Check-Liste zum Lernen

Stand: 2010-06-12

Bei der Prüfung zur Vorlesung Datenkommunikation kommen ausschließlich Fragen zu den nachfolgenden Themen. Wenn Ihnen zu zu jedem Stichwort etwas einfällt sollte eine gute positive Note sehr wahrscheinlich erreichbar sein.
Achtung: Dies ist kein Fragenkatalog! Sie sollten zu jedem Thema ein tieferes Verständnis gewonnen haben und vernünftige Fragen (zB warum? wie? was?) beantworten können.
"Querfragen" sind natürlich möglich, um das Verständnis zu prüfen. Zum Beispiel erbt SONET/SDH alle Charakteristiken von Circuit Switching (Kapitel Multiplexing Methods).
Achtung: Diese Liste wird während des Semesters noch aktualisiert, d. h. mit den Themen der aktuellen Vorlesung synchronisiert. Bis Mitte Juni 2010 wird diese Liste praktisch vollständig sein.

Contents

Communication Basics

Symbols, information rate versus symbol rate
Bitsynchronisation
Serial vs parallel transmission
Asynchronous vs synchronous bit serial transmission
Line codes (reason, know at least the following: NRZ, RZ, Manchester, basic idea of AMI and HDB3)
What is scrambling (only basic idea and reason, no need to learn the example scrambler in detail)
Components of a transmission system
Characteristics of a communication channel, typical spectra
Nyquist rate
Channel capacity
QAM: Basic idea, principles, examples

Network Layers

Why layers?
The 7 OSI layers: name them, explain their tasks, give examples
Encapsulation principle

Protocol Principles

Link layer tasks
Typical frame structure (explain each field; what is bit- or byte-stuffing? use for code violations?)
Connection-oriented vs connection-less protocols (difference?)
ARQ methods (important, know all in detail! understand windowing issues such as empty pipe problem, sliding window, etc)
Flow control

HDLC

What is this, history, why is it important?
Basic characteristics (who created it? idea of building blocks, station types and modes)
Default ARQ method?

Multiplexing methods

Explain basic idea of TDM, SDM, FDM, DWDM, and CDM.
Very important: Synchronous (deterministic) versus asynchronous (statistic) TDM - know concepty, characteristics, pros and cons.
Metcalfe's law
Circuit switching (also DSU/CSU and typical physical interfaces)
Packet switching (datagram versus virtual call, PVC and SVC)

X.25

Characteristics, typicall applications of X.25
UNI, DTE and DCE
LCN
Layers; LAPB, error recovery on two layers
X.121 addresses
PAD

Frame Relay

Basic concepts (UNI, DLCIs)
Design goals, typical applications (bursty traffic)
Important players: GoF, CCITT, ANSI, FRF
NNI (reason?)
Local Management Interface
ITU-T Layer model; what means Annex A? Why is the model vertically divided? What is LAPF and Q.933?
Know the meaning of FRF.4, FRF.11, and FRF.12 (you may ignore the details on the slide "Voice over FR" (Slide 20))
Know typical FR interfaces: G.704, X.21, G.703, V.35, HSSI
CRC size of FR
Idea of FECN, BECN, and DE bit
Basic idea only of CLLM (ignore frame details etc)
Why is FR good for bursty traffic? What is AR, CIR, EIR, Bc, Be, Tc? Understand the diagrams!
Difference traffic shaping and policing
Importance of Tc. What is default and what are voice requirements?
Explain reason, concept and procedures of LMI; which three types (but ignore message format), which DLCIs are reserved for LMI?
Explain Inverse ARP
Where is Bidirectional LMI used?

ATM

Idea of cells
ATM design ideas, idea of B-ISDN, UNI and NNI
VPI/VCI
Facts only: E.164, PNNI (what is it? and where?)
Frame format and header structure (what is PT and CLP? HEC and usage for framing)
Idea of AAL Concept, know basic features/applications of AAL1, AAL2, AAL3/4, and AAL5. What does the convergence sublayer, and what the SAR? Understand AAL2 importance for mobile radio networks (ignore AAL details such as in slide 36). Which one is important for IP?
Idea of VP and VC switching
ATM topologies (p2p and p2mp)
What is I-LMI? (only basic idea, see LMI in FR)
On which physical media is ATM typically carried?
What are OAM cells?
Any ATM issues if bit error rate is too high? (Slide 43) What is Intelligent Packet Discard?
Basic structure of 20 byte ATM address (ignore details such as in slide 49)

ISDN

Original idea of ISDN
BRI and PRI, B and D channels, Europe and USA
TE1, TE2, NT1, NT2, TA and reference points R, S, T, U, especially concept of S/T-bus
2B1Q coding (ignore the precise voltage levels), Echo cancellation or ping pong (where?)
Layer model, especially know and explain Q.931 and LAPD, also know which layer-1 is used for BRI and PRI; what is the user plane?
S/T-bus characteristics, total bit rate and why, idea of echo-bit
What is Q.921?
Which ISDN switch types? (Europe vs USA)
What are Information Elements (only the idea of, not details)

Telco Backbones

Voice sampling, Shannon's theorem, how to get to 64 kbit/s
What are synchronous networks? Plesiochronous?
Idea of A-law and mu-law? (Note that the greek mu-sign might be obfuscated in the slides)
What was the idea of pulse stuffing in PDH?
Understand PDH hierarchy, E1, E2, E3, E4 and T1, T2, T3. Which level is synchronous? Which rather asynchronous?
What is a DS0?
Add/drop multiplexing at any level?
Structure of E1 frame, meaning of slot 0 and 16
CCS versus CAS
Multiframe, how is framing implemented?, where is CRC?
How is framing done in T1? What is robbed bit signalling?
PDH problems (overhead, rates, compatibility)
SONET versus SDH (differences?)
SONET/SDH Network structure (Path, Line, Section, ADM, Regenerators, Path Termination.
OC-n, STS-n, STM-n (meaning, SONET or SDH, approximate data rates (note: x4 at each level)
Idea of floating payload to deal with phase differences at each node
What is protection switching?

PPP

Why and where is PPP needed?
LCP versus NCP (tasks)
Basic frame structure (but ignore magic numbers on slide 8)
CHAP

Ethernet

History: Aloha, Metcalfe at Xerox, orignally Xerox on workstations (system clock became network clock) and coax cables, DIX, Ethernet 2, IEEE 802.3
Explain purpose of 802.1 and 802.2
Also know about existence of 802.5 (Token Ring) and 802.11 (WLAN).
What is a NIC?
CSMA/CD, Exponential Backoff Algorithm
Slot time and collision domain, diameter limitations, minimum frame lenght
Maximum frame length, MTU
Explain 10Base2, 10Base5, 10BaseF, 10BaseT, 100BaseT, 1000BaseT, 1000BaseX, Jam signal
MAC address structure
802.2 (LLC) and 802.3 header structure
Ethernet frame structure
SNAP header
Twisted pair cables (how many wires?), what does "Cat 5" mean for example?
NIC design: Explain PHY, AUI, MII, GMII, MDI

Bridging and VLAN Introduction

Idea of transparent bridging, collision domain?, broadcast domain?, comparison to routing?
Learning, forwarding, filtering (and flooding)
Bridge versus Switch
Bridging problems, broadcast storm
Spanning Tree, important content of BPDUs
Bridging and routing comparison
VLANs and tagging via 802.1Q (or ISL)
Principle of inter-VLAN routing

Spanning Tree Details

Important parameters (Bridge-ID, port cost, Port-ID), STP (802.1D) mechanism
Root Bridge, Designated ports etc.
State diagram, 15 seconds forwarding delay
7-bridge limit
2 second hello timer, 20 second age
TCN mechanism
What is the Extended System ID?
Port cost calculation (old and newer methods, know Cost 19 for Fast Ethernet, 4 for Gigabit Ethernet, and 802.1T as latest method)
DSAP and SSAP value for BPDUs
Only know the idea of Port Fast (very important practically!) but ignore Uplink Fast and Backbon Fast
RSTP concepts and important properties
Backup and alternate port
Issues with: shared ports, point-to-point ports, and edge ports
What is the sync operation?
TCN handling in RSTP
PVST+ concepts, advantages and problems
MSTP ideas and concepts
Regions, 16 instances, mandatory attributes
What is the purpose of the CST?

Ethernet Evolution

Consider history (from bus to star, from coax to twisted pair, from hubs to full duplex switches)
Ethernet as WAN technology
Explain idea of Etherchannels (which negotiation protocols are common?)
Idea of Frame Bursting and Carrier Extension
Pause frame
Auto negotiation (NLP, FLPs)
Explain shortly 100BaseX, 100BaseFX, 100BaseTX, 100BaseT4
4B/5B Coding (idea, why?)
Explain shortly 1000Base-X versis 1000Base-T, 1000Base-LX and -SX
8B/10B Coding (idea, why, where?)
What is defined by 802.3ab? How many wires are used by 1000Base-T? (By the way: How many wires are used by Fast Ethernet?)
Which wavelengths are most important in modern fibers?
What is defined by 802.3ae?

IP

Reason for IP and its features
Important mandatory helper protocols: ICMP and ARP -- reason, basic functionality
The whole IP header! You don't need to know the exact position of its fields but it is important to know what is communicated there so you can also explain why and how it is used.
The IP address, address classes, special addresses, RFC 1918, subnet mask
IP Fragmentation: How does it work, do we use/want it today, why?
Variable Length Subnet Mask (VLSM) -- be able to solve typical address plan examples!

Address Resolution

Important ICMP examples (echo, unreachables, TTL exceeded, redirect). Where is Inverse ARP needed?
Direct vs indirect delivery. How is a packet send from host to another host trough a network? Explain every step!
Proxy ARP: Only basic idea! How can you get your own host doing Proxy ARP?

BOOTP and DHCP

Basic idea of BOOTP and its shortcomings.
Differences to DHCP; how does the DHCP handshake work (messages).
Can DHCP messages reach other networks? How?
How is BOOTP and DHCP transported (also port numbers)?
DHCP timers T1 and T2 (basic idea).

TCP and UDP

This is a very important chapter! Understand the idea of TCP or UDP communication using sockets, well-known port numbers, etc
Know all header fields of TCP (the order is not important, only size and meaning!)
Understand all details how a TCP connection is established and destroyed!
Understand how TCP transmits and repairs data!
Understand the (Sliding) Windowing mechanism!
Explain the checksum used by UDP and TCP
Understand TCP Retransmission Timeout (RTO) ideas (no detailed formulae, only idea)
Explain reason for TCP persist timer!
Understand TCP Delayed ACKs and Nagle Algorithm.
Understand TCP Slow Start and Congestion Control plus Fast Retransmit and Fast Recovery extension.
Know tail dropping, its consequences and what RED does.
Understand Explicit Congestion Notification
Details of the UDP header

NAT

Understand the central principles of NAT (inside vs. outside, local vs. global)
Which translation tables are used with NAT and which with PAT?
Static versus dynamic translations
Consequences of NAT/PAT (Application layer issues)

Routing Introduction

Types of routing (in/direct delivery, static, dynamic, default)
Difference classful/classless routing (longest match principle)
The IP Routing Paradigm
What is a metric? What is an Administrative Distance? (Know the AD of RIP, OSPF and static routes)
Difference classful vs. classless routing protocols
Difference IGP vs. EGP
Explain differences and ideas of distance vector vs. link state
Important columns of a routing table

RIP and RIPv2

Understand how RIP works, including Split Horizon, Max Hop Count, Hold Down and Triggered Updates
Know three timers: Update, Invalid, and Holddown.
How is RIP transported? (UDP 520, message size limits, broadcast issues)
Main differences of RIPv2
Know well-known (destination) address of RIPv2

OSPF

Basic principles (OSPF metric details, well-known OSPF multicast addresses, "LSA", ...)
Link state establishment procedure (7 states, which messages, when ACKs?, etc)
How is convergence enforced? (30 min LSA timers, flash updates)
Hello intervals
OSPF on multiaccess networks (DR, BDR, well-known address, Network LSA)
Reason and use for a OSPF Router ID? How is it chosen?
Understand the OSPF area concept, area types, and corresponding LSAs! Which LSAs remain within the local area? Which ones are flooded throughout the whole domain? Why do LSA 4 and LSA 5 belong together? When do we need LSA 7? Understand idea of stub areas and NSSA. How does the area concept relate to the IP addressing plan? Explain the idea of virtual links.
Understand how Dijkstra's Shortest Path First algorithm works!

Chapter 25 (OSPF LSAs -- why there is a dirty dozen of them) can be skipped for the exam.

BGP

What does CIDR mean? What are the three basic ideas here? (only know essential ideas, you can skip the history and organizations etc)
Understand basics of BGPv4 (why "path vector protocol"?, AS-numbers, demand for policy routing, ...)
Understand basic message types (open, notification, update, keepalive) What is a withdraw message?
Understand the Routing Information Base and the idea of inbound and outbound policies
Understand the BGP attributes concept. Which attribute types exist?
Understand the following attributes: AS_PATH, Next_Hop, Origin, Local Preference, MED, Community, and Weight.
What is AS aggregation?
In the 10-step decision hierarchy you don't need to learn all details except that Weight > Local Preference > shortest AS-path > MED and that EBGB path is better than any IBGP path.
Differences EBGP and IBGP, admin distances, loop detection issues, IGP synchronization
Understand concept and need for Route Reflectors (you may skip the Confederations concept)

Chapter 31 (BGP Packet Structure) can be skipped for the exam.

MPLS and MCAST

Multicast

You only need to understand the following topics:

Understand reason for multicast technology! What is an MDT?
Understand concepts of Shortest Path Trees vs Shared Trees
Know only basics about RTP and RTCP (UDP-based, one-way, sequence numbers and timestamps, RCTP provides basically quality feedback)
Know Class D mcast address block and only most important details such as idea of local scope (and 224.0.0.1, 224.0.0.2), global scope, and administratively scoped addresses (but no further details).
IGMP concepts (query/report) and differences between versions 1,2, and 3. Note the destination addresses used by query and reports!
Mapping of IP to MAC address and consequences!
Understand basic idea of IGMP snooping
Multicast routing basics: RPF and TTL scoping (OIL = Outgoing Interface List)
Idea of Dense and Sparse multicast routing protocols
Understand concepts of PIM-DM and PIM-SM. What are prune and graft messages? What is the PIM assert mechanism good for? Understand PIM-SM details including the concept of register packets and when to perform a switchover.

MPLS

Understand MPLS Transport, the concept of a control plane and data plane within a router (including FIB and LFIB), how labels are distributed and why Penultimate Hop Popping is done. (No details about LDP and TDP messaging, except that the labels are sent reliable via TCP)
Understand the advantage of MPLS Transport in the example "BGP Standard Behavior" vs "MPLS and BGP".
Understand MPLS TTL usage (TTL propagation)
Understand basic idea of MPLS-VPN (advantages compared to traditional VPNs) but no details needed

DNS

Basic concepts only! Here is a checklist for you:

What is a FQDN?
How is the name tree? What are zones?
What is the root domain (".")?
What are root name servers, practically, how many?
What are Top Level Domains?
Understand recursive vs. iterative query!
Idea of caching name server
Reverse lookups (why? where to start here?)
Concept of primary and secondary name servers
Resource records, basic structure (TTL!) and most importantly the A, NS, CNAME, PTR, and MX records (why they are good for)