CS4470 Computer Networking Protocols 5/5/2019 CS4470 Computer Networking Protocols Final Review Huiping Guo Department of Computer Science California State University, Los Angeles

Final Time Closed book, closed note You may need scratch paper 3:40pm – 5:40pm , Tuesday 12/05 No office hours in the finals week Closed book, closed note You may need scratch paper You may need to bring your calculator You can bring two pages of cheat sheet (letter size, back and front) Final Review

Outline Network layer Transport layer Application layer Final Review

Network layer Routing algorithms Routing protocols Link State Distance Vector Routing protocols Internet routing Intro-AS Routing RIP OSPF Inter-AS Routing BGP Final Review

Transport layer ICMP Network Address Translation (NAT) DHCP What is ICMP for? How to transmit an ICMP message? How to avoid infinite loop? Network Address Translation (NAT) Why NAT How it works DHCP What is DHCP for? How it works? Final Review

User Datagram Protocol (UDP) Services UDP provides The applications that use UDP UDP header Some important fields Compute the checksum Final Review

Principles of reliable transfer Errors A segment is corrupted A segment is lost Automatic retransmission request (ARQ) When errors occur, the receiver sends a message to the sender asking for retransmission Types of ARQ Stop and wait Sliding window (Go back N) Final Review

Pros and Cons of Stop-and-wait Stop-and-wait is a complete reliable transfer protocol It’s very simple Cons Inefficient While the sender is waiting for an ACK, it doesn’t do anything. Why not the sender sends multiple segments at a time? Need more than 1 bits for the sequence number. Final Review

Go-Back-N Based on a sliding window Use window to control number of segments to send Number of segments that the sender can send N-(nextseqnum – send_base) Final Review

Go-Back-N Cumulative ACKs ACK (n): ACKs all segments up to, including seq # n - 1 Timer Only one timer is used. The timer is for the oldest transmitted, yet un-acked segment Final Review

TCP What services TCP provides The TCP connection TCP header format TCP reliable transfer TCP vs. GBN Vs. SR How TCP detects data lost? How to calculate the timeout value? TCP flow control How it works Flow control vs. congestion control Final Review

TCP header format Some most important fields SYN, FIN Seq, ACK Receive Window Final Review

TCP connection management Connection establishment Three-way handshake In each step, what the send and the receiver do? Connection teardown The steps Final Review

TCP congestion control Slow start When the phase starts and ends Congestion avoidance Timeout How to adjust the two variables 3 duplicate ACKs Final Review

HTTP The service it uses Stateless HTTP connections Cookies Non-persistent Persistent Cookies How do cookies work? Final Review

FTP What is FTP for? How it works? Two connections: control connection, data connection Which connection is for transferring which kinds of data? Final Review

Email Components Send an email Receive an email user agents mail servers SMTP Send an email SMTP is used Between Sender’s agent and sender’s mail server Sender’s mail server and receiver’s mail server Receive an email POP3 or IMAP is used Between receiver’s mail server and receiver’s agent Differences between POP3 and IMAP Final Review