Learning Outcome

1. EEC4113Data Communication &Multimedia SystemChapter 8: Transport Layerby Muhazam Mustapha, November 2011

2. Learning Outcome • By the end of this chapter, students are expected to be able to explain issues related to internetworking protocols and a few routing algorithms

3. Chapter Content • Internetworking Protocol • X.25, Frame Relay, ATM • IP Address • Routing Algorithms

4. Internetworking Protocols CO1

5. Internetworking • Internetworking, or internet, is a set of standards involved in connecting LAN-s to form a huge system of WAN • Can be implemented as hardware or software • Involves some algorithms on routing • Involves IP address assignment CO1

6. Internetworking • Connection standards: • X.25 • Frame Relay • Asynchronous Transfer Mode (ATM) CO1

7. X.25 • Old ITU (International Telecommunication Union) standard • Older and wasn’t part of OSI or TCP/IP • Interface between host and packet switched network • Almost universal on packet switched networks and packet switching in ISDN (Integrated Services Digital Network) CO1

8. X.25 • Defines three layers • Physical • Link • Packet CO1

9. X.25 CO1

10. X.25 - Physical • Interface between station node link • Two ends are distinct • Data Terminal Equipment, DTE (user equipment) • Data Circuit-terminating Equipment, DCE (node) • Physical layer specification is X.21 • Can be implemented as EIA-232 (formerly RS-232) CO1

11. Frame Relay / X.25 X.25 - Physical CO1

12. X.25 - Link • Implemented as Link Access Protocol Balanced (LAPB) • Subset of HDLC • Provides reliable transfer of data over link • Sending as a sequence of frames CO1

13. X.25 - Packet • Provides a logical connections (virtual circuit) between subscribers • All data in this connection form a single stream between the end stations • Established on demand • Termed external virtual circuits CO1

14. Issues with X.25 • Key features include: • Calling of control packets, in-band signaling • Multiplexing of virtual circuits at layer 3 (network layer) • Layers 2 (data link) and 3 include flow and error control • Hence have considerable overhead • Not appropriate for modern digital systems with high reliability CO1

15. Frame Relay • Designed before ATM to eliminate most X.25 overhead • Has larger installation base than ATM • Frame relay is for internet, ATM is for LAN • Provides LAN-LAN connection • Implemented as virtual circuit just like X.25 CO1

16. Frame Relay • Key differences from X.25: • Call control carried in separate logical connection • Multiplexing and switching at layer 2 • No hop by hop error or flow control • Hence end to end flow and error control (if used) are done by higher layer • A single user data frame is sent from source to destination and higher layer ACK sent back CO1

17. X.25 vs Frame Relay CO1

18. X.25 vs Frame Relay • Many X.25 networks have been replaced by Frame Relay or X.25 over Frame Relay Networks • X.25 still in use for low bandwidth applications such as credit card verification • It is likely that ATM Networks will ultimately replace Frame Relay and X.25 Networks CO1

19. ATM • Also called cell relay because it transfers data as FIXED cell size • More favorable than frame relay for LAN • Provides much higher data rate • Still implemented as virtual circuit like frame relay and X.25 CO1

20. ATM vs Frame Relay CO1

21. IP Addressing CO1, CO2

22. IPv4 • In general, IP address is the identifier used in the network layer of the TCP/IP model to identify each device connected to the Internet – called the IP address or Internet address • The current version of IP address widely used is IPv4 with a 32-bit binary address • IP addresses are universal & unique CO1, CO2

23. IPv4 • Universal because the addressing system must be accepted by any host that wants to be connected to the Internet • Unique because two devices on the Internet can never have the same IP address at the same time • 32-bit binary gives total of 232 = 4,294,967,296 unique IP addresses CO1, CO2

24. IPv4 • There are 2 common notations to show an IP address • Binary notation • Dotted-decimal notation CO1, CO2

25. Network Classes • The three principal network classes are best suited to the following conditions : • Class A : Few networks, with many hosts • Class B : Medium number of networks, each with medium number of hosts • Class C : Many networks, with a few hosts • Two other classes : • Class D : Used for multicast • Class E : For future use CO1, CO2

26. Network Classes • The address is coded to allow a variable allocation of bits to specify network & host (netid & hostid) CO1, CO2

27. Class A • Start with binary 0 • First decimal number in the range from 0 (00000000) to 127 (01111111) • Only 126 usable network address although there are 128 possible combinations • Because decimal number of 0 and 127 are reserved • Number of addresses per network = 224 = 16,777,216 • Each Class A network address can accommodate 16,777,216 hosts netid hostid CO1, CO2

28. Class A CO1, CO2

29. Class B • Start with binary 10 • First decimal number in the range of 128 (10000000) to 191 (10111111) • 16,384 possible network addresses (214) • Number of addresses per network = 216 = 65,536 • Each Class B network address can accommodate 65,536 hosts netid CO1, CO2

30. Class B CO1, CO2

31. Class C • Start with binary 110 • First decimal number in the range of 192 (11000001) to 223 (11011111) • 2,097,152 possible network addresses (221) • Number of addresses per network = 28 = 256 netid hostid CO1, CO2

32. Class C CO1, CO2

33. Subnet and Subnet Masks • Allows arbitrary complexity of internetworked LANs within organization • Insulate overall internet from growth of network numbers and routing complexity • Site looks to rest of internet like single network CO1, CO2

34. Subnet and Subnet Masks • Each LAN assigned subnet number • Local routers route within subnetted network • IP addresses are partitioned into subnet number and host number • Subnet mask indicates which bits are subnet number and which are host number CO1, CO2

35. Subnet and Subnet Masks CO1, CO2

36. Subnet and Subnet Masks CO1, CO2

37. IPv6 • IP v 1-3 defined and replaced • IP v4 - current version • IP v5 - streams protocol - never implemented • IP v6 - replacement for IP v4 • during development it was called IPng (IP Next Generation) CO1

38. IPv6 – Why? • Address space exhaustion • two level addressing (network and host) wastes space • network addresses used even if not connected • growth of networks and the Internet • single address per host • Requirements for new types of service CO1

39. IPv6 – Why? • Security • IPv6 includes MAC address information, hence individual network card can be resolved • Faster • Better geographical location assignment • IPv4 has unfairly assigned less addresses to recently growing China and India CO1

40. IPv6 – Examples • Full (128 bits) – 3ffe:1900:4545:0003:0200:f8ff:fe21:67cf • Zeros MSB can be omitted – 3ffe:1900:4545:3:200:f8ff:fe21:67cf • Complete zero can be omitted all over – fe80:0:0:0:200:f8ff:fe21:67cf or fe80::200:f8ff:fe21:67cf CO1

41. Congestion Detection & Avoidance CO1

42. Congestion • Definition of CONGESTION • Different from collision • Situation that occurs when network is over utilized • Stations could not serve requests on time • Results in: • Packet loss • Delay • Blocking connection • Queue (buffer) overflow CO1

43. Congestion Detection • Two schemes: • Drop-tail queue management • Random Early Detection (RED) CO1

44. Drop-Tail Queue Management • Default queue management mechanism • Packets accepted if there is room in queue, regardless of who sent it • Packets dropped upon queue overflow, regardless of who sent it • If the queue is consistently full for some period of time, congestion is assumed and notification is sent CO1

45. Drop-Tail Queue Management • Excess packet loss due to late congestion notification • Congestion notification is too late and results in: • Global synchronization – because during congestion drop-tail does not discriminate sender, all senders slows down transmission • Poor link utilization • Potentially large queuing delay CO1

46. Random Early Detection (RED) • Randomize congestion detection • Early notification of congestion • Steps: • Average queue size is monitored • Packets can be dropped even if the queue is not full • Including packets from senders that don’t heavily utilization the link (drop-tail discriminates heavy users) • Done by some statistical calculation • More you send more probable you will be dropped CO1

47. Random Early Detection (RED) • Steps (cont): • If the queue is almost empty, everyone is accepted • If the queue size is more than some max threshold value (but NOT full), everyone will be dropped and early congestion notification is sent – hence a real congestion is avoided CO1

48. Random Early Detection (RED) • RED works by: • Not discriminating packets drop when the queue is wide open NOR when the queue is almost full • Hence everyone experiences global synchronization at more later time • Notifying congestion before it takes place CO1

49. Weighted RED (WRED) • A variant of RED • Includes sender priority in the random statistical calculation for packet dropping • Discriminates low priority sender CO1

50. Routing Algorithms CO1, CO2