DiffServ-aware-MPLS Networking: a Promising Traffic Engineering for Next Generation Internet (NGI)

1
DiffServ-aware-MPLS Networkinga Promising
Traffic Engineering forNext Generation Internet
(NGI)
2002. 9. 25. Youngtak Kim Advanced Networking
Technology Lab. (ANT Lab.) Dept. of Information
Communication Engineering, YeungNam University,
Korea (ytkim_at_yu.ac.kr)
2
Outline

• Networking Model and Traffic Engineering of NGI
• Differentiated Service (DiffServ)
• MPLS (Multi-protocol Label Switching)
• Traffic Engineering with DiffServ-over-MPLS
• Internet Traffic Engineering Measurement,
  Performance Monitoring
• MPLS Fault Restoration
• DiffServ-aware-MPLS TE of Commercial Routers
• Summary and Discussions

3
Networking Model and Traffic Engineering of
Next Generation Internet (NGI)
4
Required Features of Next Generation Internet

• Guaranteed Bandwidth QoS
• Bandwidth
• peak information rate (PIR), committed
  information rate (CIR), minimum information rate
• Peak Burst Size (PBS), Committed Burst Size
  (CBS), Excess Burst Size (EBS)
• End-to-end packet transfer delay
• Jitter (delay variation)
• Packet loss ratio
• Differentiated Service provisioning with
  different priority/weight
• Premium service, time-critical real-time service,
  controlled service, best effort service
• Efficient Traffic Engineering for WDM optical
  lambda/fiber channels

5
NGI with IP, MPLS and WDM Optical Network
6
Inter-networking with GMPLS-based WDM Optical
Network
7
Protocol Layers of Optical Internet
8
MPLS LSR (Label Switching Router)
9
Optical Lambda Switching and Fiber Switching
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Hierarchical Traffic Grooming in GMPLS Network
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Traffic Engineering

• Traffic Engineering
• Performance evaluation and optimization of
  operational networks
• Encompasses the technologies of measurement,
  modeling, characterization, and control of
  traffic
• Goal of Internet Traffic Engineering
• Facilitate efficient and reliable network
  operations while simultaneously optimizing
  network resource utilization and traffic
  performance
• Enhance and guarantee the QoS delivered to end
  users
• Optimize the resource utilization by optimized
  routing, efficient capacity management and
  traffic management
• Traffic oriented performance measures delay,
  delay variation, packet loss, and throughput
• Enhanced network integrity with network
  survivability

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Internet Traffic Engineering

• Capacity Management
• Capacity planning, routing control, resource
  management
• Network resources link bandwidth, buffer space,
  computational resource
• Traffic Management
• Nodal traffic control traffic conditioning,
  queue management, scheduling
• Regulating traffic flow traffic shaping,
  arbitration of access to network resources
• Traffic-oriented performance measures
• Delay, delay variation
• Packet loss
• Throughput

13
Traffic Control and Management Functions
14
ITU-T I.371 Traffic Management Framework
UPC Usage Parameter Control CAC Connection
Admission Control PC Priority Control
NPC Network Parameter Control RM Resource
Management Others Spacing, Framing, Shaping, etc
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Internet Traffic Engineering with DiffServ and
GMPLS
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Traffic Engineering with DiffServ-aware-MPLS

• Differentiated Service (DiffServ)
• 7 differentiated class-types (traffic aggregates)
• QoS and traffic parameters are specified for each
  class-type
• Priority or Weight is assigned for each
  class-type
• Per-class level fine-grained optimization by
  DiffServ Aggregated level optimization by MPLS
  LSP
• MPLS-based Traffic Engineering
• MPLS LSP provides constraint-based routing for
  traffic trunk provisioning
• Connection-oriented traffic trunk (CR-LSP)
  planning and provisioning
• Network load-balancing is possible by controlling
  the traffic trunk
• By using EXP (CoS) fields in MPLS LSP Shim
  header, differentiated packet processing
  (DiffServ-aware) is possible
• Efficient flexible resource utilization with
  bandwidth borrowing among LSPs (traffic trunks)

17
Service Level Agreement (SLA)

• Service Level Agreement (SLA) ?
• A contract between a service provider and a
  customer
• Specifies, usually in measurable terms, what QoS
  the service provider will provide
• Generic QoS parameters
• Availability
• Delivery
• Latency
• Bandwidth
• Mean Time Between Failures (MTBF)
• Mean Time to Restoration of Service (MTRS)

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Example of Service Level Specification

• Service Level Specification in TEQUILA
• Scope the geographical/topological region over
  which the QoS is to be enforced (possible
  topology 1-to-1, 1-to-N, 1-to-all, N-to-1,
  all-to-1)
• Flow Identification DSCP, Source, Destination,
  Application
• Traffic Conformance Testing in-profile,
  out-profile with peak rate (P), token bucket rate
  (R ), bucket depth (B), Minimum packet size (M),
  Maximum transfer Unit (MTU)
• Marking and Shaping services prior to conformance
  testing
• Excess traffic treatment
• Performance parameters delay, jitter, packet
  loss, throughput
• Service schedule time of the day range, day of
  the week range, month of the year range, year
  range
• Reliability mean down time, maximum time to
  repair

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Traffic / QoS Parameters of Bearer Service among
IP Routers

• Traffic parameters
• Peak Data Rate (PDR)
• Average Data Rate, Sustainable Data Rate with
  burst tolerance
• Minimum Data Rate
• Frame rate with max. frame size
• QoS Parameters
• End-to-end transfer Delay
• Delay variance (Jitter) tolerance
• Bit/Packet/Frame loss ratio

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Closed-loop Control in Traffic Engineering
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Differentiated Service (DiffServ)
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Differentiated Service

• Goal of DiffServ
• Service differentiation without scalability
  problem
• A scalable mechanism for categorization of
  traffic flow into behavior aggregates
• Each behavior aggregate is defined as a
  class-type by DS field in IP header
• Each class-type is treated differently by its
  Per-Hop Behavior (PHB) using different
  classification, policing, shaping, and scheduling
  rules.
• End user of differentiated network service should
  have a Service Level Agreement (SLA) with Traffic
  Conditioning Agreement (TCA)
• TCA defines classifier rules as well as metering,
  marking, discarding, and shaping rules
• Packets are classified, and possibly policed and
  shaped at the ingress to a DiffServ Network
• When a packet traverses the DiffSev Domain
  boundaries, the DS field may be re-marked

23
Packet Classification

• BA (Behavior Aggregate) Classifier
• Classifies packets based on the DS code-point
  only
• MF (Multi-field) Classifier
• Selects packets based on the value of a
  combination of one or more header fields
• IP packet header fields
• Source address, destination address
• DS field
• Protocol ID
• Source Port, Destination port
• Other information, such as incoming interface

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Per Hop Behavior (PHB)

• Per-Hop Behavior (PHB)
• The externally observable forwarding behavior
  applied at a DS-compliant node to a DS behavior
  aggregate
• The means by which a node allocates resources to
  behavior aggregates
• Defines hop-by-hop resource allocation mechanism
• Example of PHB
• Guarantee minimal bandwidth allocation ( x of a
  link or tunnel)
• Guarantee minimal bandwidth allocation (x of a
  link or tunnel) with proportional fair sharing of
  any excess link capacity
• Buffer allocation
• Priority relative to other PHBs
• PHBs are specified as a group (PHB group) for
  consistency
• PHBs are implemented in nodes by means of some
  buffer management and packet scheduling mechanisms

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Example of DiffServ Class-type
Class-type Objective Example Delay Jitter packet Loss Ratio Bandwidth definition DSCP
NCT1/ NCT0 Minimized error, high priority RIP, OSPF, BGP-4 100 msec U 10-3 Committed rate 111 000 / 110 000
EF Jitter sensitive, real-time high interaction VoIP 100 msec 50 msec 10-3 Committed rate 101 110
AF4 Jitter sensitive, real-time high interaction Video conference 400 msec 50 msec 10-3 Committed rate Peak rate 100 000
AF3 Transaction data, interactive Terminal session Custom app 400 msec U 10-3 Committed rate Peak rate 011 000
AF2 Transaction data Data base Web 400 msec U 10-3 Committed rate Peak rate 010 000
AF1 Low loss bulk data FTP E-mail 1 sec U 10-3 Committed rate Peak rate 001 000
BE Best effort Best effort service U U 10-3 U 000 000
(Note a) U undefined, b) Drop precedence of
AF4AF1 010, 100, 110)
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Differentiated Packet Processing
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DiffServ Traffic Handler
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Packet Classifier and Traffic Conditioner
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Traffic Policing, Metering / Marking and
Re-marking
Parameters Red Yellow Green
Single Rate Three Color Marker (SRTCM) CIR/CBSEBS TE(t)-B lt 0 TE(t)-B ? 0 and TC(t) B lt 0 TC(t) B ? 0
Two Rate Three Color Marker (TRTCM) PIR/PBS CIR/CBS TP(t)-B lt 0 TP(t)-B ? 0 and TC(t) B lt 0 TC(t) B ? 0
(Note B arrived packet size, TE(t) token count
of excess rate token bucket, TC(t) token
count of committed rate token bucket, TP(t)
token count of peak rate token bucket)
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Per Class-Type Queuing (1) Tail-Drop Q
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Per Class-Type Queuing (2) RED (Random Early
Detection) Queue
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Per Class-Type Queuing (3) WRED (Weighted
Random Early Detection) Queue
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Per Class-Type Queuing (4) RIO (RED with
In/Out-Profile) Queuing
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DiffServ Packet Scheduler (1)

• Priority-based, Weight-based Packet Scheduler

(b) Weight-based Scheduler
(a) Priority-based Scheduler
(c) Hierarchical Packet Scheduler
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DiffServ Packet Scheduler (2)

• Hierarchical Packet Scheduler

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Traffic Shaping
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Multi-Protocol Label Switching (MPLS)
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MPLS (Multi-Protocol Label Switching)
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Label Distribution Protocol (LDP)

• Labels
• - short fixed identifier, meaningful only at the
  segment between LSR pair
• - assigned according to FEC (Forwarding
  Equivalent Class)
• Label assignment distribution
• - assigning label(s) to a FEC binding a label L
  to a particular FEC F by down stream LSR switch
• - Label distribution by i) upstream node, ii)
  down stream node, or iii)downstream-on-demand

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Hierarchical Label Stacking
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MPLS Traffic Engineering

• Connection-oriented LSP (Label Switched Path)
• Constraint-based Routing
• Traffic Engineering (TE) requirements of LSP
• Constraint-based Shortest Path First (CSPF)
• Forwarding Equivalent Class (FEC) multiple
• source IP address range min, max
• destination IP address range min, max
• source port range min, max
• destination port range min, max
• service type
• MPLS FEC-to-NHLFE (FTN) structure
• FEC Forwarding Equivalent Class
• NHLFE Next Hop Label Forwarding Entity

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Constraint-based Routing in MPLS

• Traffic parameters of the constraint-based
  routing for LSP
• bandwidth of LSP peak data rate, committed data
  rate
• Modification of Link State Database for
  constraint-based routing
• traffic parameter
• available bandwidth at each link number of
  lambda channels, bandwidth of each lambda
  channels
• Additional QoS parameter
• propagation delay
• Combined cost metric
• Modification of OSPF shortest path routing
• constraint-based routing with traffic parameters
  bandwidth, QoS, resource class, class of failure
  protection
• SRLG (Shared Risk Link Group)

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Constraint-Routed LDP (CR-LDP)
44
CR-LDP Traffic Parameters
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RSVP-TE

• RSVP-TE Message
• Path, Resv
• PathTear, ResvTear
• PathErr, ResvErr
• ResvConf, Hello, Notify

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Traffic Policing for CR-LSP

• Three token buckets Peak Rate, Committed Rate,
  Excess
• When a packet of size B bytes arrives at time t,
• if TP(t) B ? 0, the packet is not in excess of
  the PDR gt TP(t) TP(t) B
• else the packet is in excess of the PDR gt
  Packet Marking (and optionally discarding)
• if TC(t) B ? 0, the packet is not in excess of
  the CDR gt TC(t) TC(t) B
• else if TE(t) B ? 0, the packet is in
  excess of the CDR but is not in excess of the EBS
  
• gt TE(t) TE(t) B
• else the packet is in excess of both the
  CDR and EBS gt Packet Marking (and optionally
  discarding)

Token count Initial value Increment rate (per second)
TP PBS (Peak Bucket Size) PDR (Peak Data Rate)
TC CBS (Committed Burst Size) CDR (Committed Data Rate)
TE EBS (Excess Burst Size) CDR (Committed Data Rate)
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Discarding Options of Marked Packet

• Simple packet discarding policy (example)
• if any packet is in excess of the PDR, then
  discard the packet
• if any packet is in excess of both the CDR and
  EBS, then mark the packet and discard considering
  the relative packet drop precedence of the
  packet
• Other considerations
• relative packet drop precedence of Assured
  Forwarding (AF)
• relative share (defined by weight) of the
  possible excess bandwidth above its committed
  rate among CR-LSPs
• Packet scheduling for EF (Expedited Forwarding)
  packet to minimize delay jitter
• optional traffic shaping

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MPLS OAM

• IETF draft document OAM Functionality for MPLS
  Networks (Neil Harrison et. al, Expr. date Aug.
  2001)
• OAM (Operation and Maintenance) for the
  user-plane in MPLS network
• CV (connectivity verification) OAM Function
• used to detect defects related to misrouting of
  LSPs as well as link and nodal failure
• if connectivity error is detected, it may trigger
  protection switching of the working path to the
  pre-established protection path
• Performance OAM Function
• FDI (Forward Defect Indicator)/ BDI (Backward
  Defect Indicator) OAM Function
• ? triggers fault management function LSP
  restoration/rerouting

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MPLS OAM Packets (Example)
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IP Performance Measurements

• Connectivity (RFC 2678)
• Instantaneous unidirectional connectivity
• Instantaneous bi-directional connectivity
• Interval unidirectional connectivity
• Interval bi-directional connectivity
• Interval temporal connectivity
• Delay metric for IPPM (RFC 2679)
• One-way delay Poisson stream
• Packet loss metric for IPPM (RFC 2680)
• One-way packet loss Poisson stream

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Fault Management Flow (Example)
52
MPLS Fault Management (FM) OAM
53
Constraint-based Shortest Path First (CSPF)
Routing
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OSPF, CR-LDP and Resource Allocation
Traffic Engineering Manager (Backbone Trunk LSP
Information)
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DiffServ-aware-MPLS Traffic Engineering
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DiffServ-over-MPLS Traffic Engineering
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MPLS support of DiffServ

• E-LSP (Exp-inferred-LSPs)
• LSPs which can transport multiple Ordered
  Aggregates
• the EXP field of the MPLS shim header conveys to
  the LSR the PHB to be applied to the packet
  (conveying both information about the packets
  scheduling treatment and its drop precedence)
• L-LSP (Label-only-inferred-LSPs)
• only transports a single Ordered Aggregates
• the packets scheduling treatment is inferred
  exclusively from the packets label value
• the packets drop precedence is conveyed in the
  EXP field of the MPLS shim header or in the
  encapsulating link layer specific selective drop
  mechanism (ATM, FR, 802.1)

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E-LSP (Exp-inferred-LSPs) Mapping
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L-LSP (Label-only-inferred-LSPs) mapping
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Mapping DiffServ Class Type into E-LSP

• Mapping DiffServ Class-type into MPLS E-LSP
• One DiffServ Class-type contains multiple
  DiffServ Classes
• 4 Assured Forwarding (AF) with 3 packet drop
  precedence at each AF gt 12 DSCPs DSCP 001,
  010, 011, 100 010, 100, 110
• Expedited Forwarding (EF) for minimized delay
  jitter DSCP 101 110
• Network Control Traffic DSCP 11x 000
• Default Forwarding for Best Effort (BE) traffic
• E-LSP uses EXP field (3-bit) of MPLS Shim header
• E-LSP allow multiple OAs (ordered aggregates) to
  be carried over a single LSP
• 8 different PHBs can be specified (one PHB per
  each ordered aggregate (OA) in the E-LSP)

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Usefulness of E-LSP

• It is easier to create end-to-end services for a
  customer if a single LSP is used, instead of
  setting up, maintaining, administering and
  monitoring multiple LSPs (as in L-LSP) one for
  each OA (ordered aggregate) of the customers
  traffic.
• E-LSPs reduce the number of LSPs needed to deploy
  end-to-end services in a network.
• Path protection and switching mechanisms are more
  easily applied to a single LSP than a group of
  related LSPs.
• Bandwidth borrowing among the OAs (using a single
  LSP) of a customer while restricting bandwidth
  borrowing between customers.

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Example Mapping of EXP and PHB
DSCP Class (DSCP) EXP code (suggested) Per-Hop-Behavior (suggested)
Best Effort (000 000) 000 Default Forwarding with best effort (highest drop precedence)
AF 1, High Drop Precedence (001 110) 001 Assured Forwarding 1, High Drop Precedence for non-real time bulk data transfer
AF 2, Med Drop Precedence ( 010 100) 010 Assured Forwarding 2, Med Drop Precedence for non-real time ABR
AF 3, Med Drop Precedence ( 011 100) 011 Assured Forwarding 3, Med Drop Precedence for non-real time VBR data
AF 4, Low Drop Precedence (100 010) 100 Assured Forwarding 4, Low Drop Precedence for real-time VBR data
Expedited Forwarding (EF) (101 110) 101 Minimized delay jitter for Real-time CBR traffic
Network Control Traffic (110 000) (User-to-user control traffic) 110 Minimized error, high priority
Network Control Traffic (111 000) 111 Minimized error, highest priority
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MPLS LSP Stacking and Bandwidth Borrowing
64
Hierarchical Packet Scheduling and Recursive
Bandwidth Borrowing
(C) Recursive Bandwidth Borrowing
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Fault Restoration in MPLS Network
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Protection Switching Types
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Link-, Path-, Span-Restoration
(b) Path Switching/protection
(a) Normal Operation
(d) Link/Line Protection
(c ) Span Protection
68
Path Restoration vs. Segment-Restoration
(d) Segment Restoration
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Ring-based protection switching algorithms

• SONET Self-healing Rings
• UPSR (Uni-directional Path-Switched Ring)
• 11 protection, Selection at receiver node
• Protection ring has reverse direction
• Used in access network
• BLSR (Bi-directional Line Switched Ring)
• Also referred to as shared protection ring
  (SPRING)
• 2-fiber BLSR or 4-fiber BLSR
• Used in core network

70
Restoration using p-Cycles
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Shared Risk Link Group (SRLG)

• Examples of SRLG id in Optical Link

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Differentiated Fault Restoration Policy

• Differentiated Backup Path Reservations (Example)
• Backup Path Utilization
• Reservation with NO Traffic
• Reservation with Lower Priority Traffic
• Allow working path traffic at restoration

MPLS Service Class Bandwidth Reservation () Setup Priority Preemption Priority Application
Platinum 100, 11 Highest Highest High Priority VPN
Gold 100, 11 Higher Higher VPN
Silver 80, 11 Normal Normal Premium service
Bronze 50, 11 Lower Lower Controlled traffic
Best effort 0 Lowest Lowest Best Effort
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DiffServ-aware-MPLS Traffic Engineering of
Cisco Routers
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DiffServ Functions in Commercial Routers

• DiffServ Capability of Cisco Router
• DiffServ Queuing
• Flow-based WFQ, Flow-based Distributed WFQ
• Class-based WFQ
• Priority Queuing
• Packet Scheduling
• Modified Weighted Round Robin (MWRR)
• Modified Deficit Round Robin (MDRR)
• Congestion Avoidance and Packet Drop Policy
• RED, WRED, Flow WRED
• Traffic Class Definition (class-map) IP address,
  precedence, DSCP, MAC address, interface,
  protocol
• Policy Definition (policy-map) edge QoS feature
  (rate-limiting, rate-shaping, IP precedence, DSCP
  setting), core QoS feature (WFQ, WRED)

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MPLS Functions in Commercial Router

• MPLS functions in Cisco Router
• TE-RSVP to support LSP path signaling
• MPLS QoS defined by the CoS field of Shim header
• Class 0 (available)
• Class 1 (Standard)
• Class 2 (Premium)
• Class 3 (Control)
• MPLS Traffic Engineering Tunnel
• Priority
• Bandwidth
• Path option dynamic routing, explicit routing
• MPLS-VPN
• VPN Routing and Forwarding (VRF)
• MPLS VPN QoS premium and standard service levels

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Network Management System to support
DiffServ-aware-MPLS Traffic Engineering
77
Explicit establishment DiffServ-aware-LSP
Constraint-based Shortest Path First (CSPF)
Routing
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Performance measurement of QoS, Transfer Rate
and Connectivity checks
(a) Traffic monitoring
(d) Transmission Data rate
(b) Traffic analysis (per Protocol)
(e) Packet Drop rate
(c) IP Connectivity check
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Test Networking Configuration
(a) Physical topology
(b) Logical topology
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Test Results

• Test Configuration
• Flow 1, 3 (200Kbps CBR), rate limit 200 Kbps,
  Burst size Bc5Kbytes, Be5Kbytes
• Flow 2, 4 (300500 Kbps VBR), rate limit 300
  Kbps, Burst size Bc5Kbytes, Be5Kbytes
• MPLS LSP 1-3 Bandwidth500Kbps, Burst Size
• MPLS LSP 2-4 Bandwidth 500Kbps
• DiffServ-aware MPLS packet scheduling
• Traffic generation model fixed packet size

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Concluding Remarks

• Networking Model of Next Generation Optical
  Internet
• Networking with IP, MPLS and WDM Optical Network
• Required features guaranteed QoS, differentiated
  service provisioning, efficient traffic
  engineering
• DiffServ-aware-MPLS Traffic Engineering
• Per-class level fine-grain optimization by
  DiffServ
• Aggregated level optimization by MPLS LSP
• Connection-oriented traffic trunk (CR-LSP)
  planning and provisioning for logical topology
• Network-wide periodic load re-balancing is
  possible for increased network throughput
  performance
• Efficient and flexible resource utilization with
  bandwidth borrowing among CR-LSPs
• Contemporary commercial routers are supporting
  DiffServ and MPLS capabilities.

82
References

• 1 IETF RFC 3272, Overview and Principles of
  Internet Traffic Engineering, May 2002.
• 2 IETF Internet Draft, Traffic Engineering
  QoS Methods for IP-, ATM-, TDM-based
  Multiservice Networks, October, 2001.
• 3 IETF Internet Draft, Network Survivability
  Considerations for Traffic Engineered IP
  Networks, IETF draft-owens-te-network-survivabilit
  y-03.txt, May 2002.
• 4 IETF Internet Draft, A Traffic Engineering
  MIB, draft-ietf-tewg-mib-02.txt.
• 5 IETF Internet Draft, Requirements for support
  of Diff-Serv-aware MPLS Traffic Engineering, June
  2002.
• 6 IETF Internet Draft, TE LSAs to extend OSPF
  for Traffic Engineering, January 4, 2002.
• 7 IETF Internet Draft, Applicability Statement
  for Traffic Engineering with MPLS, August 2002.
• 8 IETF Internet Draft, A Framework for Internet
  Traffic Engineering Measurement, March 2002.
• 9 IETF Internet Draft, Network Hierarchy and
  Multilayer Survivability, July 2002.
• 10 IETF Internet Draft, Protocol extensions for
  support of Diff-Serv-aware MPLS Traffic
  Engineering, June, 2002.
• 11 IETF Internet Draft, Use of IGP Metric as a
  second TE Metric, March, 2002
• 12 IETF Internet Draft, Alternative Technical
  Solution for MPLS DiffServ TE, August 2001.

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• 13 IETF RFC 2475, An Architecture for
  Differentiated Services, December 1998.
• 14 IETF RFC 2702, Requirements for Traffic
  Engineering Over MPLS, September 1999.
• 15 IETF RFC 2330, Framework for IP Performance
  Metrics, May 1998.
• 16 IETF RFC 3031, Multi-Protocol Label
  Switching (MPLS) Architecture, January 2001.
• 17 IETF RFC 3270, Multi-Protocol Label
  Switching (MPLS) Support of Differentiated
  Services, May 2002.
• 18 IETF RFC 3209, RSVP-TE Extensions to RSVP
  for LSP Tunnels, December 2001.
• 19 IETF Draft, MPLS Support of Differentiated
  Services using E-LSP, S. Ganti et. al, April
  2001.
• 20 IETF RFC 2836, Per-Hop-Behavior
  Identification Codes, S. Brim et. al, May 2000.
• 21 IETF Draft, An Expedited Forwarding PHB
  (Updates RFC 2598), Bruce Davie et. al, April
  2001.
• 22 IETF RFC 2597, Assured Forwarding (AF) PHB
  Group, J. Heinanen et. al, June 1999.
• 23 IP Quality of Service The complete
  resource for understanding and deploying IP
  quality of service for Cisco networks, Srinivas
  Vesesna, Cisco Press, 2001.
• 24 MPLS and VPN Architectures A Practical
  guide to understanding, designing and deploying
  MPLS and MPLS-enabled VPNs, Ivan Pepelnjak and
  Jim Guichard, Cisco Press, 2001.

84
Thank You !!! Youngtak Kim, Ph.D., Associate
Professor Dept. of Information and Communication
Engineering, College of Engineering, Yeungnam
University (Tel [phone], Fax
82-53-814-5713, E-mail ytkim_at_yu.ac.kr)