1 A Course-End Conclusions and Future Studies Dr. Rocky K. C. Chang 28 November 2005.
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1 A Course-End Conclusions and Future Studies Dr. Rocky K. C. Chang 28 November 2005
2 The internetworking problem The internetworking problem Different data-link protocols Different MAC address spaces Different MTUs An hour-glass model (end-to-end argument) IP as the glue IP addresses IP fragmentation and reassembly IP over anything and everything
3 All boil down to the design goals Best effort IP service Reliability requirement: trusting states to the end hosts Requirement for supporting a variety of TOS Requirement for accommodating a variety of networks End-to-end argument Keep the network simple: IP packets go in and IP packets come out. Implement applications at the network edge.
4 The forwarding problem Main issues of concerns Who knows what Speed (forwarding table size and lookup) Not responsible for the correctness of the routes Hop-by-hop forwarding as a result of the best-effort approach. Source routing and tunnels Virtual circuit switching IP switching From classful to classless routing
5 The routing problem THE intelligence of the IP layer Use a hop-by-hop protocol to deliver packets end-to-end. Main issues of concerns Speed of convergence Prone to routing loops Efficiency Two main approaches (in midst of many other differences and variations) Distance vector and link state
6 A tale of two routing problems All routing protocols concern delivering packets from one point to another. An intradomain routing additionally concerns optimizing certain costs of a route. An interdomain routing additionally concerns satisfying certain policies of an AS. Current Internet characteristics Asymmetric routes Packet reordering Packet losses Nonfriendly intermediaries
7 The end-to-end problems TCP adds the following services to IP: Multiplexing (through the port number) Inordering (through the TCP SN) At-most-one-copy (through the TCP SN) Arbitrarily large application messages (through the wraparound TCP SN space) Flow control (through advertised window) End-to-end reliability (through the sliding window protocol and retransmission) Congestion control (through ACK clocking, congestion window, slow start, etc)
8 The congestion control problem Congestion control and/or resource allocation hold one of the keys to the Internet stability. A TCP sender interprets packet losses (without receiving ACKs) as a sign of congestion. Slow starting to trigger packet losses (reaching the network capacity) Next time, perform congestion avoidance when approaching to the congestion point. Other approaches do not induce packet losses. TCP/Vegas, Explicit Congestion Notification
9 Two Internet applications DNS provides a distributed database for domain names and protocols to obtain their resource records. Web provides A global naming system to identify resources A text-based language to facilitate a navigation across various related resources, and A protocol for requesting and responding Interaction between TCP and HTTP Web proxies: not longer end-to-end
11 What’s next? From IPv4 to IPv6 From insecure to secure TCP/IP From unicast IP to multicast IP From fixed IP to mobile IP From data network to multimedia network
12 What’s next? From IPv4 to IPv6 (deployment in 2005?) U. S. Army IPv6 Initiatives Improvements: Plenty of IP addresses Overhauled packet structures Better support for real-time data and mobility Better configuration schemes Co-existing with IPv4
13 Internet security: An after-thought? Security mechanisms at each layer IP packet security (IPSec) Encryption and authentication TCP security Issues that we have talked about Transport-level security SSL and TLS Application-level security, e.g., DNS, email PKI and virtual private networks Denial-of-service, worms and viruses
14 From IP unicast to IP multicast Unicast: Send a packet to an IP address Multicast: Send a packet to a group of IP addresses Anycast: Send a packet to any IP address in a group of IP addresses. Multicast routing Intra-domain and inter-domain Source-specific and core-specific distribution trees Others: low control, congestion control, reliability, and security
15 From fixed IP to mobile IP From stationary IP networks to mobile hosts and mobile routers Evolving from mobile laptops to mobile IP phones Support IP mobility in the current IPv4 and IPv6 infrastructures. Mobile IPv4 and Mobile IPv6 Mobile IP network security Authentication, Authorization and Accounting (AAA)
16 From data networking to multimedia networking Timing requirement (synchronization) Bandwidth and QoS requirements Stored and live multimedia sessions Support various audio and video encoding methods Media scecurity IP telephony Control and establishment of sessions (signaling).