Network Elements

The previous sections have introduced networks with a brief overview of some of their components and management infrastructure. This section examines NEs a little more closely. Figure 2-6 illustrates (in no particular order) some of the typical software components that combine to make up an NE.

Figure 2-6. Typical NE software components.

An example of an NE is an intelligent line card, which is hosted inside another system, such as a PABX, ATM/MPLS switch, or IP router. An intelligent line card is essentially a computer inside another computer and may contain millions of lines of source code hosted on an embedded real-time operating system, such as pSOS or VxWorks. Some characteristics of intelligent line cards include the following:

• They can extend the lifespan of the host by adding advanced functions such as SNMP and VoIP for a PABX.

• They can take a long time to develop.

• Operators like to extract the maximum performance from them ”for example, port bandwidth.

• They increasingly incorporate numerous layer 1, 2, and 3 protocols.

An NMS interacts with the SNMP agent in Figure 2-6, getting and setting MIB object instances and also receiving notifications. Clearly, the SNMP agent in the NE competes for compute and I/O resources with all the other onboard software entities. During times of high device loading, the SNMP agent may become starved of resources. This is a bad thing because the management facility can become essentially disabled. High loading can occur when:

• Many voice calls are in transit through a PABX.

• Large numbers of ATM virtual circuits are transporting many ATM cells .

• Large numbers of IP packets are in transit across a router.

• Network topology changes result in routing protocol convergence.

Compute resource depletion is one type of NE congestion. It can sometimes be cured by some combination of changing process priority, adding extra memory, or adding extra processing power. A more subtle problem is one in which the number of managed objects becomes so great that the NMS finds it hard to keep up with changes. This is the general area of scalability and is discussed in Chapter 3, "The Network Management Problem."