Chapter Summary and Review

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In this chapter, we have discussed the importance of measuring, marking, and policing packets in a data network, and we have identified the three measurements historically used for measuring QoS – latency, jitter, and dropped packets. In addition, you have seen that QoS can also be measured with perceived quality measurements, such as MOS.

Packets can be marked at several levels: in the Local Area Network using 802.1Q/p, in an Intranet using DiffServ, and over the WAN using MPLS. Marking packets alone does not provide for QoS. In addition to marking, you must check for instantaneous bandwidth and also reserve bandwidth. Even with these protocols running, a policing function is needed.

To police networks, a policy-based device is needed. Some systems have built-in policy systems, such as a multi-layer system of switches or a stand-alone, policy-based switch. In all cases, in order to achieve true Quality of Service, packets must be managed (i.e., packets must be marked, classified, and policed throughout the network).

The pendulum swings both ways. Those in the service-and-hospitality industry have found that, as money gets tighter and people travel less, Quality of Service is once again an issue.

It the telecommunications world, that pendulum can swing from inexpensive bandwidth to expensive bandwidth. As the number of carriers decreases under financial hardships, you will find that BW once again becomes expensive, and that the management of bandwidth and true network QoS will need to be achieved.

Between the combination of protocols and policy management, true QoS is a realistic goal that can be achieved in data networks.

Answer the following questions.

1. 

List two methods for mapping ToS to MPLS services.

there are two methods: the l-lsp and the e-lsp methods.

2. 

Explain the use of RED and its effect on traffic shaping.

random early detection (red) is a threshold monitoring system. traffic between the lower and upper threshold is eligible to be randomly discarded. all traffic over the upper threshold is discarded and traffic below the lower threshold is not discarded. red takes traffic as shown in figure 8.20 and shapes it to look like figure 8.21 . red is an effective method to keep routers out of the non-linear mode of operations.

3. 

Explain the challenges of mapping DiffServ to EXP bits.

diffserv has six usable bits: three bits are used for class and three are used for drop precedence. mpls uses 3 bits for exp field. it is difficult to map 6 bits into a three-bit field.

Answers

1. 

There are two methods: the L-LSP and the E-LSP methods.

2. 

Random Early Detection (RED) is a threshold monitoring system. Traffic between the lower and upper threshold is eligible to be randomly discarded. All traffic over the upper threshold is discarded and traffic below the lower threshold is not discarded. RED takes traffic as shown in Figure 8.20 and shapes it to look like Figure 8.21. RED is an effective method to keep routers out of the non-linear mode of operations.

3. 

DiffServ has six usable bits: three bits are used for class and three are used for drop precedence. MPLS uses 3 bits for EXP field. It is difficult to map 6 bits into a three-bit field.



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Rick Gallagher's MPLS Training Guide. Building Multi-Protocol Label Switching Networks
Rick Gallahers MPLS Training Guide: Building Multi Protocol Label Switching Networks
ISBN: 1932266003
EAN: 2147483647
Year: 2003
Pages: 138

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