Wireless and Mobile Networks: context

 more wireless (mobile) phone subscribers than fixed (wired) phone

subscribers (10-to-1 in 2019)!
 more mobile-broadband-connected devices than fixed-broadband-
connected devices devices (5-1 in 2019)!
• 4G/5G cellular networks now embracing Internet protocol stack,
including SDN
 two important (but different) challenges
• wireless: communication over wireless link
• mobility: handling the mobile user who changes point of attachment to
network

Wireless and Mobile Networks: 7-2

Elements of a wireless network

wired network
infrastructure

Wireless and Mobile Networks: 7- 4

Elements of a wireless network
wireless hosts
 laptop, smartphone, IoT
 run applications
 may be stationary (non-mobile) or mobile
wired network • wireless does not always mean mobility!
infrastructure

Wireless and Mobile Networks: 7- 5

Elements of a wireless network
base station
 typically connected to wired network
 relay - responsible for sending packets
between wired network and wireless
wired network host(s) in its “area”
infrastructure • e.g., cell towers, 802.11 access points

Wireless and Mobile Networks: 7- 6

Elements of a wireless network
wireless link
 typically used to connect mobile(s) to
base station, also used as backbone link
 multiple access protocol coordinates link
access
wired network  various transmission rates and distances,
infrastructure frequency bands

Wireless and Mobile Networks: 7- 7

Characteristics of selected wireless links

14 Gbps 802.11ax
10 Gbps 5G

3.5 Gbps 802.11ac

802.11 af,ah
600 Mbps 802.11n
4G LTE
54 Mbps 802.11g
11 Mbps 802.11b
2 Mbps Bluetooth
Indoor Outdoor Midrange Long range
outdoor outdoor
10-30m 50-200m 200m-4Km 4Km-15Km

Wireless and Mobile Networks: 7- 8

Elements of a wireless network
infrastructure mode
 base station connects mobiles into
wired network
 handoff: mobile changes base station
wired network
providing connection into wired
infrastructure network

Wireless and Mobile Networks: 7- 9

Elements of a wireless network
ad hoc mode
 no base stations
 nodes can only transmit to
other nodes within link
coverage
 nodes organize themselves
into a network: route among
themselves

Wireless and Mobile Networks: 7- 10

Wireless network taxonomy
single hop multiple hops
host connects to base host may have to relay
infrastructure station (WiFi, cellular) through several wireless
(e.g., APs) which connects to nodes to connect to larger
larger Internet Internet: mesh net

no base station, no no base station, no connection

no connection to larger to larger Internet. May have
infrastructure Internet (Bluetooth, ad to relay to reach other a given
hoc nets) wireless node MANET, VANET

Wireless and Mobile Networks: 7- 11

Wireless link characteristics: fading (attenuation)
Wireless radio signal attenuates (loses power) as it propagates (free
space “path loss”)

Free space path loss ~ (fd)2

f: frequency
d: distance

higher frequency or larger free space

longer distance path loss

Wireless and Mobile Networks: 7- 13

Wireless link characteristics: multipath
multipath propagation: radio signal reflects off objects ground, built
environment, arriving at destination at slightly different times

reflected path

line of sight reflected path

(LOS) path

Wireless and Mobile Networks: 7- 14

Wireless link characteristics: multipath
multipath propagation: radio signal reflects off objects ground, built
environment, arriving at destination at slightly different times
Coherence time:
 amount of time bit is present
transmitted
pulses in channel to be received
time  influences maximum possible
received
received multipath
LOS pulse pulses
received
received multipath
LOS pulse pulses
transmission rate, since
received coherence times can not
pulse
time
overlap
Tc: coherence time  inversely proportional to
• frequency
• receiver velocity
Wireless and Mobile Networks: 7- 15
Wireless link characteristics: noise
 interference from other sources on 10-1

wireless network frequencies: motors, 10-2

appliances 10-3

 SNR: signal-to-noise ratio

BER
10-4

• larger SNR – easier to extract signal 10-5

from noise (a “good thing”) 10-6

 SNR versus BER tradeoff 10-7

• given physical layer: increase power -> 10 20
SNR(dB)
30 40

increase SNR->decrease BER

QAM256 (8 Mbps)
• SNR may change with mobility: QAM16 (4 Mbps)
dynamically adapt physical layer
BPSK (1 Mbps)
(modulation technique, rate)
Wireless and Mobile Networks: 7- 16
Wireless link characteristics: hidden terminals
Hidden terminal problem Attenuation also causes “hidden
terminals”
C
A B C
B
A C’s signal
A’s signal
strength strength
 B, A hear each other
 B, C hear each other space
 A, C can not hear each other means A,  B, A hear each other
C unaware of their interference at B  B, C hear each other
 A, C can not hear each other interfering
at B

Wireless and Mobile Networks: 7- 17

Code Division Multiple Access (CDMA)
 unique “code” assigned to each user; i.e., code set
partitioning
• all users share same frequency, but each user has own “chipping”
sequence (i.e., code) to encode data
• allows multiple users to “coexist” and transmit simultaneously with
minimal interference (if codes are “orthogonal”)
 encoding: inner product: (original data) X (chipping sequence)
 decoding: summed inner-product: (encoded data) X (chipping
sequence)

Wireless and Mobile Networks: 7- 19

CDMA encode/decode
channel output Zi,m
Zi,m= di.cm
data d0 = 1
1 1 1 1 1 1 1 1
d1 = -1
bits -1 -1 -1 -1 -1 -1 -1 -1

sender 1 1 1 1 1 1 1 1 slot 1 slot 0

code channel channel
-1 -1 -1 -1 -1 -1 -1 -1
output output
slot 1 slot 0

M
Di = S Zi,m.cm
m=1
M
receiver received
-1 -1 -1
1
-1
1 1 1 1 1 1
-1
1
-1 -1 -1
d0 = 1
input d1 = -1

1 1 1 1 1 1 1 1 slot 1 slot 0
code channel channel
-1 -1 -1 -1 -1 -1 -1 -1
output output
slot 1 slot 0

… but this isn’t really useful yet!

Wireless and Mobile Networks: 7- 20
CDMA: two-sender interference
channel sums together
transmissions by sender
Sender 1 1 and 2

Sender 2

using same code as sender

1, receiver recovers sender
1’s original data from
summed channel data!
… now that’s useful!
Wireless and Mobile Networks: 7- 21
IEEE 802.11 Wireless LAN
IEEE 802.11 Year Max data rate Range Frequency
standard
802.11b 1999 11 Mbps 30 m 2.4 Ghz
802.11g 2003 54 Mbps 30m 2.4 Ghz
802.11n (WiFi 4) 2009 600 70m 2.4, 5 Ghz
802.11ac (WiFi 5) 2013 3.47Gpbs 70m 5 Ghz
802.11ax (WiFi 6) 2020 (exp.) 14 Gbps 70m 2.4, 5 Ghz
802.11af 2014 35 – 560 Mbps 1 Km unused TV bands
(54-790 MHz)
802.11ah 2017 347Mbps 1 Km 900 Mhz

 all use CSMA/CA for multiple access, and have base-station and ad-hoc
network versions
Wireless and Mobile Networks: 7- 23
802.11 LAN architecture

Internet
 wireless host communicates with
base station
• base station = access point (AP)
switch  Basic Service Set (BSS) (aka “cell”)
or router in infrastructure mode contains:
• wireless hosts
BSS 1
• access point (AP): base station
• ad hoc mode: hosts only

BSS 2
Wireless and Mobile Networks: 7- 24
802.11: Channels
 spectrum divided into channels at different frequencies
• AP admin chooses frequency for AP
• interference possible: channel can be same as that chosen by
neighboring AP!

Example: 2.4 GHz

Class 22: 25
802.11: Association

 arriving host: must associate

with an AP
• scans channels, listening for
beacon frames containing AP’s
name (SSID) and MAC address
• selects AP to associate with
• then may perform
authentication [Chapter 8] BSS

• then typically run DHCP to get IP

address in AP’s subnet

Class 22: 26
802.11: passive/active scanning
BBS 1 BBS 2 BBS 1 BBS 2

1
1 1 AP 2 2 2 AP 2
AP 1 AP 1
2 3
3 4

H1 H1

passive scanning: active scanning:

(1) beacon frames sent from APs (1) Probe Request frame broadcast from H1
(2) association Request frame sent: H1 (2) Probe Response frames sent from APs
to selected AP (3) Association Request frame sent: H1 to
(3) association Response frame sent selected AP
from selected AP to H1 (4) Association Response frame sent from
selected AP to H1

Wireless and Mobile Networks: 7- 27

IEEE 802.11: multiple access
 avoid collisions: 2+ nodes transmitting at same time
 802.11: CSMA - sense before transmitting
• don’t collide with detected ongoing transmission by another node
 802.11: no collision detection!
• difficult to sense collisions: high transmitting signal, weak received signal
due to fading
• can’t sense all collisions in any case: hidden terminal, fading
• goal: avoid collisions: CSMA/CollisionAvoidance

A B C
C

A’s signal C’s signal

B strength
A strength

space
Wireless and Mobile Networks: 7- 28
IEEE 802.11 MAC Protocol: CSMA/CA
802.11 sender
sender receiver
1 if sense channel idle for DIFS then
transmit entire frame (no CD)
DIFS
2 if sense channel busy then
start random backoff time
timer counts down while channel idle data
transmit when timer expires
if no ACK, increase random backoff interval, repeat 2
SIFS

802.11 receiver ACK

if frame received OK
return ACK after SIFS (ACK needed due to hidden
terminal problem)

Wireless and Mobile Networks: 7- 29

Avoiding collisions (more)
idea: sender “reserves” channel use for data frames using small
reservation packets
 sender first transmits small request-to-send (RTS) packet to BS using
CSMA
• RTSs may still collide with each other (but they’re short)
 BS broadcasts clear-to-send CTS in response to RTS
 CTS heard by all nodes
• sender transmits data frame
• other stations defer transmissions

Wireless and Mobile Networks: 7- 30

Collision Avoidance: RTS-CTS exchange
A B
AP

reservation collision

time
DATA (A)
defer

Wireless and Mobile Networks: 7- 31

802.11 frame: addressing
2 2 6 6 6 2 6 0 - 2312 4
frame duration address address address seq address payload CRC
control 1 2 3 control 4

Address 1: MAC address Address 4: used only in

of wireless host or AP to ad hoc mode
receive this frame
Address 3: MAC address of
Address 2: MAC address router interface to which AP
of wireless host or AP is attached
transmitting this frame

Wireless and Mobile Networks: 7- 32

802.11 frame: addressing

Internet
H1 R1

802.3 Ethernet frame

R1 MAC addr H2 MAC addr

MAC dest addr MAC source addr

AP MAC addr H1 MAC addr R1 MAC addr

address 1 address 2 address 3

802.11 WiFi frame

Wireless and Mobile Networks: 7- 33
802.11 frame: addressing
duration of reserved frame sequence # (for reliable data
transmission time (RTS/CTS) transfer)

2 2 6 6 6 2 6 0 - 2312 4
frame duration address address address seq address payload CRC
control 1 2 3 control 4

2 2 4 1 1 1 1 1 1 1 1
protocol to from more power more
type subtype retry WEP rsvd
version AP AP frag mgt data

frame type (RTS, CTS, ACK, data)

Wireless and Mobile Networks: 7- 34

802.11: mobility within same subnet

 H1 remains in same IP subnet: IP

address can remain same
 switch: which AP is associated
with H1?
• self-learning (Ch. 6): switch
will see frame from H1 and
“remember” which switch
port can be used to reach H1
H1 BBS 2
BBS 1

Wireless and Mobile Networks: 7- 35

802.11: advanced capabilities
Rate adaptation
 base station, mobile dynamically 10-1
10-2
change transmission rate (physical 10-3
layer modulation technique) as

BER
10-4

mobile moves, SNR varies 10-5

10-6
10-7
1. SNR decreases, BER increase as node moves 10 20 30 40
away from base station SNR(dB)

2. When BER becomes too high, switch to lower QAM256 (8 Mbps)

QAM16 (4 Mbps)
transmission rate but with lower BER BPSK (1 Mbps)
operating point

Wireless and Mobile Networks: 7- 36

802.11: advanced capabilities
power management
 node-to-AP: “I am going to sleep until next beacon frame”
• AP knows not to transmit frames to this node
• node wakes up before next beacon frame
 beacon frame: contains list of mobiles with AP-to-mobile
frames waiting to be sent
• node will stay awake if AP-to-mobile frames to be sent;
otherwise sleep again until next beacon frame

Wireless and Mobile Networks: 7- 37

4G/5G cellular networks
 the solution for wide-area mobile Internet
 widespread deployment/use:
• more mobile-broadband-connected devices than fixed-
broadband-connected devices devices (5-1 in 2019)!
• 4G availability: 97% of time in Korea (90% in US)
 transmission rates up to 100’s Mbps
 technical standards: 3rd Generation Partnership Project (3GPP)
• wwww.3gpp.org
• 4G: Long-Term Evolution (LTE)standard

Wireless and Mobile Networks: 7- 43

4G/5G cellular networks
similarities to wired Internet differences from wired Internet
 edge/core distinction, but both  different wireless link layer
belong to same carrier  mobility as a 1st class service
 global cellular network: a  user “identity” (via SIM card)
network of networks  business model: users
 widespread use of protocols subscribe to a cellular provider
we’ve studied: HTTP, DNS, TCP, • strong notion of “home network”
UDP, IP, NAT, separation of versus roaming on visited nets
data/control planes, SDN, • global access, with authentication
Ethernet, tunneling infrastructure, and inter-carrier
 interconnected to wired settlements
Internet
Wireless and Mobile Networks: 7- 44
Elements of 4G LTE architecture

Mobile device:
Mobility
 smartphone, tablet, laptop, Mobile device
(UE)
Management
Entity (MME)
Home Subscriber
Service (HSS)
Base station
IoT, ... with 4G LTE radio (eNode-B)

 64-bit International Mobile to

Internet
Subscriber Identity (IMSI),
stored on SIM (Subscriber PDN gateway (P-GW)

Identity Module) card Serving Gateway (S-GW)

…
 LTE jargon: User Equipment
(UE)
radio access
network all-IP Enhanced Packet Core (EPC)

Wireless and Mobile Networks: 7- 45

 Elements of 4G LTE architecture
Base station:
 at “edge” of carrier’s network
 manages wireless radio Mobile device
Mobility
Management Home Subscriber
Service (HSS)
resources, mobile devices in its (UE)
Base station
Entity (MME)

coverage area (“cell”) (eNode-B)

to
 coordinates device Internet
authentication with other PDN gateway (P-GW)
elements
 similar to WiFi AP but: …
Serving Gateway (S-GW)

• active role in user mobility

• coordinates with nearly base
stations to optimize radio use
 LTE jargon: eNode-B
Wireless and Mobile Networks: 7- 46
Radio Access Network: 4G radio
Mobile device
(UE)
Base station

 connects device (UE) to a base station (eNode-B) (eNode-B)

• multiple devices connected to each base station

 many different possible frequencies bands, multiple channels in each
band
• popular bands: 600, 700, 850, 1500, 1700, 1900, 2100, 2600, 3500 MHz
• separate upstream and downstream channels
 sharing 4G radio channel among users:
• OFDM: Orthogonal Frequency Division Multiplexing
• combination of FDM, TDM
 100’s Mbps possible per user/device

Class 23: 47
OFDMA: time division (LTE)

Subcarrier frequencies

time (symbols)

Class 23: 49
OFDMA: time division (LTE)
Physical Resource Block (PRB ): blocks of 7x12=84 resource elements
 unit of transmission scheduling

Subcarrier frequencies

time to transmit one OFDM symbol on subcarrier frequency

Class 23: 50
 OFDMA: Transmission Time Interval (TTI): 1 ms

PRB PRB
Transmission
scheduling
example: Subcarrier frequencies
• Send to 7 UEs in 7
blocks of REs in
one PRB
UE1
UE2
UE3
UE4
UE5
UE6
UE7
time (symbols)

Class 23: 51
Elements of 4G LTE architecture
Home Subscriber Service
 stores info about mobile Mobility
Management Home Subscriber
devices for which the HSS’s Mobile device
(UE) Entity (MME) Service (HSS)
Base station
network is their “home (eNode-B)

network” to
Internet
 works with MME in device PDN gateway (P-GW)
authentication
Serving Gateway (S-GW)
…

Wireless and Mobile Networks: 7- 52

Elements of 4G LTE architecture
Serving Gateway (S-GW),
PDN Gateway (P-GW) Mobility
Management Home Subscriber
 lie on data path from mobile
Mobile device Service (HSS)
(UE) Entity (MME)
Base station
to/from Internet (eNode-B)

to
 P-GW Internet
• gateway to mobile cellular PDN gateway (P-GW)
network
• Looks like nay other …
Serving Gateway (S-GW)

internet gateway router

• provides NAT services
 other routers:
• extensive use of tunneling
Wireless and Mobile Networks: 7- 53
Elements of 4G LTE architecture
Mobility Management
Entity Mobility
Management Home Subscriber
Mobile device Service (HSS)
Entity (MME)
 device authentication (UE)
Base station
(eNode-B)
(device-to-network, network-
to
to-device) coordinated with Internet
mobile home network HSS PDN gateway (P-GW)

 mobile device management: Serving Gateway (S-GW)

…
• device handover between cells
• tracking/paging device location
 path (tunneling) setup from mobile
device to P-GW
Wireless and Mobile Networks: 7- 54
LTE: data plane control plane separation
HSS control plane
 new protocols for mobility
management , security,
base station
MME
P-GW authentication (later)
S-GW

data plane
 new protocols at link, physical
base station S-GW P-GW
layers
 extensive use of tunneling to
IP tunnels facilitate mobility

Wireless and Mobile Networks: 7- 55

 LTE data plane protocol stack: first hop
Application LTE link layer protocols:
Transport  Packet Data Convergence: header
IP IP compression, encryption
Packet Data
Convergence
Packet Data
Convergence  Radio Link Control (RLC) Protocol:
Link

Radio Link Radio Link fragmentation/reassembly, reliable data

Medium Access Medium Access transfer
Physical Physical  Medium Access: requesting, use of radio
transmission slots (OFDM)

data
plane
base station S-GW P-GW

Wireless and Mobile Networks: 7- 56

LTE data plane protocol stack: packet core
tunneling:
GTP-U
 mobile datagram
GTP-U GTP-U
UDP UDP UDP encapsulated using GPRS
IP IP IP IP Tunneling Protocol (GTP),
Packet Data
Convergence sent inside UDP
Radio Link link link link
Medium Access datagram to S-GW
Physical Physical Physical Physical  S-GW re-tunnels
datagrams to P-GW
 supporting mobility: only
\ tunneling endpoints
base station S-GW P-GW change when mobile
user moves
Wireless and Mobile Networks: 7- 57
LTE data plane: associating with a BS
1
2
3 data
plane
base station S-GW P-GW

1 BS broadcasts primary synch signal every 5 ms on all frequencies

 BSs from multiple carriers may be broadcasting synch signals
2 mobile finds a primary synch signal, then locates 2nd synch signal on this freq.
 mobile then finds info broadcast by BS: channel bandwidth, configurations;
BS’s cellular carrier info
 mobile may get info from multiple base stations, multiple cellular networks
3 mobile selects which BS to associate with (e.g., preference for home carrier)
4 more steps still needed to authenticate, establish state, set up data plane
Wireless and Mobile Networks: 7- 58
LTE mobiles: sleep modes
ZZZZ...

data
plane

as in WiFi, Bluetooth: LTE mobile may put radio to “sleep” to conserve

battery:
 light sleep: after 100’s msec of inactivity
 wake up periodically (100’s msec) to check for downstream transmissions
 deep sleep: after 5-10 secs of inactivity
 mobile may change cells while deep sleeping – need to re-establish association

Wireless and Mobile Networks: 7- 59

 Global cellular network: a network of IP networks
home network HSS:
Home
Subscriber
Server
 identify & services info,
while in home network
home mobile and roaming
carrier network P-GW
public Internet
and
inter-carrier IPX
all IP:
in home network  carriers interconnect
with each other, and
public internet at
exchange points
P-GW
SIM card: global visited mobile  legacy 2G, 3G: not all IP,
identify info in carrier network handled otherwise
home network
roaming in
visited network
Wireless and Mobile Networks: 7- 60
 On to 5G: motivation

From Next Generation Mobile Networks (NGMS) alliance: 2020 white paper

Hype/wishes need to be separated from reality or likely nearer-term reality

Class 23: 61
On to 5G: motivation
“initial standards and
launches have mostly
focused on enhanced
Mobile Broadband, 5G is
expected to increasingly
enable new business
models and countless new
use cases, in particular
those of massive Machine
Type Communications and
Ultra-reliable and Low
Latency Communications.”
Figure: from Recommendation ITU-R M.2083-0 (2015)
Class 23: 62
On to 5G: motivation

eMBB Industry verticals:

 Manufacturing
 Constructions
 Transport
 Health
 Smart
communities
 Education
mMTC URLLC  Tourism
 Agriculture
 Finance
K. Schwab, “The Fourth Industrial Revolution,” World Economic Forum.
Class 23: 63
On to 5G: Radio
 goal: 10x increase in peak bitrate, 10x decrease in latency, 100x increase
in traffic capacity over 4G
 5G NR (new radio):
 two frequency bands: FR1 (450 MHz–6 GHz) and FR2 (24 GHz–52 GHz): millimeter wave
frequencies
 not backwards-compatible with 4G
 MIMO: multiple directional antennae
 millimeter wave frequencies: much higher data rates, but over shorter
distances
 pico-cells: cells diameters: 10-100 m
 massive, dense deployment of new base stations required
Class 23: 64
On to 5G: SDN-like architecture
Serving gateway (S-GW) PDN gateway (P-GW)
public Internet
and
inter-carrier IPX

4G mobile core:
boxes and protocols

Mobility
Management Home Subscriber
Entity (MME) Service (HSS) public Internet
and
inter-carrier IPX

5G: microservice-like architecture

Class 23: 65
Functional elements: communication, computation, data
User control, Mobile
Core implemented in
“edge” data center (DC)

RAN RAN
Far Edge Far Edge
DC DC

UE UE
Edge DC
Core DC Edge DC
Mobile Core
Mobile Core
RAN RAN
Far Edge Far Edge
DC DC

UE UE
Edge Network Global Core Edge Network
Operator A Operator B

Class 23: 66
Control plane: resource control
Real-time (< ms) Near real-time (> ms) Non real-time (>> ms) control plane

RAN RAN
Far Edge Far Edge
DC DC

UE UE
Edge DC
Core DC Edge DC
Mobile Core
Mobile Core
RAN RAN
Far Edge Far Edge
DC DC

UE UE
Edge Network Global Core Edge Network
Operator A Operator B Class 23: 67
User plane: resources, as used by users (application)
User plane
“local breakout” within one operator multi-operator end-end edge/core edge/core

RAN RAN
Far Edge Far Edge
DC DC

UE UE
Edge DC
Core DC Edge DC
Mobile Core
Mobile Core
RAN RAN
Far Edge Far Edge
DC DC

UE UE
Edge Network Global Core Edge Network
Operator A Operator B Class 23: 68
On beyond 5G?
 “6G” not obviously next: “NextG” and “Beyond 5G” heard more
often than “6G”
 5G on an evolutionary path (like the Internet)
• agility: cloud technologies (SDN) mean new features can be introduced
rapidly, deployed continuously
• customization: change can be introduced bottom-up (e.g., by enterprises and
edge cloud partners with Private 5G)
• No need to wait for standardization
• No need to reach agreement (among all incumbent stakeholders)

Class 23: 69
What is mobility?
 spectrum of mobility, from the network perspective:
no mobility high mobility

device moves device moves device moves device moves

between within same AP in among APs in among multiple
networks, but one provider one provider provider networks,
powers down network network while maintaining
while moving ongoing
We’re interested in these!
connections
Wireless and Mobile Networks: 7- 71
Mobility challenge:
content
provider
If a device moves from network datacenter
network
Verizon
one network another:
 How will the public Internet
“network” know to
forward packets to
the new network?
client moves from
Verizon to AT&T
AT&T

Wireless and Mobile Networks: 7- 72

Mobility approaches
 let network (routers) handle it:
• routers advertise well-known name, address (e.g., permanent 32-
bit IP address), or number (e.g., cell #) of visiting mobile node via
usual routing table exchange
• Internet routing could do this already with no changes! Routing
tables indicate where each mobile located via longest prefix match!

Wireless and Mobile Networks: 7- 73

Mobility approaches
 let network (routers) handle it:
• routers advertise well-known notname, address (e.g., permanent 32-
bit IP address), or number (e.g., cell #) of visiting mobile node via
scalable
to billions of
usual routing table exchange
mobiles
• Internet routing could do this already with no changes! Routing
tables indicate where each mobile located via longest prefix match!
 let end-systems handle it: functionality at the “edge”
• indirect routing: communication from correspondent to mobile
goes through home network, then forwarded to remote mobile
• direct routing: correspondent gets foreign address of mobile, send
directly to mobile
Wireless and Mobile Networks: 7- 74
Contacting a mobile friend: I wonder where
Alice moved to?
Consider friend frequently changing
locations, how do you find him/her?
 search all phone books?
 expect her to let you know
where he/she is?
 call his/her parents?
 Facebook!

The importance of having a “home”:

 a definitive source of information about you
 a place where people can find out where you are
Wireless and Mobile Networks: 7- 75
 Home network, visited network: 4G/5G
Home
home network:
Subscriber
Server
 (paid) service plan with
cellular provider, e.g.,
home mobile
carrier network P-GW
Verizon, Orange
public Internet  home network HSS stores
and
inter-carrier IPX identify & services info
in home network

visited network:
 any network other than
P-GW your home network
SIM card: global visited mobile
identify info carrier network  service agreement with
including home other networks: to provide
network roaming in
visited network access to visiting mobile
Wireless and Mobile Networks: 7- 76
 Home network, visited network: ISP/WiFi
ISP/WiFi: no notion of global “home”
authentication  credentials from ISP (e.g.,
access
server
username, password) stored
on device or with user
public  ISPs may have national,
Internet
attach
international presence
 different networks: different
credentials
• some exceptions (e.g.,
authentication
eduroam)
access
server
• architectures exist (mobile
IP) for 4G-like mobility, but
attach
not used
Wireless and Mobile Networks: 7- 77
Home network, visited network: generic
Home Network Visited Network
e.g.,: 128.119/16 e.g.,: 79.129/16

Permanent IP: Home NAT IP:

128.119.40.186 Subscriber 10.0.0.99
IMSI Server IMSI Mobility
78:4f:43:98:d9:27 manager
78:4f:43:98:d9:27

Mobility Visited
manager Home network
network
Home gateway gateway
gateway
public or private
Internet

Correspondent

Wireless and Mobile Networks: 7- 78

Registration: home needs to know where you are!
Home Network Visited Network
e.g.,: 128.119/16 e.g.,: 79.129/16
1 mobile associates
Permanent IP: Home
128.119.40.186 Subscriber
2
NAT IP:
10.0.0.99
with visited
IMSI Server Mobility
78:4f:43:98:d9:27 IMSI
78:4f:43:98:d9:27 manager mobility manager
Mobility
Home
Visited visited mobility
manager network
network
Home gateway gateway manager registers
gateway
public or private mobile’s location
Internet with home HSS
end result:
 visited mobility manager knows about mobile
 home HSS knows location of mobile

Wireless and Mobile Networks: 7- 79

 Mobility with indirect routing
Home Network Visited Network
e.g.,: 128.119/16 e.g.,: 79.129/16

Permanent IP: Home NAT IP:

128.119.40.186 Subscriber 10.0.0.99 3
IMSI Server IMSI Mobility
78:4f:43:98:d9:27 manager
78:4f:43:98:d9:27
visited gateway router
2
Mobility Visited forwards to mobile
manager Home 4a network
network
Home gateway gateway
gateway
home gateway receives public or private
Internet
datagram, forwards (tunnels) 1
visited gateway router forwards
to remote gateway 4b
reply to correspondent via home
correspondent uses home network (4a) or directly (4b)
address as datagram Correspondent
destination address
Wireless and Mobile Networks: 7- 80
Mobility with indirect routing: comments
 triangle routing:
• inefficient when correspondent
and mobile are in same network
 mobile moves among visited networks: transparent to correspondent!
• registers in new visited network
• new visited network registers with home HSS
• datagrams continue to be forwarded from home network to mobile
in new network
• on-going (e.g., TCP) connections between correspondent and mobile
can be maintained!
Wireless and Mobile Networks: 7- 81
Mobility with direct routing
Home Network Visited Network
e.g.,: 128.119/16 e.g.,: 79.129/16

Permanent IP: Home NAT IP:

128.119.40.186 Subscriber 10.0.0.99 4
IMSI Server IMSI Mobility
78:4f:43:98:d9:27 manager
78:4f:43:98:d9:27
visited gateway router
Mobility Visited forwards to mobile
manager network
Home gateway gateway
2
public or private 3
Internet
correspondent contacts 1
home HSS, gets mobile’s Correspondent
visited network addresses datagram to
visited network
Correspondent
address

Wireless and Mobile Networks: 7- 82

Mobility with direct routing: comments
 overcomes triangle routing inefficiencies
 non-transparent to correspondent: correspondent must get care-of-
address from home agent
 what if mobile changes visited network?
• can be handled, but with additional complexity

Wireless and Mobile Networks: 7- 83

Mobility in 4G networks: major mobility tasks
Mobility 1 base station association:
manager
Home  covered earlier
Subscriber 2 1
Server
MME  mobile provides IMSI –
Home 3 base station identifying itself, home network
network P-GW S-GW 4
2 control-plane configuration:
Internet  MME, home HSS establish
P-GW Visited network control-plane state - mobile
is in visited network
Streaming
server 3 data-plane configuration:
 MME configures forwarding tunnels for mobile
 visited, home network establish tunnels from
4 mobile handover: home P-GW to mobile
 mobile device changes its point of attachment to visited network
Wireless and Mobile Networks: 7- 85
Configuring LTE control-plane elements
Mobility
manager
Home
Subscriber MME
2
Server
Home base station
network P-GW P-GW S-GW
Visited network

 Mobile communicates with local MME via BS control-plane channel

 MME uses mobile’s IMSI info to contact mobile’s home HSS
• retrieve authentication, encryption, network service information
• home HHS knows mobile now resident in visited network
 BS, mobile select parameters for BS-mobile data-plane radio channel
Wireless and Mobile Networks: 7- 86
Configuring data-plane tunnels for mobile
Mobility
 S-GW to BS tunnel: when Home
manager
Subscriber
mobile changes base Server
MME

stations, simply change Home

network S-GW
base station

P-GW
endpoint IP address of
tunnel Internet
P-GW Visited network
 S-GW to home P-GW
tunnel: implementation of Streaming
server
indirect routing
 tunneling via GTP (GPRS tunneling protocol): mobile’s datagram to
streaming server encapsulated using GTP inside UDP, inside datagram

Wireless and Mobile Networks: 7- 87

Handover between BSs in same cellular network

data path before handover

source BS
1 current (source) BS selects
S-GW 3 target BS, sends Handover
1 4 Request message to target BS
2
P-GW
2 target BS pre-allocates radio
data path after
time slots, responds with HR
handover MME target BS ACK with info for mobile

3 source BS informs mobile of new BS

 mobile can now send via new BS - handover
looks complete to mobile
4 source BS stops sending datagrams to mobile, instead forwards to new BS
(who forwards to mobile over radio channel)
Wireless and Mobile Networks: 7- 88
Handover between BSs in same cellular network
source BS

S-GW 3
1 4 5 target BS informs MME that it is
2 6
P-GW new BS for mobile
5 7  MME instructs S-GW to
5 change tunnel endpoint to be
MME target BS (new) target BS

6 target BS ACKs back to source BS: handover complete, source BS can

release resources
7 mobile’s datagrams now flow through new tunnel from target BS to S-GW

Wireless and Mobile Networks: 7- 89

Mobile IP
 mobile IP architecture standardized ~20 years ago [RFC 5944]
• long before ubiquitous smartphones, 4G support for Internet protocols
• did not see wide deployment/use
• perhaps WiFi for Internet, and 2G/3G phones for voice were “good enough” at
the time
 mobile IP architecture:
• indirect routing to node (via home network) using tunnels
• mobile IP home agent: combined roles of 4G HSS and home P-GW
• mobile IP foreign agent: combined roles of 4G MME and S-GW
• protocols for agent discovery in visited network, registration of visited location in
home network via ICMP extensions

Wireless and Mobile Networks: 7- 90

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 handover loss
• TCP interprets loss as congestion, will decrease congestion window un-
necessarily
• delay impairments for real-time traffic
• bandwidth a scare resource for wireless links

Wireless and Mobile Networks: 7- 91