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Considerations for 3G
and 4G over VSAT
Michele Di Paolo
VP, Mobile Network Operator (MNO) Solution and Business Development
ComtechEFData
Considerations for 3G
over VSAT
( and why 3G failed to deliver over VSAT)
2
UMTS (3G) Topology
• The Universal Mobile Telecommunications
System (UMTS) is a third generation mobile cellular
system
3
Considerations for 3G over VSAT
• MNO expectations:
– Deliver services with terrestrial level KPIs.
– Respect existing network transport (L2 transport)
– Respect MNO defined QOS
– High availability
4
• Keys to achieving MNO expectations:
– Low jitter and delay variations
– Support L2 protocols (VLAN/MPLS) and L3
– 3GPP Compliant QOS performance
– Error free delivery (AUPC/ACM)
Maintaining highest KPI
• Most significant KPI moving forward to 3G is RRC (Radio
Resource Control) Success Rate which manages the control
plane between RNC and the Ue and is responsible for Radio
Resource management.
• Jitter in excess of 10msecs resulting in packets not being
delivered on time, retransmissions, dropped Ues, etc.
5
It is not just about delivering bandwidth
RRC KPI
Success rate
of 99.95%
recorded.
Maintaining highest throughput
• 3G NodeB manages UL traffic from the Ues.
• Additional delay and/or jitter variation in UL traffic is
detected at RNC which sends congestion notification
to NodeB to throttle down UL.
• This results in FLOW control which negatively impact
UL and DL traffic which we call the Bart effect.
6
3G traffic expectations
• TCP session throughput expectation across GEO satellite
<1Mbps/session.
• The disruptive effect of packet loss, congestion control, etc
can reduce effective real-life speeds to 160kbps or less.
• Packet loss is a real issue for 3G Iub with reported 5% RAN
packet being considered lost/delayed over TDMA… source
Ericsson.
7
Packet per second considerations
• Requires highly capable processing engines to deal
with high packet per second rates found in 3G
environment.
• Expect 2000 packets per 1 Mbps of 3G traffic!
8
Overhead: Iub Voice
Comtech EF Data Confidential 9
• IP NodeB voice is supported via R99 techniques
which call for voice to be encapsulated in
IP/UDP/tunnels and so also carry significant
overhead.
– L2/L3 overhead greater than 50%
benefits from header compression are well known with savings on the order of 55% (AMR 12.2) to 75% (AMR 4.7).
Total bytes 4
# of Bytes 14 8 20 8 7 1 1 12-32 2 4
L1 HDR L2 HDR IP HDR UDP HDR FP HDR MAC HDR RLC HDR AMR CODEC FP CRC FCS
COMP HDR
# of Bytes 1-3
50 23-43
COMP PAYLOAD
variable
Overhead: Iub Data
Comtech EF Data Confidential 10
• Data (3G) consists of multiplexed traffic from multiple
users segmented into 40/80 bytes slices every
2msec.
• Iub data average overhead is in the range of 27%.
Typical benefit of Header and payload compression can deliver 30%
savings.
Total bytes 4
# of Bytes 14 8 20 8 7 1 1 12-1600 2 4
L1 HDR L2 HDR IP HDR UDP HDR FP HDR MAC HDR RLC HDR DATA (3G) FP CRC FCS
COMP HDR
# of Bytes 1-3
50 23-1600
COMP PAYLOAD
variable
Why can’t we optimize 3G
performance?• PDU are segments/slices of traffic from End User
equipment which are multiplexed together at the RNC
to fill a 2msec burst time at the NodeB.
11tr
FP
MU
X
User traffic is segmented into 40 and 80 bytes
PDU at the RNC.
The RNC multiplexes up to 21 or 42 PDU into a
single FP mux equivalent to 2msec radio burst.
Do we need Jumbo frames?
• 3 types of HSDPA codes per cell are defined which also defines
the type and size of PDU and FP frames.
• HSDPA can support 5, 10, and 15 codes per cell across 3 cells.
** requires Jumbo frame support
* average Iub data overhead 1.27
12
Codes/
cell
PDU
(bytes)
PDU/
FP
FP MTU
(bytes)
PPS/
cell/
BW/ cell
(Mbps)
Iub BW/ cell
(Mbps)
5 40 21 840* 500 3.4Mbps 4.3Mbps
10 80 21 1680** 500 6.8Mbps 8.5Mbps
15 80 42 3360** 500 13.6Mbps 17.1Mbps
5
5
5
10
10
10
15
15
15
High availability and QOS
• QOS and two way AUPC/ACM required to maintain
highest site availability.
13
> 17 dB Fade
(VSAT BW
reduced
~80%)
Conclusion on 3G
• Need to maintain highest level of KPI by minimizing
delay and jitter
• Support for different MNO backhaul preferences - L2
(VLAN/MPLS) and/or L3 IP processing
• Need to support high pps rate, provide effective
3GPP compliant QOS and high availability
mechanisms to ensure RIGHT traffic is prioritized and
delivered.
14
Introduction to LTE
performance
(and what it means for end users throughput.)
15
LTE rollout
16
• Most commercial rollout started with Cat 3 or 4
networks supporting 100/150Mbps over 20Mhz
spectrum.
• Carrier Aggregation evolved to raise capacities.
• In most Urban areas, 2/3/4CA are prevalent while the
race is on for 1G using either 100Mhz spectrum or
4CA with 4x4 MIMO (and newer 256QAM MCS)
Definitions and speed?
• What does a 20Mhz 2X2 MIMO (referred to as 150Mbps link)
actually mean?
– 20Mhz – 10% guard band = 18Mhz
– LTE subcarrier are 15khz (18Mhz/15khz=1200 subcarriers)
– 12 subcarriers are combined into a Resource block (1200/12 =
100RB which is also equivalent to 12X15khz=180khz).
– Time domain slots is 0.5msecs
– There are 7 OFDM symbols in normal case.
– Finally, Resource Element (RE) is smallest element and defined the how many modulated symbols can be processed in 1msec:
▪ 1200 subcarrier X 7 OFDM symbols X 2 Time slots = 16800 REs
17
Actual speed…
– With 16800 RE and LTE 64QAM modulation we get :
▪ 16800 x 6 bits/hz = 100.8Mbps
– 2 X 2 MIMO implies 2 outbounds so:
▪ 2 x 100.8Mbps = 201.6Mbps
– Overhead and additional elements reduce BW by 25%.
▪ 201.6Mbps X (1-25%) = 150Mbps
18
• BUT, those are ideal conditions…actual throughput is
determined by RF performance of receiving handset.
How much backhaul is enough?
• Reality check.. 90% of subscribers in
rural are medium to far distance from
tower.
• eNb selects from 28 MCS (Modulation
and Coding Scheme) to find best match
for transmission.
• Assumption for average BW: – 10% close, 60% medium, 30% far -> 50/60Mbps
19
How does CA play into this?
• For rural applications, lower frequency range is best suited for
wide coverage (700/800/900khz).
• Overlays of higher frequency can be added to provide “boost”
capacity.
20
• Devices which do not support
CA can be pushed onto best
access frequency and operate
in single frequency mode.
• CA supporting devices can
receive load balanced BW from
both carriers.
• Carriers to be aggregated need
not be same size (10+10,
10+20, 20+20+10 etc)
CA allows for exciting deployment options!
• CA two way communications
• CA with supplemental downlink
21
So where are we now?
22
5G?
LTE capacity conclusions
• LTE backhaul capacity needs are regularly over-
stated
• Reported capacity is fixed per site and only
determined by base station technology… need to
work through the information to determine the
backhaul requirement.
• When it comes to rural, extended range (low
frequency) is best way to monetize the investment.
23
Optimizing LTE for
Quality of Experience
24
LTE Network Topology
25
Key backhaul interface is S1
interface between the Serving
GW and the eNb.
Main advantage of LTE eNb vs 3G RNC/NodeB is the unification of the radio
resource and packet management into the eNb.
26
Ue HTTP
Ue TCP
Ue IP
GTP
UDP
IP
L2
L1
HTTP
TCP
IP
Ue HTTP
Ue TCP
Ue IP
GTP
UDP
IP
L2
L1
S1
PDCP
RLC
MAC
L1
PDCP
RLC
MAC
L1
HTTP
TCP
IP
SGW/PGW (4G)) InterneteNb (4G)Ue)
TCP Session#1
LTE Traffic encapsulation
• LTE traffic between SGW/PGW and the eNb is
encapsulated across GPRS Tunneling Protocol.
• Opening up the GTP tunnel allows for vendors to
provide optimization solutions across actual Ue traffic
Why optimize LTE protocol?
• High bandwidth = better Quality of Experience (QoE)
• Contributors to poor QOE:
– Web sites complexity has grown: 4 yrs ago average website
size was 750kB and consisted of 20-30 objects. Today, average website in 2MB+ and consist of 200+ objects across dozens of
domain/hosts.
– Problem 1: DNS lookups must be performed to identify hosts server addresses on the internet before object DL can commence.
Over terrestrial links DNS lookups account for roughly 1/3 the time
to DL the site.
– Problem 2: Typical browsers can open 6 simultaneous TCP sessions per domain. If there are dozens of objects to DL from a
particular domain, those are managed sequentially.
27
Contributors to poor QOE
– Problem 3: TCP “Slow Start mechanism” highly sensitive to network delay
(greater the delay, the longer it takes TCP session to ramp up). More than
80% of web downloads are small files (<100kbytes) which means TCP
seldom reach full speed and most transfers are in “Slow Start”.
– Problem 4: Autoplay media downloads and buffers traffic slowing down
other object downloads.
– Problem 5: Encryption. Encryption. Encryption.
28
0
10000
20000
30000
40000
50000
600 1200 1800 2400 3000 3600 4200 4800
Byte
s
msec
100kB transfer over VSAT
Understanding Internet Traffic
• Sandvine predicts that “by the end of 2017… Internet traffic that
is more 75 to 80% encrypted in most markets. “
• It is expected that Internet encryption levels will stabilize at
roughly 90% within the next 2 yrs.
29
Internet Traffic (2015)
Encrypted Not Encrypted
Internet Traffic (2016)
Encrypted Not Encrypted
Internet Traffic (2017)
Encrypted Not Encrypted
LTE Optimization solutions
LTE optimization objectives:– Provide mobile users a better internet/broadband experience
though faster reaction time and DL speeds.
– More efficient backhaul bandwidth utilization (backhaul link is fuller
.. Longer)
– More efficient remote site radio management since DL are faster
thereby allowing radio resources to be re-allocated more often.
– Local acknowledgements at the remote so re-transmissions are managed locally (no end to end retransmissions across satellite).
– Optimization solution to scale to meet widest range of support LTE
capability deployments (integrated solution vs external appliance).
– Critical -> transparency to ensure accurate Bytes IN vs Bytes OUT
for billing purposes
30
Optimization: as fully perfect, functional, or effective as possible
Improve Mobile User Experience
• Over traditional IP networks (such as ISP or enterprise
networks), TCP acceleration has been used to mitigate and
resolve those performance limitations to improve Internet user
experience.
– TCP acceleration provides breaking of long end-to-end 3WHS
control loops to several smaller control loops by intercepting and
relaying TCP connections within the network
31
@
No TCP Acceleration –long end-to-end 3WHS (SYN,
SYN-ACK, ACK) and “slow start” for TCP ramp up.
VSAT
With TCP Acceleration – local 3WHS and local ACKs
mitigates the “slow start” for TCP.
Local TCP session Local TCP sessionPacket secure “relay”
TCP Acceleration benefit
• Faster throughput ramp up
• Higher throughput
• Faster packet loss recovery .. important in the case of
supporting LTE over Ka band.
32
DNS Caching
• DNS Caching is often performed in ISP environment to
“speed up” host address resolution over VSAT.
– Example: Modern websites such as CNN require 70+ DNS
inquiries, DNS inquires take 1/3rd of the time to DL a site and so
DNS caching significantly improves website QOE (see cnn-with-
dns-caching video)
• LTE optimization should provide DNS Caching to
eliminate long VSAT delays in Host name resolution
WHILE preserving and respecting BYTE counts for
billing.
33
What about overhead?
• LTE is very efficient at the radio level BUT it comes with significant
overhead. Considering L2 transport, each GTP packet has 94bytes
of overhead.
• Internet packet distribution: 55% < 100, 15% < 1200, 35% >1200
bytes, LTE overhead would average 12%.
– Example:
▪ TCP ACK is 4bytes but requires 98byte across LTE (20x overhead to payload ratio)
▪ TCP average packet size of 700bytes + 94bytes overhead = 12% overhead!!
34
EPC/LTE overhead (94 bytes per user TCP payload)MAC = 14 bytes, VLAN = 4 bytes, IP = 20 bytes, UDP = 8 bytes, GTP = 8 bytes, Ue IP = 20 bytes, Ue TCP = 20 bytes
Effectiveness of LTE Protocol
Optimization
Technique Technology Benefit
BW saving
optimizations
Image resizing, object caching, byte
caching
Data traffic savings: ???:
too much encryption).
Voice traffic: 50% or more
TCP Acceleration: Optimizes the TCP protocol across
VSAT eliminating the speed barrier of
modern OS.
Good (standard SCPC is
good for large transfers but
not as effective for small
transfers).
DNS Caching provides local DNS cache lookup to
eliminate long VSAT delays in Host
name resolution.
HIGH (speeds up time to
first byte and total DL time)
Web evolution (http2
and/or CEFD
Turbostreaming)
efficient multiplexing of single domain
objects into persistent high bandwidth
TCP connection
HIGH (multiplexing allows
small and large object
multiplexing into same TCP
flows allowing higher BW
and efficiency)
35
What about the modem side?
• Pt2MPt is more suited to LTE than Pt2Pt.
• High throughput LTE needs to be supported by high PPS
modem with high peak DL (100s of Mbps) and UL
(dozens of Mbps) traffic rates support.
• As higher BW tend toward Ka/Ku, dynamic two way BW
management and 3GPP compliant QOS is required to
maintain high availability and KPIs.
36
LTE Conclusion
• Performance optimized LTE over VSAT – Available,
proven, deployed with major operators worldwide.
• Traditional deployment options:
– Rural Macro cells: combine LTE with existing 2G/3G to provide
highest consumer coverage options.
– Rural Macro cells and small cells: exciting deployment options
using CA concepts.
• New markets:
– Small cells: fill “blank” spots in network coverage.
– Metro-edge market: provide highspeed LTE overlay capacity to
existing terrestrial backhaul.
37
Comtech EF Data
2114 West 7th Street
Tempe, AZ 85281
USA
Tel +1.480.333.2200
FAX +1.480.333.2540
sales@comtechefdata.com
www.comtechefdata.com
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