Enterasys Networks CSX7000 Manuel d'utilisateur télécharger pdf (Page 253)

Central Site Remote Access Switch 253

ONFIGURING

LTERNATE

CCESSES

X.25 Accesses

NONSTANDARD DEFAULT RECEIVE WINDOW SIZE

The number of frames that a DTE can receive without receiving an acknowledgment. Using

modulo 128, the DTEs can send up to 127 frames without receiving an acknowledgment. Using

modulo 8, the DTEs can send up to 7 frames without receiving an acknowledgment. The default

value for both modulo 8 and modulo 128 is 2.

ONSTANDARD DEFAULT TRANSMIT PACKET SIZE

The size of a packet that a DTE can transmit. The choice of a packet size must be weighed against

the requirements for larger buffers at all the machines that process the packet. Larger packet sizes

reduce the opportunity for other devices to share the channel. On the other hand, a larger packet

reduces the ratio of overhead fields to user data. The default transmit packet size is 128 bytes.

ONSTANDARD DEFAULT RECEIVE PACKET SIZE

The size of a packet that a DTE can receive. The choice of a packet size must be weighed against the

requirements for larger buffers at all the machines that process the packet. Larger packet sizes

reduce the opportunity for other devices to share the channel. On the other hand, a larger packet

reduces the ratio of overhead fields to user data. The default transmit packet size is 128 bytes.

ONSTANDARD DEFAULT TRANSMIT THROUGHPUT CLASS

Transmit throughput describes the maximum amount of data that can be sent through the network,

when the network is operating at saturation. Factors influencing throughput are line speeds,

window sizes, and the number of active sessions in the network. The default value is 19,200 BPS.

ONSTANDARD DEFAULT RECEIVE THROUGHPUT CLASS

Receive throughput describes the maximum amount of data that can be received through the

network, when the network is operating at saturation. Factors influencing throughput are line

speeds, window sizes, and the number of active sessions in the network. The default value is 19,200

BPS.

X.25 ACCESS BACKGROUND INFORMATION

X.25 was developed to provide an interface that would allow computers or terminals that use

different data communications protocols to exchange data across wide area packet-switching

networks. Since its inception by CCITT in 1974, it has been expanded to include many options,

services, and facilities.

Packet-switching is a transmission method in which data is broken down into packets. The packets

are sent across a shared medium from source to destination. The transmission may use any

available circuit. The next packet in the transmission may take a different route. Multiple packets

from the same transmission can be sent at the same time. Because of the switching, the packets may

not all take the same route, and they may not arrive in the order that they were sent. When they

arrive at their destination, the packets are reassembled in the proper order, and a check is done to

see if all expected packets arrived.

X.25 provides common procedures between a device (DTE) and a packet network (DCE) for

establishing a connection to the network, exchanging data with another DTE, and releasing the

connection. X.25 contains no algorithms for routing the packets across the wide area network.

Consequently, an X.25 Network does not mean that the internal operations of the network use X.25.

It simply means that the interface to a packet data network is governed by the X.25 protocol.

Virtual circuits are used to establish a virtual path from one DTE to another. This virtual path

appears to have the same characteristics that you might get from a physical telephone circuit. With

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Enterasys Networks CSX7000 Manuel d'utilisateur Page 253

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