Chapter 6 slides, Computer Networking, 3rd edition

1
Chapter 6Wireless and Mobile Networks Part B
The majority of these slides are adapted from Jim
Kurose, Keith Ross, Addison-Wesley, July
2004.Slides from other sources and from Vasos
Vassiliou may have been included in this
presentation.
2
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

3
What is mobility?

• spectrum of mobility, from the network
  perspective

mobile wireless user, using same access point
mobile user, passing through multiple access
point while maintaining ongoing connections (like
cell phone)
mobile user, connecting/ disconnecting from
network using DHCP.
4
Mobile Communication

• Two aspects of mobility
• user mobility users communicate (wireless)
  anytime, anywhere, with anyone
• device portability devices can be connected
  anytime, anywhere to the network
• Wireless vs. mobile Examples ? ?
  stationary computer ? ? notebook in a
  hotel ? ? wireless LANs in historic
  buildings ? ? Personal Digital Assistant
  (PDA)

5
What is Mobility?

• A device that moves
• Between different geographical locations
• Between different networks
• A person who moves
• Between different geographical locations
• Between different networks
• Between different communication devices
• Between different applications

6
Device mobility

• Plug in laptop at home/work on Ethernet
• Occasional long breaks in network access
• Wired network access only (connected gt
  well-connected)
• Network address changes
• Only one type of network interface
• May want access to information when no network is
  available hoard information locally
• Cell phone with access to cellular network
• Continuous connectivity
• Phone remains the same (high-level network
  address)
• Network performance may vary from place to place

7
Device mobility, continued

• Can we achieve best of both worlds?
• Continuous connectivity of wireless access
• Performance of better networks when available
• Laptop moves between Ethernet, WLAN and Cellular
  networks
• Wired and wireless network access
• Potentially continuous connectivity, but may be
  breaks in service
• Network address changes
• Radically different network performance on
  different networks

8
People mobility

• Phone available at home or at work
• Multiple phone numbers to reach me
• Breaks in my reachability when Im not in
• Cell phone
• Only one number to reach me
• Continuously reachable
• Sometimes poor quality and expensive connectivity
• Cell phone, networked PDA, etc.
• Multiple numbers/addresses for best quality
  connection
• Continuous reachability
• Best choice of address may depend on senders
  device or message content

9
Mobility means changes

• How does it affect the following?
• Hardware
• Lighter
• More robust
• Lower power
• Wireless communication
• Cant tune for stationary access
• Network protocols
• Name changes
• Delay changes
• Error rate changes

10
Changes, continued

• Fidelity
• High fidelity may not be possible
• Data consistency
• Strong consistency no longer possible
• Location/transparency awareness
• Transparency not always desirable
• Names/addresses
• Names of endpoints may change
• Security
• Lighter-weight algorithms
• Endpoint authentication harder
• Devices more vulnerable

11
Changes, continued, again

• Performance
• Network, CPU all constrained
• Delay and delay variability
• Operating systems
• New resources to track and manage energy
• Applications
• Name changes
• Changes in connectivity
• Changes in quality of resources
• People
• Introduces new complexities, failures, devices

12
Mobile and wireless services Always Best
Connected
13
Example changes

• Addresses
• Phone numbers, IP addresses
• Network performance
• Bandwidth, delay, bit error rates, cost,
  connectivity
• Network interfaces
• PPP, eth0, strip
• Between applications
• Different interfaces over phone laptop
• Within applications
• Loss of bandwidth triggers change from color to
  BW
• Available resources
• Files, printers, displays, power, even routing

14
Effects of device portability

• Power consumption
• limited computing power, low quality displays,
  small disks due to limited battery capacity
• CPU power consumption CV2f
• C internal capacity, reduced by integration
• V supply voltage, can be reduced to a certain
  limit
• f clock frequency, can be reduced temporally
• Loss of data
• higher probability, has to be included in advance
  into the design (e.g., defects, theft)
• Limited user interfaces
• compromise between size of fingers and
  portability
• integration of character/voice recognition,
  abstract symbols
• Limited memory
• limited value of mass memories with moving parts
• flash-memory or ? as alternative

15
Mobile devices
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Summing up

• Generally, mobility stresses all resources
  further
• CPU
• Power
• Bandwidth
• Delay tolerance
• Radio spectrum
• Human attention
• Physical size
• Constraints on peripherals and GUIs (modality of
  interaction)
• Locations (body parts!) for device placement

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Mobility Vocabulary
home network permanent home of mobile (e.g.,
128.119.40/24)
home agent entity that will perform mobility
functions on behalf of mobile, when mobile is
remote
wide area network
Permanent address address in home network, can
always be used to reach mobile e.g.,
128.119.40.186
correspondent
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Mobility more vocabulary
visited network network in which mobile
currently resides (e.g., 79.129.13/24)
Permanent address remains constant (e.g.,
128.119.40.186)
Care-of-address address in visited
network. (e.g., 79,129.13.2)
wide area network
home agent entity in visited network that
performs mobility functions on behalf of mobile.
correspondent wants to communicate with mobile
19
How do you contact a mobile friend
I wonder where Alice moved to?
Consider friend frequently changing addresses,
how do you find her?

• search all phone books?
• call her parents?
• expect her to let you know where he/she is?

20
Mobility approaches

• Let routing handle it routers advertise
  permanent address of mobile-nodes-in-residence
  via usual routing table exchange.
• routing tables indicate where each mobile located
• no changes to end-systems
• Let end-systems handle it
• indirect routing communication from
  correspondent to mobile goes through home agent,
  then forwarded to remote
• direct routing correspondent gets foreign
  address of mobile, sends directly to mobile

21
Mobility approaches

• Let routing handle it routers advertise
  permanent address of mobile-nodes-in-residence
  via usual routing table exchange.
• routing tables indicate where each mobile located
• no changes to end-systems
• let end-systems handle it
• indirect routing communication from
  correspondent to mobile goes through home agent,
  then forwarded to remote
• direct routing correspondent gets foreign
  address of mobile, sends directly to mobile

not scalable to millions of mobiles
22
Mobility registration
visited network
home network
wide area network

• End result
• Foreign agent knows about mobile
• Home agent knows location of mobile

23
Mobility via Indirect Routing
visited network
home network
wide area network
24
Indirect Routing comments

• Mobile uses two addresses
• permanent address used by correspondent (hence
  mobile location is transparent to correspondent)
• care-of-address used by home agent to forward
  datagrams to mobile
• foreign agent functions may be done by mobile
  itself
• triangle routing correspondent-home-network-mobil
  e
• inefficient when
• correspondent, mobile
• are in same network

25
Indirect Routing moving between networks

• suppose mobile user moves to another network
• registers with new foreign agent
• new foreign agent registers with home agent
• home agent update care-of-address for mobile
• packets continue to be forwarded to mobile (but
  with new care-of-address)
• mobility, changing foreign networks transparent
  on going connections can be maintained!

26
Mobility via Direct Routing
correspondent forwards to foreign agent
visited network
home network
wide area network
correspondent requests, receives foreign address
of mobile
27
Mobility via Direct Routing comments

• overcome triangle routing problem
• non-transparent to correspondent correspondent
  must get care-of-address from home agent
• what if mobile changes visited network?

28
Accommodating mobility with direct routing

• anchor foreign agent FA in first visited network
• data always routed first to anchor FA
• when mobile moves new FA arranges to have data
  forwarded from old FA (chaining)

foreign net visited at session start
anchor foreign agent
wide area network
new foreign network
correspondent agent
new foreign agent
correspondent
29
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

30
Mobile IP

• RFC 3220
• has many features weve seen
• home agents, foreign agents, foreign-agent
  registration, care-of-addresses, encapsulation
  (packet-within-a-packet)
• three components to standard
• indirect routing of datagrams
• agent discovery
• registration with home agent

31
Mobile IP indirect routing
Permanent address 128.119.40.186
Care-of address 79.129.13.2
32
Mobile IP agent discovery

• agent advertisement foreign/home agents
  advertise service by broadcasting ICMP messages
  (typefield 9)

H,F bits home and/or foreign agent
R bit registration required
33
Mobile IP registration example
34
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

35
Components of cellular network architecture
recall
correspondent
wired public telephone network
different cellular networks, operated by
different providers
36
Handling mobility in cellular networks

• home network network of cellular provider you
  subscribe to (e.g., Sprint PCS, Verizon)
• home location register (HLR) database in home
  network containing permanent cell phone ,
  profile information (services, preferences,
  billing), information about current location
  (could be in another network)
• visited network network in which mobile
  currently resides
• visitor location register (VLR) database with
  entry for each user currently in network
• could be home network

37
Mobility and handover issues

• Mobility allows the possibility for the mobile
  subscriber of being reachable anywhere and at
  anytime.
• Managing the mobile terminal mobility is one of
  the most essential parts of cellular system
  functionality.
• In a radio communication system Paging, Location
  Update and Handover Operations provide the User
  mobility.
• Handover is one of the essential means to
  guarantee the User Mobility in a mobile
  communications network
• The basic concept of handover control is that
  when the subscriber moves from the coverage area
  of one cell to another, a new connection with the
  new target cell has to be set-up and the
  connection with the old cell may be released.

38
Mobility and handover issues - Handover Control
39
Mobility and Handover Issues -Reasons behind the
Handover

• The basic reason behind the handover is that the
  air interface connection does not fulfil the
  desired criteria set for it any more resulting in
  unacceptable QoS and thus either the Mobile
  Station or the Network initiates Handover in
  order to improve the procedure.
• The decision of whether the handover should be
  performed or not is based on handover criteria.
• Handover may occur due to Signal Quality, User
  Mobility, Traffic Distribution etc.

40
Mobility and Handover Issues -Reasons behind the
Handover

• Signal Quality handover
• occurs when the quality or the strength of the
  radio signal falls below certain parameters
  specified in handover criteria.
• deterioration of the signal is detected by
  constant signal measurements carried out by both
  the Mobile Terminal and the Base Station.
• The signal quality reason handover may be applied
  both for the uplink and downlink radio links.
• Traffic handover
• occurs when the traffic capacity of a cell has
  reached its maximum or is approaching it
• the UE near the edges of the cell with high load
  may be handed over to neighbouring cells with
  less traffic load.
• the system load can be distributed more uniformly.

41
Mobility and Handover Issues -Reasons behind the
Handover

• The number of handovers depends on the degree of
  mobility.
• It is obvious that the faster the mobile node
  (MN) is moving, the more handovers it causes to
  the Network.
• To avoid undesirable handovers the MN with high
  motion speed may be handed over from micro-cells
  to macro-cells.
• On the other hand, if the MN moving slowly or not
  at all, it can be handed over from macro-cells to
  micro-cells to improve the radio signal strength
  and avoid consuming its battery.

42
Overlay Networks - The Global Goal
integration of heterogeneous fixed andmobile
networks with varyingtransmission characteristics
regional
vertical handover
metropolitan area
campus-based
horizontal handover
in-house
43
Mobility and Handover Issues Handover Process

• A basic handover process consists of three main
  phases

44
Mobility and Handover Issues Handover Process

• Handover measurement provision is a very
  important task for the system performance. This
  is because the signal strength of the radio
  channel may vary drastically due to fading and
  signal path loss, resulting from the cell
  environment (e.g. buildings, mountains) and user
  mobility.
• Decision phase consists of assessment of the
  overall QoS of the connection and comparing it
  with the requested QoS attributes and estimates
  measured from neighboring cells. Depending on the
  outcome of this comparison, the handover
  procedure may or may not be trigger.
• The Network checks whether the values indicated
  in the measurement reports meet the QoS specified
  for the end-user service. If not, then it allows
  executing the handover.

45
GSM indirect routing to mobile
home network
correspondent
Public switched telephone network
mobile user
visited network
46
GSM handoff with common MSC

• Handoff goal route call via new base station
  (without interruption)
• reasons for handoff
• stronger signal to/from new BSS (continuing
  connectivity, less battery drain)
• load balance free up channel in current BSS
• GSM doesnt mandate why to perform handoff
  (policy), only how (mechanism)
• handoff initiated by old BSS

new routing
old routing
old BSS
new BSS
47
GSM handoff with common MSC
1. old BSS informs MSC of impending handoff,
provides list of 1 new BSSs 2. MSC sets up path
(allocates resources) to new BSS 3. new BSS
allocates radio channel for use by mobile 4. new
BSS signals MSC, old BSS ready 5. old BSS tells
mobile perform handoff to new BSS 6. mobile, new
BSS signal to activate new channel 7. mobile
signals via new BSS to MSC handoff complete.
MSC reroutes call 8 MSC-old-BSS resources
released
old BSS
new BSS
48
GSM handoff between MSCs

• anchor MSC first MSC visited during cal
• call remains routed through anchor MSC
• new MSCs add on to end of MSC chain as mobile
  moves to new MSC
• IS-41 allows optional path minimization step to
  shorten multi-MSC chain

correspondent
anchor MSC
PSTN
(a) before handoff
49
GSM handoff between MSCs

• anchor MSC first MSC visited during cal
• call remains routed through anchor MSC
• new MSCs add on to end of MSC chain as mobile
  moves to new MSC
• IS-41 allows optional path minimization step to
  shorten multi-MSC chain

correspondent
anchor MSC
PSTN
(b) after handoff
50
Mobility GSM versus Mobile IP
51
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

52
Wireless, mobility impact on higher layer
protocols

• logically, impact should be minimal
• best effort service model remains unchanged
• TCP and UDP can (and do) run over wireless,
  mobile
• but performance-wise
• packet loss/delay due to bit-errors (discarded
  packets, delays for link-layer retransmissions),
  and handoff
• TCP interprets loss as congestion, will decrease
  congestion window un-necessarily
• delay impairments for real-time traffic
• limited bandwidth of wireless links