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2-18 TN3270 Design and Implementation Guide

• CP-to-CP connection using virtual routing node parameters and implementing APPN on the router using the

connection network conﬁguration

• CP-to-CP connection conﬁguring APPN with VTAM and implementing APPN on the router using the NN

conﬁguration

Addressing End User Service Level Requirements

As trafﬁc on the Internet increases, there is increased congestion. One way to address this problem is to

discriminate between different types of trafﬁc and provide the appropriate quality of service (QoS). For example,

interactive trafﬁc should have a higher priority than bulk data transfer. IP precedence and type of service (ToS)

is part of the IP speciﬁcation that provides this prioritization.

The TN3270 Server allows you to specify IP precedence and ToS. At the protocol level, IP precedence allows a

router network to discriminate between different types of trafﬁc by assigning different priorities to them. IP ToS

allows router networks to discriminate between different types of trafﬁc by assigning different routing

characteristics to them. Precedence and ToS values complement one another and provide ﬂexibility in managing

your network trafﬁc.

In TN3270 Server, two types of TN3270 clients can be connected: screens or printers. Screens are interactive and

printers need bulk data transfer. IP ToS and IP precedence allow you to discriminate between these types of

sessions and assign different precedence values to the interactive connection and the bulk data connection.

IP ToS and IP precedence values can be speciﬁed for either the TN3270 Server as a whole or individual PUs.

Values can be speciﬁed on both levels,in which case siftdown determines the value on anindividual PU. Siftdown

allows you to conﬁgure values that apply to all entities of the server in TN3270 Server conﬁguration and to

conﬁgure values for individual PUs at the PU conﬁguration mode.

The Cisco implementation of IP precedence allows values of 0 to 7. The Cisco implementation of ToS allows

values from 0 to 15. It is up to the administrator to choose values consistent with organizational policies when

conﬁguring IP precedence and ToS. Also, whether these values work depends on what the organization or

Internet Service Provider’s (ISP’s) router does with packets with different IP ToS/precedence values. If you are

using a Cisco router network, conﬁguring weighted fair queuing (WFQ) or priority queuing allow you to

prioritize trafﬁc using IP precedence. The Open Shortest Path First (OSPF) protocol can discriminate between

different routes based on IP ToS value; functions such as WFQ and NetFlow switching are also affected by ToS

values.

Addressing Availability Requirements (Redundancy/Load Balancing)

Moving the 3270 access from the host to an outboard server provides many beneﬁts, but also raises the issues of

server redundancy. Having a “single point of failure” is an issue for sites that cannot allow for disruptive session

failure. With legacy SNA, when a path is broken, the session is lost and the user must reconnect. With the

outboard gateways, the data travels from the client to the server via TCP and then from the server to VTAM via

SNA. As a result, any loss between the server and VTAM will result in a disrupted session.

Cisco offers several options for providing redundancy, including LocalDirector, DistributedDirector, and Hot

Standby Router Protocol (HSRP).

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Cisco 11.0 BT Manual de usuario Pagina 18