and implementation engineers will be working together to remove any discrepancies they have discovered during the implementation phase. During implementation, engineers will ensure that all aspects of design will be correctly and completely carried out, and both design and implementation engineers must agree that the next part of the network deployment is in accordance with the initial network requirement analysis.

When network engineers complete the implementation of the network design, maintenance will take priority over network planning. Maintenance is an ongoing process to stay current with network operations and enhancement. Engineers will maintain and monitor the network's health and performance

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in order to support organizational goals and objectives. Enhancements to the network will be applied as needed after a change management board approves alterations. At this point, any changes to the network will be controlled and updated if they are determined to be beneficial.

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