Telecommunications

The Hybrid Fiber Coaxial HFC Network

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...

History of DSL

In the 1980s, Bellcore developed high-data-rate DSL (HDSL) technology. HDSL was developed to enhance the capabilities of T1 technology by replacing alternate mark inversion (AMI) encoding with 2 binary 1 quaternary (2B1Q) encoding. HDSL reduces the need for repeaters, and it causes less electromagnetic interference (EMI) in cable bundles. In the 1990s, technology vendors began to see an explosion in the use of the Internet. This Internet revolution increased the demand for pure data, as opposed...

Digitalto Analog Converters

DACs convert between digital and analog signals. Two common implementations of this type of equipment are modulator-demodulators (modems) and the conversion that is applied at the CO for each analog circuit. A modem converts the unipolar digital signals that are transmitted by your computer into an analog signal stream. A unipolar signal is a signal that has only a single voltage polarity. So, instead of having both positive and negative sides to a signal stream, only a positive or negative...

Signal Attenuation and Noise

The first problem that you face with electrical current flow is the ability to maintain the signal strength. As a signal is transported down a facility, it gradually weakens with distance, as shown in Figure 1-4. The vector in Figure 1-4 illustrates the area of the signal that is attenuated as the signal travels away from the signal source. Figure 1-4 A Vector of Attenuation on an Analog Signal Stream Attenuation affects both analog and digital signal streams. Because the signal degrades over...

Tip and Ring Circuits

The analog connection that is provided to you is referred to as a tip and ring circuit. The name comes from the tip and ring portions of the old connectors in manual switchboards. Today, the tip and ring are the two wires that compose the analog connection. Typically deployed over a two-wire circuit, the center two pins are the most commonly used in RJ-11 modular plugs. Basically, the way the phone circuit functions is that while your phone is on hook, or hung up, the physical circuit between...

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...

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...

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...

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...

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...

Review Questions Urw

Give the best answer or answers to the following questions. The answers to these questions can be found in Appendix A, Answers to Review Questions. 1 What sort of framing is used in DOCSIS-based cable IP networks What other devices in the cable network use the same framing 2 What types of modulation transmit data upstream and downstream Why is one type of modulation preferable to another 3 What are the requirements for cable plant quality Why are they important What factors lead to poor plant...

ATM Functionality

This section details the technical foundation for ATM. In subsequent sections, you will see the five-octet header formats used with ATM. You will then see ATM as a layered model, much as any other layered approach to comprehending a protocol by classifying and ordering its core components, after which you will be presented with a discussion on topics that deal with how user information is adapted for cell production and how different traffic is classified for QoS treatment. Generally speaking,...

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...

Summary Ais

Synchronous technology has emerged to become the most prolific telecommunication technology on the market today. The initial drafts of SONET were based on a technology called SYNTRAN, which basically transmits DS3 signals in a synchronous format. The timing in the synchronous network distinguishes it from all other mediums because of its accuracy. The definition of synchronous means that all timing can be traced back to a single time source. Most timing in synchronous networks is derived from...

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...

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...

Called and Calling Party lEs

The calling and called number IEs specify the originating and destination numbers associated with the call. The numbers can be a variety of coding structures but are generally seen as ITU E.164 numbers, which mimic telephone numbers. Figure 8-19 shows the formats associated with the calling and called party IEs. Figure 8-19 Calling and Called Party IE Format Called Party Number The called party IE contains several significant fields. The type of number field describes what kind of number the...

Frequency Scanning

After a cable modem has powered on and has loaded operating system files from memory it begins to scan known frequencies for a downstream DOCSIS signal. Because of the differences in frequency splits and channel plans among regions and countries, a cable modem might need to scan hundreds of frequencies before finding an appropriate signal. Frequency-scanning algorithms are specific to the vendor who created the cable modem and have a direct impact on the speed with which a cable modem...

Network Congestion

Network congestion is a common occurrence within well-used networks. The only true way to avoid congestion is to over-engineer your network, which results in more expense than necessary for the preponderance of operating conditions. Different network implementations might employ equally distinct methods of dealing with congestion. For example, in the case of Ethernet, network congestion results in the expected collision of frames, thus destroying the actual information that is being transmitted...

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...

Core Aspects Specifications

The specifications that deal with the core aspects of Frame Relay are ITU-T Q.922 and ANSI T1.618. Parenthetically, be careful not to get drawn into an office argument over the ANSI specifications. You might be used to higher-level specifications having higher numerical components in their naming, but ANSI throws you a curve with T1.618 and T1.617. Although ITU-T's corresponding specifications are numbered in logical order (Q.933 is higher level than Q.922), ANSI reverses their numbering,...

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...

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...

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)...

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...

DSL Technologies

Several different DSL technologies exist in the world today. These vary dramatically in their reach capability and bandwidth capacity. The reach capability is the maximum distance that the signal can traverse while still maintaining a connection. In Table 12-2, it is listed as maximum distance. The bandwidth capacity varies based on a couple of factors. First, some DSL technologies use symmetric bandwidths for the upstream and downstream data. Others use asymmetric. The symmetric is primarily...

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...

E1 Physical Characteristics

Similar to T1 technology, an E1 refers to the carrier facilities associated with the digital signal. E1 circuits are also dedicated point-to-point synchronous circuits. Similar to T1, E1 circuits are equally susceptible to timing issues associated with multiple clock sources. Don't confuse the synchronous circuit with the plesiochronous network structure. Remember that plesiochronous networks contain multiple synchronous circuits with different clock sources. An E1 circuit differs in several...

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...

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,...

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...

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....

Dynamic Host Configuration Protocol DHCP Request Response

After power ranging is complete, the modem, now capable of Layer 1 and Layer 2 communication, establishes Layer 3 (IP) connectivity. IP connectivity is accomplished with the aid of DHCP. DHCP is widely used in IP-based systems to supply dynamic IP addresses and other network configuration information to IP-enabled devices. DOCSIS networks use standard DHCP systems (as defined in RFC 2131) to configure cable modems with IP addressing and other network information. When the cable modem begins the...

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....

Cisco Systems

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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...

Modulation Types

Both DOCSIS and Euro-DOCSIS dictate that digital information be modulated and demodulated between modem devices on the cable network using QAM, which is a type of phase-amplitude modulation. The phase and amplitude of the signal are modulated to encode 0s and 1s. QAM modulation encodes symbols on RF waveforms. The number of symbols per second is represented by a modulated signal that is proportional to the bandwidth of the transmission frequency. For example, an 8-MHz wide channel can carry...

CRC4 Framing

CRC-4 framing uses a CRC to verify the integrity of the framing sequence. When you use CRC-4 framing, the frames are broken down a bit differently. CRC-4 framing splits each MF16 into two equal segments, often called submultiframes. The first submultiframe groups frames 0 through 7, and the second submultiframe groups frames 8 through 15. Within each submultiframe, the even frames (0, 2, 4, 6, and so on) place the CRC bits in the first bit position. CRC bits located in 0, 2, 4, and 6 act as a...

Basic E1 Controller Configuration

To access any type of controller for configuration, you have to be in global configuration mode. After you are there, select the appropriate E1 controller. Example 6-1 shows the commands required to configure an E1 controller for normal operation. Example 6-1 Configuring an E1 Controller for Normal Operation 2600-1(config) controller el 0 0 2600-1(config-controller) framing no-crc4 2600-1(config-controller) linecode hdb3 2600-1(config-controller) clock source line primary...

ADSL Components

The physical ADSL infrastructure is made up of several components (see Figure 12-4). Each component plays a role in some aspect of the DSL connection. The following is a list of some of the most common components in a DSL environment DSL access multiplexer (DSLAM) DSLAM is the device that aggregates and terminates the DSL circuits. It contains multiple ADSL transmission unit central offices (COs) (ATU-Cs), and some type of network interface to uplink to the network access point (NAP). (See the...

DB15 connector

If using twisted pair, you are using pins 1, 2, 4, and 5 of the modular plug. Pins 1 and 4 are a pair, as are pins 2 and 5. Similar to T1, to make a cross over you cross pins 1 and 4 and cross pins 2 and 5. If using balanced coax cable, you most likely have two BNC connectors one for Tx and one for Rx. DB-15 connectors are more common with T1 deployments, but you can use them with E1 circuits. A DB-15 connector has 15 pins and is similar to a monitor cable connector. DB-15s are only found...

T1 Physical Characteristics

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...

Information Elements

The last field that is included in the Q.931 message format is the information or information element (IE) field. This field can consist of many different IEs that describe the features and capabilities of a given call. For instance, a single Setup message contains more than 15 different IEs including called party number, calling party number, bearer capability, transit network selection, and date and time. IEs are categorized as either single octet or multiple octet IEs. Figure 8-16 shows the...

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...

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...

Inverse ARP

Although this book is not an IP-centric work, nor does it dwell on any particular Layer 3 protocol unless it is part of the protocol stack featured by a particular chapter, we would be remiss if we did not discuss Frame Relay's interesting method of tying in with the Layer 3 address (often referred to in literature as the protocol address). Although in Ethernet environments, for example, an ARP cache table is constructed to map already-known Layer 3 addresses to learned MAC addresses for local...

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...

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...

Circuit Testing Patterns

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...

BRI Capabilities and Features

ISDN BRI can support up to eight devices on the S T bus, but you are limited by the number of B channels that your circuit has. Most service providers don't tell you this, but if you have two B channels with your ISDN service, you can only use two devices at any one given time. After both B channels are in use, you cannot add any other services without disconnecting something. So if your ISDN TA is using both B channels for a data call and you want to place or receive a voice call, you have to...

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...

Trellis Coding

Trellis coding is the process of altering the QAM constellation to provide better performance in a noisy environment. Trellis uses a coding algorithm that allows modems to compensate for minor phase or amplitude variations that are caused by noise on the transmission path. The combination of modulation technique and code allows operation at a higher data rate for a given SNR than could be accomplished without the Trellis code. The net coding gain (equivalent improvement in noise margin) from...

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...

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...

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...

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...

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)...

Review Questions Dzi

Give or select the best answer or answers to the following questions. The answers to these questions can be found in Appendix A, Answers to Review Questions. 1 At which layer of the ISDN stack does Q.931 operate 2 What type of device is commonly found between the S and T interfaces 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 5 If your local CO does not...

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...

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...

Telecommunications Pri

PRI is a larger offering of N-ISDN that accommodates more bandwidth and that offers more flexibility. For PBX uses or where SS7 is not readily available, PRI allows for the transmission of voice and data over a single link. In North America and Japan, PRI is deployed over a T1 facility and comprises 23 B channels and a full 64-kbps D channel. In most other international countries, PRI is deployed over E1 facilities using 30 B channels and a 64-kbps D channel. International PRI is also referred...

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...

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...

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...

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...

Configuring Isdn Bri

The first of two types of ISDN that you will configure is ISDN BRI service. Make sure that before you go to set up your ISDN TA, you have the proper ISDN switch type, your SPIDs, and any telephone numbers that are associated with your circuit. You will be configuring a basic BRI application by using a Cisco router. Figure 8-25 shows a diagram of the network that you will configure in this example. Figure 8-25 BRI Configuration Example ISDN Switch Type NI1 Figure 8-25 BRI Configuration Example...

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...

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...

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...

Synchronous or Asynchronous

As you learned in Chapter 5, the T1 circuits are synchronous technology. It would be easy to assume that a T3 is automatically synchronous, but in most cases that is simply not true. In a channelized environment, a single T3 can contain 28 T1 circuits. Each of the T1 circuits is synchronous, but their relation to one another is asynchronous. Typically, T3 circuits are considered to be asynchronous because they take 28 circuits (each with its own clock source) and modify them so that they can be...

T3 Line Coding

T3 circuits use one type of line coding, which is similar to bipolar 8-zero substitution (B8ZS) that is used on T1 circuits. Bipolar 3-zero substitution (B3ZS) is used for both T3 circuits and SONET links. Similar to B8ZS, B3ZS inserts a unique bipolar violation (BPV) in the event that a series of three 0s are detected. The insertion of the BPV is to ensure that 1s density requirements are met. Even though it operates in a similar way to B8ZS, some rules are specific to the way the B3ZS...

Configuration of a Channelized T3 Interface on a Cisco 10000 ESR

This section focuses on the configuration of a channelized T3 interface for a Cisco 10000 ESR. This expansion card is normally used for channelized applications, but it can be used in an unchannelized mode, if necessary. Each CT3 card has a total of six T3 ports, each denoted by a Tx and Rx pair of 75-ohm female BNC connectors. This basic configuration gives you an idea of some of the things that you can configure on the card. For more information on the topology, refer to Figure 7-12. The T3...

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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...

Binary Docsis Configuration Files

Most operational parameters that are transmitted to a cable modem as it initializes are contained in a binary configuration file in a type-length-value (TLV) format as defined in the DOCSIS specification. The DOCSIS 1.0 specification and DOCSIS 1.1 specification each define a configuration file format and parameters that are contained in the file. As a rule, the information contained in the DOCSIS 1.1 configuration file is a superset of that contained in the 1.0 configuration file. Although...

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...

Configuring a T1 Hairpin

Figure 5-8 shows the use of a drop and insert function, which is also referred to as a hairpin connection. This allows you to redirect timeslots and then drop out the remaining timeslots to another device. Here, timing is important to remember because the same circuit's DS-0s travel through multiple devices. In Example 5-2, the clock source internal command at the end of the controller t1 0 1 configuration is necessary if this controller will be providing the timing to the device at the other...

T1 Troubleshooting

There is a variety of testing that can be done to baseline or troubleshoot a T1 circuit, regardless of the frame formatting in use. With ESF formatting, there are even more benefits because testing and messaging can be performed without first taking the circuit out of service, as is necessary in the case of D4 formatting. ESF formatting makes use of the FDL bits to send a special data unit toward the CO equipment. At the CO, a device called a linemonitoring unit (LMU) is non-intrusively bridged...

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...

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...

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...

Address Subscription

Even though SMDS addresses appear as phone numbers, they behave more like MAC addresses on LANs. Recall that SMDS was derived from DQDB as a mechanism for data exchange across MANs or WANs. Also recall that SMDS had unicast and multicast routing, address screening, and source address verification as design goals. For the SMDS service to provide these features, a mechanism is needed to allow for address subscription, so that customers can build SMDS networks that are flexible, easy to...

Bridge Taps

Bridge taps are unterminated extensions of the telephone line or loop. They can alter the impedance of the local loop, especially at DSL frequencies. Because wavelength and frequency have an inverse relationship, short bridge taps have the greatest impact on wideband services, and long bridge taps have a greater impact on narrowband services. With DC voltage, the bridge tap behaves as an open circuit, but with high frequencies, the loop becomes a transmission line stub. This impedance mismatch...

Configuring a T1 Controller

This section gives two examples of how to configure a T1 controller on Cisco networking devices. To access the T1 controllers for configuration, you have to be in global-configuration mode and then select the appropriate T1 controller. Example 5-1 shows the simple configuration of a T1 controller for ESF framing and B8ZS line coding. Additionally, the controller is being configured to supply equalization (gain) for cables up to 133 feet. Example 5-1 Configuration of a T1 Controller router...

Configuring a T1 and E1 PRI Connection

T1 and E1 PRI configuration is simple. The first thing that you must do is configure the ISDN switch type in global configuration mode and then configure the T1 or E1 controller. Example 8-6 shows a T1 configuration. Raleigh(config) isdn switch-type primary-ni Raleigh(config) controller t1 7 0 Raleigh(config-controller) framing esf Raleigh(config-controller) linecode b8zs Raleigh(config-controller) clock source line primary Raleigh(config-controller) cablelength short 133...

Standards Bodies and the Frame Relay Forum FRF

In the previous section, you might have noticed a certain amount of credit given to the ITU-T. Although the ITU-T's contribution should not be minimized, there are actually three noteworthy groups in the Frame Relay arena American National Standards Institute (ANSI) The ITU-T and ANSI are international and U.S. standards bodies, respectively, and the Frame Relay Forum is an association of vendors, carriers, users and consultants committed to the education, promotion, and implementation of Frame...

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...

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...

Sio Sin Sios Ss7

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...

BRI Circuit Provisioning

Each BRI circuit is provisioned into the switch framework. The provisioning on the BRI circuits is completed through capability packages. The capability packages, also called ISDN Ordering Codes (IOCs), offer different combinations of bandwidth and service. Not only can the physical characteristics change (1B+D, 2B+D, just D), but the service types also can be modified. That means that a circuit can be provisioned for just voice, just data, or a combination of the two. These capability packages...

ATM and BISDN

ATM is a cell-switching (actually packet-switching, such as X.25 and Frame Relay) technology that quickly switches fixed-length frames through a network infrastructure that is finely tuned to QoS parameters. ATM allows every manner of digitized traffic to be transmitted with attention to priority, based on delay sensitivity and other special requirements. ATM can be thought of as a more refined version of Frame Relay. Frame Relay allows frames, with almost any length up to 1600 octets, and ATM...

Standards Bodies and the ATM Forum

The standards bodies that have the greatest influence over how ATM is accepted and implemented throughout the world and that ensure multivendor interoperability are as follows The Development of ATM and B-ISDN 302 ITU-T (well over 100 specifications) American National Standards Institute (ANSI) T1S1 Committee (more than 20 specifications) Internet Engineering Task Force (IETF) (more than 40 specifications) Even the FRF has about four IAs that treat ATM, especially its interworking with Frame...

The Bisdn Reference Model and ATM

Figure 10-7 shows the ATM B-ISDN reference model. This model actually represents the functions of ATM that are inserted into the B-ISDN model, as presented in ITU-T recommendation I.121. The model is three dimensional in nature, as opposed to the two dimensions you might be used to with the Open System Interconnection (OSI) reference model. You might want to refer to Figure 10-7 as you read through the paragraphs in the remainder of this section. Figure 10-7 The ATM B-ISDN Reference Model Layer...

SAR sublayer

Common part convergence sublayer (CPCS) Service specific convergence sublayer (SSCS) The CS is responsible for directly interfacing with the higher layers. With this in mind, the general function of the CS is to transfer the data units from the ATM user interface to the SAR and back. Specific functions of the CS can be derived from the characteristics of the SSCS and CPCS sublayers. Some applications do not use an SSCS, in which case the SSCS is considered null, and the CPCS comprises the...

Power Levels in DSL Services

DSL power levels are much higher than those levels used in voice, fax, or analog data services. This is simply because of the much greater attenuation of signals at DSL frequencies that are caused by the electrical characteristics of telephone lines. Because the attenuation of a phone line is much greater at ADSL frequencies than at voice frequencies, the phone line is much more attenuative to DSL than to voice, fax, or analog modems. To recover a usable signal at the end of 18 kft of cable,...

Configuring a Cisco Router for DDSSW56

This section details how to configure a Cisco router with a WAN interface card (WIC)-1DSU-56K4 for DDS or SW56 operation. Just as you do with the test patterns, you must enter the proper serial interface that is associated with your WIC for DDS SW56 configuration From this interface you can begin to configure the DDS circuit. The first command to enter is whether you are using DDS or SW56. If you use switched, you also have to specify dialer in-band for the dialing method Router(config-if)...

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Channelized and Unchannelized T3

Asynchronous T3 circuits have two modes that they can be leased in channelized or unchannelized. The difference between the two of them is rather simple. The channelized T3 is composed of 28 T1s (672 DS0s) and has all the associated overhead and bit stuffing. Unchannelized T3 circuits are composed of a single, non-multiplexed DS3 signal. Because unchannelized T3 has no bit stuffing or overhead, all the bandwidth is available for user transmission. A T3 is clocked at 44.736 Mbps. A channelized...

SS7 Node Types

Several devices in this chapter pertain to the SS7 network infrastructure. As a whole, the SS7 network has been built by using links and nodes. The network nodes, also referred to as signaling points, are physical entities on the SS7 network, and the links are the signaling communication paths between them. The three devices you see the most are the Service Switching Point (SSP), Signal Transfer Point (STP), and the Service Control Point (SCP). It is important to note that in most international...

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....

Originating Destination and Adjacent Point Codes

When referring to point codes, four different types illustrate different placements throughout the network. The Originating Point Code (OPC) describes the network device that originates the call. If you are a service provider that is just starting up, you use an OPC to identify your local switch. From your perspective, you are always the originating point for your SS7 traffic, and your point code is the destination point code for bearer traffic that you receive. As an OPC, you are the...

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...

SS7 and ISDN

Because ISDN is a local loop technology, it needs to interface to other signaling methods to transport calls all the way through the service provider's network. The call is transported through the network as ISDN, converted to SS7, transported through the service provider's network, and then converted back into ISDN, with protocol conversions taking place at the ingress and egress ISDN switch points within the network. Figure 8-20 shows a general protocol-to-protocol call flow as it is seen in...

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...

Resolving Issues with Isdn Pri

Many of the same troubleshooting techniques involved with PRI circuits are standard with T1 and E1 circuits. First and foremost, check to make sure that your controller is up and that no alarms are being detected. As a refresher, a red alarm is if you are receiving a loss of frame (LOF) or LOS. This means that you are unable to receive the proper information from the service provider's network. Next, look for a yellow or blue alarm, also called and alarm indication signal (AIS). If you are...

Introduction to DDS

This chapter provides an overview of the DDS, how it is deployed, and how it operates. Although it is fast becoming antiquated, it remains an integral part of understanding how digital services are deployed. This chapter also discusses the similarities between DDS and SW56 and details about the differences between these closely related service offerings. DDS is referred to as a digital signal customer service (DS-CS) and is deployed on a four-wire metallic interface. DDS was originally...

Docsis The Cable Modem Standard

A bi-directional cable modem technology must take into account existing CATV networks and CATV network quality and requirements for supporting IP networks. Although several proprietary cable modem network technologies exist, the internationally accepted (and by far the most popular) standard for cable IP networking is DOCSIS. Created by the MCNS to drive superior cable IP technology and to encourage competition between equipment vendors, DOCSIS and the analogous European standard Euro-DOCSIS...

Echo Cancellation

Echo cancellation is used on BRI circuits because there is only a single pair for both transmitting and receiving information. PRI circuits do not have this problem because they run off of either coaxial cable or two copper twisted pairs, one pair for transmit and one for receive. Echo cancellation is designed to remove the signal echo from a circuit so that your equipment knows what information is being sent to it. Too much echo without cancellation measures can cause problems with the network...

The Continuous State Leaky Bucket Algorithm

The continuous state leaky-bucket algorithm can be viewed as a bucket of limited capacity, the content of which drains out at a continuous rate of one unit of content per unit of time. Additionally, the bucket's content is increased by the increment, I, for each conforming cell that arrives. In practice, this limited bucket is a bounded counter that is capable of holding floating-point values. If the content of the bucket is less than or equal to the limit value, L, when a cell arrives, the...

Analog Service Deployments

Typically when you think about analog service, you imagine huge telecommunication corporations with hundreds of switches and millions of customers. This concept contains several general ideas about what the service provider or the public switched telephone network (PSTN) really is. Even if you are new to the industry, chances are you have been exposed to the infamous cloud. The cloud that encompasses anything and everything related to the service provider. These companies provide services to...

Moving Picture Experts Group MPEG Framing

In 1994, an international body of telecommunications companies, equipment manufacturers, and other interested parties agreed upon the (MPEG) standard as the preferred method to compress and distribute digital television and other video signals. DOCSIS and Euro-DOCSIS specify the transmission of IP packets over the cable plant by using this standard MPEG framing MPEG frames 188 bytes in size with a 4-byte header. MPEG framing was chosen for the specification in part because of the prevalence of...

D3 and D1D Channel Banks

While AT& T was attempting to produce a cheaper D1 channel bank, they discovered that much of the technology of the D2 channel bank also needed to be included. As a result, the D3 channel bank was suitable for long-haul connections, as was the D2. Similar to the D1, the D3 only operates on 24 channels. Unlike the D1, the D3 does so in a single stream, which precludes the need for interleaving non-consecutive channel-bytes. Nevertheless, an upgrade was made available to give D1 channel banks...

Byte Interleaved Multiplexing

SONET and SDH are based on byte-interleaved multiplexing technology. Asynchronous multiplexing, with T3 and E3 technology, uses a bit interleaved multiplexing technology. Because the interleaving takes place at the bit level, individual DS1 signals from the T3 or E3 circuits cannot be accessed individually without a complete demultiplexing of the signal. Byte-interleaved multiplexing takes a slightly different approach to multiplexing. By interleaving at the byte level (every 8 bits), each...

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...

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...

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...

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...

ABR Service Category Definition

ABR is an ATM layer service category for which the limiting ATM layer transfer characteristics, which are provided by the network, can change subsequent to connection establishment. A flow-control mechanism is specified that supports several types of feedback to control the source rate in response to changing ATM layer transfer characteristics. This feedback is conveyed to the source through specific control cells called resource management cells (RM-cells). It is expected that an end system...

Interregister Signaling

Interregister signaling is considered a multitone (MT) signaling type. Each digit dialed is collected as two discrete tones from a set of six possible tones in both directions, which combine to form the specified MT value. The use of MT signaling identifies single tone signals as faulty. A common form of MT is dual tone multifrequency (DTMF). Although not the same as R2, anytime you pick up a touch-tone phone and dial a number, the tones that you hear in your ear are DTMF tones. MT signaling is...

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...

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...

The Local Loop

The signal travels from the CO, through the copper pairs, until it reaches the mid-span repeater. At that point, the mid-span repeater dusts off and regenerates the digital signal by locking onto the combination of 1s that are being transmitted from the network. The ISDN loop can travel another 18 kft because the mid-span repeater now looks similar to the origination point of the signal. The mid-span repeater functions the same way in both directions and is not limited to network to user...

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...

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...

Alarm Conditions

T1 alarm states are commonly referred to based on the colors of the lights that the original T1 equipment used to designate that particular alarm condition. Each of the three alarms discussed in this section are considered major alarms and are not usually declared for events that do not directly result in some form of failed signal state or OOF LOS condition. In fact, many manufacturers specify a set of minor alarm conditions that serve to alert administrators to the impending risk of a major...

Upstream Signaling and Transmission with DOCSIS

Transmission of upstream data is more complex than that of downstream data. DOCSIS accepted substantial complexity to enable high theoretical upstream performance when there are many upstream transmission sources. To obtain high efficiency, traffic must be transmitted in such a way as to minimize collisions. To minimize collisions a combination of contention-based and reservation-based transmission windows are used in a method called time-division multiple access (TDMA). The CMTS controls all...

Payload CRC Field

The CRC mechanism detects single or multiple bit errors during transmission. Because the L3_PDU 32-bit CRC is not required, the 10-bit payload CRC is the only mechanism available in SMDS to accomplish this. The payload CRC uses a 10-bit generator polynomial (x10 + x9 + x5 + x4 + x1 + 1) as the divisor and the entire L2_PDU as the dividend. The remainder is placed in the payload CRC field. SIP Level 1 is broken into two major functions physical medium dependent (PMD) functions and physical layer...

PLCP for DS1 Media

The DS1 PLCP is carried in the DS1 ESF payload, such that the PLCP frame begins immediately following an F-bit anywhere in the ESF payload. The format of the DS1 PLCP frame is shown in Figure 11-22. Figure 11-22 PLCP Frame Format for DS1 Media 2 Bytes 1 Byte 1 Byte 53 Bytes 6 Bytes 2 Bytes 1 Byte 1 Byte 53 Bytes 6 Bytes In Figure 11-22, the PLCP frame is made up of ten rows, all of which have four columns except the last row which has a fifth trailer column. The first column is made up of PLCP...

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...

The Virtual Scheduling Algorithm

The virtual scheduling algorithm assumes that the source sends equally spaced cells and, based on this assumption, updates a theoretical or nominal arrival time (TN). If the actual arrival time of a cell (TA) is not early, relative to the theoretical time tempered by L (TA is after TN - L), the cell is conforming otherwise, the cell is non-conforming. Here's how all of the variables fit together. The theoretical arrival time, TN, is initially set equal to the actual arrival time of the first...

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...

Other GCRA Issues

Multiple, but generally no more than two, instances of the GCRA with independent I and L parameters can be applied to the same flow (similar CLP settings) or to multiple flows (CLP 0 and CLP 0+1) of the same connection. Technically, a cell can be considered to be conforming only if it conforms to all instances of the GCRA that apply to cells with a matching CLP state. In other words, if one instance of the GCRA tests the CLP 0 flow and another instance tests the CLP 0+1 flow, a cell with CLP 0...

Bursty Errors

Bursty errors are multiple errors that occur in short timeframes. For example, in a 1-minute timeframe, there might have been a total of 100 errors, but the 100 errors occurred in bursts of 10 errors at a time, spaced several seconds apart. To determine if errors are bursty, inspect the total DSL trained-up time and errored-seconds counters. If a unit has been trained for 1 hour, has reported 100 errors, and 1 errored second, the errors are bursty. If the unit has been trained for 1 hour, has...

Path Protection Switched

A dual-fed unidirectional path switched ring (UPSR), or path protection switching can also be used. The UPSR uses a path layer indicator to facilitate the failover process. Two fibers typically run in the ring, and traffic flows on each in the opposite direction (dual-fed). The basic operation premise of this topology is that traffic flows in opposite directions around the network on the working and protection fibers at the same time. The same information reaches RTP, but from different nodes....