1. Network: Traditional Routing
Y. Richard Yang
3/28/2011

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3. Recap: Basic Network Layer Model
Each node is a network attachment point (e.g., router, base station), to which hosts/user equipment attaches
Problems:
Location management
Routing for wireless A E D C B F
User device identified by addressing scheme
locator: identifies attachment point
identifier: independent of location

4. Recap: Location Management
Two primitives of location management (find out where a MS is) in a cellular network
update (a proactive approach)
paging (a reactive approach upon request)
Hybrid update/paging tradeoff
The location area (LA) approach
Distributed approaches
timer based
movement based
distance based
profile based

5. Remaining Issue: Handoff
A MS may be in a call during mobility
Issue:
the signal to/from the current serving base station (e.g., Node B in 3G) may gradually degrade as the MS moves away
the signal to/from the next base station may become better, but the signal strength is hard to know, if the MS is not actively communicating w/ the next base station

6. WCDMA Soft Handoff An MS communicates with multiple Node Bs
Downlink: multiple base stations send to the MS and the MS combines the received signals
Uplink: multiple base stations receive data from the MS and forward to a RNC to combine
The combing RNC is called the serving RNC

7. Serving RNC and Drift RNC
Serving RNC handoff
RNC1: Serving RNC RNC2: Drift RNC
RNC1: Serving RNC

8. UMTS Serving RNC Handoff
Drift RNC

9. Outline
Admin.
Location management
cellular networks
IP networks

10. Mobile IP: Architecture
The current architecture to handle mobility in Internet is Mobile IP
Assume the current Internet addressing and routing architecture
Design extensions to handle out of network devices
Similar to cellular, but simpler
Not widely deployed

11. Mobile IP: Terminology
Mobile Node (MN)
the node under consideration
Home Agent (HA)
a stationary network node (e.g., a router) at the home network
Foreign Agent (FA)
a network node (e.g. a router) in the foreign network
Care-of Address (COA)
the address in the foreign network
Correspondent Node (CN)
communication partner

12. Illustration HA MN FA CN mobile node Internet router home network
(physical home network
for the MN) FA
foreign network
router
end-system CN
router
(current physical network for the MN)

13. Mobile IP Operations Basic idea of Mobile IP:
a MN acquires a COA in a foreign network from a foreign agent
registers to the home agent (location update)
all messages sent to its home address is arrived at the home agent, who forwards to COA

14. Discovering the Agents and Care-of Address
Mobile IP discovery process
(home or foreign) agent broadcasts advertisements at regular intervals
announce the network
list one or more available care-of addresses
mobile node takes a care-of address
mobile node can also send solicitation to start the process

15. Registering the Care-of Address
Mobile node sends an update (called) registration request) to its home agent with the care-of address information
Home agent approves/disapproves the request
Home agent adds the necessary information to its routing table
Home agent sends a registration reply back to the mobile node

16. Registration Operations in Mobile IP
MH = Mobile Host HA = Home Agent
FA = Foreign Agent

17. Data Transfer from the Mobile NodeHA 1 MN
Internet
home network
sender FA
foreign network
1. Sender sends to the IP address of the receiver as usual, FA works as default router CN
receiver

18. Data Transfer to the Mobile NodeHA 2 MN
Internet
home network 3
receiver FA
foreign
network
1. Sender sends to the IP address of MN,
HA intercepts packet
2. HA tunnels packet to COA, here FA,
by encapsulation
3. FA forwards the packet to the MN 1 CN
sender

19. Tunneling Operations in Mobile IP
Correspondent
Node X

20. Discussion
Any problems of the Mobile IP approach?

21. Triangular Routing Triangular Routing “Solution”
CN sends all packets via HA to MN
higher latency and network load
“Solution”
CN learns the current location of MN
direct tunneling to this location
HA or MN informs a CN about the location of MN
Problem of the solution
big security problems !

22. Handoff Change of FA (COA) “Solution”
packets on-the-fly during the change can be lost
“Solution”
new FA informs old FA to avoid packet loss, old FA buffers and then forwards remaining packets to new FA
this information also enables the old FA to release resources for the MN

23. Summary: Mobile IP
An out-of-network mobile node (MN) registers its current reachable address (COA) with its home agent
Home agent forwards packets to the MN
Several optimization techniques to improve efficiency and reduce packet losses during mobility

24. Recap: Key Problems Location managementD C B F
Location management
Routing with lossy and dynamic wireless
when infrastructure is wireless
discussion: will this be a real issue?

25. Routing Overview
The problem of routing is to find a good path for each source destination pair
Issues
How to define a path to be good?
How do we compute the path? A E D C B F

26. Link Metric
A typical measure for a good path is that it is the shortest path according to some metric
One possibility is to assign each link a metric of 1 (hop-count based routing)
problems
maximizes the distance traveled by each hop
low signal strength -> high loss ratio
uses a higher TxPower -> interference
different links have different qualities A E D C B F

27. Performance of Shortest Hop CountD C B F

28. Example Metric: ETX
ETX: The predicted number of data transmissions required to successfully transmit a packet over a link
the ETX of a path is the sum of the ETX values of the links over that path
Examples:
ETX of a 3-hop route with perfect links is 3
ETX of a 1-hop route with 50% loss is 2
“A High-Throughput Path Metric for Multi-Hop Wireless Routing” by D. De Couto, D. Aguayo, J. Bicket, R. Morris. Mibicom 2003.

29. Acquiring ETX
Measured by broadcasting dedicated link probe packets with an average period τ (jittered by ±0.1τ)
Delivery ratio:
– count(t-w,t) is the # of probes received during window w
– w/τ is the # of probes that should have been received

30. ETX: Example

31. ETX: Advantage
Tends to minimize spectrum use, which can maximize overall system capacity (reduce power too)
each node spends less time retransmitting data
ETX has problems
It considers only ETX, but links may have different rates (how to fix?)

32. Outline Admin and recap Routing Overview Routing metric
Computing shortest path routing A E D C B F 2 1 3 5
How does Internet (Yale) computes shortest path routing?

33. Design Dimensions What does each node know? When to know?
Whole network topology and per link cost
Set of neighbors that can reach dest
Neighbors’ costs to destination
When to know?
All the time (proactive)
Upon a need to forward a data packet (reactive/on demand)

34. Design Dimensions What does each node know?
Whole network topology and per link cost (link state)

35. Link-State Routing Algorithms
Separation of topology distribution from route computation
Used in OSPF, the dominant intradomain routing protocol used in the Internet
Net topology, link costs are distributed to all nodes
Link state distribution accomplished via “link state broadcast”
Each node (locally) computes its paths to all destinations

36. Link State Broadcast B A S E F H J D C G I K M N L
represents a node that has received update
represents link

37. Link State Broadcast S E F B C M L J A G H D K I N

38. Link State Broadcast S E F B C M L J A G H D K I N
To avoid forwarding the same update multiple times, each update has a
sequence number. If an arrived update does not have a higher seq, discard!
- The packet received by E from C is discarded
- The packet received by C from E is discarded as well
- Node H receives packet from two neighbors, and will discard one of them

39. Summary of Link State Routing
Separation of topology distribution from route computation
Whenever a link metric changes, the node broadcasts new value
Q: What is the scope of updates when a link changes status?
Q: Does link state routing work well in a network with dynamic link status?

40. Design Dimensions What does each node know?
Whole network topology and per link cost
Set of neighbors that can reach dest.
Link reversal

41. Motivation Link reversal algorithms maintain a mesh
(hopefully) local adaptation

42. Links and DAG up stream down stream A B F Links are bi-directional
But algorithm imposes
logical directions on them C E G
Maintain a directed acyclic
graph (DAG) for each
destination, with the destination
being the only sink
This DAG is for destination
node D D C E
up stream
down stream

43. Link Reversal Algorithm: Illustration of IdeaB F C E G
Link (G,D) broke D
Any node, other than the destination, that has no outgoing links
reverses some incoming links.
Node G has no outgoing links

44. Link Reversal Algorithm: IllustrationB F C E G
Represents a
link that was
reversed recently D
Now nodes E and F have no outgoing links, the process continues.

45. Link Reversal Algorithm: IllustrationB F C E G
Represents a
link that was
reversed recently D
Now nodes B and G have no outgoing links

46. Link Reversal Algorithm: IllustrationB F C E G
Represents a
link that was
reversed recently D
Now nodes A and F have no outgoing links

47. Link Reversal Algorithm: IllustrationB F C E G
Represents a
link that was
reversed recently D
Now all nodes (other than destination D) have an outgoing link

48. Link Reversal Algorithm: IllustrationB F C E G D
DAG has been restored with only the destination as a sink

49. Summary: Link Reversal
Motivations
maintain a mesh
(hopefully) local adaptation
Remaining questions:
how to implement it?
will reversal stop?
Next we will look into the questions using partial reversal (not full reversal, as the preceding example)

50. Link Direction Through Heights
A node i contains a triple (i, i, i)
i : an integer (the major integer)
i : another integer (the minor integer)
i : node index (to impose a total order)
The triple of a node is called the height of the node
Suppose there is a link from node i to node j, the direction is determined by their heights
i -> j: if (i, i, i) > (j, j, j)
For destination D, the height is (0, 0, D)

51. Illustration of Heights

52. Partial Reversal Algorithm
If the height of node i is lower than all of its neighbors, i.e., (i, i, i) < (j, j, j) for all j in Ni,
Increases i to
where Ni is the neighbors of i.
Set i to
if there exists a neighbor j with the same  value after i has increased its ; otherwise i not changed

53. min  of all neighbors with new 
Illustration
min  of all neighbors with new 
min  of all neighbors

54. Example
(0,4,1)
(0,3,2)
(0,2,3)
(0,5,4)
(0,1,6)
(0,2,5)
Destination: (0,0,0)

55. Example: Link from 6 to 0 is down
(0,4,1)
(0,3,2)
(0,2,3)
(0,5,4)
(0,1,6)
(0,2,5)
Destination: (0,0,0)

56. Example: After Node 6 Reverses
(0,4,1)
(0,3,2)
(0,2,3)
(0,5,4)
(1,1,6)
(0,2,5)
1 = min{0,0}+1
Destination: (0,0,0)

57. Example: After Nodes 3 and 5 Reverse
1 = min{0,1}+1; 0 = min{1}-1
(0,4,1)
(0,3,2)
(1,0,3)
(0,5,4)
(1,1,6)
(1,0,5)
Destination: (0,0,0)

58. Example: After Nodes 2 Reverses
(0,4,1)
(1,-1,2)
(1,0,3)
(0,5,4)
(1,1,6)
(1,0,5)
Destination: (0,0,0)

59. Example: After Nodes 1 Reverses
(1,-2,1)
(1,-1,2)
(1,0,3)
(0,5,4)
(1,1,6)
(1,0,5)
Destination: (0,0,0)

60. Backup Slides

61. Change of Foreign AgentCN HA
FAold
FAnew MN
Data
Data
Data
Update
ACK
Data
Data
MN changes location
Registration
Update
ACK
Data
Data
Data
Warning
Request
Update
ACK
Data
Data t

62. Micro Mobility
A very typical scenario of Mobile IP is that a MN visits a company or university
the MN may change foreign networks multiple times in the foreign network, generating much control traffic

63. Handoff Aware Wireless Access Internet Infrastructure (HAWAII)
Operation:
MN obtains co-located COA and registers with HA
Handover: MN keeps COA, new BS answers Reg. Request and updates routers
MN views BS as foreign agent
Backbone
Router
Internet BS MN
Crossover
DHCP
Server HA
Mobile IP 1 2 4 1 2 3 4 BS 3