Chapter 2 Network Management

Over the past decades there has been tremendous growth in the size and complexity of networks. networksNetworks have formed channels of communication to cover the whole world. Many companies have brought out packages using their own protocols and standards. To provide communication between different brands the International Standards Organisation has sought to get these different vendors to work together. The international standard for data networks as recommended by the ISO is Open Systems Interconnection (OSI).OSI

Section 2.1 breaks the network up into layers. Section 2.2 explains why network management is needed and introduces section 2.3 which breaks management up into types. Finally section 2.4 gives a brief look at Telecommunications Network Management.

2.1 Anatomy of a Network

Figure 2.1: The layers of a network

2.1.1 Physical Layer

The wired up network elements. This includes routers and switches.

2.1.2 Network Layer

The protocols that get the elements to communicate. This would handle ways to optimise routing. subnetworksTo increase security and aid management the network may be divided into subnetworks. This layer is where the routing table is stored that directs packets to the right subnetwork.

2.1.3 Services

The programs that operate on the network. For example: to check quotas, accounts, traffic, planning. Generally these monitor the network and keep statistical data.

2.2 Management

To allow different layers to interact
To keep track of a large number of elements
To automate the interaction between different networks
To manage faults that may arise
To reduce the costs of supervising a network
To improve customer care and efficiency

The management system provides services, not only to the network operator, but also to the end users.

2.2.1 Management Model

Management sits above the network. Agents inside the network provide information at the request of the manager. Agents can also perform operations on the managed objects at the request of the manager.

The user accesses the manager through a top layer. The Manager confers with agents in the lower layer. This process can be defined recursively with the agent below acting as a manager to a further lower level. Finally the agent interfaces with the managed objects, which may be hardware devices, switches, routers and so on.

2.3 Functional Areas of Management

To help bring about better compatibility between different vendors the OSI OSI have formulated five functional areas of management. They are as follows:

Fault Management
Configuration Management
Accounting Management
Performance Management
Security Management

2.3.1 Fault Management

The first task of fault management is to locate faults as they occur. This becomes difficult since it has to rely on alarms which are the symptoms of faults. One fault may lead to many alarms generated as messages traversing the network encounter difficulties.

The next task is to take steps to repair the faults, or at least minimise their impact on the system.

2.3.2 Configuration Management

Keeping tabs on all the elements of the network. On a small scale, remembering where your desktop computer is and where you have your printer, mouse and modem is an easy task. On the scale of a large network there needs to be a comprehensive system for keeping track of all the components of a network. This includes the make and model of each component and their physical location.

2.3.3 Accounting Management

Billing, keeping stock of every individual's use of the network. Keeping track of individual differing requirements. For a system with many users there needs to be a system whereby the users may check their quotas and change their preferences for their accounts. In a telecommunication network this is especially important, considering that almost every household in the area has an account to maintain.

2.3.4 Performance Management

Keeping up with traffic information, make predictions about peak usage, modifying things to optimise efficiency. Statistics are collected about the available bandwidth of different channels at different times. These have to be processed into meaningful information about the network to help plan around heavy usage.

2.3.5 Security Management

Keeping the password information, encryption of data, monitoring in case users are accessing things they shouldn't. This is important, not only for personal privacy, but also for commercially sensitive information.

2.4 Telecommunications Management Network

TMN

ITU-T has introduced a standard of network management for use in telecommunications. This enables complex information to be accessed globally.

One difference between TMN and conventional network management is that the management network is separated from the telecommunications network. The network for transferring management information is called the Data Communication Network (DCN). Figure 2.2 shows how the DCN presides over the telecommunications network.

Telecommunication networks are designed for telephony rather than data transfer. Rather than using an asynchronous data transfer by packets of varying length, the telecommunication network provides an isochronous type of service which means all the signals are of the same length and sent in a continuous sequence. This requires synchronisation. [Pras etal., 1999]

Figure 2.2: The TMN and the telecommunication network

2.4.1 Four Management Architectures

To better understand how things fit together TMN has described four architectures to classify tasks. They are each complementary ways of organising the multitude of functions that go into managing a Telecommunications Network.

Functional Architecture

Here you can find the functions that the manager will use to monitor the various network elements. Different function blocks are defined for making the applications modular. Function blocks are designated to accessing network elements, interfacing with workstations and other processing tasks.

Each of these `talk' through reference points to obtain and pass on information. The reference points are standardised within the TMN across different vendors. This makes managing heterogeneous networks possible.

Physical Architecture

This maps to the functional layer. Each of the functions is represented by a physical device. For example, the function that mediates between two platforms in the functional layer has a corresponding mediating device in the physical layer.

Information Architecture

Here information is represented as objects. Object oriented programming is a useful way to do network management. The managed objects have attributes which can be accessed by the manager.

Logical Layered Architecture

This architecture is to help understand the layers that go into a network. In the previous chapter we saw how the network elements are the lowest level, then management layers are built on top. In Figure 2.3 the manager - agent functions are shown passing information between the layers.

Figure 2.3: Logically Layered Functions

Each of these layers deals with aspects of the five OSI management areas, fault, configuration, accounting, performance and security. For example, the Element Management Layer would work collecting data about account details, faults arising, changes in configuration, high traffic conditions and access to security sensitive elements. Splitting up these management areas into the layers of a network helps to see where different functions fit.

Fault management works on all the layers, from the network elements to the business layer. Here we can see how one management area is implemented in all the logical layers of a network.

The element layer is concerned with logging alarms as they occur.
The network layer provides a view of the network as a whole, independent of the different vendors.
The service layer is there to maintain the network. As faults arise the service layer may instruct the network layer to reroute some paths to minimise the disruption to the network. The service layer also has to report to the clients with updated information about the faults.
The business layer supports decisions about the allocation of resources and plans how to best fix the faults. They bear in mind the trade offs between the cost of investment and the benefits to the network.

2.5 Summary

Network management is a complex task which has been broken up by functional areas and also by layers of abstraction. Applications pass information to each other in the same layer or to different layers by passing information to the relevant managers.

Fault management is important in the smooth running of any network. It spans from the physical elements of a network right up to the planning of the business. This work is mainly concerned with fault management on a network level.