1. Network Layer: Location/Service Management
Y. Richard Yang
11/27/2012

2. Outline Admin. and recap Network layer Intro
Location/service management

3. Admin.
Project meeting slots to be posted on classesv2

4. Recap: Improving Wireless Capacity
Reduce interf. area
Radio interface constraint
Interference constraint
a single half-duplex transceiver at each node
transmission successful if there are no other transmitters within a distance (1+D)r of the receiver
Multiple transceivers
Approx. optimal
Reduce L
Increase W
rate*distance capacity:

5. Recap: RRC State and App
Given the large overhead for radio resource control (RRC), wireless networks implement RRC state machine on mobile devices for data connection
Channel
Radio Power
IDLE
Not allocated
Almost
zero
CELL_FACH
Shared, Low Speed
Low
CELL_DCH
Dedicated, High Speed
High
Courtesy: Erran Li.

6. Case Study: Pandora Streaming
Problem: High resource overhead of periodic audience measurements (every 1 min)
Recommendation: Delay transfers and batch them with delay-sensitive transfers

7. Recap: Wireless Link Layer
The basic services of the link layer
framing, link reliability, etc
link access: interference, quality of service (and fairness) control, link state management
Guided by network layer
transmit to which neighbor at what quality B A S E F H J D C G I K M N L

8. Outline
Admin. and recap
Network layer
Intro to networks

9. Network Layer Services
Transport packets from source to dest
Network layer protocol in host and router
Basic functions:
Control plane
compute routing from sources to destinations
Data plane: forwarding
move packets from input interface to appropriate output interface(s) B A S1 E D2 S2 J D1 C G I K M N L

10. Network Layer: API src dst API (provided to upper layer)
transmit( info, src, dest, …);
A key decision in network layer design is how to represent destinations?
we refer to how client specifies destination as the addressing scheme
the supported addressing scheme(s) can have profound impacts on usability, flexibility, scalability
request
src
dst
result

11. Discussion: How to Specify a Destination?B A S E F H J D C G I K M N L

12. Two Basic Approaches for Identifying Destinations
Locators
Encode locations on network topology
Identifiers (ID)
Independent of network topology A E D C B F

13. Addressing Scheme: Telephone
Very first scheme: connection by operators to business
Identifier or locator?

14. Addressing Scheme: Telephone
The telephone numbering scheme:
invented in 1888 by Almon Strowger, an undertaker: “No longer will my competitor steal all my business just because his wife is a BELL operator.”

15. Addressing Scheme: Telephone
E.164: Maximum 15 digits
Hierarchical addressing scheme: country code + national destination (area) code (optional) + subscriber number
e.g.,
Why hierarchical addressing scheme?
uniquely determines the switch upon which the telephone is attached to B A S E D F J C G I K M N L

16. Evolution of Telephone Addressing Scheme
Identifier (business, person)
Locator (hierarchical phone #)
Identifier (person again w/ mobile phones)

17. IP Addressing Also a hierarchical locator addressing scheme
Also a hierarchical locator addressing scheme
network part (high order bits)
host part (low order bits)
What’s a network? (from IP address perspective)
device interfaces with same network part of IP address
link layer can reach each other

18. Addressing Scheme: Sensornet Example
Destination: message to a sensor (e.g., who detected fire)
<ID = D>
<Lat= ; Long= >
<temperature = highest>
// id.
// loc
// id B A S E D F J C G I K M N L

19. Addressing Scheme: Printer
How may we specify the destination as the color printer on the 2nd floor of AKW
Internet domain name: lw2c.cs.yale.edu
Internet protocol (IP) address:
[building = AKW; floor=2; entity = printer; quality = color]

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

21. Routing in IP/Telephone Networks
Represent a network as a graph
Determine a path to each destination on the graph
Key problems
Location management
Find attached point for id-based naming
Routing
Find path from src to dst attach point A E D C B F 2 1 3 5

22. Outline Admin. Network layer Intro to networks Location management
service discovery

23. The Service Discovery Problem
request
src
dst
result
How does a src connect to a dst in an ID-based addressing scheme?
ID-based phone#
IP address difficult to remember, uses domain name lw2.cs.yale.edu

24. <hostname, service>
Today’s Internet
clients
Naming scheme:
Domain name hierarchy
DNS
<hostname, service>
IP address
Name resolution: Two steps:
DNS looks up name for IP address
TCP connection to server
routers
Lots of problems with what the Internet is tuned to do today
DNS is rather static
servers

25. DNS: Domain Name System
Function
map domain name (e.g. cs.yale.edu) and service type (e.g., ) to IP address (e.g )
Domain name: a hierarchical name space implemented by a distributed database to allow distributed, autonomous administration
called a zone

26. RR format: (name, value, type, ttl)
DNS: Naming Scheme
Each DNS server stores resource records (RR)
RR format: (name, value, type, ttl)
Type=A
name is hostname
value is IP address
Type=CNAME
name is an alias name for some “canonical” (the real) name
value is canonical name
Type=NS
name is domain (e.g. yale.edu)
value is the name of the authoritative name server for this domain
Type=MX
value is hostname of mail server associated with name

27. DNS Name Resolution
A host queries local DNS server, who may forward the query to the corresponding DNS server

28. Problems of Traditional DNS Service Discovery
Support fixed types of services, e.g., A, NS, CNAME, MX
static and fixed record structure makes it difficult to introduce new services or non-trivial service queries
Depends on infrastructure: a DNS server

29. General Naming Paradigm: Linda
“Distributed workspace” by David Gelernter in the 80’s at Yale
Very influential in naming and resource discovery
                                                                                       

30. General Naming Paradigm: Linda
Naming scheme:
arbitrary tuples (heterogeneous-type vectors)
Name resolution:
Nodes write into shared memory
Node read matching tuples from shared memory
exact matching is required for extraction
                                                                                       

31. Linda: Core API out(): writes tuples to shared space
example: out("abc", 1.5, 12).
result: insert (“abc”, 1.5, 12) into space
read(): retrieves tuple copy matching arg list (blocking)
example: read(“abc”, ? A, ? B)
result: finds (“abc”, 1.5, 12) and sets local variables A = 1.5, B = 12. Tuple (“abc”, 1.5, 12) is still resident in space.
in(): retrieves and deletes matching tuple from space (blocking)
example: same as above except (“abc”, 1.5, 12) is deleted
eval(expression): similar to out except that the tuple argument to eval is evaluated
example: eval("ab",-6,abs(-6)) creates tuple (“ab”, -6, 6)
                                                                                       
eval()
evaluates a tuple on the server

32. Linda Extension: JavaSpaces
Industry took Linda principles and made modifications
add transactions, leases, events
store Java objects instead of tuples
a very comprehensive service discovery system
Definitive book, “JavaSpaces Principles, Patterns, and Practice”
2 of 3 authors got Ph.D.’s under Gelernter on Linda-related subjects

33. JavaSpaces – Visual Overview
                                                                                                                   

34. DNS without Central DNS Server: mDNS
Multicast in a small world
no central address server
each node is a responder
link-local addressing
send to multicast address:
Leverage DNS format—DNS-SD
each node picks own name: <instance name> . <app-proto> . <service> . <domain>
Printer
Network

35. DNS without Central DNS Server: mDNS
PC_BILL
Laserjet in the
Closet Under
the Stairs
Bill’s Files
Printer
Network lj
PC_LARRY
Larry’s Tunes

36. mDNS: Example Use the mDNS command on Mac as example
Advertise an LPR printer on port 515 mDNS -R "My Test" _printer._tcp pdl=application/postscript
Advertise a web page on local machine mDNS -R "My Test" _http._tcp . 80 path=/path-to-page.html
Browse web pages on local machines mDNS -B _http._tcp

37. Service Discovery in Android
Based on mDNS/DNS-SD
Foundation for Wi-Fi Direct
See

38. Service Registration in Android
public void registerService(int port) {
NsdServiceInfo serviceInfo = new NsdServiceInfo();
serviceInfo.setServiceName("NsdChat");
serviceInfo.setServiceType("_http._tcp.");
serviceInfo.setPort(port);
mNsdManager = Context.getSystemService(Context.NSD_SERVICE);
mNsdManager.registerService(
serviceInfo, NsdManager.PROTOCOL_DNS_SD, mRegistrationListener); }

39. Service Discovery in Android
mNsdManager.discoverServices(
SERVICE_TYPE, NsdManager.PROTOCOL_DNS_SD, mDiscoveryListener);
public void initializeDiscoveryListener() {
// Instantiate a new DiscoveryListener
mDiscoveryListener = new NsdManager.DiscoveryListener() {
// Called as soon as service discovery begins.
@Override
public void onDiscoveryStarted(String regType) {
Log.d(TAG, "Service discovery started"); }
public void onServiceFound(NsdServiceInfo service) {
// A service was found! Do something with it.
Log.d(TAG, "Service discovery success" + service);
if (!service.getServiceType().equals(SERVICE_TYPE)) {
// Service type is the string containing the protocol and
// transport layer for this service.
Log.d(TAG, "Unknown Service Type: " + service.getServiceType());
} else if (service.getServiceName().equals(mServiceName)) {
// The name of the service tells the user what they'd be
// connecting to. It could be "Bob's Chat App".
Log.d(TAG, "Same machine: " + mServiceName);
} else if (service.getServiceName().contains("NsdChat")){
mNsdManager.resolveService(service, mResolveListener);
...

40. Challenge of using Name Resolution in Mobile Computing
src
dst
location
name/ ID
dst
Name -> location binding can be dynamic as a mobile device changes attach point

41. Mobile Name-Loc Binding Design Space
Binding database update
Hand off

42. Outline Admin. Network layer Intro to networks
Location/service management
service discovery
cellular network location management

43. Location Registration
MS (mobile station)
BSC (base station controller)
BTS (base transceiver station)
MSC (mobile switching center)
GMSC (gateway MSC)
GSM
fixed network
Network & Switching Subsystem
and Operation Subsystem
Location Registration
GMSC
MSC
MSC
BSC MS
BSC MS
BTS
Radio Subsystem MS MS MS
BTS MS
BTS
BTS
BTS

44. LM in Cellular Networks
Problems
Location Registry (LR) update: How to update the mapping between ph# and current attachment point (BTS) of the phone.
Handoff: a user may move during a phone call, how to not drop the call?

45. Two Primitives for Cellular Location Management
Mobile station: reports to the network of the cell it is in
called update
uses the uplink channel
Network: queries different cells to locate a mobile station
called paging
uses the downlink channel

46. Performance of the Two Primitives
A city with 3M users
During busy hour (11 am - noon)
Update only
total # update messages: millions
on average each user visited > 8 cells
Paging only
call arrival rate: 1433 calls/sec
total # paging transactions: 5.2 millions

47. Discussion
A user receives one call for ~5 cells (25M vs 5M) visited, thus may not need to update after every switching of cell
However, if no update at all, then paging cost can be high—may need to page the MS at every cell
Q: how do you page?

48. Location Management Through Location Areas (LA)
Used in the current cellular networks
A hybrid of paging and update
Partitions the cells into location areas (LA)
e.g., around 10 cells in diameter in current systems
A global home location register (HLR) database for a carrier
An MSC of each LA maintains a visitor location register (VLR) of the LA

49. GSM Radio Subsystem MS (mobile station) BSC (base station controller)
BTS (base transceiver station)
MSC (mobile switching center)
GMSC (gateway MSC)
GSM
fixed network
Network & Switching Subsystem
and Operation Subsystem
HLR
GMSC
MSC
MSC
VLR
VLR
BSC MS
BSC MS
BTS
Radio Subsystem MS MS MS
BTS MS
BTS
BTS
BTS

50. LA Based Update/Paging
Each cell (BTS) of an LA periodically announces its LA id
If a MS moves to a new LA, it reports its location to visiting MSC
MSC/VLR notifies HLR that it currently has MS
When locating a MS, the network pages the cells in an LA

51. GSM Location Update: Example

52. GSM Location Update: Example

53. GSM Location Update: Example

54. GSM Location Update: RR Connection Setup

55. GSM Location Update: Update

56. GSM Location Update: Update

57. GSM Location Update: Update

58. GSM Location Update : Authenticate Subscriber

59. GSM Location Update: Enable Ciphering

60. GSM Location Update: RR Connection Release

61. How to Decide the LAs: A Simple Model
Assume the cells are given
Cell i has on average Ni users in it during one unit time; each user receives  calls per unit time
There are Nij users move from cell i to cell j in a unit of time
Cell 1
Cell 2 N1 N2
N12
N21

62. How to Decide the LAs: A Simple Scenario
Cell 1
Cell 2 N1 N2
N12
N21
Separate LAs for cells 1 and 2
#update:
#paging:
Merge cells 1 and 2 into a single LA
N12 + N21
C_u(N12 + N21) ? \lamda (N1 + N2)
 (N1 + N2)
2  (N1 + N2)

63. Cost Comparison
Separate
Merge
where C_update is relative cost of update to paging, assuming paging cost per cell is 1
C_u(N12 + N21) ? \lamda (N1 + N2)
At the same mobility, if call arrival rate is high, more likely separate
At the same call arrival rate, if higher mobility, more likely to merge

64. Extension: From GSM to GPRS to 3G UMTS

65. Extension: From GSM to GPRS to 3G UMTS
Issue: it is anticipated that users will make more connections in data network
Same mobility but higher lambda => smaller location area

66. UMTS Location Update

67. Summary The LA/RA/UTRANA design considers
call pattern: when (how often) does a mobile station receive a call
mobility model: how does a mobile station move
Issues of LA based approaches
Users roaming in LA borders may generate a lot of updates

68. Distributed Location Management Schemes
Timer based
A MS sends an update after some given time T
Movement based
A MS sends an update after it has visited N different cells
Distance based
A MS sends an update after it has moved away for D distance (need ability to measure distance)
Profile based
A MS predicts its mobility model and updates the network when necessary

69. Timer-based Location Management
A MS sends an update after some given timer T
The network pages the MS upon a call request at all cells which the MS can potentially arrive during T
cells reachable from last update cell, e.g., within distance vmax * T, where vmax is the maximum speed
Question: how to determine T?

70. Timer-based Location Management
Assume time between call arrivals is Tcall
Cell radius is dcell
Total bandwidth cost:
Take derivative and set it to 0 to derive the optimal value:

71. Summary: Location Management
Two primitives of location management in cellular networks
update (a proactive approach)
paging (a reactive approach)
Hybrid update/paging tradeoff
The location area (LA) approach
Distributed approaches
timer based
movement based
distance based
profile based

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

73. 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

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

75. UMTS Serving RNC Handoff
Drift RNC

76. Outline
Admin.
Location management
cellular networks
IP networks

77. 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

78. 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

79. 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)

80. 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

81. 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

82. Discussion
Any problems of the Mobile IP approach?

83. 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 !

84. 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
Multiple optimization techniques to improve efficiency and reduce packet losses during mobility

85. Recap: Key Problems Location managementD C B F
Location management
Routing in wireless/mobile networks

86. Backup Slides