Review Questions

1.       What caused the development of several models of IP WANs (pure IP, IP over ATM, IP over Frame Relay, and IP over MPLS)?

Each of the models is answering the particular problem of the IP WANs. Pure IP WANs had been very popular for a long time because the Internet wasn’t a commercial tool then and transferred only elastic non-critical traffic of e-mails and ftp archives of the education and research community. The IP over frame relay/ATM models appeared in mid 90s when the Internet started to play a role of a commercial tool as well. Since that time the support of QoS and traffic engineering started to gain a significant importance as mechanisms of guaranteed quality of providers’ services and frame relay and ATM played a role of the QoS/traffic engineering supporting layer  for the combined IP networks at that time.  When the optical high speed links became rather cheap in the end 90s the pure IP model returned to the scene again as a prime one as oversubscribed network didn’t require QoS and traffic engineering support. The IP over MPLS model combines the benefits of the datagram and the virtual circuit approaches providing strong background for QoS and traffic engineering.  


2.       Is it correct to state that an IP-over-ATM or IP-over-Frame Relay network consists of two levels of packet-switched networks and that an IP-over-MPLS network consists of only one layer? Justify your answer.

No, an IP-over-MPLS network also consists of 2 layers: the layer of IP routing and the layer of the MPLS switching; however these layers in the IP-over-MPLS model are integrated more tightly.

3.       Compare the main properties of HDLC and PPP. Which of them are advantages, and which ones are drawbacks, under which conditions?

4.       What is the purpose of the connection establishment procedure in the HDLC protocol and in PPP?

5.       What is the mechanism used by HDLC for restoring lost or damaged packets?

Sliding window

6.       What are PPP multiprotocol functions?

To transfer packets of different protocols such as IP, IPS, NetBIOS etc.

7.       Why is the mutual authentication procedure provided by PPP needed?

To minimize a risk of a session establishing with unauthorized network devices  which can try to intercept traffic.    

8.       List the main stages of the router configuration procedure for operation using a
leased line.

9.       What are the functions of the АТМ layer in the IP-over-ATM model?

To provide QoS and traffic engineering functionality.

10.    Which new ideas were implemented in the IP switching technology?

Combining of the virtual circuit functionality of the second layer and the IP routing functionality of the third layer. Besides of this, both were tightly integrated.

11.    Which ideas of IP switching were preserved in MPLS, and which ones were modified?

The preserved ideas: combining the 2nd layer switching and IP routing functionality in the same device; the use of IP routing protocols for topology learning; forwarding on the basis of labels. The concepts changed: the data-driven creation of virtual circuits – it was replaced by the preliminary circuit creation according to a network topology;  taken into account the short-lived and long-lived character of the flows.

12.    List the main functional moduls of an IP router that are used in an LSR.

13.    What new possibilities are ensured by the use of the MPLS label stack?

·         An arbitrary number of the hierarchy of LSPs.

·         Effective way of multi-domain networks’ building.

·         Implementation of an additional functionality, e.g. VPN


14.    Suppose that an LSR uses the Ethernet frame format. Does this mean that this device forwards frames on the basis of the routing table obtained on the basis of the IEEE 802.1D standard?

No, LSR forwards frames on the basis of a MPLS forwarding table, which is not formed according the IEEE 802.1D standard rules.

15.    How is it possible to establish an LSP passing through several MPLS domains?

Manually or automatically using a label hierarchy.  

16.    What is the difference between MPLS IGP and MPLS TE?

The MPLS IGP application aims to accelerate the forwarding of data along the same routes that a normal IP forwarding uses. The MPLS TE application tries to change the routes in the way which providesw the most rationale utilization of network resources.

17.    Is it necessary to manually configure LSRs for operation in MPLS IGP?

No, most jobs in this mode  are fulfilled automatically by Label Distribution Protocol (LSP).

18.    What is the analogue of MPLS TE tunnels in the АТМ and Frame Relay technologies?

Permanent Virtual Circuits (PVCs)  

19.    Is it possible to pass part of the traffic using normal IP forwarding in an
MPLS-enabled network?

Yes, it is.

20.    List the groups of network management system functions according to the
X.700 standard

21.    Are there any differences between network management systems and systems management systems? If yes, what are those differences?

22.    Which functions in a network management system are delegated to an agent and which functions are carried out by a manager?

23.    List the standard MIBs.

24.    Which types of names are used in SNMP for MIB objects — symbolic or numeric?

25.    When is the Trap command used?

When an agent discovers a critical change in a controlled object state.


1.       Assume that you are an IP WAN network architect. What questions would you ask a customer that wants you to develop a large IP network so that you can choose the type of a multilayer model (non-overlay IP, IP over ATM, IP over Frame Relay, or IP over MPLS)?

2.       Measurements have shown that the BER value of a communications link is 10−4. Which type of a protocol would you choose for this link — HDLC or PPP?

HDLC as this protocol is able to correct errors using  frames retransmission on the basis of the sliding window algorithm.

3.       Compose a forwarding table for LSR1 shown in Fig. 22.13.

Let’s assume that the interface s0 connects LSR1 to the external network; the interface s1 leads to LSR2 and the interface s2 leads to LSR4. Let’s choose the label 237 for LSP1 and  the label 141 for LSP2.  Please pay attention t0 the fact that packets entering a network through the interface s0 don’t have labels as LSR1 is LER for both LSPs.  


Input interface

Destination IP address


Next hop























4.       What initial data have to be collected for the network shown in Fig. 22.14 to enable a network administrator to solve a traffic engineering problem? Suggest your version of this data and solve the formulated problem.