Comp 346/446 Final Exam Study Guide
Solutions are here.
Here is a summary of the sections (ninth, eighth & seventh editions) that may be covered on the final:
Chapter 5: (also on midterm)
5.2: FSK (also used in Ch 9)
Chapter 8: (also on midterm)
8.1: FDM (traditional)
8.2: TDM, revisited. Lots on SONET.
Chapter 9: Spread Spectrum, intro to cellular phones
9.1: basic concepts
9.2: frequency hopping
9.3: Theoretically this is a prereq to 9.4, but I think you can safely omit this.
9.4: CDMA
Chapter 11:
11.3: ATM connections & paths
11.4: ATM cell format
11.5: ATM over SONET, etc
11.6: ATM service categories: CBR, VBR-rt, VBR-nrt, ABR, UBR
Chapter 13:
13.1: Congestion basics
13.2: Summary of congestion options
13.3: More congestion appreaches
13.4: Congestion summary (very short)
13.5: ATM traffic management, GCRA, Token Buckets and Leaky Buckets. Note that GCRA is not actually in Stallings.
13.6: ATM-GFR traffic management
Chapter 14:
14.3: (2nd-generation) CDMA cellular networks
Chapter 20 (Chapter 19 in 8th edition)
20.1: ISA & Queuing Disciplines
20.2: RSVP
20.3: Differentiated Services
Chapter 21:
21.3: MPLS
Also covered:
GCRA(T,𝝉): General Cell Rate Algorithm
Here are a few exercises. Problem numbers are 9th/8th/7th editions
Also study the Review Questions at the end of each of the relevant chapters.
Chapter 8
7/7/7 Meant to be straightforward
9/9/9 Comparative bandwidth problem; less important
Chapter 9
4/4/4 4 & 5 are about FHSS. There's a lot of relatively
5/5/5 obscure detail here
IMPORTANT: Be familiar with the calculations in Table 9.1 (7th, 8th, 9th editions)
Chapter 11
3ab/2ab/2ab Calculations on fixed v variable-sized ATM cells
4b/3b/3b ATM cell size
Chapter 13
1/1/1 "Isarithmic" control proposal; less important
4/6/4 ATM v Frame Relay terminology; less important
Chapter 14
2/2/2 Meant to be easy
4/4/4 Relatively straightforward bandwidth calculation
8abcdef/8abcdef/- IMPORTANT cdma-encoding problem
Here is the above problem:
Consider a CDMA system in which users A and B have the Walsh chipping
codes (-1 1 -1 1 -1 1 -1 1) and (-1 -1 1 1 -1 -1 1 1), respectively.
(a) Show the output at the receiver if A transmits a data bit 1 and B does not transmit.
(b) Show the output at the receiver if A transmits a data bit 0 and B does not transmit.
(c) Show the output at the receiver if A transmits a data bit 1 and B
transmits a data bit 1. Assume the received power from both A and B is
the same.
(d) Show the output at the receiver if A transmits a data bit 0 and B
transmits a data bit 1. Assume the received power from both A and B is
the same.
(e) Show the output at the receiver if A transmits a data bit 1 and B
transmits a data bit 0. Assume the received power from both A and B is
the same.
(f) Show the output at the receiver if A transmits a data bit 0 and B
transmits a data bit 0. Assume the received power from both A and B is
the same.
Chapter 20
3/chapter19.#19/- Straightforward give-examples problem
Here is the problem:
Provide three examples (each) of elastic and inelastic Internet
traffic. Justify each example's inclusion in its respective category.
6/ch19.21/ch19.7 Token-bucket calculation
Recall the GCRA algorithm (this same definition will be given to you
on the exam):
GRCA(T,𝝉): Avg time T between packets, 𝝉 = variation
Suppose current cell is expected at time tat, actually arrives at t
Case 1: t < tat - 𝝉 (too EARLY): NONCONFORMING; do not change tat
Case 2: t >= tat - 𝝉: CONFORMING; newtat = max(t,tat) + T
Consider the following set of packet arrival times.
0 0 3 5 7 9 16 16
1. For GCRA(3,2), which packets are compliant?
2. For GCRA(3,1), which packets are compliant?
3. For GCRA(2,10), which packets are compliant?
For each example, also give the values for the theoretical arrival times (tat).
4. For a GCRA(4,25) flow,
(a) how many packets can be sent as a burst at T=0?
(b) if that burst is sent, at what time can the next packet be sent?
5. For each of the ATM traffic classes CBR, rt-VBR, nrt-VBR, and UBR,
list the Quality-of-Service (QoS) and Traffic parameters they request.
6. Outline the differences between AAL3/4 and AAL5 in terms of:
(a) data bytes per packet
(b) bits used in ATM header
(c) error detection
7. Suppose an ATM connection meets GCRA(6, 18).
(a) What is the maximum size of a packet burst?
(b) Assume the available output bandwidth is 1 packet per 4 time units. How long does it take to send a packet burst?
(c). What outbound bandwidth is needed if the maximum delay is 8 time units?
(d). What outbound bandwidth is needed if the maximum delay is 20 time units?
8. Compare and contrast ATM connection admission with RSVP.
9. Give an equivalent definition of GCRA(T,𝝉) in terms of token buckets.
10. Explain the differences and similarities between admission control and policing.
11. Suppose packets arrive at times 0.0, 1.0, 1.9, 3.0, 4.1, 5.0,
5.9,
7.1, 8.0, ...; that is, they arrive on whole-number times within ±0.1.
What 𝝉 is needed so that this stream satisfies GCRA(1.0, 𝝉)?
12. Consider the arrangement of routers below:
Internet −−−−−−RISP−−−−−−−−RU−−−user
Router RU belongs to the user. Why is it difficult for RU to set aside some bandwidth for high-priority inbound traffic (eg voice)?
13. Suppose we have a SIP phone and want to register it with our provider, but a NAT firewall intervenes:
provider.com −−−− RNAT−−−−phone
NAT firewalls rewrite the port numbers for all devices behind the firewall.
(a) How do provider.com and the phone initially get in touch via SIP?
(b) Suppose a call is initiated. The phone and provider.com exchange
SIP packets identifying the addresses and ports of the actual RTP
endpoints that will carry the voice data. The phone sends
provider.com its private IP address and private port but RNAT will rewrite both of these. How do the phone and provider.com eventually figure out how to exchange RTP traffic?
14. Compare RSVP with DS. Describe one way by which DS may fail to maintain service targets.