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Ch 5 : Multimedia Network Standardization, QoS, Access Media

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1 Ch 5 : Multimedia Network Standardization, QoS, Access Media
Science and Technology Faculty Informatics Arini, ST, MT Com

2 Contents Multimedia Presentation
Charactersitic of Multimedia Application Networked Multimedia Classification Multimedia Networked Consideration of Networked Multimedia Standardizations QoS Metrics Media Access

3 I. Multimedia Presentation
Local vs Networked multimedia Local Multimedia : Storage and presentation of multimedia information in standalone computers Networked Multimedia Involve transmission and distribution of multimedia information on the network (wired and wireless)

4 II. Networked Multimedia Classification
Real Time: Require bounds on end-to-end packet delay & jitter. Subdivided into: Discrete Media: MSN/Yahoo Messenger Continuous Media: Continuous message stream with inter-message dependency. Further divided into: Delay Tolerant (called : streaming) e.g Internet webcast Delay Intolerant (called : interactive) e.g. audio, video streams in conferencing systems Non-Real Time: No strict delay constraints (e.g. text, image files) May be highly sensitive to errors

5 II. Networked Multimedia Classification Streaming :
Live media transmission system (live broadcasting) Send stored media across the network (On Demand file) Hybrid (Progressive Download) : interactive

6 II. Networked Multimedia Classification Streaming :
Live media transmission system (live broadcasting) Capture, compress, and transmit the media on the fly (TV Streaming) Captured” from live camera, radio, T.V. 1-way communication, maybe multicast Examples: concerts, radio broadcasts, lectures RealPlayer, Media Player and Quicktime Limited interactivity… Delays of 1 to 10 seconds or so Not so sensitive to jitter

7 II. Networked Multimedia Classification Streaming :
Live media transmission system (live broadcasting) Send stored media across the network (On Demand file) Media is pre-compressed and stored at the server. This system delivers the stored media to one or multiple receivers (video conferencing, Youtube) Examples: pre-recorded songs, video-on-demand RealPlayer, Media Player and Quicktime Interactivity, includes pause, ff, rewind… Delays of 1 to 10 seconds or so Not so sensitive to jitter

8 II. Networked Multimedia Classification
Streaming : Live media transmission system (live broadcasting) Send stored media across the network (On Demand file) Hybrid (Progressive Download) : (called : interactive) 2-way communication Examples: Internet phone, video conference Very sensitive to delay < 150ms very good < 400ms ok > 400ms crappy

9 II. Networked Multimedia Classification

10 Digital Media: from desktop, to Internet, to hand-helds, to wireless, and to Peer-to-Peer
Edge server Data Farms / Storage Web Server Apps/DB Server E-Commerce Server Media Server Wireless Comm Server

11 III. Characteristics of multimedia Application
Interactive, High Performance, Enriched Media, Large data volume, Real-time property (Continuous display). How to transmit across network? Properties of current Internet Best effort network, cannot guarantee quality of multimedia applications Limitation of bandwidth Heterogeneity Different user requirements Different user network conditions

12 IV. Multimedia Networking
Multimedia networking deals with the design of networks that can handle multiple media types (see II. Networked Multimedia classification) with ease and deliver scalable performance Points : Required The Standardization (at a graph bellow) Technology Multimedia Supporting Consideration of Networked Multimedia A measure of the ability of network and computing systems to provide different levels of services to selected applications and associated network flows is Quality of Service (QoS)


14 4.2. Technologies of Multimedia Networking
Media compression – reduce the data volume Address the1st challenge Image compression Video compression Audio compression Multimedia transmission technology Address the 2nd and 3rd challenges Protocols for real-time transmission Rate / congestion control Error control

15 4.3. Consideration of Networked Multimedia
Network Requirements a. Traffic Requirements: Have implications for basic Internet infrastructure Delay & Jitter Bandwidth Reliability b. Functional Requirements: Require enhancements to TCP/IP stack in the form of additional network protocols Multicasting Mobility Session Management

16 4.3. Consideration of Networked Multimedia
Requirements Delay & Jitter Metrics Packet Processing delay Packet Transmission delay Propagation delay Routing and Queuing Delay Bandwidth Reliability Multicasting Session Management Security Mobility

17 4.3.1. Delay Related Metrics Maximum end to end delay Delay variance
Jitter : non-monotonic variation in delay in given stream For a video stream jitter would result in a shaky picture Jitter can be removed by buffering at the receiver side Skew: constantly increasing difference between the expected arrival time and the actual arrival time For a video stream skew could be a slower or faster moving picture

18 4.3.1. Delay Packet Processing Delay
Constant amount of delay at both source and destination A/D, D/A conversion time and time taken to packetize it through different layers of protocols Typically a characteristic of the operating system and the multimedia application Delay can become significant under high load conditions Reductions in delay imply software enhancements including use of multimedia operating systems that provide enhanced resource, file and memory management with real-time scheduling

19 4.3.1. Delay Packet Transmission Delay
Time taken by the physical layer at the source to transmit packets. Depends on Number of active sessions. Typically physical layer processes packets in FIFO order. Delay can become significant if OS does not support real-time scheduling for multimedia traffic MAC access delay: Widespread Ethernet networks cannot provide any firm guarantees on medium access delay due to inherent indeterminism in CSMA/CD (carrier sense multiple access/collision detection). Isochronous Ethernet (802.9) integrated voice data LAN and demand priority Ethernet (802.12) provide QoS but market potential remains low

20 4.3.1. Delay Propagation Delay
Flight time of packets – limited by speed of light. Can’t do anything about it For a distance of 20,000 km this would be about sec Significant part of a desirable ~200 msec delay budget

21 4.3.1. Delay Routing and Queuing Delay
Best-effort Internet treats every packet equally Packets arriving at a queue have to wait a random amount of time depending on current router load Delay is variable and is the major contributor to jitter Techniques to reduce this include IntServ MPLS DiffServ

22 Audio & Video Quality Requirements

23 4.3.2. Bandwidth Requirements
Multimedia traffic streams have high bandwidth Uncontrolled transmissions at high rates can cause heavy congestion in the network Elastic applications that use TCP take advantage of built in congestion control Most multimedia applications use UDP for transmitting media streams To remove these shortcomings an enhanced internet service model would require Admission control: application must first get permission from some authority to send traffic at a given rate with given traffic characteristics Bandwidth reservation: if admission is given, appropriate resources (buffers, bandwidth) will get reserved along the path Traffic policing mechanisms: to ensure that applications do not send data at a rate higher than what was negotiated

APPLICATION PERFORMANCE DIMENSIONS Bandwidth Sensitivity to Delay Jitter Loss IP Telephony Low High Med Video Conferencing Streaming media Low-High Client / Server Transactions High1 (store/forward) Best Effort Traffic Low-Med

25 Bandwidth Text Bandwidth requirements depend on size
Can be easily reduced by compression techniques Some text applications require complete freedom from loss & errors – use TCP. E.g. FTP Others are error and loss tolerant – use UDP e.g. instant messaging

26 Bandwidth Audio Bandwidth requirements depend on dynamic range and/or spectrum Narrowband speech ( Hz) 6.4 Kbps (G.723.3) to 64 Kbps (G.711) Wideband audio (CD quality music) KHz Kbps (MP3) Can tolerate 1-2% packet loss Real-time nature depends on extent of interactivity VoIP requires strong bounds on delay/jitter (Real-Time Intolerant) < 250 ms end to end delay Internet Webcast is more delay/jitter tolerant (Real-Time Tolerant)

27 Bandwidth Video High bandwidth requirements
Efficient compression schemes MPEG-I (1.2 Mbps) VCR quality compression MPEG-II (3-100 Mbps) broadcast quality video, HDTV MPEG-IV (64 Kbps) for low bandwidth video compression; supports audio, video, graphics, animation, text H.261 (px64 Kbps) H.263 (18-64 Kbps) Error requirements and real-time characteristics similar to audio

28 Bandwidth Graphics and Animation
Examples: Digital images, flash presentations Large in size but lend themselves well to compression Progressive compression techniques enable image to be initially displayed in low-quality and gradually improved as more information is received Error-tolerant and can sustain packet loss provided application knows how to deal with packet loss No real-time constraints

29 4.3.3. Reliability Pertains to loss and corruption of data
Can be measured in terms of loss probability Requires methods for dealing with erroneous/lost data Error correction Sender Based Repair Active : ARQ Passive : Interleaving, FEC Error Concealment Error Recovery for Different Applications Admission Control Traffic Shaping/Policing Packet Classification Packet Dropping

30 a. Error Correction Sender Based Repair
Active Repair - Automatic retransmission request (ARQ) Suitable for error intolerant applications Passive Repair Interleaving FEC: Forward Error Correction. Media Independent – independent of the content/nature of the stream Media Dependent - use knowledge of the stream in the repair process Error Concealment (Receiver Based Repair)

31 Passive Repair : Interleaving
Can be used when media unit size is smaller than packet size (as may be the case with audio) and end-to-end delay is not important Units are resequenced before transmission so that originally adjacent units are separated by a guaranteed distance and returned to original order at the receiver Disperses the effect of packet loss – loss of a single packet would causes multiple smaller gaps among original media units In case of audio a phoneme originally encapsulated in one packet would get split across multiple packets Loss of small parts of several phonemes is easier to deal with than loss of entire phonemes Disadvantage: increased latency – not well suited for interactive applications Advantage: does not increase bandwidth usage – does well for non-interactive use

32 Passive Repair : FEC Introduce repair data in traffic from which lost packets may be recovered Media Independent: use block or algebraic codes to produce additional packets which aid in loss recovery Each code takes a codeword of k data packets and generates n-k additional check packets i-th bit in check packet is generated from the i-th bits of each associated data packet Parity Coding: XOR is applied across groups of packets to generate parity packets Reed-Solomon Coding: Based on properties of polynomials over particular number bases Take a set of codewords and use these as coefficients of a polynomial f(x) The transmitted codeword is determined by evaluating the polynomial for all nonzero values of x over the number base Disadvantage: Cause additional delay, increase bandwidth usage and exacerbate congestion

33 Passive Repair : Media Dependent FEC
Exploit media characteristics For audio, could send each unit of audio in multiple packets Primary encoding: first transmission Secondary encoding: additional transmissions Secondary encoding could be of lower bandwidth and quality than the primary coding May not be necessary to transmit FEC for every packet due to nature of media Advantage : low latency – only single packet delay added Suitable for interactive applications * A Survey of Packet Loss Recovery Techniques for Streaming Audio, Colin Perkins et al IEEE Network Sep/Oct 1998

34 Error Concealment Producing a replacement for a lost packet which is similar to the original Work for relatively small loss rates (< 15%) and for small packets (4-40 ms) Types in increasing order of computational cost and improved performance: Insertion based: insert a fill-in packet that contains silence, noise or a repitition of an adjacent packet Interpolation-based: some form of pattern matching and interpolation to derive the missing packet (waveform, pitch or timescale based) Regeneration-based: derive decoder state from packets surrounding the loss and generate a lost packet from that (model based recovery)

35 b. Error Recovery for Different Applications
Non-interactive Applications Multicasts (e.g. radio) Interleaving is suitable (bandwidth efficient, though high latency) Use error concealment – repetition with fading Media-independent FEC better than a retransmission based scheme Interactive Applications (e.g. IP telephony) Media Dependent FEC Error concealment using packet repetition

36 c. Admission Control Pro-active form of congestion control
Takes requested traffic description as input including (in terms of leaky bucket parameters Maximum burst size ( b = bucket size) Peak rate Average rate Decides to accept or reject a flow including consideration of impact to existing flows Admission control unit must also use measurements of current network load and packet delay in its admission decisions

37 d. Traffic Shaping/Policing
Token bucket algorithm is used for traffic shaping. Limits the average rate and allows a degree of burstiness. Token bucket depth ‘b’ in which tokens are collected at rate ‘r’ When bucket becomes full extra tokens are dropped Source can send data only if it can grab and destroy sufficient tokens from the bucket Leaky bucket algorithm is used for traffic policing, in which excessive traffic is dropped Bucket depth ‘b’ with hole at the bottom If bucket is full extra packets are dropped

38 e. Packet Classification
In order to prevent all packets from being treated equally some mechanism to distinguish between real-time and non-real time packets is needed Done by packet marking e.g. use Type of Service (ToS) field in IP header MPLS uses short labels

39 f. Packet Scheduling FIFO scheduling traditionally used in routers needs to be replaced with more sophisticated queuing Disadvantage: possible starvation of low priority flows Weighted Fair Queuing has different queues for different classes. However every queue is assigned a certain weight. Packets in that queue get a fraction of the total bandwidth proportional to their weight

40 g. Packet Dropping Routers can randomly drop packets under congestion
This can be a problem since certain packets may carry more information than others

41 4.3.4. Multicasting – IP Multicast
Can be done in several ways Send packets to multicast IP address (Class D) Hosts willing to receive multicast messages for particular multicast groups inform immediate-neighboring routers using IGMP Multicast routers exchange group information using a variety of algorithms: Flooding Spanning tree Reverse path broadcasting Reverse path multicasting Protocols that use some of these algorithms include Distance Vector Muticast Routing Protocol (DVMRP) Multicast extension to Open Shortest Path First (MOSPF) Protocol Independent Multicast (PIM)

42 4.3.4. Multicasting – IP Multicast
Application Layer Multicasting SIP and H.323 support multicasting through a multi-point control unit that provides mixing and conferencing functionality

43 4.3.5. Session Management Media Description
Session Description Protocol Session Announcement Session Announcement Protocol Session Control

44 4.3.5. Session Management Media Description
Enables application to distribute session information Media Type Encoding Scheme Session Start Time Session Stop Time IP Addresses of involved hosts

45 4.3.5. Session Management Session Description Protocol
SDP developed by IETF can be used to describe media type, media encoding used for session More of a description syntax than a protocol – augmented by SIP for media negotiation Media descriptions encoded in text format SDP message contains a series of lines called fields with single letter abbreviations. Each field has a <tag>=<value> format Session Announcement Allows participants to announce future sessions E.g. for Internet radio stations to distribute information about scheduled shows

46 4.3.5. Session Management Session Announcement Protocol
Used for advertising multicast conferences and sessions SAP announcer periodically multicasts announcement packets to a well-known multicast address and port (9875) with the same scope as the session being announced Recipients of announcement are also potential recipients of sessions being advertised Multiple announcers may announce a single session for more robustness Announcement interval chosen to ensure total bandwidth used by announcements is below a pre-configured limit Each announcer is expected to listen to other announcements in order to determine the total number of sessions being announced on a group Involves large startup delay before complete set of announcements is heard by a listener Contains mechanisms for ensuring integrity, authenticating the origin and encryption of announcements

47 4.3.5. Session Management Session Control
Information in multiple media streams may be inter-related Network must guarantee to maintain such relationships – Multimedia Synchronization Can be achieved by putting timestamps in every media packet Internet multimedia users may want to control playback of continuous media – similar to what a VCR or CD player provides E.i : RTP, RTCP, RTSP, H.323, SIP

48 A. Session Control - RTP RTP runs on top of UDP
Carries chunks of real-time (audio/video) data Provides Sequencing: sequence number in RTP header helps detect lost packets Payload Identification: payload identifier included in each RTP packet describes encoding of the media Frame Indication: video and audio sent in logical units called frames. A frame marker bit indicates the beginning and end of a frame Source Identification: To identify the originator of a frame in a multicast session a Synchronization Source (SSRC) identifier Intramedia Synchronization: To compensate for different delay and jitter for packets within the same stream RTP provides timestamps, which are needed by play-out buffers Additional media information can be inserted using profile headers and extensions

49 B. Real-Time Control Protocol - RTCP
RTCP is a control protocol that works in conjunction with RTP Provides useful statistics: packets sent, lost, jitter, round-trip time Sources can use this to adjust their data rate Other information includes address, phone number, name – allow users to know the identities of other users in the session

50 C. Real-Time Streaming Protocol
RTSP is an out-of-band control protocol that allows the media player to control the transmission of the media stream including functions such as Pause Resume Repositioning Playback

51 D. H.323 Umbrella recommendation that specifies components, protocols and procedures multimedia conferencing over a packet network Defines four components Terminals: These are the endpoints Gateway: For interoperation between clients using different H.32x flavors Gatekeeper: Control functions including admission control, bandwidth management, call routing Multi-point Control Unit: For point to multipoint conferencing capability Uses H.245 to determine common capabilities of terminals Two kinds of call control models Gatekeeper routed (preferred mode in carrier environments) Direct (not scalable)

52 E. Session Initiation Protocol - SIP
Application-layer signaling protocol for initiating, modifying and terminating interactive sessions. Defined in RFC 3261 Does not define what a “session” is. Text-encoded protocol based on elements from HTTP and SMTP “SIP supports five facets of establishing and terminating multimedia communications: User location: determination of the end system to be used for communication; User availability: determination of the willingness of the called party to engage in communications; User capabilities: determination of the media and media parameters to be used; Session setup: "ringing", establishment of session parameters at both called and calling party; Session management: including transfer and termination of sessions, modifying session parameters, and invoking services” (RFC 3261)

53 SIP – Key Capabilities A stateful SIP server can split or "fork" an incoming call so that several extensions can be rung at once The first extension to answer can take the call SIP can return different media types within a single session Participants can be invited to existing sessions Media can be added (removed from) an existing session Supports mobility

54 Elements of a SIP Network
Three main elements in a SIP network User Agent: end device in a SIP network. User Agent Client (UAC) initiates requests. User Agent Server (UAS) responds to requests. Roles may change in the course of a session. Server: There are three main types Proxy: Receives requests from UAs or other proxy and forward the request to another location Redirect: Receives a request from a UA or proxy and returns a redirect response (3XX) indicating where the request should be retried Registrar: Receives SIP registration requests and updates UA’s information to a location server (e.g. LDAP server) or other database Location Server: General term for a database. Non-SIP protocol is used to interact with it.

55 SIP Methods SIP Methods are commands supported by SIP:
INVITE: Invites a user to a call ACK: Used to facilitate reliable message exchange for INVITEs BYE: Terminates a connection between users or declines a call CANCEL: Terminates a request, or search, for a user OPTIONS: Solicits information about a server's capabilities REGISTER: Registers a user's current location INFO: Used for mid-session signallingSIP responses The following are SIP responses: 1xx Informational (e.g. 100 Trying, 180 Ringing) 2xx Successful (e.g. 200 OK, 202 Accepted) 3xx Redirection (e.g. 302 Moved Temporarily) 4xx Request Failure (e.g. 404 Not Found, 482 Loop Detected) 5xx Server Failure (e.g. 501 Not Implemented) 6xx Global Failure (e.g. 603 Decline)

56 SIP Signaling

57 SIP & H.323 Comparison SIP is largely equivalent to the Q.931 and H.225 components of H.323 ( SIP H.323 PHILOSOPHY "New World" - a relative of Internet protocols - simple, open and horizontal "Old World" - complex, deterministic and vertical IETF ITU Carrier-class solution addressing the wide area Borne of the LAN - focusing on enterprise conferencing priorities CHARACTERISTICS A simple toolkit upon which smart clients and applications can be built. It re-uses Net elements (URLs, MIME and DNS) H.323 specifies everything including the codec for the media and how you carry the packets in RTP Leaves issues of reliability to underlying network Assumes fallibility of network - an unnecessary overhead SIP messages are formatted as text. (Text processing lies behind the web and ) Binary format doesn't sit well with the internet - this adds complexity SIP allows for standards-based extensions to perform specific functions. Extensions are added by using vendor-specific non-standard elements Hierarchical URL style addressing scheme that scales Addressing scheme doesn't scale well Minimal delay - simplified signalling scheme makes it faster Possibilities of delay (up to 7 or 8 seconds!) Slim and Pragmatic The suite is too cumbersome to deploy easily

58 SIP & H.323 Comparison SIP H.323 SERVICES Standard IP Centrex services
H.323 SERVICES Standard IP Centrex services Ability to 'fork' calls Not possible in the existing standard User profiling - 'Unified messaging' Presence management Unique ability to mix media (e.g. IVR) Cannot mix media within a session URLs can be embedded in web browsers and tools H.323 has no URL format Works smoothly with media gateway controllers controlling multiple gateways - crucial in a multi-operator environment "Shoehorn" interworking with SS7 is problematic - H.323 has trouble connecting calls to and from PSTN endpoints Seamless interaction with other media - services are only limited by the developers imagination Services are nailed-down and constricted - voice only ceiling STATUS Industry endorsed Popularity due to the fact that it was the first set of agreed-upon standards Many vendors developing products The majority of existing IP telephony products rely on the H.323 suite

59 4.3.6. Security Integrity Authenticity Encryption
Intellectual rights protection Digital watermarking techniques embed extra information into multimedia data Imperceptible to normal user and irremovable

60 Security At the IP layer security can be provided by IPSec
Secure RTP (RFC 3711) Provides 128 bit AES encryption Confidentiality, authentication and replay protection SHA-1 (Secure Hash Algorithm) for authentication

61 4.4. QoS Quality of Service (QoS) methods aim at trading quality vs. resources to meet the constraints dictated by the user, the functionality and the platform. QoS originally developed in network communication, and recently extended to the domain of multimedia communication. QoS relevant in multimedia scalable systems, where the resources and the functionality can be controlled by a set of parameters. Match the performance needs of applications to available network resources

62 Quality of Experience (QoE) is subjective and relates to the actual perceived quality of a service by the user QoE is the fundamental determinant of performance for any technology and is the user perception of quality This applies to voice, multimedia, and data Quality of service (QoS) is an optimization tool designed to deliver a certain Quality of Experience (QoE) by ensuring that network elements apply consistent treatment to traffic flows as they traverse the network QoS is a mechanism to help achieve QoE.

63 QoS mechanisms can only be effective, must implement the critical concepts are:
Separate transmission medium in each direction Sending device has complete control over what is sent No other device can interfere with the transmission

64 QoS doesn’t improve all network traffic performance.
Much has been written about QoS, and can be summarized into three primary jobs: To minimize end-to-end delay through the network (VoIP traffic to front of the line) To minimize the variability in end-to-end delay, that is, jitter (VoIP traffic to front of the line) To prevent packet loss (separate queues for the VoIP traffic) QoS doesn’t improve all network traffic performance.

65 From three primary jobs above will be delivered into :
QoS Parameter Metrics From three primary jobs above will be delivered into : availability delay (latency) delay variation (jitter) throughput (average and peak rates) packet loss

66 4.4.2. IETF QoS Efforts Policy based IP QoS Solutions
Integrated Services (RSVP protocol): flow based Differentiated Services (DiffServ byte settings): packet based Multi-Protocol Label Switching (MPLS): flow+packet based

67 a. Int-Serv (Integrated Services): IETF RFC 1633
Defined by RSVP requires resource reservation at each hop end-to-end for each IP packet flow, and end-to-end signaling along nodes in the path Reserve resources at the routers so as to provide QoS for specific user packet stream This architecture does not scale well (large amount of states)

68 Integrated Services IntServ Internet Services model developed by IETF
Requires applications to know their QoS requirements beforehand and signal intermediate network to reserve resources (bandwidth, buffers) Requires use of packet classifiers as well as packet schedulers Almost exclusively concerned with controlling the queuing component of end to end delay Has three service classes Guaranteed Service (RTI) Controlled Load (RTT) Best-effort

69 IntServ Flow descriptor specifies QoS requirements
Filter spec – specifies information for the identifying a packet with a given flow Flow spec – specifies traffic spec in terms of token bucket parameters (Tspec) and QoS parameters (Rspec) in terms of bandwidth, delay, jitter and packet loss Resource Reservation Protocol (RSVP) used to signal network nodes about required resources

70 RSVP The sender sends a PATH message to the receiver specifying traffic characteristics Every intermediate router along the path forwards the path to the next hop determined by the routing protocol The receiver responds with RESV message

71 Integrated Services / RSVP
Sender sends a “PATH” message to the receiver specifying characteristics of traffic every intermediate router along the path forwards the “PATH” message to the next hop determined by the routing protocol Receiver responds with “RESV” message after receiving “PATH”. “RESV” requests resources for flow

72 Disadvantages of IntServ
Routers having to maintain per-flow state for every flow is a large overhead Does not scale in the core network Router state has to be refreshed at regular intervals increasing traffic overhead However, RSVP has a place at the edge of the network

73 b. Diff Serv IETF RFC 2474 Mark IP packet to specify treatment
Per Hop Behaviors (PHBs) based on network-wide traffic classes Flows are classified at the edge router based on rules, and are aggregated into traffic classes, allowing scalability Diff Serv uses the IP header TOS byte (first 6 bits), which is renamed the DS field Diff Serv defines code points (DSCP) for the DS field, DE (default) = = best effort, and EF (Expedited Forwarding) = = low latency, etc.

74 (service level agreement)
DiffServ Operation Each ISP configures its own routers to match the service that it offers, and each ISP has its own DiffServ Domain. ASP Customer Site Voice Video PHB PHB PHB DS Domain DS Domain SLA (service level agreement) SLA SLA Edge Router Interior Nodes

75 DiffServ Removes some of the shortcomings of the IntServ architecture
Divides network into regions called DS domains. Each domain is controlled by a single entity To provide service guarantees the entire path between source and destination must be in some DS domain Nodes in a DS domain can be of following types: Boundary node Interior node

76 DiffServ Boundary Node
Performs admission control to limit the number of flows in a domain Performs packet classification by marking each packet with a service class called “Behavior Aggregate” Each Behavior Aggregate is assigned an 8- bit code word called a DS code point IP ToS field is updated with the code-point

77 DiffServ Interior Node
Lies completely within a DS domain. Connects with other interior nodes or boundary nodes within the domain Only performs packet forwarding Packets are forwarded according to some pre-defined rule associated with the packet class (as indicated by the code point) These pre-defined rules are called Per-Hop Behaviors (PHBs)

78 DiffServ PHB Two commonly used PHBs are
Assured Forwarding (AF): Divides incoming traffic into four classes where each class guarantees a minimum bandwidth and buffer space Within each class packets are further assigned one of three drop priorities Expedited Forwarding (EF): Departure rate of a traffic class must equal or exceed the configured rate Queuing delay is guaranteed to be bounded Used to provide Premium Service Requires strict admission control and traffic policing

79 c. MPLS Fundamentals (IETF RFC 3031)
MPLS is a forwarding scheme that tags packets with labels (independent of layers 2,3) that specify routing and priority Enables scalability by alleviating IP over ATM problems Defines a homogeneous network based upon label-switching Requires all devices (i.e., ATM switches) to be capable of routing Enables differentiated services via QoS- aware label switched paths (LSPs) Designed to run over a wide range of media ATM, frame relay, and Ethernet 11

80 MPLS A router determines the next hop of a packet by doing a longest prefix match of an IP destination address against entries in a routing table This introduces some latency as routing tables can be very large Same process repeated for every packet even if these are in the same flow IP switching gets around this: Short label is attached to every packet and is updated at every hop This label is used at the next hop as an index into the routing table to get the next hop (happens in constant time) and next label Label is replaced and packet is forwarded to the next hop Lends itself to being done in (low-cost) hardware resulting in very high speeds

81 MPLS Like DiffServ MPLS network is divided into domains with boundary nodes called Label Edge Routers (LER) and interior nodes called Label Switching Routers (LSR) Packets entering an MPLS domain are assigned a label at the ingress LER and are switched inside a domain by a simple label lookup Labels determine QoS Labels may get stripped off at egress LER and then get routed conventionally outside the domain A sequence of LSR to be followed by a packet in an MPLS domain is called a Label Switched Path (LSP) To guarantee QoS both source and destination have to be attached to the same domain or the different domains have to have service level agreements among them

82 MPLS A group of packets that are forwarded in the same manner are said to belong to the same Forward Equivalence Class (FEC)- FECs form the basis of service differentiation No limit on number and granularity of FECs Labels only have local significance Two LSRs agree upon using a particular label for a given FEC Necessary to do label assignments including label allocation and label to FEC binding on every hop of the LSP before the traffic flow can use the LSP Labels can be stacked in FILO order – can be used in tunneling applications In a domain only the topmost label is used to make forwarding decisions Can be useful in providing mobility Home agent can push a label on incoming packets and forward them to a foreign agent Foreign agent pops of its label and forwards the packet to the destination mobile host

83 MPLS Label Assignment Label assignment can be done in the following ways: Topology-driven: LSPs for every possible FEC are automatically set up between every pair of LSR (zero call setup delay) Request driven: LSPs set up based on explicit requests. RSVP can be used Traffic driven: LSPs set up only when LSR identifies traffic patterns requiring a new LSP Traffic patterns not requiring an established LSP use the normal routing method Combines advantages of above two

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