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Chapter 11: Internet Operation

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1 Chapter 11: Internet Operation
Business Data Communications, 7e

2 Objectives Internet Addressing Internet Routing Protocols
The Need for Speed and Quality of service Differentiated Services

3 Internet Addressing 32-bit global internet address for source & destination in the IP header (base on IPv4) Includes a network identifier and a host identifier Dotted decimal notation (binary) (decimal)

4 Class-Based IP Addresses
Rightmost bits of the 32-bit IP address designate a host The leftmost bits of the 32-bit address designate a network Class-based, or classful, IP addressing was adopted to allow for a variable allocation of bits to specify network and host The first few leftmost bits specify how the rest of the address should be separated into network and host fields This provides flexibility in assigning addresses to hosts and allows a mix of network sizes on an internet In general terms, the rightmost, or least significant, bits of the 32-bit IP address designate a host, and the leftmost, or most significant, bits designate a network. A fixed allocation of bits, such as 16 bits for network number and 16 bits for host, was deemed inadequate to handle the global Internet, where some organizations might have a few networks, each with many hosts and some organizations might have many networks, each with a few hosts. Therefore, a scheme known as class-based , or classful , IP addressing was adopted. Class-based IP addresses allow for a variable allocation of bits to specify network and host. For this scheme, the first few leftmost bits specify how the rest of the address should be separated into network and host fields. This encoding provides flexibility in assigning addresses to hosts and allows a mix of network sizes on an internet.

5 Network Classes Class A: Few networks, each with many hosts All addresses begin with binary 0 Class B: Medium networks, medium hosts All addresses begin with binary 10 Class C: Many networks, each with few hosts All addresses begin with binary 110

6 Format of IP Address Short for multicast backbone. A small set of Internet sites, each of which can transmit real-time audio and video simultaneously to all the others. MBONE sites are equipped with special software to send and receive packets at high speed using the IP one-to-many multicasting protocol. The MBONE has been used for video conferencing and even for a Rolling Stones concert in 1994.

7 Network Classes (cont.)
IP addresses are usually written in: “Dotted Decimal Notation”, i.e. a decimal number represent each byte of the 32-bit address. Example: Binary representation of an IP is : Decimal representation is: (decimal).

8 Network Classes (cont.)
Class A Network begins with 0 Note: Network addresses ( ) and ( ) are reserved Therefore Class A contains: ( = = 126) network numbers Range of the 1st decimal number for Class A: 1.***.***.*** to 127.***.***.***

9 Network Classes (cont.)
Class B begin with binary 10 starts from (128) ends to (191) i.e. Range of the 1st decimal number for Class B: 128.***.***.*** to 191.***.***.*** the 2nd Byte is also part of class B i.e. there are 214 = 16,384 Class B addresses Class B

10 Network Classes (cont.)
Class C begin with binary 110 starts from (192) ends to (223) Range of the 1st decimal number for class C: 192.***.***.*** to 223.***.***.*** the 2nd & 3rd Byte is also part of class C There are 221 = 2,097,152 Class C addresses

11 Subnets & Subnet Masks Allows for subdivision of internets within an organization and add a number of LANs to the internet and insulate their internal complexity within their organization by assigning a single “network number” to all the LANs Each LAN can have a subnet number, allowing routing among networks Host portion is partitioned into subnet and host numbers From the point of view of the rest of the internet, there is a single network at that site. This simplifies addressing and routing.

12 Subnets & Subnet Masks (Cont.)
Then to allow the Routers within the site to function properly, each LAN is assigned a subnet number. 32-bit Source Address 32-bit Source Address

13 Subnets & Subnet Masks (Cont.)
To include the subnet number, the host portion of the internet address is partitioned into a subnet number and a host number to accommodate this new level of addressing. Network Portion: Class A: 7 + 1bits Class B: 14+2 bits Class C: bits Host Portion: Class A: 24bit Class B: 16 bit Class C: 8 bit Extended Network Number or Address Mask: Network Host Within the subnetted network, the local Routers must route on the basis of an extended network number Network Subnet Host

14 Subnets & Subnet Masks (Cont.)
The use of address mask allows the host to determine whether an outgoing datagram is destined for a host on the same LAN (send directly) or another LAN (send datagram to router) Some methods (manual config.) are used to create address masks and make them known to the local routers

15 Subnets & Subnet Masks (Cont.)
The effect of the subnet mask is to erase the portion of the host field that refers to an actual host on a subnet. What remains is the network number and the subnet number.

16 Subnets & Subnet Masks (Cont.)

17 Subnets & Subnet Masks (Cont.)
A local complex consisting of 3 LANs and 2 Routers. To the rest of the internet, this complex is a single network with a class C address of the form X, where 192 ( ) is the network number and x the host number. Example of Subnetworking:

18 Subnets & Subnet Masks (Cont.)

19 Subnets & Subnet Masks (Cont.)
IP Address: Host number:25 IP Address: Host number:1 Net ID/subnet ID: Subnet number:1 Net ID/subnet ID : Subnet number:2 IP Address: Net ID/subnet ID : Subnet number:3 IP Address: Example1: A datagram with the destination address arrives at R1 from the rest of the internet or from LAN Y. R1 has addresses of LAN X, LAN Y, LAN Z. R1 doesn’t know about hosts internal to these LANs. In order to determine where R1 should send the datagram with receiver address R1 bitwise AND the subnet mask: ( ) i.e. ( ) and IP address ( ) to determine that destination address refers to subnet: ( ) i.e. 1, which is LAN X, and so forward the datagram to LAN X. For both R1 & R2 Routers The effect of the subnet mask is to erase the portion of the host field that refers to an actual host on a subnet. What remains is the network number and the subnet number.

20 IP Address & Subnet Masks
Binary Representation Dotted Decimal IP Address Subnet Mask for both R1 & R2 Routers Bitwise AND of address and mask (resultant network/subnet number) Subnet number 1 Host number 25 1 . 25

21 IP Address & Subnet Mask
1 . 25

22 Hosts must also employ a subnet mask to make routing decisions.
Example2: If a datagram with destination address ( ) arrives at R2 from LAN Z, R2 applies the mask and then determines from its forwarding database that datagrams destined for subnet 1 should be forwarded to R1 Hosts must also employ a subnet mask to make routing decisions. The default subnet mask for a give class of addresses is a null mask, which yields the same network and host number as the non-subnetted address. IP Address: Host number:25 IP Address: Host number:1 Net ID/subnet ID: Subnet number:1 Net ID/subnet ID : Subnet number:2 IP Address: Net ID/subnet ID : Subnet number:3 IP Address: Subnets & Subnet Masks (Cont.)

23 Classless Inter-Domain Routing (CIDR)
Makes more efficient use of the 32-bit IP address than the class-based method Does away with the class designation and with the use of leading bits to identify a class Each 32-bit address consists of a leftmost network part and a rightmost host part, with all 32 bits used for addressing Associated with each IP address is a prefix value that indicates the length of the network portion of the address A CIDR IP address is written as a.b.c.d/p a is the value of the first byte of the address b the value of the second byte c the value of the third byte d the value of the fourth byte p is in the range of 1 through 32 and indicates the length of the network portion of the address By the mid-1990s, it became evident to Internet designers and administrators that the 32-bit class-based addressing scheme was woefully inadequate for the growing demand for IP addresses. The long-term solution to this problem, as described in Chapter 8, was the development of IPv6, which includes 128-bit address fields. The use of 128-bit addresses increases the number of possible unique addresses by a factor of almost compared to the use of 32-bit addresses. However, the deployment of IPv6 would take many years so, as an interim measure, CIDR was adopted. CIDR makes more efficient use of the 32-bit IP address than the class-based method primarily because it makes more efficient use of the address space. With class-based addressing, an organization can request a block of addresses that provides 8, 16, or 24 bits for host addresses. Because Internet addresses were typically only assigned as blocks of a certain class, there were a lot of wasted addresses. CIDR does away with the class designation and with the use of leading bits to identify a class. Instead, each 32-bit address consists of a leftmost network part and a rightmost host part, with all 32 bits used for addressing. Associated with each IP address is a prefix value that indicates the length of the network portion of the address. A CIDR IP address is written as a .b .c .d /p , where a is the value of the first byte of the address, b the value of the second byte, c the value of the third byte, and d the value of the fourth byte. Each of these values is in the range of 0 to 255. The prefix value p is in the range of 1 through 32 and indicates the length of the network portion of the address. In CIDR notation, a prefix is shown as a 4-octet quantity, just like a traditional IPv4 address or network number, followed by the “/” (slash) character, followed by a decimal value from 0 through 32. For example, the legacy “Class B” network , with an implied network mask of , is defined as the prefix /16, the “/16” indicating that the mask to extract the network portion of the prefix is a 32-bit value where the most significant 16 bits are ones and the least significant 16 bits are zeros. Similarly, the legacy “Class C” network number is defined as the prefix /24; the most significant 24 bits are ones and the least significant 8 bits are zeros. Note that each 32-bit address still has (and must have) a unique interpretation. That is, each IP address must have associated with it a prefix value p for proper routing to the correct network and delivery to the correct host. However, the IP address field only provides space for the 32-bit IP address and not for the prefix value. Accordingly, each CIDR routing table entry in each Internet router contains a 32-bit IP address and a 32-bit network mask, which together give the length of the IP prefix. Clearly, it would be impractical to have an entry for each of the 232 possible IP addresses together with a mask at each router. Instead, multiple IP addresses referring to a block of CIDR addresses can be identified with a single mask, a process known as supernetting. Examples: Class B Network with an implied network mask is defined as /16 16 bits 1 and 16 bits 0 Class C Network with /24 24 bits 1 and 8 bits 0 Supernetting: Multiple IP addresses referring to a block of CIDR addresses can be identified with a single mask.

24 IPv6 Addresses IPv6 addresses are 128 bits in length. Addresses are assigned to individual interfaces on nodes, not to the nodes themselves. A single interface may have multiple unique unicast addresses. Any of the unicast addresses associated with a node’s interface may be used to uniquely identify that node. As with IPv4, IPv6 addresses use CIDR rather than address classes. IPv6 addresses are 128 bits in length. Addresses are assigned to individual interfaces on nodes, not to the nodes themselves. A single interface may have multiple unique unicast addresses. Any of the unicast addresses associated with a node’s interface may be used to uniquely identify that node. As with IPv4, IPv6 addresses use CIDR rather than address classes. The combination of long addresses and multiple addresses per interface enables improved routing efficiency over IPv4. Longer internet addresses allow for aggregating addresses by hierarchies of network, access provider, geography, corporation, and so on. Such aggregation should make for smaller routing tables and faster table lookups. The allowance for multiple addresses per interface would allow a subscriber that uses multiple access providers across the same interface to have separate addresses aggregated under each provider’s address space. IPv6 allows three types of addresses (Figure 11.2): • Unicast: An identifier for a single interface. A packet sent to a unicast address is delivered to the interface identified by that address. • Anycast: An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to an anycast address is delivered to one of the interfaces identified by that address (the “nearest” one, according to the routing protocols’ measure of distance). • Multicast: An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to a multicast address is delivered to all interfaces identified by that address. The notation for an IPv6 address uses eight hexadecimal number to represent the eight 16-bit blocks in the 128-bit address, with the numbers divided by colons. For example: FE80:0000:0000:0000:0001:0800:23E7:F5DB To make the notation more compact, leading zeroes in any hexadecimal number are omitted. For the preceding example, the result is: FE80:0:0:0:1:800:23E7:F5DB To further compress the representation, a zero or any contiguous sequence of zeroes is replaced by a double colon. For our example, the result is: FE80::1:800:23E7:F5DB Anycast Address

25 Internet Routing Protocols
Routers are responsible for receiving and forwarding packets between interconnected networks Routers make decisions based on the knowledge of the topology and traffic/delay conditions of the Internet. (based on topology leads to a static -permanent- route based on the traffic makes it a dynamic route) Must dynamically adapt to changing network conditions to avoid congested and failed portions of the network. Two key concepts to distinguish in routing function: Routing information RI: Information about topology & delays Routing algorithm: The algorithm used to make a routing decision for a particular datagram, based on the current RI The routers in an internet are responsible for receiving and forwarding packets through the interconnected set of networks. Each router makes routing decisions based on knowledge of the topology and traffic/delay conditions of the internet. In a simple internet, a fixed routing scheme is possible, in which a single, permanent route is configured for each source–destination pair of nodes in the network. The routes are fixed, or at most only change when there is a change in the topology of the network. Thus, the link costs used in designing routes cannot be based on any dynamic variable such as traffic. They could, however, be based on estimated traffic volumes between various source–destination pairs or the capacity of each link. In more complex internets, a degree of dynamic cooperation is needed among routers. In particular, routers must avoid portions of the network that have failed and should avoid portions of the network that are congested. To make such dynamic routing decisions, routers exchange routing information using a special routing protocol for that purpose. Information is needed about which networks can be reached by which routes, and the delay characteristics of various routes. In considering the routing function, it is important to distinguish two concepts: • Routing information: Information about the topology and delays of the internet • Routing algorithm: The algorithm used to make a routing decision for a particular datagram, based on current routing information

26 Autonomous Systems (AS)
To proceed with Routing Protocol let’s introduce AS: Key characteristics of an AS Set of routers and networks managed by a single organization Set of routers exchanging information via a common routing protocol Connected (in a graph-theoretic sense); that is, there is a path between any pair of nodes (except in times of failure). Interior Router Protocol (IRP) passes information between routers within an AS Exterior Router Protocol (ERP) passes information between routers in different ASs The protocol used within the AS does not need to be implemented outside of the system This flexibility allows IRPs to be custom tailored to specific applications and requirements To proceed with our discussion of routing protocols, we need to introduce the concept of an autonomous system (AS) . An AS exhibits the following characteristics: 1. An AS is a set of routers and networks managed by a single organization. 2. An AS consists of a group of routers exchanging information via a common routing protocol. 3. Except in times of failure, an AS is connected (in a graph-theoretic sense); that is, there is a path between any pair of nodes. A shared routing protocol, which we shall refer to as an interior router protocol (IRP) , passes routing information between routers within an AS. The protocol used within the AS does not need to be implemented outside of the system. This flexibility allows IRPs to be custom tailored to specific applications and requirements.

27 Application of Interior and Exterior Routing Protocols
It may happen, however, that an internet will be constructed of more than one AS. For example, all of the LANs at a site, such as an office complex or campus, could be linked by routers to form an AS. This system might be linked through a wide area network to other ASs. The situation is illustrated in Figure In this case, the routing algorithms and information in routing tables used by routers in different ASs may differ. Nevertheless, the routers in one AS need at least a minimal level of information concerning networks outside the system that can be reached. We refer to the protocol used to pass routing information between routers in different ASs as an exterior router protocol (ERP) . In general terms, IRPs and ERPs have a somewhat different flavor. An IRP needs to build up a rather detailed model of the interconnection of routers within an AS in order to calculate the least-cost path from a given router to any network within the AS. An ERP supports the exchange of summary reachability information between separately administered ASs. Typically, this use of summary information means that an ERP is simpler and uses less detailed information than an IRP. In the remainder of this section, we look at what are perhaps the most important examples of these two types of routing protocols: BGP and OSPF. Autonomous System 1 Autonomous System 2 Interior router Protocol Exterior router protocol

28 IRP & ERP IRP: Interior router protocol ERP: Exterior router protocol
Needs to build up a detailed model of the interconnection of routers within an AS in order to calculate the least-cost path from a given router to any network within the AS ERP: Exterior router protocol Supports the exchange of summary reachability information between separately administered ASs. Use of summary information means that an ERP is simpler and uses less detailed information than an IRP

29 Border Grouping Protocol (BGP)
BGP was designed to allow routers (called gateways) in different AS to cooperate in the exchange of routing information. BGP has become the preferred ERP (Exterior Router Protocol) for the internets that employ TCP/IP suite. BGP has 3 functional procedures: 1. Neighbor acquisition 2. Neighbor reachability 3. Network reachability BPG: Preferred exterior router protocol for the Internet. Neighbors: Two routers are considered as Neighboring routers if attached to the same network or share the same network. Routers in different autonomous systems may wish to exchange routing information. For this purpose, it is necessary to perform neighbor acquisition. Neighbor acquisition occurs when two neighboring routers in different autonomous systems agree to exchange routing information regularly. Protocol does not address how one router knows the address/existence of another, it is decided at the configuration time by network manager. To perform neighbor acquisition one router send an open message to another. If the target router accepts the request, it returns a keepalive message. Neighbor reachability procedure is used after neighbor relationship is established in order to maintain the relationship by each partner periodically send keepalive messages to each other. Network reachability is that each router maintains a database of the networks that it can reach and the preferred route for reaching each network. When a change is made to this database, the router broadcast an update message and all BGP routers can build up and maintain their routing information.

30 Open Shortest Path First (OSPF)
Widely used as IRP (Interior Router Protocol) in TCP/IP networks Uses link state routing algorithm Routers maintain topology database of AS Topology is express as directed graph consisting of: Router Network Carry data that neither originates nor terminates on an end system attached to this network Vertices or Nodes: Transit: Stub: Open Shortest Path First is an interior router protocol (IRP) for TCP/IP. Each router maintains descriptions of the state of its local links to networks, and transmits updates from time to time. OSPF computes a route through the internet that incurs the least cost based on a user-configurable metric of cost base on either delay, data rate, dollar cost, etc. OSPF is able to equalize loads over multiple equal-cost paths. Each router maintains a database that reflects the known topology of the autonomous system of which it is a part. The topology is expressed as a directed graph, consisting of the Vertices,… If it is not a transit network Connecting router vertices of two router connected by point-to-point link. Connecting router vertex to network vertex of directly connected. Edges

31 Open Shortest Path First (OSPF)Cnt’d
An Autonomous System Directed Graph of the Autonomous System Routers 6 & 10: Joined by a point-to-point link are represented by a pair of edges directly connected by a pair of edges in the graph. Routers 1,2,3, and 4 to network 3: Multiple routers are attached to a network. The directed graph shows all routers bi-directionally connected to the network vertex. Network 7: A single router is attached to a network, the network will appear in the graph as a stub. Host 1: an end system is directly connected to a router. Networks 12 to 15: A router is connected to other autonomous systems, then the path cost to each network in the other system must be obtained by some exterior routing protocol (ERP).Each such network is represented on the graph by a stub and an edge to the router with the known path cost.

32 Open Shortest Path First (OSPF)Cnt’d
Routers 6 & 10: Joined by a point-to-point link are represented by a pair of edges directly connected by a pair of edges in the graph. Routers 1,2,3, and 4 to network 3: Multiple routers are attached to a network. The directed graph shows all routers bi-directionally connected to the network vertex. Network 7: A single router is attached to a network, the network will appear in the graph as a stub. Host 1: an end system is directly connected to a router. Networks 12 to 15: A router is connected to other autonomous systems, then the path cost to each network in the other system must be obtained by some exterior routing protocol (ERP).Each such network is represented on the graph by a stub and an edge to the router with the known path cost. Directed Graph of the Autonomous System SPF tree for R6 An Autonomous System

33 SPF tree & Routing Table for Router R6
-A cost is associated with the output side of each router interface. -This cost is configurable by the system administrator. -Arcs on the graph are labeled with the cost of the corresponding router output interface (NOT INPUT, e.g. cost of Arc between R6 to R5 =6 but R6 to R5 = 7 therefore 6 should be taken not 7). Arcs with no label cost have a cost of 0. Arcs from networks to routers always have a cost of 0. A database of the directed graph is maintained by each router. This database is pieced together from link state messages from other routers in the internet. A router uses an algorithm to calculate the least-cost path to all destination networks. SPF tree for R6

34 Multicasting Sending a packet from a source to the members of a multicast group Multicast addresses Addresses that refer to a group of hosts on one or more networks Practical applications include: Multimedia Teleconferencing Database Distributed computation Real-time workgroup Typically, an IP address refers to an individual host on a particular network. IP also accommodates addresses that refer to a group of hosts on one or more networks. Such addresses are referred to as multicast addresses , and the act of sending a packet from a source to the members of a multicast group is referred to as multicasting . Multicasting has a number of practical applications. For example, • Multimedia: A number of users “tune in” to a video or audio transmission from a multimedia source station. • Teleconferencing: A group of workstations form a multicast group such that a transmission from any member is received by all other group members. • Database: All copies of a replicated file or database are updated at the same time. • Distributed computation: Intermediate results are sent to all participants. • Real-time workgroup: Files, graphics, and messages are exchanged among active group members in real time. Multicasting done within the scope of a single LAN segment is straightforward. IEEE 802 and other LAN protocols include provision for MAC-level multicast addresses. A packet with a multicast address is transmitted on a LAN segment. Those stations that are members of the corresponding multicast group recognize the multicast address and accept the packet. In this case, only a single copy of the packet is ever transmitted. This technique works because of the broadcast nature of a LAN: a transmission from any one station is received by all other stations on the LAN.

35 Illustration of Multicasting
In an internet environment, multicasting is a far more difficult undertaking. To see this, consider the configuration of Figure 11.5, in which a number of LANs are interconnected by routers. Routers connect to each other either over high-speed links or across a wide area network (network N4). A cost is associated with each link or network in each direction, indicated by the value shown leaving the router for that link or network. Suppose that the multicast server on network N1 is transmitting packets to a multicast address that represents the workstations indicated on networks N3, N5, and N6. Suppose that the server does not know the location of the members of the multicast group. Then one way to assure that the packet is received by all members of the group is to broadcast a copy of each packet to each network in the configuration, over the least-cost route for each network. For example, one packet would be addressed to N3 and would traverse N1, link L3, and N3. Router B is responsible for translating the IP-level multicast address to a MAC level multicast address before transmitting the MAC frame onto N3.

36 Traffic Generated by Various Multicasting Strategies
Table 11.2 summarizes the number of packets generated on the various links and networks in order to transmit one packet to a multicast group by this method. In this table, the source is the multicast server on network N1 in Figure 11.5; the multicast address includes the group members on N3, N5, and N6. Each column in the table refers to the path taken from the source host to a destination router attached to a particular destination network. Each row of the table refers to a network or link in the configuration of Figure Each entry in the table gives the number of packets that traverse a given network or link for a given path. A total of 13 copies of the packet are required for the broadcast technique. Now suppose the source system knows the location of each member of the multicast group. That is, the source has a table that maps a multicast address into a list of networks that contain members of that multicast group. In that case, the source need only send packets to those networks that contain members of the group. We could refer to this as the multiple unicast strategy. Table 11.2 shows that in this case, 11 packets are required. Both the broadcast and multiple unicast strategies are inefficient because they generate unnecessary copies of the source packet. In a true multicast strategy, the following method is used: 1. The least-cost path from the source to each network that includes members of the multicast group is determined. This results in a spanning tree of the configuration. The spanning tree is a set of all the networks that include multicast members, plus sufficient links between networks to establish a route from a source to all multicast members. 2. The source transmits a single packet along the spanning tree. 3. The packet is replicated by routers only at branch points of the spanning tree.

37 Multicast Routing Protocols
At the local level, individual hosts need a method of joining or leaving a multicast group Internet Group Management Protocol (IGMP) Used between hosts and routers on a broadcast network such as Ethernet or a wireless LAN to exchange multicast group membership information Supports two principal operations: Hosts send messages to routers to subscribe to and unsubscribe from a multicast group defined by a given multicast address Routers periodically check which multicast groups are of interest to which hosts For multicasting to work, the source of a multicast packet, together with Internet routers, must identify networks that include hosts with the given multicast address and determine a route that will reach all hosts in the group. For this purpose, a number of address discovery and routing protocols are used at different levels of the Internet architecture. At the local level, individual hosts need a method of joining or leaving a multicast group. The host needs to be able to alert a router on its local network of its membership status in a multicast group. On a broadcast network, such as Ethernet or a wireless LAN, the Internet Group Management Protocol (IGMP) is used between hosts and routers to exchange multicast group membership information. IGMP takes advantage of the broadcast nature of a LAN to provide an efficient technique for the exchange of information among multiple hosts and routers. In general, IGMP supports two principal operations: 1. Hosts send messages to routers to subscribe to and unsubscribe from a multicast group defined by a given multicast address. 2. Routers periodically check which multicast groups are of interest to which hosts.

38 Interior Routing Protocols
Routers must cooperate across an organization’s internet or across the Internet to route and deliver multicast IP packets Routers need to know which networks include members of a given multicast group Routers need sufficient information to calculate the shortest path to each network containing group members Multicast Extensions to OSPF(open shortest path first) (MOSPF) Enhancement to OSPF for the exchange of multicast routing information Protocol Independent Multicast (PIM) Designed to extract needed routing information from any unicast routing protocol and may support routing protocols that operate across multiple ASs with a number of different unicast routing protocols IGMP enables a router to know of hosts on an attached network that are using a particular multicast IP address. Next, routers must cooperate across an organization’s internet or across the Internet to route and deliver multicast IP packets. Routers must exchange two sorts of information. First, routers need to know which networks include members of a given multicast group. Second, routers need sufficient information to calculate the shortest path to each network containing group members. These requirements imply the need for a multicast routing protocol. Within an AS, a number of alternative multicast routing protocols have been developed. We mention two here. Multicast Extensions to OSPF (MOSPF) is an enhancement to OSPF for the exchange of multicast routing information. Periodically, each router floods information about local group membership to all other routers in its AS. The result is that all routers in an AS are able to build up a complete picture of the location of all group members for each multicast group. Each router constructs the shortest-path spanning tree from a source network to all networks containing members of a multicast group. Protocol Independent Multicast (PIM) provides a more general solution to multicast routing than MOSPF. As the name suggests, PIM is a separate routing protocol, independent of any existing unicast routing protocol. PIM is designed to extract needed routing information from any unicast routing protocol and may support routing protocols that operate across multiple ASs with a number of different unicast routing protocols.

39 Emergence of High-Speed LANs
In recent years two significant trends altered the role of the personal computer and therefore the requirements on the LAN: The more powerful platforms of personal computers support graphics-intensive applications and ever more elaborate graphical user interfaces to the operating system Information technology (IT) organizations have recognized the LAN as a viable and essential computer platform, resulting in the focus on network computing Traditionally, office LANs provided basic connectivity services—connecting personal computers and terminals to mainframes and midrange systems that ran corporate applications and providing workgroup connectivity at the departmental or divisional level. In both cases, traffic patterns were relatively light, with an emphasis on file transfer and electronic mail. The LANs that were available for this type of workload, primarily Ethernet and token ring, were well suited to this environment. In recent years, two significant trends altered the role of the personal computer and therefore the requirements on the LAN: 1. The speed and computing power of personal computers continued to enjoy explosive growth. These more powerful platforms support graphics-intensive applications and ever more elaborate graphical user interfaces to the operating system. 2. IT (information technology) organizations have recognized the LAN as a viable and essential computing platform, resulting in the focus on network computing. This trend began with client/server computing, which has become a dominant architecture in the business environment and the more recent Web-focused intranet trend. Both of these approaches involve the frequent transfer of potentially large volumes of data in a transaction-oriented environment. The effect of these trends has been to increase the volume of data to be handled over LANs and, because applications are more interactive, to reduce the acceptable delay on data transfers. The earlier generation of 10-Mbps Ethernets and 16-Mbps token rings is simply not up to the job of supporting these requirements.

40 The need for speed and QoS
The Emergence of High-Speed LANs Role of PCs & requirements of LANs in need for High-speed: More powerful PCs, graphical applications & GUI -MIS Recognition of LAN as a viable computing platform, -C/S computing in business, -Graphics in transaction, -interactive applications on the Internet, -need to reduce the acceptable delay on data transfer creating large volume of data to be handled over LANs. So that 10Mbps Ethernets and 16 Mbps token rings are not adequate for High-speed LANs. Effect has been to increase volume of traffic over LANs: Examples of requirements calling for high speed LAN Centralized server farm (e.g. color publishing operation) Power workgroup (e.g. software developers, CAD users transferring huge files across the Internet to share with piers.) High-speed local backbone (i.e. interconnection of these LANs) Convergence and unified communications (voice/video, and collaborative applications have increased the LAN traffic)

41 The need for speed and QoS
Corporate Wide Area Networking Greater dispersal of employee base Changing application structures Increased client/server and intranet Wide deployment of GUIs Dependence on Internet access More data must be transported off premises and into the wide area Digital Electronics Major contributors to increased image and video traffic Digital Versatile Disc (DVD) Increased storage means more information to transmit Digital Still Camera Camcorders Still Image Cameras

42 Quality of Service (QoS)
Real-time voice and video don’t work well under the Internet’s “best effort” delivery service Best effort? fair delivery service, internet treats all packets equally. During congestion packet delivery slows down. In severe congestions, packets are dropped at random to ease congestion. No distinction is made in terms of the relative importance or timeliness of traffic/packets. (ATM)-”Asynchronous Transfer Mode”, a packet switching with fix size cells of 53 octet QoS provides for varying application needs in Internet transmission

43 Categories of Traffic Elastic Inelastic
Can adjust to changes in delay and throughput access Examples: File transfer, , web access Inelastic Does not adapt well, if at all, to changes Examples: Real-time voice, audio and video

44 Inelastic Traffic Requirements
Throughput Requires a firm minimum value for throughput Delay result in acting late to disadvantage (e.g. stock trading) Delay Variation RT applications (e.g. teleconferencing) require an upper bound. As the allowable delay gets larger, real delay in delivering the data gets longer and a larger delay buffer is required at the receivers Packet loss RT applications can sustain packet loss with varying amount These requirements are difficult to meet in an environment with variable queuing delay and congestion losses.

45 Requirements of Inelastic Applications
1. Application need to state their requirements either: In advance by service request on the fly by means of fields in the IP The 1st approach is preferred because the network can anticipate demands and deny new requests if the resources are limited. 2. During congestion, elastic traffic need still be supported by: introducing a reservation protocol to deny service requests that would leave too few resources available to handle current elastic traffic

46 A Comparison of Application Delay Sensitivity and Criticality in an Enterprise
Sensitivity ==> demand Qos to provide TIMELY and HIGH data rate Criticality ==> QoS to provide RELIABILITY

47 Differentiated Services (DS)
Key characteristics: No change is required to IP Existing applications need not be modified to use DS Provides a built-in aggregation mechanism – all traffic with the same DS octet is treated the same by the network service Routers deal with each packet individually and do not have to save state information on packet flows Provide QoS on the basis of the needs of different groups of users Most widely accepted QoS mechanism in enterprise networks As the burden on the Internet grows, and as the variety of applications grows, there is an immediate need to provide differing levels of QoS to different users. The differentiated services (DS) architecture is designed to provide a simple, easy-to-implement, low-overhead tool to support a range of network services that are differentiated on the basis of performance. In essence, differentiated services do not provide QoS on the basis of flows but rather on the basis of the needs of different groups of users. This means that all the traffic on the Internet is split into groups with different QoS requirements and that routers recognize different groups on the basis of a label in the IP header. Several key characteristics of DS contribute to its efficiency and ease of deployment: • IP packets are labeled for differing QoS treatment using the 6-bit DS field in the IPv4 and IPv6 headers (Figure 8.7). No change is required to IP. • A service level agreement (SLA) is established between the service provider (internet domain) and the customer prior to the use of DS. This avoids the need to incorporate DS mechanisms in applications. Thus, existing applications need not be modified to use DS. • DS provides a built-in aggregation mechanism. All traffic with the same DS octet is treated the same by the network service. For example, multiple voice connections are not handled individually but in the aggregate. This provides for good scaling to larger networks and traffic loads. • DS is implemented in individual routers by queuing and forwarding packets based on the DS octet. Routers deal with each packet individually and do not have to save state information on packet flows. Today, DS is the most widely accepted QoS mechanism in enterprise networks.

48 Services A DS framework document lists all the following detailed performance parameters that might be included in an SLA Service performance parameters, such as expected throughput, drop probability, and latency Constraints on the ingress and egress points at which the service is provided, indicating the scope of the service Traffic profiles that must be adhered to for the requested service to be provided Disposition of traffic submitted in excess of the specified profile The DS type of service is provided within a DS domain, which is defined as a contiguous portion of the Internet over which a consistent set of DS policies are administered. Typically, a DS domain would be under the control of one administrative entity. The services provided across a DS domain are defined in a service level agreement, which is a service contract between a customer and the service provider that specifies the forwarding service that the customer should receive for various classes of packets. A customer may be a user organization or another DS domain. Once the SLA is established, the customer submits packets with the DS octet marked to indicate the packet class. The service provider must assure that the customer gets at least the agreed QoS for each packet class. To provide that QoS, the service provider must configure the appropriate forwarding policies at each router (based on DS octet value) and must measure the performance being provided to each class on an ongoing basis. If a customer submits packets intended for destinations within the DS domain, then the DS domain is expected to provide the agreed service. If the destination is beyond the customer’s DS domain, then the DS domain will attempt to forward the packets through other domains, requesting the most appropriate service to match the requested service. A DS framework document lists the following detailed performance parameters that might be included in an SLA: • Service performance parameters, such as expected throughput, drop probability, and latency • Constraints on the ingress and egress points at which the service is provided, indicating the scope of the service • Traffic profiles that must be adhered to for the requested service to be provided • Disposition of traffic submitted in excess of the specified profile

49 DS Services Provided Traffic offered at service level A will be delivered with low latency Traffic offered at service level B will be delivered with low loss 90% of in-profile traffic delivered at service level C will experience no more than 50 ms latency 95% of in-profile traffic delivered at service level D will be delivered Traffic offered at service level E will be allotted twice the bandwidth of traffic delivered at service level F Traffic with drop precedence X has a higher probability of delivery than traffic with drop precedence Y The framework document also gives some examples of services that might be provided: 1. Traffic offered at service level A will be delivered with low latency. 2. Traffic offered at service level B will be delivered with low loss. 3. Ninety percent of in-profile traffic delivered at service level C will experience no more than 50 ms latency. 4. Ninety-five percent of in-profile traffic delivered at service level D will be delivered. 5. Traffic offered at service level E will be allotted twice the bandwidth of traffic delivered at service level F. 6. Traffic with drop precedence X has a higher probability of delivery than traffic with drop precedence Y. The first two examples are qualitative and are valid only in comparison to other traffic, such as default traffic that gets a best-effort service. The next two examples are quantitative and provide a specific guarantee that can be verified by measurement on the actual service without comparison to any other services offered at the same time. The final two examples are a mixture of quantitative and qualitative.

50 Value of field is “codepoint”
Packets are labeled for handling in 6-bit DS field in the IPv4 header, or the IPv6 header Value of field is “codepoint” 6-bits allows 64 codepoints in 3 pools Form xxxxx0 - reserved for assignment as standards Form xxxx11 - reserved for experimental or local use Form xxxx01 - also reserved for experimental or local use, but may be allocated for future standards action as needed Precedence subfield indicates urgency Route selection, Network service, Queuing discipline RFC 1812 provides two categories of recommendations for queuing discipline Queue Service Congestion Control DS Field Packets are labeled for service handling by means of the 6-bit DS field in the IPv4 header or the IPv6 header (Figure 8.7). The value of the DS field, referred to as the DS codepoint , is the label used to classify packets for differentiated services. With a 6-bit codepoint, there are, in principle, 64 different classes of traffic that could be defined. These 64 codepoints are allocated across three pools of codepoints, as follows: • Codepoints of the form xxxxx0, where x is either 0 or 1, are reserved for assignment as standards. • Codepoints of the form xxxx11 are reserved for experimental or local use. • Codepoints of the form xxxx01 are also reserved for experimental or local use but may be allocated for future standards action as needed.

51 Differentiated Services (DS)
Functionality in the internet and private internets to support specific QoS requirements for a group of users, all of whom use the same service label in IP packets. All the traffic on the Internet is split into groups with different QoS requirements and that routers recognize different groups on the basis of a label in the IP header. In DS Traffic on the internet is split into groups with different QoS requirements Routers recognize different groups based on the label in the IP heads. IPv4 or IPv6 uses Type of Service

52 Differentiated Services (DS)-Cont.
Provides QoS based on “user group needs” rather than traffic flows Key characteristics of DS: Differing QoS are labeled using the “6-bit DS field” in the IPv4 and IPv6 headers Service-Level Agreements (SLA) govern DS, eliminating need for application-based assignment DS provides a built-in aggregation mechanism. All traffic with the same DS octet is treated the same by the network service DS is implemented in individual router by queuing and forwarding packets based on the DS octet

53 Allows the user to guide IP and router.
Ipv4 Header Allows the user to guide IP and router. This field was not used until recent introduction of Differentiated Services Type of Service Field

54 Ipv4 Type of Service Field
Explicit congestion notification field Differentiated service field Ipv4 Type of Service Field The DS type of service is provided within a DS domain, which is defined as a contiguous portion of the Internet over which a consistent set of DS policies are administered. Typically, a DS domain would be under the control of one administrative entity. The services provided across a DS domain are defined in a service-level agreement (SLA), which is a service contract between a customer and the service provider that specifies the forwarding service that the customer should receive for various classes of packets. A customer may be a user organization or another DS domain. Once the SLA is established, the customer submits packets with the DS octet marked to indicate the packets class. The service provider must assure that the customer gets at least the agreed QoS for each packet class. To provide that QoS, the service provider must configure the appropriate forwarding policies at each router (based on DS octet value) and must mearure the performance being provided to each class on an ongoing basis. If a customer submits packets intended for destinations within the DS domain, then the DS domain is expected to provide the agreed service. If the destination is beyond the customer’s DS domain, then the DS domain will attempt to forward the packets through other domain, requesting the most appropriate service to match the requested service. DS/ECN (8 bits): Prior to the introduction of differentiated services, this field was referred to as the Type of Service field and specified reliability, precedence, delay, and throughput parameters. This interpretation has now been superseded. The first 6 bits of the TOS field are now referred to as the DS (differentiated services) field. The remaining 2 bits are reserved for an ECN (explicit congestion notification) field.

55 DS Framework Document A DS framework document lists the following detailed performance parameters that might be included in an SLA: Service performance parameters (e.g. expected throughput, drop probability, and latency) Constraints on the ingress (right to enter) and egress (right of going out) points at which the service is provided, indicating the scope of the service Traffic profiles that must be adhered to for the requested service to be provided, such as token bucket parameters Disposition of traffic submitted in excess of the specified profile

56 DS Framework Document The framework document also gives some examples of services that might be provided: Qualitative Examples: Traffic offered at service level A will be delivered with low latency Traffic offered at service level B will be delivered with low loss Quantitative Examples: 90% of in-profile traffic delivered at service level C will experience no more than 50 ms latency 95% of in-profile traffic delivered at service level D will be delivered. Mixed Qualitative and Quantitative Examples: Traffic offered at service level E will be allotted twice the bandwidth of traffic delivered at service level F Traffic with drop precedence X has a higher probability of delivery than traffic with drop precedence Y

57 DS Octet Packets are labeled for service handling by means of the DS octet, which is placed in the Type of Service field of an IPv4 header or the Traffic Class field of IPv6 header. IP Header

58 DS Octet IPv4 Type of Service Field
Packets are labeled for service handling by means of the DS octet, which is placed in the Type of Service field of an IPv4 header or the Traffic Class field of IPv6 header. IP Header

59 DS Field DS Field: Packets are labeled for service handling by means of the 6-bit DS field, in the IPv4 or IPv6. The value of the DS field, referred to as the DS codepoint, is the label used to classify packet for differentiated services. IP Header

60 DS Field 6 bit DS field is used to label packets for service handling.
The value of the DS field is referred to as the DS codepoint. 6 bits provide 64 (i.e. 26 = 64) classes of traffic. 6 bit code point is divided into 3 categories.

61 DS Field/DS Octet Format
Request For Comments 2474 defines the DS octet as having the following format: The left most 6 bits form a DS codepoint and the rightmost 2 bits are currently unused. The DS codepoint is the DS label used to classify packets for differentiated services. With a 6-bit codepoint, there are, in principle, 64 different classes of traffic that could be defined. These 64 codepoints are allocated across 3 pools (categories) of codepoints, as follows:

62 DS Octet Format (x is either 0 or 1)
1. Standard Default Packet Class (best-effort forwarding) Backward Compatibility (or equivalent) with the IPv4 precedence service 2. Experimental/Local Use 3. Experimental/Local Use or Future Standards

63 DS Octet Format (x is either 0 or 1)
1. Standard Default Packet Class (best-effort forwarding), in order they are received, and as soon as link capacity becomes available. 2. Experimental/Local Use 3. Experimental/Local Use or Future Standards

64 DS Field xxx 000 Backward Compatibility (or equivalent) with the IPv4 precedence service. To explain the requirement of Codepoints, precedence field of IPV4 should be described. The original IPv4 includes “type of service” field which has two subfields: a 3-bit precedence subfield, and a 4-bit TOS These subfields serve complementary functions: The precedence subfield provides guidance about the relative allocation of router resources for the datagram. TOS provides guidance to the IP entity in the source or router on selecting the next hop for each datagram.

65 What is Precedence Field?
Precedence field is set to indicate the degree of urgency or priority to be associated with a datagram. If a router supports the precedence subfield, there are 3 approaches to responding: Route selection: A particular route may be selected if the router has a smaller queue for that route or if the next hop on that route supports network precedence or priority (e.g. a token ring network supports priority). Network service: If the network on the next hop supports precedence, then that service is invoked Queuing discipline: A router may use precedence to affect how queues are handled. For example a router may give preferential treatment in queues to datagrams with higher precedence.

66 Request For Comments 1812 RFC 1812 ( Requirementes for IPV4) provides recommendations for queuing discipline that falls into 2 categories. Queue Service Congestion Control • Queue service (a) Routers SHOULD implement precedence-ordered queue service. Precedence-ordered queue service means that when a packet is selected for out- put on a (logical) link, the packet of highest precedence that has been queued for that link is sent. Any router MAY implement other policy-based throughput management procedures that result in other than strict precedence ordering, but it MUST be configurable to suppress them (i.e., use strict ordering). • Congestion control. When a router receives a packet beyond its storage capacity, it must discard it or some other packet or packets. (a) A router MAY discard the packet it has just received; this is the simplest but not the best policy. (b) Ideally, the router should select a packet from one of the sessions most heavily abusing the link, given that the applicable OoS policy permits this. A recommended policy in datagrarn environments using FIFO queues is to discard a packet randomly selected from the queue. An equivalent algorithm in routers using fair queues is to discard from the longest queue. A router MAY use these algorithms to determine which packet to discard. (c) If precedence-ordered queue service is implemented and enabled, the router MUST NOT discard a packet whose IP precedence is higher than that of a packet that is not discarded. (d) A router MAY protect packets whose IP headers request the maximize reliability TOS, except where doing so would be in violation of the previous rule. (e) A router MAY protect fragmented IP packets, on the theory that dropping a fragment of a datagram may increase congestion by causing all fragments of the datagrarn to be retransmitted by the source. (f) To help prevent routing perturbations or disruption of management func- tions, the router MAY protect packets used for routing control, link control, or network management from being discarded. Dedicated routers (i.e., routers that are not also general purpose hosts, terminal servers, etc.) can achieve an approximation of this rule by protecting packets whose source or destination is the router itself. The DS codepoints of the form xxxOOO should provide a service that at rninimum is equivalent to that of the lPv4 precedence functionality.

67 DS Configuration & Operation
A DS domain consists of a set of contiguous routers, that is, it is possible to get from any router in the domain to any other router in the domain by a path that does not include routers outside the domain. Within a domain interpretation of DS codepoints is uniform, so that a uniform, consistent service is provided.

68 DS Configuration & Operation
Figure 11.6 illustrates the type of configuration envisioned in the DS documents. A DS domain consists of a set of contiguous routers; that is, it is possible to get from any router in the domain to any other router in the domain by a path that does not include routers outside the domain. Within a domain, the interpretation of DS codepoints is uniform, so that a uniform, consistent service is provided.

69 DS Configuration & Operation
In a DS domain Routers are either boundary nodes or interior nodes Interior nodes use per-hop behavior (PHB) rules Routers in a DS domain are either boundary nodes or interior nodes. Typically the interior nodes implement simple mechanisms for handling packets based on their DS codepoint values. This includes a queuing discipline to give preferential treatment depending on codepoint value, and packet-dropping rules to dictate which packets should be dripped first in the event of buffer saturation. The DS specifications refer to the forwarding treatment provided at a router as per-hop behaviour (PHR). This PHB must be available at all routers, and typically PHB is the only part of DS implementation in interior routers.

70 DS Configuration & Operation
The boundary nodes include PHB mechanisms but also more sophisticated traffic conditioning mechanisms required to provide the desired service. Thus interior routers have minimal functionality and minimal overhead in providing the DS service, while most of the complexity is in the boundary nodes. The boundary node function can also be provided by a host system attached to the domain, on behalf of the applications at that host system. Routers in a DS domain are either boundary nodes or interior nodes. Typically the interior nodes implement simple mechanisms for handling packets based on their DS codepoint values. This includes a queuing discipline to give preferential treatment depending on codepoint value, and packet-dropping rules to dictate which packets should be dripped first in thed event of buffer saturaion. The DS specifications refer to the forwarding treatment provided at a router as per-hop behaviour (PHR). This PHB must be available at all routers, and typically PHB is the only part of DS implementation in interior routers.

71 Elements of Traffic Conditioning Functions
Boundary nodes have PHB (per-hop behavior) & traffic conditioning. The traffic conditioning function consists of five elements: Classifier: Classifies based on DS codepoints Meter: Measures that the packet traffic meets packet class or exceeds Marker: re-marking packets that exceed the profile for the best-effort Shaper: Delaying packet stream as necessary. Dropper: Drops packets if the rate of packets exceeds profile specification.

72 Traffic Conditioning Function Elements:
Classifier Separates submitted packets into different classes Meter Measures submitted traffic for conformance to a profile Marker Re-marks packets with a different codepoint as needed Shaper Delays packets as necessary so that the packet stream in a given class does not exceed the traffic rate specified in the profile for that class Dropper Drops packets when the rate of packets of a given class exceeds that specified in the profile for that class The traffic conditioning function consists of five elements: • Classifier: Separates submitted packets into different classes. This is the foundation of providing differentiated services. A classifier may separate traffic only on the basis of the DS codepoint (behavior aggregate classifier) or based on multiple fields within the packet header or even the packet payload (multifield classifier). • Meter: Measures submitted traffic for conformance to a profile. The meter determines whether a given packet stream class is within or exceeds the service level guaranteed for that class. • Marker: Re-marks packets with a different codepoint as needed. This may be done for packets that exceed the profile; for example, if a given throughput is guaranteed for a particular service class, any packets in that class that exceed the throughput in some defined time interval may be re-marked for best-effort handling. Also, re-marking may be required at the boundary between two DS domains. For example, if a given traffic class is to receive the highest supported priority, and this is a value of 3 in one domain and 7 in the next domain, then packets with a priority 3 value traversing the first domain are re-marked as priority 7 when entering the second domain. • Shaper: Delays packets as necessary so that the packet stream in a given class does not exceed the traffic rate specified in the profile for that class. • Dropper: Drops packets when the rate of packets of a given class exceeds that specified in the profile for that class.

73 Relationships Between the Elements of Traffic Conditioning
After a flow is classified, its resource consumption must be measured. The metering function measures the volume of packets over a particular time interval to determine a flow’s compliance with the traffic agreement. If the host is bursty, a simple data rate or packet rate may not be sufficient to capture the desired traffic characteristics. A token bucket scheme is an example of a way to define a traffic profile to take into account both packet rate and burstiness.

74 Traffic Conditioning Diagram
Figure 11.7 illustrates the relationship between the elements of traffic conditioning. After a flow is classified, its resource consumption must be measured. The metering function measures the volume of packets over a particular time interval to determine a flow’s compliance with the traffic agreement. If a traffic flow exceeds some profile, several approaches can be taken. Individual packets in excess of the profile may be re-marked for lower-quality handling and allowed to pass into the DS domain. A traffic shaper may absorb a burst of packets in a buffer and pace the packets over a longer period of time. A dropper may drop packets if the buffer used for pacing becomes saturated.

75 Service Level Agreements (SLA)
Contract between the network provider and a customer that defines specific aspects of the service to be provided Typically includes: A description of the nature of service to be provided Expected performance level of the service Process for monitoring and reporting the service level A service level agreement (SLA) is a contract between a network provider and a customer that defines specific aspects of the service that is to be provided. The definition is formal and typically defines quantitative thresholds that must be met. An SLA typically includes the following information: • A description of the nature of service to be provided: A basic service would be IP-based network connectivity of enterprise locations plus access to the Internet. The service may include additional functions such as Web hosting, maintenance of domain name servers, and operation and maintenance tasks. • The expected performance level of the service: The SLA defines a number of metrics, such as delay, reliability, and availability, with numerical thresholds. • The process for monitoring and reporting the service level: This describes how performance levels are measured and reported.

76 Typical Framework for SLA
Figure 11.8 shows a typical configuration that lends itself to an SLA. In this case, a network service provider maintains an IP-based network. A customer has a number of private networks (e.g., LANs) at various sites. Customer networks are connected to the provider via access routers at the access points. The SLA dictates service and performance levels for traffic between access routers across the provider network. In addition, the provider network links to the Internet and thus provides Internet access for the enterprise. An SLA can be defined for the overall network service. In addition, SLAs can be defined for specific end-to-end services available across the carrier’s network, such as a virtual private network, or differentiated services.

77 IP Performance Metrics Working Group (IPPM)
Chartered by IETF (The Internet Engineering Task Force) to develop standard metrics that relate to the quality, performance, and reliability of Internet data delivery Trends dictating need: The Internet has grown and continues to grow at a dramatic rate The Internet serves a large and growing number of commercial and personal users across an expanding spectrum of applications The IP Performance Metrics Working Group (IPPM) is chartered by IETF to develop standard metrics that relate to the quality, performance, and reliability of Internet data delivery. Two trends dictate the need for such a standardized measurement scheme: 1. The Internet has grown and continues to grow at a dramatic rate. Its topology is increasingly complex. As its capacity has grown, the load on the Internet has grown at an even faster rate. Similarly, private internets, such as corporate intranets and extranets, have exhibited similar growth in complexity, capacity, and load. The sheer scale of these networks makes it difficult to determine quality, performance, and reliability characteristics. 2. The Internet serves a large and growing number of commercial and personal users across an expanding spectrum of applications. Similarly, private networks are growing in terms of user base and range of applications. Some of these applications are sensitive to particular QoS parameters, leading users to require accurate and understandable performance metrics. A standardized and effective set of metrics enables users and service providers to have an accurate common understanding of the performance of the Internet and private internets. Measurement data is useful for a variety of purposes, including • Supporting capacity planning and troubleshooting of large complex internets • Encouraging competition by providing uniform comparison metrics across service providers • Supporting Internet research in such areas as protocol design, congestion control, and quality of service • Verification of service level agreements

78 Table 11.3 (a) Sampled Metrics
Table 11.3 lists the metrics that have been defined in RFCs at the time of this writing. Table 11.3a lists those metrics which result in a value estimated based on a sampling technique. The metrics are defined in three stages: • Singleton metric: The most elementary, or atomic, quantity that can be measured for a given performance metric. For example, for a delay metric, a singleton metric is the delay experienced by a single packet. • Sample metric: A collection of singleton measurements taken during a given time period. For example, for a delay metric, a sample metric is the set of delay values for all of the measurements taken during a one-hour period. • Statistical metric: A value derived from a given sample metric by computing some statistic of the values defined by the singleton metric on the sample. For example, the mean of all the one-way delay values on a sample might be defined as a statistical metric. Src = IP address of a host Dst = IP address of a host

79 Table 11.3(b) Other Metrics
The measurement technique can be either active or passive. Active techniques require injecting packets into the network for the sole purpose of measurement. There are several drawbacks to this approach. The load on the network is increased. This in turn can affect the desired result. For example, on a heavily loaded network, the injection of measurement packets can increase network delay, so that the measured delay is greater than it would be without the measurement traffic. In addition, an active measurement policy can be abused for denial-of-service attacks disguised as legitimate measurement activity. Passive techniques observe and extract metrics from existing traffic. This approach can expose the contents of Internet traffic to unintended recipients, creating security and privacy concerns. So far, the metrics defined by the IPPM working group are all active. Table 11.3b lists two metrics that are not defined statistically. Connectivity deals with the issue of whether a transport-level connection is maintained by the network. The current specification (RFC 2678) does not detail specific sample and statistical metrics but provides a framework within which such metrics could be defined. Connectivity is determined by the ability to deliver a packet across a connection within a specified time limit. The other metric, bulk transfer capacity, is similarly specified (RFC 3148) without sample and statistical metrics but begins to address the issue of measuring the transfer capacity of a network service with the implementation of various congestion control mechanisms.

80 Model for Defining Packet Delay Variation
Figure 11.9 illustrates the packet delay variation metric. This metric is used to measure jitter, or variability, in the delay of packets traversing the network. The singleton metric is defined by selecting two packet measurements and measuring the difference in the two delays. The statistical measures make use of the absolute values of the delays.

81 Summary Chapter 11: Internet Operation Quality of service
Emergence of high-speed LANs Corporate WAN needs Internet traffic Differentiated services DS field DS configuration and operation SLAs IP performance metrics Internet addressing IPv4 addressing IPv6 addressing Internet routing protocols Autonomous systems Border gateway protocol OSPF protocol Multicasting Multicast transmission Multicast routing protocols Chapter 11 summary. Chapter 11: Internet Operation

82 Token Bucket Scheme

83 Service Level Agreements (SLA)
Contract between the network provider and customer that defines specific aspects of the service provided. Typically includes: -Service description -Expected performance level -Monitoring and reporting process -Service description A basic service would be IP-based network connectivity of enterprise locations plus access to the Internet. The service may include additional functions such as Webhosting, maintenance of domain name servers, and operation and maintenance tasks -Expected performance level The SLA defines a number of metrics, such as, delay reliability, and availability, with numerical thresholds. -Monitoring and reporting process This describes how performance levels are measured and reported.

84 SLA Example MCI Internet Dedicated Service
100% availability Average round trip transmissions of ≤ 45 ms with the U.S. Successful packet delivery rate (reliability) ≥ 99.5% Denial of Service response within 15 minutes Jitter performance will not exceed 1 ms between access routers

85 IP Performance Metrics
Three Stages of Metric Definitions -Singleton -Sample -Statistical Active techniques require injecting packets into the network Passive techniques observe and extract metrics

86 Model for Defining Packet Delay Variation

87 Token Bucket Scheme Bucket represents a counter, indicating allowable number of octets Bucket fills with octet token R := average data rate supported B := Bucket size Therefore, During any time period T: The amount of data sent < RT +B If a traffic flow exceeds some profile, several approaches can be taken. Individual packets in excess of the profile may be re-marked for lower-quality handling and allowed to pass into the DS domain. A traffic shaper may absorb a burst of packets in a buffer and pace the packets over a longer period of time. A dropper may drop packets if the buffer used for pacing becomes saturated. R:=input rate M:=output rate T: Duration of the max-rate burst B+RT = MT T = B/(M-R) sec


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