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TN3270 Server Implementation 2-3

• Deﬁning LUs

• Addressing LAN Printing Requirements

• Addressing SNA Routing in Multi-Domain Environments

• Addressing End User Service Level Requirements

• Addressing Availability Requirements (Redundancy/Load Balancing)

• Satisfying Expanding Network Address Requirements

Where to Place the TN3270 Server and How Many Servers You Need

The TN3270 Server can be placed on a local router (one that is directly attached to the mainframe) or a remote

router. If the router is local, the TN3270 Server resides on a CIP or CPA that is connected to the mainframe via

ESCON or bus-and-tag. However, many organizations use the TN3270 Server on remote routers as an

intermediate step in their migration to using the CIP or CPA as the host connection option. In this case, the

TN3270 Server is placed on a routerthat is connected to the mainframe via any channel connection device, such

as the FEP. Although placing the TN3270 Server on a remote router is not an optimal, long-term solution, it

allows sites that are migratingfrom theFEP to theCIP orCPA tohave TN2370 server functionality immediately.

The Cisco TN3270 Server provides up to 16,000 concurrently active LUs per channel-attached router at a rate

of 850 transactions per second. The TN3270 server will support considerably more LUs at a lower throughput

rate. While most organizations would never reach 16,000 concurrent sessions in a production environment, the

TN3270 Server was designed to accommodate this number of sessions to account for day-to-day usage and to

provide a buffer for failover LUs in the event of a failure of another TN3270 Server. Most large companies use

their TN3270 servers at 12,000 to 14,000 users on a daily basis. On average, they install eight to ten CIPs or

CPAs to provide TN3270 access for approximately 100,000 users.

The number of sessions a single TN3270 Server can handle is directly related to the number of transactions per

second and the amount of memory available to the CIP or CPA. The 16,000 LU session capacity is based on 850

transactions per second and a session size of 200 bytes inbound (from the terminal) and 800 bytes outbound (to

the terminal). Normally, a single terminal (or LU) is rated at one transaction per minute. Therefore, if a server

can handle 1 transaction per second, then it can accommodate 60 terminals. At a rate of 850 transactions per

second, it can accommodate 16,000 terminals. Printer LUs and ﬁle transfers reduce the number of available

sessions.

Although the TN3270 Server can manage tens of thousands of sessions, you should consider the impact of

gateway disruption when designing your network. How many users can you afford to disrupt if a gateway goes

down? A typical number is 12,000 to 14,000 sessions, which allows them to beneﬁt from the increased

throughput rate.

The TN3270 Server has been tested with up to 30,000 concurrently active LUs.

Implementing TN3270 Server on a CIP/CPA

The TN3270 Server feature of Cisco IOS software can be implemented on either a CIP or a CPA.

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