Bjorn Landfeldt, The University of Sydney 1 NETS 3303 Networked Systems Revision

Bjorn Landfeldt, The University of Sydney 2 Overall Understand WHY protocols were designed the way they were Understand what is good and bad with the designs Read through relevant RFCs There are some fundamental mechanisms in the protocol stack. Understand these mechanisms.

Bjorn Landfeldt, The University of Sydney 3 Layered Model Divide a task into pieces and then solve each piece independently (or nearly so). Establishing a well defined interface between layers makes porting easier. Major Advantages:  Code Reuse  Extensibility

Bjorn Landfeldt, The University of Sydney 4 IP Model Basics Physical Voltage Modulation Data-link Framing Local Addressing Network Global Addressing Packetisation Transport End-to-end flow control Multiplexing Application User data Synchronisation Example functions In different layers

Bjorn Landfeldt, The University of Sydney 5 Data-link Layer Provides access to local network Supplies local address Transports traffic over one hop only Many different technologies with different characteristics Wired and wireless

Bjorn Landfeldt, The University of Sydney 6 IP IP operates in the network layer –packet delivery service (end-to-end). –translation between different data-link protocols.

Bjorn Landfeldt, The University of Sydney 7 IP IP provides connectionless, unreliable delivery of IP datagrams. Connectionless: each datagram is independent of all others. Unreliable: there is no guarantee that datagrams are delivered correctly or at all.

Bjorn Landfeldt, The University of Sydney 8 IP Addresses IP addresses are logical addresses (not physical) 32 bits. Includes a network ID and a host ID. Every host must have a unique IP address. IP addresses are assigned by a central authority (the NIC at SRI International).

Bjorn Landfeldt, The University of Sydney 9 ICMP “Companion” to IP, used for queries and error signalling. Common usage: –Host or network unreachable –Redirect –Echo request/reply (ping)

Bjorn Landfeldt, The University of Sydney 10 Transport Layer User Datagram Protocol, UDP adds: –Multiplexing (ports) –Error detection (CRC over entire packet) Transport Control Protocol, TCP also adds: –Error correction –Flow control –Robustness in case of failure

Bjorn Landfeldt, The University of Sydney 11 TCP Characteristics Connection oriented –Three way handshake Reliable –Error detection –Error correction Buffer management and flow control –Sliding window –Slow Start and Congestion Avoidance Stream oriented

Bjorn Landfeldt, The University of Sydney 12 UDP vs. TCP TCP introduces latencies –Session set-up –Data retransmission Flow control mechanism unsuitable for CBR applications TCP – Stream oriented, UDP – Datagram oriented TCP – reliable, UDP - unreliable

Bjorn Landfeldt, The University of Sydney 13 Types of Traffic Different applications generate different types of traffic e.g. –Web pages (delay sensitive) –FTP (BW sensitive) –Streamed Media (BW sensitive) –Conversational Multimedia (delay and BW)

Bjorn Landfeldt, The University of Sydney 14 Cast? Unicast – flow from one host to another host Broadcast – flow from one host to all local hosts Directed Broadcast – flow from one host to all hosts on a foreign network Multicast – flow between hosts in a group

Bjorn Landfeldt, The University of Sydney 15 RTP TCP unsuitable for RT media UDP has two major drawbacks: –Lack support for lost or reordered packets –Lack support for jitter compensation RTP provides these functions

Bjorn Landfeldt, The University of Sydney 16 That’s it