Week 8 multimedia 2 wireless 1
Advanced Network Technologies
Multimedia 2/2
School of Computer Science
Dr. Wei Bao | Lecturer
SIP: Session Initiation Protocol [RFC 3261]
long-term vision:
› all telephone calls, video conference calls take place over Internet
› people identified by names or e-mail addresses, rather than by
phone numbers
› can reach callee (if callee so desires), no matter where callee
roams, no matter what IP device callee is currently using
SIP services
› SIP provides
mechanisms for call
setup:
– for caller to let callee
know she wants to
establish a call
– so caller, callee can
agree on media type,
encoding
– to end call
› determine current IP
address of callee:
– maps mnemonic identifier
to current IP address
› call management:
– add new media streams
during call
– change encoding during
call
– invite others
– transfer, hold calls
› Alice’s SIP invite message
indicates her port number, IP
address, encoding she prefers
to receive (PCM µlaw)
› Bob’s 200 OK message
indicates his port number, IP
address, preferred encoding
(GSM)
› SIP messages can be sent
over TCP or UDP; here sent
over RTP/UDP
› Default SIP port # is 5060
› Actually, Bob and Alice talks
simultaneoulsy
› SIP is out-of-bandtime time
Bob’s
terminal rings
Alice
167.180.112.24
Bob
193.64.210.89
port 5060
port 38060
µ Law audio
GSM
port 48753
INVITE .210.89c=IN IP4 167.180.112.24m=audio 38060 RTP/AVP 0
port 5060
200 OK
c=IN IP4 193.64.210
.89
m=audio 48753 RTP
/AVP 3
ACK
port 5060
Example: setting up call to known IP address
Setting up a call (cont’d)
› codec negotiation:
– suppose Bob doesn’t have
PCM µlaw encoder
– Bob will instead reply with
606 Not Acceptable Reply,
listing his encoders. Alice
can then send new
INVITE message,
advertising different
encoder
› rejecting a call
– Bob can reject with
replies “busy,” “gone,”
“payment required,”
“forbidden”
› media can be sent
over RTP or some
other protocol
Name translation, user location
› caller wants to call callee,
but only has callee’s name
or e-mail address.
› need to get IP address of
callee’s current host:
– user moves around
– Dynamic Host Configuration
Protocol (DHCP)
(dynamically assign IP
address)
– user has different IP devices
(PC, smartphone, car device)
› result can be based on:
– time of day (work, home)
– caller (don’t want boss to call
you at home)
– status of callee (calls sent to
voicemail when callee is
already talking to someone)
SIP registrar
REGISTER sip:domain.com SIP/2.0
Via: SIP/2.0/UDP 193.64.210.89
From: sip:
To: sip:
Expires: 3600
v one function of SIP server: registrar
v when Bob starts SIP client, client sends SIP
REGISTER message to Bob’s registrar server
register message:
SIP proxy
› another function of SIP server: proxy
› Alice sends invite message to her proxy server
– contains address sip:
– proxy responsible for routing SIP messages to callee, possibly through
multiple proxies
› Bob sends response back through same set of SIP proxies
› proxy returns Bob’s SIP response message to Alice
– contains Bob’s IP address
› SIP proxy analogous to local DNS server
1
1. Alice sends INVITE
message to UMass
SIP proxy.
2. UMass proxy forwards request
to Poly registrar server
2 3. Poly server returns redirect response,
indicating that it should try
3
5. eurecom
registrar
forwards INVITE
to 197.87.54.21,
which is running
Bob’s SIP client
5
4
4. Umass proxy forwards request
to Eurecom registrar server
8
6
7
6-8. SIP response returned to
Alice
9
9. Data flows between clients
UMass
SIP proxy
Poly SIP
registrar
Eurecom SIP
registrar
Bob
197.87.54.21
Alice
128.119.40.186
SIP example: calls
Network support for Multimedia
Network support for multimedia
Approach Granularity Guarantee Mechanisms Complex Deployed?
1. Making best
of best effort
service
All traffic
treated
equally
None No network
support(all at
app)
low everywhere
2. Differentiated
service
Traffic class None or soft Packet mark,
scheduling,
policing
medium some
3. Per-
connection
QoS
Per-
connection
flow
Soft or hard
after flow
admitted
Packet mark,
scheduling
policing
high Little to none
Three broad approaches towards providing network-level support for multimedia apps
Providing multiple classes of services
› thus far: making the best of best effort service
– one-size fits all service model
› alternative: multiple classes of service
– partition traffic into classes
– network treats different classes of traffic differently (analogy: VIP service
versus regular service)
0111
› granularity: differential
service among multiple
classes, not among
individual connections
› How: ToS bits
R1 R2
H1
H2
H3
H4
1.5 Mbps linkR1 output
interface
queue
Multiple classes of services: scenarios
Scenario 1: mixed HTTP and VoIP
› example: 1Mbps VoIP (Video and Voice), HTTP share 1.5 Mbps link.
– HTTP bursts can congest router, cause video/audio loss
– want to give priority to audio over HTTP
packet marking needed for router to distinguish
between different classes; and new router policy to
treat packets accordingly
Principle 1
R1 R2
Principles for QOS guarantees
› what if applications misbehave (VoIP sends higher than declared rate)
– policing: force source adherence to bandwidth allocations
› marking, policing
provide protection for one class from others
Principle 2
R1 R2
1.5 Mbps link
1 Mbps
phone
packet marking and policing
Principles for QOS guarantees (con’t)
› allocating fixed (non-sharable) bandwidth to flow: inefficient use of
bandwidth if flows doesn’t use its allocation
while providing protection, it is desirable to use
resources as efficiently as possible
Principle 3
R1
R2
1.5 Mbps link
1 Mbps
phone
1 Mbps logical link
0.5 Mbps logical link
Scheduling and policing mechanisms
› scheduling: choose next packet to send on link
› FIFO (first in first out) scheduling: send in order of arrival to queue
– real-world example?
– discard policy: if packet arrives to full queue: who to discard?
– tail drop: drop arriving packet
– priority: drop/remove on priority basis
– random: drop/remove randomly
queue
(waiting area)
packet
arrivals
packet
departureslink
(server)
Scheduling policies: priority
priority scheduling: send
highest priority queued packet
non-preemptive
› multiple classes, with different
priorities
– class may depend on marking
or other header info, e.g. IP
source/dest, port numbers, etc.
– real world example?
high priority queue
(waiting area)
low priority queue
(waiting area)
arrivals
classify
departures
link
(server)
1 3 2 4 5
5
5
2
2
1
1
3
3 4
4
arrivals
departures
packet
in
service
Scheduling policies: priority
low priority queue
(waiting area)
arrivals
classify
departures
link
(server)
Scheduling policies: priority
low priority queue
(waiting area)
arrivals
classify
departures
link
(server)
Scheduling policies: priority
low priority queue
(waiting area)
arrivals
classify
departures
link
(server)
Scheduling policies (con’t)
Round Robin (RR) scheduling:
› multiple classes, with equal priority
› cyclically scan class queues, sending one complete packet from
each class (if available)
1 23 4 5
5
5
2
3
1
1
3
3 4
4
arrivals
departures
packet
in
service
Scheduling policies: RR
low priority queue
(waiting area)
arrivals
classify
departures
link
(server)
Scheduling policies: RR
low priority queue
(waiting area)
arrivals
classify
departures
link
(server)
Scheduling policies: RR
low priority queue
(waiting area)
arrivals
classify
departures
link
(server)
Scheduling policies: RR
low priority queue
(waiting area)
arrivals
classify
departures
link
(server)
Scheduling policies (con’t)
Weighted Fair Queuing (WFQ):
› generalized Round Robin
› each class gets weighted amount of service in each cycle
Scheduling policies (con’t)
Weighted Fair Queuing (WFQ):
› Each class i is assigned a weight wi
› Guarantee: if there are class i packets to send (during some interval) then class i
receives a fraction of service which is
wi / ( ∑wj )
› On a link with transmission rate R, class i achieves throughput
Rwi / ( ∑wj )
› WFQ is part of routers QoS [Cisco 2012]
2
1
3
Scheduling policies (con’t)
Example:
One link has capacity 1 Mbps. Three flows: Flow 1 is
ensured with 0.5 Mbps data rate; Flow 2 is ensured
with 0.25 Mbps; Flow 3 is ensured with 0.25 Mbps.
Weighted queue: w1=2, w2=1, w3=1
Efficiency:
When flow 3 has nothing to transmit, but flow 1 and
flow 2 have many packets to send
Flow 1: 2/3 Mbps
Flow 2: 1/3 Mbps
Marking and Policing
Policing mechanisms
goal: to limit traffic to not exceed declared parameters (the rate at which
a class or flow is allowed to inject packets into the network)
› Three important policing criteria (differing on the time scale):
› 1. (long term) average rate: how many pkts can be sent per unit of time (in
the long run)
– e.g., 6000 packets per min
– 2.peak rate: limit the number of packets can be sent over a
relatively shorter period of time, e.g., 6000 pkts per minute (ppm) in
average but 3000 packets per 5 second peak rate max.
– 3. (max.) burst size: max number of pkts sent “instantaneously” into
the networks, e.g., 1500 packets.
Policing mechanisms: implementation
token bucket: limit input to specified burst size and average rate (useful to police
the flow)
› bucket can hold b tokens
› a packet must remove a token from bucket to be transmitted into the network
› tokens generated at rate r token/sec unless bucket full (token ignored)
› over interval of length t: number of packets admitted less than or equal to (rt + b)
› Token-generation rate r limits the rate at which packets enter the network
t->0, b packets t->∞, (rt+b)/t = r packets/second
Policing and QoS guarantees
› Combining token bucket and WFQ to provide guaranteed upper
bound on delay, i.e., QoS guarantee!
WFQ
token rate, r1
bucket size, b1
per-flow
rate, R
D = Lb1 / (Rw1 / ( ∑wj ))max
arriving
traffic
arriving
traffic
› Packets arrive while the bucket is full (b1). The last packet has a
maximum delay of Dmax. L packet size.
Differentiated services in reality
› want “qualitative” service classes
– relative service distinction: Platinum (VIP), Gold, Silver
› scalability: simple functions in network core, relatively complex
functions at edge routers (or hosts)
Diffserv architecture
edge router:
› per-flow traffic management
› marks packets as differently
› E.g. Alice’ traffic： high
› Bob’s traffic: high
› Chris’s traffic: low
core router:
› per class traffic management
› buffering and scheduling based on
marking at edge
› Red packets vs green packets
r
b
marking
scheduling
…
› class-based marking: packets of different classes marked differently
› intra-class marking: conforming portion of flow marked differently compared with non-conforming one
› Bob agrees to transmit at 1Mbps, but he is transmitting at 2Mbps
› Half of them (conforming) are marked green.
› Others (non-conforming) are marked red (lower priority) or dropped.
› profile: pre-negotiated rate r, burst (bucket) size b
› packet marking at edge based on per-flow profile
Example:
user packets
rate r
b
Edge-router packet marking
› green > yellow >red .
› 2Mbps link, Bob, telephone traffic, declare 1 Mbps
› Green if conforming, red if not conforming
› Chris, web browsing traffic
› Yellow
› Priority queue in the core network
› Bob can guarantee 1Mbps data rate
› If Bob transmits >1Mbps
› If Chris transmits at 1Mbps, all red will be dropped. Bob gets 1Mbps
› If Chris transmits at <1Mbps, some red will still get through.
› Example
Edge-router packet marking
Classification, conditioning
› user declares traffic profile (e.g., rate, burst size)
› traffic metered, shaped if non-conforming
› the meter compares the incoming flow to the negociated traffic
profile. Network administrator can decide whether to remark,
forward, delay, or drop a non- conforming packet
Per-connection QoS guarantees
› basic fact of life: cannot support traffic demands beyond link
capacity
call admission: flow declares its needs, network may
block call (e.g., busy signal) if it cannot meet needs
Principle 4
R1
R2
1.5 Mbps link
1 Mbps
phone
1 Mbps
phone
Reject!
Wireless and mobile networks
Elements of a wireless network
Wireless and Mobile Networks: 7- 41
wired network
infrastructure
Elements of a wireless network
Wireless and Mobile Networks: 7- 42
wired network
infrastructure
wireless hosts
§ laptop, smartphone, IoT
§ run applications
§ may be stationary (non-mobile) or mobile
• wireless does not always mean mobility!
Elements of a wireless network
Wireless and Mobile Networks: 7- 43
wired network
infrastructure
base station
§ typically connected to wired network
§ relay - responsible for sending packets
between wired network and wireless
host(s) in its “area”
• e.g., cell towers, 802.11 access points
Elements of a wireless network
Wireless and Mobile Networks: 7- 44
wired network
infrastructure
wireless link
§ typically used to connect mobile(s) to base
station, also used as backbone link
§ multiple access protocol coordinates link
access
§ various transmission rates and distances,
frequency bands
Characteristics of selected wireless links
Wireless and Mobile Networks: 7- 45
Indoor Outdoor Midrange
outdoor
Long range
outdoor
10-30m 50-200m 200m-4Km 4Km-15Km
2 Mbps
4G LTE
802.11ac
802.11n
802.11g
802.11b
3.5 Gbps
600 Mbps
54 Mbps
11 Mbps
Bluetooth
802.11ax14 Gbps
5G10 Gbps
802.11 af,ah
IEEE 802.11 WiFi
Wireless and Mobile Networks: 7- 46
IEEE 802.11
standard
Year Max data
rate
Range Frequency
802.11b 1999 11 Mbps 30m 2.4 Ghz
802.11a 1999 54 Mbps 30m 5 Ghz
802.11g 2003 54 Mbps 30m 2.4 Ghz
802.11n (WiFi 4) 2009 600 Mbps 70m 2.4, 5 Ghz
802.11ac (WiFi 5) 2013 3.47Gpbs 70m 5 Ghz
802.11ax (WiFi 6) 2020 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
Elements of a wireless network
Wireless and Mobile Networks: 7- 47
wired network
infrastructure
infrastructure mode
§ base station connects mobiles into
wired network
§ handoff: mobile changes base
station providing connection into
wired network
Elements of a wireless network
Wireless and Mobile Networks: 7- 48
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 network taxonomy
Wireless and Mobile Networks: 7- 49
single hop multiple hops
infrastructure
(e.g., APs)
no
infrastructure
host connects to base
station (WiFi, cellular)
which connects to
larger Internet
no base station, no
connection to larger
Internet (Bluetooth, ad
hoc nets)
host may have to relay
through several wireless
nodes to connect to larger
Internet: mesh net
no base station, no connection
to larger Internet. May have to
relay to reach other a given
wireless node MANET, VANET
Wireless link characteristics
Wireless Link Characteristics (1)
important differences from wired link ….
- decreased signal strength: radio signal attenuates as it
propagates through matter (path loss)
- interference from other sources: standardized wireless
network frequencies (e.g., 2.4 GHz) shared by other
devices (e.g., phone);
- multipath propagation: radio signal reflects off objects
ground, arriving at destination at slightly different times
…. make communication across (even a point to point)
wireless link much more “difficult”
dB decibel
› logarithmic unit used to express the ratio of two (power) values
› 10*log10（PS/PN）
› PS/PN=10 10 dB
› PS/PN=100 20 dB
› PS/PN=1000 30 dB
› PS/PN=10000 40 dB
› …
Wireless Link Characteristics (2)
› SNR: signal-to-noise ratio
- larger SNR – easier to extract
signal from noise (a “good thing”)
- BER: bit error rate
› SNR versus BER tradeoffs
- given physical layer modulation:
increase power -> increase SNR ->
decrease BER
– Different physical layer modulation:
10 20 30 40
QAM256 (8 Mbps)
QAM16 (4 Mbps)
BPSK (1 Mbps)
SNR(dB)
B
ER
10-1
10-2
10-3
10-5
10-6
10-7
10-4
Quadrature amplitude modulation
Binary Phase-shift keying
Higher data rate -> Higher BER
Wireless Link Characteristics (2)
› SNR: signal-to-noise ratio
– larger SNR – easier to extract
signal from noise (a “good thing”)
– BER: bit error rate
› SNR versus BER tradeoffs
– given SNR, BER requirement: choose
modulation to achieve highest
throughput
– 15 dB, require 10-3 BER
– Which modulation?
– QAM16
BPSK (1 Mbps)
10 20 30 40
QAM256 (8 Mbps)
QAM16 (4 Mbps)
SNR(dB)
B
ER
10-1
10-2
10-3
10-5
10-6
10-7
10-4
Wireless network characteristics (3)
Multiple wireless senders and receivers create additional
problems (beyond multiple access):
A
B
C
Hidden terminal problem
v B, A hear each other
v B, C hear each other
v A, C can not hear each other
means A, C unaware of their
interference at B
A B C
A’s signal
strength
space
C’s signal
strength
Signal attenuation:
v B, A hear each other
v B, C hear each other
v A, C can not hear each other
interfering at B
CDMA
Code Division Multiple Access (CDMA)
› unique “code” (chipping sequence) assigned to each user;
› all users share same frequency, but each user has own “chipping” sequence
(i.e., code) to encode data
– length of sequence: M
– allows multiple users to “coexist” and transmit simultaneously with minimal
interference (if codes are “orthogonal”)
– orthogonal:
– inner product of ci,1 ci,2 …ci,M and cj,1 cj,2 …cj,M is Sm ci,m.cj,m
– inner product(user i’s chipping sequence, user j’s chipping sequence) =0
– inner product(user i’s chipping sequence, user i’s chipping sequence) =M
› encoded signal = (original data) X (chipping sequence)
› decoding: inner-product of encoded signal and chipping sequence
CDMA encode/decode
slot 1 slot 0
d1 = -1
1 1 1 1
1- 1- 1- 1-
Zi,m= di.cm
d0 = 1
1 1 1 1
1- 1- 1- 1-
1 1 1 1
1- 1- 1- 1-
1 1 11
1-1- 1- 1-
slot 0
channel
output
slot 1
channel
output
channel output Zi,m
sender
code
data
bits
slot 1 slot 0
d1 = -1
d0 = 1
1 1 1 1
1- 1- 1- 1-
1 1 1 1
1- 1- 1- 1-
1 1 1 1
1- 1- 1- 1-
1 1 11
1-1- 1- 1-
slot 0
channel
output
slot 1
channel
outputreceiver
code
received
input
Di = S Zi,m.cmm=1
M
M
di
cm -1 -1 -1 1 -1 1 1 1
-11
-1 -1 -1 1 -1 1 1 1
Zi,m -1 -1 -1 1 -1 1 1 1 1 1 1 -1 1 -1 -1 -1
sender
receiver -1 -1 -1 1 -1 1 1 1 1 1 1 -1 1 -1 -1 -1
Inner product -1 -1 -1 1 -1 1 1 1 -1 -1 -1 1 -1 1 1 1
Di = S Zi,m.cmm=1
M
M
8/8=1 -8/8=-1
Di
1+1+1+1+1+1+1+1
uses its chipping sequence to send and to receive: receive the correct bits
User i receives user i‘s signals
di
cm -1 -1 -1 1 -1 1 1 1
-11
-1 -1 -1 1 -1 1 1 1
Zi,m -1 -1 -1 1 -1 1 1 1 1 1 1 -1 1 -1 -1 -1
sender 1’s
bits
receiver 2 -1 -1 -1 1 -1 1 1 1 1 1 1 -1 1 -1 -1 -1
Inner product 1 1 -1 1 1 1-1 1
Di = S Zi,m.c’mm=1
M
M
0/8=0 0/8=0Di
-1-1+1+1-1+1-1+1=0!
1 1-1 1 1 1 -1 1
Use 1’s chipping sequence to send and use 2’s chipping sequence to receive:
receive nothing!
Reason: 1’s chipping sequence is orthogonal to 2’s chipping sequence.
User 2 receives user 1‘s signals
Sender 1
Sender 2
…
Sender N
1’s chipping
sequence
+
2’s chipping
sequence
N’s chipping
sequence
…
1’s chipping
sequence
inner product (
1’s bit * 1’s chipping sequence
+2’s bit * 2’s chipping sequence
+…
+N’s bit * N’s chipping sequence,
1’s chipping sequence)/M
1’s bit * 1’s chipping sequence
+2’s bit * 2’s chipping sequence
+…
+N’s bit * N’s chipping sequence,
x
x
x
+
1’s chipping
sequence
= 1’s bit * inner product (
1’s chipping sequence,
1’s chipping sequence)/M
+ 2’s bit * inner product (
2’s chipping sequence,
1’s chipping sequence)/M
+…
+ N’s bit * inner product (
N’s chipping sequence,
1’s chipping sequence)/M
0
0
Sender 1
Sender 2
…
Sender N
1’s chipping
sequence
2’s chipping
sequence
N’s chipping
sequence
…
x
x
x
+
1’s chipping
sequence
= 1’s bit * inner product (
1’s chipping sequence,
1’s chipping sequence)/M
=1’s bit
Sender 1
Sender 2
…
Sender N
1’s chipping
sequence
2’s chipping
sequence
N’s chipping
sequence
…
x
x
x
CDMA: two-sender interference
using same code as
sender 1, receiver recovers
sender 1’s original data
from summed channel
data!
Sender 1
Sender 2
channel sums together
transmissions by sender 1
and 2