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Telecommunications Essentials

Chapter 7 of Telecommunications Essentials introduces Wide Area Networking (WAN), defining networks that interconnect over long distances and integrate voice, data, and video. This chapter explores various WAN technologies including circuit-switched and packet-switched methods, such as DDS, ISDN, X.25, Frame Relay, and ATM. It discusses equipment like DSU/CSU, routers, and intelligent multiplexers, including their roles in traffic management and connectivity. Key concepts of bandwidth allocation and different service classes are also examined, emphasizing the pros and cons of each technology.

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Telecommunications Essentials

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  1. Telecommunications Essentials Chapter 7 Wide Area Networking

  2. WANs • Networks connected over long distances • Integrate voice, data, & video • Can be circuit or packet switched

  3. DDS Equipment • Digital Data Service • Leased lines operate at 56 or 64 kbps (or multiples) • DDS Hub is a digital circuit switch • DSU/CSU acts as a digital modem

  4. WAN Switching • Circuit Switched • Leased lines • ISDN • Packet Switched • X.25 • Frame Relay • ATM

  5. WAN Equipment • DSU – Controls the flow between the CPE and CSU • CSU – Performs the line conditioning • Mux – Intelligent time division multiplexer • Routers – Forward the packets • Backbones – T1/T3 or SONET paths

  6. Point to Point • Circuit switched • i.e. A head office has links to each subsidiary • No contention • Limited expansion capability

  7. Multipoint • Circuit Switched • A backbone network is shared by all offices • Competition for resources

  8. WAN Example 1 • Enterprise with 4 separate networks

  9. WAN Example 2 • Enterprise backbone network • Requires intelligent multiplexers

  10. Fractional T-1 • Multiple DS-0s can be concatenated • Supports high speed LAN interconnect • Supports video conferencing • 384 kbps required for full motion video • Frame rate is lowered to 10-15 fps on lower speed links

  11. Bandwidth Allocation • Static • Bandwidth is assigned in 64 kbps chunks • Dynamic • Bandwidth can be assigned in any increment

  12. ISDN • Circuit switched • BRI – 2B+D • Lots of different configurations • PRI – 23B+D (30B+D in Europe) • LAN/WAN integration • www.cisco.com

  13. X.25 • First generation packet system • A virtual circuit system • Designed for data over analog networks • Packet size: 128 or 256 bytes • Error checking occurs at every intermediate node • www.cisco.com

  14. X.25 • Advantages • Addressing capabilities • Can be statistically multiplexed • Basic congestion control • Error control • Disadvantages • Queuing delays • Small packet size • No QoS guarantees • Data only

  15. Frame Relay • Second generation packet system • Used by 60,000 enterprises worldwide • Used in burst environments • Supports SVC & PVC services

  16. Frame Relay • Removes the error correcting from X.25 • Digital transmission media is assumed noise free • The packet is dropped if an error is detected • The end-user application requests a retransmission • Can carry voice and video • Can encapsulate any type of data into the frame • Maximum packet size - 4096 bytes • Cannot predict delay/congestion • Frame Relay Forum

  17. Frame Relay • Advantages • Cheaper than leased lines • Runs on multiprotocol networks • Bandwidth efficient • Disadvantages • Variable delay • Assumed high quality digital links

  18. ATM • Designed to handle data, video, etc. • Can support voice • Provides QoS • 80% of Internet backbones use ATM • www.cisco.com

  19. ATM Cell • 5 byte header • 48 byte payload • Connection oriented • All cells follow the same route as defined by the VPI and VCI

  20. AAL Service Classes • AAL 1 => Service Class A (used for streams) • AAL 2 => Service Class B • AAL 3/4 => Service Class C or D • AAL 5 => Service Class C (used for most other packets)

  21. ATM • Advantages • Supports bandwidth on demand • Provides QoS • Scales in speed and network size • Disadvantages • High overhead • High service cost

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