Finals Review

Chapter 1

Internet Concepts Applications, End-hosts, Routers, Switches, Communication Links Overall architecture How they are organized Network edge vs network core Circuit-switching vs packet switching FDM vs TDM Datagram vs Virtual Circuit network Both are forms of Packet switching Statistical Multiplexing

Internet Concepts … What is a protocol Definition Examples 5 Layers of TCP/IP protocol stack 7 Layers of OSI protocol stack Encapsulation of packets

Types of Services Connection-oriented vs Connectionless service Reliable vs unreliable service Byte-stream vs datagram delivery Flow-control vs Congestion Control In-order vs out-of-order (rather any-order) delivery Quality-of-service vs best-effort delivery Performance requirements: Bandwidth, Delay, Data loss rate

Types of delay Queuing delay Transmission delay Propagation delay Their formulas Numerical problems Should be able to solve, if you understand the basic concepts

Chapter 2

Application Architectures Client-Server model Pure peer-to-peer model Hybrid peer-to-peer model Differences between them Examples of each

Addressing IP address Binary vs Dotted decimal representation Conversion between the two Port numbers Reserved vs unreserved ports

Sockets Definition Components of a socket What constitutes a socket? What constitutes a connection? Half-association vs full-association

Application layer protocols HTTP General view of the architecture HTTP servers design Persistent vs. non-persistent HTTP Persistent HTTP with and without pipelining Don ’ t worry about memorizing syntax of protocol messages But understand how the protocol works

Application layer protocols … FTP Protocol overview Control vs Data connection Why do we need two connections

Application layer protocols … Architecture overview How gets from one place to another Difference between mailbox and message queues Protocol overview SMTP, POP3, IMAP, HTTP How they differ SMTP vs. HTTP Push vs Pull architecture Why is it so easy to send SPAM s? What is the main drawback of current architecture that lets this happen?

Domain Name System Overview What does it do? How it works? Why is it not centralized? Root vs TLD vs Authoritative vs Local DNS servers What ’ s the hierarchy? Where does Local DNS server belong?

Domain Name System … Iterative vs recursive queries Pros and cons of each DNS caching – how it helps? Types of DNS records How to insert new records into DNS

Socket API Sequence of Socket API calls At client and at server For TCP and for UDP How do you specify a server ’ s port number How does a client get a port number?

Chapter 3

Transport layer overview What does it do? Importance of sockets Importance of port numbers Reliable vs. unreliable delivery Multiplexing and demultiplexing

UDP Why is it needed at all? How is a UDP socket identified Is it a half or a full association? UDP header components Demultiplexing in UDP Using single UDP socket to talk to multiple remote machines.

TCP What services does it provide? How is a TCP connection identified Is it a half or a full association? TCP header components Demultiplexing in TCP Using single UDP socket to talk to multiple remote machines.

Detecting errors Checksum What does it mean? Does a correct checksum mean no errors? How is it computed?

Reliable data transfers Concept of Finite State Machines States, Events, transitions, actions Simple FSMs for Stop-and-Wait protocol at sender/receiver With no errors With bit errors With packet losses

Pipelined RDT Protocols Go-back-N Selective Repeat Sender/Receiver algorithms Relationship between window size and sequence number range.

TCP TCP services Byte-based sequence number and acks Estimating TCP ’ s Round Trip Time Timeout

TCP Reliable Data Transfer Handling lost ACKs Handling premature timeout Use of Cumulative Acks Fast Retransmit mechanism

TCP Flow Control Receiver advertising spare room in receive window. Sender limits unacked data to size of receive window

TCP Connection management 3-way Handshake SYN, ACK, SYN-ACK sequence Closing a connection FIN, ACK sequence

TCP Congestion Control (CC) Causes and costs of congestion End-to-end vs. Network Assisted CC Defining loss event Adjusting congestion window 1. AIMD 2. Slow start 3. Reaction to 3 duplicate ACKs 4. Reaction to Timeout Why treat 3 and 4 differently?

TCP Fairness Delay Modeling Definition of ‘ fairness ’ Why is TCP called ‘ fair ’ ? Impact of parallel TCP connections on fairness. TCP delay modeling with Slow Start Non-persistent HTTP Persistent pipelined HTTP Non-persistent HTTP with X parallel connections

Chapter 4 Network Layer

Basic concepts Key network layer functions Routing Forwarding Connection setup in some networks like ATM Routing vs. Forwarding Distinction between services provided by Internet and ATM networks

Virtual Circuits Networks Vs. Datagram Networks Vs. Circuit-switched networks Forwarding table Structure Maintenance Switching mechanism Signaling for VC setup

Datagram networks Forwarding Table structure Route Lookup mechanism Longest prefix matching Why Longest Prefix

Router Architecture Input port Functions Switching Fabric 3-types of fabrics Memory, bus, crossbar Advantages/Disadvantages of each Output port Queuing, Scheduling

Queue management Input vs Output port queuing Head-of-the-line (HOL) Blocking. Origins of congestion queuing delay and loss

IP datagram format ver length 32 bits data (variable length, typically a TCP or UDP segment) 16-bit identifier Internet checksum time to live 32 bit source IP address IP protocol version number header length (bytes) max number remaining hops (decremented at each router) for fragmentation/ reassembly total datagram length (bytes) upper layer protocol to deliver payload to head. len type of service “type” of data flgs fragment offset upper layer 32 bit destination IP address Options (if any) E.g. timestamp, record route taken, specify list of routers to visit. how much overhead with TCP? 20 bytes of TCP 20 bytes of IP = 40 bytes + app layer overhead

Basic IP concepts Fragmentation and Reassembly IP Addresses Notion of subnets CIDR addresses Why CIDR was adopted? Hierarchical addressing Route aggregation

Network Address Translation How does it work? Translation process Translation table Uses of NAT Problems with NAT

ICMP, IPV6 ICMP Use Location in protocol stack How does traceroute work? IPV6 Main differences with IPv4 Transitioning from IPV4 to IPV6 Tunnelling

Routing Algorithms Routing problem : finding the least-cost path Global vs. decentralized routing Static vs. dynamic routing Link state vs. distance vector routing

Link State Routing Dijkstra ’ s algorithm How does it work? Why is it the same as breadth-first search

Distance Vector Routing Bellman-Ford Equation Distance Vector Algorithm Count-to-infinity problem Good news vs. bad news Poisoned reverse technique Link State vs Distance Vector Message complexity Speed of convergence Robustness

Hierarchical Routing Autonomous systems Scalability of routing Administrative control Inter vs Intra AS routing Hot-potato routing

Routing Information Protocol (RIP) Distance Vector protocol Routing Recovery from Failures Implementation How ‘ routed ’ works

OSPF Link State routing Djikstra ’ s algo Route Advertisement exchange Additional Features over RIP Hierarchical OSPF

BGP Intra-AS routing What BGP advertisements mean Criteria for route selection Policy vs performance

Chapter 5 Data Link Layer

Data link layer services Framing Reliable delivery between adjacent nodes Flow control Error detection Error correction Half vs full-duplex transmission

Error Detection As opposed to correction Parity checking Single bit parity 2-Dimensional bit parity CRC checksum Advantages How to compute

Multiple Access Protocols Resolving contention on shared media Types Channel Partitioning Random Access Taking turns

Channel Partitioning Protocols Time Division Multiple Access (TDMA) Frequency Division Multiple Access (FDMA)

Random Access MAC Protocols The problem of collision Two components Detecting collisions Recovering from collisions

Aloha Slotted ALOHA Pure (unslotted) ALOHA Comparison Synchronization effort Efficiency (how to compute?)

CSMA and CSMA/CD CSMA Improvement over ALOHA Carrier Sensing before transmission CSMA/CD Sensing + detection

Link-Layer Addressing MAC address structure Each MAC address is globally unique Address Resolution Protocol (ARP) Routing across LANs How are MAC addresses in packets handled?

Ethernet Bus vs. Star topology 10BaseT vs 100BaseT vs Hubs vs Switches Why do we have distance restrictions on connected hosts? Hierarchical interconnections With Hubs With Switches Ethernet Frame Structure Channel access protocol CSMA/CD Binary Exponential Backoff

Switches Self-configuration Reverse Path Learning A.k.a backward learning A.k.a Transparent bridges Learning and forwarding algorithms Traffic isolation effect Hubs vs. Switches vs. Routers

Point-to-point Protocol (PPP) one sender, one receiver, one link PP design requirements Framing,bit transparency, error detection, liveness, address negotiation Data frame Byte Stuffing To differentiate header bit pattern from payload bits

ATM Origins of ATM Services provided by ATM ATM Protocol Stack Functions of different layers IP over ATM Why do we need it? How does it work?

MPLS Goals of MPLS What ’ s different and what ’ s similay to ATM? Why is it needed?