4.3 Weighting Criteria Algorithm
4.3.5 Criteria Weights for Classes of Service
This subsection describes the applicability of the criteria weighting algorithm to derive weights from ITU-T Y.1541 [ITU-T, 2006] Classes of Service (CoS).
Diverse options could be pursued, when considering classes of service [Stankiewicz et al., 2011]. The IETF model in RFC 4594 [Babiarz et al., 2006] specifies 12 classes, which have been aggregated, later in RFC 5127 [Chan et al., 2008]. Nonetheless, all these classes appear associated with Diffserv mechanisms and do not provide any values (or bounds) regarding TP criteria. Other models, such as IEEE 802.1p [Choi et al., 2007] are associated with specific technologies and also fail to establish limits for TP criteria. The ITU-T Y.1541 [ITU-T, 2006] recommendation specifies 7 classes of ser- vice, summarized in Table 4.4, in two types: mandatory, where all parameters should be within bounds; and provisional, where values do not pose stringent requirements. As applicability is envisioned for a full range of applications, MeTHODICAL consid- ers the ITU-T Y.1541 classes of service, because bounds for TP criteria are well defined, and are not tied to any particular technology or architecture.
The preferences for different classes regarding TP criteria are established by con- sidering the purpose of the class (e.g. the service associated with the class), the bounds established for the diverse criteria, and by comparing the different classes. Comparing Class 0 and Class 1, for example, it is noticed that the latter supports higher values of OWD, thus the IPDV criterion is more important, as packet loss is similar. Moreover, between Class 3 and Class 4, delay is restricted with higher bounds, therefore Class 4 gives preference to packet loss. In Class 5, all parameters are unspecified, as such traditional Internet applications are more affected by RTT, and mechanisms to react
4.3 Weighting Criteria Algorithm
Table 4.4: Classes of Service in ITU-T Y.1541, values are based on ITU-T Y.1541 [ITU-T, 2006] and ITU-T G.1050 [ITU-T, 2007].
CoS
type CoS OWD IPDV
Packet Loss
Reorder
Description Services/Applications
Mandatory
0 100ms 50ms 10−3 U.a Real-Time, jitter sensitive,
high interaction
High quality VoIP and video, Video Teleconfer- ence. Multiplayer Inter- active Gaming.
1 400ms 50ms 10−3 U. Real-Time, jitter sensitive,
interaction
VoIP, Video Teleconfer- ence.
2 100ms U. 10−3 U. Transaction data, highly
interactive
Signalling, lower quality video and VoIP.
3 400ms U. 10−3 U. Transaction data, interac-
tive Signalling.
4 1s U. 10−3 U. Low loss, short transac-
tions, bulk data Video streaming.
5 U. U. U. U. Traditional Internet Ap-
plications
Web Browsing (HTTP), Instant Messaging, Media content downloads.
Pr
ovisional
6 100ms 50ms 10−5 10−6
Loss sensitive Applications
Television transport, high-capacity TCP trans- fers, time-division multi- plexing. 7 400ms 50ms 10−5 10−6 Television transport, high-capacity TCP trans- fers. aU.-Unspecified
to packet losses are widely implemented for this type of applications. Classes 6 and 7 can be related to Classes 0 and 1, as jitter and delay have the same values, respec- tively. Nonetheless, in Classes 6 and 7 packet loss tolerance is lower, therefore these two classes give preference to jitter and packet loss criteria. The difference relies on the reordering importance for Class 7 applications.
Multihoming and TP criteria are configured by considering two representative configurations: prefMH- giving preference to Multihoming goals, with priority for Re- silience, Ubiquity and then to TP criteria (i.e. in the same line of the resilience pref- erence example). prefTP- gives preference to Traffic Performance criteria and then to
Table 4.5: Weights of Benefits criteria with Multihoming (prefMH) and Traffic Per- formance (prefTP) preferences.
Pref Class Availability Efficiency Quality Coverage Velocity SecurityPath capacity
prefMH APa 0.48 0.024 0.096 0.09 0.03 0.18 0.1
prefMH ACb 0.48 0.096 0.024 0.09 0.03 0.18 0.1
prefTP AP 0.08 0.004 0.016 0.09 0.03 0.18 0.6
prefTP AC 0.08 0.016 0.004 0.09 0.03 0.18 0.6
aAP applies to all classes with 1:1 protection model. bAC applies to all classes with 1+1 protection model.
multihoming goals with preference for ubiquity and then to resilience. In both cases, level one benefits criteria are configured identically to level one costs (e.g. resilience, ubiquity and TP).
Moreover, a distinction between the desired protection model is also performed. The (P)-primary backup and (C)-concurrent protection models can lead to different criteria preferences. For instance, it is assumed that the concurrent protection model has preference for recovery efficiency than to recovery quality. Table 4.5 summarizes weights of benefits criteria for (A)-all the classes with (P)-primary backup and (C)- concurrent protection models, for prefMH and prefTP configuration cases. Weights of TP costs criteria type are depicted in Table 4.6 for prefMH and prefTP configuration cases. Costs are specific to each class but do not have any difference between the diverse protection models. The following paragraphs present the reasoning to deter- mine such values.
For a judgment matrix ˜A (see Equation 4.6) of 2×2, judgments in extreme positions are not considered, i.e. those that reduce the importance of one criterion over the others (e.g. 90%, 10%). As such, values lying in the middle are chosen. For instance, taking the example of the judgment matrix for resilience sub-criteria, preference is given to (Av)-Availability and then to (Rc)-Recovery. Matrix 4.12 illustrates the logic that is applied to all the criteria in a 2 × 2 matrix.
" Availability Recovery Availability (I) (W +) Recovery (W +)−1 (I) # wAv= 0.8 wRc= 0.2 (4.12)
4.3 Weighting Criteria Algorithm
Table 4.6: Weights of Costs criteria with Multihoming (prefMH) and Traffic Performance (prefTP) preferences.
Pref Class Impact Cost Energy HO delay
OWD IPDV RTT Loss Reorder Duplicate
pr efMH 0Aa 0.6 0.048 0.192 0.06 0.020 0.019 0.016 0.018 0.017 0.009 1A 0.6 0.048 0.192 0.06 0.019 0.020 0.016 0.018 0.017 0.009 2A 0.6 0.048 0.192 0.06 0.020 0.009 0.018 0.019 0.017 0.016 3A 0.6 0.048 0.192 0.06 0.020 0.009 0.018 0.019 0.016 0.017 4A 0.6 0.048 0.192 0.06 0.019 0.009 0.018 0.020 0.017 0.016 5A 0.6 0.048 0.192 0.06 0.018 0.017 0.020 0.019 0.016 0.009 6A 0.6 0.048 0.192 0.06 0.018 0.020 0.009 0.019 0.017 0.016 7A 0.6 0.048 0.192 0.06 0.017 0.020 0.016 0.019 0.018 0.009 pr efTP 0A 0.1 0.048 0.192 0.06 0.120 0.114 0.099 0.109 0.104 0.054 1A 0.1 0.048 0.192 0.06 0.114 0.120 0.099 0.109 0.104 0.054 2A 0.1 0.048 0.192 0.06 0.120 0.054 0.109 0.114 0.104 0.099 3A 0.1 0.048 0.192 0.06 0.120 0.054 0.109 0.114 0.099 0.104 4A 0.1 0.048 0.192 0.06 0.114 0.054 0.109 0.120 0.104 0.099 5A 0.1 0.048 0.192 0.06 0.109 0.104 0.120 0.114 0.099 0.054 6A 0.1 0.048 0.192 0.06 0.109 0.120 0.054 0.114 0.104 0.099 7A 0.1 0.048 0.192 0.06 0.104 0.120 0.099 0.114 0.109 0.054
a0A applies to all protection models for CoS0.
For judgment ˜A with 3 × 3, it is considered that the importance of each criterion over another should be clearly distinct, that is no marginal importance differences between criteria should be given (e.g. one with 10% and other with 5%). The logic applied in the general case of 2 × 2 matrices is also employed here, thus the values employed in judgments do not rely on extremes, but rather on the middle. Matrix 4.13 demonstrates judgments for sub-criteria of benefits ubiquity type, where preferences occur in the following order: First (Cov)-coverage; Second (Vel)-Velocity; and finally (Sec)-Security.
Coverage V elocity Security
Coverage I E E+−1 V elocity E−1 I F S+−1 Security E+ F S+ I wCov = 0.6 wV el= 0.3 wSec= 0.1 (4.13)
The most complex judgments are depicted in Matrix 4.14. The 6 × 6 matrix com- pares TP cost criteria, namely One Way Delay (OWD), IP Delay Variation (IPDV), RTT, Loss, Reorder and (Dup)-Duplicate.
OW D IP DV RT T Loss Reorder Duplicate
OW D I E E E E E+ IP DV E−1 I E E E E+ RT T E−1 E−1 I E E E+ Loss E+−1 E−1 E−1 I E E+ Reorder E−1 E−1 E−1 E−1 I E+ Duplicate E+−1 E+−1 E+−1 E+−1 E+−1 I wOW D = 0.20 wIP DV = 0.19 wRT T = 0.18
wLoss= 0.17 wReord = 0.16 wDup= 0.1
(4.14)
To enable a fair judgment between criteria, weights are set according to Matrix 4.14. It is considered that a single criterion should not be disregarded due to the weak impor- tance.
As MeTHODICAL organizes criteria in a hierarchical form, the final weights of criteria must consider all the levels. For instance, the weight for security must consider the weight of ubiquity. Considering the prefMH case, the security weight is wSec =
wubiquity× wlevelSec= 0.3 × 0.1 = 0.03.