Internet Communications Using SIP : Delivering VoIP and Multimedia Services With Session Initiation Protocol {2Nd Ed.}

Table 18.2 (continued)

OPTION FOR HIGHLIGHTS AND

NETWORK QOS ISSUES

Network Layer RSVP requires state in all nodes

in the path.

Multiprotocol Label MPLS establishes label-switched

Switching (MPLS) paths. MPLS can invoke DS and

RSVP.

Is one option for intradomain

traffic engineering in the IP core,

but is not usable on access links

where QoS may be a problem.

Link Layer 802.1q and 802.1p VLAN specifications with a 3-bit

priority field that can be mapped

to DS.

802.11e Can support QoS on wireless

LANs using eight traffic classes.

DOCSIS 1.1 Data Over Cable System

specification enhanced to

support 802.1q.

Data in Table 18.2 leads to three important conclusions:

1. QoS based on best effort is the only one available for interdomain traffic
   over the Internet. We will expand later in this chapter on the reasons for
   the persistence of best-effort interdomain traffic.


2. Differentiated Services (DS) is the only technology for QoS support that
   is stateless and also has no scalability problems.


3. MPLS is not applicable on access links where most of the QoS issues
   originate in the first place. MPLS technology is considered a successor
   of ATM and has inherited, in our opinion, the same mindset leading to
   similar problems that ATM had. MPLS has also been described as a
   security risk for the Internet, and as leading to unmanageable routing
   table complexity for ISPs [14], [15]. (Such concerns by network experts
   have led to a flood of white papers to the contrary written by router
   and network marketers.)
   QoS on access links can, however, be easily implemented, and many resi-
   dential and small office routers support setting the DSCP for the access link, in
   case DS is provided by the ISP.

312 Chapter 18