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Week 3: Protocols

Week 3: Protocols. Protocols. Protocols Protocol Design. Packet Length Conveyance Acknowledgement Methodology Error Checking / Correcting Compression Encryption Packet Control. Protocols Packet Structure. Layout Header = Protocol Manifest Payload = BLOB (binary large object)

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Week 3: Protocols

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  1. Week 3: Protocols Protocols

  2. ProtocolsProtocol Design • Packet Length Conveyance • Acknowledgement Methodology • Error Checking / Correcting • Compression • Encryption • Packet Control

  3. ProtocolsPacket Structure • Layout • Header = Protocol Manifest • Payload = BLOB (binary large object) Optional: • Footer = Stop Bit, Magic # (uncommon in app layer) • Serialization • In Game = Struct, Class, … • On Network = Byte array (bits in link layer)

  4. ProtocolsSerialization Gottcha’s • Pointers • Large Arrays • Variable size Arrays • ADT’s • Integer Alignment • Endianess(HtoN, NtoH) • Processor dependant intrinsic type size (int, long) • Unsupported types (unsigned -> signed long) • Strings • Unicode vs. ASCII • NULL terminated, Pascal, or ADT

  5. ProtocolsRequest for Comments • RFC web site • http://www.rfc-editor.org/ • Protocol Specifications • Definitive Resource • Public Criticism • Future Protocols

  6. Week 3: Protocols Protocol Stack

  7. Protocol StackOpen System Interconnect

  8. Protocol StackPhysical Layer • Bandwidth • Width of data pipe • Measured in bps = bits per second • Latency • Travel time from point A to B • Measured in Milliseconds • The Medium • Fiber, FireWire, IrD , CDMA & other cell Table 1: Max Bandwidth Specifications

  9. Protocol StackSI units • 1 kbit = 1,000 bits Decimal • 1 kiB = 1,024 bits Binary • 1 kB = ??? Bin or Dec

  10. Protocol StackData Link Layer • Serializes data to/from physical layer • Network Interface Card • Ethernet • MAC Address

  11. Protocol StackNetwork Layer • Packet Routing • Hops • Routers, Hubs, Switches • Internet Protocol (IP) • Contains Source & Destination IP Address • IPv4 • Widespread Infrastructure • IPv6 • Larger IP address

  12. Protocol StackNetwork Layer: IP Address • Unicast • Static • DHCP • Multicast • Requires multicast capable router • Broadcast • Local • Directed • Loop Back • Send to self • AddrAny • 0 = address before receiving an address

  13. Protocol StackNetwork Layer: DNS • Domain Name Service • Converts text name to IP address • Must contact one or more DNS servers to resolve • Local cache resolution possible • Game Tips • Store local game cache to use when DNS out of order. • DNS resolution often slow, use cache for same day resolution.

  14. Protocol StackTransport Layer • Manage data deliver between endpoints • Error recovery • Data flow • TCP and UDP used with IP • Contains Source and Destination Port • Port + IP = Net Address • Port Range = 0-64k • Well known Ports 0-1k

  15. Protocol StackTransport Layer: TCP • Guaranteed Correct In Order Delivery • Acknowledgement system • Ack, Nack, Resend • Checksum • Out of Band • Connection Required • Packet Window • Packet Coalescence • Keep Alive • Streamed Data • User must serialize data • Header • http://www.networksorcery.com/enp/protocol/tcp.htm

  16. Protocol StackTransport Layer: UDP • Non Guaranteed Delivery • No Acknowledgement system • May arrive out of order • Checksum • Not Connected • Source not verified • Hop Count Limit = TTL (time to live) • Required for Broadcasting • Datagram • Sent in packets exactly as user sends them • Header • http://www.networksorcery.com/enp/protocol/udp.htm

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