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Chapter 6

Chapter 6. Wide Area Networking Concepts, Architectures, and Services. Objectives. Study WAN switching: Circuit and Packet switching Study the concepts of different WAN transmissions and services: Local Loop transmissions alternatives: POTS ISDN ADSL (xDSL) Cable TV

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Chapter 6

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  1. Chapter 6 Wide Area Networking Concepts, Architectures, and Services

  2. Objectives • Study WAN switching: Circuit and Packet switching • Study the concepts of different WAN transmissions and services: • Local Loop transmissions alternatives: • POTS • ISDN • ADSL (xDSL) • Cable TV • WAN architecture and services: • X.25 • Frame Relay • SMDS • ATM (cell-relay ATM) • Broadband ISDN Goal: To understand the basic concepts of WAN Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  3. Basic Principles of WAN • Business Issues in wide area networking, like in most businesses, the desire to maximize the impact of any investment in technology is a central focus. • Technical concepts the two basic principles involved in sharing a single data link among multiple sessions are: • Packetizing – the segmenting of data transmission between devices into structured blocks or packets of data. • Multiplexing – takes packetized data from multiple sources and sends over a single wide area connection. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  4. System 1A System 1B System 2A System 2B System 3A System 3B System 4A System 4B System 5A System 5B A. Dedicated Multiple Wide Area System-to-System Connections • Dedicated point to point connections Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  5. System 1A System 1B System 2A System 2B System 3A System 3B System 4A System 4B System 5A System 5B B. Single Wide Area Link Shared to Provide Multiple System-to-System Connections • Single shared WAN link Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  6. WAN Design Principles • Performance • Cost Reduction • Security/Auditing • Availability/Reliability • Manageability & Monitoring • Quality of Service/Class of Service • Support for Business Recovery Planning Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  7. Residential and business user demands are driving forces behind WAN services. Running from customer to the entry point or gateway to the carrier’s network. The transparent interoperability of network services from different carriers. Provides the circuit or data highways over which the information is actually delivered. Circuit switching or packet switching, proper routing information. Major Components of a WAN Architecture Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  8. Wide Area Network Architecture WAN Architecture = Switching Architecture + Transmission Architecture • Switching Architecture: Methods to ensure proper routing of information from source to destination. • Transmission Architecture: Circuits or data highway over which the information is actually delivered. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  9. Broadband Transmission • T-1 • SONET (Synchronous Optical NETwork) Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  10. T-1 • It is the standard high capacity digital transmission service in America  1.544 Mbps • In other parts of the world the standard is E-1  2.048 Mbps • T-1 is divided into twenty four 64K channels. Each of which is known as DS-0. Some may be used for voice and some for data. • Each channel consists of group of 8-bits known as time slot. Each time slot represents one voice sample or a byte of data to be transmitted. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  11. T-1 Frame Layout • A T-1 frame consists of a framing bit & 24 DS-0 channels, each containing eight bits, for a total of 193 bits per frame. Figure 8-18 T-1 Frame Layout Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  12. 12 Superframes and Extended Superframes Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  13. Digital Service (DS) Hierarchy Digital Service Number of Voice Transmission Rate Corresponding Level Channels Transmission Service DS-0 1 64 Kbps DS-0 or switched 64K DS-1 24 1.544 Mbps T-1 or switched T-1 DS-1C 48 3.152 Mbps T-1C DS-2 96 6.312 Mbps T-2 DS-3 672 44.736 Mbps T-3 DS-4 4032 274.176 Mbps T-4 • T-1 and T-3 are by far the most common service levels delivered. • T-1 service is most often delivered via 4 copper wires (2 twisted pair). • T-3 service is most commonly delivered via optical fiber. • Some T-1 marketing practices is to sell Fractional T-1 or FT-1. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  14. CCITT Digital Hierarchy Digital Service Number of Voice Transmission Rate Corresponding Level Channels Transmission Service 1 30 2.048 Mbps E-1 2 120 8.448 Mbps E-2 3 480 34.368 Mbps E-3 4 1920 139.264 Mbps E-4 5 7680 565.148 Mbps E-5 • CCITT Digital Hierarchy Figure 8-20 Digital Service Hierarchy and CCITT Standards Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  15. T-1 Technology • The fundamental piece of T-1 hardware is the T-1 CSU/DSU (Channel Service Unit/Data Service Unit). Two devices are packaged as a single unit. • The CSU is a device that connects a terminal to a digital line. The DSU is a device that performs protective and diagnostic functions for a telecommunications line. Can be thought of as a very high-powered and expensive modem. • Their primary job is to convert a digital data frame from a local area network (LAN) into a frame appropriate to a wide-area network (WAN) and vice versa. • Such a device is required for both ends of a T-1 connection, and the units at both ends must be set to the same communications standard. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  16. T-1 Technology • A T-1 is commonly delivered as a 4-wire circuit (2 wires for transmit and 2 wires for receive) physically terminated with a male RJ-48c connector. • The T-1 CSU/DSU (provide the RJ-48c female connector) will transfer the 1.544 Mbps of bandwidth to local devices like, routers, over high speed connections such as V.35, RS-530, RS-449 or Ethernet that are provided on the customer side of the CSU/DSU. • A CSU/DSU are often able to communicate status and alarm information to network management systems via the Simple Network Management Protocol (SNMP). Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  17. Used to digitize analog voice and multiplex them into the DS-0 channels of T-1 frame. Commonly found in CO. Inverse MUX - Able to combine multiple T-1 output lines to provide high bandwidth requirements like video conferencing. T-1 Technology Implementation Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  18. SONET (Synchronous Optical Network) • SONET is an optical transmission service delivering multiple channels of data from various sources using periodic framing or TDM. • Much like T-1 service, but with higher capacity due to the following: • uses fiber optics. • uses slightly different framing technique. • ANSI defined it in T1.105 and T1.106 standards. • SONET in North America, SDH (Synchronous Digital Hierarchy) in the rest of the world. SDH is growing in popularity and is currently the main concern with SONET now being considered as the variation. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  19. SONET's OC (Optical Carrier) Standards Digital Service Transmission Rate Level OC-1 51.84 Mbps OC-3 155.52 Mbps OC-9 466.56 Mbps OC-12 622.08 Mbps OC-18 933.12 Mbps SONET/SDH card OC-24 1.244 Gbps OC-36 1.866 Gbps OC-48 2.488 Gbps Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  20. SONET Framing 3 Octets for control information or overhead 87 Octets for data, also called as payload 9 Frames = 1 SONET superframe Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  21. SONET Architecture • SONET network is based on layered hierarchy of transport elements and associated technology. • Section: Basic building block of a SONET network. It is built by using a single fiber optic cable between two fiber optic transmitter/receivers. A transmitter/receiver is sometimes referred to as optical repeater or also as STE (section terminating equipment). • Line: Multiple sections combine to form a SONET line. It is terminated with LTE such as add/drop MUXs. • Path: Multiple lines combine to form a SONET path. A path is an end-to-end circuit terminating in SONET access MUXs that have channel interfaces to lower speed or digital electronic transmission equipment. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  22. SONET and SDH • Section, Line and Path overhead in a SONET Frame. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  23. Add/Drop Multiplexer Note: the new signal being added can use the same optical channel (wavelength) as the dropped signal. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  24. SONET Deployment • SONET services are usually available in large metropolitan areas (MANs). • Some ATM switches are equipped with SONET interfaces for direct access to either a local SONET ring. • Carrier bring the fiber ring directly to a corporate location and assign dedicated bandwidth to each SONET customer. • Fault tolerant and reliable. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  25. SONET Architectures for Deployment • Two main types of architectures: • UPSR (Unidirectional Path-Switched Rings): Share the Capacity. • BLSR (Bidirectional Line-Switched Rings): Redundant media, traffic can be re-routed in case of fiber failure. • SONET services cost 20% more than conventional digital services of the same bandwidth. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  26. Unidirectional Path-Switched Rings(UPSR) • All users share transmission capacity around the ring rather than using dedicated segments. • Mostly used in access networks. • Provides duplicate, geographically diverse paths for each service  protecting against cable cuts and node failures. • As data travels in one direction duplicate travels in other direction for protection. • It automatically switches to the protection signal if there is a problem with primary data signal. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  27. optical access and transport node single pair fiber-optic cable UPSR Ring optical access and optical access and transport node transport node protection signal primary signal optical access and transport node Unidirectional Path-Switched Rings (UPSR) Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  28. Bidirectional Line-Switched Rings(BLSR) • In this, each user’s traffic is specifically rerouted in the case of fiber failure. • It employs 2 fiber rings with bidirectional traffic flow with each ring’s capacity divided equally between working and protection bandwidth. • BLSR survives in the event of electronic, node, cable failure by automatically routing traffic away from faults within 50msec. • Mostly used in carrier backbone networks. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  29. Each fiber has 6 STS-1a for working traffic and 6 STS-1a for protection optical access and transport node optical access and optical access and OC-12 transport node transport node Two-Fiber Bidirectional Line-Switched Ring optical access and transport node Each fiber has 6 STS-1a for working traffic and 6 STS-1a for protection Bidirectional Line-Switched Rings (BLSR) • STS-1 (Synchronous Transport Signal-level 1) bit rate is 51.84 Mbps, accommodates up to 28 T1 lines (672 multiplexed voice channels). Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  30. WaveLength Division Multiplexing (WDM) • WDM can be used only on fiber optic circuits. • It works by sending multiple simultaneous bits of information using different wavelengths of light (colors). • WDM on a single fiber can produce transmission capacity in the range of Terabits (1000 Giga) per second. • Multiplexing 8 or more wavelength is called Dense WDM (DWDM). • Individual DWDM wavelengths are called Lambdas and have a capacity of 2.4 Gbps each. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  31. WAN Switching • Circuit Switching • Packet switching (Already covered in detail in Chapter 2) Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  32. Switching Circuit switching Packet switching Leased lines Dial-up circuits Fast packet switching Original packet switching X.25 Frame relay Cell relay ATM MPLS Switched Network Services Hierarchy Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  33. X.25 • A popular standard for packet-switching networks. The X.25 standard was approved by the CCITT (now the ITU) in 1976 (30 yrs). • It defines the interface between Data Terminal Equipment (DTE) and any packet-switched network. • It is a layer 3 protocol stack OSI Reference Model. The aim is to produce packets in a standard format acceptable by any X.25 compliant public network. • It provides transparency to other upper 4-7 layers. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  34. It describes the data transfer protocol in the PDN at the network layer level. PLP manages packet exchanges between DTE devices across virtual circuits. The PLP operates in five distinct modes: call setup, data transfer, idle, call clearing, and restarting. 7. Application X.25 provides transparency to upper layers; the top 6. Presentation 4 layers need not worry about delivery of data via a packet switched network. 5. Session It enables to form a logical link connection. LAPB is a bit-oriented protocol ensures that frames are error free and in the right sequence. OSI Model 4. Transport Packet Layer Protocol 3. Network (PLP) High-Level Data Link Control Link Access Procedure-Balanced 2. Datalink X.25 (HDLC) (LAP-B) 1. Physical RS-232 OSI Model and X.25 Applications running on one computer that wish to talk to another computer do not need to be concerned with anything having to do with the packet-switched network connecting the two computers. So X.25 is a transparent delivery service between computers. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  35. Address Control Information Frame check Flag Flag field field field sequence 8 bits 8 bits 8 bits Variable 16 bits 8 bits X.25 Data-Link Layer Protocol: HDLC • The Flag fields indicate the start and end of the frame. • The Address field contain the address of the DTE/DCE, it is most important in multi-drop lines, where it is used to identify one of the terminals. • The Control field contains sequence numbers, commands and responses for controlling the data flow between the DTE and the DCE. • The Checksum field indicates whether or not errors occur in the transmission. It is the Cyclic Redundancy Codes (CRCs), also called as Frame Check Sequences (FCSs). Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  36. X.25 PAD X.25 Packet Mainframe with X.25 assembler/ X.25 disassembler protocol software Packet switched network X.25 X.25 Minicomputer with X.25 protocol software Ethernet LAN X.25 Gateway (Proxy/Firewall) X.25 Technology Implementation Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  37. X.25 Technology • Data must be properly packetized into X.25 packets before it enters the cloud. • If terminals do not possess X.25 protocol stack, they must use PAD to generate these packets. • Inside the cloud, X.25 switches are connected together in a mesh topology most often using T-1 lines. • 30 years ago, long distance circuits connecting X.25 packet switches were not as error free as they are today. So it was necessary to check for errors and request retransmissions on a point-to-point basis at every X.25 packet switch in the network. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  38. X.25 Technology Implementation Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  39. Frame Relay • Two layer protocol (physical and data link) • Frame relay is similar to X.25, but removes the error detection/correction at each of the packet switches. • So, it increases performance by using only end-to-end error correction and flow control instead of point-to-point. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  40. Error Detection and Correction • X.25 and Frame Relay use CRC for error detection on point-to-point basis. • While X.25 uses Discrete ARQ for error correction; Frame Relay does not use point-to-point error correction, it simply discards the frame. • By removing this point-to-point overhead, Frame Relay can offer speeds of T-1 and T-3 while X.25 is limited to 9.6 Kbps. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  41. X.25 Packet-switched network PAD X.25 X.25 X.25 X.25 2 4 6 7 1 3 5 PAD X.25 X.25 X.25 X.25 Steps in X.25 Error Correction 1. Regenerate CRC-16 2. Compare with transmitted CRC-16 Point-to-Point error 3. Send ACK or NAK to sending node detection and correction 4. Wait for retransmitted packet and repeat Point-to-Point vs. End-to-End Error Correction Also called as store and forward switching methodology. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  42. End-to-End error Frame relay network correction FRAD FR FR FR FR 1 FRAD FR FR FR FR Steps in Frame Relay Error Correction Point-to-Point error 1. Regenerate CRC-16 detection 2. Compare with transmitted CRC-16 3. Discard bad frames 4. Repeat process on next frame Point-to-Point vs. End-to-End Error Correction Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  43. Frame Relay Frame Layout Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  44. Frame Relay (cont'd) • A FRAD (Frame Relay Access Device) is used instead of a PAD for frame relay networks. • Frames can be variable in length, up to approx. 8000 characters. • Variable-length frames can be a problem, not good for carrying voice and video because of variable delay. • Combining these potentially large, variable-length frames with the low overhead and faster processing of the frame relay switching delivers a key characteristic of the frame relay network: High throughput with low delay. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  45. Frame Relay (cont'd) • Frame relay transmission rates can be as high as 1.544 Mbps. • bandwidth can be dynamically allocated in the mesh network of frame relay cloud. • frame relay is well suited to moving bursts of data by simply assembling and forwarding more frames per second onto the frame relay network. • Frame relay encapsulates user data and forwards it to its destination, thereby making it protocol independent. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  46. Virtual Circuits • Frame Relay networks most often employ Permanent Virtual Circuits (PVC) to forward frames from source to destination through the frame relay cloud. • Switched Virtual Circuits (SVC) standards have been defined but are not readily available from all carriers. It is analogous to dial-up call. • SVC based frame relay networks use call set-up information to the frame relay network before sending information to or receiving information from a remote frame-relay device. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  47. ATM • Asynchronous Transfer Mode (ATM) is a cell relay (or switching) architecture and standard. • Fast Packet Switching methodology • A fixed packet size (cell) makes fast switching possible, and makes it different from Frame Relay • ATM is well suited to data, voice, and digital video transmissions, because of predictable delivery time. • ATM standards are still emerging, so many incompatibilities currently exist. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  48. ATM Bandwidth Management • Three kinds of bandwidth management schemes in ATM, also known as classes of service (CoS): • CBR (Constant Bit Rate) • VBR (Variable Bit Rate) • ABR (Available Bit Rate) Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  49. Constant Bit Rate (CBR) • Guaranteed amount of bandwidth, equivalent to T-1 or T-3. This is analogous to a leased line. • Disadvantage: if the bandwidth is not required 100% of the time no other application can use the unused bandwidth Modified by Masud-ul-Hasan and Ahmad Al-Yamani

  50. Variable Bit Rate (VBR) • Provides a minimum amount of constant bandwidth, below which the available bandwidth will not drop. • This is a popular choice for voice and video conferencing data. • If more bandwidth is required it will be dynamically assigned. Modified by Masud-ul-Hasan and Ahmad Al-Yamani

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