Switching to VoIP

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

206

|

Chapter 9: Quality of Service

To recap, VLAN accomplishes several things that can improve VoIP service:

• Divides and partitions Ethernet broadcast domains

• Provides a best-effort CoS prioritization scheme for traffic on each switch’s back-

plane

• Creates a standard for dividing traffic logically across large routed and switched

networks using VLAN trunking

For much more detailed information on VLAN, segmentation, and Ethernet in gen-

eral, read O’Reilly’s Ethernet: The Definitive Guide.

Quality of Service

Quality of Service is sometimes meant to refer to all measures that are geared toward

improving the performance of voice on the converged network: 802.1p, VLAN, Diff-

Serv, RSVP, and so forth. But within the context of VoIP, QoS is also a way of saying

“more elaborate than CoS.” That is, QoS takes additional steps beyond those CoS

solutions that 802.1p and DiffServ take. The two key QoS standards are RSVP and

MPLS.

Intserv and RSVP

Intserv (Integrated Services) is an IETF recommendation for provided dedicated

bandwidth to individual flows, or media channels, on an IP network. The media

channels are referred to by their sockets, just as they are in DiffServ. But, the differ-

ence is that all routers, whether at the edge or core of the network, play an active role

in the policy decision ...