Computer Networks and Internets 5 e By Douglas
Computer Networks and Internets, 5 e By Douglas E. Comer Lecture Power. Points By Lami Kaya, LKaya@ieee. org © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 1
Chapter 19 Networking Technologies Past and Present © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 2
Topics Covered • • 19. 1 19. 2 19. 3 19. 4 Introduction Connection and Access Technologies LAN Technologies WAN Technologies © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 3
19. 1 Introduction • This brief chapter – highlights some of the major technologies – describes the significant features and characteristics of each – The examples • illustrate the variety of technologies that have been created • show quickly technologies change © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 4
19. 2 Connection and Access Technologies • Early chapters describe the most significant access and connection technologies (DSL and cable modems) • A variety of additional technologies have been defined – including a technology that delivers data over power lines and wireless access mechanisms • The set of technologies can be summarized as follows: – – – 19. 2. 1 19. 2. 2 19. 2. 3 19. 2. 4 19. 2. 5 19. 2. 6 Synchronous Optical Network or Digital Hierarchy (SONET/SDH) Optical Carrier (OC) Digital Subscriber Line (DSL) and Cable Modems Wi. MAX and Wi-Fi Very Small Aperture Satellite (VSAT) Power Line Communication (PLC) © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 5
19. 2 Connection and Access Technologies 19. 2. 1 Synchronous Optical Network or Digital Hierarchy (SONET/SDH) • SONET and the associated TDM hierarchy was originally designed as a system to carry digital voice telephone calls – The technology has become the standard for the digital circuits used throughout the Internet • SONET permits a physical ring to be constructed with the purpose of providing redundancy • The hardware can automatically detect and correct problems – even if one part of the ring is damaged, data can still get through • An Add-Drop Multiplexor is used to connect a site to a SONET ring • SONET uses TDM to multiplex the circuits onto the underlying fiber © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 6
19. 2 Connection and Access Technologies 19. 2. 2 Optical Carrier (OC) • The OC standards specify the signaling used on an optical fiber SONET ring • OC standards are associated with higher data rates than the T-series standards provided by SDH • A private company might choose to lease an OC circuit to connect two of the company sites • Tier-1 ISPs use circuits of OC-192 (10 Mbps) and OC-768 (40 Mbps) in the backbone of the Internet © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 7
19. 2 Connection and Access Technologies 19. 2. 3 Digital Subscriber Line (DSL) and Cable Modems • These two technologies have emerged as the principal means of providing broadband Internet access – to private residences and small businesses, known as SOHO • DSL makes use of existing telephone land lines • Cable modem technology makes use of existing cable television infrastructure • DSL offers data rates of 1 -6 Mbps – depending on the distance between a central office and a subscriber • Cable modems offer up to 52 Mbps – but the bandwidth is shared among a set of users • Both technologies are viewed as transitory – until optical fiber is available to the curb or to the home © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 8
19. 2 Connection and Access Technologies 19. 2. 4 Wi. MAX and Wi-Fi • Wi-Fi comprises a set of wireless technologies – widely used to provide Internet access in homes, cafes, airports, hotels, and other locations • Successive generations of Wi-Fi technologies have increased overall data rates • Wi. MAX is an emerging wireless technology – that can be used to form a MAN • Wi. MAX provides either access or backhaul capabilities – A connection from a remote location or access point back to a provider's central facility is known as backhaul • Two versions are defined to support fixed and mobile endpoints © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 9
19. 2 Connection and Access Technologies 19. 2. 5 Very Small Aperture Satellite (VSAT) • VSAT technologies – Generally, have a dish size of less then 3 meters • VSATs use satellite to provide Internet access to individuals or small businesses • VSATs provides high data rates • VSAT incurs long delays • Details of VSATs were given in earlier chapters © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 10
19. 2 Connection and Access Technologies 19. 2. 6 Power Line Communication (PLC) • PLC uses high frequencies to send data along power lines • The idea is to use existing infrastructure to deliver Internet access • Although much research has been done – the technology has not enjoyed widespread deployment © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 11
19. 3 LAN Technologies • Many groups proposed designs or built experimental LAN prototypes • The development of new LANs continued for many years • Several LAN technologies enjoyed popularity and commercial success • LAN technologies have begun to converge – new LANs are unexpected • The following subsections discuss some LAN technologies: – 19. 3. 1 IBM Token Ring – 19. 3. 2 Fiber and Copper Distributed Data Interconnect (FDDI and CDDI) – 19. 3. 3 Ethernet © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 12
19. 3 LAN Technologies 19. 3. 1 IBM Token Ring • IBM chose to create a token passing LAN technology that was known as IBM Token Ring • The original version of IBM's Token Ring operated at 4 Mbps – compared to the competitor, Ethernet, that operated at 10 Mbps • Later, IBM introduced a 16 Mbps version of Token Ring • Despite a lower data rate and high cost – IBM's Token Ring was widely accepted by corporate IT departments – It was a major LAN technology for many years © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 13
19. 3 LAN Technologies 19. 3. 2 Fiber and Copper Distributed Data Interconnect (FDDI and CDDI) • By the late 1980 s – it became apparent that the two chief LAN technologies • Ethernet at 10 Mbps • IBM's Token Ring at 16 Mbps had insufficient data rates to meet growing demand • The FDDI standard was created to operate at 100 Mbps • Designers argued that higher data rates required the use of optical fiber instead of copper wiring – and suggested rewiring offices to deliver fiber to the desktop • In addition, FDDI used a pair of counter-rotating rings • If an FDDI ring was cut – hardware automatically looped the data path to route traffic around the failure and keep the ring active © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 14
19. 3 LAN Technologies 19. 3. 2 Fiber and Copper Distributed Data Interconnect (FDDI and CDDI) • FDDI introduced one of the earliest LAN switches – each computer connected directly to a central FDDI mechanism – it was possible to have a physical star topology and a logical ring • It offered the highest available data rate and the opportunity for redundancy – FDDI became popular as a high-speed interconnect among computers in a data center • The high cost and special expertise needed to install fiber discouraged most organizations from replacing copper • As work on Fast Ethernet progressed – FDDI proponents created a version of FDDI • called CDDI that ran over copper wiring – Ultimately, Ethernet proved to have lower cost • and FDDI technologies vanished © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 15
19. 3 LAN Technologies 19. 3. 3 Ethernet • Ethernet has won the race and completely dominates the LAN market – Indeed, there are more Ethernets deployed than any other LAN type • Original Ethernet has disappeared completely! – and has been replaced by new technology that is still called Ethernet • There is almost no similarity between the heavy coaxial cable and RF signaling used in early Ethernet and the wiring and signaling used with gigabit Ethernet • In addition to changes in data rate, the physical and logical topologies have changed: – hubs replaced cables – Ethernet switches replaced hubs – and VLAN switches replaced switches © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 16
19. 4 WAN Technologies • Many technologies have been created for experimental and production use in WANs • This section presents a few examples that illustrate some of the diversity – – – – 19. 4. 1 19. 4. 2 19. 4. 3 19. 4. 4 19. 4. 5 19. 4. 6 19. 4. 7 ARPANET X. 25 Frame Relay Switched Multi-Megabit Data Service (SMDS) Asynchronous Transfer Mode (ATM) Multi-Protocol Label Switching (MPLS) Integrated Services Digital Network (ISDN) © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 17
19. 4 WAN Technologies 19. 4. 1 ARPANET • In the late 1960 s, the Advanced Research Projects Agency (ARPA) funded research on networking for the U. S. Department of Defense • A major ARPA research project developed a WAN to determine whether packet switching technology would be valuable for the military – It is known as the ARPANET – The network was one of the first packet switched WANs • The ARPANET connected researchers from academia and industry © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 18
19. 4 WAN Technologies 19. 4. 1 ARPANET • Although by current standards the ARPANET was slow (operated at only 56 Kbps) – the project left a legacy of concepts, algorithms, and terminology that are still in use • When the Internet project began – the ARPANET was used as the backbone • In 1983, ARPA ordered everyone connected to the ARPANET to stop using the original protocols – and begin using the Internet protocols • Thus, the ARPANET became the first Internet backbone © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 19
19. 4 WAN Technologies 19. 4. 2 X. 25 • International Telecommunications Union (ITU) – developed an early standard for WAN technology – that became popular among public carriers • The ITU was known as the Consultative Committee for International Telephone and Telegraph (CCITT) • The standard is still known as the CCITT X. 25 standard • X. 25 network consisted of 2 or more X. 25 packet switches – interconnected by leased lines – computers connected directly to packet switches • X. 25 used a connection-oriented paradigm – analogous to a telephone call; a computer was required to open a connection before transferring data © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 20
19. 4 WAN Technologies 19. 4. 2 X. 25 • X. 25 was invented before PCs became popular – many early X. 25 networks were engineered to connect ASCII terminals to remote timesharing computers • As a user entered data on a keyboard – an X. 25 network interface captured keystrokes, placed each in an X. 25 packet, and transmitted the packets across the network • When a program running on a remote computer has output – the computer passed the output to the X. 25 network interface • which placed the information in X. 25 packets for transmission back to the user's screen • Although telephone companies pushed X. 25 services – The technology was expensive for the performance it delivered – It has been replaced by other WAN technologies © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 21
19. 4 WAN Technologies 19. 4. 3 Frame Relay • It was designed to accept and deliver blocks of data – where each block can contain up to 8 K octets of data • Motivation for the large data size arises – because the inventors envisioned using Frame Relay service to bridge LAN segments • An organization with remote offices could obtain a Frame Relay service for each office – and then use the Frame Relay to forward packets from a LAN segment at one site to a LAN segment at the other • The designers chose a connection-oriented paradigm – that was acceptable to corporations with multiple offices © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 22
19. 4 WAN Technologies 19. 4. 3 Frame Relay • Frame Relay was popular – until lower-cost alternatives became available • It was designed to handle data from a LAN segment – the designers envisioned Frame Relay running at speeds between 4 and 100 Mbps (the speed of LANs when Frame Relay was created) • The high cost of Frame Relay service led many customers to choose slower connections – running at 1. 5 Mbps or 56 Kbps © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 23
19. 4 WAN Technologies 19. 4. 4 Switched Multi-megabit Data Service (SMDS) • SMDS is a high-speed wide area data service offered by long-distance carriers • It was based on IEEE standard 802. 6 DQDB – and is considered a precursor to ATM • Instead of voice traffic, SMDS is designed to carry data • SMDS is optimized to operate at the highest speeds • Header information in packets can require a significant amount of the available bandwidth • To minimize header overhead – SMDS uses a small header and constrains each packet to contain no more than 9188 octet of data • SMDS also defined a special hardware interface used to connect computers to the network © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 24
19. 4 WAN Technologies 19. 4. 4 Switched Multi-Megabit Data Service (SMDS) • The special interface makes it possible to deliver data as fast as a computer can move the data into memory • SMDS networks often operate at speeds faster than 1 Mbps (i. e. , faster than a typical Frame Relay) • The two services differed in the way they could be used – SMDS was connectionless, which gave it flexibility • Telephone companies were more comfortable with connection-oriented technologies – which meant that SMDS was not popular and has been replaced © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 25
19. 4 WAN Technologies 19. 4. 5 Asynchronous Transfer Mode (ATM) • The telecommunications industry designed ATM as an alternative to the Internet – emerged in the 1990 s • ATM had ambitious goals – designers claimed that it would replace all WAN and LAN technologies – and led to a completely uniform communication system worldwide • ATM was designed to handle video transmission as well as conventional voice telephone traffic • ATM would scale to much higher data rates than other packet switching technologies © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 26
19. 4 WAN Technologies 19. 4. 5 Asynchronous Transfer Mode (ATM) • ATM introduced a concept known as Label Switching • ATM is a connection-oriented technology – but packets do not have addresses as usual • A packet carries a small ID known as a label – a label can be changed each time the packet passes through a switch • When a connection is set up – a unique label is chosen for each link in the path – the labels are placed in tables in the switches • When a packet arrives – the switch looks up the current label – and substitutes a replacement label • In theory, label switching can be performed in hardware – it can operate at higher speed than conventional forwarding © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 27
19. 4 WAN Technologies 19. 4. 5 Asynchronous Transfer Mode (ATM) • To accommodate all possible uses – designers added many features to ATM – including mechanisms to provide end-to-end guarantees on service (e. g. , guaranteed bandwidth and bounds on delay) • When they began to implement ATM, engineers discovered – that the plethora of features meant that the hardware was complex and expensive – the mechanism created to establish label switched paths was so cumbersome that it was not used • Thus, ATM was not widely accepted and is disappearing © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 28
19. 4 WAN Technologies 19. 4. 6 Multi-Protocol Label Switching (MPLS) • MPLS is a notable result of the ATM effort; engineers adapted label switching for use in Internet routers • MPLS can be implemented in software as an extra feature • An MPLS router – – – accepts Internet packets places each packet in a special wrapper uses label switching to transport the packet across an MPLS path unwraps the packet and continues normal forwarding • Tier-1 ISPs use MPLS to allow some packets to follow a specific path – (e. g. , a large customer that pays more can have packets follow a shorter path that is not available to lower-paying customers) © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 29
19. 4 WAN Technologies 19. 4. 7 Integrated Services Digital Network (ISDN) • Chapter 12 covers ISDN in detail – this chapter only contains a short summary • ISDN was created to provide network service at a higher data rate than could be achieved with a dial-up modem • When it was first proposed, 128 Kbps seemed fast – by the time it was available, the technology seemed slow for the price • In most parts of the world, ISDN has been replaced – by DSL – by cable modems – or 3 G cellular systems since they offer much higher data rates © 2009 Pearson Education Inc. , Upper Saddle River, NJ. All rights reserved. 30
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