Transcript Review, GSM Numbers, cont…

Southern Methodist University Fall 2003
EETS 8316/NTU CC745-N
Wireless Networks
Lecture 5: CDMA, Mobile Data
Instructor: Jila Seraj
email: [email protected]
http://www.engr.smu.edu/~jseraj/
tel: 214-505-6303
EETS 8316/NTU TC 745, Fall 2003
SMU
ENGINEERING
#1
Session Outline
Review of the last week
CDMA essentials
Primer to performance metric
Primer to switching systems
Midterm exam, Oct 26, One hour at the end
of the class. Covers first 6 sessions
EETS 8316/NTU TC 745, Fall 2003
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#2
Review, GSM General Architecture
PSTN
VLR
GSM Public
land mobile
network
(PLMN)
MSC
HLR
OMC
AUC
A
EIR
Abis
BSC
BTS
BSS
BSS
ADC
BTS
OSS
Um
MT
TE
MS
EETS 8316/NTU TC 745, Fall 2003
NMC
OSS: operation subsystem
BSS: base station subsystem
MS: mobile station
MS
SMU
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#3
Review, GSM Logical and Physical Channels
Um interface: various logical channels are
mapped to physical channels
A physical channel is a timeslot with
timeslot number in a sequence of TDMA
frames
8 physical channels mapped onto 8
timeslots within TDMA frame per frequency
carrier
EETS 8316/NTU TC 745, Fall 2003
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#4
Review, GSM Physical Channels
TDMA frame = 4.615 ms
Timeslot 1
2
3
4
5
6
7
8
Frequency 1
Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8
Frequency 2
Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8
:
:
:
:
Frequency 124
Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8
EETS 8316/NTU TC 745, Fall 2003
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#5
Review, GSM Logical Channel Structure
TCH/F
TCH/H
BCH
FCCH SCH
CBCH
CCH
TCH
CCCH
BCCH
DCCH
PCH AGCH RACH
SACCH
EETS 8316/NTU TC 745, Fall 2003
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ACCH
SDCCH
FACCH
#6
Review, OSI Model for SS7
Layer 4-7
MUP
TCAP
ISUP
MAP
INAP
OMAP
SCCP
Layer 3
Layer 1-2
MTP
Signaling link function, Signaling link physical requirement
EETS 8316/NTU TC 745, Fall 2003
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#7
Review, GSM Interfaces, cont..
Air Interface
Um
Abis
A
CM
CM
MM
MM
LAPD
RF
RRM
RRM
RRM
LAPD LAPD
RF
EETS 8316/NTU TC 745, Fall 2003
RF
SCCP
SCCP
LAPD LAPD
LAPD
RF
SMU
RRM
ENGINEERING
RF
RF
#8
Review, GSM Protocol Layers
RF : Physical Layer
LAPD: Link Layer, ISDN protocol based
SCCP: Signal Connection Control Layer,
part of link layer
RR: Radio Resource
MM: Mobility Management
CC: Call Control
EETS 8316/NTU TC 745, Fall 2003
SMU
ENGINEERING
#9
Review, GSM Interfaces
VLR
Switching
System
AUC
MAP
VLR
MAP HLR
MAP
MSC
BSSAP
EETS 8316/NTU TC 745, Fall 2003
EIR
MAP
Base Station
Subsystem
BSS
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#10
Review, GSM Interfaces, cont…
Switching
System
BSSAP
BSC
LAPD
Base Station Subsystem
BSS
BTS
MS
EETS 8316/NTU TC 745, Fall 2003
SMU
ENGINEERING
#11
Review, GSM Numbers
International mobile station equipment
identity (IMEI). IMEI= TAC + FAC + SNR + SP
— TAC = Type Approval Code, 6 decimals
— FAC = Final Assembly Code, 6 decimals, assigned
by manufacturer
— SNR = Serial Number, 6 decimals, assigned by
manufacturer
— SP = Spare, 1 decimal place
EIR has while, black and optionally grey
list.
EETS 8316/NTU TC 745, Fall 2003
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ENGINEERING
#12
Review, GSM Numbers
International mobile station equipment
identity (IMEI). IMEI= TAC + FAC + SNR + SP
— TAC = Type Approval Code, 6 decimals
— FAC = Final Assembly Code, 6 decimals,
assigned by manufacturer
— SNR = Serial Number, 6 decimals, assigned by
manufacturer
— SP = Spare, 1 decimal place
EIR has while, black and optionally grey list
EETS 8316/NTU TC 745, Fall 2003
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#13
Review, GSM Numbers, cont…
International mobile Subscriber Identity
(IMSI). Stored on the SIM (Subscriber
Identity Module) card. IMSI is obtained at
the time of subscription. IMSI is not made
public.
IMSI = MCC + MNC + MSIN
MCC = Mobile Country Code, 3 decimals
MNC = Mobile Network Code, 2 decimals
EETS 8316/NTU TC 745, Fall 2003
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#14
Review, GSM Numbers, cont…
MSIN = Mobile Subscriber Identification
Number, maximum 10 decimal digits
Mobile Station ISDN number (MSISDN), is
the real phone number of the subscriber.
Stored in HLR and on SIM card
MSISDN = CC + NDC + SN
CC = Country Code, up to 3 decimals
EETS 8316/NTU TC 745, Fall 2003
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#15
Review, GSM Numbers, cont…
NDC = National Destination Code, typically
2-3 decimals
SN = Subscriber Number, maximum 10
decimals.
Mobile Station Roaming Number (MSRN),
same format as MSISDN. A temporary
location dependent ISDN number.
Is assigned in two cases, at registration or
at call set up.
EETS 8316/NTU TC 745, Fall 2003
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#16
Review, GSM Numbers, cont…
Location Area Identity (LAI). Regularly sent
on BCCH LAI = CC + MNC + LAC,
LAC = Location Area Code, max 5 decimals
(<FFFFhex).
Temporary Mobile Subscriber Identity
(TMSI). Stored only in the VLR and SIM
card. Consists of 4*8 bits excluding value
FFFF FFFFhex
EETS 8316/NTU TC 745, Fall 2003
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#17
Review, GSM Numbers, cont…
TMSI has only local meaning and can be
defines according to operator’s
specifications.
LAI + TMSI uniquely identifies the user, I.e.
IMSI is no longer needed for ongoing
communication
EETS 8316/NTU TC 745, Fall 2003
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#18
Review, GSM Numbers, cont..
Local Mobile Subscriber Identity (LMSI).
Created in VLR and stored in HLR.
Like TMSI is operator defined.
Used in communication with VLR to speed
the search for mobile records.
Speed is essential to achieve short call
setup times.
EETS 8316/NTU TC 745, Fall 2003
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#19
Review, GSM Numbers, cont…
Global Cell Id = LAI + CI
CI = Cell id, unique id within the LAI.
Maximum 2*8 bits
Base Transceiver Station Identity Code
(BSIC) = NCC + BCC
EETS 8316/NTU TC 745, Fall 2003
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#20
GSM Numbers, cont…
BSIC is broadcast periodically by the base
station on the synchronization channel.
NCC = Network Color Code, 3 bits
BCC = Base Station Color Code, 3 bits
EETS 8316/NTU TC 745, Fall 2003
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#21
Review, GSM Roaming From Another PLMN
VLR registers users roaming in its area
—Recognizes mobile station is from another
PLMN
—If roaming is allowed, VLR finds the mobile’s
HLR in its home PLMN
—VLR constructs a global title from IMSI to
allow signaling from VLR to mobile’s HLR
via public telephone network
EETS 8316/NTU TC 745, Fall 2003
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#22
Review, GSM Roaming, cont...
VLR registers users roaming in its area
—VLR generates a mobile subscriber roaming
number (MSRN) used to route incoming
calls to mobile station
—MSRN is sent to mobile’s HLR
EETS 8316/NTU TC 745, Fall 2003
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#23
Review, GSM Roaming, cont…
VLR contains
—MSRN
—TMSI
—Location area where mobile station has
registered
—Info for supplementary services (if any)
—IMSI
—HLR or global title
—Local identity for mobile station (if any)
EETS 8316/NTU TC 745, Fall 2003
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#24
Review, GSM Security
3 security problems: unauthorized access,
privacy from eavesdropping, protection of
subscriber identity/location
Unauthorized (fraudulent) access
—GSM handsets must be presented with a
subscriber identity module (SIM)
—SIM must be validated with personal
identification number (PIN)
EETS 8316/NTU TC 745, Fall 2003
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#25
Review, GSM Security, cont…
Unauthorized (fraudulent) access
—SIM also stores subscriber authentication
key, authentication algorithm, cipher key
generation algorithm, encryption algorithm
—During registration (when roaming), mobile
station receives “challenge” and uses
authentication key and authentication
algorithm to generate “challenge response”
to verify user’s identity
EETS 8316/NTU TC 745, Fall 2003
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#26
Review, GSM Security, cont…
Privacy from eavesdropping
—Temporary encryption key is used for
privacy of data, signaling, and voice
—Info is encrypted before transmission
EETS 8316/NTU TC 745, Fall 2003
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#27
Review, GSM Security, cont…
Anonymity of users
—Supported by temporary mobile subscriber
ID (TMSI)
—When registered, mobile station sends
globally-unique international mobile
subscriber ID (IMSI) to network
—Network assigns TMSI for use during call IMSI is not sent over radio link
EETS 8316/NTU TC 745, Fall 2003
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#28
Review, GSM Security, cont…
Anonymity of users
—Only network and mobile station know true
identity
—New TMSI is assigned when roam into new
area
EETS 8316/NTU TC 745, Fall 2003
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#29
Review, GSM Security, cont..
Fetched triplets are stored in VLR
— Every call uses up one triplet (discarded)
— Another set must be fetched when exhausted
Visited system
IMSI/TMSI
+ LAI
Registration request
IMSI/TMSI identifies user,
LAI points to old VLR,
requests data to
authenticate user
Subscriber data
Old VLR
EETS 8316/NTU TC 745, Fall 2003
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#30
Review, GSM Security, cont..
Visited system
Calculates
response
by authentication
algorithm
Requests triplets
from home system,
chooses a triplet
Challenge
Challenge response
New TMSI
Compares to stored
response in triplet,
registration successful
if matches
Assigns new TMSI
Acknowledge
EETS 8316/NTU TC 745, Fall 2003
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#31
Review, GSM Security, cont..
Visited system
Location update
HLR
Acknowledge
Registration
cancel
Old VLR
EETS 8316/NTU TC 745, Fall 2003
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#32
Review, GSM Handoffs
3 types of handoffs
—Intra-BSS: if old and new BTSs are attached
to same base station
• MSC is not involved
—Intra-MSC: if old and new BTSs are
attached to different base stations but within
same MSC
—Inter-MSC: if MSCs are changed
EETS 8316/NTU TC 745, Fall 2003
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#33
Review, GSM Intra-MSC Handoff
Mobile station monitors signal quality and
determines handoff is required, sends signal
measurements to serving BSS
Serving BSS sends handoff request to MSC
with ranked list of qualified target BSSs
MSC determines that best candidate BSS is
under its control (assumed here)
MSC reserves a trunk to target BSS
EETS 8316/NTU TC 745, Fall 2003
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#34
Review, GSM Intra-MSC Handoff, cont..
Target BSS selects and reserves radio
channels for new connection, sends Ack to
MSC
MSC notifies serving BSS to begin handoff,
including new radio channel assignment
Serving BSS forwards new radio channel
assignment to mobile station
Mobile station re-tunes to new radio channel,
notifies target BSS on new channel
EETS 8316/NTU TC 745, Fall 2003
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ENGINEERING
#35
Review, GSM Intra-MSC Handoff, cont..
Target BSS notifies MSC that handoff is
detected
Target BSS and mobile station exchange
messages to synchronize transmission in
proper timeslot
MSC switches voice connection to target BSS,
which responds when handoff is complete
MSC notifies serving BSS to release old radio
traffic channel
EETS 8316/NTU TC 745, Fall 2003
SMU
ENGINEERING
#36
Review, GSM Inter-MSC Handoff
Mobile station monitors signal quality and
determines handoff is required, sends signal
measurements to serving BSS
Serving BSS sends handoff request to MSC
with ranked list of qualified target BSSs
Serving MSC determines that best candidate
BSS is under control of a target MSC
(assumed here) and calls target MSC through
PSTN
EETS 8316/NTU TC 745, Fall 2003
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#37
Review, GSM Inter-MSC Handoff, cont..
Target MSC notifies its VLR to assign a TMSI
Target VLR returns TMSI
Target MSC reserves a trunk to target BSS
Target BSS selects and reserves radio
channels for new connection, sends Ack to
target MSC
Target MSC notifies serving MSC that it is
ready for handoff
EETS 8316/NTU TC 745, Fall 2003
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ENGINEERING
#38
Review, GSM Inter-MSC Handoff, cont..
Serving MSC notifies serving BSS to begin
handoff, including new radio channel
assignment
Serving BSS forwards new radio channel
assignment to mobile station
Mobile station re-tunes to new radio channel,
notifies target BSS on new channel
Target BSS notifies target MSC that handoff is
detected
EETS 8316/NTU TC 745, Fall 2003
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ENGINEERING
#39
Review, GSM Inter-MSC Handoff, cont..
Target BSS and mobile station exchange
messages to synchronize transmission in
proper timeslot
Voice connection is switched to target BSS,
which responds when handoff is complete
Target MSC notifies serving MSC
Old network resources are released
EETS 8316/NTU TC 745, Fall 2003
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#40
IS-95 CDMA
Digital AMPS increased capacity of AMPS
by factor 3
First code division multiple access (CDMA)
cellular system was developed 1990,
claimed to increase capacity by factor 20
EETS 8316/NTU TC 745, Fall 2003
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#41
IS-95 CDMA - Radio Aspects
Spread spectrum techniques adapted from
military (used since 1950)
—Narrowband signal is multiplied by very
large bandwidth signal (spreading signal)
—All users, each with own pseudorandom
codeword approximately orthogonal to all
other codewords, can transmit
simultaneously with same carrier frequency
EETS 8316/NTU TC 745, Fall 2003
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#42
IS-95 CDMA - Radio Aspects (cont)
—Receiver performs a time correlation
operation to detect only desired codeword
—All other codewords appear as noise due to
decorrelation
—Receiver needs to know only codeword
used by transmitter
—In other words, users are separated by their
codes rather than frequency and time slot
EETS 8316/NTU TC 745, Fall 2003
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#43
IS-95 CDMA Interesting Features
Multiple users can share same frequency
Soft capacity limit: more users raises noise
floor linearly, no absolute limit on number of
users - performance degrades gradually for all
users
Multipath fading is reduced by signal spreading
EETS 8316/NTU TC 745, Fall 2003
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#44
IS-95 CDMA Interesting Features (cont)
Spatial diversity provides soft handoff: MSC
monitors signal of a user from multiple base
stations and chooses best version of signal at
any time
Self-jamming is a problem: because spreading
sequences of different users are not exactly
orthogonal
—When despreading, other users can
contribute significantly to receiver decision
statistic
EETS 8316/NTU TC 745, Fall 2003
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#45
IS-95 CDMA Interesting Features (cont)
Near-far problem: if power of multiple users are
unequal, strongest received mobile signal will
capture demodulator at base station
—Base stations must implement power control
to ensure that each mobile within coverage
area provides same signal level to base
station receiver
CDMA is dual mode like TDMA.
EETS 8316/NTU TC 745, Fall 2003
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#46
IS-95 CDMA Interesting Features (cont)
The system can move a call from digital to
analog when the call enters the coverage area
of a cell that does not have CDMA capability.
The opposite does not work.
EETS 8316/NTU TC 745, Fall 2003
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#47
IS-95 CDMA Channels
Types of channels
Forward channels
Pilot
Synchronization
Paging
Traffic
Reverse channels
Application
System mon.
Sync.
Signaling
Voice/data
Access
Signaling
Traffic
Voice/data
EETS 8316/NTU TC 745, Fall 2003
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#48
IS-95 CDMA Channels (cont)
Traffic channel on the forward direction has
three components
— user data
— power control (puncturing convolutional code)
— signaling message
Traffic channel on the reverse direction has
two components
— user data
— signaling message
EETS 8316/NTU TC 745, Fall 2003
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#49
Handoff in CDMA
Two types of handoffs
—hard handoff
—Soft handoff
Hard handoff is needed when the call is
moved from one frequency to another and
when the mobile moves the coverage area
of another MSC
EETS 8316/NTU TC 745, Fall 2003
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#50
Soft handoff
Two base stations receive signals from the
mobile. The signals are sent to the MSC that
decides which one has lowest bit error rate.
Vocoder in CDMA is in the switch.
Mobile receives signals from two base
stations and combine them before
decoding. Uses rake receiver. Each tunes to
one base station.
EETS 8316/NTU TC 745, Fall 2003
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#51
Soft handoff (cont)
This requires synchronization of the base
stations. All base stations are equipped
with GPS and receive information from it,
including lat.., long and time.
It also requires that the mobile dedicates
one correlator for searching other pilot
channels.
EETS 8316/NTU TC 745, Fall 2003
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#52
Soft handoff (cont)
Mobile
Current
BS
Conversation
MSC
Candidate
BS
Neighbor pilot
can be a candidate
Measure the strength of pilot
New Active Set, handoff direction
Conversation
Measurements
Conversation
Measurements
Handoff
Handoff
Conversation
EETS 8316/NTU TC 745, Fall 2003
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#53
Mobility Management in CDMA
Five type of registration
—Periodic
—Power up
—Power down
—Zone change
—Distance. When the distance between the
current base station and the previously
registered base station exceeds a certain
limit.
EETS 8316/NTU TC 745, Fall 2003
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#54
Performance Metrics
Performance metrics are defined to
measure the behavior of network
objectively
Availability
Retainability
Integrity
Delays: Dial tone delay, post dialing delay,
through connection delay
EETS 8316/NTU TC 745, Fall 2003
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#55
Performance Metrics, cont…
Two types of performance metrics
―Customer perceived. This type is what a
customer notices, such as connection
delays, voice quality, etc
—Operator Defined. This type is not directly
noticed by the customer, such as congestion
on trunks. A call can encounter congestion
and re-routed via another trunk. Not visible
to customer but provide important
information to the operator.
EETS 8316/NTU TC 745, Fall 2003
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#56
Performance Metrics, cont…
Specific metrics defined for different
signaling systems and nodes
Standards and reference models are
defined
Mostly on the wire line side, government
control
EETS 8316/NTU TC 745, Fall 2003
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#57
Performance Metrics, cont…
One of the challenges of a network
performance is to predict the capacity of
the system (also called dimensioning
resources)
—Erlang is the unit used when dealing with
traffic. One Erlang is one call held for one
hour.
EETS 8316/NTU TC 745, Fall 2003
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#58
Performance Metrics, cont…
—Erlang-B formula provided blocking
probability, I.e. the probability of an
incoming call can not find an idle device.
C= Number of devices
A= Offered traffic in Erlang
Pr{blocking}=
C
C
A
C!
k
A
k!
K=0
EETS 8316/NTU TC 745, Fall 2003
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#59
Performance Metrics, cont…
Delay within switching network is of
concern, timers that are defined in
intermediate switches.
Erlang C formula is used to calculate the
probability of delay in a wait system.
C
A
Pr [ Delay >0 ] =
C
A + C!
C-1
(
1- A
C
)
k
A
k!
K=0
EETS 8316/NTU TC 745, Fall 2003
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#60
Performance Metrics, cont…
Performance metrics in wireless and wire
line are similar, but not identical
 Accessibility
- Ability to make and receive
calls
 Retainability
- Ability to maintain a call
 Voice quality
- Voice quality during the call
EETS 8316/NTU TC 745, Fall 2003
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#61
Performance Metrics, cont…
How do we calculate these metrics?
No common standards are defined. Only
operator defined standards.
Measurements are collected from network
elements
Formulas are developed per vendor product
EETS 8316/NTU TC 745, Fall 2003
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#62
Performance Metrics, cont…
Performance metrics can be
—Theoretically calculated
—Measured using counters produced at each
node
—Verified by drive testing
EETS 8316/NTU TC 745, Fall 2003
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#63
Performance Metrics, cont…
Theoretical estimation
—Normally used during the network design.
—Queuing theory, traffic forecast, statistical
estimates and product specification are the
corner stone of this work
—Result are good for this phase but are not
always correct
EETS 8316/NTU TC 745, Fall 2003
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#64
Performance Metrics, cont…
Calculating metrics using counters
—All switching nodes produce counters.
—These counters represent events in the
network
—Using these counters metrics are defined.
—Each vendor has its own counters, thus the
formula for deriving performance metric
varies for each vendor.
—Counters are produced on different levels,
MSC level, BSC level, cell level, etc.
EETS 8316/NTU TC 745, Fall 2003
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#65
Performance Metrics, cont…
Example of counters are
MSC level
# of page attempts
BSC level
# of intra-BSC handoff
Cell level
# page responses
VLR level
# of visiting mobiles
HLR level
Length of mobile activity
EETS 8316/NTU TC 745, Fall 2003
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#66
More on Counters
Typical counters in MSC/BSC
# of page request from HLR
# of page response after one attempt
# of pager response after second attempt
# of page with no response
What metric use this information?
EETS 8316/NTU TC 745, Fall 2003
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#67
More on Counters
Answer: Availability
Typical counters in BSC/MSC
# of measured RXQUAL=n
# of dropped calls
# of call attempts
Duration of call (average)
What are these counters used for?
EETS 8316/NTU TC 745, Fall 2003
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#68
More on Counters
Answer:
# of Dropped calls and # of call attempts are
used for retainability
# of measure RXQUAL=n is used for voice
quality
# of call attempts and duration of call is used
for dimensioning
A counter may many uses.
EETS 8316/NTU TC 745, Fall 2003
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#69
Verification, Drive Test
A commonly used method
Expensive and time consuming
Good tool for trouble shooting
Mobile handset is connected to a computer. All
communication between the mobile handset
and the base station is recorded. For example,
layer three messages, layer 2 messages,
measures signal strength, quality, etc.
EETS 8316/NTU TC 745, Fall 2003
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#70
Verification, Drive Test, cont…
Normally, the test calls are done towards a
test number that sends a tone for
verification of voice quality
The quality of the test equipment influences
the result
Reliability of the test software is a key.
EETS 8316/NTU TC 745, Fall 2003
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#71
Primer to switching systems
Two basic types of Switching
—Circuit switched
—Packet switched
EETS 8316/NTU TC 745, Fall 2003
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#72
Circuit Switched Connection
Connection has three phase: setup,
transmission, disconnection.
—Bandwidth is reserved end-to-end for
duration of connection
—Congestion and delay in the setup phase
—Only propagation delay during transmission
—Well suited for real-time, continuous traffic,
e.g., speech
EETS 8316/NTU TC 745, Fall 2003
SMU
ENGINEERING
#73
Circuit Switched Connection, Cont…
—Example, Public Switching Telephone
Network
—Require time and space switch
EETS 8316/NTU TC 745, Fall 2003
SMU
ENGINEERING
#74
Circuit Switched Connection, Cont…
Traffic can be concentrated for better use of
resources
Channel 1
:
:
1
1
:
K
:
M
Channel N
Concentrator
EETS 8316/NTU TC 745, Fall 2003
SMU
ENGINEERING
#75
Packet Switch Connection
—Information is packetized, i.e. segmented
and padded with header and trailer
information.
—Contents of header and trailer information is
determined by the protocol governing the
packet switched network, origination and
destination of the information and other
services invoked.
EETS 8316/NTU TC 745, Fall 2003
SMU
ENGINEERING
#76
Packet Switch Connection, Cont…
—Packets are relayed through network by
store-and-forward method. This means that
the each node in the packet switched
network receives each packet, store it until it
can be sent successfully.
—Packet switch node receives packets on the
input links, processes packet header to
determine next node towards the desired
destination
EETS 8316/NTU TC 745, Fall 2003
SMU
ENGINEERING
#77
Packet Switch Connection, Cont…
—Packets are buffered for transmission on
each output link
—Packets experience processing + queuing +
propagation delays in each node it
traverses.
—Depending on the protocol and services
invoked, packet may arrive out-of-order. In
that case the final destination node is
responsible for assembling the packets in
order before submitting it to the receiver of
information
EETS 8316/NTU TC 745, Fall 2003
SMU
ENGINEERING
#78
Packet Switch Connection, Cont…
No resources/trunks are reserved.
All network resources are shared by all
users.
Delay is variable based on the load level in
the network.
EETS 8316/NTU TC 745, Fall 2003
SMU
ENGINEERING
#79
Packet Switch Connection, Cont…
—Well suited for non-real-time, bursty traffic
—2 types of packet switching, connectionless
and connection oriented:
• Connectionless: each packet is routed
independently
–Packets can arrive out of order
–Example: Internet protocol (IP)
EETS 8316/NTU TC 745, Fall 2003
SMU
ENGINEERING
#80
Packet Switch Connection, Cont…
• Connection-oriented: packets follow
same route along “virtual circuit”
–Packets arrive in same order
–3 phase connection: setup,
transmission, termination
–Examples: ATM, frame relay, X.25
EETS 8316/NTU TC 745, Fall 2003
SMU
ENGINEERING
#81