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

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Chapter 11:Internet Operation

Business Data Communications, 7e

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Objectives

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

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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)– 192.228.17.57 (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

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Network Classes

• Class A: Few networks, each with many hostsAll addresses begin with binary 0

• Class B: Medium networks, medium hostsAll addresses begin with binary 10

• Class C: Many networks, each with few hosts All addresses begin with binary 110

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Format of IP Address

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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 : 11000000 11100100 00010001

00111001Decimal representation is:

192.228.17.57 (decimal).

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• Class A Network begins with 0– Note:

Network addresses(0000 0000) and (0111 1111) are reservedTherefore Class A contains: (27 - 2 = 128 - 2 = 126) network

numbers– Range of the 1st decimal number for Class A:

1.***.***.*** to 127.***.***.***

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• Class B begin with binary 10starts from 1000 0000 (128)ends to 1011 1111 (191)i.e. Range of the 1st decimal number for Class B:

128.***.***.*** to 191.***.***.***the 2nd Byte is also part of class Bi.e. there are 214 = 16,384 Class B addresses

1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Class

B

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• Class C begin with binary 110starts from 11000000 (192)ends to 11011111 (223)

Range of the 1st decimal number for class C:192.***.***.*** to 223.***.***.*** the 2nd & 3rd Byte is also part of class CThere are 221 = 2,097,152 Class C addresses

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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.

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Subnets & Subnet Masks (Cont.)

• Then to allow the Routers within the site to function properly, each LAN is assigned a subnet number.

32-bitSource

Address

32-bitSource

Address

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• 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: 24bitClass B: 16 bit Class C: 8 bit

Network Portion:Class A: 7 + 1bitsClass B: 14+2 bitsClass C: 21+ 3 bits

Network Host

Network Subnet Host

Extended Network Number or Address Mask:

Within the subnetted network, the local Routers must route on the basis of an extended network number

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• 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

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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.


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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:


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• Example1: A datagram with the destination address 192.228.17.57 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 192.228.17.57. R1 bitwise AND the subnet mask: (1111 1111.1111 1111.1111 1111.1110 000) i.e. (255.255.255.224) and IP address (192.228.17.57) to determine that destination address 192.228.17.57 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:192.228.17.57Host number:25


Net ID/subnet ID:192.228.17.32Subnet number:1

Net ID/subnet ID :192.228.17.64Subnet number:2




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.


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IP Address & Subnet Masks

Binary Representation Dotted Decimal

IP Address 11000000.11100100.00010001.00111001

192.228.17.57

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)

1100000.11100100.00010001.00100000

192.228.17.32

Subnet number 11000000.11100100. 00010001.001 1

Host number 00000000.00000000.00000000.00011001

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1 1 0 0 0 0 0 0 . 1 1 1 0 0 1 0 0 . 0 0 0 1 0 0 0 1 . 0 0 1 1 1 0 0 1 192.228.17.57

1 1 1 1 1 1 1 1 . 1 1 1 1 1 1 1 1 . 1 1 1 1 1 1 1 1 . 1 1 1 0 0 0 0 0 255.255.255.224

1 1 0 0 0 0 0 0 . 1 1 1 0 0 1 0 0 . 0 0 0 1 0 0 0 1 . 0 0 1 0 0 0 0 0 192.228.17.32

1 1 0 0 0 0 0 0 . 1 1 1 0 0 1 0 0 . 0 0 0 1 0 0 0 1 . 0 0 1 1

0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0 . 0 0 0 1 1 0 0 1 25

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• Example2: If a datagram with destination address (192.228.17.57) 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.



Net ID/subnet ID:192.228.17.32Subnet number:1






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 0Class C Network with 192.168.99.0/2424 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 interfaceson nodes, not to the nodes themselves. A single interface may have multipleunique unicast addresses. Any of the unicast addresses associated with a node’sinterface may be used to uniquely identify that node. As with IPv4, IPv6 addressesuse CIDR rather than address classes.

Anycast Address

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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

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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

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Application of Interior and Exterior Routing Protocols

Interior router ProtocolExterior router protocol

Autonomous System 1Autonomous System 2

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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

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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

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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

NetworkTransit:

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

EdgesConnecting router vertices of two router connected by point-to-point link.

Connecting router vertex to network vertex of directly connected.

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Open Shortest Path First (OSPF)Cnt’d

An Autonomous SystemDirected Graph of the Autonomous System

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Open Shortest Path First (OSPF)Cnt’d

An Autonomous System Directed Graph of the Autonomous System

SPF tree for R6

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SPF tree & Routing Table for Router R6

Routing Table for R6SPF 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

Illustration of

Multicasting

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 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

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

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The need for speed and QoSThe 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 LAN1. 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)

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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

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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

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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

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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

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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

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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

Differentiated Services (DS)

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 IPExisting applications need not be modified to use DSProvides a built-in aggregation mechanism – all traffic with the same DS octet is treated the same by the network serviceRouters deal with each packet individually and do not have to save state information on packet flows

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

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

DS FieldPackets 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

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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.

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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

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Ipv4 Header

Type of Service Field

Allows the userto guide IP and router.

This field was not used until recent

introduction of Differentiated Services

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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

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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

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DS Framework DocumentThe 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

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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

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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.

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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:

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DS Octet Format (x is either 0 or 1)

x x x x x 0 U U

1. Standard

x x x x 1 1 U U2. Experimental/Local Use

x x x x 0 1 U U3. Experimental/Local Useor Future Standards

0 0 0 0 0 0 U U

Default Packet Class(best-effort forwarding)

x x x 0 0 0 U UBackward Compatibility (or equivalent) with the IPv4 precedence service

8 7 6 5 4 3 2 1

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DS Octet Format (x is either 0 or 1)

x x x x x 0

1. Standard

2. Experimental/Local Use

3. Experimental/Local Useor Future Standards

x x x x 1 1

00 00 00 Default Packet Class (best-effort forwarding), in order they are received, and as soon as link capacity becomes available.

x x x x 0 1

6 5 4 3 2 1

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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.

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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.

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Request For Comments 1812

• RFC 1812 ( Requirementes for IPV4) provides recommendations for queuing discipline that falls into 2 categories.

– Queue Service– Congestion Control

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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

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69


• In a DS domain• Routers are either boundary nodes or interior

nodes• Interior nodes use per-hop behavior (PHB)

rules

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• 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.

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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

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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.

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.

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Traffic Conditioning Diagram

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

Typical Framework for SLA

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

Table 11.3(b) Other Metrics

Model for Defining Packet Delay Variation

Summary Internet addressing

IPv4 addressing IPv6 addressing

Internet routing protocols Autonomous systems Border gateway protocol OSPF protocol

Multicasting Multicast transmission Multicast routing

protocolsChapter 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

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Token Bucket Scheme

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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

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SLA ExampleMCI 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

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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

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Model for Defining Packet Delay Variation

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Token Bucket SchemeBucket represents a counter, indicating allowable number of octetsBucket fills with octet tokenR := average data rate supportedB := Bucket sizeTherefore, 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

Documents

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