Formula Sheets: Application Layer | Computer Networks - Computer Science Engineering (CSE) PDF Download

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Application La y er F orm ula Sheet
Application La y er Ov erview
• F unctions : Pro vides user in terfaces, supp orts services (e.g., email, file transfer, w eb bro wsing).
• Throughput : S =
D
data
T
total
, where D
data
is application data size, T
total
includes proto col o v erhead
and dela ys.
• Latency : T
latency
=T
app
+T
trans
+T
prop
+T
queue
, whereT
app
is application pro cessing time.
Domain Name Service (DNS)
• Query Resolution Time : T
DNS
= T
lo okup
+N
hops
·(T
prop
+T
pro c
) , where N
hops
is n um b er of
DNS serv ers queried.
• Cac he Hit Time : T
cac he-hit
˜O(1) , t ypically 1-10 ms.
• Cac he Miss Time : T
cac he-miss
=T
recursiv e
+T
iterativ e
, up to 100-500 ms.
• DNS Record Size : S
record
=S
name
+S
t yp e
+S
v alue
, t ypically 50-200 b ytes.
• Num b er of Queries : N
queries
?N
clien ts
·F
request
, whereF
request
is query frequency .
Electronic Mail (SMTP , POP3, IMAP , MIME)
• SMTP (Simple Mail T ransfer Proto col) :
– T ransaction Time: T
SMTP
=T
connect
+T
HELO
+T
MAIL
+T
R CPT
+T
D A T A
+T
QUIT
, t ypically
100-500 ms.
– Message Size: S
message
=S
header
+S
b o dy
+S
MIME
, whereS
MIME
is MIME o v erhead.
• POP3 (P ost O?ice Proto col) :
– Do wnload Time: T
POP3
=T
auth
+
?
S message
i
R
, whereR is data rate.
– Command Ov erhead: T
command
˜N
messages
·T
RETR
, t ypically 10-50 ms p er message.
• IMAP (In ternet Message A ccess Proto col) :
– Sync Time: T
IMAP
=T
auth
+T
sync
+T
fetc h
, whereT
sync
dep ends on folder size.
– Bandwidth Usage: B
IMAP
>B
POP3
due to serv er-side storage access.
• MIME (Multipurp ose In ternet Mail Extensions) :
– Ov erhead: O
MIME
=S
b oundary
+S
enco ding
, t ypically 10-20% of message size.
– Base64 Enco ding: S
enco ded
=
4
3
·S
binary
.
Hyp ertext T ransfer Proto col (HTTP)
• Request-Resp onse T ime : T
HTTP
=T
connect
+T
request
+T
resp onse
+T
data
, whereT
connect
˜RTT .
• P ersisten t Connection Throughput : S
p ersisten t
>S
non-p ersisten t
, reducesT
connect
o v erhead.
• HTTP/1.1 Pip elining : T
pip eline
=T
connect
+max(T
request
i
)+T
resp onse
, forN requests.
• HTTP/2 Multiplexing : S
HTTP/2
˜
N·L
data
T connect+T stream
, whereT
stream
is stream pro cessing time.
• Resp onse Size : S
resp onse
=S
header
+S
con ten t
, t ypicallyS
header
˜ 200-500 b ytes.
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Application La y er F orm ula Sheet
Application La y er Ov erview
• F unctions : Pro vides user in terfaces, supp orts services (e.g., email, file transfer, w eb bro wsing).
• Throughput : S =
D
data
T
total
, where D
data
is application data size, T
total
includes proto col o v erhead
and dela ys.
• Latency : T
latency
=T
app
+T
trans
+T
prop
+T
queue
, whereT
app
is application pro cessing time.
Domain Name Service (DNS)
• Query Resolution Time : T
DNS
= T
lo okup
+N
hops
·(T
prop
+T
pro c
) , where N
hops
is n um b er of
DNS serv ers queried.
• Cac he Hit Time : T
cac he-hit
˜O(1) , t ypically 1-10 ms.
• Cac he Miss Time : T
cac he-miss
=T
recursiv e
+T
iterativ e
, up to 100-500 ms.
• DNS Record Size : S
record
=S
name
+S
t yp e
+S
v alue
, t ypically 50-200 b ytes.
• Num b er of Queries : N
queries
?N
clien ts
·F
request
, whereF
request
is query frequency .
Electronic Mail (SMTP , POP3, IMAP , MIME)
• SMTP (Simple Mail T ransfer Proto col) :
– T ransaction Time: T
SMTP
=T
connect
+T
HELO
+T
MAIL
+T
R CPT
+T
D A T A
+T
QUIT
, t ypically
100-500 ms.
– Message Size: S
message
=S
header
+S
b o dy
+S
MIME
, whereS
MIME
is MIME o v erhead.
• POP3 (P ost O?ice Proto col) :
– Do wnload Time: T
POP3
=T
auth
+
?
S message
i
R
, whereR is data rate.
– Command Ov erhead: T
command
˜N
messages
·T
RETR
, t ypically 10-50 ms p er message.
• IMAP (In ternet Message A ccess Proto col) :
– Sync Time: T
IMAP
=T
auth
+T
sync
+T
fetc h
, whereT
sync
dep ends on folder size.
– Bandwidth Usage: B
IMAP
>B
POP3
due to serv er-side storage access.
• MIME (Multipurp ose In ternet Mail Extensions) :
– Ov erhead: O
MIME
=S
b oundary
+S
enco ding
, t ypically 10-20% of message size.
– Base64 Enco ding: S
enco ded
=
4
3
·S
binary
.
Hyp ertext T ransfer Proto col (HTTP)
• Request-Resp onse T ime : T
HTTP
=T
connect
+T
request
+T
resp onse
+T
data
, whereT
connect
˜RTT .
• P ersisten t Connection Throughput : S
p ersisten t
>S
non-p ersisten t
, reducesT
connect
o v erhead.
• HTTP/1.1 Pip elining : T
pip eline
=T
connect
+max(T
request
i
)+T
resp onse
, forN requests.
• HTTP/2 Multiplexing : S
HTTP/2
˜
N·L
data
T connect+T stream
, whereT
stream
is stream pro cessing time.
• Resp onse Size : S
resp onse
=S
header
+S
con ten t
, t ypicallyS
header
˜ 200-500 b ytes.
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File T ransfer Proto col (FTP)
• T ransfer Time : T
FTP
=T
con trol
+
S
file
R
, whereT
con trol
is command o v erhead,R is data rate.
• Con trol Connection Ov erhead : T
con trol
˜N
commands
·(T
request
+T
resp onse
) , t ypically 10-100 ms
p er command.
• Data Connection Mo des :
– A ctiv e: Clien t op ens p ort,T
setup
˜RTT .
– P assiv e: Serv er op ens p ort,T
setup
˜ 2·RTT .
Simple Net w ork Managemen t Proto col (SNMP)
• Query Time : T
SNMP
=T
request
+T
resp onse
+T
pro c
, t ypically 10-100 ms.
• Message Size : S
SNMP
=S
OID
+S
v alue
+S
header
, whereS
OID
is ob ject iden tifier size.
• P olling F requency : F
p oll
=
1
T
in terv al
, t ypicallyT
in terv al
= 5-60 s.
• T rap Ov erhead : T
trap
=T
generate
+T
trans
, whereT
trans
=
S trap
R
.
Dynamic Host Configuration Proto col (DHCP)
• T ransaction Time : T
DHCP
=T
DISCO VER
+T
OFFER
+T
REQUEST
+T
A CK
˜ 4·RTT .
• Lease Duration : T
lease
, t ypically hours to da ys.
• A ddress P o ol Size : N
addresses
= 2
32-n
-N
reserv ed
, wheren is subnet mask bits.
• Renew al Time : T
renew
=
T
lease
2
(default).
T elnet and SSH
• T elnet :
– Latency: T
T elnet
=RTT +T
pro c
, t ypically lo w due to plain text.
– Ov erhead: O
T elnet
˜S
command
, minimal headers.
• SSH (Secure Shell) :
– Connection Setup Time: T
SSH
=T
handshak e
+T
auth
, whereT
handshak e
˜ 2·RTT .
– Encryption Ov erhead: T
encrypt
?S
data
·C
algo
, whereC
algo
is computational cost (e.g., AES).
Wi-Fi Application La y er (WPS, WP A)
• WPS (Wi-Fi Protected Setup) :
– Setup Time: T
WPS
=T
pair
+T
config
, t ypically 10-30 s .
– Securit y Ov erhead: T
auth
˜T
handshak e
+T
k ey-exc hange
.
• WP A (Wi-Fi Protected A ccess) :
– 4-W a y Handshak e Time: T
WP A
= 4·RTT +T
pro c
, t ypically 50-200 ms.
– Key Deriv ation Time: T
k ey
?C
PBKDF2
, where PBKDF2 is k ey deriv ation function.
P erformance Metrics
• Throughput : S =
D
application-data
T
total
, excludes proto col o v erhead.
• Latency : T
latency
=T
app
+
?
N
i=1
(T
prop
i
+T
transi
+T
queue
i
) , whereN is hops.
• Jitter : s
dela y
=
v
1
n
?
n
i=1
(d
i
-d)
2
, whered
i
is pac k et dela y ,d is mean dela y .
• Error Rate : P
error
= 1-(1-P
bit
)
L
, whereP
bit
is bit error rate,L is message length.
• Connection Setup Ov erhead : T
setup
=T
connect
+T
auth
+T
config
.
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