Specifications

10-22
Cisco IGX 8400 Series Provisioning Guide, Release 9.3.3 and Later Releases
OL-1166-04
Chapter 10 Cisco IGX 8400 Series IP Service
IP Service—Functional Overview
Packets have precedence bits in the type of service field of the IP header, set at either the host or an
intermediate router, which could be the edge label switch router (LSR). The precedence bits define a
CoS 0-3, such as available, standard, premium, or control.
To establish CoS operation when the IGX and the associated LSC router are initially configured, the
binding type assigned each LVC interface on the IGX is configured to be multiple LVCs.
Then under the routing protocol (OSPF, for example), four LVCs are set up across the network for each
IP source to destination requirement. Depending on the precedence bits set in the packets that are
received by the edge LSR, the packet ATM cells that are sent to the ATM LSR will be one of four classes
(as determined by the cell label, that is, VPI.VCI). Furthermore, two subclasses are distinguishable
within each class by the use of the cell loss priority (CLP) bit in the cells.
Then the ATM LSR performs a MPLS data table lookup and assigns the appropriate CoS template and
Qbin characteristics. The default mapping for CoS is listed in Table 10-8.
Figure 10-9 shows an example of IP traffic across an ATM core consisting of IGX-ATM LSRs. The host
is sending two types of traffic across the network, interactive video, and nontime-critical data. Because
multiple LVCs have automatically been generated for all IP source-destination paths, traffic for each
source destination is assigned to one of four LVCs, based on the precedence bit setting in the IP packet
header.
In this case, the video traffic might be assigned to the premium CoS, and transmitted across the network.
This starts with the cell label “51” out of the Edge LSR-A, and continues across the network with the
cell label “91” applied to the Edge LSR-C. In each IGX-ATM LSR, the cells are processed with the
preassigned bandwidth, queuing, and other ATM QoS functions suitable to “premium” traffic.
In a similar fashion, low-priority data traffic cells with the same IP source-destination might be assigned
label “53” out of Edge LSR-A and arrive at Edge LSR-C with the label “93,” receiving preassigned
bandwidth, queuing, and other ATM QoS functions suitable to “available” traffic.
Table 10-8 Type of Service and Related CoS
Class of Service Mapping Class of Service IP ToS
Available 0 ToS 0/4
Standard 1 ToS 1/5
Premium 2 ToS 2/6
Control 3 ToS 3/7