1. DNS, Web, TCP Sequence Numbers EE122 Discussion 10/19/2011

2. DNS Mapping between names (e.g., www.cnn.com) and addresses (e.g., 157.166.255.18) Hierarchy of DNS servers – Root servers – Top-level domain (TLD) servers – Authoritative DNS servers – Default Name Server

3. HTTP Request-response protocol Based on a global naming system – …which uses the DNS for resolution HTTP runs on top of TCP

4. TCP Sequence Numbers Initial sequence number for the connection is not zero Sequence number refers to the first byte in the TCP packet payload

5. Example (from class) Packet arrives: –S–Seq: 2323 –A–Ack: 4001 –W–W=3000 –[–[no payload] Appropriate response? Seq: 4001, payload: 4001-8000 Seq: 2001, payload: 2001-5000 Seq: 4001, payload: 4001-5000 Seq: 5001, payload: 5001-6001 Seq: 8001, payload: 8001-9000