Resolving Issues with Isdn Bri

Just as with any technology, there are many things that can go wrong on an ISDN circuit, particularly a BRI circuit that is weighed down with services. This section is intended to serve as a set of pointers for troubleshooting BRI circuits and not just Cisco equipment. First, make sure that your SPIDs and your switch type are correct. Even some vendor equipment that employs auto-SPID download can malfunction and cause a SPID mismatch. You also want to make sure that the SPIDs given to you by...

Switched Multimegabit Data Service 372

SMDS Features 376 Addressing 376 Multiple Access Speeds 376 Seamless Internetworking of Network Layer Protocols 377 Internetworking LAN Protocols over SMDS 405 Resolving SMDS Problems 407 DXI Problems 407 SNI Problems 408 Multiple Interfaces in the Same Group and the Pseudo-LAN Serial Problem 409

Dribbling Errors

Dribbling errors occur usually one at a time (spaced by milliseconds to seconds), and continue to occur over any given timeframe. To determine if errors are dribbling, inspect the total DSL trained-up time and errored-seconds counters. If a unit has been trained for 1 hour, has reported 1000 errors, and 1000 errored seconds, the errors are dribbling. If the unit has been trained for 1 hour, has reported 100 errors, and 1 errored second, the errors are bursty. To treat a steady stream of...

Minimum Cell Rate MCR

If you have been considering the PCR as a counterpart to Frame Relay's CIR, consider the relationship between PCR and MCR. Although the network allows the user to burst up to the PCR when such bandwidth is available, network connections that are based on service classes that specify an MCR (see the ABR and GFR sections later in this chapter) commit that although available bandwidth can vary, it should never drop below the MCR. Translate this as meaning that it is not a breach of contract by the...

Circuit Switching

ISDN is referred to as a circuit-switching technology. If you think back to Chapter 2, The Signaling System 7 Network, you'll remember that Signaling System 7 (SS7) operates by routing calls on a hop-by-hop basis. Don't think about the signaling path, but think about the actual path that the bearer traffic takes. The call moves from switch to switch until it arrives at its final destination. After it is there, a circuit path is opened from one end of the call to the other. That circuit remains...

CBR Service Category Definition

The CBR service category is used by connections that request a static amount of bandwidth that is continuously available during the connection lifetime. This amount of bandwidth is characterized by a PCR value. CBR service is intended to support real-time applications that require tightly constrained delay variation (e.g., voice, video, and circuit emulation), but it is not restricted to these applications. In the CBR capability, the source can emit cells at or below the negotiated PCR (and can...

Nfas

NFAS is a function of ISDN that is typically only supported in the U.S. and that allows your equipment to be more efficient with channel use if more than one PRI circuit is in use. The basic premise of NFAS is to take a single D channel and configure it so that it can control multiple PRI circuits (up to 479 B channels). NFAS is limited to 479 B channels because the D channel is only 64 kbps. If you have five PRI circuits coming into the same router, you can use NFAS to reclaim a 64-kbps B...

Frame Check Sequence FCS Field

The FCS field is either a 16 or 32-bit CRC that is calculated over the entire DXI frame except the flags. The CRC calculation is performed using one of the following two-generator polynomials G(x) x32 + x26 + x23 + x22 + x16 + x12 + x11 + x8 +x7 + x5 + x4 + x2 + x1 + 1 A 32-bit CRC value is more accurate in detecting bit errors than a 16-bit CRC. However, because no negotiation mechanism for detecting the CRC value is present, it must be preconfigured to match between the SMDSU and router...

PLCP for DS3 Media

The DS3 PLCP frame is shown in Figure 11-24. The alignment of the DS 3 PLCP frame within the DS3 M-frame is constantly changing. This is because each DS3 M-frame has a duration that is 106.4 usec (see Chapter 7, T3 and E3 Technology), and each PLCP frame averages 125 usec in duration (see the C1 byte description that follows). The PLCP frame can begin anywhere in the DS3 M-frame, as long as the first bit of a PLCP frame nibble (4 bits) immediately follows a DS3 framing bit. The PLCP format and...

Frame Relay Configuration on Cisco Devices

Now that you have learned the Frame Relay basics, this section details how to configure Cisco devices for use with a Frame Relay network. As a quick review, it is essential to know what kind of circuit you are using for the Frame Relay connection. Many Cisco devices that have channel service unit data service unit (CSU DSU) functionality already have Frame Relay capability built into the IOS. Verify that your IOS supports what you need in Frame Relay. It is also important to know what your CIR...

DSL Modem TrainUp and Framing

The start sequence conducted between two modems is referred to as training or train-up. During train-up, DSL modems start with no data interleaving and no line coding. (Interleaving and line coding must be negotiated between the two modems.) The signal-to-noise level is calculated across the DSL spectrum, and a DSL line rate is established based on three essential factors Provisioning DSL modems will not establish a faster DSL rate than what is specified (provisioned) in the DSLAM. The DSL...

Control Bits for Congestion

Occasionally, network congestion can run so completely out of control that the only solution is for the end devices to throttle back on their transmission of frames into the network. An often less agreeable solution is for the network devices to randomly discard frames in an attempt to restore order. Unfortunately, end devices only attempt retransmission, possibly making the situation even worse. Refer back to Figure 9-7, noting the single-bit fields labeled forward explicit congestion...

Building Integrated Timing Supply BITS

BITS is a North American term that describes a building-centric timing system. Also referred to as a Synchronization Supply Unit (SSU), the BITS system efficiently manages the number of timing interfaces within a structure. Without something such as BITS SSU in place, you can feasibly have many different timing sources within the same building because of the number of synchronous links that the building might contain. BITS operates by providing the only ingress and egress external timing...

PLCP for E3 Media

Figure 11-26 shows the E3 PLCP frame format. As expected, the E3 PLCP frame is nearly identical to the DS3 PLCP frame, with the exception being the number of rows (9 instead of 12) and the size range for the trailer field. The derivation of the E3 PLCP trailer size and the payload efficiency are left as exercises to the reader. 2 Bytes 1 Byte 1 Byte 53 Bytes 17 to 21 Bytes 2 Bytes 1 Byte 1 Byte 53 Bytes 17 to 21 Bytes

Why SS7 Was Developed

The introduction of the SSX infrastructure has allowed for the telco to provide a better QoS for its customers. It is intentionally stated as SSX because there are several common channel-signaling systems. From a historical point of view, there was SS4, SS5, SS6, and now SS7. SS4, SS5, and SS6 are legacy systems that are not discussed in detail because they are no longer used and are outside the scope of this book. Prior to the creation of the SSX infrastructure, call control was inefficient....

Answers to Chapter 6 Review Questions

How many DS0s are included in an E1 circuit Remember that there are 32 DS0s. 30 or 31 are for bearer traffic, and the other one or two are reserved for signaling and framing. 31 is not listed as a choice, but it is also correct. a. Incorrect. There are 16 frames in a multiframe. b. Incorrect. There are 24 DS0s in a T1 circuit. d. Incorrect. There are 30 or 31 useable DS0s in an E1 circuit, but not 32 because the first timeslot can never be reclaimed for bearer traffic. 2. What similar function...

DSL Network Architectures

The DSL network architecture is made up of three segments the CPE, the NAP, and the network service provide (NSP). This section contains a brief explanation of the three components. Figure 12-7 shows these three components in a generic DSL network architecture. Figure 12-7 does not show a POTS splitter because it is not a requirement. However, if one were present, it would be placed between the CPE and the DSLAM. Figure 12-7 General DSL Network Architecture

Service Profile Identifiers SPIDs and Telephone Numbers

Possibly the most important single piece of information for a BRI subscriber in the United States is the SPID. SPIDs identify the BRI circuit on the switch along with the circuit ID, and the services that the circuit has assigned to it. For each B channel assigned to the circuit, there is a SPID associated with it, and for each SPID there is an associated telephone number. When you look at the format of a SPID, it looks a lot like a regular telephone number with an added extension. The most...

Answers to Chapter 9 Review Questions

On what technology is Frame Relay largely based Answer ISDN. The specifications and operation of Frame Relay are similar to that of ISDN, and are based off of protocols such as LAPD. 2. Which of the following companies was not a part of the original Gang of Four b. Digital Equipment Corporation IBM was not a member of the original Gang of Four. 3. What is the CIR used for on Frame Relay circuits Answer The CIR identifies the amount of bandwidth that the service provider can guarantee that your...

Answers to Chapter 8 Review Questions

At which layer of the ISDN stack does Q.931 operate Answer Layer 3, and it is roughly equivalent to the Network Layer of the OSI model. 2. What type of device is commonly found between the S and T interfaces Answer An NT2. 3. How does ISDN BRI service provide both transmit and receive on a single pair of wires 4. On a Cisco router, what command would give you the following output 0x8090A2 What does it mean Answer debug isdn q931. It is the type of call capability that is transmitted through the...

Nsp

The NSP segment is responsible for providing services over the DSL network. The NSP can be the same organization as the NAP or a totally separate organization. The services provided by the NSP can be Internet access with Internet service provider (ISP) services such as mail, web hosting, and network security. As the technology matures, other services, such as telephony and video, might become prevalent. Figure 12-8 shows the protocol stack in a DSL network. End User Telco I NAP ISP I NSP...

Always On Dynamic Isdn Aodi

AO-DI is a relatively new addition to the ISDN scene. It allows you to maintain a permanent connection to the Internet by using the ISDN D channel. Remember that in BRI service the D channel is 16 kbps and that it is used for call-control and channel management signaling. AO-DI takes approximately 9.6 kbps of the 16 kbps for a link back to the service provider's ISDN switch. With this link, you can download stock tickers, e-mail, and other streaming desktop applications. One of the main...

Network Interface Device NID

NID is a common term that describes the interface at which an ISDN BRI circuit connects to the customer's premises in North American implementations. The NID separates the service provider's portion of the ISDN circuit from the customer's ISDN equipment and inside wiring (ISW). This device is a result of the deregulation of the phone company after the divestiture of 1984. A typical NID is a grey box that sits on the side of the customer's house or office, and it is split into two halves. The...

Cable Modem Technology and CATV

CATV networks originated in the U.S. in the late 1940s as a way of distributing broadcast television channels to locations with poor reception. Antennas were placed on the top of tall hills or other high points and a cable connected homes to the antennas. Using cabled connections, individual homes received strong clear CATV reception. In the 1950s an estimated 14,000 individual homes were connected to a CATV network. Since that time, subscriber penetration has grown to an average of around 70...

Vci

The VCI makes up the second of two parts of the locally significant identifier pair that was explained in the previous section, VPI. Figure 10-3 shows a graphical representation of virtual path and virtual channel connections (VPCs and VCCs). VPC and VCC describe possibly multiple VPIs and VCIs, respectively, along the path from endpoint to endpoint. VPC Virtual Path Connection (Identified by VPCI or Multiple VPIs) VCC Virtual Channel Connection (Identified by VCCI or Multiple VCIs)...

Analog Signal Basics

Telecommunication, as it is currently deployed throughout the world, is based on the flow of electricity from one location to another. Whether you are surfing the Internet or talking to your friend on the phone, electricity is constantly flowing throughout the infrastructure. As you might have guessed, there are different types of signals that can be transmitted. The two main types that this book focuses on are analog and digital signals. One difference is that some mediums, such as fiber...

Signaling Types

This chapter covers two main types of signaling CAS and CCS. CAS is a common type of signaling in TDM-based technologies such as T1, E1, or J1. CAS is a way of providing signaling in-band or on the same path as the data. The in-band features are functions such as dual tone multifrequency (DTMF) transmission. These features are interwoven into the data fabric and cannot be separated. Also signaling that accompanies each call for call state control exists and is transported using the least...

Payload Length Field

The payload length field indicates the total number of data octets in the segmentation unit of an L2_PDU. Because the L3_PDU is aligned on a 32-bit boundary, this field has a set number of possible values. For BOM and COM segments, the value must be 44. For the EOM, the value can be any multiple of 4 between 4 and 44 (4, 8, 12, 16, , 44). SSM segments can have values between 28 and 44 (in multiples of 4). Using the payload length field, the receiving CPE can determine where the data ends and...

Troubleshooting Cer Issues In Cable Plant

The CER, along with the following two parameters, although not contractually negotiated, provides an indication of intrinsic network performance. Specifically, CER represents the ratio between the number of cells that are delivered with at least one error to the total number of cells delivered (both successfully and errored). The catch is not to count any component cells that were part of blocks that were severely errored, regardless of the disposition of the cells themselves (don't count them,...

Q921 Timers

Although it does not contain an exhaustive list of ISDN timers, this section discusses the more common timers that you need to understand to troubleshoot ISDN circuits at Layer 2. The timers included are T200 to T203 and N200 to N202 and their default values are shown in Table 8-3. Table 8-3 Q.921 Timers and Their Default Values Table 8-3 Q.921 Timers and Their Default Values Table 8-3 Q.921 Timers and Their Default Values (Continued) Table 8-3 Q.921 Timers and Their Default Values (Continued)...

About the Contributing Authors

Christian Martin (CCIE 4487) is a Network Architecture Consultant for Verizon Internet Services, where he has worked for the past 5 years. Among his responsibilities is the network support and evolution of an SMDS aggregation network composed of over 300 DS3 circuits, 700 T1s, and over 1000 routers. He was also responsible for the deployment of Verizon's current NMS, the design of Verizon's first long-distance IP network, and continues to provide technology oversight on all products and...

Frequency Allocation

Broadcast channel allocation is different in every region and country. In the U.S., frequency allocation is the responsibility of the Federal Communications Commission (FCC). The FCC decides which entities are authorized to broadcast at specific frequencies. Most regions and countries have authorities responsible for frequency allocation. Types of broadcast signals are usually restricted to specific frequencies by law. Figure 13-4 shows U.S. over-the-air frequency allocation for those...

The Cable Plant

CATV was initially deployed to bring nearby broadcast television stations to areas where reception was poor or non-existent. In this manner it served subscribers as a unidirectional (one-way) video distribution mechanism, wherein television broadcasts were transmitted downstream from the CATV video distribution point (known as the headend) to the subscriber. This CATV distribution network, often referred to as a cable plant, traditionally consists of branched metallic (aluminum and copper)...

Foreign Exchange FX

To deploy BRI circuits to customer sites, the service provider's switch must be able to accommodate the ISDN equipment. This typically includes a fairly large switch such as a Lucent 5ESS or Nortel DMS-100, with adequate port density and a series of line cards both at the CO and IDLCs. When deployed in IDLCs, BRI service typically takes up three full DS0s, so available bandwidth is also a factor. In areas that can't support these requirements, an FX of the circuit might be necessary. At its...

Isup Telecommunications

The ITU's answer to the shortcomings of TUP was the creation of ISUP. ISUP is the most widely used protocol for call setup transport worldwide, and it is designed to provide call management and access to services for both voice and data calls. ISUP has been designed as an extensible protocol suite that can be modified as needed by different country requirements. For example, say that Country A specifically needs a field for a proprietary billing system. The extensible nature of this protocol...

ATM Service Classes

Although it would be ideal to have one AAL in its entirety for all applications of ATM networking, the one AAL chosen would be a watered-down version of what is required by all applications. The restriction might be so limiting that certain applications, no matter how you tried to fit them in, would never work out. At the very least, certain features that optimize the performance of an application might interfere with the performance of another. By omitting these features, all applications...

Non Associated Signaling

Non-associated signaling is similar to quasi-associated signaling but with one major difference. With non-associated signaling, signaling takes place between STPs, as shown in Figure 2-8. In this case, signaling is not necessarily within one hop of the actual call. Every time you add another hop between STPs, you add more and more delay in the signaling network. Significant enough delay can cause problems, including calls being dropped by SSPs and link problems. Non-associated signaling is...

Headends and Hubs

Simple cable plants that serve a single geographic area can be represented as having a single source for video signal, often a satellite, antenna, or other type of receiver. This source, called the headend, transmits data through a set of fiber nodes throughout the geographic region. Each fiber node then connects to a coaxial distribution network that delivers video to individual subscriber premises. Each fiber node is often analogous to a group of subscribers such as an apartment complex, city...

NOCRC4 Framing

The first bit in each frame is a reserved bit that can be used for a CRC if you are using CRC framing. CRC-4 framing is the most common type of CRC framing and is discussed further in the next section. CRC-8 and CRC-16 framing also exist, and the number specifies how many bits are set aside for the CRC. However, CRC-8 and CRC-16 are rarely if ever used. In the event that you are not using CRC, the first bit is flagged as a 1 if the circuit is connected between two different countries. If the...

Cisco Systems

Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134-1706 USA http www.cisco.com Tel 408 526-4000 800 553-NETS (6387) Fax 408 526-4100 Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134-1706 USA http www.cisco.com Tel 408 526-7660 Fax 408 527-0883 Level 17, 99 Walker Street North Sydney NSW 2059 Australia http www.cisco.com Tel +61 2 8448 7100 Fax +61 2 9957 4350 Cisco Systems has more than 200 offices in the following countries. Addresses, phone numbers, and fax numbers are...

History of SMDS

During the early to mid 1980s, the U.S. Regional Bell Operating Companies (RBOCs) were looking at ways to transform the public switched telephone network (PSTN) into a digital network capable of supporting a vast array of services that allowed for high-speed connectivity, limited error rates, rapid provisioning, and better performance monitoring. As an additional goal, these providers were seeking ways to increase revenues in the data services arena, where, at the time, LAN-to-LAN...

T1 Technology

This chapter introduces you to a specific digital circuit that is known as T1. You will become familiar with the method by which data is transformed into pulses of electricity, light, or some other media-dependent signal. This chapter also details the framing formats that the industry uses to form the T1 signal before it is transmitted. Finally, you will learn some valuable troubleshooting techniques and be presented with a sample configuration for Cisco devices. By the end of this chapter, you...

M23 and CBit Parity

The main difference between M23 and C-bit parity framing has to do with the DS2 multiplexing. In M23 multiplexing, bit stuffing is required to ensure that any differences in the DS2 clock source is removed. Thus, M23 framing uses all the overhead bits that are associated with DS3 signal streams (X, P, M, F, and C). The C-bits identify whether bit stuffing has occurred in a specific DS2 frame. In other words, if you were to have at least two C-bits toggled to 1 in DS2 5, that identifies DS2 5 as...

Answers to Chapter 13 Review Questions

What sort of framing is used in DOCSIS-based cable IP networks What other devices in the cable network use the same framing Answer DOCSIS networks use MPEG-2 framing to transmit IP packets. MPEG-2 also transmits digital video signals, digital audio, and other data. More information on MPEG-2 is at mpeg.telecomitalialab.com. 2. What types of modulation transmit data upstream and downstream Why is one type of modulation preferable to another Answer DOCSIS 1.0 and 1.1 use QPSK and 16 QAM to...

Evolution of the North American Digital Hierarchy

As explained in Chapter 5, T1 Technology, DS1 technology was introduced to groom several telephony pairs in a single circuit (24 DS0s), which resulted in savings for telephone companies (telcos) in copper, office space, and other equipment. In the same way, DS1c (48 DS0s), DS2 (96 DS0s), DS3 (672 DS0s), and DS4 (4032 DS0s) were defined to groom more and more telephony circuits. The DS0, DS1, DS1c, DS2, DS3, and DS4 hierarchy is the NADH, also referred to as the plesiochronous digital hierarchy...

ISDN Specifications

ISDN has been standardized in a host of different specifications from groups such as the International Telecommunication Union (ITU), Telcordia (formerly Bellcore), and the American National Standards Institute (ANSI). These groups, along with the ISDN forum, are responsible for modeling the ISDN industry. Standards that are in the I group consist of standards set forth for ISDN, both narrow and broadband. The Q group of standards has to do with switching and signaling. The Q standards also...

D1 Channel Banks

The original channel-bank standard was developed in 1962 by Western Electric and was called D1. D1 was characterized by the use of the LSB of every channel byte for on-hook off-hook signaling. This left only 56 kbps on each channel for user traffic, a limitation that could not be lifted, even with the use of a line-coding technique designed for clear-channel transmission, such as B8ZS. Fortunately, this practice would change with future implementations. Recall, however, that this initial format...

Signaling Area Network Code SANC Designations

The table in this appendix shows SANC country designations United Kingdom of Great Britain and Northern Ireland United Kingdom of Great Britain and Northern Ireland United Kingdom of Great Britain and Northern Ireland United Kingdom of Great Britain and Northern Ireland United Kingdom of Great Britain and Northern Ireland United Kingdom of Great Britain and Northern Ireland United Kingdom of Great Britain and Northern Ireland United Kingdom of Great Britain and Northern Ireland United Kingdom...

SID and Service Flow Identifier SFID

DOCSIS and Euro-DOCSIS 1.0 identify individual cable modems and other cable devices (such as set-top boxes) by a unique SID. This 13-bit Layer 2 identifier value allows traffic to be directed to specific cable modems. Each SID is subsequently allocated specific class of service (CoS) parameters. The DOCSIS 1.0 SID mechanism is efficient in environments where a single traffic stream is associated with each cable device. However, cable modem users often use their transmission ability to send and...

The Development of Frame Relay

Frame Relay was developed as public networks matured, thus gradually replacing another packet-switching technology X.25. Paired with analog transmission media, X.25 became obviated in many markets, because Frame Relay avoids all the inefficiencies that lurk in the shadows of analog technology. Because analog is such a potentially lossy service and because end devices were dumb in the X.25 era, error detection and correction were built into every part of the X.25 infrastructure. Both X.25 and...

Baseline Privacy Initialization

After a cable modem has initialized and come online, BPI negotiation begins. To initiate negotiation the cable modem confirms with the CMTS that both are configured to support baseline privacy. The cable modem then sends the CMTS a public key and begins the key exchange process. The cable modem sends the CMTS a public key. After it is received, the CMTS confirms that the sending cable modem's MAC address belongs to a modem authorized to receive keys and then uses the public key to encrypt a...

ISDN Reference Points

ISDN specifies a set of reference points that describe the various network functions associated with an ISDN BRI circuit. These reference points are shown in Figure 8-5. The reference points and equipment include U, S, T, TE1, TE2, and R. The U interface or reference point, also known as the user interface, describes the access point from the service provider's network into the customer's Network Terminator Type 1 (NT1). Also referred to as the U-loop interface, it is normally represented with...

Cisco Avvid Ip Telephony Solutions

Cisco IP Telephony is based on the successful CIPT training class taught by the author and other Cisco-certified training partners. This book provides networking professionals with the fundamentals to implement a Cisco AVVID IP Telephony solution that can be run over a data network, therefore reducing costs associated with running separate data and telephone networks. Cisco IP Telephony focuses on using Cisco CallManager and other IP telephony components connected in LANs and WANs. This book...

ISDN Call Flows

During a basic call flow, the calling party is the origination of the call and the called party is the destination of the call. The calling party sends a Setup message to the called party through the ISDN network. The calling party gets a Setup Acknowledgment and Call Proceeding from the local ISDN switch. The Setup Acknowledge is only used for overlap signaling. If en-bloc signaling is used, Call Proceeding is sent without a Setup Acknowledge. The remote ISDN switch sends a Setup message to...

HDB3 Line Coding

HDB3 line coding is the ITU answer to the 1s density problems associated with phase locked loop (PLL) circuits. The history of HDB3 is somewhat interesting. Believe it or not, it was actually created by the ITU prior to the development of bipolar 8-zero substitution (B8ZS) by ANSI. So in essence, this was the ITU's answer to the limitations set forth by AMI. When using HDB3, no more than three consecutive 0s are allowed on the circuit. As with B8ZS, HDB3 inserts a unique bipolar violation that...

Power Ranging

Modems in the process of initialization must determine a signal strength at which to transmit upstream. Determining the signal strength needed for the CMTS to reach the cable modem is relatively simple because DOCSIS was designed to be compatible with typical signal levels found in the residential environment of a cable network. However, the upstream path of the cable network has substantial variation in signal level from inside each home passed. Therefore, a cable modem transmitting upstream...

Noise Margin and Attenuation

In many data transmission technologies, you need to establish a noise margin or additional buffer zone between the signal and noise levels present on the physical transmission medium. Establishing a minimum noise margin is done to maintain a 10-7 or better bit error rate (BER), and noise levels increase slightly or while signal levels decrease slightly. When the signal-to-noise ratio (SNR) becomes too low, excessive errors begin to occur in the data stream. The actual noise margin at any...

DDS Circuit Deployment

The DDS connection from the service provider uses a four-wire interface. There are two pairs of wires, one for Transmit (Tx) and one for Receive (Rx). Almost all DDS deployments use twisted copper pairs, and the pins within the modular plugs (RJ-48S) are 1, 2, 7, and 8. DDS circuits within the United States are separated into two halves at the network interface (NI), the user side and the network side, as shown in Figure 4-1. This is due to the divestiture of 1984. DDS circuits are commonly...

Forward Error Correction

Forward error correction (FEC) refers to the process of correcting errors mathematically at the receiving end of a transmission path, rather than calling for a retransmit of the errored data. Retransmitting data to correct errors uses the available bandwidth to repeatedly send the same information, and the user perceives extremely slow throughput. FEC results in greater effective throughput of user data because valuable bandwidth is not being used to retransmit errored data. However, in the...

Review Questions

Give or select the best answer or answers to the following questions. The answers to these questions are in Appendix A, Answers to Review Questions. 1 What is the main difference between analog and digital signal streams a Digital signal streams are immune to line problems such as crosstalk and attenuation. b Digital communication is a continuous signal stream that contains a varying range of frequencies and amplitudes. c Analog signal streams are composed of discrete values that can be...

D2 Channel Banks and the SF

D1 channel banks were originally designed to connect a pair of nearby COs, where the analog signals would then be switched locally. When AT& T decided to use T1 to connect offices in tandem, the switches required analog signals for processing, so the digital signal would be converted back and forth from analog to digital and back again. The repetitive re-sampling of the analog signal resulted in increased quantizing noise by the time the signal made it to its final destination. The D2...

ITU Point Code Format

The ITU point code format is a little different than that of ANSI. The ITU point code is organized into three fields, just as the ANSI point code, but the ITU point code differs in how many bits are in each field. The ITU format calls for a 3-bit field, followed by an 8-bit field, and then by another 3-bit field. This gives the ITU point code a final size of 14 bits. The first octet indicates the zone identifier (zone ID) of the point code. The zone ID is the geographical zone that the point...

Line Signaling

Line signals apply functions such as seizing a circuit, clearing a circuit in a forward or backward direction, answering signals, and blocking signals, as described in Table 6-2. Table 6-2 Forward and Backward Line Signals Table 6-2 Forward and Backward Line Signals At the beginning of a call, reserves a circuit for a call in the Terminates a call in the forward direction. Starts an international assistance operator. Acknowledges receipt of the Seize signal in the backward direction and changes...

Answers to Chapter 1 Review Questions

What is the main difference between analog and digital signal streams a. Digital signal streams are immune to line problems such as crosstalk and attenuation. b. Digital communication is a continuous signal stream that contains a varying range of frequencies and amplitudes. c. Analog signal streams are composed of discrete values that can be transmitted as 1s or 0s. d. Analog signals are considered continuous signal streams and digital signals are discrete signals, which are commonly...

DQDB Overview

The DQDB protocol was discussed earlier as a precursor to the SMDS service developed by Bellcore. To be clear, this was not the intention of the IEEE when defining DQDB. The IEEE 802 working group is responsible for defining physical and data-link layer standards for use in intraLAN and interLAN networks. Thus, DQDB is part of a larger group of technologies such as Ethernet (802.3), Token Ring (802.5), bridges and switches (802.1), wireless LANs (802.11), and so on. The primary purpose of DQDB...

Service Provider Portability

The FCC First Report and Order (96-286) required all LECs to begin a phased deployment of service provider LNP in the 100 largest Metropolitan Statistical Areas (MSAs) no later than October 1, 1997, and to complete deployment in those MSAs by December 31, 1998. Service provider portability allows subscribers to keep their existing telephone number (for incoming calls, outgoing caller identification, and billing) when changing to a different telephone company. At this time, service provider...

M12 Multiplexing

When you look at DS3 carrier systems, you see a slew of references to M12, M23, and M13 multiplexing. These are merely different stages in the DS3 multiplexing process. Bit stuffing makes sure that all lower level digital signals are transmitting at the same rate through the network. This process is necessary to synchronize several different asynchronous circuits. Bit stuffing is also referred to as justification. Although a DS1c circuit does exist (two DS1s), it is not used in the M12, M23, or...

Peakto Peak CDV

Peak-to-peak CDV represents the difference between the best (fixed CTD) and worst (maxCTD) cases for CTD. In Figure 10-10, fixed delay is the CTD that can be experienced by any delivered cell on the connection during the entire connection holding time. This fixed CTD value can be thought of as being indirectly negotiated because its value is subtracted from the directly negotiated maxCTD to provide the directly negotiated peak-to-peak CDV. As networks have a limited ability to control...

T1 Framing and Formatting

You've been introduced to the concept of multiplexing multiple source flows into a single circuit. How the receiving end knows where in the resulting stream of bits each channel's traffic can be found is the result of two processes, known as framing and formatting. Recall from Chapter 3, that each 64-kbps bit stream is created from 8000 samples per second, each sample being represented by a single 8-bit byte of information. A T1 multiplexer does not buffer traffic from the channel sources. As a...

DDS Equipment Overview

Before discussing DDS line operation, several devices should be examined Office channel unit-data port (OCU-DP) You can use a CSU in DDS and numerous other technologies. Typically referred to in tandem with DSUs (CSU DSU), you can use these devices in DDS, FT1 T1, FE1 E1, and several other technologies. The CSU is the interface that communicates directly with the service provider network (see Figure 4-2). The CSU terminates the DDS circuit, allows for maintenance through loopback and test...

T3 and E3 Technology

As the technology in telecommunications advanced, so did the requirements for customer circuits. As more and more businesses and users were connected to the infrastructure, it became apparent that even DS1 and E1 circuits would no longer be sufficient. Higher bandwidth circuits were required to allow for growth and to provide more services to subscribers. DS3 carrier systems, just as DS1 carrier systems, allow for a level of pair gain. NOTE Remember, pair gain is the function of gaining pairs...

Capability Set 2 CS2

CS-2 expands on the types and complexity of services that CS-l might not have been able to provide completely. Both CS-1 and CS-2 are subsets of the complete IN architecture. CS-2 provides several types of services, including Telecommunication Services, Service Management Services, and Service Creation Services. Service Management Services and Service Creation Services are new service types with the advent of CS-2. Table 2-6 lists a subset of the additional services added by CS-2. Table 2-6...

Cisco Interactive Mentor

CIM Voice Internetworking VoIP Quality of Service Cisco Systems, Inc. 1-58720-050-3 Availabe Now With CIM Voice Internetworking VoIP Quality of Service, you acquire the skills needed to implement and fine tune QoS for Voice over IP routing on Cisco routers. From an overview of QoS concepts to detailed examination of Cisco IOS(r) Software QoS and VoIP routing commands, you will learn how to solve call quality problems caused by delay and inefficient packet compression in Voice over IP networks....

Answers to Chapter 4 Review Questions

How many wires do you use on a DDS circuit A DDS circuit uses two pairs of wires for a total of 4. a. Incorrect. DDS circuits use two pairs of wires, not two wires. In some proprietary SW56 applications it is possible to run over a single pair, but it isn't common. c. and d. Incorrect. These values are too large for DDS circuits. 2. Which pins does a DDS circuit use DDS uses pins 1, 2, 7, and 8 for communication. a. Incorrect. Some technologies such as ISDN use pins 4 and 5, but not DDS. b. and...

Other Equipment

The last few pieces of equipment found in optical networks do not necessarily fall into any of the listed categories but are certainly worth mentioning. Optical routers are quickly becoming more popular in a fiber-based network. They are exactly what they sound like, routers with optical interfaces. Many uses exist for them, and as the data and voice networks continue to converge with the next generation of IP networks you will see them deployed more often. Directly related to Cisco products,...

DS3 Monitoring with CBit Parity Framing

Each of the 21 C-bits can be used for a specific line monitoring function. Refer to Table 7-3 for a complete listing of the bits and their function. Table 7-3 C-Bit Functions with C-Bit Framing This bit is toggled to a 1 state to identify the use of C-bit parity. Identifies the far-end alarm and control (FEAC). The FEAC identifies remote problems with the circuit and initiates a loopback of the DS3 or individual DS1 circuit. Further identify parity traffic through the DS3 network. Designated as...

B1Q Line Coding

2B1Q is composed of four different discrete voltage states, and it transmits two binary digits during each pulse. This is in contrast with most other coding standards such as B8ZS and High Density Bipolar of Order 3 (HDB3), which only transmit one binary digit per pulse. As shown in Table 8-7, each voltage state has a specific value attached to it that does not change. Table 8-7 2B1Q Binary Voltage Values Table 8-7 2B1Q Binary Voltage Values When 2B1Q codes binary digits, it looks a bit...

Circuit Testing Patterns

Line Loop Equipment Loopback

In the event of a suspected faulty circuit or equipment, you need to have a way to determine the source of the errors. Circuit testing patterns identify problems with equipment on both the customer's and service provider's end. Modern CSU DSUs can loop up the circuit, in either direction, to test and isolate problems (see Figure 4-10). If a pattern is sent and it doesn't receive the same pattern back, it is likely an issue with the remote equipment. Figure 4-10 Equipment Loopback for Problem...

T1 Line Coding Schemes

After all traffic is in digital form, whether by conversion or naturally, to transmit it across the T1 circuit you need to choose a line-coding scheme that allows the signal to make it across the physical medium without attenuating to the point of becoming unrecognizable. Internal wiring is in a more controlled environment and usually conforms to stricter standards than outside plant with regard to noise, interference, crosstalk, and capacitance. As a result, it is not as important to worry...

Mtp2

MTP2 provides the required Layer 2 functionality in the SS7 network. It is responsible for providing a reliable link for the upper-layer protocols. The explicit device name used at MTP2 is a Signaling Link Terminal (SLT). It is normally built into the signaling point fabric. The functions of MTP2 are as follows Separation of signal units MTP2 provides identification of individual signal units with a flag. Bit stuffing The transmission of six consecutive 1s within a signal unit causes it to...

Answers to Chapter 2 Review Questions

What is the main difference between CAS and CCS Signaling a. CAS is logically in-band but physically out-of-band. b. CCS isn't intrusive to the data, and it is considered in-band. c. CAS is considered in-band signaling, and it is intrusive to the data. d. There is no difference between them. CAS signaling is in-band signaling, which is intrusive to the data. CCS is out-of-band signaling, but it can be physically in-band and logically out-of-band. a. Incorrect. You wouldn't be logically in-band...

Bandwidth and Signal Distortion

The basic analog signal structure suffers from several limiting factors. First and foremost, the analog signal is limited by the amount of bandwidth or number of bits that it can transmit during a given period of time. Remember that bandwidth does not equal speed. Electrons are transmitted through the infrastructure at a constant rate, regardless of the medium. Even when fiber optics are in use, the optic medium does not physically transmit light any faster. The key to bandwidth is how many...

Concatenation

Although most SONET and SDH links are channelized, a provision exists that allows for unchannelized transmission of information. Concatenated or unchannelized SONET and SDH links form a single large synchronous payload envelope (SPE), and do not specify any lower level digital signals. Even though the circuit is concatenated, the same section, line, and path overhead is used. SONET identifies concatenated signals by using a c marker at the end of the signal. For example, a concatenated OC-3 is...

Line Coding

The topics covered in this section include the following Alternate mark inversion (AMI) To quickly review Chapter 3, Analog-to-Digital Conversion, encoding is the last step in the pulse code modulation (PCM) process. Encoding allows the digital equipment to transmit a digital signal through a network by using 1s and 0s. The line coding scheme that you use with DDS is called AMI. AMI is a bipolar return to zero (RZ) type of encoding. To simplify this, bipolar means that there are two different...

DOCSIS 10 Configuration File

The DOCSIS 1.0 configuration file specifies the operational parameters for a DOCSIS 1.0 cable modem in the following list. Because of the limit of a single SID per cable modem, the operational parameters included define a set of parameters that are applied to all traffic traversing the cable modem. The list of available parameters configured in a DOCSIS 1.0 configuration file includes the following Radio frequency Defines downstream frequency and upstream channel ID. In the case of the cable...

D5 Channel Banks and the ESF

The D5 channel bank is basically a D4 channel bank with the ability to multiplex 72 and 96 channels for direct connection to a T2 line. Additionally, the D5 channel bank introduces the ESF format. Although the D4 SF format was a vast improvement over the framing format of the D1 channel bank, it lacked certain accommodations for management and signaling. Although this was not a huge problem for voice traffic, as signaling could be included through RBS, data traffic could not use RBS and still...

The Hybrid Fiber Coaxial HFC Network

Hfc Node Fiber Tail

The first networks to include a fiber node-type technology were built beginning in 1990. CATV networks today are built exclusively using HFC design and older networks are being retrofitted to receive the benefits of HFC. As a result, most CATV networks today are based on fiber node-based architecture, but they also include elements of the older coaxial networks. The HFC network design helps reduce many of the amplification and attenuation issues and other issues associated with all coaxial...

Throughput for Docsis and EuroDOCSIS

Although it is easy to determine the theoretical maximum throughput for a DOCSIS channel based upon raw data rates, it is not simple to compute the real maximum throughput. DOCSIS control messages, error correction, MPEG headers, and other types of overhead on the cable IP network limit the total available throughput for DOCSIS devices. To determine more realistic throughput numbers, you must calculate the overhead per DOCSIS channel and subtract it from the total theoretical throughput....

Other Security Concerns and Features

Device cloning is the most frequently used method of gaining unauthorized access to network services in cable IP networks. By mimicking a valid modem's MAC address, IP address, or configuration file a malicious individual can transmit and receive traffic without being billed for the service. To prevent device cloning, several features have been developed by CMTS vendors. MAC address cloning can be detected and flagged by the CMTS, and network access for all devices with that address can simply...

Signaling Links and Link Sets

Signaling links are physical connections between SS7 nodes and are responsible for the reliable transmission of SS7 signaling messages between those nodes, as shown in Figure 2-9. Signaling links can be configured so that they load share traffic over any or all of the links in a designated link set between signaling points. Even distribution of traffic is only achieved if there are several signaling links of the power 2 (2, 4, 8, and so on). Figure 2-9 Signaling Links Between SS7 Network Nodes...

Fiber Node Combining

Typical CMTS configurations include DOCSIS MAC domains with one downstream transmission source (a single downstream channel on the CMTS) and multiple upstream transmission sources (one or more upstream channels each with multiple cable modems). In most cases a CMTS controls multiple DOCSIS MAC domains on several DOCSIS modem cards. Each DOCSIS MAC domain consists of a downstream transmit port and one or more upstream receive ports. Because each downstream port and upstream port has a finite...

Expert White Board Configuring an E1 Hairpin

The second type of configuration for E1 controllers is an advanced and specific configuration known as a hairpin. Figure 6-8 shows the use of a hairpin configuration, also known as a drop and insert, to connect a Cisco network to a traditional TDM-based SS7 infrastructure. This connection allows you to redirect timeslots carrying SS7 signaling out through an Ethernet interface and then drop the remaining timeslots to another device. You typically see this type of configuration in some of...

T1 Physical Characteristics

Smart Jack

Recall from Chapter 3 that signals attenuate, or lose strength, as they travel along the transmission medium. Analog technology combats this loss with the use of amplifiers, which strengthen the level of any analog interference that also might have been picked up. For digital technology, such as T1, repeaters replace amplifiers. Repeaters are devices that regenerate a weakened signal, allowing noise and interference to be filtered out, thereby reconstructing the signal in its original form. The...

Bearer Capability

The bearer capability IE identifies which capabilities a call is requesting from the network. This IE must be present in the Setup message or the call fails. This can be one of the largest IEs, ranging from 4 to 12 octets, and it contains information such as the type of service (ToS), rate multiplier (if necessary), user information Layer 1 protocol, and asynchronous control information, if needed (start and stop bits parity). Figure 8-17 shows the fields that are contained in the bearer...

Upstream Signaling Enhancements with DOCSIS

Because of the static provisioning architecture in DOCSIS and Euro-DOCSIS 1.0, the DOCSIS 1.1 specification includes several new signaling mechanisms to help improve upstream throughput and latency characteristics especially for real-time services such as voice. These features are the following Unsolicited Grant Service (UGS), UGS with Activity Detection (UGS-AD), and real-time polling. The DOCSIS 1.0 optional features of fragmentation and concatenation were made mandatory in DOCSIS 1.1....

The Signal Conversion Process

By way of review, an analog signal is one in which each point on the waveform is meaningful (a continuous waveform). Analog signals are graphically depicted as sinusoidal waves (see Figure 3-2). This is also the motion that a guitar string exhibits when plucked. The string moves through and past the origin (the x-axis showing time, here), which is nearly an equivalent distance toward the guitar as away from the guitar. Figure 3-2 Sinusoidal Analog Waveform Figure 3-2 Sinusoidal Analog Waveform...

DOCSIS 11 Configuration File

The DOCSIS 1.1 configuration file format is somewhat more complex than that for a DOCSIS 1.0 cable modem. This is because a DOCSIS 1.1 configuration file must include a set of operational parameters for multiple service flows. Information required for the classification, marking, and rate management of each service flow must be included in the file. The following list includes only those parameters that differ materially from DOCSIS 1.0. A DOCSIS 1.1 configuration file is not complete unless it...

Common Cable Plant Issues

As a CATV or cable modem signal is transmitted downstream through the branched cable topology, the signal becomes attenuated and weaker at each branching and with cable distance. What is initially a strong signal requires amplification to adequately reach the subscriber. Noise or interference in downstream frequencies that enters the cable system at some distance from the headend only affects customers past that point. It does not affect all subscribers, as it does not originate at the headend....

M23 Multiplexing

M23 multiplexing involves the combination, using bit interleaving, of seven DS2 signals into a single DS3 signal stream. Hopefully, you are beginning to see a pattern. DS1 to DS2 multiplexing is M12, and DS2 to DS3 multiplexing is M23. The first number in these acronyms stands for the DS level that is multiplexed, and the second number stands for the new DS hierarchy level that is created. Thus, M23 is the function of multiplexing DS2s into a DS3. Figure 7-7 shows the M23 process. 4 DS1s 4 DS1s...

Contractual Values in Frame Relay

There are several key values that are agreed upon during the negotiation of the contract and SLA, entered into by the service provider and the subscriber. Those presented here are as follows Committed information rate (CIR) Committed rate measurement interval (Tc) These values (except MBR), and a few more, are defined in ITU-T I.233.1 Annex A. The primary value recognized and agreed upon contractually when subscribing to Frame Relay service is CIR. The CIR is the average transmission rate for...