Chapter 6 Wireless and Mobile Networks

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Computer Networking: A Top Down Approach

6 th edition Jim Kurose, Keith Ross Addison-Wesley March 2012 Wireless, Mobile Networks 6-1

Elements of a cellular wireless network

network infrastructure

This is the figure your textbook uses.

I Like these figures better.

"PSTN" means the Public Switched Telephone Network "PDN" means the Public Data Network Wireless, Mobile Networks 6-2

Elements of a cellular wireless network

Wireless, Mobile Networks 6-3

Chapter 6 outline

6.1

Introduction Wireless 6.2 Wireless links, characteristics  CDMA 6.3 IEEE 802.11 wireless LANs ( “ Wi-Fi ” ) 6.4

Cellular Internet Access   architecture standards (e.g., GSM) Mobility 6.5

Principles: addressing and routing to mobile users 6.6

Mobile IP 6.7

Handling mobility in cellular networks 6.8

Mobility and higher-layer protocols 6.9

Summary Wireless, Mobile Networks 6-4

Code Division Multiple Access (CDMA)

   unique “ code ” assigned to each user; i.e., code set partitioning  all users share same frequency, but each user has own “ chipping ” sequence (i.e., code) to encode data  allows multiple users to simultaneously with minimal interference (if codes are “ orthogonal ” ) “ coexist ” and transmit

encoded signal

sequence) = (original data) X (chipping

decoding:

inner-product of encoded signal and chipping sequence Wireless, Mobile Networks 6-5

CDMA encode/decode

sender data bits d 1 = -1 code 1 1 1 1 1 slot 1 d 0 = 1 1 1 1 1 1 slot 0 Z i,m = d i .

c m channel output Z i,m 1 1 slot 1 1 1 1 1 1 1 channel output 1 1 slot 0 channel output received input 1 1 1 1 1 1 1 1 1 1 receiver code 1 1 1 1 1 slot 1 1 1 1 1 1 slot 0 D i = M S m=1 Z i,m .

c m M d 1 = -1 slot 1 channel output d 0 = 1 slot 0 channel output Wireless, Mobile Networks 6-6

CDMA: two-sender interference

channel sums together transmissions by sender 1 and 2 Sender 1 Sender 2 using same code as sender 1, receiver recovers sender 1’s original data from summed channel data!

Wireless, Mobile Networks 6-7

Chapter 6 outline

6.1 Introduction Wireless 6.2

Wireless links, characteristics  CDMA 6.3

IEEE 802.11 wireless LANs ( “ Wi-Fi ” ) 6.4 Cellular Internet access   architecture standards (e.g., GSM) Mobility 6.5

Principles: addressing and routing to mobile users 6.6

Mobile IP 6.7

Handling mobility in cellular networks 6.8

Mobility and higher-layer protocols 6.9

Summary Wireless, Mobile Networks 6-8

Components of cellular network architecture

 MSC connects cells to wired tel. net.

  manages call setup (more later!) handles mobility (more later!) cell  covers geographical region 

base station

(BS) analogous to 802.11 AP 

mobile users

attach to network through BS 

air-interface:

physical and link layer protocol between mobile and BS Mobile Switching Center Mobile Switching Center Public telephone network wired network Wireless, Mobile Networks 6-9

Cellular networks: the first hop

Two techniques for sharing mobile-to-BS radio spectrum  GSM/TDMA: divide each channel into time slots  CDMA: code division multiple access Wireless, Mobile Networks 6-10

2G (voice and text) network architecture

Base station system (BSS) BTS BSC MSC G Gateway MSC Public telephone network Legend Base transceiver station (BTS) Base station controller (BSC) Mobile Switching Center (MSC) Mobile subscribers Wireless, Mobile Networks 6-11

3G (voice+data) network architecture

MSC radio network controller G Gateway MSC Public telephone network G

Key insight:

new cellular data network operates in parallel (except at edge) with existing cellular voice network   SGSN voice network unchanged in core data network operates in parallel GGSN Public Internet Serving GPRS Support Node (SGSN) Gateway GPRS Support Node (GGSN) Wireless, Mobile Networks 6-12

3G (voice+data) network architecture

MSC radio network controller SGSN G Gateway MSC Public telephone network G Public Internet GGSN radio interface (WCDMA, HSPA ) radio access network Universal Terrestrial Radio Access Network (UTRAN) core network General Packet Radio Service (GPRS) Core Network public Internet Wireless, Mobile Networks 6-13

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Wireless, Mobile Networks 6-14