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Wired and Wireless Phone Networks

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  1. Wired and Wireless Phone Networks An overview of telephony network technology Dean Churchill, Ph.D. Enterprise Architecture, AT&T Wireless, Bothell dean.churchill@attws.com

  2. 1. History of phone networks – analog, and digital 2. Circuit switched vs. packet switched networks 3. Architecture of cellular networks 4. Multiplexing – TDMA and GSM networks 5. GPRS: Internet on a cell phone 6. GPRS Network Architecture Outline of Talk Mobile Phone Networks

  3. History • First networks (1800s) were “point-to-point”. Required N*(N-1)/2 phone lines between N phones. • First telephone offices used patch panels with human operators. Required N phone lines, but required a manual connection for each call placed. • First mechanical switches developed in late 1800s. • Digital “land-line” connections began in 1960s. • Analog wireless phones took off in 70s. Mobile Phone Networks

  4. Circuit Switched Architecture Mobile Phone Networks

  5. Circuit Switched Networks • Dedicated connections: local loop, switch, and trunk resources are dedicated to the two end-points. • Must be heavily over-designed to handle peak call volumes • Expensive, inefficient • Good for voice quality; bad for Internet connections • Billing is based on duration of call. Mobile Phone Networks

  6. Packet Switched Land-line Networks Mobile Phone Networks

  7. Packet Switched Attributes • Voice, video, images, pure data, get broken into small segments • called packets. • Each packet is encapsulated in a frame • Packet streams from multiple users are combined into a single stream • More economical, as multiple users share a common resource. Mobile Phone Networks

  8. Connection-less packet services • Connection-less packet-switched services send packets that • are routed independently of each other. • Can be routed through the network however the network • prefers. • Packets may arrive out of order, and higher-level protocol • may be needed to reorder packets. • Internet Protocol is an example (with TCP used to reorder) • Very stable networks are produced, that work around failures. • Has high overhead – lots of redundant routing information Mobile Phone Networks

  9. Connection-oriented packet services • All packets sent from same source access the same path • across the network, ensuring sequential delivery. • Has low overhead – little redundant routing information • Requires a very reliable infrastructure ( like fiber optics) • Example protocols: X.25, Frame Relay, and ATM Mobile Phone Networks

  10. Voice Wireless Architecture Mobile Phone Networks

  11. Provisioning Data Architecture Mobile Phone Networks

  12. GSM attributes • Voice and high-speed data (27-115 kbps) - carried over Internet Protocol (IP) • Packet switched rather than circuit switched • Short Message Service (over 1 billion messages per month are passed over GSM systems worldwide) • Unified messaging: integrates e-mail with voice mail. Access both from one mailbox using any phone or Internet-connected computer. Users can listen to their e-mail. • mobile commerce applications • E911 location service Mobile Phone Networks

  13. General Packet Radio Service (GPRS) • Wireless extension of the Internet all the way to mobile device • Optimized for “bursty” packet-data traffic (e.g. web site downloads). • Billing may be based on the amount of data transferred, rather than duration of call. • Allows a customer to view web pages “on line” without incurring additional cost. • Has higher transfer rates, shorter access times, improved utilization of radio spectrum Mobile Phone Networks

  14. GPRS Description continued • Provides packet-data transport at rates from 40 to 271 kilobits per seconds (as one to eight channels are used) • Voice and data operations can occur concurrently. Mobile Phone Networks

  15. GPRS Spectrum Utilization Mobile Phone Networks

  16. GPRS Characteristics • A single mobile device can transmit on one to eight channels of the same frame. • Channels are allocated only when data packets are sent or received, and they are released after the transmission. • Users experience being “on-line”, though the data channels of the radio connection may have been reallocated. • Channels can be mapped dynamically into packet switched (GPRS) service or circuit switched (conventional) service on demand. Mobile Phone Networks

  17. GPRS Characteristics (continued) • Multiple users can share one channel • Upload and download can occur simultaneously • High speed downloads available on demand • Command and control channels allow mobile device to acquire data channels dynamically. Mobile Phone Networks

  18. GPRS Network Mobile Phone Networks

  19. Gateway GRPS Support Node (GGSN) • GGSN is the interface between GPRS Network and external packet data networks (e.g. Internet). • Converts GPRS packets from SGSN into IP packets • Receives IP packets and converts them into GPRS packets • Sends packets to the SGSN • Performs authentication and charging functions Mobile Phone Networks

  20. Authentication Center (AuC) • Stores security-related data, such as encryption keys. • Indexed by the IMSI • Stores a secret key (Ki) • Key, Kc, is used for data encryption of the radio channel using the value of Ki • Kc is requested by the VLR during the setup of a connection. • The Ki and Kc pair are used for authentication and identification. Mobile Phone Networks

  21. Authentication and Encryption Mobile Phone Networks

  22. Summary • Phone networks are evolving from analog-only, land-line circuit switched networks to include wireless digital packet-switched networks • Next phase of the industry is to provide high-speed Internet service on top of voice phone service. • Heavy reliance on TCP/IP networking for the digital, packet-based components. • Global roaming on GSM phones is a likely result in the long run. Mobile Phone Networks