Topic 6: Network Layer - Chapter 5 : The Internet: Addressing & Services

1. Topic 6: Network Layer- Chapter 5 : The Internet: Addressing & Services Business Data Communications, 4e

2. Internet Addressing • 32-bit global internet address • Includes network and host identifiers • Dotted decimal notation • 11000000 11100100 00010001 00111001 (binary) • 192.228.17.57 (decimal)

3. Types of addresses Address Example Software Example Address Application Layer Web browser ike.ba.ttu.edu Network Layer TCP/IP 129.118.49.189 Data Link Layer Ethernet 00-A0-C9-96-1D-90

4. Addressing The network layer determines the best route through the network to the final destination. Based on this routing, the network layer identifies the data link layer address of the next computer to which the message should be sent.

5. Assigning Addresses In general, the data link layer address is permanently encoded in each network card, and as part of the hardware that cannot be changed. Network layer addresses are generally assigned by software. Every network layer software package usually has a configuration file that specifies the network layer address for that computer.

6. Assigning Addresses Application layer addresses (or server addresses) are also assigned by a software configuration file. Virtually all servers have an application layer address, but most client computers do not. Network layer addresses and application layer addresses go hand in hand. (ruby.bus.utexas.edu - means 146.6.44.95 at the network layer.)

7. *How IP Addresses Distributed • Internet Corporation for Assigned Names and Numbers (ICANN) oversees the Internet Assigned Numbers Authority (IANA) and controls how the Net's 4.29 billion IP addresses are used. • IANA distributes address space to three geographically diverse Regional Internet Registries (RIRs) and encourage three RIRs to operate so that addresses remain unique, are mapped efficiently, and are treated as a precious resource. • Three RIRs dole out available pools of IP based on a shared criteria. All deploy numerical address space to ISPs, local registries, and in some cases small users.

8. IP Address Allocation IANA InterNIC America RIPE Europe APNIC Asia National Regional Consumer

9. Three RIRs • American Registry for Internet Numbers (ARIN) • Reseaux IP Europeen (RIPE) • Asia Pacific Network Information Centre (APNIC)

10. Internet Addresses InterNIC is responsible for network layer addresses (IP addresses) and application layer addresses or domain names (www.ttu.edu). There are five classes of Internet addresses. Classes A, B, and C are available to organizations Class D and E are reserved for special purposes and are not assigned to organizations.

11. Internet Address Classes • Class A (/8 address) • The first digit is fixed, ranging 1-126 (01-7E), 16 million addresses • 127.x.x.x is reserved for loopback • Class B (/16 address) • First two bytes are fixed with the first digit ranging 128-191 (80-BF), 65,000 addresses. • Class C (/24 address) • First 3 bytes are fixed, with the first digit ranging 192-223 (C0-DF), 254 addresses. • Class D & E • The first digit is 224-239 (E0-EF) and 240-255 (F0-FF) respectively. • Reserved for special purposes and not available to organizations.

12. Internet Address Classes Ranges of the first byte for different classes: 224 239 126 128 191 192 223 1 240 255 1/2 1/4 1/8 1/16 1/16 Class A Class B Class D Class E Class C Class A: 0xxxxxxx Class B: 10xxxxxx.xxxxxxxx Class C: 110xxxxx.xxxxxxxx.xxxxxxxx Class D: 1110xxxx.xxxxxxxx.xxxxxxxx Class E: 1111xxxx.xxxxxxxx.xxxxxxxx Note: The IP addresses with the first byte as 0 and 127 are reserved

13. Internet Address Classes # of Addresses Class Available Addr-Structure Example Available# Class A 16 million First byte fixed 50.x.x.x 126 Organization assigns last three bytes Class B 65k First two bytes fixed 128.192.x.x 16k Organization assigns last two bytes Class C 254 First three bytes fixed 192.1.56.x 2 millions Organization assigns last byte

14. Internet Addresses The Internet is quickly running out of addresses. Although there are more than 1 billion possible addresses, the fact that they are assigned in sets (or groups) significantly restricts the number of usable addresses. The IP address shortage was one of the reasons behind the IPv6, providing in theory, 3.2 x 1038 possible addresses. How to apply for IP address?

15. Subnets Assign IP addresses to specific computers so that all computers on the same local area network have a similar address. Each LAN that is logically grouped together by IP number is called a TCP/IP subnet. Benefit: • allows it to be connected to the Internet with a single shared network address • an necessary use of the limited number of network numbers • Overload Internet routing tables on gateways outside the organization

16. Gateway 146.7.11.1 128.192.254.2

17. Subnet Mask Subnet mask enables a computer to determine which computers are on the same subnet. This is very important for message routing. E.g. IP address: 129.118.49.189 Subnet mask: 255.255.255.0 IP address: 129.118.49.x is for the computers in the same subnet

18. Subnet Subnet with partial bytes addresses. E.g. 129.118.49.1 to 129.118.49.126 Subnet mask: 255.255.255.128 Subnet address: 129.118.49.0 Subnet broadcast address: 129.118.49.127

19. Subnet IP address: 129.118.49.111 1000 0001.0111 0110.0011 0001.0110 1111 Subnet mask: 255.255.192.0 1111 1111.1111 1111.1100 0000.0000 0000 The IP prefix 1000 0001.0111 0110.00 Destination IP: 129.118.51.254 1000 0001.0111 0110.0011 0011.0110 1111 Destination IP: 128.83.127.1 1000 0000.0101 0011.0111 1111.0000 0001

20. 128 192 192 224 224 240 240 248 248 252 252 254 255 Subnet Mask Template Broadcast Address 150.1.0.0 255 255 0 0 Host Address 150 1 128 64 32 16 8 4 2 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 0 0 1 Network ID–Class B 128 Mask Numbers Possible Subnet Address

21. Dynamic Addressing An address assignment problem: Each time the computer is moved, or its network is assigned a new address, the software on each individual computer must be updated. Solution: dynamic addressing With this approach, a server is designated to supply a network layer address to a computer each time the computer connects to the network.

22. Dynamic Addressing Two standards for dynamic addressing are commonly used in TCP/IP networks: • Bootstrap Protocol (bootp) for dial-up networks (1985) • Dynamic Host Control Protocol (DHCP) for non-dial-up networks (1993)

23. Dynamic Addressing The Bootp or DHCP server can be configured to assign the same network layer address to the computer each time it requests an address or it can lease the address to the computer by picking the “next available” network layer address from a list of authorized addresses. Dynamic addressing greatly simplifies network management in non-dial-up networks too.

24. Address Resolution Address resolution: The sender translates the application layer address (or server name) of the destination into a network layer address; and in turn translates that into a data link layer address. Two approaches used in TCP/IP: • Server address resolution • Data link layer address resolution.

25. Domain • A domain refers to a group of networks that are under the administrative control of a single entity, such as a company.

26. Server Name Resolution Domain Name Service (DNS) Used for translating application layer addresses into network layer addresses. InterNIC Keeps the name and IP addresses of the name server that will provide DNS information for your address classes.

27. Domain Name System • 32-bit IP addresses have two drawbacks • Routers can’t keep track of every network path • Users can’t remember dotted decimals easily • Domain names address these problems by providing a name for each network domain (hosts under the control of a given entity) • See Figure 5.6 for example of a domain name tree

28. DNS Database • Hierarchical database containing name, IP address, and related information for hosts • Provides name-to-address directory services • Key features: • Variable-depth hierarchy. Unlimited levels • Distributed database. Scattered throughout the Internet and private intranet. • Distribution controlled by the database. Thousands of separately managed zones managed by separate administrators

29. Server Name Resolution Server address resolution process: • TCP/IP sends a special TCP-level packet to the nearest DNS server asking for the requesting computer the IP address that matches the Internet address provided. • If the DNS does not have the answer for the request, it will forward the request to another DNS. This is why it sometimes takes a long time to access certain sites. IP addresses are then temporarily stored in a server address table.

30. Data Link Layer Address Resolution In order to actually send a message, the network layer software must know the data link layer of the destination computer. In the case of a distant computer, the network layer would route the message by selecting a path through the network that would ultimately lead to the destination.

31. Data Link Layer Address Resolution The process: • TCP/IP software sends a broadcast message (using Address-Resolution-Protocol or ARP) to all computers in its subnet requesting the data link layer address. • The computer with the right IP address responds with its data link layer address • The message is sent to the destination computer

32. Routing There are many possible routes or paths a message can take to get from one computer to another. Routing The process of determining the route or path through the network that a message will travel from the sender to the receiver. Routing table The routing information on each router, which specifies how message will travel through the network.

33. Dynamic Routing There are three commonly used dynamic routing protocols • Routing Information Protocol (RIP) - used by the network manager to develop the routing table. Used by both TCP/IP and IPX/SPX. • Internet Control Message Protocol (ICMP) - used on the internet with TCP/IP. • Open Shortest Path First (OSPF) uses the number of computers in a route as well as network traffic and error rates to select the best route.

34. Connectionless vs. Connection-Oriented Routing Two ways a group of packets can be routed: • Connectionless routing • Each packet is treated separately and makes its own way through the network. • Connection-Oriented routing • Sets up a virtual circuit between the sender and receiver. Appears to use point-to-point circuit-switching, but actually uses store-and-forward. • Has greater overhead than connectionless, due to the routing information.

35. Connectionless vs. Connection-Oriented Virtual Circuit • Appears to the application software to use a point-to-point circuit • The network layer makes one routing decision and all packets follow the same route

36. Connectionless vs. Connection-Oriented TCP vs. UPD • TCP is used for connection-oriented routing • TCP establishes the virtual circuit and IP routes the messages. • UDP is used for connectionless routing

37. Multicast Unicasting The usual transmission between two computers. Broadcasting Sending messages to all computers on a LAN or subnet. Multicasting Sending the same message to a group of computers temporarily in a class D IP address. IGMP is used for multicast. Anycasting An IPv6 transmission method allowing messages to be sent to any one of the host in a sub-network.

38. Quality of Service Quality of Service (QoS): • The idea that transmission quality (rates, error rates, bandwidth and jitter) can be measured, improved, and, to some extent, guaranteed in advance. QoS routing: • A special type of connection-oriented dynamic routing in which different messages or packets are assigned different priorities.

39. Categories of Traffic • Elastic traffic, such as FTP, email, etc • Allow fluctuating bandwidth, the total transmission time is important • The data must correctly transmitted • Real-time traffic, such as videoconferencing. • Demands certain bandwidth with isochronous features • Tolerates some level of errors. • Service quality includes: Throughput, Delay, Delay variation, and Packet loss.

40. Routing at Routers • Bandwidth schedule • First in first out • Round robin • Prioritization • Queue management • Packet discard policy • Congestion control Packet arrival Packet forward Packet Drop

41. Network Congestion • What is traffic congestion? • The buffer in a forwarding device overflows. This results packet losses and incur retransmission. The transmission will worsen the situation. • Network congestion control is very important in flow management

42. Internet Flow Control • Internet flow control algorithm • Slow start, congestion avoidance • Router queue management • Random early detection (RED) for packet dropping • Data flow scheduling • FIFO, round robin, priority queueing, weighted fair queueing

43. Internet Flow Control • Slow Start algorithm (RFC2001). To avoid router running out of space • Two windows: advertised window by receiver and congestion window by sender. The congestion window is flow control imposed by the sender, while the advertised window is flow control imposed by the receiver. • The congestion window is initialized to one segment. Each time an ACK is received, the congestion window is increased by one segment. The sender can transmit up to the minimum of the congestion window and the advertised window. • The sender starts by transmitting one segment and waiting for its ACK. When that ACK is received, the congestion window is incremented from one to two, and two segments can be sent. • When each of those two segments is acknowledged, the congestion window is increased to four. This provides an exponential growth. • At some point the capacity of the internet can be reached, and an intermediate router will start discarding packets. This tells the sender that its congestion window has gotten too large.

44. Internet Flow Control • Congestion Avoidance (RFC2001) • Sets congestion window to one segment. • When congestion occurs (indicated by a timeout or the reception of duplicate ACKs), one-half of the current window size (the minimum of congestion window and the receiver's advertised window, but at least two segments) is saved as X. • When new data is acknowledged by the other end, increase congestion window, but the way it increases depends on whether TCP is performing slow start or congestion avoidance. If congestion window is less than or equal to X, TCP is in slow start; otherwise TCP is performing congestion avoidance. • Slow start continues until TCP is halfway to where it was when congestion occurred (since it recorded half of the window size that caused the problem in step 2), and then congestion avoidance takes over. • Congestion avoidance dictates that congestion window be incremented a linear growth of congestion window, compared to slow start's exponential growth.

45. Internet transmission services • Best-effort services • The Internet treats all packet equally. • Integrated services (IntServ) • IntServ refers to mechanisms that enable users to request a particular QoS for a flow of data. • Differentiated Services (DiffServ) • DiffServ Use type-of-service in IPv4 header to indicate the required service quality.

46. Integrated Services • Routers require additional functionality to handle QoS-based service • IETF is developing suite of standards to support this • Two standards have received widespread support • Integrated Services Architecture (ISA): To enable the provision of QoS support over IP-based Internet. • Resource ReSerVation Protocol (RSVP)

47. Integrated Services Architecture • Enables provision of QoS over IP-networks • Features include • Admission Control: A new flow needs a reservation for QoS • Routing Algorithm: more parameters are considered other than just delay • Queuing Discipline: Queuing policy takes into account of different requirements • Discard Policy: Particularly for congestion management

48. Resource Reservation Protocol (RSVP) • A tool for prevention of congestion through reservation of network resources • Can be used in unicast or multicast transmissions • Receivers (not senders) initiate resource reservations • Operation: • Complexity is in multicast transmission • RSVP uses two basic messages: Resv and Path. In multicast, Resv messages generated by one of the multicast group receivers propagate upstream through distribution tree and create soft state in routers. Once it reaches the sender, hosts are enabled to set parameters for the first hop. Path is used to provide upstream routing information and sent from senders via the down stream tree to all receivers

49. Differentiated Services (DiffServ) • Provides QoS based on user group needs rather than traffic flows • Can use current IPv4 octets • Service-Level Agreements (SLA) govern DiffServ, eliminating need for application-based assignment

50. IPv4 Type of Service Field • Allows user to provide guidance on individual datagrams • 3-bit precedence subfield • Indicates degree of urgency or priority • Queue Service & Congestion Control • 4-bit TOS subfield • Provides guidance on selecting next hop • Route selection, Network Service, & Queuing Discipline 1 2 3 4 5 6 7 0 Precedence TOS 0