Presentation on theme: "1 Chapter 11: Internet Operation Business Data Communications, 7e."— Presentation transcript:
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 –11000000 11100100 00010001 00111001 (binary) –188.8.131.52 (decimal)
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
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
7 Network Classes (cont.) byteIP 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 : 11000000 11100100 00010001 00111001 Decimal representation is: 184.108.40.206 (decimal).
8 Network Classes (cont.) Class A Network begins with 0 –Note: Network addresses (0000 0000) and (0111 1111) are reserved Therefore Class A contains: (2 7 - 2 = 128 - 2 = 126) network numbers –Range of the 1 st decimal number for Class A: 1.***.***.*** to 127.***.***.***
9 Network Classes (cont.) Class B begin with binary 10 starts from 1000 0000 (128) ends to 1011 1111 (191) i.e. Range of the 1 st decimal number for Class B: 128.***.***.*** to 191.***.***.*** the 2 nd Byte is also part of class B i.e. there are 2 14 = 16,384 Class B addresses Class B
10 Network Classes (cont.) Class C begin with binary 110 starts from 11000000 (192) ends to 11011111 (223) Range of the 1 st decimal number for class C: 192.***.***.*** to 223.***.***.*** the 2 nd & 3 rd Byte is also part of class C There are 2 21 = 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
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. Host Portion: Class A: 24bit Class B: 16 bit Class C: 8 bit Network Portion: Class A: 7 + 1bits Class B: 14+2 bits Class C: 21+ 3 bits NetworkHost Network SubnetHost Extended Network Number or Address Mask: Within the subnetted network, the local Routers must route on the basis of an extended network number
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 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. Subnets & Subnet Masks (Cont.)
17 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 192.228.17.X, where 192 (1100 0000) is the network number and x the host number. Example of Subnetworking: Subnets & Subnet Masks (Cont.)
19 Example1: A datagram with the destination address 220.127.116.11 arrives at R1 from the rest of the internet or from LAN Y. R1 has addresses of LAN X, LAN Y, LAN Z. R1 doesnt know about hosts internal to these LANs. In order to determine where R1 should send the datagram with receiver address 18.104.22.168. R1 bitwise AND the subnet mask: (1111 1111.1111 1111.1111 1111.1110 000) i.e. (255.255.255.224) and IP address (22.214.171.124) to determine that destination address 126.96.36.199 refers to subnet: (11000000.111.00100.00010001.001) i.e. 1, which is LAN X, and so forward the datagram to LAN X. IP Address:188.8.131.52 Host number:25 IP Address:184.108.40.206 Host number:1 Net ID/subnet ID:220.127.116.11 Subnet number:1 Net ID/subnet ID :18.104.22.168 Subnet number:2 IP Address:22.214.171.124 Host number:1 Net ID/subnet ID :126.96.36.199 Subnet number:3 IP Address:188.8.131.52 Host number:1 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. Subnets & Subnet Masks (Cont.)
20 IP Address & Subnet Masks Binary Representation Dotted Decimal IP Address 11000000.11100100.00010001.001110 01 184.108.40.206 7 Subnet Mask for both R1 & R2 Routers 111111.1111111.11111111.11100000 255.255.255. 224 Bitwise AND of address and mask (resultant network/subnet number) 1100000.11100100.00010001.0010000 0 220.127.116.11 2 Subnet number 11000000.11100100. 00010001.001 1 Host number 00000000.00000000.00000000.000110 01 25 11000000.11100100.00010001.00111001 18.104.22.168 11111111.11111111.11111111.11100000 255.255.255.224 11000000.11100100.00010001.00100000 22.214.171.124 11000000.11100100.00010001.001 1 00000000.00000000.00000000.00011001 25
22 Example2: If a datagram with destination address (126.96.36.199) 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:188.8.131.52 Host number:25 IP Address:184.108.40.206 Host number:1 Net ID/subnet ID:220.127.116.11 Subnet number:1 Net ID/subnet ID :18.104.22.168 Subnet number:2 IP Address:22.214.171.124 Host number:1 Net ID/subnet ID :126.96.36.199 Subnet number:3 IP Address:188.8.131.52 Host number:1 Subnets & Subnet Masks (Cont.)
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 Examples: Class B Network with an implied network mask 255.255.0.0 is defined as 172.16.0.0/16 16 bits 1 and 16 bits 0 Class C Network with 192.168.99.0/24 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.
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 nodes interface may be used to uniquely identify that node. As with IPv4, IPv6 addresses use CIDR rather than address classes. Anycast Address
25 Internet Routing Protocols Routers are responsible for receiving and forwarding packets between interconnected networks topologytraffic/delayRouters 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
26 Autonomous Systems (AS) To proceed with Routing Protocol lets 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
27 Application of Interior and Exterior Routing Protocols Interior router Protocol Exterior router protocol Autonomous System 1 Autonomous System 2
28 IRP & ERP IRP: Interior 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
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 Transit: Stub: Vertices or Nodes: Carry data that neither originates nor terminates on an end system attached to this network If it is not a transit network Edges Connecting router vertices of two router connected by point-to-point link. Connecting router vertex to network vertex of directly connected.
31 Open Shortest Path First (OSPF) Cntd An Autonomous System Directed Graph of the Autonomous System
32 Open Shortest Path First (OSPF) Cntd An Autonomous System Directed Graph of the Autonomous System SPF tree for R6
33 SPF tree & Routing Table for Router R6 Routing Table for R6 SPF tree for R6
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
Traffic Generated by Various Multicasting Strategies
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
Interior Routing Protocols Routers must cooperate across an organizations 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
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
40 The need for speed and QoS The Emergence of High-Speed LANs Role of PCs & requirements of LANs in need for High-speed: 1.More powerful PCs, graphical applications & GUI 2.-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 1.Centralized server farm (e.g. color publishing operation) 2.Power workgroup (e.g. software developers, CAD users transferring huge files across the Internet to share with piers.) 3.High-speed local backbone (i.e. interconnection of these LANs) 4.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 dont work well under the Internets 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 –Can adjust to changes in delay and throughput access –Examples: File transfer, e-mail, 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
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 Sensitivity ==> demand Qos to provide TIMELY and HIGH data rate Criticality ==> QoS to provide RELIABILITY A Comparison of Application Delay Sensitivity and Criticality in an Enterprise
Provide QoS on the basis of the needs of different groups of users Most widely accepted QoS mechanism in enterprise networks 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
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
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 precedenc e X has a higher probability of delivery than traffic with drop precedenc e Y
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
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.
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 Ipv4 Header Type of Service Field Allows the user to guide IP and router. This field was not used until recent introduction of Differentiated Services
54 Ipv4 Type of Service Field 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. Differentiated service field Explicit congestion notification field
55 DS Framework Document performance parametersA 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: 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 Quantitative Examples: 3.90% of in-profile traffic delivered at service level C will experience no more than 50 ms latency 4.95% of in-profile traffic delivered at service level D will be delivered. Mixed Qualitative and Quantitative Examples: 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
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 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 IPv4 Type of Service Field
59 DS Field 6-bitDS field DS codepoint 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. 2 6 = 64) classes of traffic. 6 bit code point is divided into 3 categories.
61 DS Field/DS Octet Format R equest F or C omments 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 2. Experimental/Local Use 3. Experimental/Local Use or Future Standards Default Packet Class (best-effort forwarding) Backward Compatibility (or equivalent) with the IPv4 precedence service
63 DS Octet Format (x is either 0 or 1) 1. Standard 2. Experimental/Local Use 3. Experimental/Local Use or Future Standards 00 00 00 Default Packet Class (best-effort forwarding), in order they are received, and as soon as link capacity becomes available.
64 DS Field 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. xxx 000 Backward Compatibility (or equivalent) with the IPv4 precedence service.
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: 1.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). 2.Network service: If the network on the next hop supports precedence, then that service is invoked 3.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 R equest F or C omments 1812 RFC 1812 ( Requirementes for IPV4) provides recommendations for queuing discipline that falls into 2 categories. –Queue Service –Congestion Control
67 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. DS Configuration & Operation
69 DS Configuration & Operation In a DS domain Routers are either boundary nodes or interior nodes Interior nodes use per-hop behavior (PHB) rules
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.
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.
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
73 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 flows 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. Relationships Between the Elements of Traffic Conditioning A token bucket scheme is an example of a way to define a traffic profile to take into account both packet rate and burstiness.
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
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
Table 11.3 (a) Sampled Metrics Src = IP address of a host Dst = IP address of a host
Internet addressing IPv4 addressing IPv6 addressing Internet routing protocols Autonomous systems Border gateway protocol OSPF protocol Multicasting Multicast transmission Multicast routing protocols 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
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
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
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 R:=input rate M:=output rate T: Duration of the max-rate burst B+RT = MT T = B/(M-R) sec