Computer Networking: A Top-Down Approach, CH6


Terms in this set (...)

MOBILE: 2 mobile challenges
MOBILE: communication over wireless links, handling user who changes point of attachment to network
MOBILE: elements of wireless network
MOBILE: 1. wireless hosts (laptop, run apps, may be stationary or mobile)
2. base station (connected to wired network, relay responsibility of sending packets between wired and wireless)
3. wireless link (connect mobile to base station, backbone, multiple access protocol)
MOBILE: wireless modes
MOBILE: infrastructure and ad-hoc
MOBILE: infrastructure mode
MOBILE: base station connects mobiles to wired
handoff: mobile changes base station providing connection into wired
MOBILE: adhoc mode
MOBILE: no base stations
nodes can only transmit to other nodes in coverage
nodes organize network and routes
MOBILE: wireless link characteristics
MOBILE: decreased signal strength (signal attenuates as propagates)
interference from other sources (share frequencies)
multipath propagation (signal reflections arriving at dest at different times)
MOBILE: signal-to-noise ratio, larger means easier to extract signal from noise
MOBILE: physical: increase power -> increase SNR -> decrease BER
Choose physical layer that meets BER requirement at highest throughput
MOBILE: hidden terminal problem
MOBILE: B, A hear each other, B,C hear each other , A,C cannot hear each other meaning A,C unaware of interference at B (signal attenuation)
MOBILE: code division multiple access
unique code assigned to each user
share freq., but encode data with code
allows simultaneous transmission with minimal interference
orthogonal codes
MOBILE: encoded signal (CDMA)
MOBILE: original data * chipping sequence (code)
MOBILE: decoding (CDMA)
MOBILE: inner product of encoded signal and chipping sequence
MOBILE: CDMA with 2 senders
MOBILE: channel sums transmissions by both senders
MOBILE: 802.11 speeds
MOBILE: 802.11b - 2.4-5 GHz range, 11 Mbps
802.11a - 5-6 range, 54 Mbps
802.11g - 2.4-5 range, 54 Mbps
802.11n - 2.4-5 range, 200 Mbps
MOBILE: direct sequence spread spectrum, all hosts use same chipping code, 802.11b
MOBILE: 802.11 common characteristics
all have base station and ad-hoc versions
MOBILE: base station
MOBILE: access point
MOBILE: basic service set
MOBILE: BSS, aka cell, in infrastructure mode contains wireless hosts, access point, in ad-hoc mode contains hosts only
MOBILE: 802.11 channels and association
MOBILE: 802.11b divided into 11 channels, AP admin choose freq for AP, interference if channel the same as neighbor AP, host must associate with AP, scans channels for beacon frames with AP name and MAC addr, may perform authentication, run DHCP to get IP in AP's subnet
MOBILE: Passing scanning
MOBILE: 1. beacon frame sent from APs
2. send association request frame from selected AP
3. send association response frame to AP
MOBILE: Active scanning
MOBILE: 1. probe request sent from host
2. probe response from APs
3. association request from host
4. association response from selected AP
MOBILE: collision avoidance
Cant use CD due to fading signals and hidden terminals
MOBILE: CSMA/CA algorithm
MOBILE: Sender
1. if channel idle for DIFS, transmit entire frame
2. else start random backoff timer, transmit after expires, if no ACK, increase backoff interval and repeat
ACK after SIFS (need ACK cause of hidden terminal problem)
MOBILE: CTS-RTS exchange
MOBILE: collision avoidance
allow sender to reserve channel
sender transmits small request-to-send (RTS) to BS using CSMA
BS broadcasts clear-to-send (CTS)
all nodes defer transmission
MOBILE: Frame addressing
MOBILE: Address 1: MAC address of host/AP receiving
Address 2: MAC address of host/AP sending
Address 3: MAC address of attached AP
Address 4: used in ad-hoc
MOBILE: Duration (frame header)
MOBILE: duration of reserved transmission time (RTS/CTS)
MOBILE: Type (frame header)
MOBILE: frame type (RTS, CTS, ACK, data)
MOBILE: Seq control (frame header)
MOBILE: RDT sequence number
MOBILE: rate adaptation
MOBILE: base station, mobile dynamically change transmission rate as mobile moves (SNR varies)
1. SNR decreases, BER increase as node moves from BS
2. When BER becomes too high, switch to lower transmission rate but with lower BER
MOBILE: Power management
MOBILE: node-to-AP: node will sleep until next beacon frame, AP won't transmit to this node, node stays awake if AP-to-mobile frames to be sent
MOBILE: beacon frame
MOBILE: contains list of mobiles with AP-to-mobile frames waiting to be sent
MOBILE: 802.15
MOBILE: personal area network
<10m diameter
cable replacement
master/slaves/parked (inactive)
evolved from Bluetooth
MOBILE: components of cellular network architecture
MOBILE: cell
MOBILE: covers geographical region
base station
users attach through BS
MOBILE: mobile switching center
connects cells to wire tel. net.
manages call setup
handles mobility
MOBILE: techniques for sharing mobile-to-BS spectrum
MOBILE: base station system of multiple base stations connected to a base station controller (BSC)
MOBILE: voice; BSS -> BSC -> MSC -> Gateway MSC -> tel. net
MOBILE: voice + data; data network operates in parallel with voice network.
MOBILE: Serving GPRS Support node
MOBILE: Gateway GPRS support node
MOBILE: general packet radio service
MOBILE: Spectrum of mobility
MOBILE: no mobility: mobile wireless user, same access point
mid-mobility: mobile user connecting/disconnecting via DHCP
high mobility: mobile user passing through multiple access points while maintaining ongoing connections like cell phone
MOBILE: home network
MOBILE: permanent home of mobile
MOBILE: home agent
MOBILE: entity that will perform mobility functions on behalf of mobile when remote
MOBILE: permanent address
MOBILE: address in home network, can always be used to reach mobile, remains constant
MOBILE: visited network
MOBILE: network in which mobile currently resides
MOBILE: foreign agent
MOBILE: entity in visited network that performs mobility functions on mobile behalf
MOBILE: correspondent
MOBILE: wants to communicate with mobile
MOBILE: care-of-address
MOBILE: address in visited network
MOBILE: routing mobility approach
MOBILE: routers advertise permanent address of mobile-nodes-in-residence, no change to end-systems, doesn't scale
MOBILE: end-system mobility approach
MOBILE: indirect/direct routing
MOBILE: indirect routing
MOBILE: communication from correspondent to mobile goes through home agent, forwarded to remote. uses permanent address and care-of-address, mobile location is transparent to correspondent
MOBILE: direct routing
MOBILE: correspondent gets foreign address of mobiles, sends directly to mobile. overcome triangle routing problem. non-transparent to correspondent.
MOBILE: mobility registration
MOBILE: mobile contacts foreign agent on entering visited network and foreign agent contacts home agent saying this mobile is in my network -> foreign knows about mobile and home knows where mobile is
MOBILE: indirect routing steps
MOBILE: 1. correspondent sends packets to home address
2. home agent intercepts, forwards to foreign agent
3. foreign agents sends to mobile
4. mobile replies directly to correspondent
MOBILE: triangle routing
MOBILE: in indirect routing, but inefficient when correspondent and mobile in same network
MOBILE: moving in indirect routing
MOBILE: new foreign agent registers with home agent, update care-of-address
MOBILE: direct routing steps
MOBILE: 1. correspondent requests to home agent, receives foreign address
2. correspondent forwards to foreign agent
3. foreign agent forwards to mobile
4. mobile replies directly to correspondent
MOBILE: moving in direct routing
MOBILE: anchor first foreign agent, data always routed there, when mobile moves, new FA arranges to have data forwarded from old FA (chaining)
MOBILE: mobile IP components
MOBILE: indirect routing of datagrams, agent discovery, registration with home agent
MOBILE: mobile IP indirect routing
MOBILE: 1. packet sent by correspondent
2. encapsulated packet sent by home agent to foreign agent
3. foreign-agent sends to mobile
MOBILE: mobile IP agent discovery
MOBILE: agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages
MOBILE: mobile IP registration
MOBILE: foreign agent sends ICMP agent advertisement to mobile. Mobile sends registration request to foreign agent. Foreign agent sends registration request to home agent. Home agent send reg. reply to foreign agent. FA sends reg. reply to mobile
MOBILE: mobile ip home network
MOBILE: network of cellular provider subscribe to
MOBILE: home location register (HLR)
MOBILE: database in home network with permanent cell #, profile, current location
MOBILE: mobile ip visited network
MOBILE: network in which mobile currently resides. has visitor location register (VLR). could be home network
MOBILE: GSM: indirect routing
MOBILE: 1. call routed to home network
2. home MSC consults HLR, get roaming # in visited network
3. home MSC sets up 2nd leg of call to visited network
MOBILE: GSM: handoff
MOBILE: handoff goal: route call via new base station without interruption, initiated by old BSS
MOBILE: Handoff reasons
MOBILE: stronger signals, load balance, GSM mandate how