Radio Transmission

Radio encompasses the electromagnetic spectrum in the range of 3 kHz to 300 GHz. In radio communications the signal is transmitted into the air or space, using an antenna that radiates energy at some carrier frequency. For example, in QAM modulation the information sequence determines a point in the signal constellation that specifies the amplitude and phase of the cosine wave that is transmitted. Depending on the frequency and the antenna, this energy can propagate in either a unidirectional...

Label Stack

Labels are attached and removed from packets as follows. When a packet enters a particular domain, the ingress LSR creates a new label for the packet by performing a label push. Subsequent LSRs in the domain only swap the incoming label to the outgoing label. When the packet leaves the domain, the egress LSR performs a label pop. It is possible for a packet to have a stack of m labels (or m levels). In a given domain the label at the top of the stack (depth 1) is the only one that determines...

Lane

LAN emulation (LANE) is an ATM Forum specification intended to accelerate the deployment of ATM in the enterprise network. Typically, a host runs an internetwork layer protocol such as IP over a legacy LAN such as Ethernet or token ring. LANE enables any software that runs on a legacy LAN to also run on an ATM network without any modification. LANE works by presenting the network layer with an interface that is identical to that of legacy LANs. Figure 10.3 illustrates the changes in the lower...

LAN emulation configuration server LECS

A LEC resides in the end system (e.g., host, server, bridge, etc.) and performs data forwarding, address resolution, and control functions. Each LEC is identified by a unique ATM address. A LES responds to LEC address resolution requests by resolving MAC addresses to ATM addresses. A BUS handles broadcast, multicast and initial (i.e., before a VCC is established) traffic in a given ELAN. One main purpose of the LAN Emulation Configuration Server (LECS) is to assign LECs to the corresponding...

Baset Ethernet

The 100BASE-T Ethernet LAN is also known as Fast Ethenet. As indicated by the designation, 100BASE-T Ethernet operates at a speed of 100 Mbps using twisted-pair wire. The computers are connected to a hub or a switch in a star topology, and the distance of the twisted pairs is limited to 100 meters. Operating 100 Mbps on UTP is challenging, and so three options for doing so were developed, one for category 3 UTP, one for shielded twisted pair, and one for category 5 UTP. One problem with...

Cellular Telephone Networks

Cellular telephone networks extend the basic telephone service to mobile users with portable telephones. Unlike conventional telephone service where the call to a telephone number is directed to a specific line that is connected to a specific switch, in cellular telephony the telephone number specifies a specific subscriber's mobile station (telephone). Much of the complexity in cellular telephony results from the need to track the location of the mobile station. In this section we discuss how...

Link Sharing Using Packet Multiplexers

In Chapter 1 we discussed how applications in early terminal-oriented networks were found to generate data in a bursty fashion Message transmissions would be separated by long idle times. Assigning a dedicated line to transmission from a single terminal resulted in highly inefficient use of the line. Such inefficiency became a serious issue when the transmission lines involved were expensive, as in the case of long-distance lines. Statistical multiplexers were developed to concentrate data...

Book Overview

This chapter provides the big picture of the communication network. We have identified fundamental concepts that form the basis for the operation of these networks. These fundamental concepts appear in various forms in different network architectures. The particular form at any given time depends on the available technology and the prevailing commercial and regulatory environment. Concepts appear, disappear, and reappear as demonstrated by the example of the digital network in telegraphy that...

RTP Scenarios and Terminology

Let's introduce some terminology, using first an audio conference example and then an audiovisual conference example. An RTP session is an association among a group of participants communicating via RTP. Suppose for now that the RTP session involves an audio conference. The chair of the conference makes arrangements to obtain an IP multicast group address and a pair of consecutive UDP port numbers that identify the RTP session. The first port number (even) is for RTP audio and the other port...

Networks And Services

A communication network, in its simplest form, is a set of equipment and facilities that provides a service the transfer of information between users located at various geographical points. In this textbook, we focus on networks that use electronic or optical technologies. Examples of such networks include telephone networks, computer networks, television broadcast networks, cellular telephone networks, and the Internet. Communication networks provide a service much like other ubiquitous...

Speech Interpolation and the Multiplexing of Packetized Speech

In telephone networks a connection is set up so that speech samples traverse the network in a single uninterrupted stream. Normal conversational speech, however, is moderately bursty as it contains silence periods. In this section we consider the multiplexing of packetized speech. First, consider n one-way established telephone connections. In a typical conversation a person is actively speaking less than half of the time. The rest of the time is taken up by the pauses inherent in speech and by...

Summary Of Digital Transmission

This chapter had two primary objectives. The first was to introduce a discussion of the protocols that operate within a layer and to the services that they provide to the layer above them. We considered the simplest case in which only two peer processes are involved in executing a protocol to provide a service, namely, the transfer of information in a manner that satisfies certain conditions. The second primary objective was to introduce the two important examples of such peer-to-peer protocols...

Shannon Channel Capacity Of Telephone Channel

Consider a telephone channel with W 3.4 kHz and SNR 10,000. The channel capacity is then C 3400 log2(1 + 10000) 44,800 bits second The following identities are useful here log2x lnx ln2 log10x log102. We note that the SNR is usually stated in dB. Thus if SNR 10,000, then in dB the SNR is 10 logi0 SNR dB 10 logi0 10000 40 dB The above result gives a bound to the achievable bit rate over ordinary analog telephone lines. FIGURE 3.24 Probability of error for an interior signal level

Fragmentation and Reassembly

One of the strengths of IP is that it can work on a variety of physical networks. Each physical network usually imposes a certain packet-size limitation on the packets that can be carried, called the maximum transmission unit (MTU). For example, Ethernet specifies an MTU of 1500 bytes, and FDDI specifies an MTU of 4464 bytes. When IP has to send a packet that is larger than the MTU of the physical network, IP must break the packet into smaller fragments whose size can be no larger than the MTU....

Wireless LANs and IEEE 80211 Standard12

The case for wireless LANs is quite compelling. All you have to do is look under the desks in a typical small business or home office. You will find a rat's nest of wires in addition to a variety of power cords and adapters, you have cables for a telephone modem, a printer, a scanner, a mouse, and a keyboard. In addition, there is the need for communications to synchronize files with laptop computers and personal organizers. And, of course, there is still the need to connect to other computers...

Timing Recovery for Synchronous Services

Many applications involve information that is generated in a synchronous and periodic fashion. For example, digital speech and audio signals generate samples at the corresponding Nyquist sampling rate. Video signals generate blocks of compressed information corresponding to an image 30 times a second. To recover the original signal at the receiver end, the information must be input into the decoder at the same rate at which it was produced at the encoder. Figure 5.28 shows the effect of a...

Ihl Telecommunication

Transmitted according to network byte order bits 0-7 first, then bits 8-15, then bits 16-23, and finally bits 24-31 for each row. The meaning of each field in the header follows. Version The version field indicates the version number used by the IP packet so that revisions can be distinguished from each other. The current IP version is 4. Version 5 is used for a real-time stream protocol called ST2, and version 6 is used for the new generation IP know as IPng or IPv6 (to be discussed in the...

Key Factors In Communication Network Evolution

In the previous section we traced the evolution of communication networks from telegraphy to the emerging integrated services networks. Before proceeding with the technical details of networking, however, we pause to discuss factors that influence the evolution of communication networks. Figure 1.19 shows the three traditional factors technology, regulation, and market. To these we add standards, a set of technical specifications followed by manufacturers or service providers, as a fourth...

Multiple Access Communications

FIGURE 6.2 Approaches to sharing a transmission medium Networks based on radio communication provide examples where a medium is shared. Typically, several stations share two frequency bands, one for transmitting and one for receiving. For example, in satellite communications each station is assigned a channel in an uplink frequency band that it uses to transmit to the satellite. As shown in Figure 6.3 the satellite is simply a repeater that takes the uplink signals that it receives from many...

Example Using RSA

Let us consider the following simple example. Suppose we have chosen p 5, and q 11. Then n 55, and p 1 q 1 40. Next find a number e that is relatively prime to 40, say, 7. The multiplicative inverse of 7 modulo 40 yields d 23. From number theory we can find such a d only if e is relatively prime to p 1 q 1 . Now the public key is 7, 55 , and the private key is 23, 55 . Suppose a message RSA is to be protected. For simplicity the message is represented numerically as 18, 19, 1 and uses three...

Transmission Facilities

The user's telephone is connected to its local telephone office by twisted-pair copper wires that are called the local loop. The wire pairs are stranded into groups, and the groups are combined in cables that can hold up to 2700 pairs. Wire pairs connect to the telephone office at the distribution frame as shown in Figure 4.33. From the local office the feeder cables extend in a star topology to the various geographic serving areas. Each feeder cable connects to a serving area interface....

Nhrp

Responsible for answering NHRP resolution requests by means of NHRP replies. Both NHC and NHS maintain an address resolution cache. An NHC in NHRP basically replaces an ATMARP client in the classical IP model, and an NHS basically replaces an ATMARP server. The NHRP protocol works as follows. When node S which contains an NHC wants to transmit data to the destination node D, S may want to send the data through a VCC. If S does not know the ATM address of D, station S first sends an NHRP...

Frame Structure

The structure of the token and data frames for the IEEE 802.5 standard is shown in Figure 6.61. The token frame consists of three bytes. The first and last bytes are the starting delimiter SD and ending delimiter ED fields. The standard uses differential Manchester line coding. Recall from Chapter 3 Figure 3.25 that this line coding has transitions in the middle of each bit time. The SD and ED bytes are characterized by the fact that they contain symbols that violate this pattern the J symbol...

Comparison of Random Access and Scheduling Medium Access Controls

The two classes of medium access control schemes, random access and scheduling, differ in major ways, but they also share many common features. Their differences stem primarily from their very different points of departure. Scheduling techniques have their origins in reservation systems that attempt to emulate the performance of a centrally scheduled system such as a multiplexer. Random access techniques, on the other hand, have their origins in the ALOHA scheme that involves transmitting...

Problems

Describe the step-by-step procedure that is involved from the time you deposit a letter in a mailbox to the time the letter is delivered to its destination. What role do names, addresses, and mail codes such as ZIP codes or postal codes play How might the letter be routed to its destination To what extent can the process be automated b. Repeat part a for an e-mail message. At this point you may have to conjecture different approaches about what goes on inside the computer network. c. Are...

Classical IP Over ATM

The classical IP over ATM CLIP model RFC 2255 is an IETF specification whereby IP treats ATM as another subnetwork to which IP hosts and routers are attached. In the CLIP model multiple IP subnetworks are typically overlaid on top of an ATM network. The part of an ATM network that belongs to the same IP subnetwork is called a logical IP subnetwork LIS , as shown in Figure 10.2. All members IP end systems in the same LIS must use the same IP address prefix e.g., the same network number and...

Gigabit Ethernet

The IEEE 802.3z Gigabit Ethernet standard was completed in 1998 and established an Ethernet LAN that increased the transmission speed over that of Fast Ethernet by a factor of 10. The goal was to define new physical layers but to again retain the frame structure and procedures of the 10 Mbps IEEE 802.3 standard. The increase in speed by another factor of 10 put a focus on the limitations of the CSMA-CD MAC algorithm. For example, at a 1 Gbps speed, the transmission of a minimum size frame of 64...

Tcp 302

Timing recovery 300, 335, 645 Burst error model 157, 166-67, 176-77, 293 Bursty 21, 22, 29, 313-14, 318, 322, 340-41, 347, 380, 382, 396, 450, 466, 503-04, 628, 638-39 Busy hour 233 C language programs 72-79, 160 Cable modem 143, 344 Cable television CATV 2, 31, 33, 42, 110, 140-43, 195, 253, 258 CAIDA 86, 93 Care-of address 589-90 Carried load 824 Carrier sensing 26, 359, 361, 427, 450 Carrier sensing multiple access CSMA 359-61, 365, 425, 428, 454 Carrier sensing multiple access with...

Fast Ethernet

The IEEE 802.3u standard was approved in 1995 to provide Ethernet LANs operating at 100 Mbps. We refer to systems that operate under this standard as Fast Ethernet. To maintain compatibility with existing standards, the frame format, interfaces, and procedures have been kept the same. Recall that the performance of the CSMA-CD medium access control is sensitive to the ratio of the round-trip propagation delay and the frame transmission time. To obtain good performance, this ratio must be small....

Nyquist Sampling Theorem

We now explain how the Nyquist sampling theorem comes about. Let x kT be the sequence of samples that result from the sampling of the analog signal x t . Consider a sequence of very narrow pulses S t kT that are spaced T seconds apart and whose amplitudes are modulated by the sample values x kT as shown in Figure 12.16. Signal theory enables us to show that y t has the spectrum in Figure 12.16, where the spectrum of x t is given by its Fourier transform The spectrum X f is defined for positive...

Token Ring and IEEE 8025 LAN Standard

Several versions of token-ring networks were developed in the 1970s and 1980s in token rings a number of stations are connected by point-to-point transmission links in a ring topology. Information flows in one direction along the ring from the source to the destination and back to the source. The key notion is that medium access control is provided via a small frame called a token that circulates around a ring-topology network. Only the station that has possession of the token is allowed to...

Emd0 Network Interface

The IP layer in the end-system hosts and in the routers work together to route packets from IP network sources to destinations. The IP layer in each host and router maintains a routing table that it uses to determine how to handle each IP packet. Consider the action of the originating host. If its routing table indicates that the destination host is directly connected to the originating host by a link or 3150 128 16 4 2, which gives 1001 0110 similarly 100 64 32 4 15 8 4 2 1 11 8 2 1. by a LAN,...

PNNI Signaling

Pnni Signaling Images

The ATM Forum has developed the PNNI specification for use between private ATM switches private network node interface and between groups of private ATM switches private network-to-network interface as shown in Figure 9.24. The PNNI specification includes two types of protocols. 1. A routing protocol that provides for the selection of routes that can meet QoS requirements this routing protocol is discussed in the next section . 2. A complementary signaling protocol for the exchange of messages...

Arq Selective Repeat Diagram

Selective Repeat Arq Timing Diagram

Suppose that the data link control just transfers frames and does not implement error control. Find the probability that the message arrives without errors at station p. b. Suppose that error recovery is carried out end to end and that if there are any errors, the entire message is retransmitted. How many times does the message have to be retransmitted on average c. Suppose that the error recovery is carried out end to end on a packet by packet basis. What is the total number of packet...

Info

Finally, consider the World Wide Web WWW application that potentially includes the requirements of many of the previous applications. This application builds on a page of text and image information to include audio, video, and varying degrees of interactivity. The point-and-click nature of the application implies responsiveness requirements that have yet to be met by existing networks. In addition, the use of the Web for electronic commerce brings security concerns to the forefront. Together...

Consider The Synchronous Multiplexing In Fig 4.17. Explain How The Pointers In The Outgoing Sts-1 Signal Are Determined

A television transmission channel occupies a bandwidth of 6 MHz. a. How many two-way 30 kHz analog voice channels can be frequency-division multiplexed in a single television channel b. How many two-way 200 kHz GSM channels can be frequency-division multiplexed in a single television channel c. Discuss the trade-offs involved in converting existing television channels to cellular telephony channels 2. A cable sheath has an inner diameter of 2.5 cm. a. Estimate the number of wires that can be...

The Nyquist Signaling Rate

Nyquist Rate Transmission

Let p t be the basic pulse that appears at the receiver after it has been sent over the combined transmitter filter, communication channel, and receiver filter. The first pulse is transmitted, centered at t 0. If the input bit was 1, then Ap t FIGURE 3.19 Digital baseband signal and baseband transmission system FIGURE 3.19 Digital baseband signal and baseband transmission system should be received if the input was 0, then Ap t should be received instead. For simplicity, we assume that the...

Optical Fiber

The deployment of digital transmission systems using twisted pair and coaxial cable systems established the trend toward digitization of the telephone network during the 1960s and 1970s. These new digital systems provided significant economic advantages over previous analog systems. Optical fiber transmission systems, which were introduced in the 1970s, offered even greater advantages over copper-based digital transmission systems and resulted in a dramatic acceleration of the pace toward...

Dic

Selective Repeat Lost

FIGURE 5.22 Maximum window size in Selective Repeat ARQ FIGURE 5.22 Maximum window size in Selective Repeat ARQ Wait ARQ. Of course, this performance level is in exchange for significantly greater complexity. Example Transmission Control Protocol The Transmission Control Protocol TCP uses a form of Selective Repeat ARQ to provide end-to-end error control across a network. TCP is normally used over internets that use IP to transfer packets in connectionless mode. TCP must therefore contend with...

Transmission Efficiency of ARQ Protocols

Arq Delay Diagram

In the previous sections we already introduced the performance differences between Stop-and-Wait, Go-Back-N, and Selective Repeat ARQ protocols. In this section we discuss performance results for these protocols and present a quantitative comparison of their transmission efficiency. We show that the delay-bandwidth product, the frame error rate, and the frame length are key parameters in determining system performance. For simplicity we focus here on the case where the information is...

Error Detection

In this section we discuss the idea of error detection in general terms, using the single parity check code as an example throughout the discussion. The basic idea in performing error detection is very simple. As illustrated in Figure 3.49, the information produced by an application is encoded so that the stream that is input into the communication channel satisfies a specific pattern or condition. The receiver checks the stream coming out of the communication channel to see whether the pattern...

Twisted Pair

The simplest guided transmission medium consists of two parallel insulated conducting e.g., copper wires. The signal is transmitted through one wire while a ground reference is transmitted through the other. This two-wire system is susceptible to crosstalk and noise. Crosstalk refers to the picking up of electrical signals from other adjacent wires. Because the wires are unshielded, there is attenuation for wireless media is proportional to n log10 d dB also a tendency to pick up noise, or...

Tcp Connection Termination

Tcp Connection Termination

TCP provides for a graceful close that involves the independent termination of each direction of the connection. A termination is initiated when an application tells TCP that it has no more data to send. The TCP entity completes transmission of its data and, upon receiving acknowledgment from the receiver, issues a segment with the FIN bit set. Upon receiving a FIN segment, a TCP entity informs its application that the other entity has terminated its transmission of data. For example, in Figure...

Token Passing Rings

Polling can be implemented in a distributed fashion on networks with a ring topology. As shown in Figure 6.30, such ring networks consist of station interfaces that are connected by point-to-point digital transmission lines. Each interface acts like a repeater in a digital transmission line but has some additional functions. An interface in the listen mode reproduces each bit that is received at its input at its output after some constant delay, ideally in the order of one bit time. This delay...

Ip Forwarding Architectures

1 Pure destination-based forwarding lookup based on IP address a Overlay model b Peer model a Overlay model b Peer model typically required implementation in software or firmware. Category 2 can be further classified into the overlay model and the peer model. In the overlay model, ATM switches are not aware of IP addresses and IP routing protocols. This model overlays an IP network onto an ATM network, essentially creating two network infrastructures with two addressing schemes and two routing...

Typical Frame Exchanges

We now consider a number of simple examples to show how the frames that are defined for HDLC can be used to carry out various data link control procedures. We use the following convention to specify the frame types and contents in the following figures. The first entry indicates the contents of the address field the second entry specifies the type of frame, that is, I for information, RR for receive ready, and so on the third entry is N S in the case of I-frames only, the send sequence number...

T

b Combined signal transmits 1 unit every T seconds At Bt Ct A B2 C2 gt 0T 1T 2T 3T 4T 5T 6T t The T-l system uses a transmission frame that consists of 24 slots of eight bits each. Each slot carries one PCM sample for a single connection. The beginning of each frame is indicated by a single bit that follows a certain perodic pattern. The resulting transmission line has a speed of l 24 x 8 bits frame x 8000 frames second 1.544 Mbps Note how in TDM the slot size and the repetition rate...

Network Services And Internal Network Operation

The essential function of a network is to transfer information among the users that are attached to the network or internetwork. In Figure 7.1 we show that this transfer may involve a single block of information or a sequence of blocks that are temporally related. In the case of a single block of information, we are interested in having the block delivered correctly to the destination, and we may also be interested in the delay experienced in traversing the network. In the case of a sequence of...

Subnet Addressing

The original IP addressing scheme described above has some drawbacks. Consider a typical university in the United States that has a Class B network address which can support about 64,OOO hosts connected to the Internet . With the original addressing scheme, it would be a gigantic task for the local network administrator to manage all 64,OOO hosts. Moreover, a typical campus would have more than one local network, requiring the use of multiple network addresses. To solve these problems, subnet...

Cellular Bucket

Suppose that instead of ATM, BISDN had adopted a transfer mode that would provide constant-bit-rate connections with bit rates given by integer multiples of 64 kbps connections. Comment on the multiplexing and switching procedures that would be required to provide this transfer mode. Can you give some reasons why BISDN did not adopt this transfer mode 2. a. Compare the bandwidth management capabilities provided by ATM virtual paths to the capabilities provided by SONET networks. b. Can ATM...

A5 Erlang B Formula Mmcc System

In Figure A.14 we show the M M c c queueing model that can be used to model a system that handles trunk connection requests from many users. We assume trunk requests with exponential interarrival times with rate A requests second. Each trunk is viewed as a server, and the connection time is viewed as the service time X. Thus each trunk or server has a service rate x 1 E X . We assume that connection requests are blocked if all the trunks are busy. The state of the preceding system is given by N...

That Digital Signal Processing Software Can Be Used To Do The Particular Required Processing. Suppose That A Software

Repeat part a using the m 3 and m 5 codes from Figure 12.6. 7. Consider a binary source that produces information bits bt independent of each other and where P bt 0 p and P bt 1 1 p. Let l be the number of consecutive 0s before a 1 occurs. a. Show that P l i 1 p pi, for i 0,1, 2, b. Show that P l gt L pL 1. c. Find the performance of the run-length code in Figure 12.5 for m 4 when p16 1 2. d. Find the performance of the run-length code in Figure 12.7 for m 4 when p16 1 2 and compare it to...

Performance Of Linear Codes

In Figure 3.51 we showed qualitatively that we can minimize the probability of error-detection failure by spacing codewords apart in the sense that it is unlikely for errors to convert one codeword into another. In this section we show that the error-detection performance of a code is determined by the distances between codewords. The Hamming distance d b1, b2 between the binary vectors b1 and b2 is defined as the number of components in which they differ. Thus the Hamming distance between two...

SNR Performance of Quantizers

We now derive the SNR performance of a uniform quantizer. When the number of levels M is large, then the error values are approximately uniformly distributed in the interval A 2, A 2 . The power in the error signal is then given by Let o2x be the average power of the signal x t . Then the SNR is given by From the definition of the quantizer, we have that A 2V M and that M 2m therefore SNR _fL J L. 3 V 3 222' A2 12 4V2 M2 V V The SNR, stated in decibels, is then SNR dB 10log10 ct2 o2 6m 10log10...

Comparison of Scheduling Approaches to Medium Access Control

We have discussed two basic scheduling approaches to medium access control reservations and polling. Token-passing rings are essentially an extension of the polling concepts to ring-topology networks. The principal strength of these approaches is that they provide a relatively fine degree of control in accessing the medium. These approaches can be viewed as an attempt to make timedivision multiplexing more efficient by making idle slots available to other users. Reservation systems are the most...

Effectiveness Of Errordetection Codes

The effectiveness of an error-detection code is measured by the probability that the system fails to detect an error. To calculate this probability of error-detection failure, we need to know the probabilities with which various errors occur. These probabilities depend on the particular properties of the given communication channel. We will consider three models of error channels the random error vector model, the random bit error model, and burst errors. Suppose we transmit a codeword that has...

Group Of 32 Stations Is Serviced By A Token Ring

Compare the two-channel approach Figure 6.4 with the single-channel approach Figure 6.5 in terms of the types of MAC protocols they can support. 4. Consider an open concept office where 64 carrels are organized in an 8 x 8 square array of 3 m x 3 m space per carrel with a 2 m alley between office rows. Suppose that a conduit runs in the floor below each alley and provides the wiring for a LAN to each carrel. a. Estimate the distance from each carrel to a wiring closet at the side of the...

Example Using the UDP Protocol

Let us now take a look at client server programs using the UDP protocol. The following source code is a program that uses the UDP server as an echo server as before. Note that data receipt can be done in a single call with recvfrom, since UDP is blocked oriented. Echo server using UDP include lt stdio.h gt include lt sys types.h gt include lt sys socket.h gt include lt netinet in.h gt define SERVER_UDP_PORT 5000 well-known port define MAXLEN 4096 maximum data length port SERVER_UDP_PORT break...