1. Transmission Quality of Service (QoS) in IPCablecom
European
Cable
Communications
Association
Transmission Quality of Service (QoS) in IPCablecom
ITU-T Workshop on Multimedia Convergence
Geneva, March 2002
Dipl.-Ing. Volker Leisse
Institute for Communications Technology
Braunschweig Technical University
© 2002

2. Introduction (1)
Term QoS (over-)used in many contexts with differing implications
QoS in video services = (objectively) measurable perceived picture quality
QoS in voice services = (objectively) measurable perceived speech quality
application QoS = collection of user requirements to define perceived service quality
Here: Transmission QoS = (dynamic) allocation of resources to provide guaranteed transmission characteristics in network

3. Introduction (2)
Many common communication systems offer best-effort service
transmission properties depend on network load
transmission properties cannot be guaranteed in any way
New multimedia applications require deterministic transmission properties
real-time applications need strict temporal relation between sender and receiver
varying network load requires bandwidth allocation
logical connections avoid variable delay

4. Requirements in IPCablecom
Provision of resources to authenticated and authorised users only
Two-phase protocol for separated reservation and commitment of resources
resources should be reserved before accounting is started
resources should be available before media is cut through
Segmented resource assignment (local access network, backbone network, far-end access network) with support of different QoS models and granularity
Dynamic binding of resources
Fast operation of protocol

5. QoS in IPCablecom - Architecture
IP Network
Provider A
Border Router
Edge Router
PSTN Gateway
MANAGED IP
BACKBONE
Provider B
IN-HOME NETWORK
ACCESS NETWORK
Access Node
Private IP Network
MTA
Cable Network CM
Access Node
Cable Network
MTA CM
ACCESS NETWORK

6. QoS in IPCablecom - ExampleAN CM
MTA
Far-end client
Managed IP Backbone
Call proceeds with required Quality of Service
MTA signals AN to commit resources
MTA signals AN to reserve resources
Call Agent directs MTA to proceed by reserving resources
Call Agent directs MTA to play ringback
Call Agent directs MTA to commit resources and complete connection
MTA notifies Call Agent, which will manage signaling required to establish connection
AN matches authorization and sets up J.112 flows
Originating MTA goes off-hook, collects digits
Gate Controller authorizes resources and installs gate on AN
CMS
CMS may be decomposed into its logical functions: Call Agent and Gate Controller
Call Agent collects info and coordinates with remote Call Agent and local Gate Controller
Call Agent
Gate Controller

7. QoS in Access Network - DQoS
DQoS is an optimization technique to enhance J.112 QoS mechanisms on session-by-session basis
Facilitates preferential, predictable service during periods of network congestion
Application layer QoS requirements are communicated and translated into J.112 QoS parameters
J.112 flows are established on demand and released upon session completion
Cable operator always maintains authoritative control through policy rules
Bandwidth is managed efficiently

8. QoS in Access Network (cont’d)
User
Description of subjective perception
Voice call, satisfactory quality
Application Layer
SDP: type of media, Codec, packet length, sampling rate
Audio, G.729E, packet length 10 ms, sampling rate 8 kHz
Network Layer
RSVP: buffer size, data rate, latency
buffer size 55 Byte, 5500 Bytes/s
Data-Link Layer
MAC: Access method and its parameters
J.112 B: Unsolicited Grant Service, 86 Byte every 10 ms
J.112 A: Fixed-rate Access, 2 ATM cells every 60 slots
Services exhibit varying QoS needs, architecture should reflect these needs

9. QoS Interfaces (1) Policy Admission control
consists of rules for resource access and usage
defined by cable operators to manage network resources
potential criteria: class of service, time of day, credit rating, existing resource utilization, etc.
Admission control
authenticate request
apply policy rules to requested resource envelope to make authorization decision
install policy decision (i.e. gate) on AN, contingent upon resource availability

10. QoS Interfaces (2) Resource management
based on RSVP or MAC control interface
AN acts as proxy for far-end terminal to enable segmented resource assignment
resources in the access segment are reserved in both directions over the private IP and the cable network
dynamic binding of resources (one set of resources is bound to a group of reservations; e.g. call waiting)
support of two phase resource reservation
support of header compression and suppression

11. QoS Interfaces (3) Packet forwarding
access methods and scheduling services defined in J.112
Unsolicited Grant Service for constant bit-rate services (voice and video communication, VoD)
Polling Services for variable bit-rate services (games, peer-to-peer interaction, VPN)
Hybrid Services for constant bit-rate services with periodic inactivity (e.g., silence suppression codecs)
Even though UGS is almost exclusively used for voice, underlying J.112 mechanisms are significantly more powerful and are accommodated by DQoS

12. QoS in Managed IP Backbone - IQoS
Based on Integrated Services (IntServ) and Differentiated Services (DiffServ) architectures defined by IETF
Edge router defines border of network segments  flexible choice of QoS mechanisms in the different segments
Border router maintains integrity of IPCablecom domains
Several approaches to resource reservation specified
Trade-off between level of guaranty and scalability, delay, efficiency
Usage of MPLS in the IQoS context is analyzed as well

13. QoS in Managed IP Backbone (cont’d)
Per-flow RSVP
- individual reservation for each session
- across all network segments
Guaranty decreases
Effort decreases
Aggregate RSVP
- aggregation of sessions with similar requirements
- reduction in number of reservation states to be maintained
- reduced satisfaction of individual session
DiffServ
- no preceding reservation, treatment of marked packets according to per-hop behaviour
- no reservation states to be maintained
Overprovisioning also possible, but not really a management method

14. Conclusion
IPCablecom establishes end-to-end QoS guaranties by employing several mechanisms optimized for the underlying network
Available mechanisms provide sufficient flexibility for future services
QoS interfaces support high-quality voice services

15. Thank you for your attention !