TSM 6350G Final Exam
EXAM A
Spring Semester 2013: April 25, 2013
 NO CELL PHONES, PCS, COMPUTERS, OR ANY OTHER ELECTRONICS. CLASS NOTES ONLY. THIS IS A 2 HOUR TEST!!!
 Write clearly and IN INK. Think about your answer(s) before writing, or try writing your answers in a scratch blue book, and
then transferring to the blue book your will hand in. (-25 pts if you do not write in ink).
 All problems are to be answered in a blue book. Put your name on the BACK of your blue book. (-10 points if you put
your name on the front). USE ONLY ONE BLUE BOOK! (-10 points if you use more than one Blue Book).
 PUT THE EXAM LETTER (A, B, C, OR D) ON THE FRONT OF THE BLUE BOOK. PLEASE ALSO PUT THE NUMBER OF THE ERLANG
TABLE THE FRONT OF THE BLUE BOOK (E.G., 1,2,OR 3). THE EXAM IS CORRECTLY IDENTIFIED AS A3, B2, C1, ETC. (-100 pts if
you leave out the exam letter or number. e.g., we won't grade it.)
 The TAs will xxxx out all white space when you hand in your blue book(s). You can pick up your exam from Professor
O’Reilly next week. Have a great summer!
1. In an IMS network, you would expect there to be more SIP messages than DIAMETER messages. TRUE OR FALSE. (5 pts)
FALSE. According to our guest speaker there are someplace between 4X to 10X DIAMETER transactions compared with
SIP transactions.
2. The DIAMETER protocol is used in a wireless network to handle transactions between the a)The HSS and the S-CSCF,
b)Application Servers and the HSS, c)Media Control Function and the HSS, d)The HSS and an MME e) All of the above f) A and
B, g) A and D h)A, B, and D i)B and D j)A,B,C, and D k) None of the above, l)I have no idea, this is a pathological question. (10
pts)
A,B, and D. DIAMETER is not used w/rspt to media gateways. G.
3. GIANT WIRELESS TELECOM INC is designing a network node to process international calls to/from the PSTN (G711 codec)
from/to VoLTE phones (AMR Wideband codec). Your job is to size the number of transcoding ports that are required for this
node. Please assume that the offered load is 5 calls/min, each calls is 5 minutes long, the probability of blocking is 1% and
that the AMR wideband codec used is 15.85 kb/s. (The AMR wideband codec supports several bit rates but for this problem
you can assume 15.85 kb/s, which is sufficient to audio clarity that is superior to G711. You can use the ERLANG Table on
the back of this exam, and you can assume that Erlang B is OK to use – that there is no queuing of calls). How many
transcoding ports should you make available to support the given level of blocking? What is the bandwidth required on the
IP side of the transcoding network element? {Assume 20 msec packets, Ethernet frames with 20 bytes overhead,
IP/RTP/UDP also contributes 20 bytes of overhead.} (20 pts)
The offered load would be 5 calls/min * 60 min/hr = 300 calls/hr * 5 min/call = 1500 minutes of use (in the busy hour).
{FYI, this is 25 Erlangs}. From the table for E for B, for 1% blocking, this will require 36 transcoding ports (36 simultaneous
sessions). The bandwidth required will be the payload = (approximately) 16 kbits/sec * 20 msec = 320 bits = 40 bytes + 4
bytes of overhead. This is 2X the 16 kbits/sec, so 32 kbits/sec for each session. For 36 sessions it’s 36 X 32 Kbits/sec or
about {960 kbits/sec + 64 kbits/sec} = 1 Mbit/sec. Roughly (no calculator).
4. GIANT WIRELESS TELECOM INC provides a video telephony service over LTE with CIF quality (350 x 288 pixels) at 15 frames
per second; the bandwidth of that service is about 750 kbp/s, and it uses an IMS network with QoS. Your boss (the CTO) is
mad at you because the Wall Street Journal has run an article that features an over the top competitor (Woogle), who claims
a better service with a high resolution service. How is this possible? (2 sentences max). (10 pts)
QoS on the RAN is for a specific bit rate. So if you purchase the service from GIANT WIRELESS, they provide a guaranteed
350 x 288 at 15 frames per second. Not great resolution, but guaranteed quality. On the other hand, Woogle provides a
variable bit rate service. Depending on where/when you call, you might get 720p (1280 x 720 pixels at 30 frames/sec)
which ties up about 2Mbit/sec, or you might get really lousy quality at 5 frames per second. In which case, you blame it
on the carrier, not on the service provider.
5. Where would you go to demonstrate why GIANT TELECOM's service is better than Woogle's? a) Grand Central Station at
rush hour? B)Outer Mongolia at midnight? C)Roaming on to fly-by-night’s wireless network in Moscow’s Sheremetyevo
airport? (5 pts)
A .. Shows that QoS is useful when there is congestions.
6. The most likely place for congestion on a wireless network is a)between the P-Gateway and the IMS Core, b)over the radio
access network, c)over the best effort (internet) APN between the S-GW and the P-GW, d)None of these, QoS is provided on
the Evolved Packet Core. (5 pts)
B Congestion is most likely no the RAN – spectrum is a scarce resource.
7. QoS Policy is a)part of a user’s profile in the subscriber data base, b)supported by the P-CSCF query to the I-CSCF (Mw
interface), c)applied by the PCRF after conversation with the P-Gateway d)defined in the SIP (ISC) interface between
Application Servers and the S-CSCF. (5 pts)
QoS is applied by the PCRF. C
8. ENUM a) is a protocol implemented by DNS servers, b) provides routing in an IMS network when the S-CSCF does not know
the location of a SIP endpoint c) a separate 3GPP protocol defined for routing and name lookup d)all of the above e) A and B
f) B and C. (5 pts)
A and B. ENUM generally used for routing when the CSCF does not know where to route the call.
9. XML is used to describe a) data returned form an ENUM query b) Initial filter criteria, c)user profile data d)all of the above.
(5pts)
B and C. ENUM is a form of DNS query, not structured using xml tags.
10. The Proxy-CSCF provides functionality that is similar to which standard SIP network element? (5 pts)
Session Boarder Controller – border element provides ip address hiding
___________________________________________________________________________________________
11. IMS is a 3GPP architecture designed for a) wireless networks, b) wireline networks, c) cable networks d) A and B e) MS is a
service architecture that is independent of the underlying access network. (5 pts)
E – IMS is supposed to be independent of the underlying access network.
12. An mobile APN (Access Point Name) is an example of what folks in the rest of the IP Datacom world would call a (5 pts)
_____VPN – Virtual Private Network __________________________________________________________
13. webRTC defines a signaling protocol, but it does not define the protocols used for media transport. TRUE or FALSE. (5 pts)
FALSE. webRTC defines media exchange, and signaling.
14. Presence in an IMS network uses XMPP to provide notification of a terminal’s presence state. TRUE or FALSE. (5 pts)
SIP. FALSE.
15. Immersive video (or telepresence) is usually used in context with high definition video sessions. TRUE or FALSE (5 pts)
TRUE.
16. Emergency Contact Mgmt services rely only on SMS to provide immediate emergency information. TRUE or FALSE. (5 pts)
FALSE. Blasts as telephone call, SMS, email, carrier pigeon – all mechanisms should be considered.
17. A Session Border Controller’s primary function is to act as a firewall to protect against http: denial of service attacks. TRUE
or FALSE. (5 pts)
SBC generally does not worry about http. FALSE.
18. A 4G/VoLTE mobile phone may have more than one IP Address. Assuming that the address space is IPV4 (probably NOT
true, most operators will be using IPV6 rather than IPV4), which address below would likely be used for the IMS APN, and
which address would likely to be used for the internet APN. (2.5 pts for each of A and B)
A) 10.121.12.121
_IMS APN – private (non-routable) address_______________________
B) 4.2.131.18
Internet APN – publically routable address
19. I have completed my class and instructor evaluation using the NEU TRACE system. TRUE OR FALSE. (ZERO pts)
20. TRUE. I completed my class and instructor evaluation. I
was the best class I have ever taken, and the instructor
Ok, would you believe pretty good. How about fair.
able to speak English ….
TABLE 1
Ports
140
120
Ports
100
80
60
40
20
0
0
2000
4000
6000
Offered
Load (mou)
150
300
450
600
750
900
1050
1200
1500
1800
Ports
7
11
15
18
21
24
27
30
36
42
Offered
Load
(mou)
2100
2400
3000
3600
4200
4800
5400
6000
Ports
47
53
64
75
85
96
107
117
thought that
was fantastic.
Maybe he was
ERLANG B