1. Any Questions?

2. Chapter 16-WAN Concepts WAN Technologies
IP Services for Internet Access

3. Do I know this?
Go through the Quiz-
5 minutes

4. 1. Which of the following best describes the function of demodulation by a modem?
a. Encoding an incoming analog signal from the PC as a digital signal for transmissio into the PSTN
b. Decoding an incoming digital signal from the PSTN into an analog signal
c. Encoding a set of binary digits as an analog electrical signal
d. Decoding an incoming analog electrical signal from the PSTN into a digita signal
e. Encoding a set of binary digits as a digital electrical signal

5. 2. Which of the following standards has a limit of 18,000 feet for the length of the local loop?
a. ADSL
b. Analog modems
c. ISDN
d. Cable Internet service

6. 3. Which of the following is true regarding the location and purpose of a DSLAM?
a. Typically used at a home or small office to connect the phone line to a DSL router
b. Typically used at a home or small office instead of a DSL router
c. Typically used inside the telco’s CO to prevent any voice traffic from reaching the ISP’s router
d. Typically used inside the telco’s CO to separate the voice traffic from the data traffic

7. 4. Which of the following remote-access technologies support specifications that allow both symmetric speeds and asymmetric speeds?
a. Analog modems
b. WWW
c. DSL
d. Cable modems

8. 5. Which of the following remote-access technologies, when used to connect to an ISP, is considered to be an “always on” Internet service?
a. Analog modems
b. DSL
c. Cable modems
d. All of these answers are correct.

9. 6. For a typical Internet access router, using either cable or DSL, which of the following does the router typically do on the router interface connected to the LAN with the PCs in the small or home office?
a. Acts as a DHCP server
b. Acts as a DHCP client
c. Performs NAT/PAT for the source address of packets that exit the interface
d. Acts as DNS server

10. 7. For a typical Internet access router, using either cable or DSL, which of the following does the router typically do on the router interface connected toward the Internet?
a. Acts as a DHCP server
b. Acts as a DHCP client
c. Performs NAT/PAT for the source address of packets that exit the interface
d. Acts as DNS server

11. 8. This question examines a home-based network with a PC, a DSL router, and a DSL line. The DSL router uses typical default settings and functions. The PC connected to the router has IP address This PC opens a browser and connects to the web server. Which of the following are true in this case?
a. The web server can tell it is communicating with a host at IP address
b. The PC learns the IP address of the web server as a public IP address.
c. The address would be considered an inside local IP address.
d. The address would be considered an inside global IP address.

12. Any Questions?

13. WAN Connection DSL, Modems, Cable, ATM PSTN CO
Designed for Voice-Analog
Can support data now
DSL, Modems CO
Convert to Digital
Pg 516

14. Modem Modulator/Demodulator Modem dials ISP router and gets an IP
Convert the digital signal from computer to analog signal for local loop
Modem dials ISP router and gets an IP
Pg 518

15. DSL Just connectivity-utility service
Can’t dial any number like modem
DSL allows analog voice signals and digital data signals to be sent over the same local loop wiring at the same time.
The local loop must be connected to something besides a traditional voice switch at the local CO, in this case a device called a DSL access multiplexer (DSLAM).
DSL allows for a concurrent voice call to be up at the same time as the data connection.
Unlike modems, DSL’s data component is always on; in other words, you do not have to signal or dial a phone number to set up a data circuit.
Pg 519

16. DSL
At CO
DSLAM separates out DSL signal on higher frequencies
The distance between the CO and the consumer (the longer the distance, the slower the speed)
The quality of the local loop cabling (the worse the wiring, the slower the speed)
The type of DSL (each standard has different maximum theoretical speeds)
The DSLAM used in the CO (older equipment may not have recent improvements that allow for faster speeds on lower-grade local loops) Pg

17. Cable Internet Similar idea to DSL Higher overall speed
Shared access on head-end

18. Summary
Pg 525

19. Asynchronous Transfer Mode
Packet Switching (like frame relay)
Or Switching technology in core network
ATM connection like Frame
VCs
48 byte payload and 5 byte header
53 byte CELL

20. Packet vs. Circuit Switching
Pg 527

21. Ethernet as WAN
Metro Ethernet
Limited to contract speed

22. Address assignment on Internet routers
The Internet-facing interface needs one public IP address so that the routers in the Internet know how to route packets to the access router.
The ISP typically assigns that public (and globally routable) IP address dynamically, using DHCP.
The local PCs typically need to dynamically learn IP addresses with DHCP, so the access router will act as a DHCP server for the local hosts.
The router needs a statically configured IP address on the local subnet, using a private network number.
The local LAN subnet will use addresses in a private network number.
Pg 529

23. Routers and DHCP
Pg 530

24. Network Address Translation
Hides the Private addresses behind the public address of the router
NAT/PAT server keeps track of TCP/UDP port numbers of outgoing requests and maps them to a port on the outgoing public address

25. NAT

26. What PAT does
More generally, the PAT feature causes the router to translate the source IP address and port for packets leaving the local LAN, and to translate the destination IP address and port on packets returning to the local LAN. The end result is that, as far as hosts in the Internet are concerned, all the packets coming from this one customer are from one host ( in Figure 16-10), for which all the routers in the Internet should have a matching route. This allows the ISP to conserve public IPv4 addresses.
Pg 534

27. PAT Terminology
Inside host: Refers to a host in the enterprise network, like PC1 and PC2 in the last few figures.
Inside local: Refers to an IP address in an IP header, with that address representing a local host as the packet passes over the local enterprise network (not the Internet). In this case, and .102 are inside local IP addresses, and the packets at steps 1 and 4 in Figure show inside local IP addresses.
Inside global: Refers to an IP address in an IP header, with that address representing a local host as the packet passes over the global Internet (not the enterprise). In this case, is the one inside global IP address, and the packets at steps 2 and 3 in Figure show the inside global IP address.
Inside interface: The router interface connected to the same LAN as the inside hosts.
Outside interface: The router interface connected to the Internet.

28. Any Questions?