Mobility and cellular networks

Transcription

Wireless WANs
Mobility and cellular networks
Cellular radio and PCS networks
Wireless data networks
Satellite links and networks
Basic concepts and directions in telecommunications
Cellular networks
Cellular networks
First generation: initially debuted in Japan in
1979, analog transmission system
Second generation (2G): introduced digital
transmission, operational in 1992
2.5G: offers enhancements to the data services
on existing second-generation digital platforms
Third generation (3G): digital, permit per-user
and terminal mobility, broadband applications
(voice, data, and multimedia streams) at higher
data speeds 144Kbps to 384Kbps, up to 2Mbps
C. Courcoubetis
Mobility, etc.- 2
C. Courcoubetis
Mobility, etc.- 3
Mobile users use for a given time period channels
(frequency pairs) to connect to base station
Problem: interference from remote stations and
users
frequencies
control
channels
fixed network
C. Courcoubetis
Mobility, etc.- 4
The concept of a cell
The digital cellular architecture
Interference: reduced when cells are small (1 / r 2 )
Possibility of frequency reuse
Size of cell: function of density of users and of
demand, possibility of breaking large cells into
smaller ones
Need for hand-off
Cell 2
Cell 2
Cell 3
Cell 7
Cell 5
Cell 4
Cell 2
Cell 5
Cell 4
Cell 6
Cell 4
Cell 6
Cell 1
Cell 6
Cell 1
Cell 1
Cell 3
Cell 7
Cell 3
Cell 7
Cell 2
Cell 3
Cell 7
Cell 1
Cell 5
Cell 4
Cell 6
A seven-cell cluster
variable size
cells
Cell 5
frequency ruse
Cell 1
Cell 2
channels
C. Courcoubetis
Mobility, etc.- 5
The digital cellular architecture (2)
TDMA: time slots /frequency channel
C. Courcoubetis
Mobility, etc.- 6
GSM (2G)
GSM supports 124 channel pairs with a
200KHz spacing to prevent channel
interference
TDM with 8 slots: eight callers per channel
Basic GSM: data rates 9.6Kbps
International roaming with a single invoice,
SIM card security, SMS
C. Courcoubetis
Mobility, etc.- 7
C. Courcoubetis
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GPRS (2G+)
GSM evolution
Always-on data service, <115Kbps
Packets sent over the 8 time slots of GSM
More architectural components added to GSM
– the Gateway GPRS Service Node (GGSN)
gateway between the GPRS network and IP networks,
connect to other GPRS networks to facilitate GPRS
roaming
– the Serving GPRS Service Node (SGSN)
The SGSN provides packet routing to and from the
SGSN service area for all users in that service area,
performs mobility management functions
C. Courcoubetis
Mobility, etc.- 9
GSM
– new services, improved quality & performance, lower cost
– backward compatibility
– independent of UMTS standards
GSM phase 2+
–
–
–
–
–
–
–
new services (ΙΝ services+)
quality equal to fixed network
circuit switched data < 76.8 kbps
efficient administration (routing, packet data)
location services
GSM/DECT interworking
GPRS: wireless extension of Internet over GSM network
WWW, ftp,…, low QoS, combines 1-8 14kbps voice ch.
3G
C. Courcoubetis
Mobility, etc.- 10
3G (2)
3G is designed for high-speed multimedia data and
voice
Its goals include high-quality audio and video and
advanced global roaming, which means being able
to go anywhere and be automatically handed off to
whatever wireless system is available (4G?)
Objectives:
– improve throughput and QoS, voice quality, battery life, positionlocation services
– Coexistence with current infrastructures, including backward
compatibility, ease of migration or overlay, interoperability and
handoffs, the need for bandwidth on demand, improving
authentication and encryption methodologies to support mobile
commerce (m-commerce)
– Supporting higher bandwidths over greater allocations (that is,
5MHz to 20MHz)
UMTS is considered the proposed 3G standard towards
the IMT2000
C. Courcoubetis
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C. Courcoubetis
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Universal Mobile Telecommunications
Systems
Goal: remove any distinctions between mobile and
fixed networking
– supports the ITU's UPT concept: personal mobility across
many different networks, each user is issued a unique
UPT number
UMTS Forum: speedup processes, evolution
integrates existing technologies (GSM 2…)
proposes new ones
global technology concept
IP is pushed further into the network
– interconnection, charging, security, management, performance
– public, business to business, financial, ...
– Frequency hopping: 802.11b, Bluetooth
– Direct Sequence CDMA: 3G
user signals are spread up to a wideband by multiplication by a code
power of user wideband signal must be above the rest of the signals in
order to be successfully received at the receiver.
power
DS-CDMA
1
-1
-1 1 -1 -1 1 -1 1 1 -1 1 -1 -1 1 -1 1 1
freq
C. Courcoubetis
Mobility, etc.- 14
UMTS architecture
Can we transmit on the same frequency and the same time? Yes,
using CDMA:
power of one
wideband signal
– transparency of service access, seamless provisioning,
satellite+terrestrial,…
Content and value-added services
Code Division Multiple Access
narrowband signal
(i.e. voice call)
Mobility
Basic services
Mobility, etc.- 13
C. Courcoubetis
– low cost of new technologies
– open architectures
Telecommunications
UMTS: a whole system, not just technologies
Personal communications in the 21st century
Universality
– personal mobility, smart cards, Virtual Home Environment, service
mobility, personal service profile
– regulatory framework, spectrum, standards
– the example of GSM
–
–
–
–
The UMTS vision
New elements
– UMTS 99:
RNC, Node B
(WBTS)
– UMTS
R4:MSC
Server,
Media
Gateway
(MGW)
– UMTS R5: all
IP network
-1 1 -1 -1 1 -1 1 1 1 -1 1 1 -1 1 -1 -1
C. Courcoubetis
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UMTS architecture
Circuit core
Convergence of technologies
Initial implementation
PSTN
BS
SGSN
IP
GGSN
Packet core
PSTN
BS
SGSN
GGSN
R5 and beyond
IMS (IP)
IMS
IP Packet core
Mobility, etc.- 17
C. Courcoubetis
Next Generation Networks

Transition from single-service
networks to multi-service
networks
In NGN service intelligence is
decoupled from network
transmission
Offers converged services: fixed
telephony, mobile telephony,
broadband Internet, leased
lines, …
Traffic from various access
networks types is aggregated:
fixed (ISDN, FTTx), mobile
(PLMN), wireless (802.1x), …
Core network is IP-based
Supports QoS (G/MPLS)
Content
C. Courcoubetis
– GPRS (GSM phase 2+, point-to-point-multi-point
connectionless, connection-oriented, IP service,
tunneling), WAP
– ATM
– TCP (wireless case, new proposals: link-layer forward
error corrections, end-to-end Selective ACKs, splitconnection, Snoop protocol), QoS enhancements
– mobility management (MIPv6++)
– addressing issues
The purpose is service continuation regardless of
user’s place and client capabilities.
IP
Combine elements from 2G: GSM, IP, ATM
C. Courcoubetis
Mobility, etc.- 18
IMS - IP Multimedia Subsystem
Content
Servers
Communcation Control
IP Core Network
Access
Access
Access
Access
Access
Access
3GPP (3rd Generation
Partnership Project) is
working on IMS
– 3G Release 5
– A commercial step towards
NGN
– Enables services that are
independent from access
network technologies
– Based on Internet protocols
– 4G?
3 layer architecture
Clients
Mobility, etc.- 19
– Transport (networking fabric
& gateways)
– Control (signaling elements)
– Services (back end systems &
content)
C. Courcoubetis
Mobility, etc.- 20
IMS and mobility
IMS Main Components
SIP is the protocol used for session management
Users have a public SIP address (identifier) [email protected]
Mobility is enabled through proxy servers and registrars
– Proxy servers process/forward requests from users and other
proxies
– A registrar stores information about users (IP address of user’s
terminal or current proxy server)
“Home provider” has control on services received from
roaming user, as he participates in authentication and
performs authorization, accounting in order to bill
A 4G-provider is expected to be a 3G provider that can
interoperate with other 3G providers during the provision
of a single service
Mobility, etc.- 21
C. Courcoubetis
Example of a session between 2
roaming users in IMS
A’s visited network
Required on
registration,
optional on
session establish
GPRS
Home Subscriber Server
(HSS): a database with
subscriber information
Visited
200 OK
network
REG
P-CSCF
200 OK
REG
I-CSCF
Home
REG
200 OK
network
S-CSCF
C. Courcoubetis
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BT Fusion
The first commercially available service bringing
Fixed-Mobile Convergence (since fall 2005)
BT decides the most appropriate access network
for delivering services, based on subscriber’s
location
S-CSCF
I-CSCF
P-CSCF
I-CSCF
SIP
Optional
voice packets
B’s visited network
User B
I-CSCF
GPRS
I-CSCF
B’s home
– Proxy CSCF: UE’s first point of
contact (can be either on the
visited or home network)
– Interrogating CSCF: a type of
“proxy” for incoming SIP
requests from other networks
– Serving CSCF: session
controller assigned to
subscriber (always on the
home network)
A’s home network
User A
S-CSCF
Registration example
Call Session Control Function
(CSCF): Set of entities for
managing user sessions
Required on
registration,
optional on
session establish
P-CSCF
– 3 choices in case of telephony services: POTS, VoIP,
Mobile
– Combines functionality of a mobile phone with
reliability of fixed telephony and/or lower charges
(especially for VoIP)
Vodafone is the associated mobile operator
network
C. Courcoubetis
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C. Courcoubetis
Mobility, etc.- 24
Content strategies
BT Fusion
User owns a special access point and a dual-mode handset
User is assigned only one identifying number (from BT)
Calls routed to fixed-line network within range of Bluetooth access
point (WiFi in future)
– VoIP if quality is acceptable, POTS otherwise
– more profit for the provider
– traditional strategy of cable operators & cellular providers
Out of range calls routed to cellular network
BT has full control (not the user)!
An open access portal model allows the user
unrestricted access to whatever content is available.
Cellular
network
Convergent
Handset
PSTN
Cell site
Fusion
Access Point
Bluetooth
or WiFi
– based on the “End-to-end” principle of Internet
– network operators charge purely on traffic (bit pushers)
PSTN Link
NTE
Broadband
Link
OR
A walled garden is a mechanism for a provider to restrict
the user experience by confining the user to a specific
region/space as defined by the provider
VoIP Gateway
ADSL NTE
C. Courcoubetis
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