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This wide array of protocol support was one of the advantages of SMDS. For example, IP could use the multicast function in SMDS to perform ARPs, which saved a great deal of time normally required for manual configuration.

The following output demonstrates a typical SMDS interface configuration. Note that both static and multicast entries are present—the administrator could rely on multicasts to the group address for all traffic, yet in this instance static entries for each element were chosen to reduce queries and to facilitate troubleshooting. Also note that both IP and IPX are configured for this SMDS group.

interface Serial1/1 description SMDS Interface ip address encapsulation smds smds address c141.5555.1234 no smds dxi-mode smds static-map ip c141.5555.1111 smds static-map ip c141.5555.1120 smds static-map ipx 100.0000.3048.e909 c141.5555.1120 smds multicast IP e141.5555.0001 smds multicast ARP e141.5555.0001 smds multicast NOVELL e141.5555.0001 smds enable-arp ipx network 100 ipx output-sap-filter 1000

As with other WAN technologies, SMDS should be evaluated on availability, equipment, and cost factors. Note that many vendors, including Pacific Bell/ Southwest Bell, will no longer provision SMDS for new installations.


This chapter provided a substantial background into three different WAN technologies: Frame Relay, ATM, and SMDS. It also provided an overview of dedicated leased lines, which are also common in WAN design. As with most factors in network design, architects need to be familiar with the scalability and costs associated with their designs while considering the business factors and services that are required.

Specifically, readers should come away from this chapter with a comfortable understanding of the following:

  The WAN design factors
  Serial line encapsulations
  Frame Relay
  Frame Relay PVCs
  Inverse ARP
  Nonbroadcast multiaccess networks
  Cisco’s StrataCom product line
  Switched virtual circuits
  Permanent virtual circuits
  The AAL 5 specification
  The ATM cell format

The next chapter builds upon some of these concepts as it addresses the remote access technologies, including ISDN and X.25. Generally, these services are of lower bandwidth than ATM and Frame Relay.

Review Questions

1.  In a flat configuration, the StrataCom switch can support how many ports?
A.  12
B.  24
C.  48
D.  192
2.  Which product would be most appropriate for terminating low-bandwidth user services?
D.  eIPX
3.  Which WAN technology is best suited for integrating voice, video, and data?
A.  Frame Relay
4.  Which of the following WAN technologies is being phased out?
C.  Frame Relay
D.  T1
5.  A cell in ATM AAL 5 is:
A.  48 bytes long
B.  53 bytes long
C.  Variable in length, but never more than 48 bytes long
D.  Variable in length, up to a maximum of 1514 bytes
6.  The payload section of an AAL 3/4 cell is:
A.  5 bytes
B.  44 bytes
C.  48 bytes
D.  53 bytes
7.  The header in AAL 5 is:
A.  5 bytes
B.  9 bytes
C.  48 bytes
D.  53 bytes
8.  Which of the following is not true of an ATM cell formatted within the AAL 5 specification?
A.  It operates with PVC and SVC circuits.
B.  It provides 48 bytes per cell for payload.
C.  It provides 5 bytes per cell for header.
D.  It provides a checksum for the cell payload.
9.  In AAL 5, error checking includes:
A.  The ATM header
B.  The ATM payload
C.  Both the ATM header and the ATM payload
D.  Neither the ATM header nor the ATM payload
10.  Frame Relay provides a better pricing model for designers because of which features?
A.  Single destination per physical interface and per-mile charges
B.  Multiple destinations per physical interface and per-mile charges
C.  Multiple destinations per physical interface and distance-insensitive charges
D.  Single destination per physical interface and distance-insensitive charges
11.  The BPX switch employs which of the following?
A.  A 1.2Gbps frame-based backplane
B.  A 3.6Gbps backplane link via the Phoenix ASIC
C.  A redundant 1.2Gbps cell-switching bus
D.  A redundant 9.6Gbps crosspoint switch matrix
12.  StrataCom switches do not provide which of the following services?
B.  Video
D.  Voice
13.  Rather than disabling split-horizon, the designer of a Frame Relay network could design:
A.  A full mesh with separate subnets for each PVC
B.  A partial mesh with separate subnets for each PVC
C.  A full mesh with a single subnet
D.  A partial mesh with a single subnet
14.  Which of the following is not an encapsulation for Frame Relay?
B.  Frame Relay Forum LMI
C.  ITU-T Q.933 Annex A
D.  ANSI T1.617 Annex D
15.  Inverse ARP performs which function?
A.  Dynamic addressing of router interfaces
B.  Dynamic mapping of Layer 3 addresses
C.  Frame Relay control signaling
D.  ATM LANE address mapping
16.  NNI cells do not contain which of the following?
17.  The AAL 3/4 specification provides more user bandwidth than AAL 5. True or false?
A.  True
B.  False
18.  The structured design model for StrataCom switches employs which concept?
A.  Hierarchical domain model that supports up to 384 nodes
B.  Full-mesh model that supports up to 384 nodes
C.  Hierarchical domain model that supports up to 64 nodes
D.  Partial-mesh model that supports up to 64 nodes
19.  DLCIs must be the same throughout the entire PVC. True or false?
A.  True
B.  False
20.  Generic Flow Control provides which of the following features?
A.  Congestion control
B.  Buffering control
C.  Path determination for congestion control
D.  None of the above

Answers to Review Questions

1.  C.
2.  A.
3.  C.
4.  B.
5.  B.
6.  B.
7.  A.
8.  D.
9.  A.
10.  C.
11.  D.
12.  C.
13.  B.
14.  A.
15.  B.
16.  C.
17.  B.
18.  A.
19.  B.
20.  D.

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