Outside plant represents cabling, interfaces, and other infrastructure outside of the CO. F1 feeds the SAI and F2 typically connects directly to the subscriber drop cable. SONET or SDH rings sometimes are used to feed an SAI or provide connectivity between COs.
Frequency Division Multiplexing (FDM), an analog technology, was replaced with the more efficient and secure Time Division Multiplexing (TDM).TDM is used in various implementations throughout the communications industry.
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The SS7 stack is similar to the OSI network model and through SIGTRAN standards can also operate over IP. Security measures should be taken with all PSTN signaling protocols.
PSTN Call Flow
Digital switches still need sophisticated circuit detection capabilities for call processing.
When making SIP-based calls through an ISP, one’s call may terminate several hundred miles away and not at the local central office.
SIP-to-SIP based calls happen entirely over IP networks. SIP-to-PSTN calls start on an IP network and then get handed off to the PSTN.
PSTN Protocol Security
Use extreme caution around pre-SS7 signaling protocols like ITU-T 5 or R2 (also known as CCITT 5 or R2 because of their toll fraud potential.
Even with SS7, take precautions to limit potential damage from fraudulent or corrupted data that could arrive in your SS7 network from other carriers.
Do not use ANI or any other ISUP or QSIG information for authentication.
Q: Is the PSTN of today able to handle the demands of the customers and tech-nology of the future?
A: The answer is yes, since telecommunications companies are always enhancing the PSTN by providing more affordable or fully featured services to their customers.These changes often increase reliability while adding the capacity to offer more services.Tomorrow’s PSTN is likely to have much more packet-based technology than ever imaged. Now communications companies are burying fiber-optic cable and installing broadband wireless antennas as additional ways to deliver rich bandwidth, and cable companies often have outside plant capabilities that rival that or the primary LEC.
Q: Why is fiber-optic cable a better delivery medium than coaxial cable or twisted pair mediums?
A: Fiber-optic cable allows carriers to deliver services farther from central offices and is not readily affected by lightning strikes like copper wire, though
WDM can offer more capacity through a single fiber than a single CO could sustain in copper 15 years ago. Delivering services further from the central office allows carriers to condense network equipment, reduce service truck roll outs, and provide more service to more people for a cheaper cost. And the extra bandwidth increases the scope and range of network capabilities available to all of us.
Q: Has VoIP been used by carriers prior to end-user deployments?
A: Yes, for some time large carriers have used VoIP to deliver calls within their core networks for long distance and toll calls. Bringing the technology to the rest of us took some considerable planning, significant costs, and a vision that VoIP would be the next huge push in the delivery of voice traffic.
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Frequently Asked Questions
The following Frequently Asked Questions, answered by the authors of this book, are designed to both measure your understanding of the concepts presented in this chapter and to assist you with real-life implementation of these concepts. To have your questions about this chapter answered by the author, browse to www.syngress.com/solutionsand click on the “Ask the Author”form.
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Q: Should I be worried about my carrier’s SS7 network?
A: In general, no. But as more carriers connect and that network moves from its own dedicated, dark fiber and on to shared IP networks, there should be more attention paid to security and associated SS7 standards. It’s not a problem yet, but if the standards and industry best practices aren’t ready to implement in a few years we could see some disastrous consequences.
Q: Can I really trust my caller ID?
A: Sure, about as much as you can trust your e-mail. It won’t lie to you every day but it’s not hard to fool if you’re determined.
Q: I’d like to try phone phreaking or blueboxing sometime. Where can I go to find out more?
A: First of all, just don’t do it. It’s way too easy to get caught, and most of the old techniques won’t work. If you’re determined, you won’t find it hard to get the information you’re looking for if you Google the right names in this chapter. Personally, I think it’s more fun reading the history anyway.
Q: I heard that Kevin Poulsen still drives the Porsche 944 he nabbed from KIIS.
Is that true?
A: According to several reports, he’s been spotted in a red Porsche from time to time.
Q: People that sell me network equipment are always telling me that “circuit” is dead. Is that really true?
A: Let’s put it this way: without a live circuit to run on, the Internet is dead.
Any questions?
P.S. Anyone who really knows about packet and circuit knows that they both need each other in the end.
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H.323 Architecture
Solutions in this chapter:
■ The H.323 Protocol Specification
■ The Primary H.323 VoIP-Related Protocols
■ H.235 Security Mechanisms
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Summary
Solutions Fast Track
Frequently Asked Questions
Introduction
VoIP protocols can be classified according to their role during message transmission.
H.323 and SIP are signaling protocols—that is, they are involved in call setup, tear-down, and modification. RTP and RTCP are media transport protocols, and are involved in end-to-end transport of voice and multimedia data.TRIP, SAP, STUN, TURN, and so on comprise a group of VoIP-related support protocols. Finally, because H.323 mediated VoIP relies upon the underlying transport layer to move data, more traditional protocols such as TCP/IP, DNS, DHCP, SNMP, RSVP, and TFTP are required.