Internet Applications and the Application Layer Material from Kurose and Ross, Chapter 2: The Application Layer

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1 Midterm Study Sheet Below is a list of topics that will be covered on the midterm exam. Some topics may have summaries to clarify the coverage of the topic during the lecture. Disclaimer: the list may be incomplete. 1. Introduction to Computer Networks material from Kurose and Ross, Chapter 1: Computer Networks and the Internet Approaches to constructing the network core o Circuit switching Multiplexing in circuit switched networks Time Division Multiplexing Frequency Division Multiplexing Tip: You should know how each of these support the use of a single link by multiple users, how to calculate the transmission rate of circuit when using either of these approaches, how long it would take to transmit a file using either of these approaches, etc. o Packet switching Motivation for its use in the Internet as the network core Packet switches use store-and-forward transmission Each switch must receive the entire packet before it can begin to transmit the first bit of the packet Introduces a store-and-forward delay at the input to each link along the packet s route Store-and-forward delay at each switch responsible for forwarding a packet is L/R seconds o L is length of the packet (bits) o R is the rate of the link (bits/sec) Packet switching is a statistical multiplexing approach Tip: You should know why packet switching is called a statistical multiplexing approach, you should be able to describe the general idea of packet switching, and be able to compare it with circuit switching Introduces queuing delay o Definition o Cause Delay and Loss in Packet-Switched Networks o Types of delay Processing delay Queuing delay Traffic intensity measure Transmission delay Propagation delay

2 Tip: You should know what each of these mean and how they contribute to the end-to-end delay and the time that it takes to deliver a file or a single packet. An overview of the network protocol stack o Network layers Application Transport Network Link Physical o Encapsulation of messages at various layers Tip: see pages in section of Kurose and Ross Book is on reserve in the library if you haven t bought it yet Internet Applications and the Application Layer Material from Kurose and Ross, Chapter 2: The Application Layer Network architectures o Client-server o Peer-to-peer o Application-Layer protocols HTTP Persistent o Pipelining o No pipelining Non-persistent Cookies Web Cache/Proxy servers o How they work o Why you want to use them FTP SMTP Mail access protocols o POP o IMAP DNS What it is DNS Caching Sockets! What are they? How are they used? Different kinds of sockets o Connection-oriented o Connectionless

3 How to program client and server communication (pseudocode) Data Transfer and the Transport Layer Material from Kurose and Ross, Chapter 3: The Transport Layer Multiplexing and demultiplexing o Connectionless o Connection-oriented Connectionless service o What does it offer? o The protocol that provides it: UDP Connection-oriented service o What does it offer? o The protocol that provides it: TCP o Mechanisms, approaches for providing reliable data transfer Acks Sequence numbers Timers o Sliding window protocols Why we want them Basic approaches o Go-back-N o Selective repeat o Tip: make sure that you read sections and in Kurose and Ross that cover these protocols. I will also give a handout on them on Monday. o TCP in detail Establishing a connection 3 way handshake Setting the timeout Estimating the RTT Sequence numbers Based on # of bytes! Policy for sending acknowledgements Cumulative acks What receiver should do with out-of-order packets See table on page 245 of Kurose and Ross Sender s policy for receiving acknowledgements TCP Header fields Don t memorize the message header format, just know what fields are needed to establish a TCP connection, for acknowledgements, and for congestion control o TCP Flow Control Advertised window o TCP Congestion Control

4 Congestion window! Slow start phase Why we want to use it Congestion avoidance Why we want to use it Approaches to adjusting the congestion window Use of threshold o Determines when slow start phase ends and congestion avoidance begins o Setting threshold Upon loss, half of the current value of the congestion window Variants of TCP o TCP Tahoe Slow start Congestion avoidance On any loss: Set threshold to half of last congestion window value go back to minimum window size (e.g., 1) and begin slow start o TCP Reno Slow start Congestion avoidance Fast retransmit and fast recovery! On loss detected by timeout o Same as TCP Tahoe On loss detected by 3 duplicate acks o Begin congestion avoidance at window size = threshold o Set threshold to half of last congestion window value TCP Delay Modeling Static window Dynamic window o Tip: don t worry about formula derivations, just know how to use the formulas Network Communication and the Network Layer Material from Kurose and Ross, Chapter 4: The Network Layer o Virtual circuit networks o Datagram networks

5 o IP Addressing Scheme o Forwarding and routing o IP address Prefix matching in routing tables (pg. 312, Kurose and Ross) o Routing o Link state approaches o Distance vector approaches o Interior Gateway Protocols RIP OSPF o Border Gateway Protocol