TCP/IP Review

1. TCP/IP Review Revisit ideas about TCP/IP and Internetworking Reference: Ch.9 “Data Communications…” 2nd Edn By Fred Halsall

2. Network Layer issues • Network services • Connection-oriented vs Connectionless services • Addressing • Network Services Access Point address (PORTS) • Network Point of Attachment address (MAC address) • Routing • determination of gateways needed to route a NPDU from source ES to destination ES. • Quality of Service • transit delay, costs limit, levels of security, expected residual error probability

3. Network Layer issues • Packet size • BER, transit delay, buffer size, processing overheads;all determine maximum packet size • large packets -> fragmentation and reassembly • Small packets -> inefficiency and congestion • Flow and congestion control • Connection-Oriented -> inherent flow control • Connectionless -> flow control in Transport Layer • Error Reporting • Depends on network type. Each uses its own method

4. Router

5. Internet IP • Connectionless network service: datagrams • ISO defines Network Layer in 3 sublayers: • Subnet Independent Convergence protocol SNICP • Subnet dependent Convergence protocol SNDCP • Subnet dependent Access protocol SNDAP • ISO 8475 is SNICP corresponding to IP

6. Internet IP

7. IP Address structure 0 7-bit netid 24-bit hostid Class A 1 0 14-bit netid 16-bit hostid Class B 1 1 0 21-bit netid 8bit hostid Class C 1 1 1 0 multicast address Multicast 1 1 1 1 Reserved

8. Subnetting • Class A/B/C networks can be subnetted into small networks, eg. Monash is 130.194.0.0 (class B) and divided into 256 class C subnets • Address mask for this subnetting is 255.255.255.0 • Each class A/B/C network is assigned by central authority Network Information Center.

9. IP data unit - Datagram

10. IP Fragmentation/Reassembly • Datagram data are fragmented into smaller transfer units due to limitations of underneath networks • SNICP-IP layer- fragmentation & reassembly • Intranet fragmentation - the whole datagram is reassembled at each gateway • Internet fragmentation - the datagram is only reassembled at destination IP. • The time-to-live field defines the time left for the datagram (seconds). Source IP is notified if time expires using ICMP. Gateways simply decrement it!

11. IP Routing • SNDCP sublayer handles routing • Routing table- IP address / NPA address. • Centralised routing - central network management system to handle routing table • Distributed routing - all hosts and gateway maintain and cooperate so that routing information is consistent.

12. IP routing within a Host

13. Autonomous systems • Routing information are passed around via Interior gateways and Exterior gateways. • Hosts maintain sufficient routing info to forward datagrams to other hosts or an interior gateway in the same network • Interior gateways maintain sufficient routing info to forward datagrams to other interior gateways. • Exterior gateways maintain sufficient routing info to forward datagrams to another autonomous system or interior gateway • Each may use different protocols….

14. Address Resolution Protocol ARP • concerned with host <-> Interior gateway routing. • source send ARP request to gateway stating its IP/NPA and dest IP. • gateway relays the request to the destination • destination registers the source’s IP/NPA and send ARP reply to source. • source registers the dest’s IP/NPA and resumes sending IP data. • Reverse ARP informs host about it’s IP/NPA mapping.

15. An interior gateway protocol:Routing Information Protocol • routing between interior gateways • distributed routing protocol based on distance vector algorithm (DVA). • distance is used as a routing metric between two gateways: Hops or Netdelay • Initially all gateways only know of the netid of all adjacent networks and the IP/NPA address pair of each gateway • Setup by administrator

16. RIP • The interior gateway maintains a table of netid, distance, gateway • each gateway sends this table to its neighbours periodically, so that the whole autonomous system’s networks are recordedThe distances are added up for each subnet in system to form complete routing table • Time taken for routes to stabilise depends on network size and frequency of updates

17. Internet Control Message Protocol • Used in network management, to do: • error reporting (dest unreachable, time exceed) • reachability testing (echo request/reply) • congestion control (source quench) • route-change notification (redirect) • performance measuring (timestamp) • subnet addressing (address mask request/reply)

18. Transmission Control Protocol • Stream Oriented - guaranteed error-free delivery • Virtual Circuit Connection • Initial connection requires some setup messages between hosts to establish parameters of channel (eg buffer sizes, authorisation, error detection & recovery procedures..) • After connection, protocol software on both sides verify that data is received correctly • If transfer fails, application software on both sides can be notified and appropriate steps taken • Buffered Transfer - Efficient data communication • Unstructured Stream - Transfer boundary not sent • Full-Duplex connection - allows protocol control signals (eq ACKs) sent as part of data travelling opposite direction

19. TCP – Reliable Delivery • Positive acknowledgment with Retransmission • Arrival of each correct packet at destination is acknowledged by replying with a control signal. • Sender keeps a copy of each transmitted packet and waits for acknowledgement to arrive • Sender also starts a timer when each packet is transmitted. If Timer expires before ack is received, the packet is retransmitted (and timer restarted) • Packets identified by sequence number • Duplicate Packets (already acknowledged) are discarded

20. TCP Stream buffer and Flow Control “Sliding Windows” • Simple positive acknowledgement waits for acknowledgement before transmitting next packet • This wastes network bandwidth - especially where transmission delays are high • Transmitting several packets and keeping copies of unacknowledged packets is more efficient • Available storage space determines maximum window size • Allows efficient communication and provides flow control

21. TCP “Sliding Windows”

22. TCP “Sliding Windows” Flow Control • Window size can be changed during session • As data is acknowledged, the window sizes may be updated • Reducing window size slows data floweg when receiver's buffer space is running low • Setting window size to zero halts data exchange!

23. TCP - Congestion Avoidance • Receiver window size included in acknowledgements • Another window size is kept - Congestion Window size • Actual Window = MIN(receiver's window, congestion window) • Usually Congestion window = Receiver's window • When timeout occurs, Halve Congestion window size • Called "multiplicative decrease" • Retransmitted Segments also have timer “backed-off” • When next ACK arrives Congestion window is incremented • Called “additive increase” • TCP provides quick and significant traffic reduction • Allows gateways to clear datagrams already queued

24. Implementation of TCP/IP

25. TCP/IP Applications

26. Transport Protocol Addresses: TCP & UDP Port Numbers # This file contains port numbers for well-known services defined by IANA # Format: # <service name> <port number>/<protocol> [aliases...] [#<comment>] discard 9/tcp sink null discard 9/udp sink null qotd 17/tcp quote #Quote of the day qotd 17/udp quote #Quote of the day ftp-data 20/tcp #FTP, data ftp 21/tcp #FTP. control telnet 23/tcp smtp 25/tcp mail #Simple Mail Transfer Protocol time 37/tcp timserver time 37/udp timserver domain 53/tcp #Domain Name Server domain 53/udp #Domain Name Server bootps 67/udp dhcps #Bootstrap Protocol Server bootpc 68/udp dhcpc #Bootstrap Protocol Client tftp 69/udp #Trivial File Transfer finger 79/tcp http 80/tcp www www-http #World Wide Web