Mobile/Wireless Networking:
Overview and Principles
Dimitrios Koutsonikolas
02/03/2016
These slides contain material developed by Chunyi Peng for CSE 5469 at OSU
and by Kurose-Ross
Family of Networks
Core Network (tier-1 ISP)
Data center
Internet
Access (Edge) networks
ATM
CDN …
Wireless networks
Ethernet (LAN)
Mobile networks
Cable, DSL …
Fiber optic
WiFi (802.11a/b/g/n/ac…)
4G/3G: LTE,
HSPA, EVDO,
UMTS,…
WiMax, Satellite ….
whitespace 60GHz
Bluetooth, NFC (RFID), WSN, …
(not strictly)
2
Family of Networks
Internet
Interconnection
Access
networks
end-to-end
layering: TCP/IP
packet switched
…
Wireless
networks
Edge
last hop
Mobile
networks
Wireless
broadcast
Interference
coverage …
Mobility
3
Design Guidelines for Internet
& Wireless Mobile Networks
4
Design Guidelines
• The foundation for wireless networking is the
Internet design guidelines
– End-to-end argument
– Always applicable?
5
Key Design Decision
• How do you divide functionalities among
layers and across different components in the
network?
– Given the freedom to implement a few
functionalities in multiple “places” of the system
(physical devices, or protocol layers), where to
implement them?
• Goals:
– Correctness, completeness, performance tradeoffs
6
Options
• Telcom approach: “Smart CORE, Dumb Terminal”
– The core ensures reliability
• TCP/IP approach: “Smart Terminal, Dumb CORE”
– The terminal ensures reliability, while the core retains
simplicity
– Implicit assumption made: terminals have more
capabilities: computing power, storage, memory, etc.
7
End-to-End Argument
• Think twice before implementing a
functionality that is useful to an application at
a lower layer
• If the application can implement a functionality
correctly, implement it a lower layer only as a
performance enhancement
8
Example: Reliable File Transfer
Host A
Host B
Appl.
OS
Appl.
OK
OS
• Solution 1: make each step reliable, and then
concatenate them
• Solution 2: end-to-end check and retry
9
Discussion on Solution 1
• Ensuring reliability at every step is incomplete
– Why?
• The receiver has to do the check anyway!
• Thus, full functionality can be entirely
implemented at application layer; no need for
reliability from lower layers
10
More Discussions
• Is there any need to implement reliability at lower
layers?
• Yes, but only to improve performance
• Example:
– Assume a high error rate on a wireless channel
– Then, a reliable communication service at link layer might
help
– Assume high error rate writing to disk
– Then, a reliable service at the OS level would help
11
Tradeoffs
• Application has more information about the
data and the semantics of the service it
requires (e.g., can check only at the end of
each data unit)
• A lower layer has more information about
constraints in data transmission (e.g., packet
size, error rate)
• Note: these trade-offs are a direct result of
layering!
12
Summary: End-to-End Argument
• Add functionality in lower layers iff it is (1)
used by and improves performance of a large
number of applications, and (2) does not hurt
other applications
• Success story: Internet
13
Two Forms of E2E Guideline
• Horizontal: Push complexity outside the
network core, into the end systems
– Simple IP routers, complex TCP end hosts
• Vertical: Push design to higher layers of the
protocol stack
– End-to-end reliability at the transport layer in
TCP/IP
– Hop-by-hop reliability at the link layer in telcom
14
Remarks
• Challenge of building a network system: find
the right balance between:
Reuse, implementation effort
(apply layering concepts)
Performance
End-to-end argument
No universal answer: the answer depends
on the goals and assumptions!
15
The Problem: What is New
Compared to the Wired Internet?
• Fundamental challenges for wireless and
mobile networking design:
– WIRELESS
– MOBILITY
– Is it so obvious and too trivial???
• Map onto each layer of the protocol stack
16
Wireless Impact on Protocol Stack
Application
 Partial network connectivity
 Changing network quality:
delay, throughput
Transport Layer
 Diverse data losses
Network Layer
 Opportunistic connectivity
 Time-varying link bandwidth
Link/MAC Layer
o Location-dependent error
o Hidden terminals
17
Mobility Impact on Protocol Stack
Application
 Connection, disconnection
Transport Layer
 Mobility-induced data
losses
Network Layer
 Topology change
 Time-varying capacity
Link/MAC Layer
o Link-layer handoff
o Varying link quality
18
Example: TCP in wireless/mobile
networks
19
Review: TCP Congestion Control
• Send as fast as possible, but not causing
network congestion
– Probe and adapt
– AIMD: additive increase, multiplicative decrease
multiply
20
TCP congestion control over the
Internet
• Premise
– Packet loss is caused by congestion
• So, loss -> reducing sending rate
– Cwnd (congestion window size) reduction
– Timeout update
21
Issues for Wireless TCP
• Different packet loss behavior violates the
assumption of TCP that all packet losses are due to
congestion control:
–
–
–
–
congestion-induced loss: new flow joins, etc.
channel-error-induced loss: bursty or random channel error
handoff-induced packet loss: happens during handoff transition
routing-induced packet loss: stale routing tables (in a dynamic
ad hoc network)
• “Uniform” reaction to different losses in TCP:
– in TCP, reduce congestion window by half upon packet loss
– Does “one-fit-all” work in the wireless scenario ?
22
The Goals
• Hide impact of wireless
– SAME QUALITY AS WIRED LINK!!
• Offer seamless services while mobile
• Overall, “Anytime, anywhere” services
23
Two Popular Design Approaches
1. Adaptation
high-dimension dynamics
2. Coordination
coherent system
24
Adaptation As the Guideline
• Many concrete forms/instantiations of adaptations
– Adaptation to channel variations
– Adaptation to mobility
– …
• Adaptation at different layers of protocol stacks
– From PHY, LINK, to TRANSPORT and APP layers
• Numerous solutions/papers published
– 333000 entries for google search “wireless adaptation”
– 956000 entries for google search “mobility adaptation”
25
Research Issues in Adaptation
• What to adapt?
– Transmission power, transmission rate, # of retries, …?
• When to adapt?
– when to invoke specific adaptation?
• stability versus responsiveness
• How to adapt?
– specific mechanisms/algorithms in adaptation
26
Forms of Adaptation
• Opportunistic design approach
– Opportunistically adapt
• Model-referenced design
– Adapt to trace a reference model
27
Opportunistic Design
• Exploit the system population
• Leverage system diversity
– Multiple receivers, multiple devices, multiple
applications/flows, …
28
Example: Opportunistic Scheduling
• How to maximize system throughput by
exploiting time-varying channels for each user
in a fair way?
– Each active user gets a share of the channel
29
Dynamics for Each User
• Each user’s channel varies independently over time due to
fading etc.
• In a large network, it is very likely to find a user with a
very good channel at any time.
• Long-term total throughput can be maximized by
opportunistically serving user with the strongest channel
30
Resulting Algorithm: Proportional
Fair Scheduler
• (Used by Qualcomm EVDO system)
• Schedule the user with the highest ratio
– Rk = current requested rate of user k
– Tk = average throughput of user k in the past tc
time slots
31
Opportunistic Performance Gain
Increases with # of Users
32
Model-Referenced Adaptation
• Ideal model to capture expected behaviors
under idealized situation
– e.g., error-free, static settings
• Track the reference model under realistic
conditions/scenarios
– Mobility, wireless channel dynamics, …
33
Example: Scheduling over Channel
Errors
Goal: Each user gets 50% of channel
Reference Model for Error-Free Channels
Time 
1 2 3 4
Channel status 1
1 2
MH #1
backbone
Sender
2
Base Station
MH #2
34
Example: Scheduling over Channel
Errors
Idea: Lead/Lag to track difference with ref. model
& Swap scheduling order for 1 and 2
Time 
Reference Model for Error-Free Channels
Time 
1 2 3 4
3
Channel status 1
1 2
MH #1
backbone
Sender
2
4
Base Station
MH #2
35
Forms of Coordination
• Cross-Layer design
– Enable close interactions across non-adjacent
layers in the layered protocol stack
• Coordination via “indirection”
– Adaptation-aware proxy provides indirection
36
Cross-layer Design
• Information sharing, informed decision at other layers
• Merging layers
37
Example of Cross-layer Feedback
• PHY info to higher layers
– Link/MAC layer
• Control transmit power, modulations to reduce error
rate or retransmit
– Network layer
• Bit-error rate information in order to switch another
network interface with lower bit-error-rate
– Application layer
• Channel condition information
• Various standard coding techniques for multi-media
applications
38
Any Bad Effects?
• Undesirable consequences on overall system
performance
• The importance of architecture
– Stability
– Robustness
– Spaghetti design – hard to upkeep
–…
39
Indirection via “Proxy”
server
proxy
client
• Proxy bridges the server and the client
• Move complexity away from both server and
client
– Generalized end-to-end argument: “edge” rather than
“end” systems
• Little changes at server & client
40
Driving Factors for Wireless
(Mobile) Networking Research
Top
Down
New Applications,
Services, Requirements
Transport Layer
Network Layer
Link Layer
Up
Bottom
New Wireless
Communications Technology
41
Bottom Up Driver:
Wireless Communications
• Many of them:
– Antenna arrays, Smart antennas, …
– Adaptive modulation, OFDM, MIMO
– Spectrum sharing, cognitive radios, channel
management
– Multi-interface radios, device heterogeneity
–…
Challenge: How to exploit these new PHY
communication capabilities in the protocols?
42
Root Cause of Problems
• two largely disconnected communities
• speak different terminologies
– wireless communications:
• Symbols, signals
• probabilistic terms:
– information theoretic bounds
– confidence factor on symbol reception, …
– wireless networking
• Packets, bits
• deterministic terms
– Correct/wrong binary reception
43
Root Cause of Problems (2)
• Two largely disconnected communities
• different methodologies
– wireless communications
• solid theoretic foundation on information theory
• a set of well known assumptions: noises, interferences, etc.
• Theory Design-->Analysis-->prototype in chips-->experiments
– wireless networking
• mostly on heuristics
• network setting “ad hoc”: no agreed benchmarks/base settings
• Heuristic Design-->Simulations--Network Prototype-->Experiments
44
Perspective From Wireless
Networking
• We are not on the driver’s seat so far
– communication has driven the technology so far
– we are followers
• Still plenty of space
– the direct communication almost NEVER works in
reality at the 1st place!
45
Top Down Driver: User Demands
• New applications
– MMS, P2P image/video sharing, IP TV streaming, …
• New requirements
– Security, privacy, robustness/dependability, distributed
management
• New services
– Location-based service, Personalized service, …
• New trends
– Interoperability of different wireless technologies
Challenge: How to support such new demands?
46
Cellular Networks: Overview
Cellular Networks
• To date, the only operational large-scale
wireless network with wide-area coverage and
mobility support
48
Key Services: Connectivity and More
• Pervasive connectivity: anyone, anytime,
anywhere
– Device -> Base station -> Cellular core Network ->
External network or internal devices)
• Carrier-network services: data, voice,
messaging, …
• Two salient features
– Wide-area (e.g. nationwide) coverage: cells
– Mobility support: seamless service as we go
49
Mobile Network Evolution
3G
4G
GSM/GPRS/EDGE
cdmaOne
WCDMA/HSPA+
CDMA2000/EVDO
TD-SCDMA
LTE
LTE-advanced
1990s
2000s
2010s
Mobile
broadband
More and
Faster
1G
2G
AMPS, NMT,
TACS
1980s
analog voice Digital voice
+ Simple data
APP
50
2G (voice) network architecture
Base station system (BSS)
BTS
MSC
G
BSC
Public
telephone
network
Gateway
MSC
Legend
Base transceiver station (BTS)
Base station controller (BSC)
Mobile Switching Center (MSC)
Mobile subscribers
Wireless, Mobile Networks
6-51
3G (voice+data) network architecture
MSC
radio
network
controller
G
Public
telephone
network
Gateway
MSC
G
SGSN
Key insight: new cellular data
network operates in parallel
(except at edge) with existing
cellular voice network
 voice network unchanged in core
 data network operates in parallel
Wireless, Mobile Networks
Public
Internet
GGSN
Serving GPRS Support Node (SGSN)
Gateway GPRS Support Node (GGSN)
6-52
3G (voice+data) network architecture
MSC
radio
network
controller
G
Public
telephone
network
Gateway
MSC
G
Public
Internet
SGSN
GGSN
radio interface
(WCDMA, HSPA)
radio access network
Universal Terrestrial Radio
Access Network (UTRAN)
core network
General Packet Radio Service
(GPRS) Core Network
Wireless, Mobile Networks
public
Internet
6-53
UMTS Architecture
Mobile Station
ME
SIM
Base Station
Subsystem
BTS
BSC
Network Subsystem
MSC/
VLR
EIR
Other Networks
GMSC
PSTN
HLR
AUC
PLMN
RNS
ME
USIM
SD
+
Node
B
RNC
SGSN
GGSN
Internet
UTRAN
Note: Interfaces have been omitted for clarity purposes.
Cellular Network Architecture
• Radio access network
– Full coverage via deploying a large # of RANs
• Core Network
– Data-plane: connectivity and data/voice/etc transfer
– Control-plane, management-plane: control and
management to facilitate the data-plane transfer
Radio Access Network Core Network (3G)
MSC
SGSN
Chunyi Peng (OSU)
GMSC
GGSN
55
Architecture: More
• Hierarchical geographic coverage
– Cell, Location Area (Routing Area)
– Good for mobility support: location update,
handoff
SGSN
GGSN
SGSN
SGSN
Chunyi Peng (OSU)
56
Architecture: More
• Becoming flat and complicated
IMS
……
Middlebox
– Aka: routing
• Other core components
SGSN
HSS
VLR/
HLR
Charging
& Billing
GGSN
SGSN
GGSN
SGSN
Chunyi Peng (OSU)
57
Cellular Network Architecture:
A Simple 3G/4G Example
Circuit Switching (CS)
3G (PS + CS)
Mobile Switching Center
3G Gateways
3G Base
stations
Packet Switching (PS)
4G (PS only)
4G Gateways
Mobility Management Entity
58
LTE vs UMTS
• Functional changes compared to the current
UMTS architecture