1. Protocols for QoS Support
Communication Networks: Differential Services (DiffServ) and Multi-Protocol Label Switching (MPLS) Source and ©: Stallings Hi-Speed Networks and Internets, Ch. 17,18
Last updated: Monday, April 17, 2017
Prof. Amir Herzberg
Dept of Computer Science, Bar Ilan University
Chapter 18 Protocols for QoS Support
Chapter 18

2. Differentiated Services (DiffServ)
DiffServ (DS) routers
Support DS enhancements
DS Domain: set of contiguous DS routers
With consistent DS policy
Usually one `owner`
DS Border Routers
Interface to/from domain
Set DS Code Point (class)
6 existing bits in IP header
DS Interior Routers
Per Hop Behaviour (PHB)
Forward (by dest, class)
Chapter 18 Protocols for QoS Support

3. Differentiated Services (DiffServ)
Classify traffic in DS boundary node (router)
Based on IP src/dst, ports, protocol, …
Identify class by DS codepoint in IP header
Usually upon entering DS-domain (not by application)
DS Codepoint: 6 bits, part of DS field (byte)
IPv4: Type of Service, IPv6: Traffic Class
DS Routers queue and forward based on codepoint (stateless, simple)
Chapter 18 Protocols for QoS Support

4. DS Field and Codepoint DS field is 8 bits
2 rightmost bits used for ECN (Explicit Congestion Notify)
00: no ECN, 11: congestion, 01 and 10: EC status
Leftmost 6 bits are DS codepoint
Codepoint: DS label for a class of packets
64 different classes available
3 pools
xxxxx0 : reserved for standards, e.g. RFC 2474
: default packet class (best effort)
xxx000 : reserved for backwards compatibility with IPv4 ToS
xxx is precedence for `normal service` in IPv4 ToS
xxxx11, xxxx01 : reserved for experimental or local use
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5. DiffServ Configuration Diagram
Chapter 18 Protocols for QoS Support

6. DS Terminology
Chapter 18 Protocols for QoS Support

7. DiffServ: Services Provided within DS domain
Examples: low latency/loss, 90% of in-profile has <50ms latency...
DS Domain: contiguous part of Net with consistent DS policies
Typically under control of one administrative entity
Defined in Service Level Agreement (SLA)
Between provider (of DS domain) and customer
Customer may be user organization or other DS domain
Service provider configures forwarding policies in routers
Route (outgoing queue), discard policies
And measure performance provided for each class
Chapter 18 Protocols for QoS Support

8. Example Services Qualitative Quantitative Mixed Level A: Low latency
B: Low loss
Quantitative
C: 90% in-profile traffic delivered with no more than 50ms latency
D: 95% in-profile traffic delivered
Mixed
E: Twice bandwidth of F
F: Traffic with drop precedence X has higher delivery probability than that with drop precedence Y
Chapter 18 Protocols for QoS Support

9. DS Field and IPv4 Type of Service
Chapter 18 Protocols for QoS Support

10. Boundary Routers
Include Per Hop Behaviour (PHB) (forward, queue, discard)
Also: traffic conditioning to provide desired service
Classifier
Separate packets into classes
Based on fields in header (or even payload)
Meter
Measure traffic for conformance to profile
Marker: set/change DS Code Point [DSCP] to identify class
Re-mark codepoint if exceeds class profile (e.g. `drop precedence` - later)
Shaper/Dropper (to preserve rate in class profile)
Chapter 18 Protocols for QoS Support

11. DS Domain: Interior Routers
Classify by codepoint
Forward (by dest, class)
Queue management
By class
Packet dropping rules (when buffer saturated)
PHB: Per Hop Behaviour
Assured Forwarding (AF)
Superior to best effort
But no guarantee
Expedited Forwarding (EF)
Guaranteed QoS
Chapter 18 Protocols for QoS Support

12. Assured Forwarding (AF) PHB [RFC 2597]
Superior service to best effort
But without reservation of resources
Users choose class (from 0 (best effort) to 4)
Border router assigns drop precedence
In, out, or medium
Depending on match to traffic specifications
Interior routers use class, drop precedence
To prioritize queuing, drop decision
SLA: number of allowed (in) packets per user
From each class, for specific duration
Chapter 18 Protocols for QoS Support

13. PHB - Assured Forwarding
Four classes defined
Select one or more to meet requirements
Within class, packets marked by customer or provider with one of three drop precedence values
Used to determine importance when dropping packets as result of congestion
Chapter 18 Protocols for QoS Support

14. Expedited Forwarding (EF) PHB
Premium, reserved QoS service [RFC 3246/7]
Low (bounded) delay, jitter
No loss (if arrivals satisfy specifications)
Minimum departure rate R at routers
(Almost) empty queues for all EF traffic
Provided that arrivals rate < min departure rate
Ensured by border routers (aka Boundary conditioners)
How to bound delay, jitter? Define R?
Timescale at which to measure R
Or: a bound E on the `error` (delay on top of Rl)
Since R holds only for `sufficiently long periods`…
Cannot guarantee departure rate if queue is empty
Arrival specifications to avoid loss…
Chapter 18 Protocols for QoS Support

15. EF PHB: Arrivals Specifications
EF PHB may include arrival specifications
No (congestion) loss if total arrivals in spec
Total arrivals from all inputs for specific out interface
May use Token Bucket Conformance Parameters:
Token rate R in Bytes/second
Bucket size (or `depth`) B in Bytes
Peak traffic rate p in Bytes/sec
Minimum policed unit length m
Maximum packet size M
Chapter 18 Protocols for QoS Support

16. EF PHB: Delay Specifications
EF-able router MUST satisfy: dj,Iφ≤ fj,Iφ + EIφ
I is a specific interface, RI is specified rate
φ{A,P} (A: Aggregate, P: Per-Packet)
dj,IA is end of sending jth EF-packet from I
fj,Iφ is the `ideal` end of sending, defined by: fj,Iφ=max{aj,I , min(dj-1,Iφ, fj-1,Iφ)}+lj,Iφ / RI
aj,I is end of receiving jth packet to I
lj,IA is the length of the jth packet sent from I
f0,Iφ=0, d0,Iφ=0
EIφ caps the φ-error on interface I
Aggregate values do not cap delay of one packet
Chapter 18 Protocols for QoS Support

17. EF PHB: Per-Packet Delay Spec
EF-able router MUST satisfy: dj,Iφ≤ fj,Iφ + EIφ
I is a specific interface, RI is specified rate
φ{A,P} (A: Aggregate, P: Per-Packet)
dj,IP: end sending from I the jth packet received for I
fj,Iφ is the `ideal` end of sending, defined by: fj,Iφ=max{aj , min(dj-1,Iφ, fj-1,Iφ)}+lj,Iφ / RI
aj,I is end of receiving jth packet to I
lj,IP is the length of the jth packet received for I
EIφ caps the φ-error on interface I
Per-packet values cap delay for each packet
EF-able router specifies rate RI and error EIφ
Chapter 18 Protocols for QoS Support

18. EF PHB: Per-Packet Delay Spec
EF-able router MUST satisfy: dj,IP≤ fj,IP + EIP
dj,IP: time when router finished sending the jth packet
Received for I
With specified rate RI and error EIP for interface I
EIP caps the delay error on interface I (for rate RI)
Where: fj,IP=max{aj,I , min(dj-1,IP, fj-1,IP)}+lj,I / RI
is the `ideal` time for finishing to send the jth packet
aj,I is time when router finished receiving jth packet for I
lj,I is the length of the jth packet received for I
f0,IP=0, d0,IP=0
Spec also has aggregate delay requirements – see RFC
Different if the router is non-FIFO (as many are)
Chapter 18 Protocols for QoS Support

19. Bounding Delay and Jitter
Given:
EIP : maximal per-packet delay error on I
Total inputs towards I conform to token-bucket with rate RI and size BI
Then a bound of delay and jitter is: D=BI / RI + EIP
If there is a minimal delay Emin<EIP then we can improve bound on jitter to: J=D-Emin
How to improve bound on jitter? And what for?
Chapter 18 Protocols for QoS Support

20. Per-Domain Behaviour (PDB) and Service Level Agreement (SLA)
PDB [RFC 3086]: Edge-to-edge QoS parameters
Technical specifications:
Traffic Spec (e.g. Token bucket)
Border (admission) policy: classification, marking, shaping
Per-Hop Behaviour (PHB), or multiple PHBs
Attributes: throughput, loss, latency, jitter under specified conditions
Network parameters: max number of hops, min bandwidth, max delay,…
Allow composition of domains into DS regions
SLA: Between provider (of DS domain) and customer
Customer: user organization or other DS domain
SLS: Service Level Specifications (parameters of SLA)
Customer visible, quantified, end-to-end QoS
Provider can use PDB to meet SLS
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21. Codepoints for AF PHB
Chapter 18 Protocols for QoS Support

22. Multi-Protocol Label Switching (MPLS)
Routing algorithms provide support for performance goals
Distributed and dynamic
React to congestion
Load balance across network
Based on metrics
Develop information that can be used in handling different service needs
Enhancements provide direct support
IntServ, DiffServ, RSVP
Limited deployment (certainly cf. to MPLS)
Worse: no QOS guarantee (throughput, delay)
MPLS tries to match ATM QoS support
Chapter 18 Protocols for QoS Support

23. Multi-Protocol Label Switching (MPLS)
Widely deployed and used, covered extensively
Book chapter is also in
MPLS IETF WG, MPLS forum, MPLS Resource Center, …
Mid-1990s: Efforts to marry IP and ATM
Motivation: ATM switches were much faster than routers
IP switching (Ipsilon), Tag switching (Cisco), …
Routing (e.g. OSPF) define path between end points
Diff-Serv: assign packets to class on entering Net
MPLS: assign a fixed path for each flow
Simpler, faster routing/switching of packets
Connection-oriented QoS support (cf. DiffServ)
Traffic engineering: choose and change path for each flow
Virtual private networks
Multi-Protocol support
Chapter 18 Protocols for QoS Support

24. Protocols for QoS Support
MPLS Operation
Label Switched Routers (LSR)
Forward packets based on MPLS label, not on IP header
Add / swap / merge labels (more later)
Labels identifies flow of packets
Between end points or multicast destinations
Flow = FEC (Forward Equivalency Class)
Flow defined by src/dest IP addr, port; protocol; DSCP
Connection oriented: each flow has…
Specific path through LSRs
Specific QoS parms: resources, queue/discard policy
Path determined by routing protocol e.g. OSPF
Labels assigned manually or by proper protocol
Enhanced RSVP or LDP (Label Distribution Protocol)
DSCP = Diff-Serv Code-point (identifies class of packet)
Chapter 18 Protocols for QoS Support
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25. MPLS Domain Operation
Chapter 18 Protocols for QoS Support

26. MPLS: Connection Oriented QoS Support
Guarantee fixed capacity for specific applications
Control latency/jitter
Ensure capacity for voice
Provide specific, guaranteed and quantifiable SLAs [Service Level Agreements]
Configure varying degrees of QoS
MPLS imposes connection oriented framework on IP based internets
Chapter 18 Protocols for QoS Support

27. MPLS Traffic Engineering
Traffic Eng: select routes, reserve resources to optimize utilization based on known demands
Basic IP: per-packet routing/forwarding decision
MPLS: aware of flow traffic, QoS requirements
Load-balance – select (different) route for flows
Intelligent re-routing (of flows) when congested
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28. VPN Support
Traffic from a given enterprise or group passes transparently through an internet
Segregated from other traffic on internet
Performance guarantees
Security
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29. Multiprotocol Support
MPLS supports different network technologies IP
ATM
Frame relay
Mixed network
In all cases:
Router/switch should be MPLS-enabled
Enabled and ordinary routers/switches can co-exist
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30. MPLS Terminology
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31. Explanation - Setup Labelled Switched Path (LSP) route selection
QoS parameters established along LSP:
Resource commitment
Queuing and discard policy at LSR (PHB)
Labels assigned
Local significance only
Manually or using protocol
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32. Route Selection Selection of LSP for particular flow Hop-by-hop
LSR independently chooses next hop
Ordinary routing protocols e.g. OSPF
Doesn’t support traffic engineering or policy routing
Explicit
LSR (usually ingress or egress) specifies some or all LSRs in LSP for given flow
Allows traffic engineering and policy routing
Selected by configuration, or dynamically
Chapter 18 Protocols for QoS Support

33. Constraint Based Routing
Take into account traffic requirements of flows and resources available along hops
Current utilization, existing capacity, committed services
Additional metrics over and above traditional routing protocols (e.g. OSPF, BGP)
Maximum link data rate
Current capacity reservation
Packet loss ratio
Link propagation delay
Chapter 18 Protocols for QoS Support

34. Label Distribution and Resource Allocation
Setting up LSP for a flow… each LSR:
Assign in-label to incoming packets
Inform all upstream LSRs of in-label
Receive out-label from downstream LSR
Manually or by label-setup protocol
RFC 3031: enhanced RSVP or new
Chapter 18 Protocols for QoS Support

35. Explanation – Packet Handling
Packet enters domain through edge LSR
Edge LSR determines flow, LSP
Appends label
Forwards packet
LSR within domain:
Remove label from incoming packet
Attach outgoing label and forward
This is label switching / swapping
Egress LSR:
Strips label, reads IP header and forwards
Chapter 18 Protocols for QoS Support

36. Notes MPLS domain is contiguous set of MPLS enabled routers
Traffic may enter or exit via direct connection to MPLS router or from non-MPLS router
Flow determined by parameters, e.g.
Source/destination IP address or network IP address
Port numbers
IP protocol id
Differentiated services codepoint
IPv6 flow label
Forwarding is simple lookup in predefined table
Map label to next hop
Can define PHB at an LSR for given flow
Packets between same end points may belong to different flow
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37. MPLS Packet Forwarding
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38. MPLS Labels Stack Packet may carry a stack of MPLS labels
Processing based on top label
LSR may push or pop label
Unlimited levels
Push label of aggregate (tunnel) LSP, pop at exit
Fewer labels  smaller, more efficient tables
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39. Label Format Diagram Label value: Locally significant 20 bit
Exp: 3 bit reserved for experimental use
E.g. DS information or PHB guidance
S: 1 for oldest entry in stack, zero otherwise
Time to live (TTL): from (& to!) IP header
Processing as expected… see spec/book/hidden foil
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40. Time to Live Processing
Needed to support TTL since IP header not read
First label TTL set to IP header TTL on entry to MPLS domain
TTL of top entry on stack decremented at internal LSR
If zero, packet dropped or passed to ordinary error processing (e.g. ICMP)
If positive, value placed in TTL of top label on stack and packet forwarded
At exit from domain, (single stack entry) TTL decremented
If zero, as above
If positive, placed in TTL field of Ip header and forwarded
Chapter 18 Protocols for QoS Support

41. Label Stack
Appear after data link layer header, before network layer header
Top of stack is earliest (closest to network layer header)
Network layer packet follows label stack entry with S=1
Over connection oriented services
Topmost label value in ATM header VPI/VCI field
Facilitates ATM switching
Top label inserted between cell header and IP header
In DLCI field of Frame Relay
Note: TTL problem
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42. Position of MPLS Label Stack
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43. FECs, LSPs, and Labels Traffic grouped into FECs
Traffic in a FEC transits an MLPS domain along an LSP
Packets identified by locally significant label
At each LSR, labelled packets forwarded on basis of label.
LSR replaces incoming label with outgoing label
Each flow must be assigned to a FEC
Routing protocol must determine topology and current conditions so LSP can be assigned to FEC
Must be able to gather and use information to support QoS
LSRs must be aware of LSP for given FEC, assign incoming label to LSP, communicate label to other LSRs
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44. Topology of LSPs Unique ingress and egress LSR
Single path through domain
Unique egress, multiple ingress LSRs
Multiple paths, possibly sharing final few hops
Multiple egress LSRs for unicast traffic
Multicast
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45. Summary - QoS ISA: Queuing to prefer/guarantee QoS (e.g. WFQ)
RED, ECN: Signal congestion to slow TCP (fairly)
DiffServ: Ensure predefined QoS (PHB, PDB, SLA)
Or: RSVP - reserve resources per connection
For unicast, multicast
Traditional IP dynamic routing or…
MPLS: Fixed paths, label switching
More… (e.g. RTP – in book)
Chapter 18 Protocols for QoS Support