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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 1. History of phone networks – analog, and digital 2. Circuit switched vs. packet switched networks

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Wired and wireless phone networks l.jpg

Wired and Wireless Phone Networks

An overview of telephony network technology

Dean Churchill, Ph.D.

Enterprise Architecture, AT&T Wireless, Bothell


Outline of talk l.jpg

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

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  • 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

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Circuit Switched Architecture

Mobile Phone Networks

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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

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Packet Switched Land-line Networks

Mobile Phone Networks

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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

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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

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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

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Voice Wireless Architecture

Mobile Phone Networks

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Provisioning Data Architecture

Mobile Phone Networks

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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

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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

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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

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GPRS Spectrum Utilization

Mobile Phone Networks

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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

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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

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GPRS Network

Mobile Phone Networks

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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

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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

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Authentication and Encryption

Mobile Phone Networks

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  • 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